Synthesis, characterization, and investigation of activities of metal oxides in the presence of different ionic liquids

The increasing challenge of water pollution, particularly from dye-laden wastewater produced by the textile industry, demands the development of efficient and sustainable treatment technologies. This thesis explores the synthesis and application of innovative metal oxide photocatalysts zinc oxide (ZnO) and bismuth oxide (Bi₂O₃) modified with various ionic liquids ([BMIM]-BF₄, [BMIM]-PF₆, and [BMIM]-Cl) for the photocatalytic degradation of methyl orange (MO) and methylene blue (MB) dyes. Comprehensive material characterization, including X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV-Vis) spectroscopy, and photoluminescence (PL) spectroscopy, demonstrated that ionic liquid modification significantly alters the structural, morphological, and optical properties of the catalysts. Photocatalytic degradation experiments were conducted under various light sources (UV-A, UV-B, UV-C, halogen, visible light, and direct sunlight) and across different pH conditions. The incorporation of [BMIM]-BF₄ notably reduced crystallite size (from 64 nm to 28 nm in ZnO and from 41 nm to 8 nm in Bi₂O₃), narrowed the band gap (from 3.25 eV to 2.50 eV for ZnO and from 2.97 eV to 2.20 eV for Bi₂O₃), and suppressed electron-hole recombination, as evidenced by PL spectroscopy. These modifications significantly enhanced photocatalytic performance, achieving 100% removal of both MO and MB (25 ppm) within 30 minutes under UV-B light at ambient pH (pH 7). The optimal photocatalysts, ZnO-[BMIM]-BF₄ and Bi₂O₃-[BMIM]-BF₄, exhibited reaction rate constants of 0.16 min⁻¹ and 0.392 min⁻¹, respectively. A kinetic analysis confirmed pseudo-first-order behavior, with reaction rates and efficiencies strongly influenced by pH, light source, and the ionic liquid used. This study highlights the potential of ionic liquid-modified metal oxides for effective and eco-friendly wastewater treatment, emphasizing the importance of further research into catalyst recovery, stability, and application to real industrial effluents.