Effect of particle size on the photocatalytic activity of modified rutile sand (TiO2) for the discoloration of methylene blue in water

Abstract

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 bemodified. In this work, the effect of the particle size of modified rutile materials on the photocatalytic discolorationof methylene blue was investigated. Rutile samples with different particle sizes were obtained bymilling, and the photocatalytic reaction was carried out in a continuous magnetic stirring photoreactor underUV–vis illumination. The samples were characterized by X-ray diffraction (XRD), field emission scanning electronmicroscopy (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). Theresults showed an efficiency increase in the photocatalytic activity of the materials for the discoloration ofmethylene blue in water; the rutile hematite sand had an efficiency of 8%, while the sample that underwent thehighest energy milling had an efficiency of 64%. The improved efficiency of the photocatalytic activity occurredas the particle size decreased and the optical band gap shifted from the visible to the UV region of the lightspectrum. By eliminating the natural iron impurities (hematite, according to the DRS and XPS results) from thesurface of the rutile particles through milling, enhanced behavior was achieved. This was explained because thesmaller particle size promoted an increase in the surface area, leading to a higher number of active sites on thenanoparticle surface, which allowed an increase in the removal of water pollutants in the UV–vis range of thesolar spectrum.