Design of BiOBr0.25I0.75 for synergy photoreduction Cr(VI) and capture Cr(III) over wide pH range

Controllable fabrication of SbxBi2-xS3 solid solution photocatalysts with superior elimination for Cr(VI)

The development of environmentally friendly and cost-effective photocatalysts is of vital significance for the effective removal of heavy metal contamination in water, but it is still a crucial challenge. Herein, the novel SbxBi2-xS3 solid solution photocatalysts with a certain amount of sulfur vacancy were prepared by adjusting the molar ratio of Sb to Bi through a simple hydrothermal strategy, and was applied to the effective photocatalytic reduction of hexavalent chromium (Cr(VI)). Sb1.75Bi0.25S3 with optimized ratio has superior reduction performance of Cr(VI), and the photocatalytic efficiency of Cr(VI) can achieve 91.9 % within 1 h of visible light illumination. The remarkable catalytic efficiency is due to the more applicable band structure of the solid solution photocatalyst, which is conducive for the photocatalytic reaction. Moreover, the substitution of Bi causes the crystal distortion of Sb2S3 and induce the generation of sulfur defects, which can effectively capture photoelectrons, accelerate the carriers separation, and improve the reduction performance. This study provides a hopeful photocatalyst for wastewater purification and promotes the exploration of solid solution photocatalyst in water environment remediation.

One-Step Fabricated Sn0 Particle on S-Vacancies SnS2 to Accelerate Photoelectron Transfer for Sterling Photocatalytic CO2 Reduction in Pure Water Vapor Environment

Promoting the proton-coupled electron transfer process in order to solve the sluggish carrier migration dynamics is an efficient way to accelerate the photocatalytic CO2 reduction (PCR) process. Herein, through the reduction of Sn4+ by amino and sulfhydryl groups, Sn0 particles are lodged in S-vacancies SnS2 nanosheets. The high conductance of Sn0 particles expedites the collection and transport of photogenerated electrons, activating the surrounding surface of unsaturated sulfur (Sx 2- ) and thus lowering the energy barrier for generation of *COOH. Meanwhile, S-vacancies boost H2 O adsorption while Sx 2- increases CO2 adsorption, as demonstrated by density functional theory (DFT), obtaining a selectivity of 97.88% CO and yield of 295.06 µmol g-1 h-1 without the addition of co-catalysts and sacrificial agents. This work provides a new approach to building a fast electron transfer interface between metal particles and semiconductors, which works in tandem with S-vacancies and Sx 2- to boost the efficiency of photocatalytic CO2 reduction to CO in pure water vapor environment.

Biochar-based microporous nanosheets-mediated nanoconfinement for high-efficiency reduction of Cr(VI)

Biochar-based materials have been widely used to remove Cr(VI). However, current strategies mainly focus on slow adsorption through electrostatic and functional group properties, ignoring the confinement catalytic fast kinetics caused by inherent porous properties. Herein, we designed a confinement strategy to achieve high-efficiency Cr(VI) reduction by encapsulating the catalytic reaction of Cr(VI) and oxalic acid (OA) in the micropore of PCRN-3-10-2-800. The results showed that the removal rate constant of the PCRN-3-10-2-800/OA system was 14.3 and 146.8 times higher than that of the BC-800/OA system (low porosity) and PCRN-3-10-2-800 alone (adsorption), which was highest removal rate constant in the current reported materials under the same system. The structure-activity relationship indicated that the catalytic activity of Cr(VI) depended on the micropore characteristics of the catalyst. Density functional theory calculations confirmed that nanoscale space could enhance Cr(VI) adsorption and reduce the energy barrier of the rate-determining step. The electron paramagnetic resonance spectrum demonstrated the rapid conversion of Cr(VI) to Cr(III). Furthermore, the PCRN-3-10-2-800/OA system showed good applicability and high efficiency for Cr(VI) removal (nearly 100% in 5 min) in industrial electroplating wastewater treatment. This work first proposes a nanoconfinement-induced heavy metal reduction strategy and guides biochar's universality design in wastewater treatment.

Fabrication of Z-scheme Bi7O9I3/g-C3N4 heterojunction modified by carbon quantum dots for synchronous photocatalytic removal of Cr (Ⅵ) and organic pollutants

Chromium(VI) (Cr(VI)), a highly toxic metal ion, generally co-exists with organic pollutants in industrial effluents. The clean and effective technology for water purification is an imperative issue but still a challenging task. A series of Bi₇O₉I₃/g-C₃N₄ (BOI/CN) composites modified by lignin-derived carbon quantum dots (CQDs) were fabricated by hydrothermal method and applied for synchronous photocatalytic removal of Cr (Ⅵ) and levofloxacin (LEV). With the modification of CQDs in BOI/CN heterojunction, the 0.5-CQD/BOI/CN photocatalyst (0.5% content of CQDs) exhibited stronger light-harvesting capacity, more efficient charge separation, and faster electron transfer. Compared to those of BOI (51.2%), CN (36.8%), and BOI/CN (74.4%), the photoreduction efficiency of Cr(VI) reached up to 100% by 0.5-CQD/BOI/CN under 60 min of light irradiation, together with 94.8% degradation efficiency of LEV. The degradation of LEV was dominantly controlled by active species (•OH and •O₂^-) identified by electron paramagnetic resonance analysis and free radical trapping experiments. The intermediates of LEV were determined by LC-MS and the possible degradation pathway was speculated in combination with density functional theory calculation, involving defluorination, decarboxylation, quinolone rings opening, and piperazine moieties oxidation reactions. This work provides an advanced strategy for the fabrication of high-efficiency CQDs-based Z-scheme photocatalysts for environmental remediation.