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The development of catalysts for the treatment of volatile organic compounds (VOCs) by photocatalytic oxidation is very important for treating industrial flue gases. Although defect engineering has been developed into an effective method to improve the photocatalytic activity of TiO2 semiconductor materials, few holistic studies have been performed on the structure and properties of TiO2. Herein, a one-step hydrothermal method was used to synthesize three types of nanoscale TiO2 (p-TiO2 with only Ti vacancies, n-TiO2 with only O vacancies, and pn-TiO2 with dual Ti/O vacancies) for the photocatalytic removal of gaseous toluene to determine the relationship between the redox capacity of the electron–hole pairs and the type of conductive semiconductors. It was found that pn-TiO2 exhibited a higher gaseous toluene conversion (99.6%) within 2 h, with 2.8-fold faster photocatalytic kinetics than p-TiO2 and 1.26-fold faster than n-TiO2. Based on the results of an experimental study and theoretical calculations, it was verified that the dual vacancies in pn-TiO2 enabled the valence and conduction bands to be fully exploited to generate ·OH and ·O2–, respectively, for the synergistic degradation of gaseous toluene. Because of the characteristics of the p-n homojunction, charge transfer and separation were efficiently increased in pn-TiO2, resulting in the effective treatment of gaseous toluene. In addition, after five cycles of photocatalytic degradation of toluene, the degradation rate by pn-TiO2 remained over 80%, indicating potential applications for pn-TiO2. In this study, a rational pathway is demonstrated for photocatalysts containing dual vacancies to degrade toluene based on the synergistic effect of free radicals, providing an inspiration for designing materials with vacancies or homojunctions and providing means of eliminating VOCs in practical applications. [ABSTRACT FROM AUTHOR]

Reduction of carcinogenic hexavalent chromium (Cr(VI)) by ferrous iron (Fe(II)) to essentially nontoxic trivalent chromium (Cr(III)) is a simple and effective method for Cr(VI) decontamination. In this study, the photoreduction efficacy of Cr(VI) in acidic Fe(III)/Fe(II) solutions was examined in the presence of dicarboxylic acids (DCA) (i.e. oxalic acid (Oxal), malonic acid (Mal), succinic acid (Suc), and glutaric acid (Glu)). Rates of Cr(VI) reduction under UV irradiation depend on the photochemistry of Fe(III)/Fe(II) complexes with DCA, following the order of Oxal > Suc ≈ Glu > Mal. Fe(III)-oxalato complexes are favorable for transforming Cr(VI) due to the formation of relative abundance of Fe(II) and reductive radicals such as,after photoreaction, whereas Fe(III)-Mal complexes upon UV irradiation generate the lowest amount of Fe(II) among all the Fe-DCA complexes, and thus have poor capacity for Cr(VI) reduction. The effects of Suc and Glu on the Cr(VI) reduction are insignificant since the Fe(III)-OH complexes are still the main Fe(III) species due to their weak chelating abilities with Fe(III). This work has important implications for selecting the favorable ligands of Fe(III) for light-induced Cr(VI) transformation and designing the methods for treating wastewater with low-molecular-weight acids and Cr(VI). [ABSTRACT FROM AUTHOR]

The overall maximization of photocatalytic H 2 O 2 production efficiency urgently requires the comprehensive optimization of each step in multiplex photocatalysis. Despite numerous endeavors, isolated researches focusing on single efficiencies hinder further advancements in overall catalytic activity. In this work, a series of imine-linked COFs (TT-COF-X), incorporating electronically tunable functional groups (X = ─H, ─OMe, ─OH, ─Br), are rationally fabricated for visible-light-driven H 2 O 2 production via a dual-channel pathway involving 2e - water oxidation and 2e - oxygen reduction. Combined simulations and characterizations reveal that the synergistic modification of functional groups for electronic conjugation and locally intramolecular polarity collectively enhanced light absorption, charge separation and transfer, and interface water-oxygen affinity efficiency. Notably, femtosecond time-resolved transient absorption (fs-TA) reveals that the polarity-induced built-in electric field play a crucial role in facilitating exciton dissociation by reacting BIEF-mediated shallow trapping state. The simultaneously optimal tri-efficiency ultimately results in the highest H 2 O 2 production rate of 3406.25 µmol h -1  g -1 and apparent quantum yields of 8.1% of TT-COF-OH. This study offers an emerging strategy to rational design of photocatalysts from the comprehensive tri-efficiency-oriented perspective., (© 2024 Wiley‐VCH GmbH.)

In the domain of heterogeneous catalytic activation of peroxymonosulfate (PMS), high-valent metal-oxo (HVMO) species are widely recognized as potent oxidants for the abatement of organic pollutants. However, the generation selectivity and efficiency of HVMO are often constrained by stringent requirements for catalyst adsorption sites and electron transfer efficiency. In this study, a single-atom catalyst, Cu SA /CNP&S, is synthesized featuring multiple types (planar/axial) of heteroatom coordination via an H-bond-assisted self-assembly strategy. It is confirmed that CuN 3 active centers with axial S coordination are uniformly distributed in a carbon matrix modified by planar P atoms. Cu SA /CNP&S activated PMS to selectively generate Cu (III) ═OH species as the primary reactive oxygen species (ROS). The pseudo-first-order kinetic rate for bisphenol A degradation reached 1.51 min -1 , a 17.57-fold increase compared to the unmodified Cu SA /CN catalyst. Additionally, the Cu SA /CNP&S catalyst demonstrates high efficiency and durability in removing contaminants from various aqueous matrices. Theoretical calculations and experimental results indicate that the intrinsic electric field generated by distal planar P atoms enhances electron transfer efficiency within the carbon matrix. Meanwhile, axial S coordination elevates the d-band center and tunes the e g * band broadening of Cu, thereby enhancing the adsorption selectivity for the terminal oxygen of PMS. This multitype coordination synergistically mitigates the issues of low selectivity and yield of HVMO species., (© 2024 Wiley‐VCH GmbH.)

Taking advantage of the unique properties of reduced graphene oxide (rGO) and monoclinic crystalline titanium dioxide (TiO 2 (B)) nanomaterials, a novel rGO-TiO 2 (B) composite membrane (MrGO-TiO 2 (B)) was constructed by UV-light-assisted self-assembly of rGO and TiO 2 on a nylon membrane. The structure of MrGO-TiO 2 (B) was characterized by scanning electron microscopy, transmission electron microscopy, UV-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis. Through 2D/2D self-assembly, rGO and TiO 2 (B) were more tightly combined, and then MrGO-TiO 2 (B) exhibited outstanding photocatalytic activity and an excellent methylene blue (MB) removal rate. MB was completely removed in 60 min at a constant rate of 0.042 min -1 by the MrGO-TiO 2 (B)/H 2 O 2 /MB system upon solar simulating Xe lamp irradiation. The synergistic effect of rGO and TiO 2 (B) facilitated the photocatalytic degradation of MB. TiO 2 (B) was excited and generated electrons and holes upon irradiation. Some electrons migrated to the surface of TiO 2 (B) to react with H 2 O 2 to produce hydroxyl radicals (OH), while the other electrons migrated to the surface of rGO to react with H 2 O 2 , producing OH. In addition, a number of superoxide radicals (O 2 - ) was detected. The holes in the valence band of TiO 2 (B) directly oxidized MB. The catalytic activity of MrGO-TiO 2 (B) toward MB degradation remained stable after four rounds of reuse. Therefore, the surface modification of a nylon membrane with TiO 2 (B) and rGO can serve as a promising route to fabricate photocatalytic membranes for use in the water treatment industry., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

With the pollution of perfluoroalkyl substances (PFASs) became increasingly serious, the researches focused on removal of PFASs by adsorption-photocatalysis method has attracted considerable attention. To make the catalyst TiO 2 disperse uniformly as quantum dots onto hydrophobic surface which was liable to attract perfluorooctanoic acid (PFOA), the surfactant sodium dodecyl sulfate (SDS) were used in this work, which not only connected the hydrophilic TiCl 3 to the hydrophobic sulfonated graphene (SG) nanosheets, but also behaved as the molecular template for controlled nucleation and growth of the nanostructured TiO 2 . After 3D SG-TiO 2 QD nanosheets were fabricated, a series of 3D SG-TiO 2 QD aerogels were self-assembled by ice-template. TiO 2 uniformly distributed on the surface of SG aerogel at QD size level (2-3 nm) and the size of TiO 2 could be effectively regulated by concentration of SDS. Compared with aggregated TiO 2 material, 3D SG-TiO 2 QD aerogels owned higher adsorption and photocatalytic performance. Benefiting from the hydrophobic surface of 3D SG as well as dispersed TiO 2 QDs, 3D SG-TiO 2 QD could enrich PFOA instantaneously (0.0381/s) and photocatalytic decomposed them effectively (1.898 E -4 /s). PFOA degradation by hole and hydroxyl radicals proceeded via a stepwise mechanism. The column made of 3D SG-TiO 2 QD could remove PFOA persistently in cycles of permeation. 3D SG-TiO 2 QD possessed powerful adsorption-photocatalytic decomposition capability of PFOA and steady reusability performance. The present work highlights the individual roles and synergistic effect of TiO 2 QD and 3D SG for effectively removing PFOA., (Copyright © 2019 Elsevier B.V. All rights reserved.)