Redox-active Ziziphus lotus leaf biomass for sustainable hexavalent chromium remediation: mechanistic insights, kinetic modeling, and cost-effectiveness

This study elucidates the unprecedented bioremediative potential of Ziziphus lotus (Ziz. lotus) leaf biomass for detoxifying hexavalent chromium Cr(VI) in aqueous systems through a synergistic adsorption-reduction mechanism. Leveraging a four-factor Box–Behnken experimental design (BBD), we optimized key parameters: quantity of Ziz. lotus (m = 142 mg), medium acidity (pH = 1), thermal condition (T = 50 °C), and initial concentration of hexavalent chromium Cr(VI) (C = 100 mg L⁻¹) achieving complete transformation of Cr(VI) with a high desirability index. Rigorous statistical validation via ANOVA confirmed the quadratic model’s robustness. Morphological characterization using scanning electron microscopy (SEM) revealed a hierarchically porous, fibrillated architecture with a high specific surface area (125.174 m² g⁻¹), facilitating enhanced contaminant accessibility. Fourier-transform infrared spectroscopy (FTIR) deciphered critical functional moieties implicated in Cr(VI) reduction. Beyond its exceptional capacity, Ziz. lotus biomass offers a carbon-negative, scalable solution for industrial effluent treatment, circumventing the high operational costs and secondary pollution risks of conventional methods.