Biogenic synthesis of copper oxide nanoparticles using plant extract and its prodigious potential for photocatalytic degradation of dyes

The development of benign and efficient approaches for treating industrial grade toxic organic dyes is an ongoing challenge. To this end, copper oxide nanoparticles (CuO NPs) were prepared by a simple, environment friendly, and economical green synthesis procedure by using Psidium guajava leaf extract as reducing agent (i.e., for the reduction of metal salt) as well as capping agent and copper acetate monohydrate as metal salt. The formation of mono-dispersed and spherical (average size 2-6 nm with BET surface area 52.6 m²/g) CuO NPs was confirmed by various spectroscopic and microscopic techniques. The CuO NPs exhibited excellent degradation efficiency for the industrial dyes, i.e., Nile blue (NB) (93% removal in 120 min) and reactive yellow 160 (RY160) (81% removal in 120 min) with apparent rate constants of 0.023 and 0.014 min^-1, respectively. The CuO catalyst was found to be reusable for photocatalytic dye degradation even after five consecutive cycles. The limit of detection (LOD) values for NB and RY160 were 4 and 9 mg/L, respectively. In light of their high reusability and photocatalytic efficiency along with adaptability to green synthesis, the use of biogenic CuO NPs is a promising option for the purification of water resources contaminated with industrial dye.

Photocatalytic reduction of Cr(VI) and Ni(II) in aqueous solution by synthesized nanoparticle ZnO under ultraviolet light irradiation: a kinetic study

Photocatalytic removal of Cr(VI) and Ni(II) from aqueous solution using synthesized nanoparticle ZnO under ultraviolet (UV) light irradiation was studied in this work. Firstly, nanoparticle ZnO was prepared by the chemical method with an organic chemical inhibitor. Then removal efficiency of Cr(VI) and Ni(II) by nanoparticle ZnO was investigated with variation of the solution pH, ZnO dosage, contact time and initial Cr(VI) and Ni(II) concentration. Maximum removal of Cr(VI) and Ni(II) was observed at near-neutral pH because the reduced photocatalytic activity of ZnO at exceedingly low and high pH values originates from either acidic/photochemical corrosion of the catalyst and/or surface passivation with Zn(OH)2. As the ZnO dosage increased, the removal efficiency of Cr(VI) and Ni(II) was continuously enhanced, but was gradually decreased above 1.25 g/l due to the increased blockage of the incident UV light used for the photocatalytic reaction. The optimum ZnO dosage was determined as 1 g/l. Removal efficiencies of Cr(VI) and Ni(II) decreased as initial Cr(VI) and Ni(II) concentration increased, due to an increased inhibition effect on the surface of ZnO resulting from the decreased reaction sites on the surface of ZnO required for the further photocatalytic reaction.