Biofabrication and Characterization of Silica-coated Zinc Oxide Nanocomposite: A Sustainable Approach in Remediation of Cr(VI) Contaminated Wastewater

Present research investigates synthesis of silica-coated zinc oxide nanocomposite (Si-ZnO NC) from plant material and its application in remediation of Cr(VI) from water systems. The synthesized nanocomposite was assessed using XRD, FTIR, SEM-EDAX, and BET analysis. Si-ZnO NC possessed a mean pore diameter and volume, 27.964 nm and 0.1895 cm³g^-1_, respectively and a specific surface area of 27.113 m²g^-1. The nanocomposite had roughly spherical particles in agglomerated form as per SEM analysis. Effects of pH, metal concentration, adsorbent dose, temperature and time on Cr(VI) removal were investigated in batch mode experiments. The adsorption conditions including pH 2, metal concentration 10 mg/L, nanocomposite dose 0.4 g/L with a contact time 60 min at 25 ± 2 ^o C temperature showed 92% Cr(VI) removal. Langmuir isotherm model (R² = 0.9978) and pseudo-second-order model (R² = 0.9998) proposed a decent explanation for Cr(VI) adsorption rate. The process was found spontaneous and endothermic. Adsorption mechanism involved electrostatic interaction, redox reactions and adsorption coupled reduction. The regeneration ability of Si-ZnO NC was 86% Cr(VI) after three reusability cycles with 0.1M NaOH desorbing reagent as compared to 15% ammonia water. Si-ZnO NC proved to be sustainable and eco-accommodating due to its low-cost raw substance value, efficient adsorption efficiency and regeneration ability.

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