Tunability of physical properties of NiO by the introduction of rare earth metal (Y, Ho) dual doping for natural sunlight-driven photocatalysis

This work investigates the structural and optical features of Y/Ho-doped NiO nanoparticles fabricated through sol–gel technique and validates their photocatalytic activity for methyl red (MR) degradation. XRD peak profile study revealed that the average crystalline size and lattice parameters were increased by Y/Ho dual doping than pure NiO. FTIR results showed metal–oxygen vibrations. Raman peaks exhibited optical phonon modes shifting by dual doping. FESEM images showed nearly spherical nanoparticles with increasing particle size due to agglomeration by dual doping with particle size larger than the crystalline size calculated from XRD. EDX ascribed the existence of Ni, Y, Ho, and O elements in synthesized samples which further confirmed the successful dual doping in NiO. The direct energy bandgap was shifted to the visible region by single (Y) doping (2.62 eV) and (Y/Ho) dual doping (2.55 eV), making NiO an efficient photocatalyst under sunlight. The PL spectrum of Y/Ho dual-doped NiO nanoparticles exhibited deep-level emissions in the visible region with a decrease in PL intensity, which inhibits charge carrier recombination. The photocatalytic test under natural sunlight showed 99% degradation of Methyl Red (MR) dye in 60 min, higher than pure NiO, with reusability up to the 5th cycle. Furthermore, the present work presents the facile strategy of rare earth metal dual doping to improve the optical response of NiO, making it useful for photocatalysis under natural sunlight.