Home Room temperature silanization of Fe3O4 for the preparation of phenyl functionalized magnetic adsorbent for dispersive solid phase extraction for the extraction of phthalates in water
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Room temperature silanization of Fe3O4 for the preparation of phenyl functionalized magnetic adsorbent for dispersive solid phase extraction for the extraction of phthalates in water

  • Abdulhadi Muftah Faraj Benrabha and Kheng Soo Tay EMAIL logo
Published/Copyright: April 14, 2018
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Green Processing and Synthesis
From the journal Green Processing and Synthesis Volume 8 Issue 1

Abstract

The preparation of magnetic solid adsorbents for solid phase extraction often involved time-consuming stepwise reaction and high-temperature reaction. In this study, the coating of silica and the functionalization of magnetite were performed in a single step at room temperature. The prepared solid adsorbent was phenyl functionalized magnetic adsorbent (Fe3O4@SiO2-Ph). The Fe3O4@SiO2-Ph was used for the determination of phthalates (butyl phthalate, butyl benzyl phthalate, di-ethylhexyl phthalate and di-n-octyl phthalate) in water. Under optimized conditions, this developed magnetic solid phase extraction method achieved the pre-concentration factor of 100, low method detection limit (0.62–1.02 μg/l) and limit of quantitation (1.98–3.25 μg/l), wide linear dynamic range (0.5–100 μg/l) with good coefficient of determination (>0.9980) and good repeatability (relative standard deviation <5%) during the extraction of the selected phthalates. The developed method was also successfully applied to analyze drinking water, mineral water and lake water with good extraction efficiency (70%–102%) and a high degree of precision (≤5%).

Keywords: butyl phthalate; di-ethylhexyl phthalate; di-n-octyl phthalate; water analysis

1 Introduction

Phthalate esters (PEs) are synthetic chemicals that have been utilized since the 1930s as plasticizers in polymers and as additives to various products [1], [2]. These compounds act as the additive to promote the plasticity and flexibility of plastic materials. Phthalates have also been used to improve the property of personal-care items, such as perfumes, fragrances, nail polishes, hair sprays, etc. [3]. Due to their wide range of uses, the occurrence of PEs in the environment has been widely reported [4]. PEs are released into the environment through the disposal of PEs-containing products as well as through the migration from plastic products as these compounds are not chemically bonded to the polymeric matrix [5]. The toxicity of PEs is known for decades [6]. Studies have shown that PEs elicit reproductive and developmental toxicities in laboratory animals [7]. Some of the PEs have been reported as carcinogens, and it has also been classified as endocrine-disrupting chemicals with the potential to disrupt the human endocrine system [8]. A recent study also showed that one of the PEs, dibutyl phthalate, is toxic to aquatic plants [4]. For these reasons, several developed countries, such as the United States, Japan, China and those in the European Union have restricted the use of PEs in industrial products. Environmental and drinking water quality standards have also been developed for environmental and human health protection purposes [9].

The United States Environmental Protection Agency (US EPA) proposed the standard analytical procedure for PEs analysis in 1996. The proposed method for water matrices involved the combination of the pre-concentration method [e.g. liquid-liquid extraction (LLE) and solid phase extraction (SPE)] with gas chromatographic-based detection [10]. LLE is not an environmentally friendly method as it requires the substantial volume of organic solvents. On the other hand, SPE has been extensively used in water analysis due to its high enrichment factor and possible automation. However, this method has several deficiencies in that it requires high operational cost and complex equipment, is time consuming, and generates massive secondary wastes [11].

Recently, magnetic dispersive micro-solid phase extraction (MDSPE) has been introduced to overcome the disadvantages of the conventional extraction methods [12]. MDSPE is an improved technique of conventional dispersive micro-solid phase extraction (D-μ-SPE) wherein the solid adsorbent is replaced with magnetic particles. During MDSPE, the magnetic particle is first dispersed in water samples for the extraction of analytes. Then, the magnetic particles are separated from the water matrices after extraction by using the external magnetic field, replacing the centrifugation required by D-μ-SPE [13]. So far, most of these magnetic adsorbents with specific properties were produced through a series of reactions, including the synthesis of magnetic particles (Fe3O4), the coating of Fe3O4 with the silica layer and the functionalization of silica-coated Fe3O4. The functionalization of silica-coated Fe3O4 is often achieved via the condensation reaction with the organosilane containing various functional groups [14]. Functionalized silica-coated Fe3O4 is often further modified via various reactions to obtain the magnetic particles with specific properties [12], [15]. Therefore, the process by which to obtain the magnetic adsorbents can be time-consuming and involve high-temperature reactions.

The current study demonstrated a method that simplified the preparation of magnetically retrievable adsorbents. In this method, the coating of the silica layer and functionalization were performed in a single step at room temperature. The phenyl group functionalized adsorbent (Fe3O4@SiO2-Ph) was prepared for the extraction of phthalates in water through the MDSPE. The efficiency of the Fe3O4@SiO2-Ph in the extraction of phthalates was also evaluated. The phenyl group-modified adsorbents have been used as one of the solid phases in solid phase extraction (SPE) for the extraction of nonpolar to moderately polar aromatic compounds [16], [17], [18]. However, this functional group is seldom used to modify the adsorbents for dispersive solid phase extraction. The phenyl group was found to provide active sites for the adsorption of pesticides via the π-π interaction between aromatic rings in addition to the hydrophobic interaction [19], [20]. Phthalates are slightly polar compounds with the aromatic ring [21]. Therefore, the Fe3O4@SiO2-Ph was selected to carry out the selective extraction of phthalates in water.

2 Materials and methods

2.1 Chemicals and reagents

Analytical grade ferric chloride anhydrous, ferrous chloride tetrahydrate, ammonium hydroxide solution (25%), tetraethyl orthosilicate (TEOS, purity of 98%), phenyltriethoxysilane (PTES, purity of 98%), sodium dihydrogen phosphate monohydrate, di-sodium hydrogen phosphate, dichloromethane and methanol were purchased from Merck (Darmstadt, Germany). Acetone, acetonitrile and 2-propanol were obtained from RCI Labscan (Bangkok, Thailand). Di-n-butyl phthalate (DBP), butyl benzyl phthalate (BBP), di-(2-ethylhexyl) phthalate, (DEHP) and di-n-octyl phthalate (DNOP) were purchased from Sigma Aldrich (Munich, Germany). Ultrapure water was produced by using an Elga water purification system (Buckinghamshire, UK). The Neodymium disc magnet (20 mm diameter×3 mm height) was purchased from Eclipse Magnetics (Sheffield, UK). The stock solutions of 2000 mg/l of PEs standard were prepared by dissolving the appropriate amounts of selected phthalates in methanol. The working standard solutions were prepared daily by diluting the stock standard solution to the required concentrations. For the real water samples, surface water was collected from a local lake and stored in the glass bottle, whereas drinking water and mineral water were obtained from the local market. The water samples were filtered through a cellulose nitrate membrane filter (pore size 0.45 mm) and kept at 4°C before used.

2.2 Instrumental analysis

Fourier-transform infrared (FTIR) spectra were recorded using a Perkin-Elmer FTIR (Waltham, USA). The FTIR spectra of the synthesized adsorbents were collected in the transmission mode by pressing the sample with potassium bromide powder to form pellets. For the collection of the FTIR spectra, a resolution of 2 cm−1 and 16 scans were both applied. Hitachi Energy dispersive X-ray spectroscopy (EDX) SU8200 (Tokyo, Japan) was used for the elemental analysis. The morphologies of the synthesized Fe3O4 and Fe3O4@SiO2-Ph were obtained by scanning electron microscopy (SEM). The SEM micrographs were taken in a Hitachi SU8220 (Tokyo, Japan). The separation and detection of PEs were performed using the Agilent Model 7890A Gas Chromatograph (Santa Clara, USA), which was equipped with a split/splitless injector and a flame ionization detector (FID). SPB™-5 fused-silica capillary column (Agilent, Santa Clara, USA) (30 m length, 0.25 mm I.D. and 0.25 μm film thickness) was selected for the separation of the analytes. Nitrogen gas (with 99.999% purity) was used as the carrier gas at a constant flow rate of 10 ml/min. The GC temperature program was 100°C–310°C at 10°C/min. The injection port was operated at the splitless mode. The detector temperature was set at 320°C. The air and hydrogen flow for the detector were 400 and 30 ml/min, respectively. The flow rate of the makeup gas (nitrogen) was 18 ml/min.

2.3 Synthesis of the Fe3O4 nanoparticles

The Fe3O4 was prepared by using the co-precipitation method [22]. Briefly, FeCl2.4H2O (3.2 g) and FeCl3 (3.9 g) with the molar ratio of 2:3 were first dissolved in 50 ml deionized water. Then, 50 ml of ammonium hydroxide (25%) was added, and the mixture was stirred under vigorous mechanical stirring for 30 min at room temperature. We selected the Fe2+:Fe3+ ratio of 2:3 because it enables the synthesis of Fe3O4 in the air atmosphere [22]. After the reaction, the Fe3O4 was precipitated using the external magnet field. The obtained Fe3O4 was washed with deionized water and then vacuum dried.

2.4 Synthesis of the Fe3O4@SiO2-Ph

About 0.3 g of Fe3O4 was first dispersed in 50 ml of 2-propanol and 4 ml of deionized water through sonication for 30 min. Then, 1.9 ml of TEOS, 0.1 ml PTES and 5 ml of ammonium hydroxide solution (25%) were added. The mixture was stirred at room temperature for 12 h. The Fe3O4@SiO2-Ph was precipitated using the external magnetic field and then washed thoroughly with deionized water. The Fe3O4@SiO2-Ph was vacuum dried.

2.5 PE extraction using the optimized Fe3O4@SiO2-Ph-based MDSPE

First, 20 mg of the Fe3O4@SiO2-Ph was added to 20 ml of PEs standard solution. The vial was sealed and sonicated for 30 min. Then, the Fe3O4@SiO2-Ph was separated from the solution using an external magnetic field. The solution was decanted while the Fe3O4@SiO2-Ph was held inside the vial by an external magnet field. Then, 5 ml of water was added to the vial to rinse the Fe3O4@SiO2-Ph. The Fe3O4@SiO2-Ph was vacuum dried at room temperature. Then, 0.2 ml of methanol was used to desorb the PEs. The desorption process was performed through 1 min of sonication. The Fe3O4@SiO2-Ph was again separated from the desorption solvent using an external magnet field. Finally, 2 μl of the solution was injected into the GC-FID.

3 Results and discussion

3.1 Characterization of the Fe3O4@SiO2-Ph

The SEM images of Fe3O4 and Fe3O4@SiO2-Ph were obtained to visualize the differences in surface morphology before and after surface modification (Figure 1). The Fe3O4@SiO2-Ph exhibited smooth particle morphology with spherical shape compared with the Fe3O4. The size of the Fe3O4@SiO2-Ph was significantly larger compared with the Fe3O4. These results showed the presence of silica coating on the Fe3O4@SiO2-Ph. The FTIR analysis was carried out to verify the presence of the phenyl group and silica layer on the Fe3O4@SiO2-Ph after the coating process of Fe3O4. The FTIR spectra of the Fe3O4 showed two significant peaks at 670 and 3445 cm−1, which can be attributed to Fe-O and O-H stretching vibrations, respectively (Figure 2). After coating with the mixture of TEOS and PTES, the Fe3O4@SiO2-Ph showed additional peaks at 1101, 1640 and 2960 cm−1. The peak at 1101 cm−1 indicated the presence of Si-O bonding. The peaks at 1640 and 2960 cm−1 are attributed to the C-H and C-C stretching bands of the aromatic system, thus indicating the presence of phenyl groups in the Fe3O4@SiO2-Ph. Using EDX, the elemental analysis was performed on the Fe3O4@SiO2-Ph and Fe3O4@SiO2 (silica-coated Fe3O4) to further confirm the presence of the phenyl groups. The Fe3O4@SiO2-Ph showed the presence of 20% carbon element, whereas for the Fe3O4@SiO2, carbon was not detected (Table 1). Therefore, the phenyl groups were successfully introduced into the Fe3O4@SiO2-Ph with this simple coating method.

Figure 1: The SEM images of (A) Fe3O4 and (B) Fe3O4@SiO2-Ph.
Figure 1:

The SEM images of (A) Fe3O4 and (B) Fe3O4@SiO2-Ph.

Figure 2: The FTIR spectra of Fe3O4 and Fe3O4@SiO2-Ph (prepared using 5% of PTES in TEOS).
Figure 2:

The FTIR spectra of Fe3O4 and Fe3O4@SiO2-Ph (prepared using 5% of PTES in TEOS).

Table 1:

Elemental compositions of Fe3O4@SiO2 and Fe3O4@SiO2-Ph.

Element%
Fe3O4@SiO2Fe3O4@SiO2-Ph
Fe31.018.4
O57.851.6
Si11.010.0
C020.0

3.2 The effect of the TEOS to PTES ratio on the Fe3O4@SiO2-Ph properties

In this study, the Fe3O4 was first coated with the mixture of TEOS and PTES with different ratios to obtain Fe3O4@SiO2-Ph with the suitable properties for PEs extraction in water. These properties include the dispersibility of the Fe3O4@SiO2-Ph in water during extraction and retrievability after extraction. The percentage of PTES in TEOS varied from 50, 12.5 and 5% (v/v). The total volume of the PTES and TEOS mixture was 2 ml. The Fe3O4@SiO2-Ph were dispersed in water using sonication for 30 min. Then, the Fe3O4@SiO2-Ph were retrieved using the external magnet field. The result showed that the Fe3O4@SiO2-Ph prepared using 5% of PTES in TEOS showed good dispersibility (Figure 3A). This adsorbent showed a good property, which allows it to be retrieved entirely from water by using an external magnetic field (Figure 3B). The Fe3O4@SiO2-Ph that were prepared using 12.5% and 50% of PTES in TEOS were poorly dispersed after 30 min of sonication; moreover, part of these particles were also found to be floated on the surface of water due to the high hydrophobic property after retrieval. Therefore, the Fe3O4@SiO2-Ph that was prepared using 5% of PTES in TEOS was used as solid adsorbents for MDSPE. The selected PEs in this study were DBP, BBP, DEHP and DNOP.

Figure 3: The (A) dispersibility and (B) retrievability tests for the Fe3O4@SiO2-Ph prepared using (I) 5%, (II) 12.5% and (III) 50% of PTES in TEOS.
Figure 3:

The (A) dispersibility and (B) retrievability tests for the Fe3O4@SiO2-Ph prepared using (I) 5%, (II) 12.5% and (III) 50% of PTES in TEOS.

3.3 Optimization of the operating parameters of the MDSPE

The effect of the amount of Fe3O4@SiO2-Ph on the PEs extraction efficiency was assessed using 5–20 mg of the Fe3O4@SiO2-Ph. The peak area of the selected phthalates was found to increase with the increasing amount of Fe3O4@SiO2-Ph. This result was due to the increase in the number of adsorption sites for phthalates when the amount of Fe3O4@SiO2-Ph increased. From 10–20 mg of Fe3O4@SiO2-Ph, the peak areas of the DBP and BBP increased significantly (Figure 4). However, no significant increments in the peak areas were observed for DEHP and DNOP. Therefore, for further studies, 20 mg of Fe3O4@SiO2-Ph was selected in order to reduce the operational cost of the developed extraction method.

Figure 4: The effects of the amount of the Fe3O4@SiO2-Ph on the extraction efficiency of selected PEs. (Sonication time=30 min; desorption solvent=methanol; desorption time=1 min; without pH adjustment).
Figure 4:

The effects of the amount of the Fe3O4@SiO2-Ph on the extraction efficiency of selected PEs. (Sonication time=30 min; desorption solvent=methanol; desorption time=1 min; without pH adjustment).

The change of the solution’s pH level may ionize both the analytes and the functional groups on the solid phase, which can then influence the efficiency of D-μ-SPE [17]. In this study, the effects of the solution’s pH on PEs extraction efficiency were studied at pH 4, 7 and 9. As shown in Figure 5, no significant changes in the peak area of PEs were observed when the pH of the solution increased from 4 to 9. The PEs and phenyl group on the Fe3O4@SiO2-Ph are not ionizable compounds nor functional groups. Therefore, the extraction efficiency was not influenced by the changes of the solution’s pH. This result also indicated the versatility of the Fe3O4@SiO2-Ph in extracting PEs at different pH conditions. Hence, the pH adjustment is not required by this developed MDSPE.

Figure 5: The effects of sample pH on the extraction efficiencies of PEs. (Amount of Fe3O4@SiO2-Ph=20 mg; sonication time=30 min; desorption solvent=methanol; desorption time=1 min).
Figure 5:

The effects of sample pH on the extraction efficiencies of PEs. (Amount of Fe3O4@SiO2-Ph=20 mg; sonication time=30 min; desorption solvent=methanol; desorption time=1 min).

The dispersion of the Fe3O4@SiO2-Ph was performed using sonication. Sonication time is an important factor that allows the complete dispersal of the Fe3O4@SiO2-Ph in water for achieving the highest extraction efficiency. In this study, different sonication times ranging from 5 to 30 min were evaluated to obtain the most efficient extraction method. The peak areas, DBP, BBP, DEHP and DNOP, were found to increase from 5 to 30 min (Figure 6). In order to develop an efficient extraction method, 30 min was selected as the sonication time for the MDSPE.

Figure 6: The effects of extraction time on the PE extraction efficiency. (Amount of Fe3O4@SiO2-Ph=20 mg; desorption solvent=methanol; desorption time=1 min).
Figure 6:

The effects of extraction time on the PE extraction efficiency. (Amount of Fe3O4@SiO2-Ph=20 mg; desorption solvent=methanol; desorption time=1 min).

The effectiveness of acetonitrile, dichloromethane (DCM) and methanol as desorption solvents for the selected PEs from Fe3O4@SiO2-Ph was evaluated. The desorption process was performed using sonication for 1 min. The results showed that methanol had the highest efficiency in extracting PEs from the Fe3O4@SiO2-Ph compared with acetonitrile and DCM (Figure 7). Therefore, methanol was selected as the desorption solvent.

Figure 7: The effects of desorption solvents. (Amount of Fe3O4@SiO2-Ph=20 mg; sonication time=30 min; desorption time=1 min).
Figure 7:

The effects of desorption solvents. (Amount of Fe3O4@SiO2-Ph=20 mg; sonication time=30 min; desorption time=1 min).

3.4 The analytical performances of the developed MDSPE

The optimized operating parameters for the extraction of phthalate esters using the MDSPE were 20 mg of Fe3O4@SiO2-Ph, 30 min of sonication time and the use of methanol as the desorption solvent.

The pre-concentration factor for the optimized method was calculated using the following equation [23]:

Pre-concentration factor=V0Vf,

where V0 and Vf represent the initial volume of the water sample and the final volume of the PEs extract before the GC-FID analysis, respectively. This optimized method was used to pre-concentrate the 20 ml PEs standard solution. In this method, the final volume of the PEs extract before the GC-FID analysis was 200 μl, and the pre-concentration factor was 100. The analytical performance and the validation of the developed MDSPE method were evaluated using linearity, the method of detection limit (MDL), the limit of quantitation (LOQ) and the intra-day and inter-day precision (Table 2). The MDL and LOQ were obtained according to the guidelines set by the US EPA [24]. Briefly, a solvent blank and a method blank were first analyzed to determine the interference and contamination. The selected phthalates were not detected in both solvent blanks and method blanks. Then, the concentrations of phthalates in seven samples, which give rise to a peak with a signal-to-noise ratio of 3–5, was determined. This was followed by the calculation of the standard deviation (s). The MDL (at the 99% confident level) and LOQ were calculated using the following equations:

Table 2:

Analytical performance of the developed method.

AnalytesCalibration curveR2Linear range (μg/l)MLD (μg/l)LOQ (μg/l)RSD (%) inter-day, n=3RSD (%) intra-day, n=5
DBPy=23.6x−0.500.99801–1001.023.252.93.6
BBPy=13.6x+1.950.99501–1000.862.732.64.1
DEHPy=22.0x−0.970.99971–1000.621.981.92.0
DNOPy=19.0x−1.830.99981–1000.682.162.32.1

MDL=s×(t−value)

LOQ=s×10

where student’s t-value was equal to 3.143 for seven replicates and six degrees of freedom. The results showed that good linearity was obtained for the selected phthalates over the range of 0.1–100 μg/l (R2>0.9980). The MDL and LOQ of the developed method ranged from 0.62–1.02 μg/l and 1.98–3.25 μg/l, respectively. The intra-day and inter-day reproducibility, expressed as relative standard deviation (RSD), were obtained by analyzing sets of three and five replicates of 50 μg/l of phthalate solution, respectively. The RSD values for intra-day and inter-day ranged from 1.9%–2.9% and from 2.0%–4.1%, respectively. The selected water samples were spiked with 10, 50 and 100 μg/l of PEs to investigate the effect of water matrices on the analytical performance of the developed method. The GC-FID chromatograms of the PEs analysis in selected water samples are presented in Figure 8. The recoveries of the PEs ranged from 70%–102% with the RSD<5% (Table 3). This result indicated the water matrix does not influence the analytical performance of the developed method.

Figure 8: The GC-FID chromatograms of the PEs analysis in selected water samples with PEs spiked levels of (i) 0 μg/l, (ii) 10 μg/l, (iii) 50 μg/l and (iv) 100 μg/l.
Figure 8:

The GC-FID chromatograms of the PEs analysis in selected water samples with PEs spiked levels of (i) 0 μg/l, (ii) 10 μg/l, (iii) 50 μg/l and (iv) 100 μg/l.

Table 3:

Recoveries of PES in the real water samples.

Water sampleConcentrations of spiked PES (μg/l)Recovery±SD (%)
DBPBBPDEHPDNOP
Mineral water1070±275±1100±484±1
5070±183±182±381±2
10074±495±499±2101±3
Drinking water1070±183±196±293±1
5075±381±298±198±3
10072±180±1100±299±3
Lake water1071±195±176±174±1
5087±4102±5101±3100±3
10076±392±499±499±5

The performance of the developed Fe3O4@SiO2-Ph-based MDSPE was compared with previously reported MDSPE methods for PE extraction (Table 4). These solid adsorbents were C18-Fe3O4@mSiO2 (silica-coated Fe3O4 modified with n-octadecyltriethoxysilane), MNP@3TArH (polythiophene functionalized Fe3O4), MWCNT-PVA [magnetic multi-walled carbon nanotubes-poly (vinyl alcohol) cryogel] and magnetic MWCNTs (magnetic multi-walled carbon nanotubes). The Fe3O4@SiO2-Ph showed wider linear range in the determination of PEs compared with the MNP@3TArH and the magnetic MWCNT. The detection limit of the developed method was also much lower than those of the C18-Fe3O4@mSiO2 and MWCNT-PVA based MDSPE.

Table 4:

Comparison of the developed method with other MDSPE methods in the determination of PEs.

PhthalatesSolid adsorbentDetection methodDetection limits (μg/l)Linear range (μg/l)References
DBP, BBP, DEHP and DNOPC18-Fe3O4@mSiO2GC-MS31–7750–2500[25]
BBP, DEHP and DNOPMNP@3TArHGC-FID0.054–0.0800.1–50[26]
DBP and DEHPMWCNTs-PVAGC-FID26.3–36.425–10,000[27]
DBP, BBP and DEHPMagnetic MWCNTGC-MS/MS0.010–0.0190.05–10[28]
DBP, BBP, DEHP and DNOPFe3O4@SiO2-PhGC-FID0.62–1.020.5–100This study

4 Conclusion

The Fe3O4@SiO2-Ph was successfully synthesized by coating phenyl group-containing silica gel onto the Fe3O4 at room temperature. The Fe3O4@SiO2-Ph was employed as the solid adsorbent for the MDSPE. The Fe3O4@SiO2-Ph-based MDSPE was used for the determination of PEs in water. Under optimized conditions, the developed MDSPE method provided a wide linear range with good coefficient of determination, good inter-day and intra-day repeatability and low method of detection. The developed method also showed high extraction efficiency and repeatability when it was used to determine the selected phthalates in drinking water, lake water and mineral water. In terms of performance, the Fe3O4@SiO2-Ph prepared using the simplified method are comparable with the recently reported adsorbents in extracting selected phthalates in water.

Acknowledgments

This research was supported financially by the Ministry of Higher Education Malaysia (Fundamental Research Grant Scheme No. FP042-2016) and by the University of Malaya (Postgraduate Research Grant No. PG020-2016, Funder Id: 10.13039/501100004386).

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Received: 2017-11-19
Accepted: 2018-03-06
Published Online: 2018-04-14
Published in Print: 2019-01-28

©2019 Walter de Gruyter GmbH, Berlin/Boston

This work is licensed under the Creative Commons Attribution 4.0 Public License.

Articles in the same Issue

  1. Regular Articles
  2. Studies on the preparation and properties of biodegradable polyester from soybean oil
  3. Flow-mode biodiesel production from palm oil using a pressurized microwave reactor
  4. Reduction of free fatty acids in waste oil for biodiesel production by glycerolysis: investigation and optimization of process parameters
  5. Saccharin: a cheap and mild acidic agent for the synthesis of azo dyes via telescoped dediazotization
  6. Optimization of lipase-catalyzed synthesis of polyethylene glycol stearate in a solvent-free system
  7. Green synthesis of iron oxide nanoparticles using Platanus orientalis leaf extract for antifungal activity
  8. Ultrasound assisted chemical activation of peanut husk for copper removal
  9. Room temperature silanization of Fe3O4 for the preparation of phenyl functionalized magnetic adsorbent for dispersive solid phase extraction for the extraction of phthalates in water
  10. Evaluation of the saponin green extraction from Ziziphus spina-christi leaves using hydrothermal, microwave and Bain-Marie water bath heating methods
  11. Oxidation of dibenzothiophene using the heterogeneous catalyst of tungsten-based carbon nanotubes
  12. Calcined sodium silicate as an efficient and benign heterogeneous catalyst for the transesterification of natural lecithin to L-α-glycerophosphocholine
  13. Synergistic effect between CO2 and H2O2 on ethylbenzene oxidation catalyzed by carbon supported heteropolyanion catalysts
  14. Hydrocyanation of 2-arylmethyleneindan-1,3-diones using potassium hexacyanoferrate(II) as a nontoxic cyanating agent
  15. Green synthesis of hydratropic aldehyde from α-methylstyrene catalyzed by Al2O3-supported metal phthalocyanines
  16. Environmentally benign chemical recycling of polycarbonate wastes: comparison of micro- and nano-TiO2 solid support efficiencies
  17. Medicago polymorpha-mediated antibacterial silver nanoparticles in the reduction of methyl orange
  18. Production of value-added chemicals from esterification of waste glycerol over MCM-41 supported catalysts
  19. Green synthesis of zerovalent copper nanoparticles for efficient reduction of toxic azo dyes congo red and methyl orange
  20. Optimization of the biological synthesis of silver nanoparticles using Penicillium oxalicum GRS-1 and their antimicrobial effects against common food-borne pathogens
  21. Optimization of submerged fermentation conditions to overproduce bioethanol using two industrial and traditional Saccharomyces cerevisiae strains
  22. Extraction of In3+ and Fe3+ from sulfate solutions by using a 3D-printed “Y”-shaped microreactor
  23. Foliar-mediated Ag:ZnO nanophotocatalysts: green synthesis, characterization, pollutants degradation, and in vitro biocidal activity
  24. Green cyclic acetals production by glycerol etherification reaction with benzaldehyde using cationic acidic resin
  25. Biosynthesis, characterization and antimicrobial activities assessment of fabricated selenium nanoparticles using Pelargonium zonale leaf extract
  26. Synthesis of high surface area magnesia by using walnut shell as a template
  27. Controllable biosynthesis of silver nanoparticles using actinobacterial strains
  28. Green vegetation: a promising source of color dyes
  29. Mechano-chemical synthesis of ammonia and acetic acid from inorganic materials in water
  30. Green synthesis and structural characterization of novel N1-substituted 3,4-dihydropyrimidin-2(1H)-ones
  31. Biodiesel production from cotton oil using heterogeneous CaO catalysts from eggshells prepared at different calcination temperatures
  32. Regeneration of spent mercury catalyst for the treatment of dye wastewater by the microwave and ultrasonic spray-assisted method
  33. Green synthesis of the innovative super paramagnetic nanoparticles from the leaves extract of Fraxinus chinensis Roxb and their application for the decolourisation of toxic dyes
  34. Biogenic ZnO nanoparticles: a study of blueshift of optical band gap and photocatalytic degradation of reactive yellow 186 dye under direct sunlight
  35. Leached compounds from the extracts of pomegranate peel, green coconut shell, and karuvelam wood for the removal of hexavalent chromium
  36. Enhancement of molecular weight reduction of natural rubber in triphasic CO2/toluene/H2O systems with hydrogen peroxide for preparation of biobased polyurethanes
  37. An efficient green synthesis of novel 1H-imidazo[1,2-a]imidazole-3-amine and imidazo[2,1-c][1,2,4]triazole-5-amine derivatives via Strecker reaction under controlled microwave heating
  38. Evaluation of three different green fabrication methods for the synthesis of crystalline ZnO nanoparticles using Pelargonium zonale leaf extract
  39. A highly efficient and multifunctional biomass supporting Ag, Ni, and Cu nanoparticles through wetness impregnation for environmental remediation
  40. Simple one-pot green method for large-scale production of mesalamine, an anti-inflammatory agent
  41. Relationships between step and cumulative PMI and E-factors: implications on estimating material efficiency with respect to charting synthesis optimization strategies
  42. A comparative sorption study of Cr3+ and Cr6+ using mango peels: kinetic, equilibrium and thermodynamic
  43. Effects of acid hydrolysis waste liquid recycle on preparation of microcrystalline cellulose
  44. Use of deep eutectic solvents as catalyst: A mini-review
  45. Microwave-assisted synthesis of pyrrolidinone derivatives using 1,1’-butylenebis(3-sulfo-3H-imidazol-1-ium) chloride in ethylene glycol
  46. Green and eco-friendly synthesis of Co3O4 and Ag-Co3O4: Characterization and photo-catalytic activity
  47. Adsorption optimized of the coal-based material and application for cyanide wastewater treatment
  48. Aloe vera leaf extract mediated green synthesis of selenium nanoparticles and assessment of their In vitro antimicrobial activity against spoilage fungi and pathogenic bacteria strains
  49. Waste phenolic resin derived activated carbon by microwave-assisted KOH activation and application to dye wastewater treatment
  50. Direct ethanol production from cellulose by consortium of Trichoderma reesei and Candida molischiana
  51. Agricultural waste biomass-assisted nanostructures: Synthesis and application
  52. Biodiesel production from rubber seed oil using calcium oxide derived from eggshell as catalyst – optimization and modeling studies
  53. Study of fabrication of fully aqueous solution processed SnS quantum dot-sensitized solar cell
  54. Assessment of aqueous extract of Gypsophila aretioides for inhibitory effects on calcium carbonate formation
  55. An environmentally friendly acylation reaction of 2-methylnaphthalene in solvent-free condition in a micro-channel reactor
  56. Aegle marmelos phytochemical stabilized synthesis and characterization of ZnO nanoparticles and their role against agriculture and food pathogen
  57. A reactive coupling process for co-production of solketal and biodiesel
  58. Optimization of the asymmetric synthesis of (S)-1-phenylethanol using Ispir bean as whole-cell biocatalyst
  59. Synthesis of pyrazolopyridine and pyrazoloquinoline derivatives by one-pot, three-component reactions of arylglyoxals, 3-methyl-1-aryl-1H-pyrazol-5-amines and cyclic 1,3-dicarbonyl compounds in the presence of tetrapropylammonium bromide
  60. Preconcentration of morphine in urine sample using a green and solvent-free microextraction method
  61. Extraction of glycyrrhizic acid by aqueous two-phase system formed by PEG and two environmentally friendly organic acid salts - sodium citrate and sodium tartrate
  62. Green synthesis of copper oxide nanoparticles using Juglans regia leaf extract and assessment of their physico-chemical and biological properties
  63. Deep eutectic solvents (DESs) as powerful and recyclable catalysts and solvents for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones
  64. Biosynthesis, characterization and anti-microbial activity of silver nanoparticle based gel hand wash
  65. Efficient and selective microwave-assisted O-methylation of phenolic compounds using tetramethylammonium hydroxide (TMAH)
  66. Anticoagulant, thrombolytic and antibacterial activities of Euphorbia acruensis latex-mediated bioengineered silver nanoparticles
  67. Volcanic ash as reusable catalyst in the green synthesis of 3H-1,5-benzodiazepines
  68. Green synthesis, anionic polymerization of 1,4-bis(methacryloyl)piperazine using Algerian clay as catalyst
  69. Selenium supplementation during fermentation with sugar beet molasses and Saccharomyces cerevisiae to increase bioethanol production
  70. Biosynthetic potential assessment of four food pathogenic bacteria in hydrothermally silver nanoparticles fabrication
  71. Investigating the effectiveness of classical and eco-friendly approaches for synthesis of dialdehydes from organic dihalides
  72. Pyrolysis of palm oil using zeolite catalyst and characterization of the boil-oil
  73. Azadirachta indica leaves extract assisted green synthesis of Ag-TiO2 for degradation of Methylene blue and Rhodamine B dyes in aqueous medium
  74. Synthesis of vitamin E succinate catalyzed by nano-SiO2 immobilized DMAP derivative in mixed solvent system
  75. Extraction of phytosterols from melon (Cucumis melo) seeds by supercritical CO2 as a clean technology
  76. Production of uronic acids by hydrothermolysis of pectin as a model substance for plant biomass waste
  77. Biofabrication of highly pure copper oxide nanoparticles using wheat seed extract and their catalytic activity: A mechanistic approach
  78. Intelligent modeling and optimization of emulsion aggregation method for producing green printing ink
  79. Improved removal of methylene blue on modified hierarchical zeolite Y: Achieved by a “destructive-constructive” method
  80. Two different facile and efficient approaches for the synthesis of various N-arylacetamides via N-acetylation of arylamines and straightforward one-pot reductive acetylation of nitroarenes promoted by recyclable CuFe2O4 nanoparticles in water
  81. Optimization of acid catalyzed esterification and mixed metal oxide catalyzed transesterification for biodiesel production from Moringa oleifera oil
  82. Kinetics and the fluidity of the stearic acid esters with different carbon backbones
  83. Aiming for a standardized protocol for preparing a process green synthesis report and for ranking multiple synthesis plans to a common target product
  84. Microstructure and luminescence of VO2 (B) nanoparticle synthesis by hydrothermal method
  85. Optimization of uranium removal from uranium plant wastewater by response surface methodology (RSM)
  86. Microwave drying of nickel-containing residue: dielectric properties, kinetics, and energy aspects
  87. Simple and convenient two step synthesis of 5-bromo-2,3-dimethoxy-6-methyl-1,4-benzoquinone
  88. Biodiesel production from waste cooking oil
  89. The effect of activation temperature on structure and properties of blue coke-based activated carbon by CO2 activation
  90. Optimization of reaction parameters for the green synthesis of zero valent iron nanoparticles using pine tree needles
  91. Microwave-assisted protocol for squalene isolation and conversion from oil-deodoriser distillates
  92. Denitrification performance of rare earth tailings-based catalysts
  93. Facile synthesis of silver nanoparticles using Averrhoa bilimbi L and Plum extracts and investigation on the synergistic bioactivity using in vitro models
  94. Green production of AgNPs and their phytostimulatory impact
  95. Photocatalytic activity of Ag/Ni bi-metallic nanoparticles on textile dye removal
  96. Topical Issue: Green Process Engineering / Guest Editors: Martine Poux, Patrick Cognet
  97. Modelling and optimisation of oxidative desulphurisation of tyre-derived oil via central composite design approach
  98. CO2 sequestration by carbonation of olivine: a new process for optimal separation of the solids produced
  99. Organic carbonates synthesis improved by pervaporation for CO2 utilisation
  100. Production of starch nanoparticles through solvent-antisolvent precipitation in a spinning disc reactor
  101. A kinetic study of Zn halide/TBAB-catalysed fixation of CO2 with styrene oxide in propylene carbonate
  102. Topical on Green Process Engineering
https://doi.org/10.1515/gps-2017-0171
Keywords for this article
butyl phthalate; di-ethylhexyl phthalate; di-n-octyl phthalate; water analysis
Creative Commons
BY 4.0

Articles in the same Issue

  1. Regular Articles
  2. Studies on the preparation and properties of biodegradable polyester from soybean oil
  3. Flow-mode biodiesel production from palm oil using a pressurized microwave reactor
  4. Reduction of free fatty acids in waste oil for biodiesel production by glycerolysis: investigation and optimization of process parameters
  5. Saccharin: a cheap and mild acidic agent for the synthesis of azo dyes via telescoped dediazotization
  6. Optimization of lipase-catalyzed synthesis of polyethylene glycol stearate in a solvent-free system
  7. Green synthesis of iron oxide nanoparticles using Platanus orientalis leaf extract for antifungal activity
  8. Ultrasound assisted chemical activation of peanut husk for copper removal
  9. Room temperature silanization of Fe3O4 for the preparation of phenyl functionalized magnetic adsorbent for dispersive solid phase extraction for the extraction of phthalates in water
  10. Evaluation of the saponin green extraction from Ziziphus spina-christi leaves using hydrothermal, microwave and Bain-Marie water bath heating methods
  11. Oxidation of dibenzothiophene using the heterogeneous catalyst of tungsten-based carbon nanotubes
  12. Calcined sodium silicate as an efficient and benign heterogeneous catalyst for the transesterification of natural lecithin to L-α-glycerophosphocholine
  13. Synergistic effect between CO2 and H2O2 on ethylbenzene oxidation catalyzed by carbon supported heteropolyanion catalysts
  14. Hydrocyanation of 2-arylmethyleneindan-1,3-diones using potassium hexacyanoferrate(II) as a nontoxic cyanating agent
  15. Green synthesis of hydratropic aldehyde from α-methylstyrene catalyzed by Al2O3-supported metal phthalocyanines
  16. Environmentally benign chemical recycling of polycarbonate wastes: comparison of micro- and nano-TiO2 solid support efficiencies
  17. Medicago polymorpha-mediated antibacterial silver nanoparticles in the reduction of methyl orange
  18. Production of value-added chemicals from esterification of waste glycerol over MCM-41 supported catalysts
  19. Green synthesis of zerovalent copper nanoparticles for efficient reduction of toxic azo dyes congo red and methyl orange
  20. Optimization of the biological synthesis of silver nanoparticles using Penicillium oxalicum GRS-1 and their antimicrobial effects against common food-borne pathogens
  21. Optimization of submerged fermentation conditions to overproduce bioethanol using two industrial and traditional Saccharomyces cerevisiae strains
  22. Extraction of In3+ and Fe3+ from sulfate solutions by using a 3D-printed “Y”-shaped microreactor
  23. Foliar-mediated Ag:ZnO nanophotocatalysts: green synthesis, characterization, pollutants degradation, and in vitro biocidal activity
  24. Green cyclic acetals production by glycerol etherification reaction with benzaldehyde using cationic acidic resin
  25. Biosynthesis, characterization and antimicrobial activities assessment of fabricated selenium nanoparticles using Pelargonium zonale leaf extract
  26. Synthesis of high surface area magnesia by using walnut shell as a template
  27. Controllable biosynthesis of silver nanoparticles using actinobacterial strains
  28. Green vegetation: a promising source of color dyes
  29. Mechano-chemical synthesis of ammonia and acetic acid from inorganic materials in water
  30. Green synthesis and structural characterization of novel N1-substituted 3,4-dihydropyrimidin-2(1H)-ones
  31. Biodiesel production from cotton oil using heterogeneous CaO catalysts from eggshells prepared at different calcination temperatures
  32. Regeneration of spent mercury catalyst for the treatment of dye wastewater by the microwave and ultrasonic spray-assisted method
  33. Green synthesis of the innovative super paramagnetic nanoparticles from the leaves extract of Fraxinus chinensis Roxb and their application for the decolourisation of toxic dyes
  34. Biogenic ZnO nanoparticles: a study of blueshift of optical band gap and photocatalytic degradation of reactive yellow 186 dye under direct sunlight
  35. Leached compounds from the extracts of pomegranate peel, green coconut shell, and karuvelam wood for the removal of hexavalent chromium
  36. Enhancement of molecular weight reduction of natural rubber in triphasic CO2/toluene/H2O systems with hydrogen peroxide for preparation of biobased polyurethanes
  37. An efficient green synthesis of novel 1H-imidazo[1,2-a]imidazole-3-amine and imidazo[2,1-c][1,2,4]triazole-5-amine derivatives via Strecker reaction under controlled microwave heating
  38. Evaluation of three different green fabrication methods for the synthesis of crystalline ZnO nanoparticles using Pelargonium zonale leaf extract
  39. A highly efficient and multifunctional biomass supporting Ag, Ni, and Cu nanoparticles through wetness impregnation for environmental remediation
  40. Simple one-pot green method for large-scale production of mesalamine, an anti-inflammatory agent
  41. Relationships between step and cumulative PMI and E-factors: implications on estimating material efficiency with respect to charting synthesis optimization strategies
  42. A comparative sorption study of Cr3+ and Cr6+ using mango peels: kinetic, equilibrium and thermodynamic
  43. Effects of acid hydrolysis waste liquid recycle on preparation of microcrystalline cellulose
  44. Use of deep eutectic solvents as catalyst: A mini-review
  45. Microwave-assisted synthesis of pyrrolidinone derivatives using 1,1’-butylenebis(3-sulfo-3H-imidazol-1-ium) chloride in ethylene glycol
  46. Green and eco-friendly synthesis of Co3O4 and Ag-Co3O4: Characterization and photo-catalytic activity
  47. Adsorption optimized of the coal-based material and application for cyanide wastewater treatment
  48. Aloe vera leaf extract mediated green synthesis of selenium nanoparticles and assessment of their In vitro antimicrobial activity against spoilage fungi and pathogenic bacteria strains
  49. Waste phenolic resin derived activated carbon by microwave-assisted KOH activation and application to dye wastewater treatment
  50. Direct ethanol production from cellulose by consortium of Trichoderma reesei and Candida molischiana
  51. Agricultural waste biomass-assisted nanostructures: Synthesis and application
  52. Biodiesel production from rubber seed oil using calcium oxide derived from eggshell as catalyst – optimization and modeling studies
  53. Study of fabrication of fully aqueous solution processed SnS quantum dot-sensitized solar cell
  54. Assessment of aqueous extract of Gypsophila aretioides for inhibitory effects on calcium carbonate formation
  55. An environmentally friendly acylation reaction of 2-methylnaphthalene in solvent-free condition in a micro-channel reactor
  56. Aegle marmelos phytochemical stabilized synthesis and characterization of ZnO nanoparticles and their role against agriculture and food pathogen
  57. A reactive coupling process for co-production of solketal and biodiesel
  58. Optimization of the asymmetric synthesis of (S)-1-phenylethanol using Ispir bean as whole-cell biocatalyst
  59. Synthesis of pyrazolopyridine and pyrazoloquinoline derivatives by one-pot, three-component reactions of arylglyoxals, 3-methyl-1-aryl-1H-pyrazol-5-amines and cyclic 1,3-dicarbonyl compounds in the presence of tetrapropylammonium bromide
  60. Preconcentration of morphine in urine sample using a green and solvent-free microextraction method
  61. Extraction of glycyrrhizic acid by aqueous two-phase system formed by PEG and two environmentally friendly organic acid salts - sodium citrate and sodium tartrate
  62. Green synthesis of copper oxide nanoparticles using Juglans regia leaf extract and assessment of their physico-chemical and biological properties
  63. Deep eutectic solvents (DESs) as powerful and recyclable catalysts and solvents for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones
  64. Biosynthesis, characterization and anti-microbial activity of silver nanoparticle based gel hand wash
  65. Efficient and selective microwave-assisted O-methylation of phenolic compounds using tetramethylammonium hydroxide (TMAH)
  66. Anticoagulant, thrombolytic and antibacterial activities of Euphorbia acruensis latex-mediated bioengineered silver nanoparticles
  67. Volcanic ash as reusable catalyst in the green synthesis of 3H-1,5-benzodiazepines
  68. Green synthesis, anionic polymerization of 1,4-bis(methacryloyl)piperazine using Algerian clay as catalyst
  69. Selenium supplementation during fermentation with sugar beet molasses and Saccharomyces cerevisiae to increase bioethanol production
  70. Biosynthetic potential assessment of four food pathogenic bacteria in hydrothermally silver nanoparticles fabrication
  71. Investigating the effectiveness of classical and eco-friendly approaches for synthesis of dialdehydes from organic dihalides
  72. Pyrolysis of palm oil using zeolite catalyst and characterization of the boil-oil
  73. Azadirachta indica leaves extract assisted green synthesis of Ag-TiO2 for degradation of Methylene blue and Rhodamine B dyes in aqueous medium
  74. Synthesis of vitamin E succinate catalyzed by nano-SiO2 immobilized DMAP derivative in mixed solvent system
  75. Extraction of phytosterols from melon (Cucumis melo) seeds by supercritical CO2 as a clean technology
  76. Production of uronic acids by hydrothermolysis of pectin as a model substance for plant biomass waste
  77. Biofabrication of highly pure copper oxide nanoparticles using wheat seed extract and their catalytic activity: A mechanistic approach
  78. Intelligent modeling and optimization of emulsion aggregation method for producing green printing ink
  79. Improved removal of methylene blue on modified hierarchical zeolite Y: Achieved by a “destructive-constructive” method
  80. Two different facile and efficient approaches for the synthesis of various N-arylacetamides via N-acetylation of arylamines and straightforward one-pot reductive acetylation of nitroarenes promoted by recyclable CuFe2O4 nanoparticles in water
  81. Optimization of acid catalyzed esterification and mixed metal oxide catalyzed transesterification for biodiesel production from Moringa oleifera oil
  82. Kinetics and the fluidity of the stearic acid esters with different carbon backbones
  83. Aiming for a standardized protocol for preparing a process green synthesis report and for ranking multiple synthesis plans to a common target product
  84. Microstructure and luminescence of VO2 (B) nanoparticle synthesis by hydrothermal method
  85. Optimization of uranium removal from uranium plant wastewater by response surface methodology (RSM)
  86. Microwave drying of nickel-containing residue: dielectric properties, kinetics, and energy aspects
  87. Simple and convenient two step synthesis of 5-bromo-2,3-dimethoxy-6-methyl-1,4-benzoquinone
  88. Biodiesel production from waste cooking oil
  89. The effect of activation temperature on structure and properties of blue coke-based activated carbon by CO2 activation
  90. Optimization of reaction parameters for the green synthesis of zero valent iron nanoparticles using pine tree needles
  91. Microwave-assisted protocol for squalene isolation and conversion from oil-deodoriser distillates
  92. Denitrification performance of rare earth tailings-based catalysts
  93. Facile synthesis of silver nanoparticles using Averrhoa bilimbi L and Plum extracts and investigation on the synergistic bioactivity using in vitro models
  94. Green production of AgNPs and their phytostimulatory impact
  95. Photocatalytic activity of Ag/Ni bi-metallic nanoparticles on textile dye removal
  96. Topical Issue: Green Process Engineering / Guest Editors: Martine Poux, Patrick Cognet
  97. Modelling and optimisation of oxidative desulphurisation of tyre-derived oil via central composite design approach
  98. CO2 sequestration by carbonation of olivine: a new process for optimal separation of the solids produced
  99. Organic carbonates synthesis improved by pervaporation for CO2 utilisation
  100. Production of starch nanoparticles through solvent-antisolvent precipitation in a spinning disc reactor
  101. A kinetic study of Zn halide/TBAB-catalysed fixation of CO2 with styrene oxide in propylene carbonate
  102. Topical on Green Process Engineering
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