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Volatile organic compounds (VOCs) have attracted much attention for decades as they are the precursors of photochemical smog and are harmful to the environment and human health. Vacuum ultraviolet (VUV) photodegradation is a simple and effective method to decompose VOCs (ranging from tens to hundreds of ppmV) without additional oxidants or catalysts in the air at atmospheric pressure. In this paper, we review the research progress of VOCs removal via VUV photodegradation. The fundamentals are outlined and the key operation factors for VOCs degradation, such as humidity, oxygen content, VOCs initial concentration, light intensity, and flow rate, are discussed. VUV photodegradation of VOCs mixture is elucidated. The application of VUV photodegradation in combination with ozone-assisted catalytic oxidation (OZCO) and photocatalytic oxidation (PCO) systems, and as the pre-treatment technique for biological purification are illustrated. Based on the summary, we propose the challenges of VUV photodegradation and perspectives for its future development. [Display omitted] [ABSTRACT FROM AUTHOR]

Sulfate radical based photocatalysis is recognized as an effective approach for the photodegradation of organic pollutants in wastewater. To overcome the defects of weak visible light absorptivity and low catalytic efficiency of ZSM-5 based catalysts, MXene (Ti3C2) and a dopant were introduced to develop the multifunctional photocatalyst Metal/MXene/ZSM-5 by a modified in situ hydrothermal method, which was applied to phenol degradation under simulated solar light. The crystal growth, morphology, and structure of the prepared catalysts were systematically characterized by X-ray diffraction, scanning electron microscopy, surface area measurements, and various spectroscopy methods (UV-Raman, X-ray photoelectron, and UV-visible diffuse reflectance spectroscopies). The heterostructure of Fe(II)/Fe(III)/TiO2 in 5%Fe/5%MXene/ZSM-5 reduces the band gap and improves the visible light absorptivity, leading consequently to improved phenol photocatalytic degradation efficiency. The effects of pH, reaction temperature, initial phenol concentration, and peroxymonosulfate dosage on the catalytic performance of 5%Fe/5%MXene/ZSM-5 and the production of free active radicals in the 5%Fe/5%MXene/ZSM-5/PMS system were then investigated. 5%Fe/5%MXene/ZSM-5 achieves an efficient catalytic activity with over 98% removal of phenol within 25 min and 1O2 and ˙O2− radicals are the dominant reactive radicals in the 5%Fe/5%MXene/ZSM-5/PMS system for phenol degradation. This investigation improves the photocatalytic efficiency of the ZSM-5 zeolite-based catalyst under simulated sunlight. [ABSTRACT FROM AUTHOR]

VUV/UV photodegradation technology, which is free of catalysts or oxidants, has been regarded as an efficient method to decompose gaseous VOCs. However, the mineralization of gaseous VOCs by VUV/UV photodegradation has seldom been discussed systematically. In this work, the mineralization of benzyl chloride in humid air is comprehensively investigated and the potential contributors in the system (i.e., light wavelength, O2 and H2O) are discussed. As a result, more than 95.0% benzyl chloride is mineralized at 40 min in humid air with 80% relative humidity (RH) despite its initial concentrations (i.e., ranging from 4 to 20 ppm). It is found that both 185-nm VUV light and H2O significant contribute to the efficient mineralization of benzyl chloride in humid air, while O2 only has a limited effect to the efficient mineralization of benzyl chloride in humid air. The introduction of H2O into the VUV/UV photodegradation can reduce the emission of ozone obviously. These findings are significant inspiration to application of the VUV/UV photodegradation technology on the treatment of gaseous VOCs in the actual air atmosphere. [ABSTRACT FROM AUTHOR]

The synthesized Bi 2 Fe 4 O 9 nanosheets exhibit excellent piezocatalytic activity for molecular oxygen activation. The Fe2+ sites in Bi 2 Fe 4 O 9 nanosheets as active centers preferentially adsorb molecular oxygen and donate electrons to molecular oxygen to generate O 2 ∙ - for degrading organic pollutants, which is then regenerated by accepting the piezo-electrons, resulting in outstanding piezocatalytic performance. [Display omitted] • Bi 2 Fe 4 O 9 nanosheets exhibit outstanding piezocatalytic activity for molecular oxygen activation. • The O 2 ∙ - and piezo-holes are the major active species for piezocatalytic degradation of sulfamethoxazole. • Fe2+ in Bi 2 Fe 4 O 9 nanosheets as active sites activate molecular oxygen into O 2 ∙ - via donating electrons. • The Fe2+ can be regenerated by accepting the piezo-electrons. Piezocatalytic molecular oxygen activation has been regarded as a promising and low energy-cost strategy for environment remediation, yet the piezocatalytic activity is still far from satisfactory and little is known on its activation mechanism, which greatly hinders its further development. Herein, the piezocatalyst Bi 2 Fe 4 O 9 nanosheets (BFO NSs) are synthesized via a facile hydrothermal method, which exhibit excellent piezocatalytic performance for sulfamethoxazole degradation. O 2 ∙ - generated via the molecular oxygen reduction reaction by piezo-electrons and the piezo-holes were confirmed as major active species for organic pollutants degradation. Further theoretical calculations and XPS analyses confirm the Fe2+ sites as active centers activate molecular oxygen into O 2 ∙ - via donating the electrons to molecular oxygen and the piezo-electrons reduce Fe3+ to Fe2+. This work provides atomic-scale insights into the active sites of piezocatalytic molecular oxygen activation, which can inspire the development of more efficient piezocatalysts for environment application. [ABSTRACT FROM AUTHOR]