WO3/MIL-125 (Ti) composite material for enhancing the reduction of Cr(vi) under visible light

In wastewater containing heavy metals, Cr(vi) is a potentially toxic metal, mainly derived from production and processing processes such as textile printing, dyeing, ore mining, battery applications, metal cleaning and electroplating. WO3 is widely used in photocatalytic degradation and reduction, and its utilization rate of visible light is high. However, the rapid recombination of photogenerated electron-hole pairs of WO3 limits its use. In this work, the composite material (WxMy) of WO3 and MIL-125 (Ti) was prepared by the ball milling method, and the catalyst was used to photocatalytically reduce Cr(vi). After using W90M10 as a photocatalyst for 50 min, the reduction rate of Cr(vi) can reach 99.2%, and the reduction rate is 2.3 times that of WO3. After 5 cycles of use, the reduction rate can still reach 91.3%. It is mainly due to the formation of a II-type heterojunction between WO3 and MIL-125 (Ti), which promotes the separation of photogenerated electron-hole pairs, thus improving the efficiency of photocatalytic reduction of Cr(vi).

Fabrication of Ru-CoFe2O4/RGO hierarchical nanostructures for high-performance photoelectrodes to reduce hazards Cr(VI) into Cr(III) coupled with anodic oxidation of phenols

Dual-functional photo (electro)catalysis (PEC) is a key strategy for removing coexisting heavy metals and phenolic compounds from wastewater treatment systems. To design a PEC cell, it is crucial to use chemically stable and cost-effective bifunctional photocatalysts. The present study shows that ruthenium metallic nanoparticles decorated with CoFe₂O₄/RGO (Ru-CoFe₂O₄/RGO) are effective bifunctional photoelectrodes for the reduction of Cr(VI) ions. Ru-CoFe₂O₄/RGO achieves a maximum Cr(VI) reduction rate of 99% at 30 min under visible light irradiation, which is much higher than previously reported catalysts. Moreover, PEC Cr(VI) reduction rate is also tuned by adding varying concentration of phenol. A mechanism for the concurrent removal of Cr(VI) and phenol has been revealed over a bifunctional Ru-CoFe₂O₄/RGO catalyst. A number of key conclusions emerged from this study, demonstrating the dual role of phenol during Cr(VI) reduction by PEC. Anodic oxidation of phenol produces the enormous H⁺ ion, which appears to be a key component of Cr(VI) reduction. Additionally, phenolic molecules serve as hole (h⁺) scavengers that reduce e^-/h⁺ recombination, thus enhancing the reduction rate of Cr(VI). Therefore, the Ru-CoFe₂O₄/RGO photoelectrode exhibits a promising capability of reducing both heavy metals and phenolic compounds simultaneously in wastewater.

Organic Moiety-Regulated Photocatalytic Performance of Phosphomolybdate Hybrids for Hexavalent Chromium Reduction

Visible-light-driven photocatalytic Cr(VI) reduction is a promising pathway to moderate environmental pollution, in which the development of photocatalysts is pivotal. Herein, three hourglass-type phosphomolybdate-based hybrids with the formula of: (H₂ bpe)₃ [Zn(H₂ PO₄ )][Zn(bpe)(H₂ O)₂ ]H{Zn[P₄ Mo₆ O₃₁ H₆ ]₂ } ⋅ 6H₂ O (1) Na₆ [H₂ bz]₂ [ZnNa₄ (H₂ O)₅ ]{Zn [P₄ Mo₆ O₃₁ H₃ ]₂ } ⋅ 2H₂ O (2) and (H₂ mbpy) {[Zn(mbpy)(H₂ O)]₂ [Zn(H₂ O)]₂ }{Zn[P₄ Mo₆ O₃₁ H₆ ]₂ } ⋅ 10H₂ O (3) (bpe=trans-1,2-bi(4-pyridyl)-ethylene; bz=4,4'-diaminobiphenyl; mbpy=4,4'-dimethyl-2,2'bipyridine) were synthesized under the guidance of the functional organic moiety modification strategy. Structural analysis showed that hybrids 1-3 have similar 2D layer-like spatial arrangements constructed by {Zn[P₄ Mo₆ ]₂ } clusters and organic components with different conjugated degree. With excellent redox properties and wide visible-light absorption capacities, hybrids 1-3 display favourable photocatalytic activity for Cr(VI) reduction with 79%, 70% and 64% reduction rates, which are superior to that of only inorganic {Zn[P₄ Mo₆ ]₂ } itself (21%). The investigation of organic components on photocatalytic performance of hybrids 1-3 suggested that the organic counter cations (bpe, bz and mbpy) can effectively affect the visible-light absorption, as well as the recombination of photogenerated carriers stemmed from {Zn[P₄ Mo₆ ]₂ } clusters, further promoting their photocatalytic performances towards Cr(VI) reduction. This work provides an experimental basis for the design of functionalized photocatalysts via the modification of organic species.

Solvent-mediated synthesis of BiOI with a tunable surface structure for effective visible light active photocatalytic removal of Cr(VI) from wastewater

The present study investigated the effect of various solvents on the tunable surface morphology and photocatalytic activity (PCA) of bismuth oxyiodide (BiOI), which could be used for the reduction of Cr(VI) under visible light irradiation (VLI). BiOI samples exhibiting different morphologies, i.e., two-dimensional square-like nanosheet and three-dimensional hierarchical flower-like morphology, were synthesized by a hydro/solvothermal process using different solvents, namely H₂O, MeOH, EtOH, and ethylene glycol (EG). The crystal structure, surface morphology, surface area, light-absorption capability, and recombination rate of the photogenerated charge carriers were examined by X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller analysis, UV-vis diffuse reflectance spectroscopy, photoluminescence, and transient photocurrent analyses, respectively. The BiOI sample fabricated in EG showed excellent photocatalytic efficiency (~99%) for the reduction of Cr(VI) after 90 min under VLI. The enhanced PCA demonstrated that the high surface area and well-structured surface characteristics of flower-like 3D BiOI microspheres played important roles in the photoreduction process. Moreover, a plausible mechanism for the reduction of Cr(VI) over the EG-BiOI photocatalyst was proposed. The results of the PCA evaluation and recycle test revealed that 3D EG-BiOI microspheres could serve as promising materials for the efficient removal of Cr(VI) from wastewater. Additionally, EG-BiOI could be utilized in other environmental remediation processes.

Multifunctional Ni–Mg bimetal-activated Zn(O,S) for hydrogen generation and environmental remediation with simulated solar-light irradiation

NMZ-S10 is a powerful and robust photocatalyst that is capable of conducting the hydrogen evolution reaction, chromium (Cr6+) reduction, mixed-dye degradation, and hydrogenation reaction under solar light illumination.

Room-temperature synthesized In-BiOBr1-xIx nanosheets with visible-light-driven superior photocatalytic activity: Degradation of dye/non-dye organic pollutants for environmental remediation

Photocatalysis is extensively investigated as a green, efficient and promising technique for environmental remediation. In this study, a series of template free In-doped BiOBr_xI_1-x photocatalysts have been successfully prepared at room temperature and characterized by various methods. Complete degradation of negatively charged methyl Orange, positively charged Rhodamine B and Methylene Blue organic dyes, and neutral and colorless non-dye organic compound of furfural was attained. The flat band potential offered the possibility of reduction of dissolved O₂ to O₂^.- in the conduction band while the trapping experiment identified the (O₂^.-)is the main radical species followed by h⁺ for the photodegradation. In-BiOBrI-0.4 had an excellent photocatalytic degradation activity which could be due to the synergetic effect between metal ion doping and solid solution formation. It further promotes visible light-harvesting ability and photoinduced charge carrier separation efficiency. The order of the reaction rate was determined and the mechanism was proposed. This work can lay a base for the design of effective photocatalyst toward environmental remediation.

Photocatalytic Reduction of Cr(VI) on a 3.0% Au/Sr0.70Ce0.20WO4 Photocatalyst

Herein, a 3.0%-Au/Sr0.70Ce0.20WO4 sample was prepared for the photocatalytic reduction of the Cr2O7 2- ion. The photocatalyst was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and ultraviolet-visible diffuse reflectance spectra. The Sr0.70Ce0.20WO4 sample presented a photocatalytic reduction activity that is better than those of the Ce-doped sample and the intrinsic sample. Thereafter, different metal elements, Cu, Ag, Au, and Pt, were used as cocatalysts, which were loaded on the Sr0.70Ce0.20WO4 sample. The 3.0%-Au/Sr0.70Ce0.20WO4 photocatalyst showed optimal photocatalytic reduction activity in a 8 vol % methanol solution (pH = 7) under visible light irradiation. The kinetic constant of the optimal one is 0.0039 min-1, which is 1.86 times that of the Sr0.70Ce0.20WO4 sample. The photocatalyst is stable enough after a 24 h photocatalytic experiment.

Highly efficient In-Mo(O,S)2 oxy-sulfide for degradation of organic pollutants under visible light irradiation: An example of photocatalyst on its dye selectivity

Environmentally toxic organic pollutants, namely methylene blue (MB), neutral red (NR), Rhodamine B (RhB), and methyl orange (MO) dyes contain highly toxic, carcinogenic, non-biodegradable, and colored pigments which cause harm for humans and aquatic organisms even at low concentrations. To detoxify these toxic organic pollutants from the wastewater, the bimetallic solid solution-typed In-Mo(O,S)₂ catalyst with various indium (In) contents were synthesized at low temperature through a simple precipitation method. The morphological, structural, chemical compositions, electrochemical and optical properties of the catalysts were thoroughly characterized. The photodegradation performance of the In-Mo(O,S)₂ catalysts over the cationic, anionic and neutral dyes were studied under visible light irradiation. It has been observed that the photocatalytic activity was enhanced as In was added to the Mo(O,S)₂ catalyst, and In-Mo(O,S)₂-20 was found to be the best composition to completely degrade four organic dyes. The dye degradation had rate constant values of 9.5 × 10^-2 min^-1, 6.3 × 10^-2 min^-1, 4.4 × 10^-2 min^-1, and 15.7 × 10^-1 min^-1 for MB (20 ppm), NR (20 ppm), RhB (10 ppm), and MO (10 ppm) dyes, respectively. The active species for degradation of MB is different from those for RhB and MO. Single phase In-Mo(O,S)₂-20 capable to degrade four kinds of dyes at a fast rate is a good photocatalyst.

Highly efficient visible-light-driven reduction of Cr(vi) from water by porphyrin-based metal–organic frameworks: effect of band gap engineering on the photocatalytic activity

Highly efficient visible-light-assisted photocatalytic reduction of Cr(vi) to Cr(iii) from aqueous phase using Zr(iv)-porphyrin MOFs, Zr₆(μ₃-OH)₈(OH)₈(MTCPP)₂, (PCN-222(M)) (M = H₂, Zn^II, Cu^II, Ni^II, Co^II, Fe^IIICl, and Mn^IIICl) is presented.