Hollow-ZIF-templated formation of a ZnO@C–N–Co core–shell nanostructure for highly efficient pollutant photodegradation

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.