Anthill clay–supported TiO₂/Fe3O₄/ZnO nanocomposite for green remediation of petrochemical wastewater: simultaneous removal of COD, BOD, sulphate, and chloride

Abstract The design of sustainable multifunctional nanoadsorbents capable of addressing highly polluted petrochemical wastewaters is still a formidable environmental task. In this research, TiO₂/Fe₃O₄/ZnO ternary nanocomposites immobilized on anthill clay with different ratios of oxides (1:1:1, 1:2:1, 1:1:2 and 2:1:1) have been successfully prepared using a green impregnation technique in conjunction with Daniellia oliveri leaf extract and assessed for the adsorptive elimination of chemical oxygen demand (COD), biochemical oxygen demand (BOD), sulphate and chloride ions. The success of nanocomposite preparation was confirmed by structural analysis techniques that showed average hydrodynamic particle sizes within the range of 37.80 to 68.25 nm, while nitrogen adsorption studies revealed the mesoporous nature of the samples with BET surface areas between 190.81 and 264.42 m² g⁻¹; the 1:1:1 nanocomposite sample gave the highest BET surface area (264.42 m² g⁻¹) and pore volume (0.0248 cm³ g⁻¹). Successful immobilization of the nanoparticles TiO₂, Fe₃O₄ and ZnO onto the anthill clay was verified through XRD, FTIR, SEM, EDX and TGA techniques that gave excellent thermal stability below 5% weight loss above 500 °C. Batch adsorption studies gave very good efficiency for all the pollutants, with the nanocomposite having the highest ZnO content (1:1:2 ratio), giving removal efficiencies of 99.51%, 98.03% for COD, 93.95% for sulphate, and 96.62% for chloride at an adsorbent dosage of 0.40 g. Initial characteristics of petrochemical effluent included BOD of 56.30 mg L⁻¹, COD of 119.94 mg L⁻¹, sulphate of 297.65 mg L⁻¹, and chloride of 351.63 mg L⁻¹, which were above permissible limits. In the performance evaluation based on compositional variations, nanocomposites that were either balanced or rich in ZnO showed better pore accessibility and adsorption efficiency than those with more Fe₃O₄. Adsorption kinetics were best modeled using the pseudo-second-order kinetic model, which indicates that chemisorption is the prevalent mode of adsorption. This study reveals that the use of TiO₂/Fe₃O₄/ZnO nanocomposites derived from anthill clay is a safe, cost-effective, and efficient solution to petrochemical wastewater treatment problems.