Photocatalytic Reduction Of Aqueous Cr Research Articles

1D/2D Rod-sheet Shape Bi2S3 Photocatalyst for Photocatalytic Reduction Cr(VI) under Visible Light

The crystal structure and morphology of photocatalysts play a crucial role in determining their photocatalytic performance. In this study, we synthesized and investigated 1D/2D Bi2S3 as a potential visible-light-activated photocatalyst for the reduction of aqueous Cr(VI). The 1D/2D Bi2S3 was synthesized using hydrothermal synthesis technique by heating Bi2(H2O)2(SO4)2(OH)2 precursor and sodium sulfide at 190 ℃ for 24 h, where the molar ratio of Bi to S elements in the reaction reagents was changed from 1:6 to 2:3. The structure, composition, and optoelectronic properties of the prepared Bi2S3 were characterized using X-ray diffraction, UV-vis diffuse reflectance spectra, field emission scanning electron microscopy, electrochemical impedance spectra, and transient photocurrent. It is shown that the prepared orthorhombic Bi2S3 has full-spectrum photoresponsivity. Bi2S3-B with 1D/2D heterogeneous structure exhibits the lowest charge carrier transport resistance, and its photocurrent intensity is nearly twice that of Bi2S3-C. It demonstrates the highest photocatalytic activity in visible-light photocatalytic reduction of aqueous Cr(VI), with a reduction rate of 54.5% after 140 minutes of light exposure. According to the bandgap of Bi2S3 and radical scavenger experiments, a reaction mechanism for the photocatalytic reduction of Cr(VI) by Bi2S3 was proposed. Furthermore, the results highlight the economic and environmentally friendly nature of the hydrothermal synthesis method using homemade precursors, which allows for the regulation of Bi2S3 morphology and the enhancement of its visible photocatalytic activity. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Dual-Functional CuO-Decorated Bi3.84W0.16O6.24/Bi2WO6 Nanohybrids for Enhanced Electrochemical Hydrogen Evolution Reaction and Photocatalytic Cr(VI) Reduction Performance

The development of dual-functional nanohybrid-based electrocatalysts/photocatalysts for producing renewable energy and removing heavy metal pollutants describes an environmentally sustainable technique to address the challenges in energy and environment applications. Herein, we adopted microwave-assisted synthesis to develop CuO-decorated Bi3.84W0.16O6.24/Bi2WO6 (CuO/biphase-BW) dual-functional nanohybrids for electrochemical hydrogen evolution reaction (HER) and photocatalytic Cr(VI) reduction applications. CuO nanoparticles with ∼50 nm were uniformly distributed on an octahedron-shaped bismuth tungstate analyzed via a high-resolution transmission electron microscope technique. Biphase bismuth tungstate optimization was meticulously controlled via the amount of copper precursor added to the reaction. Among synthesized materials, CuO1.0/biphase-BW catalysts exhibit excellent HER activity in neutral media (0.5 M Na2SO4) with a relatively low overpotential of 111 mV at a current density of 10 mA/cm2, and also it exhibits a lower Tafel slope of 237 mV/dec. Moreover, CuO1.0/biphase-BW catalyst-coated carbon cloth exhibits good conductivity and excellent electrochemical stability for 24 h. Maximum photocatalytic reduction of aqueous Cr(VI) was achieved on the CuO1.0/biphase-BW catalyst. It is worth mentioning that the tremendous activity of the synthesized electrocatalyst/photocatalyst can be ascribed to the formation and electronic interaction of CuO with biphase Bi3.84W0.16O6.24/Bi2WO6, thus increasing its surface-active sites and charge transfer. Our work provides a facile and effective way to engineer dual-functional nanohybrids for efficient water splitting in a neutral medium and reducing toxic (Cr(VI)) metal.

Effect of the solution acidic-basic property on the structure and photocatalytic performance of hydrothermally-synthesized TiO2

• Phase, shape and size-tunable hydrothermal synthesis of TiO 2 in different solutions. • The photocatalytic activities are H 2 O-TiO 2 > HAc-TiO 2 > HCl-TiO 2 > NaOH-TiO 2 . • The underlying reasons for the photocatalytic activity disparity were proposed. • Helpful for future synthesis of TiO 2 -based photocatalysts by hydrothermal method. The effect of the solution acidic-basic property on the structure and photocatalytic performance of hydrothermally-synthesized TiO 2 was investigated. It was found that the solution acidic-basic property influenced the phase, morphology and size of the obtained products. Anatase TiO 2 nanoparticles, anatase TiO 2 nanoparticles, and rutile TiO 2 nanorods were synthesized in deionized water, 1.818 mol/L HAC, and 1.818 mol/L HCl aqueous solution, respectively, but phase-pure TiO 2 cannot be synthesized in 1.818 mol/L NaOH aqueous solution. For photocatalytic reduction of aqueous Cr(VI) under Xe lamp irradiation, the TiO 2 synthesized in deionized water (H 2 O-TiO 2 ) demonstrated the best photocatalytic activity. The smallest grain size, biggest specific surface area, most surface hydroxyl groups and highest photogenerated charge separation efficiency may be responsible for the greatest photocatalytic activity of H 2 O-TiO 2 . Considering that hydrothermal method is most frequently used in synthesizing TiO 2 -based photocatalysts, our finding of pure water as the best solvent for hydrothermal synthesis of TiO 2 would have great significance and provide helpful guidance.

Hydrothermal synthesis of Nb5+-doped SrTiO3 mesoporous nanospheres with greater photocatalytic efficiency for Cr(VI) reduction

The Nb 5+ -doping strategy was adopted to enhance the photocatalytic efficiency of SrTiO 3 to overcome the limitation for its practical photocatalytic applications. Different amounts of Nb 5+ doped SrTiO 3 (Nb-SrTiO 3 ) mesoporous nanospheres were synthesized via a convenient hydrothermal approach. The photocatalytic reduction of aqueous Cr(VI) using the Nb-SrTiO 3 products under xenon lamp irradiation was investigated. Results indicated that 3% Nb-SrTiO 3 was the optimum product, which exhibited a photocatalytic efficiency 3 times as much as that of SrTiO 3 and a fair reuse stability. Moreover, 3% Nb-SrTiO 3 also demonstrated higher photocatalytic efficiency than many other metal cations doped SrTiO 3 synthesized via the same process and a number of previously reported photocatalysts. The best photocatalytic activity of 3% Nb-SrTiO 3 was found to be predominantly due to its most efficient separation and transfer of photogenerated holes and electrons. This study suggests that Nb-SrTiO 3 is a potential efficient photocatalyst for the remediation of Cr(VI)-contaminated water. • Nb 5+ -doped SrTiO 3 mesoporous nanospheres were synthesized by a hydrothermal method. • 3% Nb-SrTiO 3 has far higher photocatalytic activity than SrTiO 3 in Cr(VI) reduction. • It outperforms many other metal ions doped SrTiO 3 and many reported photocatalysts. • It has good photocatalytic stability. • Its higher activity mainly results from enhanced separation and transfer of e − and h + .

UiO-66 with confined dyes for adsorption and visible-light photocatalytic reduction of aqueous Cr(VI)

• Dye molecules confined in MOFs for continuous and stable photosensitization in a photocatalytic reaction. • Photocatalytic reduction of Cr(VI) in water at neutral pH without any sacrificial reagent. • Adjustment on surface electrostatic properties of UiO-66 by dye confinement and loading of Pt nanoparticles. • A simple and feasible method to enhance the visible-light photocatalytic ability of a MOF. Dye sensitization is an important method to improve the visible-light response of a photocatalyst. In order to obtain stable dye-sensitized MOF photocatalysts, UiO-66 with confined rhodamine B (RhB) and eosin Y (EY) dye were prepared by simply adding dyes in the synthetic process in this work. In comparison with pristine UiO-66, the obtained RhB@UiO-66 and EY@UiO-66 can not only adsorb Cr(VI) from water more effectively, but also enhance the photocatalytic reduction of Cr(VI) to Cr(III) at a neutral pH under visible-light without adding any sacrificial agent. Thus, they both achieved an overall Cr(VI) removal rate of about 99%. The loading of Pt nanoparticles can further improve the photocatalytic abilities of RhB@UiO-66 and EY@UiO-66. The highest photocatalytic removal rate of Cr(VI) over Pt/RhB@UiO-66 is 66.4%. The confinement of the dyes and the loading of Pt nanoparticles largely changed the surface electrostatic properties of UiO-66. The adsorption process of Cr(VI) was therefore affected. Meanwhile, Pt nanoparticles greatly improved the utilization efficiency of photogenerated electrons.

Bimetallic CuPd nanoparticle-decorated MgAl-LDH/g-C3N4 composites for efficient photocatalytic reduction of aqueous Cr(VI)

Constructing a high-performance photocatalyst is one of the most effective approaches to remove heavy metals from wastewater. Here, we successfully synthesized MgAl-layered double hydroxide/graphitic carbon nitride/ (CuPd/LDH/CN) decorated with CuPd bimetallic nanoparticles for the first time to photocatalytically reduce hexavalent chromium (Cr(VI)) in an aqueous solution. The ternary CuPd/LDH/CN heterojunction exhibited superior photocatalytic reduction of Cr(VI) under visible light compared to those of pure CN, LDH, and the binary composites. The CuPd bimetallic nanoparticles were deposited onto the LDH/CN surfaces, as confirmed by morphological observations. Our results revealed that unique structural features endow CuPd/LDH/CN catalysts with excellent photocatalytic performance, likely attributed to abundant active sites, large specific surface areas, as well as enhanced separation and transfer efficiencies of photo-generated charge carriers. Particularly, the nanocomposite (with LDH and CuPd contents of 15 wt% and 1 wt%) exhibited the highest catalytic efficiency with 98% removal of aqueous Cr(VI) (40 mg/L) within 40 min. Furthermore, no significant change in the degradation activity of the CuPd/LDH/CN nanocomposites was observed through four successive experimental runs. This study provides new insights into the design and construction of high-performance photocatalysts with potential applications in environmental remediation and energy conversion.

Efficient photocatalytic reduction of aqueous Cr (VI) by Zr4+ doped and polyaniline coupled SnS2 nanoflakes

• Zr-SnS 2 /PANI nanocomposites were synthesized and optimized for photocatalysis. • Higher activity than SnS 2 , Zr-SnS 2 , SnS 2 /PANI, and many other photocatalysts. • Zr 4+ doping and PANI coupling synergistically enhanced the photocatalysis of SnS 2 . • Factors affecting the photocatalytic reduction of Cr (VI) were investigated. • Zr-SnS 2 /PANI can effectively treat the Cr (VI)-containing electroplating solution. The synergistic Zr 4+ doping and PANI coupling were used to improve the photocatalytic activity of SnS 2 nanoflakes for the treatment of aqueous Cr (VI). The Zr-SnS 2 /PANI photocatalyst was prepared by a facile two-step method. The optimal Zr-SnS 2 /PANI-6% (with the Zr/Sn molar ratio of 1:8 and the PANI content of 6 wt%) exhibited dramatically higher photocatalytic activity toward Cr (VI) reduction than SnS 2 , Zr-SnS 2 , SnS 2 /PANI, and many previously reported SnS 2 -based and PANI-containing visible-light photocatalysts. Moreover, Zr-SnS 2 /PANI-6% showed outstanding performance in the photocatalytic treatment of Cr (VI)-containing electroplating solution. Based on the measured photo-electrochemical properties of the samples, the increased photocatalytic efficiency of Zr-SnS 2 /PANI-6% was mainly due to the synergistic effect induced by the smaller bandgap, higher charge transfer efficiency, and lower electron-hole recombination rate. Furthermore, the effects of coexisting cations and anions, photocatalyst amount, initial pH, Cr (VI) concentration, environmental atmosphere, and co-presence of 1,4-benzoquinone or K 2 S 2 O 8 on photocatalytic Cr (VI) reduction over Zr-SnS 2 /PANI-6% were investigated.

Morphology-controlled hydrothermal synthesis and photocatalytic Cr(VI) reduction properties of α-Fe2O3

Hematite (α-Fe2O3) with different morphologies were synthesized via hydrothermal treatment of ferric acetylacetonate in deionized water, simply by changing the hydrothermal temperature and time. Their photocatalytic performance was assessed based on the photocatalytic reduction of aqueous Cr(VI) under visible-light. It was found that the α-Fe2O3 nanorods synthesized at 175 °C for 2 h (Fe2O3-175 °C/2 h) had better photocatalytic activity than the other products. Moreover, Fe2O3-175 °C/2 h also demonstrated good photocatalytic reusability and stability. The reasons underlying the photocatalytic activity difference of different morphologies of α-Fe2O3 were proposed, by comparing their specific surface area, photoabsorption capability, and photogenerated charge transfer and separation efficiency. Various factors influencing the photocatalytic reduction of Cr(VI) by Fe2O3-175 °C/2 h were also investigated. Finally, Fe2O3-175 °C/2 h was tested for photocatalytic treatment of the diluted black chromium electroplating solution under visible-light, and a good treatment result was obtained. Hence, α-Fe2O3 nanorods have great potential for photocatalytic treatment of Cr(VI) wastewater.

Effects of precursors on the phase, magnetic and photocatalytic properties of nano Fe2O3 synthesized by low temperature calcination

By calcining ferric acetylacetonate (Fe(ACAC)3), Fe(NO3)3·9H2O and FeCl3·6H2O in air at 300 °C for 5 h, maghemite (γ-Fe2O3) nanoparticles, hematite (α-Fe2O3) nanoparticles and α-Fe2O3 nanoflakes were synthesized, respectively. The γ-Fe2O3 nanoparticles demonstrated far stronger magnetism (remanent magnetization (Mr) = 9.9 emu/g) than α-Fe2O3 nanoparticles (Mr = 0.06 emu/g) and nanoflakes (Mr = 0.13 emu/g) at room temperature. For photocatalytic reduction of aqueous Cr(VI) in the presence of visible-light and citric acid, the performance of different Fe2O3 samples was found to be in the order of α-Fe2O3 from FeCl3·6H2O > γ-Fe2O3 from Fe(ACAC)3 > hydrothermally synthesized α-Fe2O3 nanorods > α-Fe2O3 from Fe(NO3)3·9H2O > hydrothermally synthesized α-Fe2O3 nanoparticles. This work reveals the decisive role of precursors in the phase, magnetic and photocatalytic properties of low temperature calcination-synthesized Fe2O3. The phase-tunable synthesis of nano Fe2O3 by low temperature calcination of easily available precursors is simple, cost-effective and practical for large scale industrial production.

One-pot synthesis of Bi3O(PO4)2(OH) embedded on rod-like BiPO4 for efficient adsorption and visible-light photocatalytic reduction of aqueous Cr(VI)

Photocatalytic reduction of Cr(VI) by visible light remains highly challenging. In this work, the composite of Bi3O(PO4)2(OH) embedded on rod-like BiPO4 synthesized by one-pot precipitation method. Changing the synthetic conditions have significant roles for controllable morphologies of BiPO4/Bi3O(PO4)2(OH) heterostructures as well as the photocatalytic efficiency. Under optimal synthetic conditions, BiPO4/Bi3O(PO4)2(OH) heterostructures showed the highest visible light photocatalytic efficiency, which was nearly 44.5 times that of pure BiPO4. The BiPO4/Bi3O(PO4)2(OH) heterostructures exhibited highly effective visible-light photocatalytic reduction of Cr(VI) by the self-photosensitization of adsorbed Cr(VI) combined with the Z-scheme heterojunction charge transfer mechanism under initial pH without adding any sacrificial agent. The report could present a significant approach towards Cr(VI) photoreduction from water through the novel BiPO4/Bi3O(PO4)2(OH) photocatalyst. It will provide an strategy for environmental wastewater treatment, making full use of solar energy. Moreover, it can contribute to future efforts designing heterostructured semiconductor photocatalysts.

Siloxene: An advanced metal-free catalyst for efficient photocatalytic reduction of aqueous Cr(VI) under visible light

In this work, we reported the synthesis of siloxene catalysts from calcium silicide at various topotactic reaction conditions and demonstrated their photocatalytic activity for Cr(VI) reduction under visible light irradiations. The topotactic reaction time influenced the surface area, structure, and optical characteristics of the siloxene, which altered the Cr(VI) photocatalytic elimination efficiency. A large specific surface area (47.04 m2 g−1) and a narrow bandgap (2.45 eV) with hydroxyl-terminated layered silicon of the S-12 h catalyst could enable more active sites for photocatalytic reaction, which results in the improved catalytic performance for Cr(VI) removal. The Density Functional Theory calculations proved the siloxene’s direct bandgap feature and narrow bandgap. The initial Cr(VI) concentration, solution pH, temperature, inert gas, and different scavenger's effects on the photocatalytic performance of the S-12 h catalyst were also investigated. The S-12 h photocatalyst exhibited the Cr(VI) reduction efficiency of 98.6% for the electroplating wastewater that demonstrates the potential application in industrial for treatment of heavy metal ions removal.

Cyano group modulated porous carbon nitride assisted by silver nanowire for boosting photoreduction of aqueous Cr(VI)

Rapid recombination of photogenerated electron-hole pairs and low utilization of visible light are still restricting the photoreduction efficiency of aqueous Cr(VI) of graphitic carbon nitride. In this work, cyano group (-C≡N) modulated porous carbon nitride assisted by silver nanowire was successfully constructed. Caused by the intense electron acceptors of -C≡N, the co-existence of both n-type and p-type semiconductor characteristics was exhibited in -C≡N modulated porous carbon nitride. The built-in electric field derived from the -C≡N modulated p-n homojunction was suitable to promote separation of electron-hole pairs and retain photogenerated charges with stronger redox capability. In addition, the assisted silver nanowire further enhanced the visible light harvesting derived from the surface plasmon resonance effect of silver nanowire. As expected, the distinctive design could synergize p-n homojunction and plasmonic metal/semiconductor, which was beneficial to strengthen photocatalytic reduction of aqueous Cr(VI) under visible light. The photocatalyst with the unique structure displayed an enhanced photocatalytic reduction efficiency of aqueous Cr(VI) under visible light in comparison with the pristine graphitic carbon nitride. After 2.5 h visible light irradiation, the aqueous Cr(VI) was almost removed. The visible light photocatalytic reaction rate constant of Cr(VI) over Ag-CN/KOH-2 is about 13.8 times than bulk g-C3N4.

Sunlight mediated photocatalytic reduction of aqueous Cr(Vl) using metal hexacyanoferrate (M = Mn, Ni, Cu and Zn)

Four different metal hexacyanoferrates, MHCF (M = Mn, Ni, Cu and Zn) were synthesized via a simple, cost effective precipitation method. The as-synthesized MHCF were characterized using XRD analysis and FESEM images were recorded for the analysis of morphology. Among the four compounds, ZnHCF exhibited most effective catalytic property for visible-light driven photoreduction of Cr(VI) to Cr(III), with excellent photochemical reducing capability of 68% within 2 h.

Synthesis and application of Fe3O4/FeWO4 composite as an efficient and magnetically recoverable visible light-driven photocatalyst for the reduction of Cr(VI)

Fe3O4/FeWO4 composites with different compositions were synthesized via hydrothermal way, and characterized by many compositional and structural analysis techniques. 20% Fe3O4/FeWO4 showed the highest efficiency in photocatalytic reduction of aqueous Cr(VI) under visible light (λ > 420 nm) irradiation. Its photocatalytic rate is about 4.4 times as that of Fe3O4 and 1.5 times as that of FeWO4. Moreover, its photocatalytic stability was also good. According to the photoelectrochemical test results, the photocatalytic improvement mechanism of 20% Fe3O4/FeWO4 was proposed. Results from photocatalytic treatment of diluted black chromium plating solution (DBCPS) indicated that 20% Fe3O4/FeWO4 had noteworthy activity in visible light-driven photocatalytic reduction of DBCPS over a wide range of pH (3–11), but its photocatalytic efficiency was higher at lower pH. Besides, 20% Fe3O4/FeWO4 had fairly strong magnetism and could be recovered efficiently using a magnet. Hence, Fe3O4/FeWO4 composite photocatalyst holds potential for application in the treatment of Cr(VI) wastewater.

Synthesis of CPVC-modified SnS2/TiO2 composite with improved visible light-driven photocatalysis

Synthesis of heterojunctions is very effective in increasing the photocatalytic activity of photocatalysts. Considering conjugated polyvinyl chloride derivative (CPVC) is capable of constituting heterojunctions with both SnS2 and TiO2, this study used CPVC to modify SnS2/TiO2 composite to develop a new high-efficiency visible light-driven ternary photocatalyst (CPVC/SnS2/TiO2). CPVC/SnS2/TiO2 was synthesized by a convenient and practical method, and its composition and structure were characterized using many means. The photocatalytic tests manifested that CPVC/SnS2/TiO2 not only had higher activity than TiO2/SnS2 and SnS2 in photocatalytic reduction of aqueous Cr(VI), but also was efficient in photocatalytic degradation of methylene blue under visible light irradiation. Besides, the effect of the dosage of CPVC/SnS2/TiO2 on its photocatalytic reduction of Cr(VI) was investigated. Also, the photocatalytic improvement mechanism of CPVC/SnS2/TiO2 was put forward, based on the results of the electrochemical impedance, transient photocurrent response and energy band structure measurements.

Phosphorus-doped g-C3N4/SnS nanocomposite for efficient photocatalytic reduction of aqueous Cr(VI) under visible light

In this study, a novel phosphorus-doped g-C3N4/SnS (P-CN/SnS) nanocomposite for photocatalytic reduction of hexavalent chromium (Cr(VI)) in aqueous solution was successfully synthesized via a hydrothermal method. The SnS nanoparticles were loaded onto the surface of P-CN nanosheets to form tight interfaces, as confirmed by morphology observations. It was found that the P-CN/SnS nanocomposite displayed higher photocatalytic ability under visible light compared to non-composite catalysts. The unique structure of the P-CN/SnS nanocomposite provides excellent photocatalytic activity for Cr(VI), which is likely attributable to a large surface area, a wide spectral response, and the inhibition of electron-hole recombination. The best photocatalytic activity was exhibited by P-CN/SnS (30 wt% of SnS on P-CN), which completely removed Cr(VI) (100 mg/L) from solution within 60 min. Moreover, the high structural stability of the nanocomposite ensured four cycles with little activity loss. The outstanding performance of this new material provides new insights into the photocatalysis of Cr(VI).

SnO2/SnS2 nanocomposite anchored on nitrogen-doped RGO for improved photocatalytic reduction of aqueous Cr(VI)

Nitrogen-doped reduced graphene oxide (NRG)/SnO2/SnS2 ternary photocatalyst was fabricated by hydrothermal methods in two steps. XRD, Raman, XPS, X-ray elemental mapping, TEM and HRTEM analyses verified the preparation of NRG/SnO2/SnS2 ternary nanocomposite. The photocurrent response, photoluminescence, electrochemical impedance and electron spin resonance measurements indicated that the three components had synergistic effects in decreasing the carrier recombination of NRG/SnO2/SnS2. For photocatalytic reduction of aqueous Cr(VI) under visible-light irradiation, the photocatalytic efficiency of NRG/SnO2/SnS2 was higher than those found for SnS2, binary composites (NRG/SnO2, NRG/SnS2 and SnO2/SnS2), and other reported ternary photocatalysts (g-C3N4/SnS2/SnO2, SnS2-BiFeO3/rGO, NRG/SnS2/PANI and SnS2/SnO2/CPVC). Moreover, NRG/SnO2/SnS2 also exhibited a high efficiency in photocatalytic treatment of the diluted black chromium electroplating solution. Based on the results of comparative photocatalytic experiments in N2 or air atmosphere, and with or without O2•– trapping agent (p-Benzoquinone), it was inferred that Cr(VI) was reduced dominantly by photogenerated electrons of NRG/SnO2/SnS2.

Adsorption and photocatalytic reduction of aqueous Cr(VI) by Fe3O4-ZnAl-layered double hydroxide/TiO2 composites

To evaluate the synergetic adsorption capacity of layered double hydroxide (LDH) and photocatalytic reduction property of TiO2 for aqueous Cr(VI), the Fe3O4-ZnAl-LDH and TiO2 composites (FLT) were prepared via sol-gel method. The removal efficiency of FLT composites for Cr(VI) changed with the mass ratio of Fe3O4-LDH/TiO2, and the optimal ratio was 20% (FLT-2). The adsorption efficiencies of 100 mg FLT-2 were 74% and 64% for 20 and 50 mg/L Cr(VI) solution, and the total removal ratios of Cr(VI) were all over 97% after UV irradiation. The experimental data of adsorption kinetic, adsorption isothermal, and photocatalytic reduction were consistent with the pseudo-second-order, Langmuir, and first-order reaction equations, respectively. From the X–ray photoelectron spectra analysis, FLT composites adsorbed Cr(VI) directly via surface complexation, also reduced aqueous Cr(VI) to Cr(III). The photocurrent and electrochemical impedance spectroscopy of FLT composites indicated the photo-induced electron-hole pairs were separated effectively. The regeneration results show that the FLT composites had good stability and reusability after five consecutive cycles. Therefore, FLT composites are promising materials in the disposal of wastewater containing Cr(VI).

Magnetically recoverable MgFe2O4/conjugated polyvinyl chloride derivative nanocomposite with higher visible-light photocatalytic activity for treating Cr(VI)-polluted water

A facile three-step method was adopted to synthesize MgFe2O4/conjugated polyvinyl chloride (CPVC) nanocomposite. XRD, Raman, XPS, SEM, EDX, element mapping, and HRTEM analyses confirmed the formation of MgFe2O4/CPVC nanocomposite. The optical and magnetic properties of the obtained MgFe2O4/CPVC nanocomposite were measured using UV–Vis spectrophotometer and vibrating sample magnetometer, respectively. Through photocatalytic reduction of aqueous Cr(VI) under visible-light (λ > 420 nm) irradiation, it can be noticed that MgFe2O4/CPVC nanocomposite had both improved visible-light photocatalytic activity (about 2.1 times that of MgFe2O4 nanoparticles) and good photocatalytic stability. Moreover, MgFe2O4/CPVC nanocomposite can also be easily recovered by use of a magnet. Based on electrochemical impedance, transient photocurrent response and Mott-Schottky measurement, the mechanism responsible for the enhanced photocatalytic activity of MgFe2O4/CPVC nanocomposite was proposed. Finally, MgFe2O4/CPVC nanocomposite was applied to photocatalytic treatment of the diluted black chromium electroplating solution at different pH. Results showed that MgFe2O4/CPVC nanocomposite had significant visible-light photocatalytic activity in treating the diluted black chromium electroplating solution over a wide pH range (1.4–10.3), and its treatment efficiency increased with the decrease of solution pH. Thus, MgFe2O4/CPVC nanocomposite has the potential to be a new magnetically recoverable, high-performance visible-light photocatalyst for treating Cr(VI)-polluted water.

Solid-phase Synthesis of Visible-light-driven BiVO4 Photocatalyst and Photocatalytic Reduction of Aqueous Cr(VI)

This communication reports a pioneering study on the synthesis of BiVO4 and photocatalytic reduction of Cr(VI)-polluted wastewaters. Monoclinic phase BiVO4 micron-crystals with adjustable morphology were synthesized via a solid-phase route. The structures, morphology, optical properties of the BiVO4 micron-crystals were characterized by X-ray diffraction, field emission scanning electron microscopy, UV-vis diffuse reflectance spectra, Fourier transform infrared spectroscopy spectra, and photocurrent measurements. Besides, their photocatalytic properties were tested for the reduction of aqueous Cr(VI) under visible light (l > 420 nm) irradiation. The photocatalytic tests showed that the photocatalytic activities of BiVO4 powders in aqueous Cr(VI) depended on the dark adsorption amount for Cr(VI) and number of photogenerated carriers. BiVO4-(c) exhibited the highest photocatalytic reduction efficiency that attributed to highest separation and transfer efficiency of photogenerated electrons and holes. Besides, effects of photocatalytic experiment parameters (including dosage of photocatalyst and coexistent anions and cations) on the Cr(VI) removal rate by BiVO4-(c) were also investigated, and •OH play an important role in the BiVO4 photocatalytic reduction Cr(VI).