From discarded to desired: valorization of Zn–C battery waste into crystalline ZnO nanoparticles with crystallographic insights and antibacterial efficacy

Abstract

This study presents a sustainable “waste-to-wealth” approach for synthesizing zinc oxide nanoparticles (ZnO NPs) from discarded Zn–C dry cell batteries. The recovered Zn shells of the batteries were processed via a wet chemical route and calcination that yielded phase-pure wurtzite ZnO with nanoscale crystallite size, as confirmed by XRD analysis. A comprehensive crystallographic analysis was carried out to estimate crystallite size by exploiting various methods where Halder–Wagner and size–strain plot methods showed best fit to the experimental data (35.10 nm size and R² = 0.967). Band structure analysis using XPS/UPS revealed valence and conduction band edges relative to the vacuum level at −11.89 eV and −7.15 eV respectively, while the optical studies showed a wide band gap of 4.74 eV. FESEM analysis revealed assorted morphologies with an average particle size of 146 ± 89 nm, while TEM showed a more resolved average primary particle size of 40 ± 27 nm, corroborating the XRD analysis. Functional group analysis by FTIR and Raman spectroscopy confirmed the characteristic Zn–O stretching and the E₂ (high) vibrational modes. The as prepared ZnO NPs displayed antibacterial activity against Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus). However, no significant activity was observed against the tested Gram-negative strains. This work demonstrates a facile route to transform hazardous battery waste into functional ZnO NPs with promising structural and antibacterial properties.