Centurial deposition records of polychlorinated biphenyls and organochlorine pesticides in sediment cores from a plateau deep-water lake of China: Significance of anthropogenic impacts, transformation signals and ecological risks revealed by full congener analysis.

Lake Fuxian, the largest deep freshwater lake in China, has been suffering from increasing ecological and environmental issues along with the rapid urbanization and industrialization in the past 40 years. To better understand the historical pollution of persistent organic pollutants (POPs) in Lake Fuxian, comprehensive analyses of 209 polychlorinated biphenyl (PCB) congeners and 20 organochlorine pesticides (OCPs) were conducted in two intact sediment cores (Core V1 and Core V2). The total mass concentrations of PCBs ranged from 7.60 to 31.47 ng/g (dry weight basis) and 5.55 to 28.90 ng/g during the period of 1908-2019 in Core V1 and 1924-2019 in Core V2, respectively. PCBs exhibited a consecutive increasing trend from 1940s to 2019 in Core V1. The temporal trend of PCBs in Core V2 basically matched to the history of PCB usage and prohibition in China (increasing from 1940s to mid-1960s, a remarkable drop in mid-1970s, and then increasing until 2019). Moreover, low-chlorinated PCBs were dominant among PCB homologues. Mono-CBs, di-CBs, tri-CBs and tetra-CBs accounted for 86.71 %-98.57 % in sediment segments. The PCB sources included unintentional emission and atmospheric deposition, as well as biological transformation. The total mass concentrations of OCPs ranged from 0.74 to 3.82 ng/g in Core V1 and 0.35 to 2.23 ng/g in Core V2, respectively. Similar trend was observed in the two sediment cores with peaks in the early 1990s. The predominant OCPs were γ-hexachlorohexane (γ-HCHs), dieldrin and p,p'-DDD. The ecological risks posed by PCBs and p-p'-DDD in Lake Fuxian were relatively low. In contrast, dieldrin might pose a potential threat to exposed organisms and apparently adverse ecological effects were caused by γ-HCH. This study will provide important baseline information on historical POPs contamination of Lake Fuxian.

Atomic Cobalt-Silver Dual-Metal Sites Confined on Carbon Nitride with Synergistic Ag Nanoparticles for Enhanced CO2 Photoreduction.

Photocatalytic reduction of CO2 to value-added solar fuels is of great significance to alleviate the severe environmental and energy crisis. Herein, we report the construction of a synergistic silver nanoparticle catalyst with adjacent atomic cobalt-silver dual-metal sites on P-doped carbon nitride (Co1Ag(1+n)-PCN) for photocatalytic CO2 reduction. The optimized photocatalyst achieves a high CO formation rate of 46.82 µmol gcat-1 with 70.1% selectivity in solid-liquid mode without sacrificial agents, which is 2.68 and 2.18-fold compared to that of exclusive silver single-atom (Ag1-CN) and cobalt-silver dual-metal site (Co1Ag1-PCN) photocatalysts, respectively. The closely integrated in situ experiments and density functional theory calculations unravel that the electronic metal-support interactions (EMSIs) of Ag nanoparticles with adjacent Ag-N2C2 and Co-N6-P single-atom sites promote the adsorption of CO2* and COOH* intermediates to form CO and CH4, as well as boost the enrichment and transfer of photoexcited electrons. Moreover, the atomically dispersed dual-metal Co-Ag SA sites serve as the fast-electron-transfer channel while Ag nanoparticles act as the electron acceptor to enrich and separate more photogenerated electrons. This work provides a general platform to delicately design high-performance synergistic catalysts for highly efficient solar energy conversion.