Min Fu

This study systematically investigated water-soluble inorganic ions (WSIIs) and their sources in PM2.5 in mountainous urban areas of Chongqing City. PM2.5 monitoring was conducted throughout 2023, spanning one year. The two districts under discussion are the Liang Jiang New Area (LJ) and He Chuan District (HC). The ion chromatography (Dionex Integrion HPIC) method was utilized to quantify eight ions (Cl⁻, SO₄²⁻, NO₃⁻, Na⁺, K⁺, Mg²⁺, Ca²⁺, NH₄⁺). The results obtained were then analyzed in conjunction with the EPA PMF 5.0 source apportionment model. The following key findings are presented: the data demonstrate that there is significant seasonal fluctuation in PM2.5 concentrations. The mean winter concentration (64 ± 27 μg/m³) was found to be 3.25 times higher than the mean summer concentration (19.7 ± 2 μg/m³). These fluctuations were primarily influenced by basin topography and unfavorable meteorological conditions. The proportion of PM2.5 mass attributable to WSII ranges from 31 to 33 percent, with the majority of this mass being attributed to secondary inorganic aerosols (SNA: SO₄²⁻, NO₃⁻, NH₄⁺; accounting for 47–85% WSII). The annual NO₃⁻/SO₄²⁻ ratio (0.69–0.80, 1 suggests increased contributions from mobile sources under low-temperature conditions. The sulfur oxidation rate (SOR: 0.35–0.37) is significantly higher than the nitrogen oxidation rate (NOR: 0.08–0.13), reflecting the efficient conversion of SO₂ through wet, low-temperature pathways. PMF identified six sources, with secondary formation (43.8–44.3%) being the primary contributor to the overall process. In urban LJ, transportation (26.1%) and industry (13.6%) have been found to contribute significantly, while in suburban HC, combustion (15.4%) and dust (8.8%) have been determined to have notable impacts. This study recommends the implementation of synergistic control of SNA precursors (SO₂, NOx, NH₃), the strengthening of transportation and industrial management in LJ, and the enhancement of biomass combustion and dust control in HC.

To address the challenge of abatement of volatile organic compounds (VOCs) in environmental catalysis, this study developed a temperature-gradient hydrothermal strategy to fabricate SrSn(OH)₆ nanocatalysts and systematically investigatd their photocatalytic performance and mechanisms for gaseous toluene degradation. SrSn(OH)₆ (SSH) was synthesized via a simple hydrothermal method with optimal preparation conditions identified as a reaction temperature of 140 °C and duration of 12 h. The crystallinity of SrSn(OH)₆ was modulated by adjusting the pH of the precursor solution, yielding materials with distinct morphologies, specific surface areas, and band gaps. The narrowed band gap of SrSn(OH)₆ nanocatalysts facilitated electron excitation to generate additional photogenerated electron-hole pairs. The SSH-10.5 sample with ordered planar and hole-like structures promoted carrier migration, effectively suppressed electron-hole recombination, and enhanced the conversion of abundant surface hydroxyl groups into hydroxyl radicals. Under UV irradiation, SSH-10.5 achieved a toluene degradation efficiency of 69.56% and showed excellent stability after five reuse cycles. Electron spin resonance analysis confirmed the presence of •OH and •O₂⁻ radicals in the reaction system, with •OH identified as the dominant active species. In situ FT-IR spectroscopy revealed that •OH and •O₂⁻ radicals attacked the methyl group of toluene, converting it into intermediates including benzyl alcohol, benzaldehyde, and benzoic acid. This work provides a novel design of high-efficiency VOC-photocatalytic materials and shows significant implications for advancing industrial exhaust gas purification technologies.

Recently, the micro-nano bubble (MB) technology has attracted people's attention due to its special advantages. Here, we carried out the technology of combining MB and hydrogen peroxide (MB/H₂O₂) to achieve efficient degradation of tetracycline wastewater. The effect of MB/H₂O₂ technology on the degradation efficiency of tetracycline was deeply analysed by investigating the reaction time, H₂O₂ dosage, pH and MB inlet flow. The results showed that the degradation rate of tetracycline hydrochloride by MB/H₂O₂ technology can reach 92.43%, which is 9.44 and 3.94 times that of MB and H₂O₂ alone. Through electron spin resonance (ESR) analysis and free radical quenching experiments, a possible mechanism for MB/H₂O₂ technology to efficiently degrade TC was proposed. In the MB/H₂O₂ system, the high temperature and high pressure environment generated when MB ruptures can activate H₂O₂ to obtain a higher number of active oxygen species. •OH is the main reactive oxygen radical in the process of MB/H₂O₂ degradation of TC, followed by HO₂•/•O₂-. In addition, the possible intermediate products of the oxidation TC process were identified by HPLC-MS technology. Under the action of •OH and HO₂•/•O₂− free radicals, TC molecules undergo demethylation and hydroxylation, ring-opening reactions, isomerization, deethylation, deacylation, deamination and dehydration reactions to generate intermediate products and finally convert them into CO₂ and H₂O. The development of MB/H₂O₂ technology can potentially be used to efficiently remove TC substances in the water environment and provide a new method for water purification. GRAPHICAL ABSTRACT

The oxygen vacancy caused by ultrathin structures would be introduced into the semiconductor photocatalyst to boost its photocatalytic activity. Herein, ultrathin Bi₂O₃–Bi₂WO₆ nanosheet composites have been successfully synthesized via a facile hydrothermal method. Compared to pure Bi₂WO₆ nanosheets, the Bi₂O₃–Bi₂WO₆ nanosheet composites possess abundant oxygen vacancies, which was confirmed by the positron annihilation spectra. The ultrathin Bi₂O₃–Bi₂WO₆ nanosheet composites exhibited remarkable photocatalytic degradation performance for oxytetracycline compared with that of pure Bi₂WO₆ nanosheets. The excellent photocatalytic activities of Bi₂O₃–Bi₂WO₆ composites could be attributed to the heterojunction structure and the oxygen vacancies caused by ultrathin structures.