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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.)