Silver nanoparticles (AgNPs) are rather mutable in water columns, and the oxidation of AgNPs to release Ag + and reduction of Ag + to regenerate AgNPs exist simultaneously in certain environments, making it rather difficult to monitor the reaction kinetics. In this study, we synthesized isotopically labeled AgNPs (99.5% AgNPs, but the reduction of 109 Ag + was not significantly affected. These findings implied that the transformation between AgNPs and Ag + was rather complex and greatly depended on the external conditions. Given the fact that Ag + has been shown to be much more toxic than AgNPs, the speciation change may dramatically impact the final toxicity and bioavailability of AgNPs, so there is a high demand for assessing the environmental risks of AgNPs under more realistic conditions.

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a b s t r a c tIn this paper, we present the preconditioned generalized accelerated overrelaxation (GAOR) method for solving linear systems based on a class of weighted linear least square problems. Two kinds of preconditioning are proposed, and each one contains three preconditioners. We compare the spectral radii of the iteration matrices of the preconditioned and the original methods. The comparison results show that the convergence rate of the preconditioned GAOR methods is indeed better than the rate of the original method, whenever the original method is convergent. Finally, a numerical example is presented in order to confirm these theoretical results.

Excessive emission of CO2 leads to global warming, and CO2 reduction is a promising method to utilize excessive emission. Light-driven reactions, including photoelectro­chemical (PEC) and photochemical (PC) systems, have been widely investigated, which can convert solar energy into chemical energy. In this review, the mechanism of CO2 reduction is discussed based on density functional theory (DFT) calculation and comparisons are also made in the representative light-driven devices. Also, the characteristics of candidate materials, such as semiconductors, metal organic frameworks (MOFs), layered double hydroxides (LDHs), and zeolites, etc., are included in details to explain how these characteristics influence the process of CO2 adsorption, activation, and desorption. Besides, several strategies to improve the efficiency and selectivity of catalytic reaction are also summarized. Finally, the challenges and outlook of light-driven reaction for CO2 reduction are presented.

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Using renewable energy to convert CO2 into liquid products, as a sustainable way to produce fuels and chemicals, has attracted intense attention. Herein, a novel heterostructured photocathode composed of Si wafer, TiO2 layer, and Sn metal particles has been successfully fabricated by combining of a facile hydrothermal and electrodeposition method. The obtained Sn/TiO2/Si photocathode shows enhanced light absorption performance by the surface plasmon resonance effect of Sn metal. Especially, the Sn/TiO2/Si photocathode together with rich oxygen vacancy defects jointly promote photoelectrochemical CO2 reduction, harvesting a high faradaic efficiency of HCOOH and a desirable average current density (−4.72 mA cm−2) at −1.0 V vs. reversible hydrogen electrode. Significantly, the photocathode Sn/TiO2/Si also shows good stability due to the design of protecting layer TiO2. This study provides a facile strategy of constructing an efficient photocathode to improve the light absorption performance and the electron transfer efficiency, exhibiting great potential in the CO2 reduction.

In December 2017, an influenza A(H9N2) virus (B51) was isolated from migratory waterfowl in Hubei Province, China. Phylogenetic analysis demonstrated that B51 is a novel reassortant influenza virus containing segments from human H7N4 virus and North American wild bird influenza viruses. This suggest that B51 has undergone multiple reassortment events.