Facile synthesis and characterization of ZnO, ZnO:Co, and ZnO/ZnO:Co nano rod-like homojunction thin films: Role of crystallite/grain size and microstrain in photocatalytic performance

Herein, to investigate the photodegradation of methylene blue (MB) under UV light irradiation and the photocatalytic activity of chemically derived ZnO, ZnO: Co 5% nano rod-like thin films and ZnO/ZnO: Co 5% homojunction, the role of grain size and microstrain on their structural, optical, electrical and photocatalytic properties were studied. Hexagonal wurtzite structure, the doping of Co2+ into ZnO host lattice, reduced crystallite/grain size, and enhanced microstrain have been confirmed by structural and morphological analysis. The presence and the atomic content of Zn/Zn2+, Co/Co2+, O/O2- elements, and ions have been confirmed by EDS and XPS measurements. The n/p-type conductivity in nano rod-like film and p-n bilayers have been verified by Hall and I-V characterizations. The PL analysis showed that the decreased luminescence intensity and the formation of defect/trapping centers by Co2+ doping and formation of p-n homojunction as crystallite/grain size decreased while microstrain increased. With 5% Co-doping and the emergence of p-n homojunction, the photocatalytic efficiency (eta %) was reduced compared with parent ZnO photocatalyst, while the crystallite/grain size decreases and microstrain enhances. The decreased eta % was attributed to the reduced crystallite/grain size, increment of microstrain, and the generation of defects/ trapping centers via 5% Co-doing and formation of ZnO/ZnO:Co 5% nano rod-like homojunction. These results demonstrate that the fabrication of p-n homojunction will not always result in an enhanced eta % even if it puts down the recombination of light-induced charge transporters. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study investigated the photodegradation of methylene blue under UV light and the photocatalytic activity of various ZnO structures. It found that factors such as grain size, microstrain, and Co doping significantly influenced the performance, with a decrease in photocatalytic efficiency observed with 5% Co doping and p-n homojunction formation.