SYNTHESIS AND CHARACTERIZATION OF TiO2, ZnO AND ACTIVATED MAIZE COB NANOCOMPOSITE FOR REMOVAL OF PHENOLIC COMPOUNDS FROM WASTEWATER

Abstract

Water pollution caused by phenolic compounds (PCs) is a significant environmental challenge due to the continuous discharge of effluents from petroleum refineries, municipal, pharmaceutical, textile and agrochemical industries. PCs are particularly problematic due to their toxicity, persistence, and resistance to biodegradation. Conventional treatment technologies, including chemical oxidation, coagulation￾flocculation, membrane filtration and biological processes are often constrained by sludge generation, membrane fouling, and reduced efficiency at low pollutant concentrations. Consequently, adsorption has emerged as an alternative water treatment method due to its high removal efficiency at low pollutant concentrations. Nanoparticle-based adsorbents further enhance adsorption through their high surface area, abundant active sites and strong surface reactivity, while green synthesis provides an environmentally friendly route by reducing hazardous chemicals and secondary pollution. This study aimed to synthesize and characterize TiO₂ and ZnO nanoparticles using green synthesis with Tithonia diversifolia leaf extract as a capping and stabilizing agent, prepare and characterize a TiO₂/ZnO/activated maize-cob composite, optimize adsorption conditions, and evaluate its efficiency for PC removal from wastewater. A 2L wastewater sample was collected from Burudika, Thika, and laboratory experiments were conducted at Murang’a University of Technology. 50g of 500g sample of ground maize cobs collected from local millers from Murang`a county was chemically activated using H₃PO₄, followed by nanoparticle incorporation and experimental evaluation under controlled batch conditions. FTIR analysis of the nanoparticles revealed O-H stretching bands at 3750 cm⁻¹ (TiO₂) and 3800 cm⁻¹ (ZnO), confirming effective stabilization of the nanoparticle surfaces. XRD analysis verified phase-pure rutile TiO₂ and hexagonal wurtzite ZnO, with average crystallite sizes of 2.13 nm and 15.33 nm, respectively. FTIR and XRD further confirmed successful nanocomposite formation through O-H, C=O, C-O, and Ti-O/Zn-O functional groups and retention of the crystalline metal oxide phases. Optimum adsorption conditions were pH 6, contact time of 150 minutes and adsorbent dosage of 0.6 g/L. Under these conditions, phenol removal efficiency was 85.02% with an adsorption capacity of 6.57 mg/g, while resorcinol removal efficiency was 88.99% with an adsorption capacity of 5.35 mg/g. Freundlich isotherm modeling (R² = 0.989 for phenol and 0.994 for resorcinol) indicated heterogeneous multilayer adsorption, while the pseudo-second-order kinetic model suggested that chemisorption governed the adsorption process. The study contributes to existing knowledge by demonstrating the synergistic effect of green-synthesized metal oxide nanoparticles with activated agricultural residue to produce a sustainable and effective adsorbent for phenolic wastewater treatment.