Startseite Graphene and carbon-based nanomaterials as highly efficient adsorbents for oils and organic solvents
Artikel Öffentlich zugänglich

Graphene and carbon-based nanomaterials as highly efficient adsorbents for oils and organic solvents

  • Shu Wan

    Shu Wan is a PhD student in the School of Electronic Science and Engineering at Southeast University. He obtained his BE degree in 2011 from Southeast University, China. His research interests focus mainly on applications of nanomaterials in environment, and 2D materials devices.

         , Hengchang Bi

    Hengchang Bi is a PhD student in the School of Electronic Science and Engineering at Southeast University. He obtained his BE degree in 2007 from Shanxi University of Science and Technology, China. His research interests mainly focus on applications of nanomaterials in environment, and 2D materials.

         und Litao Sun

    Litao Sun is currently a distinguished professor at Southeast University, China. His current research interests include in situ experimentation inside the electron microscope, graphene, and related 2D materials, new phenomena from sub-10 nm nanoparticles/nanowires, and applications of nanomaterials in environment, renewable energy, and nanoelectromechanical systems.

     EMAIL logo
Veröffentlicht/Copyright: 21. Januar 2016
Artikel downloaden (PDF)
Veröffentlichen auch Sie bei De Gruyter Brill
Manuskript einreichen Informationen für Autor*innen
Nanotechnology Reviews
Aus der Zeitschrift Nanotechnology Reviews Band 5 Heft 1

Abstract

This paper provides a comprehensive review of recent progress in the synthesis and performance of graphene and carbon-based nanomaterials as efficient adsorbents for oils and organic solvents. Several advantages of these adsorbents are emphasized, including adjustable three-dimensional networks, high surface area, high chemical/thermal stability, high flexibility and elasticity, and extremely high surface hydrophobicity/ oleophilicity. Technical challenges are discussed, and future research directions are proposed.

Keywords: adsorbents; carbon-based; graphene; sponge

1 Introduction

Scientific and technological research in electronics, biological science, energy, and environment faces challenges regarding performance, functionality, and durability of key materials [1]. Advanced materials play significant roles in overcoming major challenges and achieving breakthroughs in technological and practical application. These materials include carbon-based nanomaterials, such as carbon black, carbon nanotubes (CNTs), carbon nanofibers, and graphene. These advanced carbon nanomaterials are widely adopted in various important applications such as energy harvesting and storage, sensing, catalysis, transistors, and antipollution [2–11].

Pollution caused by crude oil, petroleum products, and toxic organic solvents is a big threat to marine ecosystem and economy. Porous adsorbents are used to resolve spills of oils and organic solvents. Natural porous adsorbers, such as wool, sawdust, expanded perlite, and zeolites, are traditionally used for spill cleanups because of their accessibility [12–14]. However, these conventional materials have low oil-adsorbing capacity (less than 10× their own weight) and high water-adsorption characteristic, hindering the extraction and recycling of these adsorbents. Hydrophobic and microporous polymers are moldable. Moreover, these materials can adsorb 5× to 25× their own weight in both oils and organic solvents, up to 80% of which can be extracted by squeezing [15, 16]. Expanded graphite is an important alternative for low-cost oil removal. This material showed high adsorption efficiency of up to 83× its own weight, and up to 70% of the adsorbates can be retrieved by vacuum filtration [17]. However, the particulates do not exhibit high adsorption of organic solvents, whereas the powder form is difficult to use, and the material can only be recycled a few times (only 17% capacity remains after five cycles) [18, 19]. Development of new materials that can effectively and reversibly remove organic solvents and oil spill contaminants is critical to future oil spill cleanup and water remediation required for environmental protection.

Three-dimensional (3D) spongy graphene with high surface area, uniform structure, chemical stability in organic solvents, ability to sustain structural completeness under high temperatures, and highly hydrophobic and oleophilic surfaces are feasible candidates for adsorbers. Graphene sponges have shown great improvement in loading capability of oils and organic liquids, as well as reusability, compared with existing adsorbents. We previously investigated the usage of spongy graphene as highly efficient adsorbent for oil and toxic organic for the first time [20]. Graphene adsorbed up to 86× its own weight. We also enhanced the loading capability of spongy graphene by one magnitude [21] and developed low-cost carbon fiber-based adsorbents fabricated from cotton [22] and waste paper [23]. Also, along with graphene, various kinds of carbon nanomaterial-based adsorbents have been widely used for the removal of organic contaminants and heavy metal ions [24–28]. This field study area has shown much development. A brief timeline of these adsorbents is shown in Figure 1A. Adsorption capacity of various 3D graphene and carbon-based materials were compared, and the results are exhibited in Figure 1B.

Figure 1: (A) Brief timeline in the development of graphene and carbon-based materials as adsorbents. (B) Comparison of adsorption capacities of various adsorbents. Estimated cost of these adsorbents was based on cost and availability of precursors, fabrication process, thermal treatment of materials, convenience, and applicability of materials and recyclability of materials. Reproduced with permission: (A), Refs. [20–23, 29, 30]. Copyright: (A) 2012 Wiley, 2013 Wiley, 2013 Royal Society of Chemistry, 2014 Wiley, and 2015 American Chemical Society.
Figure 1:

(A) Brief timeline in the development of graphene and carbon-based materials as adsorbents. (B) Comparison of adsorption capacities of various adsorbents. Estimated cost of these adsorbents was based on cost and availability of precursors, fabrication process, thermal treatment of materials, convenience, and applicability of materials and recyclability of materials. Reproduced with permission: (A), Refs. [20–23, 29, 30]. Copyright: (A) 2012 Wiley, 2013 Wiley, 2013 Royal Society of Chemistry, 2014 Wiley, and 2015 American Chemical Society.

Spongy graphene and other carbon-based adsorbents have been investigated [24–39]. The present adsorbents can be obtained through different procedures, including the direct gelling of high aspect ratio materials such as direct gelling of high-aspect ratio materials (e.g. graphene and CNTs) [20, 21, 25, 27, 30], pyrolysis of natural fibers or artificial products (e.g. cotton [22], waste paper [23], even plants [38, 39]), and chemical vapor deposition (CVD) [34–36]. These techniques are used to synthesize hydrophobic and low-density porous structures. However, each method employs distinct starting materials, temperatures, and additives according to the aimed products. Bottom-up growth of nanomaterials, such as graphene and CNTs, could offer a fundamentally different procedure to achieve a macroscale 3D architecture with strictly defined porous sponge structures. Top-down procedure, however, fully utilizes an existing porous scaffold. Hydrophobic properties of existing scaffolds can be enhanced by thermal treatments for carbonization or surface coating by hydrophobic materials. Significant development, wide potential application, and numerous variations in spongy graphene and other carbon-based adsorbents show the benefits, potential applications, and drawbacks of these materials. This paper aims to review the continued developments and challenges in fabricating adsorbents in a broad perspective. We also emphasized the fundamental understanding of the synthesis and characterization of graphene and other carbon-based materials. Future outlook and application areas of high-performance sponges in recent publications are also discussed.

2 Graphene-based adsorbents

Graphene, which is one of the advanced carbon nanomaterials, is a two-dimensional (2D) single sheet of carbon atoms arranged in a hexagonal network. Pristine graphene sheets achieved by mechanical exfoliation [40] exhibit outstanding properties, such as high surface areas (2630 m2 g-1), high thermal conductivity (5300 W mK-1), high Young’s modulus (1 TPa), strong chemical durability, and high electron mobility (2.5×105 cm2 V-1 s-1) [41]. However, this kind of graphene is not suitable for applications that require large quantities of graphene. Such kind of graphene is economically inefficient, especially, when used as adsorbents. Thus, several low-cost mass production methods have been developed.

2.1 Synthesis of graphene-based adsorbents

Graphene-based adsorbents with ordered 3D networks can generally be obtained through different procedures, including self-assembly interactions of graphene oxide (GO) during reduction, direct drying solution, CVD, surface coating on scaffold skeleton, and expansion of compact GO films. The following subsections will provide a deeper discussion on these methods.

2.1.1 Self-assembly by GO reduction

GO is currently the most common and important precursor to prepare graphene materials. Graphene could be controlled to form superhydrophobic material [42]. This material can be produced into porous sponge-like cylinder by a special drying process in which strong interactions of GO sheets in water play a significant role [43]. The change in hydrophilicity during GO reduction allows for increased strength and control of pore size. Moreover, the interactions among GO sheets are strong enough to allow solutions to directly freeze to produce ultralight sponges. Furthermore, some challenges and process variability also requires more development to achieve optimal and consistent results.

GO can be prepared by the intercalation and oxidation of graphite powder usually by modified Hummer’s method [44] in which the key components are sulfuric acid and potassium permanganate [45, 46]. Thus, functionalities consisting primarily of epoxide and hydroxyl groups could be formed, and these groups are highly hydrophilic and form strong hydrogen bonds with water [47]. Furthermore, intercalation with water can cause lattice expansion, increasing the distance between graphite planes from 0.335 nm to 0.6–1.2 nm [48]. Van der Waal’s binding forces are easily overcome after strong mixing or sonication, forming thin mono- or few-layered GO materials [49, 50]. The synthesis process is schematically shown in Figure 2.

Figure 2: Chemical route for synthesizing aqueous graphene dispersions. 1. Oxidation of graphite to graphite oxide with greater interlayer distance. 2. Exfoliation of graphite oxide in water by sonication to obtain graphene oxide (GO) colloids stabilized by electrostatic repulsion. 3. Controlled conversion of GO colloids to conducting graphene colloids through deoxygenation by hydrazine reduction. Reproduced with permission from Ref. [50]. Copyright: 2008 Nature Publishing Group.
Figure 2:

Chemical route for synthesizing aqueous graphene dispersions. 1. Oxidation of graphite to graphite oxide with greater interlayer distance. 2. Exfoliation of graphite oxide in water by sonication to obtain graphene oxide (GO) colloids stabilized by electrostatic repulsion. 3. Controlled conversion of GO colloids to conducting graphene colloids through deoxygenation by hydrazine reduction. Reproduced with permission from Ref. [50]. Copyright: 2008 Nature Publishing Group.

The 3D graphene sponges could be generated by utilizing water-soluble properties of GO to produce high-concentration solutions and gels [51]. GO sheets can easily be dispersed uniformly in water because of their strong hydrophilicity and electrostatic repulsion effects [52]. Carboxylic acid groups attached to GO sheets could ionize, resulting in carboxylic ions containing negative charges. Some carboxylic groups are removed as the reaction progresses, for example, reaction for tens of minutes, thereby decreasing the charges of some GO sheets. In addition, GO sheets without any charge tend to be attracted to those with charges to form large sheets. The basal plane of GO is eventually shifted from a hydrophilic state to a more hydrophobic regime. Hydrogen bonding with water is weakened, and van der Waal’s attraction between planes is increased, creating some sticky graphene sheets. Sheets in the solution can begin to self-assemble if undisturbed, as schematically demonstrated by Bi et al. [53] in Figure 3. However, at sufficiently high concentration, attractive forces between sheets and mutual restriction of mobility could result in assemblage of reduced graphene materials into a porous hydrogel, molded in the shape of the containment vessel [54]. Further reduction of graphene materials as the C/O ratio of the network increases leads to stronger van der Waal’s forces as well as more rigid and denser self-assembled rGO hydrogel [55]. In addition, reduction can also be performed by adding crosslinking agents or more environment-friendly reducing agents. The reduction process can be further supplemented with high-temperature annealing. After assembly, the structure is dried to prepare sponges. Two techniques, namely, freeze drying and critical point drying, are usually adopted to avoid the restacking process during dried ambient condition. Both techniques limit stress on the pore structure by replacing the liquid with gas for sponge formation, thus, avoiding restacking and resulting in high-surface area macroscale sponge. Freeze drying normally limits the capillary stress by overcoming the water’s triple point boundary. This phenomenon lowers the temperature of water and then transforms it directly from solid to gas phase via low pressure.

Figure 3: (A) Hydrothermal reduction process. The porous hydrogel is molded with the shape of the containment vessel. (B) Agglomeration with the addition of different quantities of ammonia. Graphene hydrogels with varied surface morphology were synthesized based on the amount of ammonia. Agglomeration of a relatively loose graphene hydrogel is demonstrated by the black arrows. Most GO sheets without charge were first attracted to minor GO sheets with negative charges and became large sheets. The large GO sheets finally lost charges and agglomerated easily because of the removal of carboxyl groups. Agglomeration of a relatively compact graphene hydrogel is indicated by green arrows. The carboxyl groups ionize into COO-, which reduced the partial agglomeration of the initial minor GO sheets. The GO sheets became hydrophobic, and COO- groups were removed gradually, resulting in the compact uniform agglomeration of GO sheets. Reproduced with permission from Ref. [53]. Copyright: 2012 Wiley.
Figure 3:

(A) Hydrothermal reduction process. The porous hydrogel is molded with the shape of the containment vessel. (B) Agglomeration with the addition of different quantities of ammonia. Graphene hydrogels with varied surface morphology were synthesized based on the amount of ammonia. Agglomeration of a relatively loose graphene hydrogel is demonstrated by the black arrows. Most GO sheets without charge were first attracted to minor GO sheets with negative charges and became large sheets. The large GO sheets finally lost charges and agglomerated easily because of the removal of carboxyl groups. Agglomeration of a relatively compact graphene hydrogel is indicated by green arrows. The carboxyl groups ionize into COO-, which reduced the partial agglomeration of the initial minor GO sheets. The GO sheets became hydrophobic, and COO- groups were removed gradually, resulting in the compact uniform agglomeration of GO sheets. Reproduced with permission from Ref. [53]. Copyright: 2012 Wiley.

2.1.2 Direct freeze drying

The high solubility and hydrophilic edges of the formed GO facilitates its good dispersion at high concentrations. The ungelated solution, which exhibits sufficiently strong bonding interactions, can be directly freeze dried to form GO sponges by controlling its concentration between 1 and 15 mg ml-1 [55, 56]. Figure 4A schematically illustrates graphene sponge formation during rapid solution freezing. This process caused internal expansion and macroscale cracking of the freeze-dried solution, and pore size was controlled by changing the freezing temperature [57]. This phenomenon resulted in a graphene sponge block (Figure 4B). Figure 4C–G shows the scanning electron micrographs of the porous structures of four graphene sponges fabricated at different freezing temperatures of -170°C, -40°C, -20°C, and -10°C. Qualitative schematic of the relationship between nucleation and crystal growth as a function of freezing temperature during ice solidification is shown in Figure 4H. Nucleation dominates the process at low temperatures, contrary to the favored crystal growth at high temperatures. The size of ice crystals is not drawn proportionally to that of a graphene sponge. Ice crystals are demonstrated artificially in the background, the factual scanning electron micrographs of microstructures. Improving the quality and strength of GO networks is important in the production of repeatable, scalable sponges. GO sponges were reduced to rGO sponges to change the hydrophilicity of the GO into the desired graphene hydrophobic properties to fulfill the demands as adsorbents. However, using chemical reduction in solution with a reducing agent, such as sodium borohydride, hydrazine, ascorbic acid, and HI is difficult [47, 48, 58–61] because reintroducing GO sponges to high humidity and water moisture could cause the rapid collapse of the sponge. Instead, the GO sponges can be reduced at relative high temperatures (600–1000°C) in a dry environment with inert gas atmosphere or at lower temperatures with a strong reducing vapor, such as hydrazine vapor, to form an rGO sponge [62–64]. The temperature ramp rate in this thermal reduction process should not be too high. Otherwise, the sponge would suffer thermal shock, rapidly releasing gas and disrupting the integrity of the sponge structure [56].

Figure 4: (A) Fabrication of enhanced spongy graphene. Components are intentionally not drawn into scale. (B) Macroscopic image of enhanced spongy graphene. (C–F) Scanning electron micrographs of the porous structures of four graphene sponges fabricated at different freezing temperatures of -170°C, -40°C, -20°C, and -10°C. Scale bar: 500 μm. (G) High-magnification scanning electron micrographs of pore walls composed of graphene nanosheets corresponding to (C). Mean thickness of the pore walls is 10 nm. (H) Qualitative schematic of the relationship between nucleation and crystal growth as a function of freezing temperature during ice solidification. Nucleation dominates the process at low temperatures, contrary to the favored crystal growth at high temperatures. The size of ice crystals is not drawn proportionally to that of a graphene sponge. Ice crystals are demonstrated artificially on the background, the factual scanning electron micrographs of microstructures. Reproduced with permission: (A and B), Ref. [21]; (C–H), Ref. [57]. Copyright: (A and B) 2013 Royal Society of Chemistry; (C–H) 2013 Nature Publishing Group.
Figure 4:

(A) Fabrication of enhanced spongy graphene. Components are intentionally not drawn into scale. (B) Macroscopic image of enhanced spongy graphene. (C–F) Scanning electron micrographs of the porous structures of four graphene sponges fabricated at different freezing temperatures of -170°C, -40°C, -20°C, and -10°C. Scale bar: 500 μm. (G) High-magnification scanning electron micrographs of pore walls composed of graphene nanosheets corresponding to (C). Mean thickness of the pore walls is 10 nm. (H) Qualitative schematic of the relationship between nucleation and crystal growth as a function of freezing temperature during ice solidification. Nucleation dominates the process at low temperatures, contrary to the favored crystal growth at high temperatures. The size of ice crystals is not drawn proportionally to that of a graphene sponge. Ice crystals are demonstrated artificially on the background, the factual scanning electron micrographs of microstructures. Reproduced with permission: (A and B), Ref. [21]; (C–H), Ref. [57]. Copyright: (A and B) 2013 Royal Society of Chemistry; (C–H) 2013 Nature Publishing Group.

2.1.3 CVD

CVD can be used to produce a monolayer or few layers of graphene with very high electoral conductivities comparable to that of pristine mechanically exfoliated graphene on a small scale [65]. Three main components are required in this growth process: a metal catalyst, a carbon precursor, and high temperature at approximately around 1000°C within a controlled atmosphere. Catalysts, such as Ni templates (Ni foams), generally play an important role in deriving large quantities of graphene material to synthesize 3D CVD graphene (CVD-G). The limited surface area of nickel foils traditionally prevents the extension of CVD-G to a large scale or to a 3D structure. Rapid development in this area seems to be represented by the work of Cheng et al. in 2011 [66]. An Ni sponge was prepared for graphene growth, and the possible surface oxide layer on the Ni sponge was removed by annealing for a short period at 1000°C under a 700-sccm gas flow composed of Ar:H2 at 2.5:1. A methane carbon source was introduced at a constant rate varying between 2 sccm and 10 sccm during synthesis under high temperature. Rapid convective cooling step of 100°C min-1 was applied after 5 min of carbon gas exposure (Figure 5A). The quality of graphene formed was verified using Raman spectroscopy, which showed no defect (D-Band) peak for the CVD-G materials. The shape and position of the Raman 2D peak [67] also suggested a narrow thickness distribution around only a few layers. Graphene material was obtained by etching away Ni via a hot 3-m HCl solution after the growth of the graphene coating. A sacrificial PMMA layer was added before etching to avoid collapse of the graphene network. Thus, Ni/graphene sponge was placed in a 4 wt% solution of PMMA (average molecular weight, 1 million), and then a thin layer was formed by baking at 180°C. After Ni was etched away, PMMA was gradually removed by placing the CVD-G sponge in hot acetone. The sample was then evaporated to yield a high-surface area graphene monolith with large dimensions (Figure 5B) and porous structure (Figure 5C). In addition to using Ni as the catalyst, monolayer graphene coatings were also produced using copper sponge. This sponge had lower carbon saturation level and also exhibited catalytic activity for growth of graphene materials. The growth produced a similar result; however, the growth mechanism for copper differs from that of Ni, and the collapse of the CVD-G sponges was not prevented when Cu supports were used. In addition, similar high-quality CVD-G sponges were achieved by others using ethanol as carbon source or with minor variations in flow and temperature [68–70].

Figure 5: (A) Synthesis of a GF and integration with PDMS. (1, 2) CVD growth of graphene films (Ni-G, 2) using a nickel foam (Ni foam, 1) as the 3D scaffold template. (3) As-grown graphene film after coating a thin PMMA supporting layer (Ni-G-PMMA). (4) GF coated with PMMA (GF-PMMA) after etching the Ni foam with hot HCl (or FeCl3/HCl) solution. (5) Free-standing GF after dissolution of the PMMA layer with acetone. (6) GF/PDMS composite after infiltration of PDMS into a GF. All scale bars are 500 μm. (B) Photograph of a 170×220-mm2 free-standing GF. (C) Scanning electron micrograph of a GF. Reproduced with permission from Ref. [66]. Copyright: 2011 Nature Publishing Group.
Figure 5:

(A) Synthesis of a GF and integration with PDMS. (1, 2) CVD growth of graphene films (Ni-G, 2) using a nickel foam (Ni foam, 1) as the 3D scaffold template. (3) As-grown graphene film after coating a thin PMMA supporting layer (Ni-G-PMMA). (4) GF coated with PMMA (GF-PMMA) after etching the Ni foam with hot HCl (or FeCl3/HCl) solution. (5) Free-standing GF after dissolution of the PMMA layer with acetone. (6) GF/PDMS composite after infiltration of PDMS into a GF. All scale bars are 500 μm. (B) Photograph of a 170×220-mm2 free-standing GF. (C) Scanning electron micrograph of a GF. Reproduced with permission from Ref. [66]. Copyright: 2011 Nature Publishing Group.

2.1.4 Surface coating

Surface coating provides a convenient way to control the shape and pattern growth of graphene-based adsorbent. The resultant graphene materials exhibit excellent structural integrity and reliable long-term order. The sacrificial template is used as the catalyst layer or supporting skeleton for graphene and GO. Liu et al. [71] reported graphene sponges produced using polyurethane (PU) sponge as support. Graphene sheets along with Fe3O4 nanoparticles are decorated on the PU sponge through self-assembly. The well-defined amorphous PU skeleton is covered by a thin layer of graphene and Fe3O4 nanoparticles.

2.1.5 Other synthesis techniques

Tightly stacked layers in GO films have been used to fabricate free-standing graphene sponges. Thermal shock application on GO films could lead to mixed results, achieving well-expanded GO films. This method is still not commonly used to fabricate sorbents. However, Niu et al. [63] investigated the controlled leavening of tightly packed free-standing graphite oxide films using small quantities of hydrazine. They produced flexible 3D rGO papers with surprising mechanical integrity (Figure 6), which still exhibited good oil capacity.

Figure 6: (A) Leavening process to prepare rGO foams. (B) Digital photograph of the free-standing paper-like rGO foam. (C) High magnification of the cross-sectional scanning electron micrograph of rGO foams formed after 10 h in an autoclave at 90°C with 80 μl of hydrazine monohydrate. Reproduced with permission from Ref. [63]. Copyright: 2012 Wiley.
Figure 6:

(A) Leavening process to prepare rGO foams. (B) Digital photograph of the free-standing paper-like rGO foam. (C) High magnification of the cross-sectional scanning electron micrograph of rGO foams formed after 10 h in an autoclave at 90°C with 80 μl of hydrazine monohydrate. Reproduced with permission from Ref. [63]. Copyright: 2012 Wiley.

2.2 Adsorption behavior

Several graphene sponges have been demonstrated as adsorbers for various oils, alkanes, water soluble alcohols, and organic solvents, with exceptional performance [29, 35, 72, 73]. Among these researches, we believe that we reported the first utilization of graphene sponge as adsorbent for oils and organic solvents [20]. We used 180°C autoclaved reduction to induce self-assembly and create a graphene sponge with 430 m2 g-1 surface area. This graphene sponge adsorbed many times its own weight (from 20 to 86 times). The graphene sponge with enhanced performance and utility was prepared by direct freeze drying of solutions containing giant GO sheets. In this experiment, GO sheets in the sponge created a high level of elasticity after thermal reduction. Furthermore, the sponge was highly hydrophobic, which had an ultralow density of ~0.9 mg cm-3. The fabricated graphene sponge had enhanced adsorption capacity by one magnitude compared with the previous one. The combination of these features allowed the tested ultralight sponge to reach an adsorption capacity of 110–616.4 g g-1, depending on liquid density. Photographs illustrating oil adsorption and characterization of a graphene sponge block, as well as the enhanced graphene spongy block, are presented in Figure 7A. A sharp increase in oil capacity of graphene sponge is shown in Figure 7B. Compared with conventional adsorbents, the adsorption capability of this sponge exhibited a great advantage. Additionally, heat treatment was easily applied to vaporize solvents because of the recyclability of graphene-based adsorbers caused by the thermal stability exhibited by graphene sponges (Figure 7C). This process allows the user to reuse the sponge materials (up to 99% capacity remaining after at least 10 cycles) (Figure 7D) and restore the adsorbed solvent condensate (99.9% restored for future use). Graphene sponge had strong potential to become efficient and safe adsorbers for remediation of organic media in environmental protection and industrial processes. Moreover, other groups have reported similar investigations on graphene sponge adsorbents. Zhao et al. [54] reported a 400-m2 g-1 graphene sponge prepared by a similar thermal reduction process but with the mixing of thiourea to functionalize and crosslink the material. Moreover, this graphene sponge even reached high adsorption capacities between 75 g g-1 and 154 g g-1. Dong et al. [35] utilized the CVD-G sponge to achieve 48.5–71 g g-1. Coating macroporous sponges with a dense forest of CNTs conferred superhydrophobicity (contact angle ~152°) on these sponges because of the increased surface roughness, boosting adsorption capacity to 80–130 g g-1 [34]. Sun et al. [29] presented a remarkable high-performance graphene-CNT sponge prepared by a similar direct freeze drying of GO sheets and CNT solutions. An adsorption capacity as high as 215–743 g g-1 was reached.

Figure 7: (A) Upper: Oil adsorption and characterization of an SG block adsorbing dodecane (stained with Sudan red 5B) at intervals of 40 s. Bottom: Oil adsorption and characterization of an enhanced SG block adsorbing crude oil at intervals of approximately 10 s. (B) Adsorption capacity comparison between SG and enhanced SG. Almost a magnitude enhancement was achieved using enhanced SG. (C) Four-step schematic diagram of SG recycling process. SG was regenerated and reused without affecting its performance when heated up to the temperature around the boiling point of adsorbate. The liquid could be evaporated, condensed, and recollected elsewhere. The SG material was ready to be used in the next cycle of adsorption without further process after simple heat treatment. (D) Recyclability of SG. (A) An SG repetitively adsorbed toluene and released its vapor under heat treatment (105°C) for 10 cycles. The weight of SG in each cycle was measured before (black line) and after (red dotted line; subtracted by the dormant weight of SG) heat treatment. Adsorbed mass of toluene ranged from 723 mg to 739 mg, and the SG weighed 13.7 mg. (B) Dodecane recycling (200°C). Conditions were similar to those described in (A). Adsorbed mass of dodecane ranged from 246 mg to 264 mg, and the SG weighed 5.2 mg. (E) Diagram of the experimental setup for the magnetic actuation testing. (F) Remote control of Fe3O4/GA for oil adsorption and recycling: Fe3O4/GA was guided by a magnet to move to adsorb oil. After saturation, oil was released from Fe3O4/GA by magnetic field-induced compression. The regenerated aerogels still maintained their original shapes. Reproduced with permission: (A, C, and D), Ref. [20]; (A and B), Ref. [21]; (E and F), Ref. [30]. Copyright: (A, C, and D) 2012 Wiley; (A and B) Royal Society of Chemistry 2014; (E and F) American Chemistry Society 2015.
Figure 7:

(A) Upper: Oil adsorption and characterization of an SG block adsorbing dodecane (stained with Sudan red 5B) at intervals of 40 s. Bottom: Oil adsorption and characterization of an enhanced SG block adsorbing crude oil at intervals of approximately 10 s. (B) Adsorption capacity comparison between SG and enhanced SG. Almost a magnitude enhancement was achieved using enhanced SG. (C) Four-step schematic diagram of SG recycling process. SG was regenerated and reused without affecting its performance when heated up to the temperature around the boiling point of adsorbate. The liquid could be evaporated, condensed, and recollected elsewhere. The SG material was ready to be used in the next cycle of adsorption without further process after simple heat treatment. (D) Recyclability of SG. (A) An SG repetitively adsorbed toluene and released its vapor under heat treatment (105°C) for 10 cycles. The weight of SG in each cycle was measured before (black line) and after (red dotted line; subtracted by the dormant weight of SG) heat treatment. Adsorbed mass of toluene ranged from 723 mg to 739 mg, and the SG weighed 13.7 mg. (B) Dodecane recycling (200°C). Conditions were similar to those described in (A). Adsorbed mass of dodecane ranged from 246 mg to 264 mg, and the SG weighed 5.2 mg. (E) Diagram of the experimental setup for the magnetic actuation testing. (F) Remote control of Fe3O4/GA for oil adsorption and recycling: Fe3O4/GA was guided by a magnet to move to adsorb oil. After saturation, oil was released from Fe3O4/GA by magnetic field-induced compression. The regenerated aerogels still maintained their original shapes. Reproduced with permission: (A, C, and D), Ref. [20]; (A and B), Ref. [21]; (E and F), Ref. [30]. Copyright: (A, C, and D) 2012 Wiley; (A and B) Royal Society of Chemistry 2014; (E and F) American Chemistry Society 2015.

In addition to the enhancement of oil capacity, another direction for graphene sponge synthesis is functionalization by doping. Some metal ions, such as Co2+ and Ni2+, can act as cross-linkers for assembling GO into 3D porous gels [71], which enhances the elasticity of GO spongy. Moreover, this Fe3O4/graphene aerogel (Fe3O4/GA) can exhibit up to 52% reversible magnetic field-induced strain and strain-dependent electrical resistance because of its magnetic particles, such as Fe3O4 nanoparticles [30]. This material can be used to monitor the degree of compression/stretching of the material, which will facilitate the development of smart control for the adsorption/desorption of oil (Figure 7E and F). Other groups have reported adsorbents based on graphene. Table 1 gives a brief summary of the comparison of reported graphene-based adsorbents.

Table 1

Summary of graphene sponge adsorbents.

Synthesis methodAbsorbents/absorption capability (g g-1)Desorption method/recycling timesReferences
Self-assemblySG/20–86Heating/10[20]
HGAs/21–77Heating/8[74]
ss-GF/40–198pH change/10[75]
F-rGO aerogel/34–112Heating/10[76]
GHs/30–40NA[34]
Direct dryingE-SG/110–610NA[21]
UFAs/215–743Heating/10[29]
rGO foams/98–122NA[77]
XPAA/rGO Aerogels/110–140NA[78]
GA/100–260Heating/10[79]
CVDG-CNT foam/48.5–71Heating/6[35]
Surface coatingMesoporous G/8–66Heating/10[80]
MPG/9–27Squeeze/8[71]
Thermal expansionrGO foam/8–46Heating/10[81]

GS, Graphene sponge; HGA, hierarchical porous graphene aerogels; ss-GF, smart graphene foam; F-rGO aerogels, functional rGO aerogels; GHs, graphene-based hydrogels; E-GS, enhanced graphene sponge; UFA, ultra flyweight aerogel; GA, graphene aerogels; G-CNT foam, graphene CNT hybrid foam; mesoporous G, mesoporous graphene.

3 CNT-based adsorbents

CNT-based materials are promising candidates for environmental applications, such as sorption, filtration, and separation, because of their light-weight, high porosity, and large surface area [82–84]. CNTs are considered superior adsorbents over various organic chemicals and inorganic contaminants with many advantages, such as stronger chemical-nanotube interactions, rapid equilibrium rates, high sorbent capacity, and tailored surface chemistry. The synthesis method and adsorption behaviors are as follows.

3.1 Synthesis of CNT-based adsorbents

Similar to graphene, CNT is also a feasible building block to synthesize porous, light-weight, and hydrophobic 3D structure. CVD techniques are recently used to prepare 3D structures composed of free-standing films of vertically aligned CNTs [85, 86]. However, high cost is an obstacle for adsorption development. Chemical techniques, such as aqueous self-assembly [87] and surface modification [88] were developed. These methods could utilize the properties of CNT.

3.1.1 CVD

A macroscopic, monolithic sponge can be synthesized by CVD. Gui et al. [36] used a precursor solution of ferrocene in dichlorobenzene, which was injected at 860°C for 4 h. The sponge consisted of CNTs self-assembled into a porous, interconnected, 3D framework (Figure 8A). A transmission electron micrograph of large-cavity thin-walled CNTs is shown in Figure 8B. An illustration of a sponge consisting of CNT piles (black lines) as the skeleton and open pores (void space) is exhibited in Figure 8C. During reaction, many catalyst particles were encapsulated inside the tube cavities, which might have conferred the ferromagnetic properties [89]. Growth rate along the thickness direction was approximately 2–3 mm h-1 and did not slow down during the entire process. Therefore, sponge production is scalable. Each microscale CNT makes a continuous skeleton with a high aspect ratio.

Figure 8: (A) Monolithic CNT sponge (4 cm×3 cm×0.8 cm) with bulk density of 7.5 mg cm-3. (B) Transmission electron micrograph of large-cavity, thin-walled CNTs. (C) Illustration of the sponge consisting of CNT piles (black lines) as the skeleton and open pores (void space). Reproduced with permission from Ref. [36]. Copyright: 2010 Wiley.
Figure 8:

(A) Monolithic CNT sponge (4 cm×3 cm×0.8 cm) with bulk density of 7.5 mg cm-3. (B) Transmission electron micrograph of large-cavity, thin-walled CNTs. (C) Illustration of the sponge consisting of CNT piles (black lines) as the skeleton and open pores (void space). Reproduced with permission from Ref. [36]. Copyright: 2010 Wiley.

3.1.2 Self-assembly

Functionalization of CNTs can result in the formation of free-standing CNT aerogels. CNTs, functionalized by ferrocene-grafted poly(p-phenyleneethynylene), can gelate common organic solvents, such as chloroform, to form robust 3D nanotube networks that cannot be redispersed in any organic solvent [90]. Thermally annealed CNT aerogels were mechanically stable and stiff, as well as highly porous (99%). These aerogels exhibited excellent electrical conductivity (1–2 S cm-1) and large specific surface area (590–680 m2 g-1) [91]. The resulting hydrogels exhibited an intriguing one-dimensional alignment of single-wall CNTs (SWCNT) on the surface of the gel nanofibers. This characteristic enhanced the elastic properties and thermal stability, as well as provided an interesting electrical conductivity of 3.1 S cm-1 to the resulting hydrogels. Meanwhile, the presence of functional groups on CNTs that remained available after gelation allowed the conjugation of the properties of gels and nanostructured carbon materials [92]. Thus, organogelators have multiple advantages considering that, in addition to the induction of gelation and conferring of additional properties to the resulting gels, functionalization helps CNT dispersion at the solution stage. Hence, homogeneous distribution of CNT throughout the resulting gel was achieved.

3.1.3 Surface coating

Petrov et al. reported on ice-mediated deposition of individual CNTs onto the inner surface of a preformed macroporous polymer cryogel [93]. The method is quite promising economically because it provided aerogels with a minimum amount of SWCNT (0.12–0.15 wt% with respect to the polymer), which exhibited high electrical conductivity of 1 S cm-1. Moreover, any preformed aerogel (regardless of chemical nature and morphology) could eventually be suitable for CNT surface modification considering that the process only based on freezing, and freeze drying does not require any particular property from the substrate. Moreover, surface coating treatments with multi-wall CNT (MWCNTs) can be applied to 3D collagen scaffolds, and the resulting materials can be used for bone tissue engineering [94]. The versatility in the type of substrate that can be used is not simple because CNT incorporation as surface modifiers, rather than embedded within the polymer matrix, may help preserve the intrinsic properties of the original aerogel also enhanced by coated CNTs. Moreover, Wang et al. [88] used CNTs to fabricate a reinforced superhydrophobic and superoleophilic polyurethane (PU) sponge for oil-water separation (Figure 9A). Digital photographs showed the surface difference between the pristine PU sponge and PU-CNT sponge (Figure 9B and C).

Figure 9: (A) Fabrication process of superhydrophobic and superoleophilic PU-CNT sponge. (B) Digital photographs of water and lubricating oil droplets on the pristine PU sponge. (C) Digital photograph of water and lubricating oil droplets on PU-CNT sponge. Reproduced with permission from Ref. [88]. Copyright: 2013 Royal Society of Chemistry.
Figure 9:

(A) Fabrication process of superhydrophobic and superoleophilic PU-CNT sponge. (B) Digital photographs of water and lubricating oil droplets on the pristine PU sponge. (C) Digital photograph of water and lubricating oil droplets on PU-CNT sponge. Reproduced with permission from Ref. [88]. Copyright: 2013 Royal Society of Chemistry.

3.2 Adsorption behavior

CNTs are low-surface energy materials similar to graphene. These materials could be synthesized into hydrophobic aerogels [36] using tailoring alignment, density, and porosity. Thus, CNTs can be applied as sorbents. Gui et al. [36] reported the utilization of CNT aerogels as sorbents for oils and organic solvents in 2010. Monolithic CNT aerogels with adjustable density ranging from 5 to 10 mg cm-3, surface area of 300–400 m2 g-1, and average pore size of approximately 80 nm could be fabricated by CVD. This sponge exhibited adsorption capability of 80× to 180× their own weight for various solvents and oils. The adsorption behavior is shown in Figure 10A. However, the adsorption capability of CNT aerogels was not as high as that of graphene sponge because of the denser structure of the CNT aerogels. Sorbents should have a lower density to increase adsorption capability. The prepared CNT aerogels exhibited some interesting properties, and the characteristics of CNTs could be modified by doping through synthesis. Hashim et al. [89] presented a feasible means to enhance the elastic properties of CNT aerogels by adopting a boron-doping strategy during CVD. This strategy would influence the formation of atomic-scale “elbow” junctions and nanotube covalent interconnections, resulting in ultralight weight, superhydrophobic (contact angle of ~150°), highly porous, and thermally stable material. This kind of CNT aerogel adsorbent can adsorb up to 180× its own weight. Interestingly, boron-doping CNT aerogels possessed a combination of physical properties that will impact the practical use of CNT for this application. The as-prepared CNT aerogels exhibited ferromagnetic properties because of the iron catalyst particles used in the growth process, which remained trapped in the CNT core. This trait offers a controllable and safe way for handling and recovering all CNT aerogel sorbents through magnetic fields (Figure 10B). Recycling of magnetic CNT sponges for spilled oil sorption is schematically shown in Figure 10C. Other groups have also reported graphene-based adsorbents, in particular, CNT adsorbents. Table 2 provides a brief summary of these studies.

Figure 10: (A) Adsorption process of toluene (stained with Sudan Black B) on water by CNT aerogel block within 5 s. (B) Left, boron-doped CNT aerogels burnt or squeezed (inset) to salvage the oil. Thus, CNT can be reused repetitively. Right, a magnet was used to track or move the oil; inset shows sponge after burning and before reuse. (C) Schematic of recycling Me-CNT sponges for spilled oil sorption. (I) sprinkled on the oil; (II) adsorbed spilled oil; (III) collected by magnet; (IV) regeneration; and (V) reuse. Reproduced with permission: (A), Ref. [36]; (B), Ref. [89]; and (C), Ref. [95]. Copyright: (A) 2010 Wiley; (B) 2012 Nature Publishing Group; and (C) 2013 American Chemistry Society.
Figure 10:

(A) Adsorption process of toluene (stained with Sudan Black B) on water by CNT aerogel block within 5 s. (B) Left, boron-doped CNT aerogels burnt or squeezed (inset) to salvage the oil. Thus, CNT can be reused repetitively. Right, a magnet was used to track or move the oil; inset shows sponge after burning and before reuse. (C) Schematic of recycling Me-CNT sponges for spilled oil sorption. (I) sprinkled on the oil; (II) adsorbed spilled oil; (III) collected by magnet; (IV) regeneration; and (V) reuse. Reproduced with permission: (A), Ref. [36]; (B), Ref. [89]; and (C), Ref. [95]. Copyright: (A) 2010 Wiley; (B) 2012 Nature Publishing Group; and (C) 2013 American Chemistry Society.

Table 2

Summary of CNT sorbents.

Synthesis methodAbsorbents/adsorption capability (g g-1)Desorption method/recycling timesReferences
CVDCNT sponge/80–180Burning or squeeze/10[36]
B-CNT sponge/24–130NA[89]
Me-CNT sponge/30–66Heating/1000[95]
Self-assemblyP-CNT aerogels/3.98–12Heating/10[87]
Surface coatingPU-CNT sponge/22–35Squeeze/150[88]

B-CNT sponge, Boron doped CNT sponge; Me-CNT sponge, magnetic carbon nanotube sponges; ss-GF, smart graphene foam; P-CNT aerogels, p-phenylenediamine modified carbon nanotubes aerogels; PU-CNT sponge, CNT reinforced PU sponge.

4 Carbon fiber aerogels

Resorcinol-formaldehyde organic aerogels were traditionally pyrolyzed in an inert atmosphere to form a highly cross-linked carbon structure to fabricate carbon aerogels [96, 97]. However, carbon aerogels are highly dense (100–800 mg cm-3) [98] and tend to break under compression. Meanwhile, CNTs and graphene can be employed as building blocks and assembled into macroscopic 3D architectures [99–102]. Both CNT aerogels and graphene sponges exhibited high adsorption capacity and outstanding recyclability. However, they also have some limitations. Preparation of CNT-based sponges requires expensive precursors and complex equipment, which hamper their massive production for practical applications [36, 86]. Moreover, the use of large amounts of chemicals and generation of acidic waste during GO preparation seriously restrict their current industrialization. Therefore, a facile, economic, and environmentally friendly method to produce carbon-based nanostructured aerogels should be explored.

4.1 Pyrolysis synthesis of carbon fiber aerogels

Natural porous materials and some fibers are usually used in spill events because they are easily accessible. However, natural adsorbents are often hydrophilic, which will hinder the oil adsorption ability. A feasible means to overcome this obstacle is to pyrolyze these adsorbents at high temperature to transform the natural fibers from hydrophilic to hydrophobic. Wu et al. [103] reported carbon fiber aerogels using bacterial cellulose (BC) as precursor. The dried BC aerogels were pyrolyzed at 700–1300°C under argon atmosphere to generate black and ultralight carbon fiber aerogels. After pyrolysis, the volume of obtained carbon fiber aerogel was only 15% of that of the original BC aerogel. Meanwhile, the density decreased from 9 to 10 mg cm-3 for BC aerogels to 4–6 mg cm-3 for carbon fiber aerogels because of the evaporation of volatile species. The macroscopic sizes of the as-synthesized carbon fiber aerogels were dependent on the sizes of the BC pellicles cut in the fabrication procedure. However, the production of these aerogels is still complex and expensive, thus, restricting their industrial applications. Cheap and widely available materials such as raw cotton, which is a typical natural material and sustainable and contains 90–95% cellulose, [104, 105] are promising raw materials for fabricating carbon-based aerogels. Raw cotton fibers have been used for sorption of dyes [106] and heavy metal ions [107]. However, their poor buoyancy characteristics, low oil-sorption capacity, unsatisfactory hydrophobicity, and recyclability, among others, hamper their application in the removal and separation of pollutants from water. A simple method was, therefore, adopted to pyrolyze raw cotton to generate black and light-weight twisted carbon fiber (TCF) aerogels to change hydrophilic raw cotton into hydrophobic TCF aerogels. This procedure requires a relatively high temperature. Few pieces of purified raw cotton with cylindrical shape were pyrolyzed at 800°C for 2 h at low pressure (~0.5 mbar) under argon atmosphere to generate black and lightweight TCF aerogels. After pyrolysis, the diameter of the cylindrical cotton decreased from 3 cm to 1.5 cm, and the height decreased from 1.5 cm to 0.9 cm. The volume of the TCF aerogel was, thus, only ~15% of that of raw cotton. The TCF aerogel has a low density of ~12 mg cm-3, which was measured by Archimedes’ principle. Photographs before and after pyrolysis are shown in Figure 11A and B. Structural integrity was still good, which could be observed in the scanning electron micrographs in Figure 11C and D.

Figure 11: (A) Photographs of raw cotton (left) before and (right) after a glass bottle with weight of 15.3 g was placed top of the cotton. (B) Photographs of a piece of TCF aerogel (left) before and (right) after a glass bottle with weight of 15.3 g was placed on top of the bottle. (C) Scanning electron micrograph of the cellulose fibers in raw cotton. Inset: photograph of a piece of raw cotton. (D) Scanning electron micrograph of the carbon fibers in TCF aerogel. Inset: photograph of a piece of TCF aerogel. Reproduced with permission from Ref. [22]. Copyright: 2013 Wiley.
Figure 11:

(A) Photographs of raw cotton (left) before and (right) after a glass bottle with weight of 15.3 g was placed top of the cotton. (B) Photographs of a piece of TCF aerogel (left) before and (right) after a glass bottle with weight of 15.3 g was placed on top of the bottle. (C) Scanning electron micrograph of the cellulose fibers in raw cotton. Inset: photograph of a piece of raw cotton. (D) Scanning electron micrograph of the carbon fibers in TCF aerogel. Inset: photograph of a piece of TCF aerogel. Reproduced with permission from Ref. [22]. Copyright: 2013 Wiley.

4.2 Adsorption behavior

Carbon fiber aerogel is an ideal candidate for the removal of pollutants, such as oils and organic solvents, because of their 3D porous structure, good mechanical property, and surface hydrophobicity. Strong sorption capability of TCF aerogel is demonstrated in Figure 12A and B. When the TCF aerogel was brought into contact with a heptane layer (stained with Sudan red 5B) on a water surface, the aerogel adsorbed the heptane completely and rapidly. The TCF aerogel floated on the water surface after sorption of the heptane because of its low density and hydrophobicity. This phenomenon indicates the potential use of the TCF aerogel for the facile removal of oil spillage and chemical leakage as well as for ease of recycling. In addition, the TCF aerogel can also be used to quickly adsorb chloroform, which was stained with Sudan red 5B at the bottom of water. Moreover, this aerogel also exhibits excellent recyclability and maintains high sorption capacity even after five cycles through distillation, burning (Figure 12C), or squeezing (Figure 12D).

Figure 12: Adsorption of organic liquids by TCF aerogel. Heptane (A) and chloroform (B) were stained with Sudan red 5B. These photographs show the sorption process using a TCF aerogel taken at intervals of 10 s. Recycling process of TCF aerogel via (C) combustion and (D) squeezing. Reproduced with permission from Ref. [22]. Copyright: 2013 Wiley.
Figure 12:

Adsorption of organic liquids by TCF aerogel. Heptane (A) and chloroform (B) were stained with Sudan red 5B. These photographs show the sorption process using a TCF aerogel taken at intervals of 10 s. Recycling process of TCF aerogel via (C) combustion and (D) squeezing. Reproduced with permission from Ref. [22]. Copyright: 2013 Wiley.

Based on the use of natural cellulose, Li et al. [38] synthesized carbon fiber from wintermelon, which is a typical vegetable. Wintermelon carbon aerogel achieved 16× to 50× weight gain depending on the densities of different oils and organic solvents. After the adsorption of the oils, desorption could be performed by simply heating to release the vapor of the adsorbers. Yang et al. [39] proved that bamboo could be a possible carbon source for carbon fiber fabrication. Bamboo could be synthesized into carbon fiber aerogels by adopting freeze drying combined with pyrolysis. Thus, an adsorption capability ranging from 30× to 129× its own weight was shown by bamboo. Another possible carbon source could be artificial materials full of cellulose, such as waste paper. This source is highly beneficial for the environment because waste paper, itself, as a main constituent of the municipal waste, has resulted in many environmental problems. Therefore, our group [23] has reported a simple and cost-effective method to fabricate a novel kind of carbon microbelt (CMB) aerogel with good selective sorption ability using waste paper as its precursor material. First, the waste paper was soaked in distilled water for 12 h through strong agitation under vigorous stirring, breaking down the cellulose in the paper. Then, the resulting products were freeze dried to synthesize fiber aerogel. Afterward, the products were pyrolyzed at 850°C for 2 h at low pressure (~0.5 mbar) under argon atmosphere to generate black and lightweight CMB aerogel. The as-prepared CMB aerogel exhibited highly efficient adsorption of both oils (up to 188× its own weight) and organic solvents such as chloroform (up to 151× its own weight). Moreover, the adsorption capacity of the CMB aerogel did not decrease even after numerous regenerations by simply distillation, burning, or squeezing, which depends on the characteristics of solvents. Waste paper is cheapest among all reported sorbents. All these carbon fiber aerogels are compared in Table 3.

Table 3

Summary of carbon fiber aerogel sorbents.

Synthesis methodAbsorbents/adsorption capability (g g-1)Desorption method/recycling timesReferences
PyrolysisWCA/16–50Heating/6[39]
UFC foams/68–160Heating, burning or squeezing/5[108]
CNF aerogels/106–312Heating or burning/5[103]
CMB aerogels/60–188Heating, burning or squeezing/5[23]
MCF aerogels/30–129Heating, burning or squeezing[38]
TCF aerogel/50–192Heating, burning or squeezing/5[22]

WCA, Water melon carbon aerogels; UFC foam, ultralight, fire-resistant, and compressible foam; CNF aerogels, carbon nanofiber aerogels; CMB aerogels, carbon microbelt aerogels; TCF aerogels, twisted carbon fiber aerogels.

5 Conclusion

Graphene and carbon-based sponges are 3D aerogel networks with high surface area, high chemical/electrochemical stability, and extremely high surface hydrophobicity. Thus, these materials are used to demonstrate the feasibility for bridging the nanoscale properties of carbon-based materials to practical macroscale applications in oil and organic solvent spills. This paper provides a comprehensive review of the most recent progress in the synthesis, characterization, fundamental understanding, and performance of all reported adsorbents and their practical applications. This review is expected to facilitate further improvement and development of advanced material-based adsorbents.

Several methods, such as CVD template growth of graphene on Ni foam, direct gelling of GO solutions, self-assembly, surface modification, and pyrolysis, have been successfully developed to prepare high-quality and high-performance adsorbents. Among these methods, CVD growth produced well-defined and large pore size structures with desirable properties. The quality of the material was primarily controlled by process variables during CVD growth. However, high temperature, sacrificial template, and multistep processing entail high cost and limitation for large-scale production. Self-assembly technique via reduction of GO is compatible with simultaneous growth of composite materials. The properties and performance of the formed graphene/GO sponges strongly depend on the quality and size of the GO precursor and the type of reducing agents. Although direct freeze-drying self-assembly is relatively simple, this process is heavily dependent on size and concentration, in which controlling ice crystal formation and cracking on a larger scale is a challenge. All reviewed methods require further development to promote robust, scalable sponges at low cost and with less restacking. As for the adsorption capacities, it is obvious that the adsorbents fabricated by the surface coating method generally possess the relative low oil and organic solvent adsorption capacities ranging from several times to several tens of times its initial weight. But for the self-assembled sponges/foams, the oil adsorption capacities are much larger than that of the surface-coating adsorbents, ranging from tens of times to hundreds of times the weight of original materials. What is more, direct drying carbon-based aerogels generally show the largest oil adsorption capacities. The oil-adsorption capacities can commonly reach over 100 times the weight of the initial materials, and the highest one could even achieve 743 times [29]. The difference of adsorption rate among these adsorbents may ascribe to their difference in densities. For the surface-coating method, the polymer skeleton used is usually denser than the pristine carbon-based aerogels. Graphene sheets and CNTs are typically used to realize the superhydrophobic surface of polymer skeleton. The ultralight graphene aerogels could be directly dried. For example, in Sun’s experiment [29], after hydrazine vapor reduction, the GO sheets in the sponge could create a high level of elasticity. Further, based on the direct drying method, this aerogel had an ultralow density (concentration controlled between 0.16 and 22.4 mg cm-3). More importantly, the method allowed for the scalable preparation of large sponge blocks, an integral feature for the development of materials, is needed for large-scale spill cleanup. The combination of these features allowed the tested ultralight sponge (1000 cm3, 1.4 mg cm-3). The ultralight carbon-based aerogels are the most suitable for oil removal in the view of oil adsorption capacity. However, their preparation methods are usually complicated and expensive when compared to those used for other superhydrophobic sponges. However, pyrolysis of natural fibers can be employed to fabricate low-cost undesirable adsorbents.

The development of graphene and carbon-based adsorbents not only focuses on the enhancement of adsorption capacities and lowering cost but also on the smart control of adsorption and desorption behaviors of adsorbents. A combination with functional materials, such as magnetic nanoparticles, is a possibility.

Corresponding author: Litao Sun, SEU-FEI Nano-Pico Center, Key Laboratory of MEMS of Ministry of Education, Collaborative Innovation Center for Micro/Nano Fabrication, Device and System, Southeast University, Nanjing 210096, China, e-mail: ; and Center for Advanced Materials and Manufacture, Joint Research Institute of Southeast University and Monash University, Suzhou 215123, China

About the authors

Shu Wan

Shu Wan is a PhD student in the School of Electronic Science and Engineering at Southeast University. He obtained his BE degree in 2011 from Southeast University, China. His research interests focus mainly on applications of nanomaterials in environment, and 2D materials devices.

Hengchang Bi

Hengchang Bi is a PhD student in the School of Electronic Science and Engineering at Southeast University. He obtained his BE degree in 2007 from Shanxi University of Science and Technology, China. His research interests mainly focus on applications of nanomaterials in environment, and 2D materials.

Litao Sun

Litao Sun is currently a distinguished professor at Southeast University, China. His current research interests include in situ experimentation inside the electron microscope, graphene, and related 2D materials, new phenomena from sub-10 nm nanoparticles/nanowires, and applications of nanomaterials in environment, renewable energy, and nanoelectromechanical systems.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (nos. 61274114, 51420105003, and 113279028), the Natural Science Foundation of Jiangsu Province (no. BK2012024), and Scientific Research Foundation of Graduate School of Southeast University (no. YBJJ1208 and YBPYB01).

References

[1] Chabot V, Higgins D, Yu A, Xiao X, Chen Z, Zhang J. A review of graphene and graphene oxide sponge: material synthesis and applications to energy and the environment. Energy Environ. Sci. 2014, 7, 1564–1596.Suche in Google Scholar

[2] Zhu Y, Murali S, Cai W, Li X, Suk JW, Potts JR, Ruoff RS. Graphene and graphene oxide: synthesis, properties and applications. Adv. Mater. 2010, 22, 3906–3924.Suche in Google Scholar

[3] Brownson D, Banks C. Graphene electrochemistry: an overview of potential applications. Analyst 2010, 135, 2768–2778.10.1039/c0an00590hSuche in Google Scholar

[4] Thompson B, Fréchet JMJ. Polymer–fullerene composite solar cells. Angew. Chem., Int. Ed. 2008, 47, 58–77.Suche in Google Scholar

[5] Hammel E, Tang X, Trampert M, Schmitt T, Mauthner K, Eder A, Pötschke P. Carbon nanofibers for composite applications. Carbon 2004, 42, 1153–1158.10.1016/j.carbon.2003.12.043Suche in Google Scholar

[6] Jong K, Geus J. Carbon nanofibers: catalytic synthesis and applications. Catal. Rev.Sci. Eng. 2000, 42, 481–510.Suche in Google Scholar

[7] Sherigara BS, Kutner W, D’Souza F. Electrocatalytic properties and sensor applications of fullerenes and carbon nanotubes. Electroanalysis 2003, 15, 753–772.10.1002/elan.200390094Suche in Google Scholar

[8] Thostenson ET, Ren Z, Chou TW. Advances in the science and technology of carbon nanotubes and their composites: a review. Compos. Sci. Technol. 2001, 61, 1899–1912.Suche in Google Scholar

[9] Baughman RH, Zakhidov AA, de Heer W. Carbon nanotubes – the route toward applications. Science 2002, 297, 787–792.10.1126/science.1060928Suche in Google Scholar

[10] Huang Y, Liang J, Chen Y. An overview of the applications of graphene-based materials in supercapacitors. Small 2012, 8, 1805–1834.10.1002/smll.201102635Suche in Google Scholar

[11] Gooding JJ. Nanostructuring electrodes with carbon nanotubes: a review on electrochemistry and applications for sensing. Electrochim. Acta. 2005, 50, 3049–3060.10.1016/j.electacta.2004.08.052Suche in Google Scholar

[12] Annunciado T, Sydenstricker RTHD, Amico SC. Experimental investigation of various vegetable fibers as sorbent materials for oil spills. Mar. Pollut. Bull. 2005, 50, 1340–1346.Suche in Google Scholar

[13] Radetić MM, Jocić DM, Iovantić PM, Petrović ZLJ, Thomas HF. Recycled wool-based nonwoven material as oil sorbent. Environ. Sci. Technol. 2003, 37, 1008–1012.Suche in Google Scholar

[14] Bastani D, Safekordi A, Alihosseini A, Taghikhani V. Study of oil sorption by expanded perlite at 298.15 k. Sep. Purif. Technol. 2006, 52, 295–300.Suche in Google Scholar

[15] Kulawardana EU, Neckers DC. Photoresponsive oil sorbers. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 55–62.Suche in Google Scholar

[16] Li A, Sun H, Tan D, Fan W, Wen S, Qing X, Li G, Li S, Deng W. Superhydrophobic conjugated microporous polymers for separation and adsorption. Energy Environ. Sci. 2011, 4, 2062–2065.Suche in Google Scholar

[17] Toyoda M, Inagaki M. Heavy oil sorption using exfoliated graphite: new application of exfoliated graphite to protect heavy oil pollution. Carbon 2000, 38, 199–210.10.1016/S0008-6223(99)00174-8Suche in Google Scholar

[18] Li S, Tian S, Du C, He C, Cen C, Xiong Y. Vaseline-loaded expanded graphite as a new adsorbent for toluene. Biochem. Eng. J. 2010, 162, 546–551.Suche in Google Scholar

[19] Inagaki M, Konno H, Toyoda M, Moriya K, Kihara T. Sorption and recovery of heavy oils by using exfoliated graphite. Part II: recovery of heavy oil and recycling of exfoliated graphite. Desalination 2000, 128, 213–218.10.1016/S0011-9164(00)00035-7Suche in Google Scholar

[20] Bi H, Xie X, Yin K, Zhou Y, Wan S, He L, Xu F, Banhart F, Sun L. Ruoff RS. Spongy graphene as a highly efficient and recyclable sorbent for oils and organic solvents. Adv. Funct. Mater. 2012, 22, 4421–4425.Suche in Google Scholar

[21] Bi H, Xie X, Yin K, Zhou Y, Wan S, Ruoff RS, Sun L. Highly enhanced performance of spongy graphene as an oil sorbent. J. Mater. Chem. A 2014, 2, 1652–1656.10.1039/C3TA14112HSuche in Google Scholar

[22] Bi H, Yin Z, Cao X, Xie X, Tan C, Huang X, Chen B, Chen F, Yang Q, Bu X, Lu X, Sun L, Zhang H. Carbon fiber aerogel made from raw cotton: a novel, efficient and recyclable sorbent for oils and organic solvents. Adv. Mater. 2013, 25, 5916–5921.Suche in Google Scholar

[23] Bi H, Huang X, Wu X, Cao X, Tan C, Yin Z, Lu X, Sun L, Zhang H. Carbon microbelt aerogel prepared by waste paper: an efficient and recyclable sorbent for oils and organic solvents. Small 2014, 10, 3544–3550.10.1002/smll.201303413Suche in Google Scholar PubMed

[24] Wan Ngah WS, Teong LC, Hanafiha MAKM. Adsorption of dyes and heavy metal ions by chitosan composites: a review. Carbohyd. Polym. 2011, 83, 1446–1456.Suche in Google Scholar

[25] Yu JG, Zhao XH, Yang H, Chen XH, Yang Q, Yu LY, Jiang JH, Chen XQ. Aqueous adsorption and removal of organic contaminants by carbon nanotubes. Sci. Total Environ. 2014, 482–483, 241–251.Suche in Google Scholar

[26] Gupta VK. Suhas. Application of low-cost adsorbents for dye removal – a review. J. Environ Manage. 2009, 90, 2313–2342.10.1016/j.jenvman.2008.11.017Suche in Google Scholar PubMed

[27] Yu JG, Yu LY, Yang H, Liu Q, Chen XH, Jiang XY, Chen XQ, Jiao FP. Graphene nanosheets as novel adsorbents in adsorption, preconcentration and removal of gases, organic compounds and metal ions. Sci. Total Environ. 2015, 502, 70–79.Suche in Google Scholar

[28] Yao YX, Li HB, Liu JY, Tan XL, Yu JG, Peng ZG. Removal and adsorption of p-nitrophenol from aqueous solutions using carbon nanotubes and their composites. J. Nanomater. 2014, 2014, 571745.Suche in Google Scholar

[29] Sun H, Xu Z, Gao C. Multifunctional, ultra-flyweight, synergistically assembled carbon aerogels. Adv. Mater. 2013, 25, 2554–2560.Suche in Google Scholar

[30] Xu X, Li H, Zhang Q, Hu H, Zhao Z, Li J, Li J, Qiao Y, Gogotsi Y. Self-sensing, ultralight, and conductive 3D graphene/iron oxide aerogel elastomer deformable in a magnetic field. ACS Nano 2015, 9, 3969–3977.10.1021/nn507426uSuche in Google Scholar PubMed

[31] Niu Z, Liu L, Zhang L, Chen X. Porous graphene materials for water remediation. Small 2014, 10, 3434–3441.10.1002/smll.201400128Suche in Google Scholar PubMed

[32] Yan Z, Yao W, Hu L, Liu D, Wang C, Lee C. Progress in the preparation and application of three-dimensional graphene-based porous nanocomposites. Nanoscale 2015, 7, 5563–5577.10.1039/C5NR00030KSuche in Google Scholar

[33] Nardecchia S, Carriazo D, Ferrer ML, Gutiérrez MC, del Monte F. Three dimensional macroporous architectures and aerogels built of carbon nanotubes and/or graphene: synthesis and applications. Chem. Soc. Rev. 2013, 42, 794–830.Suche in Google Scholar

[34] Wu T, Chen M, Zhang L, Xu X, Liu Y, Yan J, Wang W, Gao J. Three-dimensional graphene-based aerogels prepared by a self-assembly process and its excellent catalytic and absorbing performance. J. Mater. Chem. A 2013, 1, 7612–7621.10.1039/c3ta10989eSuche in Google Scholar

[35] Dong X, Chen J, Ma Y, Wang J, Chan-Park MB, Li X, Wang L, Huang W, Chen P. Superhydrophobic and superoleophilic hybrid foam of graphene and carbon nanotube for selective removal of oils or organic solvents from the surface of water. Chem. Commun. 2012, 48, 10660–10662.Suche in Google Scholar

[36] Gui X, Wei J, Wang K, Cao A, Zhu H, Jia Y, Shu Q, Wu D. Carbon nanotube sponges. Adv. Mater. 2010, 22, 617–621.Suche in Google Scholar

[37] Lillo-Ródenas MA, Cazorla-Amorós D, Linares-Solano A. Behaviour of activated carbons with different pore size distributions and surface oxygen groups for benzene and toluene adsorption at low concentrations. Carbon 2005, 43, 1758–1767.10.1016/j.carbon.2005.02.023Suche in Google Scholar

[38] Li Y, Samad YA, Polychronopoulou K, Alhassan SM, Liao K. Carbon aerogel from winter melon for highly efficient and recyclable oils and organic solvents absorption. ACS Sustainable Chem. Eng. 2014, 2, 1492–1497.Suche in Google Scholar

[39] Yang S, Chen L, Mu L, Hao B, Ma PC. Low cost carbon fiber aerogel derived from bamboo for the adsorption of oils and organic solvents with excellent performances. RSC Adv. 2015, 5, 38470–38478.Suche in Google Scholar

[40] Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y, Dubonos SV, Grigorieva IV, Firsov AA. Electric field effect in atomically thin carbon films. Science 2004, 306, 666–669.10.1126/science.1102896Suche in Google Scholar PubMed

[41] Novoselov KS, Fal’ko VI, Colombo L, Gellert PR, Schwab MG, Kim K. A roadmap for graphene. Nature 2012, 490, 192–200.10.1038/nature11458Suche in Google Scholar PubMed

[42] Rafiee J, Rafiee MA, Yu ZZ, Koratkar N. Superhydrophobic to superhydrophilic wetting control in graphene films. Adv. Mater. 2010, 22, 2151–2154.Suche in Google Scholar

[43] Pierre AC, Pajonk GM. Chemistry of aerogels and their applications. Chem. Rev. 2002, 102, 4243–4265.Suche in Google Scholar

[44] Hummers W, Offeman RE. Preparation of graphitic oxide. J. Am. Chem. Soc. 1958, 80, 1339–1339.Suche in Google Scholar

[45] Marcano DC, Kosynkin DV, Berlin JM, Sinitskii A, Sun Z, Slesarev A, Alemany LB, Lu W, Tour JM. Improved synthesis of graphene oxide. ACS Nano 2010, 4, 4806–4814.10.1021/nn1006368Suche in Google Scholar PubMed

[46] Park S, Ruoff RS. Chemical methods for the production of graphenes. Nat. Nanotechnol. 2009, 4, 217–224.Suche in Google Scholar

[47] Pei S, Zhao J, Du J, Ren W, Cheng HM. Direct reduction of graphene oxide films into highly conductive and flexible graphene films by hydrohalic acids. Carbon 2010, 48, 4466–4474.10.1016/j.carbon.2010.08.006Suche in Google Scholar

[48] Dreyer DR, Park S, Bielawski CW, Ruoff RS. The chemistry of graphene oxide. Chem. Soc. Rev. 2010, 39, 228–240.Suche in Google Scholar

[49] He H, Klinowski J, Forster M, Lerf A. A new structural model for graphite oxide. Chem. Phys. Lett.1998, 287, 53–56.Suche in Google Scholar

[50] Li D, Müller MB, Gilje S, Kaner RB, Wallace GG. Processable aqueous dispersions of graphene nanosheets. Nat. Nanotechnol. 2008, 3, 101–105.Suche in Google Scholar

[51] Long Y, Zhang C, Wang X, Gao J, Wang W, Liu Y. Oxidation of SO2 to SO3 catalyzed by graphene oxide foams. J. Mater. Chem. 2011, 21, 13934–13941.Suche in Google Scholar

[52] Stankovich S, Dikin DAG, Domment HB, Kohihaas KM, Zimney EJ, Stach EA, Piner RD, Nguyen ST, Ruoff RS. Graphene-based composite materials. Nature 2006, 442, 282–286.10.1038/nature04969Suche in Google Scholar PubMed

[53] Bi H, Yin K, Xie X, Zhou Y, Wan N, Xu F, Banhart F, Sun L, Ruoff RS. Low temperature casting of graphene with high compressive strength. Adv. Mater. 2012, 24, 5124–5129.Suche in Google Scholar

[54] Zhao J, Ren W, Cheng HM. Graphene sponge for efficient and repeatable adsorption and desorption of water contaminations. J. Mater. Chem. 2012, 22, 20197–20202.Suche in Google Scholar

[55] Xue Y, Liu J, Chen H, Wang R, Li D, Qu J, Dai L. Nitrogen-doped graphene foams as metal-free counter electrodes in high-performance dye-sensitized solar cells. Angew. Chem., Int. Ed. 2012, 51, 12124–12127.Suche in Google Scholar

[56] Lin Y, Ehlert GJ, Bukowsky C, Sodano HA. Superhydrophobic functionalized graphene aerogels. ACS Appl. Mater. Interfaces 2011, 3, 2200–2203.10.1021/am200527jSuche in Google Scholar PubMed

[57] Xie X, Zhou Y, Bi H, Yin K, Wan S, Sun L. Large-range control of the microstructures and properties of three-dimensional porous graphene. Sci. Rep. 2013, 3, 2117.Suche in Google Scholar

[58] Stankovich S, Dikin D, Piner RD, Kohlhaas K, Kleinhammes A, Jia Y, Wu Y, Nguyen ST, Ruoff RS. Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide. Carbon 2007, 45, 1558–1565.10.1016/j.carbon.2007.02.034Suche in Google Scholar

[59] Fernandez-Merino M, Guardia L, Paredes JI, Villar-Rodil P, Solis-Fernandez P, Martinez-Alonso A, Tascon JMD. Vitamin C is an ideal substitute for hydrazine in the reduction of graphene oxide suspensions. J. Phys. Chem. C 2010, 114, 6426–6432.10.1021/jp100603hSuche in Google Scholar

[60] Shin HJ, Kim KK, Benayad A, Yoon SM, Park HK, Jung IS, Jin MH, Jeong HK, Kim JM, Choi JY, Lee YH. Efficient reduction of graphite oxide by sodium borohydride and its effect on electrical conductance. Adv. Funct. Mater. 2009, 19, 1987–1992.Suche in Google Scholar

[61] Mi X, Huang G, Xie W, Wang W, Liu Y, Gao J. Preparation of graphene oxide aerogel and its adsorption for Cu2+ ions. Carbon 2012, 50, 4856–4864.10.1016/j.carbon.2012.06.013Suche in Google Scholar

[62] Yoo JJ, Balakrishnan K, Huang J, Meunier V, Sumpter BG, Srivastava A, Conway M, Reddy ALM, Yu J, Vajtai R, Ajayan PM. Ultrathin planar graphene supercapacitors. Nano Lett. 2011, 11, 1423–1427.Suche in Google Scholar

[63] Niu Z, Chen J, Hng HH, Ma J, Chen X. A leavening strategy to prepare reduced graphene oxide foams. Adv. Mater. 2012, 24, 4144–4150.Suche in Google Scholar

[64] Wang H, Maiyalagan T, Wang X. Review on recent progress in nitrogen-doped graphene: synthesis, characterization, and its potential applications. ACS Catal. 2012, 2, 781–794.Suche in Google Scholar

[65] Zhang HB, Wang JW, Yan Q, Zheng WG, Chen C, Yu ZZ. Vacuum-assisted synthesis of graphene from thermal exfoliation and reduction of graphite oxide. J. Mater. Chem. 2011, 21, 5392–5397.Suche in Google Scholar

[66] Chen Z, Ren W, Gao L, Liu B, Pei S, Cheng H. Three dimensional flexible and conductive interconnected graphene networks grown by chemical vapour deposition. Nat. Mater. 2011, 10, 424–428.Suche in Google Scholar

[67] Ferrari AC, Meyer JC, Scardaci V, Casiraghi C, Lazzeri M, Mauri F, Piscanec S, Jiang D, Novoselov KS, Roth S, Geim AK. Raman spectrum of graphene and graphene layers. Phys. Rev. Lett. 2006, 97, 187401.Suche in Google Scholar

[68] Dong X, Wang X, Wang L, Song H, Zhang H, Huang W, Chen P. 3D graphene foam as a monolithic and macroporous carbon electrode for electrochemical sensing. ACS Appl. Mater. Interfaces 2012, 4, 3129–3133.10.1021/am300459mSuche in Google Scholar PubMed

[69] Dong X, Wang X, Wang J, Song H, Li X, Wang L, Chan-Park MBC, Li M, Chen P. Synthesis of a MnO2–graphene foam hybrid with controlled MnO2 particle shape and its use as a supercapacitor electrode. Carbon 2012, 50, 4865–4870.10.1016/j.carbon.2012.06.014Suche in Google Scholar

[70] Cao X, Shi Y, Shi W, Lu G, Huang X, Yan Q, Zhang Q, Zhang H. Preparation of novel 3D graphene networks for supercapacitor applications. Small 2011, 7, 3163–3168.10.1002/smll.201100990Suche in Google Scholar PubMed

[71] Liu C, Yang J, Tang Y, Yin L, Tang H, Li C. Versatile fabrication of the magnetic polymer-based graphene foam and applications for oil–water separation. Colloids and Surfaces A: Physicochem. Eng. Aspects 2015, 468, 10–16.10.1016/j.colsurfa.2014.12.005Suche in Google Scholar

[72] Liang Y, Li Y, Wang H, Zhou J, Wang J, Regier T, Dai H. Co3O4 nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction. Nat. Mater. 2011, 10, 780–786.Suche in Google Scholar

[73] Wang X, Lu LL, Yu ZL, Xu XW, Zheng YR, Yu SH. Scalable template synthesis of resorcinol-formaldehyde/graphene oxide composite aerogels with tunable densities and mechanical properties. Angew. Chem., Int. Ed. 16, 54, 2397–2401.10.1002/anie.201410668Suche in Google Scholar PubMed

[74] Chi C, Xu H, Zhang K, Wang Y, Zhang S, Liu X, Liu X, Zhao J, Li Y. 3D hierarchical porous graphene aerogels for highly improved adsorption and recycled capacity. Mater. Sci. Eng. B 2015, 194, 62–67.10.1016/j.mseb.2014.12.026Suche in Google Scholar

[75] Zhu H, Chen D, Li N, Xu Q, Li H, He J, Lu J. Graphene foam with switchable oil wettability for oil and organic solvents recovery. Adv. Funct. Mater. 2015, 25, 597.Suche in Google Scholar

[76] Hong JY, Sohn EH, Park S, Park HS. Highly-efficient and recyclable oil absorbing performance of functionalized graphene aerogel. Chem. Eng. J. 2015, 269, 229–235.Suche in Google Scholar

[77] He Y, Liu Y, Wu T, Ma J, Wang X, Gong Q, Kong W, Xing F, Liu Y, Gao J. An environmentally friendly method for the fabrication of reduced graphene oxide foam with a super oil absorption capacity. J. Hazardous Mater. 2013, 260, 796–805.Suche in Google Scholar

[78] Ha H, Shanmuganathan K, Ellison CJ. Mechanically stable thermally crosslinked poly(acrylic acid)/reduced graphene oxide aerogels. ACS Appl. Mater. Interfaces 2015, 7, 6220–6229.10.1021/acsami.5b00407Suche in Google Scholar PubMed

[79] Xu L, Xiao G, Chen C, Li R, Mai Y, Sun G, Yan D. Superhydrophobic and superoleophilic graphene aerogel prepared by facile chemical reduction. J. Mater. Chem. A 2015, 3, 7498–7504.10.1039/C5TA00383KSuche in Google Scholar

[80] Fan ZL, Qin XJ, Sun HX, Zhu ZQ, Pei CJ, Liang WD, Bao XM, An J, La PQ, Li A, Deng WQ. Superhydrophobic mesoporous graphene for separation and absorption. ChemPlusChem 2013, 78, 1282–1287.10.1002/cplu.201300119Suche in Google Scholar PubMed

[81] Yang SJ, Kang JH, Jung H, Kim T, Park CR. Preparation of a freestanding, macroporous reduced graphene oxide film as an efficient and recyclable sorbent for oils and organic solvents. J. Mater. Chem. A 2013, 1, 9427–9432.10.1039/c3ta10663bSuche in Google Scholar

[82] Shannon MA, Bohn PW, Elimelech M, Georgiadis JG, Mariñas BJ, Mayes AM. Science and technology for water purification in the coming decades. Nature 2008, 452, 301–310.10.1038/nature06599Suche in Google Scholar PubMed

[83] Mauter MS, Elimelech M. Environmental applications of carbon-based nanomaterials. Environ. Sci. Technol. 2008, 42, 5843–5859.Suche in Google Scholar

[84] Pan B, Xing B. Adsorption mechanisms of organic chemicals on carbon nanotubes. Environ. Sci. Technol. 2008, 42, 9005–9013.Suche in Google Scholar

[85] Hata K, Futaba DN, Mizuno K, Namai T, Yumura M, Iijima S. Water-assisted highly efficient synthesis of impurity-free single-walled carbon nanotubes. Science 2004, 306, 1362–1364.10.1126/science.1104962Suche in Google Scholar PubMed

[86] Shi MK, Oh J, Lima M, Kozlov ME, Kim SJ, Baughman RH. Elastomeric conductive composites based on carbon nanotube forests. Adv. Mater. 2010, 22, 2663–2667.Suche in Google Scholar

[87] Sun H, La P, Zhu Z, Liang W, Yang B, Zhao X, Pei C, Li A. Hydrophobic carbon nanotubes for removal of oils and organics from water. J. Mater. Sci. 2014, 49, 6855–6861.Suche in Google Scholar

[88] Wang H, Wang E, Liu Z, Gao D, Yuan R, Sun L, Zhu Y. A novel carbon nanotubes reinforced superhydrophobic and superoleophilic polyurethane sponge for selective oil–water separation through a chemical fabrication. J. Mater. Chem. A 2015, 3, 266–273.10.1039/C4TA03945ASuche in Google Scholar

[89] Hashim DP, Narayanan NT, Romo-Herrera JM, Cullen DA, Hahm MG, Lezzi P, Suttle J, Kelkhoff RD, Muṅoz-Sandoval E, Ganguli S, Roy AK, Smith DJ, Vajtail R, Sumpter BG, Meunier V, Terrones H, Terrones M, Ajayan PM. Covalently bonded three-dimensional carbon nanotube solids via boron induced nanojunctions. Sci. Rep. 2012, 2, 363.Suche in Google Scholar

[90] Chen J, Xue C, Ramasubramaniam R, Liu H. A new method for the preparation of stable carbon nanotube organogels. Carbon 2006, 44, 2142–2146.10.1016/j.carbon.2006.03.011Suche in Google Scholar

[91] Kohlmeyer RR, Lor M, Deng J, Liu H, Chen J. Preparation of stable carbon nanotube aerogels with high electrical conductivity and porosity. Carbon 2011, 49, 2352–2361.10.1016/j.carbon.2011.02.001Suche in Google Scholar

[92] Lascialfari L, Vinattieri C, Ghini G, Luconi L, Berti D, Mannini M, Bianchini C, Brandi A, Giambastiani G, Cicchi S. Soft matter nanocomposites by grafting a versatile organogelator to carbon nanostructures. Soft Matter 2011, 7, 10660–10665.10.1039/c1sm06017aSuche in Google Scholar

[93] Petrov PD, Georgiev GL. Ice-mediated coating of macroporous cryogels by carbon nanotubes: a concept towards electrically conducting nanocomposites. Chem. Commun. 2011, 47, 5768–5770.Suche in Google Scholar

[94] Hirata E, Uo M, Takita H, Akasaka T, Watari F, Yokoyama A. Multiwalled carbon nanotube-coating of 3D collagen scaffolds for bone tissue engineering, Carbon 2011, 49, 3284–3291.10.1016/j.carbon.2011.04.002Suche in Google Scholar

[95] Gui X, Zeng Z, Lin Z, Gan Q, Xiang R, Zhu Y, Cao A, Tang Z. Magnetic and highly recyclable macroporous carbon nanotubes for spilled oil sorption and separation. ACS Appl. Mater. Interfaces 2013, 5, 5845–5850.10.1021/am4015007Suche in Google Scholar PubMed

[96] Wu DC, Fu RW, Zhang ST, Dresselhaus MS, Dresselhaus G. Preparation of low density carbon aerogels by ambient pressure drying. Carbon 2004, 42, 2033–2039.10.1016/j.carbon.2004.04.003Suche in Google Scholar

[97] Pekala RW. Organic aerogels from the polycondensation of resorcinol with formaldehyde. J. Mater. Sci. 1989, 24, 3221–3227.10.1007/BF01139044Suche in Google Scholar

[98] Fu RW, Zheng B, Liu J, Dresselhaus MS, Dresselhaus G, Satcher JH, Baumann TE. The fabrication and characterization of carbon aerogels by gelation and supercritical drying in isopropanol. Adv. Funct. Mater. 2003, 13, 558–562.Suche in Google Scholar

[99] Bryning MB, Milkie DE, Islam MF, Hough LA, Kikkawa JM, Yodh AG. Carbon nanotube aerogels. Adv. Mater. 2007, 19, 661–664.Suche in Google Scholar

[100] Worsley MA, Pauzauskie PJ, Olson TY, Biener J, Satcher JH, Baumann TF. Synthesis of graphene aerogel with high electrical conductivity. J. Am. Chem. Soc. 2010, 132, 14067–14069.Suche in Google Scholar

[101] Cong HP, Ren XC, Wang P, Yu SH. Macroscopic multifunctional graphene-based hydrogels and aerogels by a metal ion induced self-assembly process. ACS Nano 2012, 6, 2693–2703.10.1021/nn300082kSuche in Google Scholar PubMed

[102] Xu Y, Sheng K, Li C, Shi G. Self-assembled graphene hydrogel via a one-step hydrothermal process. ACS Nano 2010, 4, 4324–4330.10.1021/nn101187zSuche in Google Scholar PubMed

[103] Wu ZY, Li C, Liang HW, Chen JF, Yu SH. Ultralight, flexible, and fire-resistant carbon nanofiber aerogels from bacterial cellulose. Angew. Chem., Int. Ed. 2013, 52, 2925–2928.Suche in Google Scholar

[104] Segal L, Wakelyn PJ. In High Technology Fibers, Part A, Vol. 3, Lewin, M, Preston, J, Eds., Marcel Dekker, Inc: New York, 1985, p. 809.Suche in Google Scholar

[105] Carmody O, Frost R, Xi YF, Kokot S. Surface characterisation of selected sorbent materials for common hydrocarbon fuels. Surf. Sci. 2007, 601, 2066–2076.Suche in Google Scholar

[106] Kaewprasit C, Hequet E, Abidi N, Gourlot JP. Quality measurements-application of methylene blue adsorption to cotton fiber specific surface area measurement: Part I: Methodology. J. Cotton Sci. 1998, 2, 164–173.Suche in Google Scholar

[107] Nada AMA, El-Wakil NA, Hassan ML, Adel AM. Differential adsorption of heavy metal ions by cotton stalk cation-exchangers containing multiple functional groups. J. Appl. Polym. Sci. 2006, 101, 4124–4132.Suche in Google Scholar

[108] Yang Y, Deng Y, Tong Z, Wang C. Multifunctional foams derived from poly(melamine formaldehyde) as recyclable oil absorbents. J. Mater. Chem. A 2014, 2, 9994–9999.10.1039/C4TA00939HSuche in Google Scholar

Received: 2015-10-15
Accepted: 2015-12-7
Published Online: 2016-1-21
Published in Print: 2016-2-1

©2016 by De Gruyter

Artikel in diesem Heft

  1. Frontmatter
  2. In this issue
  3. Editorial
  4. Emerging nanotechnology for environmental applications
  5. Reviews
  6. Graphene and carbon-based nanomaterials as highly efficient adsorbents for oils and organic solvents
  7. Advanced nanoarchitectures of carbon aerogels for multifunctional environmental applications
  8. Electrochemical carbon nanotube filters for water and wastewater treatment
  9. Electrospinning: a facile technique for fabricating functional nanofibers for environmental applications
  10. Synthesis, modification, and photo/photoelectrocatalytic degradation applications of TiO2 nanotube arrays: a review
  11. Ultrafast photoinduced carrier dynamics at ZnO nanohybrid interfaces for light-harvesting applications
  12. Recent progress in red semiconductor photocatalysts for solar energy conversion and utilization
  13. Emerging nanostructured materials for the catalytic removal of volatile organic compounds
https://doi.org/10.1515/ntrev-2015-0062
Schlagwörter für diesen Artikel
adsorbents; carbon-based; graphene; sponge

Artikel in diesem Heft

  1. Frontmatter
  2. In this issue
  3. Editorial
  4. Emerging nanotechnology for environmental applications
  5. Reviews
  6. Graphene and carbon-based nanomaterials as highly efficient adsorbents for oils and organic solvents
  7. Advanced nanoarchitectures of carbon aerogels for multifunctional environmental applications
  8. Electrochemical carbon nanotube filters for water and wastewater treatment
  9. Electrospinning: a facile technique for fabricating functional nanofibers for environmental applications
  10. Synthesis, modification, and photo/photoelectrocatalytic degradation applications of TiO2 nanotube arrays: a review
  11. Ultrafast photoinduced carrier dynamics at ZnO nanohybrid interfaces for light-harvesting applications
  12. Recent progress in red semiconductor photocatalysts for solar energy conversion and utilization
  13. Emerging nanostructured materials for the catalytic removal of volatile organic compounds
Jetzt anmelden und 20% sparen
Institutioneller Zugang
Wie funktioniert Authentifizierung?
Haben Sie eine Idee, wie wir unsere Website verbessern können?
Bitte schreiben Sie uns.
© 2025 De Gruyter Brill
Heruntergeladen am 21.9.2025 von https://www.degruyterbrill.com/document/doi/10.1515/ntrev-2015-0062/html
Button zum nach oben scrollen