Huirong Chen,Kui Shen,Junying Chen,Xiaodong Chen,Yingwei Li
Semiconducting metal oxides have been considered as effective photocatalysts for the degradation of organic pollutants to decolorize contaminated water. However, the poor performance and difficulty in recycling greatly hinder their practical application. Herein, we designed and fabricated, for the first time, a novel ZnO@C–N–Co core–shell nanocomposite towards efficient and recyclable photocatalysis by directly pyrolyzing a hollow Zn/Co–ZIF matrix consisting of a ZIF-8 shell with some Co–ZIF nanoplates inside the hollow cavity. It was demonstrated that the ZIF-8-shell-derived ZnO nanoparticles could spontaneously agglomerate and move to the hollow cavity while the internal Co NPs transferred inversely to the ligand-derived N–C shell at suitable pyrolysis temperature, resulting in the unique ZnO@C–N–Co core–shell structure. This unique nanostructure possessed the following superior properties: (1) a core–shell structure may make the intermediate ZnO much more stable during the reaction; (2) a porous carbon shell can not only provide a high BET specific area and thus high adsorption capability for reactants, but can also inhibit the recombination of photogenerated electrons and holes; (3) the embedded Co NPs were able to provide richer electron traps that further suppress the recombination of electrons and holes. As exemplified for the degradation of methyl orange, the ZnO@C–N–Co showed a significantly improved performance and excellent recyclability due to the highly synergistic effects between the C–N–Co shell and the robust ZnO. This strategy for the synthesis of MOF-derived core–shell nanomaterials could offer prospects for developing highly efficient photocatalysts.
Junxiu Liu,Ruiping Wang,Dequan Liang,Shuo Zhang,Jingqi Feng,Miaojun Xu,Shuai Du,Bin Li
An urchin-like carbon and nitrogen-doped zinc oxide (U-ZnO@C-N) was prepared by calcination of zeolitic imidazolate framework-8, and it was used as synergist. Firstly, the intumescent flame retardant (IFR) containing piperazine pyrophosphate and melamine polyphosphate with a mass ratio of 2:1 was introduced into linear low density polyethylene (LLDPE). The LLDPE/IFR passed UL-94 V-0 rating during the vertical burning tests with a limiting oxygen index (LOI) of 26.0% when 25 wt% IFR was incorporated. The LLDPE composite also reached UL-94 V-0 rating when 23 wt% IFR/U-ZnO@C-N with a mass ratio of 97:3 was introduced, and its LOI value was 26.2%. It was indicated that the addition of U-ZnO@C-N enhanced the flame retardant efficiency of LLDPE. Meanwhile, the total smoke release of LLDPE/IFR/U-ZnO@C-N was reduced by 25.5% and 30.5%, respectively, compared to LLDPE/IFR and LLDPE/commercial zinc oxide (C-ZnO). It was attributed that the U-ZnO@C-N with urchin-like structure served as the skeleton and fulcrum during the formation process of char layer, which effectively improved the strength of char layer. In addition, the free electron-holes in the semiconductor U-ZnO@C-N oxidized CO to CO 2 , effectively reducing the release of toxic gas. This work provided a valuable way to prepare LLDPE composites with high flame retardancy, smoke inhibition and low toxicity, which was expected to break the limitations of LLDPE in wires and cables applications.
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