ENHANCED REMEDIATION OF TOXIC HEAVY METALS FROM INDUSTRIAL WASTEWATER USING A GREEN-SYNTHESIZED MWCNT-ZnCl @Ni NANOCOMPOSITE

Abstract

A novel nickel-decorated multi-walled carbon nanotube (MWCNT) composite, denoted MWCNT–ZnCl₂@NiNPs, was synthesized via an ecofriendly route using Vernonia amygdalina leaf extract under ultrasonic conditions. Characterization by X-ray diffraction (XRD) confirmed the presence of crystalline nickel nanoparticles (Ni⁰) on a graphitic carbon framework. Fourier-transform infrared spectroscopy (FTIR) revealed diminished O–H signatures and appearance of Ni–O vibrations after decoration. SEM/TEM imaging showed NiNPs uniformly dispersed on the CNT surfaces. Batch adsorption experiments (pH 2–6, 303–323 K) demonstrated that the composite greatly outperformed individual NiNPs or ZnCl₂-activated MWCNTs in removing Pb(II), As(V), and Cd(II). Under optimal conditions (pH 5, 43 mg/L dosage and contact time of 30 mins), removal efficiencies up to ~91% (Pb), ~88% (As), and ~81% (Cd) were obtained. Kinetic data extended with sampling at 10–15 min and 100–120 min showed excellent fit to the pseudo-second-order model (R² ≈ 0.99), indicating chemisorption dominance. Intraparticle diffusion plots exhibited multi-stage behavior, consistent with combined surface adsorption and pore diffusion processes. Equilibrium isotherms best fit the Langmuir model, yielding maximum capacities (qₘ) of ~480, 440, and 415 mg/g for Pb, As, and Cd, respectively. Thermodynamic analysis (303–323 K) indicated spontaneous (ΔG° < 0), exothermic (ΔH° < 0) adsorption. The composite shows significant potential for real-world heavy-metal remediation applications.