Core–Shell or Dimer Heterostructures? Synergistic Catalysis of an Advanced Oxidation Process at the Exposed Interface under Illumination

Carbonaceous materials are biocompatible and ecofriendly catalysts for an advanced oxidation process (AOP) in the treatment of wastewater, but their activity is not satisfactory compared to that of the conventional metal and oxide catalysts. Here, dimer heterostructures of ZnO and Ni,N-codoped carbon (NiNC) are found to possess greatly improved activity in a photoassisted AOP reaction. In the synthesis of the composite of ZnO and ZIF-8, the adding sequence of Ni(NO3)2 and 2-methylimidazole can guide the formation of ZnO@NiZIF and ZnO–NiZIF particles, which are further converted to a core–shell particle of ZnO and NiNC (ZnO@NiNC) and a dimer particle of ZnO and NiNC (ZnO–NiNC) by calcination in N2. Although these two particles have many similar physicochemical properties, the ZnO–NiNC dimer particles show greatly enhanced activity for degradation of rhodamine B (RhB) under UV–vis illumination, where its reaction constant is 43 times of its own in the dark and 13 times higher than that of ZnO@NiNC under the same condition. A group of experiments reveal a synergistic mechanism for the ZnO–NiNC catalyst under illumination, in which the photoelectrons directionally migrate toward the exposed ZnO/NiNC interface and react with potassium peroxymonosulfate to produce more-reactive hydroxyl and persulfate radicals to accelerate the AOP reaction.