Effect of particle size on the photocatalytic activity of modified rutile sand (TiO ₂ )for the discoloration of methylene blue in water

The advanced oxidation process (AOP) has been identified as a promising technology for pollutant degradation. To maximize the performance of this process, new materials need to be found or existing materials need to be modified. In this work, the effect of the particle size of modified rutile materials on the photocatalytic discoloration of methylene blue was investigated. Rutile samples with different particle sizes were obtained by milling, and the photocatalytic reaction was carried out in a continuous magnetic stirring photoreactor under UV–vis illumination. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), laser diffraction for particle size distribution (PSD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), N2 adsorption (SBET) and total X-ray fluorescence (TXRF). The results showed an efficiency increase in the photocatalytic activity of the materials for the discoloration of methylene blue in water; the rutile hematite sand had an efficiency of 8%, while the sample that underwent the highest energy milling had an efficiency of 64%. The improved efficiency of the photocatalytic activity occurred as the particle size decreased and the optical band gap shifted from the visible to the UV region of the light spectrum. By eliminating the natural iron impurities (hematite, according to the DRS and XPS results) from the surface of the rutile particles through milling, enhanced behavior was achieved. This was explained because the smaller particle size promoted an increase in the surface area, leading to a higher number of active sites on the nanoparticle surface, which allowed an increase in the removal of water pollutants in the UV–vis range of the solar spectrum.