Visible light photocatalytic NOx removal with suppressed poisonous NO2 byproduct generation over simply synthesized triangular silver nanoparticles coupled with tin dioxide.

The treatment or conversion of air pollutants with a low generation of secondary toxic substances has become a hot topic in indoor air pollution abatement. Herein, we used triangle-shaped Ag nanoparticles coupled with SnO2 for efficient photocatalytic NO removal. Ag triangular nanoparticles (TNPs) were synthesized by the photoreduction method and SnO2 was coupled by a simple chemical impregnation process. The photocatalytic NO removal activity results show that the modification with Ag TNPs significantly boosted the removal performance up to 3.4 times higher than pristine SnO2. The underlying roles of Ag TNPs in NO removal activity improvement are due to some advantages of Ag TNPs. Moreover, the Ag TNPs contributed photogenerated holes as the main active species toward enhancing the NO oxidation reaction. In particular, the selectivity toward green products significantly improved from 52.78% (SnO2) to 86.99% (Ag TNPs/SnO2). The formation of reactive radicals under light irradiation was also verified by DMPO spin-trapping experiments. This work provides a potential candidate for visible-light photocatalytic NO removal with low toxic byproduct generation.

Revisiting the Key Optical and Electrical Characteristics in Reporting the Photocatalysis of Semiconductors.

Photocatalysis has been studied and considered as a green and practical approach in addressing environmental pollution. However, factors that affect photocatalytic performance have not been systematically studied. In this work, we have presented a comprehensive roadmap for characterizing, interpreting, and reporting semiconductors' electrical and optical properties through routinely used techniques such as diffuse reflectance spectroscopy, electrochemical techniques (Mott-Schottky plots), photoluminescence, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy in the context of photocatalysis. Having precisely studied the band structure of three representative photocatalysts, we have presented and highlighted the essential information and details, which are critical and beneficial for studies of (1) band alignments, (2) redox potentials, and (3) defects. Further works with a comprehensive understanding of the band structure are desirable and hold great promise.

Comment on "removal of hexavalent chromium by biochar supported nZVI composite: Batch and fixed-bed column evaluations, mechanisms, and secondary contamination prevention".

This article aims to discuss (1) the incorrect identification of Cr(III) and Cr(VI) binding energies in the Cr 2p XPS (X-ray photoelectron spectroscopy) spectra of the laden adsorbent (the nZVI-BC sample after Cr(VI) adsorption), (2) misconception regarding the Weber-Morris intraparticle diffusion model, and (3) inconsistency between the experiential data and the Thomas adsorption rate constants. The authors hope that our comments are beneficial for other researchers to avoid the undesirable mistakes.

Investigation on Photocatalytic Removal of NO under Visible Light over Cr-Doped ZnO Nanoparticles.

Removal of nitrogen oxide pollution has attracted much attention, and photocatalysis is considered as an effective method to treat polluted gas. Currently, modified semiconductors with approximate band gap are used as visible-light-driven photocatalysts. Herein, this is the first investigation of photocatalytic removal of NO under visible light over Cr-doped ZnO nanoparticles (Cr-ZnO NPs). Furthermore, the trapping species experiment and electron spin resonance measurement were conducted to identify the primary reactive factor of the photocatalytic reaction. In this study, Cr-ZnO NPs were synthesized by the sol-gel method with a narrow band gap, enhanced NO photocatalytic degradation performance, low NO2 conversion yield, and high stability under visible light.