Upcycling Spent Lithium-Ion Battery Graphite into ZnO@ Carbon Nanocomposite for Photocatalytic Dye Degradation

Abstract

The growing generation of spent lithium-ion batteries (LIBs), coupled with the widespread release of dye-contaminated wastewater from industrial activities, has intensified the need for sustainable waste management and water purification technologies. In the present study, a ZnO-decorated carbon (ZnO@C) nanocomposite was developed by valorizing graphite recovered from spent LIBs and investigated as a photocatalyst for dye degradation in aqueous media. The material was synthesized through a straightforward impregnation–precipitation route, followed by thermal treatment at 250 °C. X-ray diffraction (XRD) confirmed the formation of crystalline hexagonal wurtzite ZnO, while Fourier-transform infrared (FT-IR) spectroscopy revealed Zn-O bonds and oxygen-containing surface functionalities. Scanning electron microscopy (SEM) demonstrated the dispersion of ZnO particles within the carbon matrix, with an average particle size of approximately 194 nm. The apparent photocatalytic degradation/decolorization of the ZnO@C nanocomposite was evaluated under irradiation (125 W, λ = 365 nm) using 0.01 g of catalyst in 50 mL of dye solution (0.2 g L−1) at 25 ± 2 °C, with an initial dye concentration of 10 mg L−1 and continuous stirring. The highest apparent degradation/decolorization was observed at pH ≈ 7.5 for MB and pH ≈ 3.5 for MO. Kinetic analysis using a pseudo-first-order model showed that the apparent rate constants under irradiation decreased from 0.0211 to 0.0039 min−1 for MB and from 0.0160 to 0.0020 min−1 for MO as the initial dye concentration increased from 10 to 150 mg L−1. The photocatalytic performance may be attributed to the combined contributions of the ZnO nanoparticles, surface functionalities, and the carbon support. In this work, the observed decrease in dye absorbance is considered evidence of apparent degradation/decolorization rather than complete mineralization. The results highlight the potential of spent LIB-derived graphite as a carbon support for ZnO-based photocatalytic materials.