Continuous synthesis of photocatalytic nanoparticles of pure ZnO and ZnO modified with metal nanoparticles

The continuous microwave synthesis of ZnO, ZnO–nAg and ZnO–nCu nanoparticles (NPs) are presented. Initially, pure ZnO nanoparticles were synthesised, studying the effect of selected parameters on the size of crystallites. In the second stage, ZnO nanoparticles modified with metal nanoparticles were obtained by conducting the process in a flow system. Tannic acid was used as a reducing agent of silver and copper ions. The structure, crystallinity and effectiveness of the deposition of metal nanoparticles were assessed by XRD, XPS, FTIR and electron microscopy techniques (SEM and TEM). The obtained materials were tested for their photocatalytic properties against methylene blue in UV light. The results of photodegradation in ultraviolet light have shown that the introduction of metal nanoparticles, especially silver nanoparticles, significantly increases catalytic efficiency (30% for pure ZnO NPs, 91% for ZnO–nAg NPs and 54% for ZnO–nCu NPs). The main advantage of the proposed ZnO/Ag semiconductor is that it delays the recombination process of electron–hole pairs generated by photon absorption, which extends the efficiency of such a photocatalyst. Based on the research, we determined that it is possible to use photocatalytically active ZnO modified with metal nanoparticles obtained in the flow process.