3-D nitrogen-doped carbon cage encapsulated ultrasmall MoC nanoparticles for promoting simultaneous ZnIn2S4 photocatalytic hydrogen generation and organic wastewater degradation.

Simultaneous redox reactions on photocatalysts make it possible to use wastewater for hydrogen production. The controlled synthesis of ultrasmall metal carbides effectively enhances the photocatalytic efficiency under this system. Here, we report a new type of cocatalyst in which a three-dimensional (3-D) nitrogen-doped carbon cage (NGC) of metal-organic framework derivatives encapsulates ultrasmall MoC nanoparticles (MoC@NGC), promoting simultaneous degradation of organic pollutants and hydrogen production by ZnIn2S4 (ZIS). Characterization analyses showed that MoC accelerated the separation of the photogenerated carrier and effectively reduced the overpotential of hydrogen evolution, while NGC promoted the good dispersion of MoC particles and provided sufficient sites. The MoC@NGC/ZIS composite exhibited a high hydrogen (H2) evolution rate of 1012 µmol g-1h-1, which exceed that of ZIS loaded with platinum. In the coupled system, where the electron donor was replaced with rhodamine B (RhB), the mechanism analysis showed that RhB and the as-generated intermediates consumed holes and facilitated hydrogen evolution. In addition, we designed a combined photocatalytic anoxic and oxic sequence process to achieve the recovery of hydrogen energy during the treatment of dye wastewater. This study provides a new way for cooperation between energy development and environmental protection.

Spatial directional separation and synergetic treatment of Cr(VI) and Rhodamine B mixed pollutants on three-layered Pd@MIL-101/P25 photocatalyst.

The development of efficacious photocatalysts for removal of heavy metal and dyes coexisting pollutants simultaneously remains a challenge. Herein, we designed a three-layered Pd@MIL-101/P25 composite photocatalyst, which had the characteristics of directional photogenerated carrier separation. Pd nanoparticles were encapsulated in the MIL-101 to enrich the e-, while P25 was loaded on the outer surface of MIL-101 as the valence band of the heterojunction with MIL-101 to enrich the h+. The photocatalytic kinetic constants (K) of Pd@MIL-101/P25 for the removal of Cr (VI) and RhB were 3.4 and 4.2 times greater than that of MIL-101, respectively. The photocatalytic efficiency of the catalyst in the mixed pollutants of Cr(VI) and RhB was much higher than that when Cr(VI) and RhB were present separately. Due to the 1.2 and 1.6 nm windows of MIL-101, two target pollutants can be directionally separated. Cr (VI) was reduced by e- on the inner surface, and RhB was blocked on the outer surface and oxidized by h+. These results suggested that the directional spatially separation of target pollutants are able to separate the reaction sites of oxidation and reduction, improving the utilization efficiency of photogenerated carriers. This work not only provided a new strategy for the design and construction of photocatalytic materials, but also provided a new idea for the treatment of mixed pollutants.