Synthesis, optimisation, and characterisation of rutile titanium dioxide (TiO₂) using Parkia biglobosa leaf extract for adsorptive treatment of mine site wastewater

A sustainable green synthesis route was developed for fabricating super-fine rutile-phase titanium dioxide (TiO₂) nanoparticles for the adsorptive treatment of mine site wastewater. Among six plants tested, aqueous extracts of Parkia biglobosa leaves served as biogenic reducing and stabilising agents. Using a factorial experimental design, synthesis parameters (precursor volume, extract dosage, stirring speed) were optimised to selectively form single-phase rutile TiO₂. X-ray diffraction confirmed an exclusive rutile phase with an exceptionally small average crystallite size of approximately 3.49 ± 0.15 nm at 200 rpm and 1:1 precursor: extract ratio, as one of the smallest rutile TiO₂ sizes reported via green synthesis. FTIR confirmed phytochemical functional groups involved in stabilisation. Electron microscopy revealed polydisperse, loosely packed nanoparticles with mesoporous morphology, while UV–vis showed an absorption edge at ∼358 nm. XPS confirmed Ti⁴⁺ oxidation state. Model validation gave a statistically significant result (p < 0.05) with a low prediction error of 0.86% . Batch adsorption on real mine wastewater achieved high efficiencies: 92.4% (Mn²⁺), 96.7% (Fe³⁺), 90.8% (Cu²⁺), and 88.5% (Pb²⁺) , showing strong affinity for divalent and trivalent metal ions. After five regeneration cycles, the material retained > 50% of its initial adsorption capacity for Mn²⁺, Fe³⁺, and Cu²⁺. This work establishes Parkia biglobosa as a novel biogenic agent for rutile-phase direction and size control, enabling cost-effective, eco-friendly TiO₂ nanomaterials for sustainable wastewater treatment.