Photocatalytic water splitting for hydrogen evolution (PHE) is an effective and sustainable strategy to alleviate energy shortages and environmental issues. However, active hydrogen (H*), as a critical intermediate, has low generation and desorption rates that limit the development of PHE. Herein, a ZnCdS/MoO 3-x heterojunction is prepared by a two-step solvothermal method and applied to a photocatalytic hydrogen evolution reaction under visible light conditions. The band structure and electron spin resonance (ESR) confirm the formation of an S-scheme heterojunction in ZnCdS/MoO 3-x , promoting the utilization of photo-generated carriers and thereby enhancing H* generation on ZnCdS. Furthermore, in-situ ESR, quasi in-situ Raman spectroscopy and in-situ DRFTIRS spectroscopy demonstrate that the H* is subsequently transferred from ZnCdS to MoO 3-x via the hydrogen spillover effect. The H* is then confined within the lattice of MoO 3-x and forms H x MoO 3-x in situ. Finally, the electrochemical tests and DFT calculations demonstrate that the H x MoO 3-x acts as a “hydrogen pump”, lowering the H* desorption barriers and ultimately enhancing the hydrogen evolution of the system. Therefore, the optimum hydrogen evolution rate of ZnCdS/MoO 3-x reaches 7.9 mmol·g −1 ·h −1 , which is 26.3 times higher than that of pure ZnCdS, along with a hydrogen storage capacity of 0.36 wt%. This work offers a novel approach for achieving efficient and sustained PHE reactions by modulating the generation and desorption rates of the intermediate H*.
Cr(VI) contaminated water usually contains other contaminants like engineered nanomaterials (ENMs). During the process of microbial treatment , the inevitable interaction of Cr(VI), ENMs, and microorganisms probably determines the efficiency of Cr(VI) biotransformation , however, the corresponding information remains elusive. This study investigated the interaction of ZnO nanoparticles (NPs), Cr(VI), and Pannonibacter phragmitetu s BB (hereafter BB), which changed the process of microbial Cr(VI) reduction. ZnO NPs inhibited Cr(VI) reduction, but had no effect on bacterial viability. In particular, Cr(VI) induced BB to produce organic acids and to drive Zn 2+ dissolution from ZnO NPs inside and outside of cells. The dissolved Zn 2+ not only promoted Cr(VI) reduction to Cr(V)/Cr(IV) by strengthening sugar metabolism and inducing increase in NAD(P)H production, but also hindered Cr(V)/Cr(IV) transformation to Cr(III) through down-regulating Cr(VI) reductase genes. A novel bacterial driven ROS scavenging mechanism leading to the inhibition of Cr(VI) reduction was elucidated. Specifically, the accumulated Cr(VI) and Cr(V)/Cr(IV) formed a redox dynamic equilibrium, which triggered the disproportionation of superoxide radicals mimicking superoxide dismutase through the flip-flop of Cr(VI) and Cr(V)/Cr(IV) in bacterial cells. This study provided a realistic insight into design the applicability of biological remediation technology for Cr(VI) contaminant and evaluating environmental risks of ENMs.
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