Volume 86, Issue 5

In order to make photovoltaics an economically viable energy solution, next-generation solar cells with higher energy conversion efficiencies and lower costs are urgently desired. Among many possible solutions, three-dimensional (3D) silicon nanostructures with excellent light-trapping properties are one of the promising candidates and have recently attracted considerable attention for cost-effective photovoltaic applications. This is because their enhanced light-trapping characteristics and high carrier collection efficiencies can enable the use of cheaper and thinner silicon materials. In this review, recent developments in the controllable fabrication of 3D silicon nanostructures are summarized, followed by the investigation of optical properties on a number of different nanostructures, including nanowires, nanopillars, nanocones, nanopencils, and nanopyramids, etc. Even though nanostructures with radial p-n junction demonstrate excellent photon management properties and enhanced photo-carrier collection efficiencies, the photovoltaic performance of nanostructure-based solar cells is still significantly limited due to the high surface recombination effect, which is induced by high-density surface defects as well as the large surface area in high-aspect-ratio nanostructures. In this regard, various approaches in reducing the surface recombination are discussed and an overall geometrical consideration of both light-trapping and recombination effects to yield the best photovoltaic properties are emphasized.

A systematic study on the fabrication of quantum dots sensitized solar cells (QDSSCs) exploiting hybrid networks of semiconducting light harvesters is presented, which shows how the engineering of band gaps of the device components by a very simple technique allows improving the solar energy conversion performances. Panchromatic devices are fabricated and tested, and correspondent functional parameters analyzed in order to highlight both advantages and drawbacks of the most common (CdS, CdSe, PbS) quantum dots applied for light collection in QDSSCs. Judicious engineering of the light harvester layer is demonstrated as a simple and powerful strategy for boosting device performances, through the management of light collection in a rather broad range of solar spectrum and photogenerated charges injection and collection.

Electrolytes play an essential role in determining the safety and electrochemical performance of Li-ion batteries. This work reported a propylene carbonate-based electrolyte with high-concentration Li salt. The fire-retardancy test and thermogravimetric analysis showed that this electrolyte is of high safety. In addition, this electrolyte exhibited superior electrochemical performance as compared with the commercial electrolyte in case of reversible capacity, rate behavior, and cycling stability.

This article reviews the research progress in the intercalation compounds for cathode materials for supercapacitors. Typical methods to prepare various intercalation compounds with different nanostructures are summarized. More specifically, the approaches can be subdivided into physical routes such as sonication and microwaves, and chemical routes such as hydrothermal, sol-gel and template methods. The most recent work on nanostructured intercalation compounds including LiCoO 2 , LiMn 2 O 4 , Li[Ni 1/3 Co 1/3 Mn 1/3 ]O 2 , Li 1+x V 3 O 8 , Na x MnO 2 , and K x MnO 2 is mainly focused including their preparation and electrochemical performance, and new trends in nanomaterials development for supercapacitors are pointed out.

Beyond activated carbon and other forms of high-surface area carbon operating solely as double layer storage materials in capacitors of high capacitance commonly somewhat imprecisely called supercapacitors other electrode materials storing electric charge by reversible and fast superficial redox processes are studied as active masses. The resulting devices combining double layer and Faradaic process-based charge storage – commonly called hybrid ones – show significantly higher capacitances at only marginally diminished power capability. Among the suggested materials metal oxides feature most prominently. Their formation, characterization and properties together with the performance of prepared devices are reviewed here.

In recent years, much attention has been paid to vanadium redox flow batteries (VRBs) because of their excellent performance as a new and efficient energy storage system, especially for large-scale energy storage. As one core component of a VRB, ion exchange membrane prevents cross-over of positive and negative electrolytes, while it enables the transportation of charge-balancing ions such as H + , SO42−,$${\text{SO}}_4^{2 - },$$ and HSO4−$${\text{HSO}}_4^ - $$ to complete the current circuit. To a large extent, its structure and property affect the performance of VRBs. This review focuses on the latest work on the ion exchange membranes for VRBs such as perfluorinated, partially fluorinated, and nonfluorinated membranes. The prospective for future development on membranes for VRBs is also proposed.

Vanadium pentoxide (V 2 O 5 ) nanoplatelet was prepared through an exfoliation method by using β-cyclodextrin (β-CD) as intercalating template. To improve its electrochemical performance in the aqueous electrolyte, the nanoplatelet was coated with amorphous AlPO 4 by sol-gel method. The effect of this coating layer on the rate and cycling properties is investigated by cyclic voltammetry and galvanostatic charge-discharge. The 1.6 % AlPO 4 -coated sample could deliver an initial capacity of 128 mAh g –1 at 0.1 C rate, and remain 99 % of the initial one after 50 cycles. The discharge capacities in the first cycle are 119, 113, and 104 mAh g –1 at the rates of 0.3, 1.5, and 3 C, respectively. The corresponding maintaining ratios are 98, 92, and 87 % after 50 cycles. The results suggest the AlPO 4 -coated V 2 O 5 nanoplatelet has good rate capability and cycling performance, indicating its promising application as an anode material in aqueous rechargeable lithium batteries.

Vanadium redox flow batteries (VRBs) are one of the most practical candidates for large-scale energy storage. Its electrolyte as one key component can intensively influence its electrochemical performance. Recently, much significant research has been carried out to improve the properties of the electrolytes. In this review, we present the optimization on vanadium electrolytes with sulfuric acid as a supporting electrolyte and their effects on the electrochemical performance of VRBs. In addition, other kinds of supporting electrolytes for VRBs are also discussed. Prospective for future development is also proposed.

Organic–inorganic hybrid materials have received great interest in the last 10 years in the controlled drug delivery area because of their excellent biocompatible, biomimetic, and pH-sensitive properties. Biomineralization is a biomineral-inspired route to prepare novel organic–inorganic hybrids, which involves a diffusion-controlled deposition of inorganic minerals within porous polymeric matrices. Proper combination of controlled biomineralization technique with the rational choice of polymer templates would lead to the successful development of smart self-assembled drug carriers. The present work mainly summarizes our recent work about the biomineralized organic–inorganic hybrid materials aiming for smart drug delivery including hybrid beads, membranes, and micro/nano gels. Furthermore, prospect for future development of the smart organic–inorganic hybrids is also discussed.

Soluble π-conjugated polymer derived from a renewable monomer, 3-amino-4-hydroxybenzoic acid (3,4-AHBA), was synthesized by an electropolymerization. The polymer has higher solubility in common solvents, compared to polyaniline, due to the polar side groups such as carboxyl and hydroxyl. The polymer showed various chromic behaviors based on the solvation and ionization of the side groups, and gave a flexible film with a conductivity as high as that of semiconductor.

Enoxaparin-immobilized gelatin/poly(ε-caprolactone) (PCL) or Eudragit ® RS230D nanogels in the presence of tetraethyl orthosilicate (TEOS) as polycondensation reagent were designed and characterized for their sustained drug delivery ability. Enoxaparin (anti-Xa 1000 UI/mL) was used as a model drug at different concentrations (300, 500, and 1000 UI/mL). The resulting nanogels were prepared using sol-gel technique and analyzed using several analytical tools such as: thermal analysis (DSC and TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning and transmitting electron microscopes (SEM and TEM). In addition to particle size, zeta potential and in vitro release profiles were also investigated. A burst effect was observed, afterwards, the release rate became steady. The immobilization of enoxaparin into the gel network led to the formation of stable nanogels with ionic functional groups, which enable the efficient loading and sustainable release. The preliminary results showed that enoxaparin-immobilized PCL-based nanogels in this study can be utilized in the design of a sustained delivery system.

In this article, a review of the chemoenzymatic synthesis of functional amylosic materials by means of a-glucan phosphorylase-catalyzed enzymatic polymerization is presented. The first topic of this review deals with the synthesis of amylose-grafted heteropolysaccharides composed of abundant polysaccharide main chains, such as chitin/chitosan, cellulose, alginate, xanthan gum, and carboxymethyl cellulose. The synthesis was achieved by combining the a-glucan phosphorylase-catalyzed enzymatic polymerization forming amylose with the appropriate chemical reaction (chemoenzymatic method). The second topic is the construction of amylosic supramolecular materials such as hydrogels and films by means of the vine-twining polymerization approach, which is a method for the formation of amylose-polymer inclusion complexes in the a-glucan phosphorylase-catalyzed polymerization field. In these studies, the designed graft copolymeric guest compounds were first synthesized. Then, the a-glucan phosphorylase-catalyzed enzymatic polymerization was carried out in the presence of the graft copolymers to produce the amylosic supramolecular materials through the formation of inclusion complexes.

Soybean hulls residue (SHR) is a kind of typical biocompatible and edible natural polymer with containing cellulose, glycoprotein and lignin. In this paper, SHR is extracted by simple method and characterized by FTIR, XRD, SEM, elemental and XPS analysis. Then, this natural polymer adsorbent is applied to remove Pb(II), and main factors on Pb(II) removal by SHR are investigated in details, such as initial concentration of lead, pH value, SHR dosage, oscillating time and temperature. It shows that the removal rate of Pb(II) quickly increases more than 90% within the first 5 min, and the removal rate get to 99% within 20 min. The isotherm, kinetic models and thermodynamic parameters are applied to test the experimental data, respectively. It indicates that Pb(II) adsorption on SHR is an endothermic and spontaneous process. The adsorption mechanism has also been investigated. In summary, SHR exhibits excellent adsorption ability for removing Pb(II), which could be used as a fast edible antidote in emergency, especially in cases of mass poisoning by lead.

To overcome the fragility of chemical cross-linked hydrogel and improve the cell compatibility of poly( N -isopropylacrylamide) hydrogel, physical cross-linker lithium magnesium silicate hydrate (LMSH) and silk sericin (SS) created by Bombyx mori (silkworms) were adopted as physical cross-linker and biocompatible monomer to prepare SS/poly(NIPAM/LMSH) nanocomposite hydrogels. The temperature sensitivity and cytocompatibility like mouse fibroblasts (L929) cell proliferation and desorption were investigated. Depending on SS content, the resultant nanocomposite hydrogels present bigger volume and rapid thermo-responsibility. The volume-phase transmittance temperature (VPTT) of SS/poly(NIPAM/LMSH) nanocomposite hydrogels increases from 32.12 to 33.34 °C with the introduction of SS content. Compared to pure poly(NIPAM/LMSH) nanocomposite hydrogel, MTT and SEM graphs have proved that the incorporation of SS could accelerate cell adhesion, spreading and detachment of L929 cells on the surface of SS/poly(NIPAM/LMSH) nanocomposite hydrogels. On culturing 5d, L929 cells have covered the whole surface of SS/poly(NIPAM/LMSH) nanocomposite hydrogels. By reducing temperature from 37 to 15 °C, L929 cells on the surface of SS/poly(NIPAM/LMSH) nanocomposite hydrogels detach spontaneously and harvested L929 cells still keep better cell activity than that via enzymatic digestion.

The copolymerization of l -lactide with ethylene carbonate carried out at 120 °C in the presence of organic derivatives of aluminum, zinc and tin as catalysts leads to the formation of linear polymers of relative molecular masses in the 10 000–30 000 range containing up to 12 mol. % of carbonate monomeric units (m.u.). A decrease in T g of copolymers down to 48 °C demonstrates the internal plasticization effect for polylactide matrix. In the first reaction step mainly lactide homopolymerization proceeds in the systems studied. Carbonate m.u. incorporate into the growing chain as a result of recurring transesterification processes. Back-biting type intramolecular transesterification reactions dominate in the system and macrocycle compounds containing 1 carbonate m.u. and 3–9 lactic acid m.u. are the main reaction products after prolonged time. On the basis of analysis of the low molecular weight products formed in the polymerization system and products of the model reaction of ethylene carbonate with metal alkoxides, the mechanism of elementary reactions leading to the incorporation of carbonate m.u. into the copolymer chains has been proposed.

The correlation between the bowl-inversion energy and the bowl depth for sumanenes monosubstituted with an iodo, formyl, or nitro group was investigated experimentally and by theoretical calculations. The bowl-inversion energies of the substituted sumanenes were determined experimentally by two-dimensional NMR exchange spectroscopy measurements. Various density functional theory methods were examined for the calculation of the structure and the bowl-inversion energy of sumanene, and it was found that PBE0, ωB97XD, and M06-2X gave better fits of the experimental value than did B3LYP. The experimental value was well reproduced at these levels of theory. The bowl structures and bowl-inversion energies of monosubstituted sumanenes were therefore calculated at the ωB97XD/6-311+G(d,p) level of theory. In both the experiments and the calculations, the correlation followed the equation Δ E = a cos 4 θ, where a is a coefficient, Δ E is the bowl-inversion energy, and cos θ is the normalized bowl depth, indicating that the bowl inversion follows a double-well potential energy diagram.

This article summarizes integrated sequential reactions with α-imino esters, where the umpolung addition reaction to the imino nitrogen followed by the second addition or oxidation is the crucial step. The following four types of reactions are discussed: (1) tandem N -ethylation/Mannich reaction; (2) N -alkylation/addition reaction; (3) synthesis of indolin-3-ones and tetrahydro-4-quinolones; (4) regioselective tandem N -alkylation/ C -acylation of β,γ-alkynyl α-imino esters.

In this paper we present characterization data for carbon nanotube (CNT)-epoxy and thermally reduced graphene oxide (TRGO)-epoxy nano-composites. The frequency-dependent ac conductivity and permittivity are examined as a function of volume fraction of carbon-based filler. The measured electrical properties and their frequency dependency are evaluated on the basis that such composites can be considered as a network of resistors and capacitors, whereby the resistors represent the conductive component (CNT or TRGO) and the capacitors are the insulating component (epoxy matrix). Differences observed between the frequency-dependent electrical properties of the CNT-epoxy and TRGO-epoxy composites are explained in terms of the different electrical conductivities of the CNT and TRGO phase.

The present study focuses on synthesis of SAPO-34 zeolite membrane on the surface of CuO–ZnO–Al 2 O 3 (CZA) catalyst particles to form CZA@SAPO-34 core@shell structured catalyst. In contrast to the traditional support of porous alumina, CZA catalyst particles have a relatively brittle surface, which leads to a big challenge to coat SAPO-34 zeolite membrane on their surface. Moreover, the hydrothermal synthesis of SAPO-34 zeolite membrane is carried out under weakly alkaline condition at 200 °C for hours, which causes part of the surface of CZA to be fragmented. To overcome these shortcomings, the intermediate layer of alumina is introduced to the surface of the CZA particles and acts as a barrier to the high-temperature hydrothermal and alkaline condition. It also takes as a transition to enhance SAPO-34 zeolite seeds adherence to the surface of CZA particles. With the help of an alumina layer, a continuous and dense zeolite membrane has been obtained on the surface of CZA particles. The prepared core@shell structured catalyst has better selectivity in CO hydrogenation for producing light hydrocarbons because of the synergetic effects between the membrane and core catalyst.

A simple, rapid (10 min), one-pot, single-step method for the preparation of solid and hollow spherical porous TiO 2 nanoparticles with large surface areas (100–211 m 2 /g) was developed in supercritical alcohols using carboxylic acids as organic additives. The shell thickness of the hollow TiO 2 nanoparticles (20–280 nm) was controlled by adjusting the heating rate (2.0–10.0 °C/min). The preparation of different spherical porous metal oxide nanoparticles, including CeO 2 , SiO 2 , TiO 2 , ZrO 2 , and ZnO, demonstrated the versatility of the synthetic approach. In addition, several rare earth-doped spherical mesoporous metal oxide nanoparticles, including CeO 2 :Er, CeO 2 :Er,Yb, ZrO 2 :Er, and TiO 2 :Er, which exhibit energy upconversion emission, were successfully prepared using this one-pot, single-step, supercritical methanol method. The obtained spherical mesoporous CeO 2 :Er and CeO 2 :Er,Yb nanoparticles emit green light upon excitation, even when irradiated with a low-power IR laser (980 nm, 10 mW) without calcination. Several other (metal) elements were also easily doped into spherical, mesoporous TiO 2 nanoparticles, such as Eu, Ce, Yb, Fe, and N, using a similar procedure. Furthermore, the spherical mesoporous TiO 2 nanoparticles were successfully applied as a new material for the transport of DNA via biolistic bombardment.

The ability of successive ionic layer deposition (SILD) technology to synthesize gold clusters on the surface of tin(IV) oxide and indium(III) oxide films is discussed. It was shown that during the process, concentration of active sites that are capable of absorbing gold ions, and the size of the gold particles thus formed, may be controlled by both concentration of the solutions used and the number of SILD cycles. Thus, SILD methodology, employing separate and multiple stages of adsorption and reduction of adsorbed species, has considerable potential for customizing the properties of the deposited metal nanoparticles. In particular, it is shown that during the deposition of gold nanoparticles on the surface of tin(IV) oxide and indium(III) oxide films by SILD methodology, conditions can be realized under which the size of gold nanoclusters may be controllably varied between 1–3 nm and 50 nm. A model is proposed for the formation of gold clusters during the SILD process.

Since crude oil and biomass differ in various properties, new primary fractionation methods of biomass, secondary conversion pathways and processes have to be developed. Biorefineries combine the necessary technologies of the biogenic raw materials with those of intermediates and final products. The chemical industry is experiencing a fundamental shift as cost competitive biobased platform chemicals become a commercial reality. The paper is focused on lignocellulosic feedstock and green biomass biorefinery concepts, which are favored in research, development and industrial implementation. The production of aromatic platform chemicals, such as furfural, hydroxymethylfurfural and derivatives as well as aliphatic platform chemicals, such as levulinic acid and formic acid is described. Futhermore, functional products, such as proteins and biotechnological produced platform chemicals are considered.

The need to change non-renewable raw materials by biomass as an oil substitute has been shown to be a strategic challenge for the 21 st century. Chemicals have the highest potential to add value to a vegetable biomass chain because of the importance of conventional chemical industry and fine chemical chemistry for different sectors of the economy; these compounds may be used as building blocks, intermediaries of synthesis, and specialties. This article deals with the economic potential of the usage of residual biomass as a raw material in chemistry, with a special interest in residues from bioenergetic chains (biodiesel and ethanol). It focus on showing a scenario related to the perspectives and challenges for the development of a Brazilian renewable chemistry, considering that Brazil is one of the largest global producers of agro-industrial biomass for several purposes, especially for bioenergy.

Biomass is a renewable and abundant feedstock that is poised to become a future alternative to petroleum as the understanding and technology surrounding catalytic biomass conversion and biorefineries progresses. A relevant research avenue explored in recent years deals with biomass deconstruction into simpler compounds (platform chemicals) by overcoming its recalcitrant and complex structure and subsequently converting these building blocks into value-added chemicals, fuels and materials in a similar way to that of current refineries. This contribution is aimed at providing a short overview of biomass processing chemistry by illustrating some relevant examples of catalytic strategies for biorefineries.

This paper shows how some existing refining technologies such as fluid catalytic cracking (FCC) can be modified to process bio-oil, derived from agricultural lignocellulosic wastes such as the sugar cane straw. Tests carried out in demonstration scale (150 kg/h) show the potential of these alternative materials to produce lignocellulosic gasoline or aromatic compounds, suitable to the petrochemical industry.

The production of fuels and chemicals from lignocellulosic biomass demands efficient processes to compete with fossil fuel-derived products. Key biorefinery processes, such as enzymatic hydrolysis of cellulose and microbial fermentation, can be monitored by advanced sensors in real time, providing information about reactant and product concentration, contamination, and reaction progress. Spectroscopic techniques such as Raman spectroscopy provide a means of quickly and accurately assessing many types of reaction mixtures non-destructively, in real time, and with no costly sample preparation and analysis time. Raman spectroscopy techniques have been developed to accurately quantify a number of compounds present in lignocellulosic processes, and methods have been developed to overcome the presence of fluorescent compounds that can increase the spectral background. Online Raman sensors also can provide the feedback measurements necessary for advanced process controls (APCs). Specifically, model predictive control, a common APC used extensively throughout similar processing industries, is especially well suited for ensuring optimal production of bio-based chemicals from lignocellulosic material.