Mechanism of p-Type Heteroatom Doping of Lithium Stannate for the Photodegradation of 2,4-Dichlorophenol: Enhanced Hole Oxidative Capability and Concentrations.

A systematic evaluation of enhancing photocatalysis via aliovalent cation doping is conducted. Cation In3+, being p-type-doped, was chosen to substitute the Sn site (Sn4+) in Li2SnO3, and the photodegradation of 2,4-dichlorophenol was applied as a model reaction. Specifically, Li2Sn0.90In0.10O3 exhibited superior catalytic performance; the photodegradation efficiency reached about 100% within only 12 min. This efficiency is far greater than that of pure Li2SnO3 under identical conditions. Density functional theory calculations reveal that introducing In3+ increased the electron mobility, yet decreased the hole mobility, leading to photogenerated carrier separation. However, photoluminescence and time-resolved photoluminescence suggest that In3+ induced nonradiative coupling in the matrix, reducing the photogenerated carrier separation ratio compared with that of Li2SnO3. The optical band gap of Li2Sn0.90In0.10O3 was almost unchanged compared with that of Li2SnO3 via ultraviolet-visible absorption. The increased photocatalytic efficiency was ascribed to the lower valence band position and enhanced hole concentrations by valence band X-ray photoelectron spectroscopy and electrochemical measurements. Finally, a 2,4-dichlorophenol degradation pathway, an intermediate toxicity assessment, and a photocatalytic mechanism were proposed. This work offers insights into designing and optimizing semiconductor photocatalysts with high performance.

Sn1/3Na2/3Sn(OH)6 Perovskite with Sn4+/Na+ Disorder for Photocatalytic Degradation of 2,4-Dichlorophenol.

Cation disorder in hydroxide-based perovskites remains relatively under-researched. In this work, novel hydroxide-based perovskite Sn1/3Na2/3Sn(OH)6 was first fabricated by a direct hydrothermal method, and its ability to photodegrade 2,4-dichlorophenol was evaluated. The synthesized photocatalyst is isostructural with MSn(OH)6 (M = Mg, Ca, Sr, Mn, Fe, Co, Ni, or Zn), where the M site is occupied by disordered Sn4+/Na+. Sn1/3Na2/3Sn(OH)6 exhibits outstanding photocatalytic activity under ultraviolet light. Specifically, 99% of 2,4-DCP is photodegraded in 40 min, with approximately 94% of its total chlorine content converted to Cl- anions. Radical trapping experiments indicated that superoxide radical anions (·O2-) play a critical role during the photocatalytic process. Finally, liquid chromatography-tandem mass spectrometry was conducted to monitor the photocatalytic intermediates. Overall, our findings demonstrate that hydroxide-based perovskites with cation disorder show promise for application in photocatalysis.

How does COVID-19 lockdown affect air quality: Evidence from Lanzhou, a large city in Northwest China.

Coronavirus disease (COVID-19) has disrupted health, economy, and society globally. Thus, many countries, including China, have adopted lockdowns to prevent the epidemic, which has limited human activities while affecting air quality. These affects have received attention from academics, but very few studies have focused on western China, with a lack of comparative studies across lockdown periods. Accordingly, this study examines the effects of lockdowns on air quality and pollution, using the hourly and daily air monitoring data collected from Lanzhou, a large city in Northwest China. The results indicate an overall improvement in air quality during the three lockdowns compared to the average air quality in the recent years, as well as reduced PM2.5, PM10, SO2, NO2, and CO concentrations with different rates and increased O3 concentration. During lockdowns, Lanzhou's "morning peak" of air pollution was alleviated, while the spatial characteristics remained unchanged. Further, ordered multi-classification logistic regression models to explore the mechanisms by which socioeconomic backgrounds and epidemic circumstances influence air quality revealed that the increment in population density significantly aggravated air pollution, while the presence of new cases in Lanzhou, and medium- and high-risk areas in the given district or county both increase the likelihood of air quality improvement in different degrees. These findings contribute to the understanding of the impact of lockdown on air quality, and propose policy suggestions to control air pollution and achieve green development in the post-epidemic era.