Photocatalytic degradation of malachite green using vanadium pentoxide-doped NiO thin film by sol–gel spin coatingN. R. Aswathy, JiJi Varghese and R. Vinod KumarEur. Phys. J. Plus, 137 12 (2022) 1344DOI: https://doi.org/10.1140/epjp/s13360-022-03559-w