Effect of doping with 3$d$ elements (Co, Ni, Cu) on the intrinsic defect structure and photocatalytic properties of nanostructured ZnO with tubular morphology of aggregates

The precursor-derived nanostructured solid solutions Zn$_{0.95}$M$_{0.05}$O (M = Co, Ni, Cu) with tubular aggregates have been investigated using optical absorption spectroscopy and electron paramagnetic resonance. The dependences of the concentration of intrinsic defects V$^+_{\mathrm{O}}$ and the effective band gap on the dopant type have been determined. It has been shown using the oxidation reaction of hydroquinone dissolved in water as an example that an increase in the photocatalytic activity in the series ZnO $\to$ Zn$_{0.95}$Ni$_{0.05}$О $\to$ Zn$_{0.95}$Co$_{0.05}$O $\to$ Zn$_{0.95}$Cu$_{0.05}$O in the ultraviolet and visible spectral regions correlates with a decrease in the band gap and with an increase in the concentration of oxygen vacancies V$^+_{\mathrm{O}}$.