Enhanced photocatalytic activity and ferromagnetic ordering in hydrogenated Zn1−xCoxO

Abstract

Impacts of hydrogen annealing on crystallographic characterization, electronic structure, and optical, photocatalytic, and magnetic properties of polycrystalline Zn_1−xCo_xO (x = 0.01–0.06) samples have been considered. Structural analyses based on powder X-ray diffraction, Rietveld refinement, and Raman spectroscopy prove all materials having the P6₃mc wurtzite-type structure. The Co-doping and hydrogenation changed the concentration of Zn– and O–related defects whose energy levels occupy the band gap. This also enhanced photocatalytic performance of hydrogenated samples with x > 0.02. X-ray and UV–Vis absorption analyses indicate the substitution of Co²⁺ for Zn²⁺ in the wurtzite-type ZnO lattice, leading to irregularly changed the unit-cell parameters. While all the as-prepared samples are paramagnetic, the hydrogenated ones exhibit weak ferromagnetism. Ferromagnetic (FM) ordering increases when x increases, particularly for x ≥ 0.02. According to the results achieved from studying crystalline and electronic structures, we believe that oxygen-vacancies-mediated interactions between Co²⁺ ions and H–Co–H exchange dimers enhanced FM ordering in hydrogenated Zn_1−xCo_xO. Computational investigations have also indicated that the magnetization value of H–Zn_1−xCo_xO is influenced by the positioning of the H dopant, meaning that the couplings between Co and H play an essential role in establishing FM order in H–Zn_1−xCo_xO.

Graphical Abstract