Tunable auto-combustion preparation of TiO2 nanostructures as efficient adsorbents for the removal of an anionic textile dye

Abstract

We have developed a new route for the synthesis of pure TiO₂ nanostructures via a facile auto-combustion method followed by heat treatment. We have tuned the produced phases, morphologies, and crystallite sizes of the nano-sized TiO₂ products through an auto-combustion method employing different fuels and various fuel-to-oxidant equivalence ratios, Φ_c. The as-synthesized products were analyzed by means of FE-SEM, FT-IR, XRD, TEM, BET, and thermal analyses. Interestingly, urea fuel at Φ_c = 1 generated a pure anatase TiO₂ phase (U1) having almost the smallest crystallite size (11.9 nm) and the highest adsorption capacity (135 mg g⁻¹) for the removal of Reactive Red 195 (RR195) dye from aqueous solutions. Moreover, the adsorption data could be described well using the pseudo-second-order kinetic and Langmuir isotherm models. Based on the calculated thermodynamic parameters: ΔH⁰ (1.343 kJ mol⁻¹), ΔG⁰ (from −4.630 to −5.031 kJ mol⁻¹), and E_a (18.46 kJ mol⁻¹), the adsorption of RR195 dye on the as-prepared TiO₂ nano-adsorbent is an endothermic, spontaneous, and physisorption process, respectively. Moreover, the as-prepared TiO₂ adsorbent is a promising candidate for the removal of RR195 textile dye from aqueous media based on its reusability, high stability, and high adsorption capacity.