Highly active photocatalyst of nickel oxide nanoparticles green-synthesized using Tinosphora cordifolia-plant extract for photocatalytic oxidation of tetracycline

The current study demonstrates the facile synthesis of nickel oxide nanoparticles (NiONPs) by using Tinosphora cordifolia as bioreductor. Structural, morphological, optical, photocatalytic activity and stability of the prepared NiONPs were investigated. From the structural and morphological studies using XRD, XPS, SEM and TEM, it was found that single phase of NiO produced with particle size of 19.5 nm. The material exhibited the band energy of 3.14 eV which support its photocatalytic activity in tetracycline removal by photocatalytic oxidation mechanism. The removal efficiency of 99.4 % was achieved by 30 min of photocatalytic oxidation treatment. Liquid chromatography-high resolution mass spectrometry analysis applied to identify the tetracycline degradation products represents the mechanism of hydroxyl attack to carbonyl, and demethylation that leads to aromatic ring opening and the formation of smaller compounds. The studies on the effect of scavenger implied that •OH and hole are participative component in the mechanism. The reusability study demonstrated that the NiONPs photocatalyst retained its stability after being used for five times without significant change of removal efficiency. Further study on chemical stability of the material suggest that structural change of NiO into α-Ni(OH)₂ occurred after 5th cycle usage.