Owing to their capability to produce reactive oxygen species (ROS) under solar irradiation, covalent organic frameworks (COFs) with pre-designable structure and unique architectures show great potentials for water purification. However, the sluggish charge separation, inefficient oxygen activation and poor structure stability in COFs restrict their practical applications to decontaminate water. Herein, via a facile one-pot synthetic strategy, we show the direct conversion of reversible imine linkage into rigid thiazole linkage can adjust the $π$-conjugation and local charge polarization of skeleton to boost the exciton dissociation on COFs. The rigid linkage can also improve the robustness of skeleton and the stability of COFs during the consecutive utilization process. More importantly, the thiazole linkage in COFs with optimal C 2p states (COF-S) effectively increases the activities of neighboring benzene unit to directly modulate the O2-adsorption energy barrier and improve the ROS production efficiency, resulting in the excellent photocatalytic degradation efficiency of seven toxic emerging contaminants (e.g. degrading \textasciitilde99% of 5þinspace}mgþinspace}L−1 paracetamol in only 7þinspace}min) and effective bacterial/algal inactivation performance. Besides, COF-S can be immobilized in continuous-flow reactor and in enlarged reactor to efficiently eliminate pollutants under natural sunlight irradiation, demonstrating the feasibility for practical application.
Surface dust from degraded lands is a major global aerosol source, mobilized by meteorological events like sandstorms. Microplastics (MPs) in dust can be enriched in the atmosphere and transported over long distances to sensitive regions during sandstorms. This study was conducted in a megacity frequently impacted by sandstorms in spring, exploring the influx, characteristics, enrichment mechanism, and transport pathway of sandstorm-derived MPs. The deposition rate of these MPs reached 1823.65 ± 892.53 items·m-2·d-1, predominantly consisting of low-density polymers and those mainly used in synthetic fiber, with an average size of 60.75 µm. Compared to MPs in annual atmospheric deposition, these MPs were smaller and contained a higher proportion of potentially harmful polymers. These factors could increase exposure risks for residents from sandstorm-derived MPs, along with distinct meteorological and ecological effects. Backward trajectory analysis suggested the observed sandstorms originated from the Mongolian Plateau, over 1000 km away. Comparisons of MPs from surface-collected dust on the Mongolian Plateau with sandstorms-delivered MPs revealed the transport was determined by MP shape, size, and density. This study highlights the critical role of sandstorms in the MP atmospheric cycling, emphasizing the extensive impacts of MPs and the need for coordinated mitigation efforts across regions.
PM2.5 pollution has been greatly alleviated in the Beijing-Tianjin-Hebei (BTH) and surrounding area since the implementation of Action Plans for blue skies. Regional air pollution covering multiple cities has recently become common, but an overview from a regional perspective is scarse. In this work, based on PM2.5 chemical composition data collected in “2 + 26” cities during four consecutive autumn-winter seasons (AWS, from October to next March) from October 2016 to March 2020, we determined the main components driving the increase in PM2.5 mass concentration within different PM2.5 concentration regimes. Regionally, in the low PM2.5 regime (daily concentration ≤ 75 μg/m3), the PM2.5 mass remained organic matter (OM)-driven during the four AWSs. In the high PM2.5 regime (daily concentration > 75 μg/m3), regional PM2.5 increase pattern rapidly transformed from OM-driven during the 2016–2017 AWS to secondary inorganics-driven during the latter three AWSs, with nitrate becoming the dominant component, driving PM2.5 increase in almost 90% cities in the region. These transitions not only reflect the effectiveness of policies to control emissions from coal combustion and biomass burning in recent years, but also highlight the need to further reduce nitrogen oxides emissions from diesel vehicles, non-road mobile machinery and industry. Besides, the control of sulfur dioxide and primary organic matter should not be neglected, given the substantial contribution of PM2.5 sulfate under stagnant and humid meteorological conditions, especially in the geographically central and southern parts of the region, and the need for in-depth air quality improvement if the PM2.5 concentration standards are tightened. Considering the dominance of nitrate in driving regional PM2.5 pollution, more research on nitrate formation and its atmospheric and climatic impacts is warranted.
