Research Article pubs.acs.org/journal/ascecg
High Efficient Photodegradation and Photocatalytic Hydrogen Production of CdS/BiVO4 Heterostructure through Z‑Scheme Process Lei Zou, Haoran Wang, and Xiong Wang* School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
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S Supporting Information *
ABSTRACT: Novel heterostructured CdS/BiVO4 nanocomposites were fabricated in a low-temperature water bath system. The uniform CdS nanoparticles with an average size of 20 nm were homogeneously interspersed on BiVO4 nanosheets. The coupling of BiVO4 and CdS nanoparticles could notably promote the photocatalytic activity. The composites reached a high H2-production rate of 0.57 mmol h−1 under visible light irradiation, about 5.18 times higher than that of pure CdS nanoparticles. The dominant active species in the photocatalytic system were also confirmed by the radical trapping test. Based on the calculation and experimental results, a Z-scheme photocatalytic mechanism was proposed, which was further confirmed by the electrochemical impedance spectroscopy and the cycling test. The Z-scheme photocatalytic system endows the CdS/BiVO4 heterostructure with strong reducibility and oxidizability and excellent stability. KEYWORDS: Photocatalystic, CdS/BiVO4, Heterostructure, Hydrogen evolution
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electron−hole pairs,27−29 it was wildly used as the hybrid component of semiconductor heterojunctions. As might be expected, it also plays a crucial role in CdS/BiVO 4 heterostructured semiconductor: CdS has an appropriate conduction band edge of −0.5 V vs. NHE,30 which can react with O2 to yield ·O2−, and the small particles on the surface of BiVO4 will provide more reaction sites, and thus improve its photocatalytic activity. Additionally, there are seldom reports on synthesis and photocatalytic performances of CdS/BiVO4 hybrid system. In this work, we prepared CdS/BiVO4 heterostructure through electrostatic interactions in water bath system. Under visible light irradiation, the photodegradtion was evaluated by the degradation of Rhodamine B (RhB), and the photocatalytic hydrogen evolution over the CdS/BiVO4 composites was investigated in methanol aqueous solution. The proposed Zscheme photocatalytic system endows the CdS/BiVO 4 heterostructure with improved photocatalytic activity and excellent stability.
INTRODUCTION Semiconductor photocatalysis has been becoming potential technology to solve the environmental pollution and energy crisis.1−3 The semiconductor TiO2 was once considered as one of the most promising photocatalysts because of its photocatalytic activity, stability, and nontoxicity.4 Unfortunately, the light response range and quantum efficiency of TiO2 limited its further application.5,6 Therefore, how to achieve high efficient visible-light-driven photocatalysts became the key point in this research field. Nowadays, two main strategies have been employed to solve above problem: modifying TiO2 or exploiting new type semiconductor photocatalytic materials.7,8 Bismuth based semiconductor has been attracting intense interest due to its special structure and unique physical properties.9−11 BiVO4 (BVO) is a typical aurivillius oxidemolybdate semiconductor with a low bandgap of 2.5 eV12,13 and the proper valence band edge located at 2.4 eV vs. NHE, providing sufficient overpotential for holes to oxide water.14 However, several drawbacks such as slow charge transportation and high recombination of photoinduced electrons and holes limit the practical application of BiVO4 for photocatalysis.15,16 Recently, it has been reported that coupling two or more semiconductors can enhance the separation of photogenerated electron−hole pairs.17−19 BiVO4 coupling with other semiconductors or metals, such as g-C3N4, Cu2O, WO3, RGO, Au QDs, to form heterojunctions has been investigated.20−24 CdS is a direct band gap semiconductor with narrow band gap of 2.4 eV and can absorb sunlight at wavelengths under 520 nm.25,26 Even though pure CdS suffered some disadvantages, such as photocorrosion, rapid recombination of photogenerated © 2016 American Chemical Society
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RESULTS AND DISCUSSION Phase Structures and Morphology. The crystalline structure of as-prepared samples was determined by XRD. Figure 1 shows the XRD patterns of blank BiVO4, pure CdS and CdS/BiVO4 nanocomposites. Characteristic diffraction peaks of CdS were detected at 2θ angles of 24.9°, 26.6°, Received: July 14, 2016 Revised: November 8, 2016 Published: November 14, 2016 303
DOI: 10.1021/acssuschemeng.6b01628 ACS Sustainable Chem. Eng. 2017, 5, 303−309
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maintained sheet-like shape during the heating process. This heterostructure would facilitate the separation of photogenerated charges and provide more active sites for photocatalytic process. The quantities of CdS nanoparticles on the BiVO4 surface gradually decreased with increasing the nanosheet content. EDS elemental mappings of CS/BVO-75 (Figure S1) confirmed that all elements (S, Cd, V, O, Bi) could be determined in the sample, and the elements Cd and S covered over the surface of BiVO4, further suggesting that the CdS nanoparticles were evenly distributed on the BiVO4 nanosheets. Figure 3 presents the TEM and HRTEM images of BiVO4 and CS/BVO-75. It could be observed from Figure 3a that the
Figure 1. XRD patterns of blank BiVO4, pure CdS, and CdS/BiVO4 nanocomposites with different chemical compositions.
28.3°, 43.7°, 47.9°, and 51.9°, and could be indexed to the (100), (002), (101), (110), (103), and (112) crystal planes of hexagonal CdS (JCPDS No. 41-1049), respectively. Blank BiVO4 was indexed to the monoclinic phase (JCPDS No. 140688) with good crystallinity. Both of the diffraction peaks of CdS and BiVO4 were observed in the CdS/BiVO4 nanocomposites without other detectable impurities. The diffraction intensity of the hexagonal phase CdS tended to be weaker with the increase of BiVO4 content. The morphology and microstructure of CdS/BiVO4 samples were observed by SEM, TEM, and EDS elemental mapping. Observed from the SEM images as shown in Figure 2, the blank BiVO4 exhibits well-defined 2D nanosheets with a thickness of 20−40 nm. For the CdS/BiVO4 composites with different contents (Figure 2b−e), CdS nanoparticles with an average size of 20 nm were closely adhered on the BiVO4 surface, which
Figure 3. TEM images of (a) BiVO4 and (b) BVO/CS-75. (c) HRTEM image of CS/BVO-75.
blank BiVO4 took on an ultrathin 2D sheet-like morphology. The uniform CdS nanoparticles with an average size of 20 nm were homogeneously interspersed on the BiVO4 nanosheets, as shown in Figure 3b. The interface between CdS nanoparticles and BiVO4 nanosheets could be observed through the HRTEM image (Figure 3c). The interlocked lattice fringes of 0.312 and 0.292 nm correspond to (101) planes of hexagonal CdS and (040) planes of monoclinic BiVO4, indicating that CdS nanoparticles were tightly attached to the surface of BiVO4 nanosheets, which was beneficial to the transport of photogenerated charges. The formation mechanism of CdS-BiVO4 composites is illustrated in Figure 4. Because of the point of zero charge of mBiVO4 at pH 2.7,31 BiVO4 surface is negatively charged over pH 2.7, which favored the adsorption of Cd2+ through electrostatic interactions in the present synthesis system. Upon addition of aqueous solution of thiourea, in situ nucleation of CdS results in the formation of a CdS-BiVO4 composite. Because of molecular interactions between −NH2 groups in thiourea (H2NCSNH2), CdS nanoparticles can be uniformly dispersed on the nanosheets as expected. UV−vis Diffuse Reflectance Spectra. Optical absorption properties of all samples were investigated by an UV−vis spectrometer. Figure 5 shows the UV−vis diffuse reflectance spectra of the as-prepared samples. The absorption edge of blank BiVO4 was located at around 510 nm, responsive to visible light. The addition of CdS apparently expanded the absorption edge of BiVO4 because CdS could harvest more photon for its wider absorption edge (∼560 nm), which was beneficial to improve the quantum efficiency of CdS/BiVO4 composites. The inset shows the corresponding Kubelka−
Figure 2. SEM images of (a) blank BiVO4, (b) CS/BVO-25, (c) CS/ BVO-50, (d) CS/BVO-75, (e) CS/BVO-100. 304
DOI: 10.1021/acssuschemeng.6b01628 ACS Sustainable Chem. Eng. 2017, 5, 303−309
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Figure 4. Illustration of the formation mechanism of CdS-BiVO4 composites. Figure 6. Photodegradation of RhB over blank BiVO4, pure CdS, and CdS/BiVO4 composites under visible light irradiation (λ > 420 nm). RhB dye concentration: 5 mg L−1, pH = 7. Catalyst suspended: 1 g L−1.
Moreover, the photodegradation efficiency at different pH from 3 to 11 was also investigated and is shown in Figure S3. The optimum solution pH for RhB photodegradation was found to be 5. Because of the diversity of RhB structure at different pH, the influence of pH on the photodegradation is more complicated. Briefly, RhB exists predominately as two forms in acidic or basic system, respectively (Figure S4).32 In a solution with much lower pH value (pH 3), the composite is positively charged. The electrostatic repulsion force between the cationic RhB molecules (acidic form) and the catalyst particles results in the decrease of adsorption amount and thus the photocatalytic efficiency. In a basic environment, RhB molecules (basic form) can attach to the photocatalyst surfaces by the carboxylic or amino group,33 which is greatly influenced by the pH value. The combined effects lead to the gradually decrease of photocatalytic activity in the basic range. Photocatalytic hydrogen production over the prepared compositions was evaluated under visible light irradiation using methanol as a sacrificial reagent to quench photoinduced holes. The cocatalyst Pt was used to reduce the overpotential for hydrogen evolution. Figure 7 shows the hydrogen evolution rate over the samples with different CdS contents under visible light irradiation. For pure CdS, due to the rapid recombination of photoinduced carriers, a relatively low H2-evolution rate was obtained (0.11 mmol h−1). A significant influence of the coupling on the photocatalytic activity could be found. The H2evolution rate was remarkably increased even at a low BiVO4 content (CS-BVO-25). The incorporation of CdS nanoparticles with BiVO4 nanosheets improved the evolution rate up to CSBVO-75, where the H2-evolution rate reached the highest value of 0.57 mmol h−1 (about 5.18 times higher than that of pure CdS) with apparent quantum efficiency of 20.6% at 420 nm. However, a further increase in the BiVO4 nanosheets content gave rise to attenuation in the H2-evolution rate. For blank BiVO4, no hydrogen was detected, indicating that BiVO4 is inactive for photocatalytic hydrogen production under the present condition. Therefore, a suitable content of BiVO4 is pivotal for optimizing the photocatalytic activity of nanocomposites.
Figure 5. UV−vis diffuse reflectance spectra (DRS) of pure CdS, blank BiVO4, and CdS/BiVO4 nanocomposites.
Munk plots. The bandgaps of blank BiVO4 and pure CdS were determined as 2.5 and 2.2 eV (vs. NHE), respectively. Photocatalytic Performances. The photocatalytic activities of as-prepared samples were evaluated by the degradation of RhB under visible light irradiation. As shown in Figure 6, RhB was stable under visible light illumination in photolysis process without any catalysts. Blank BiVO4 and pure CdS also performed poor photocatalytic activity, and only 39% and 50% of RhB were removed after 3 h irradiation, respectively, which was due to the rapid recombination of photogenerated electron−hole pairs. All CdS/BiVO4 samples exhibited improved photocatalytic activity. With increasing BiVO4 content, the photodegradation efficiency of the composites increased gradually. Among them, CS/BVO-75 represented the best performance with a degradation rate of 89% within 180 min. As compared with that of pure CdS nanoparticles (k = 3.34 × 10−3 min−1), the photocatalytic activity of CS/BVO-75 was improved by about 3.4 times (k = 11.28 × 10−3 min−1, as shown in Figure S2). Further increasing the vanadate content, the degradation efficiency was reduced. It might be due to the decrease of the contact interface and the low conduction band of BiVO4 which could not drive the photocatalytic reduction. It was suggested that there existed an optimum synergistic interaction between CdS and BiVO4 for the best photocatalytic performance. 305
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with the presence of both AN and AC in the system simultaneously. The experimental results confirmed that the h+, ·OH, and ·O2− radicals are the dominant active oxygen species in the CdS/BiVO4 photocatalytic process. The band edge position is an intrinsic property of semiconductor and closely related to the photocatalytic activity. So the band edge position of conduction band (CB) and valence band (VB) of semiconductor at the point of zero charge was calculated by the empirical equation:34 ECB = χ − Ee − 0.5Eg, where χ is the absolute electronegativity of the semiconductor, and Ee is the energy of free electrons on the hydrogen scale (4.5 eV). The χ values for BiVO4 and CdS are calculated to be 6.03 and 5.19 eV, respectively. The valence band top (EVB) and the conduction band bottom (ECB) of BiVO4 can be determined as 2.78 and 0.28 eV (vs. NHE), respectively. Whereas the EVB and ECB values of CdS are 1.79 and −0.41 eV (vs. NHE), respectively. These results confirmed that CdS and BiVO4 could form an overlapping band structure.34 If the charge carrier transfer in CdS and BiVO4 occurs through a common heterojunction mechanism, the photogenerated electrons in the CB of CdS and the holes in the VB of BiVO4 will migrate to the CB of BiVO4 and the VB of CdS, respectively. Because of the positive ECB of BiVO4, the photogenarated electrons in the CB of BiVO4 cannot reduce O2 into ·O2−, which is not in agreement with the radical trapping experimental results. Based on the above-mentioned results, a Z-scheme photocatalytic mechanism was proposed considering the charge transfer process and the schematic illustrations are shown in Figure 9. Under the illumination of visible light, these two narrow-band materials are irradiated to generate electron−hole pairs. In organic pollutant system as shown in Figure 9a, the photogenerated electrons in the CB of CdS nanoparticles will react with adsorbed O2 to yield ·O2− (E0(O2/·O2−) = −0.28 eV vs NHE) and finally form ·OH. The photogenerated holes in the VB of BiVO4 will react with H2O to yield ·OH (E0(H2O/· OH) = 2.68 eV vs NHE), and also can directly oxide organic contaminants. However, the CB electrons of BiVO4 cannot reduce O2 for its more positive CB potential (0.28 eV vs NHE), and the electrons thus cannot transfer from CdS to BiVO4. More exactly, the electron transfer from CdS to BiVO4 is a minor path.35−37 The electron flow is supported by the radical trapping experiment in which ·O2− radicals are one of the dominant active oxygen species. Because of a large number of defects easily aggregated at the contact interface between CdS and BiVO4, the energy levels of the interface are quasicontinuous.38 Thus, the solid−solid contact interface serves as the recombination center between the CB electrons of BiVO4 and the VB holes of CdS. Eventually, the ·O2− and ·OH radicals, together with the photogenerated holes in the VB of BiVO4, drive the dye oxidation reaction. The whole process is similar to the natural Z-scheme photocatalytic system.39,40 Similarly, in the visible-light-driven photocatalytic H 2 production process, the electrons excited from the VB to the CB of CdS transfer to Pt deposited on the surface and react with the adsorbed H+ ions to form H2. The holes in the VB of BiVO4 are responsible for the oxidative photodecomposition of methanol. At the CdS-BiVO4 contact interface, an Ohmic contact is formed as electron mediator (see Figure 9b). The CB electrons of BiVO4 can directly recombine with the VB holes of CdS via the Ohmic contact with low contact electric resistance, which can be further confirmed by EIS. Figure 10 shows EIS
Figure 7. Comparison of the photocatalytic H2 production from ethanol aqueous solutions for blank BiVO4, pure CdS, and CdS/ BiVO4 composites under visible light irradiation.
Based on the nitrogen adsorption−desorption isotherms (see Figure S5), the BET surface areas exhibited little difference between blank BiVO4 and CS-BVO-75, which indicates that the specific areas had little effect on the photocatalytic performance of the samples. Thus, it could be concluded that the coupling of BiVO4 nanosheets and CdS nanoparticles could generate great promotion effect to boost photocatalytic activity significantly due to the higher light harvesting and faster charge separation. Photocatalytic Mechanism of CdS/BiVO4 Nanocomposites. To investigate further the main reactive species directly involved in the photodegradation over the CdS/BiVO4, the radical trapping test was performed. Silver nitrate (AN), isopropyl alcohol (IPA), ammonium carbonate (AC), and benzoquinone (BQ) were added to the reaction solution as electron, ·OH, hole and ·O2− radical scavengers, respectively. According to Figure 8, all the scavengers could partially suppress the photocatalytic activity of CS/BVO-75, and the photocatalytic process would be almost thoroughly suppressed
Figure 8. Photodegradation of RhB over CS/BVO-75 in the presence of different scavengers. RhB dye concentration: 5 mg L−1, pH = 7. Catalyst suspended: 1 g L−1. 306
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Figure 9. Schematic sketches of (a) photodegradation of organic dye contaminants and (b) photocatalytic hydrogen production over CdS/BiVO4 heterostructure in Z-scheme photocatalysis system.
recovery process. Furthermore, no obvious crystalline structure changes could be observed from the XRD patterns for the cycled CS/BVO-75 composites (Figure S8), implying the excellent phase stability.
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CONCLUSION In summary, the heterostructured CdS/BiVO4 photocatalysts were synthesized in a water bath. The CdS/BiVO4 nanocomposites exhibited highly efficient visible-light-driven photocatalytic activities as compared with pure CdS and blank BiVO4. Sample CS/BVO-75 presented the highest efficiency among all the as-prepared photocatalysts. The enhancement of photocatalytic performance and stability was attributed to the promotion of charge separation and the efficient transfer of photogenerated carriers through the Z-scheme process. This unique Z-scheme photocatalytic system has promising potential in environmental remediation applications and photosynthesis.
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Figure 10. Electrochemical impedance spectroscopy (EIS) Nyquist impedance plots of CdS NPs, blank BiVO4, and CS/BVO-75 nanocomposites.
EXPERIMENTAL SECTION
Preparation of BiVO4. All chemicals were reagent grade and used without further purification, and deionized water was used in all experiments. BiVO4 was synthesized by a hydrothermal process: 0.97 g of Bi(NO3)3·5H2O and 0.5 g of C18H29NaO3S (SDBS) were dissolved in 20 mL of HNO3 (4 mol L−1) to form a transparent solution. Then 0.234 g of NH4VO3 dissolved in 20 mL of NaOH solution (2 mol L−1) was added into the above solution dropwise under magnetic stirring. 0.5 h later, the pH of the mixed solution was adjusted to 6.5 with NaOH solution (2 mol L−1). The resultant solution was transferred into a 100 mL Teflon-lined stainless steel autoclave and maintained at 160 °C for 1 h. The product was collected by centrifugation, washed with distilled water and absolute alcohol, and then dried at 100 °C for 4 h. Preparation of CdS/BiVO4 Heterostructure. CdS/BiVO4 composites were synthesized through electrostatic interactions. A typical synthesis process as follows: 1 mmol of Cd(CH3COO)2 was dissolved in 50 mL of deionized water, and different qualities of the asobtained BiVO4 powders (25, 50, 75, and 100 mg) were dispersed into the above solution under ultrasonication for 0.5 h. Then 10 mL of thiourea aqueous solution (0.1 M) was poured and mixed with vigorous stirring. After 20 min, the mixture was heated at 90 °C for 2.5 h. Finally, the product was collected by centrifugation, washed with distilled water and absolute alcohol, and then dried at 70 °C overnight. The obtained powders were named according to their chemical composition as CS/BVO-25, CS/BVO-50, CS/BVO-75, and CS/ BVO-100, corresponding to the weight percentage of BiVO4 in the composites from 14.8, 25.8, 34.2, and 41.0%, respectively.
spectra of blank BiVO4, pure CdS and CS/BVO-75, presented in Nyquist diagram in the frequency range of 100 kHz−0.1 Hz. The EIS data were measured by a three electrode system, and the Nyquist plot could be interpreted in terms of the equivalent circuit as displayed in the inset of Figure 10. The semicircle in the high frequency region can be ascribed to charge transfer resistance (Rct). It can be found that CS/BVO-75 has a smaller radius than that of CdS and BiVO4, implying a higher efficiency of charge transfer. Thus, the coupling of CdS with BiVO4 is beneficial for electron transport through the Z-scheme process, resulting in the longer lifetime and the enhanced separation efficiency of the photogenerated charge carriers. Moreover, the CS/BVO-75 Z-scheme photocatalytic system presents the strong reducibility of CdS and the strong oxidizability of BiVO4. More importantly, the aggregation of photoexcited electrons in the CB of CdS makes CdS an electron-rich region, which can inhibit the photo oxidation of CdS, resulting in the improved cycle ability of the composites (as shown in Figures S6 and S7). The efficiencies of photodecomposition and photocatalytic H2 production for CS/BVO-75 reduced by 5.5% and 4.8% after the fourth cycle, respectively. The slightly decline in photocatalytic activity might be partly caused by the loss of photocatalyst during the 307
DOI: 10.1021/acssuschemeng.6b01628 ACS Sustainable Chem. Eng. 2017, 5, 303−309
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ACS Sustainable Chemistry & Engineering Characterization of Photocatalysts. All of the phase compositions and crystal structures of the prepared samples were determined by powder X-ray diffraction (XRD, Bruker-AXS D8 Advance) method using Cu Kα radiation (λ = 1.541 78 Å) operated at 40 kV and 40 mA. The morphology of all samples were observed by a Quant 250FEG field emission scanning electron microscopy (FESEM) instrument operating at 25 kV, equipped with an energy-dispersive X-ray spectroscopy analyzer (EDS). The transmission electron microscopy (TEM) and high resolution electron microscopy (HRTEM) images were taken with a JEOL 2100 electron microscope. The UV−vis diffuse reflectance spectra (DRS) of the samples were determined by an UV−vis spectrophotometer (UV-2450, Shimadzu) with BaSO4 as a reflectance standard. The electrochemical impedance spectroscopy (EIS) was performed by an electrochemical workstation (CHI660E). EIS measurements were carried out in 0.5 M KCl solution by using a three-electrode system, with a platinum foil electrode as the counter electrode and a saturated calomel electrode (SCE) as the reference electrode. The Brunauer−Emmett−Teller (BET) specific surface area of the samples was analyzed by nitrogen (N2) adsorption−desorption in a surface area and pore size analyzer (V-Sorb 2800). Photocatalytic Degradation. The photocatalytic degradation activity of the as-prepared samples was evaluated by the degradation of RhB. 20 mg of the sample was dispersed into 20 mL of RhB solution (5 mg L−1) in a cylindrical quartz vessel and magnetically stirred in the dark for 1 h to establish the adsorption−desorption equilibrium. Then a 500 W Xe lamp was used as the light source equipped with a cutoff filter (λ > 420 nm) during photocatalytic process. At an interval of 30 min, the absorbance of RhB was measured by UV-2450 spectrometer at 553 nm after centrifugation. The degradation efficiency (%) was calculated as follows:
degradation (%) = (C0 − C)/C0 × 100%
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*X. Wang. E-mail:
[email protected]. ORCID
Xiong Wang: 0000-0003-2327-7427 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We gratefully acknowledge the financial supports from the NSFC (21001064) and the Natural Science Foundation of Jiangsu Province (BK2010487).
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2nH2 np
=
I×t×Α hν
(1)
(2)
(3)
where nH2 is the number of evolved H2 molecules, np is the number of incident photos, h is the Planck constant, ν is the frequency of photo, I is the illumination intensity (W m−2) determined with a Ray virtual radiation actinometer, t is irradiation time (s), and A is the irradiation area (m2).
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REFERENCES
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QE =
np =
AUTHOR INFORMATION
Corresponding Author
where C0 is the concentration of RhB after adsorption process, and C is the time-dependent concentration of dye upon irradiation. Photocatalytic Hydrogen Production. The photocatalytic H2 evolution experiments were performed in a quartz reactor at ambient temperature. A 300 W Xe arc lamp with a UV cutoff filter (>420 nm) was used as a visible light source and was positioned at 20 cm above the reactor. In a typical experiment, 10 mg of the obtained powders was dispersed in 50 mL of aqueous solution containing 25% methanol by volume. A certain amount of H2PtCl6 aqueous solution was dripped into the suspension. 0.5 wt % Pt cocatalyst was loaded by a photochemical reduction deposition. Prior to irradiation, the vessel was evacuated for 30 min to remove dissolved oxygen. The hydrogen content was analyzed by gas chromatograph (GC-14C, Shimadzu) with high-purity nitrogen as a carrier gas using TCD detector. The apparent quantum efficiency (QE) was estimated by using the following equation. number of evolved hydrogen molecules × 2 × 100% number of incident photons 2nH2 = × 100% np
EDS mapping, photodegradation kinetics of RhB, pHdependence of the degradation efficiency, N2 adsorption−desorption isotherms, cycling runs for photodegradation of RhB, cycling test of photocatalytic H2 evolution, and XRD patterns of CS/BVO-75 before/after the photocatalysis (PDF)
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b01628. 308
DOI: 10.1021/acssuschemeng.6b01628 ACS Sustainable Chem. Eng. 2017, 5, 303−309
Research Article
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DOI: 10.1021/acssuschemeng.6b01628 ACS Sustainable Chem. Eng. 2017, 5, 303−309
