Enhanced photocatalytic degradation of methylene blue dye using TiO₂ nanoparticles obtained via chemical and green synthesis: a comparative analysis

Abstract The study compares TiO 2 NPs synthesized via conventional chemical methods using Titanium Tetra Isopropoxide (TTIP) precursor versus an eco-friendly green synthesis approach using Moringa oleifera seed (MOS) extracts. Two standard fabrication routes-sol-gel and hydrothermal were employed for both chemical synthesis (CS) and green synthesis (GS) processes. The as-formed TiO 2 nanoparticles from all four synthesis conditions (CS-sol gel, CS-hydrothermal, GS-sol gel, GS-hydrothermal) exhibited a spherical shape and pure rutile crystal structure with slight variations in mean diameter based on the synthesis technique. Optical absorptions showed bandgap energies ranging from 3.14–3.28 eV and 2.24–2.59 eV for CS- and GS-TiO 2 systems respectively. The lower bandgap energy of green synthesized TiO 2 suggests higher visible light absorption, confirmed through diffuse reflectance spectroscopy where GS-TiO 2 NPs had higher base absorbance levels. The synthesized TiO 2 NPs were employed as catalysts for methylene blue (MB) dye degradation under UV and sunlight irradiation. Intriguingly, the results indicated that the degradation of MB dye under sunlight irradiation demonstrated superior efficiency compared to UV irradiation. In conclusion, the green-synthesized TiO 2 NPs showcased excellent optical properties and demonstrated enhanced photocatalytic performance in the degradation of MB dye, with an efficiency approaching 64 %.