NiO/CdO/Co3O4 nanocomposite as an efficient visible-light photocatalyst for photodegradation and water splitting synthesized by recycling spent Ni–Cd batteries

Abstract

Recycling electronic wastes containing precious metals and turning them into valuable products has economic and environmental value. In this paper, recycling spent nickel-cadmium (Ni–Cd) batteries in producing a ternary NiO/CdO/Co₃O₄ nanocomposite (BAT) was introduced as a novel, cost-effective, and environmentally friendly procedure. For this purpose, Ni, Cd, and Co elements were recovered, with leaching recoveries of 91, 99, and 99.5 %, respectively, using sulfuric acid. The leach liquor was used as the starting feed material in a sol-gel process. For a comparison matter, the same ternary nanocomposite was synthesized through a conventional co-precipitation method using nitrate precursors as a reference sample (REF). The calculated band gap energy of the BAT and REF was 2.05 and 2.40 eV. The optical properties improvement of the BAT sample, along with the proper contact interface, led to a rate constant of 0.0062 1/min in photocatalytic methylene blue (MB) degradation and 988.2 μmol/g.h in photocatalytic hydrogen evolution (PHE). A 2.5 times reduction in the charge transfer resistance from 2110 Ω in the REF sample to 849 Ω in the BAT was also observed. A combination of Z-scheme and type I charge transfer was proposed to justify the higher photocatalytic performance of the BAT sample. This work has introduced a novel approach for recycling spent Ni–Cd batteries by directly employing the leach liquor to synthesize NiO/CdO/Co₃O₄ photocatalyst.