Effect of time and temperature on the synthesis of titanium dioxide applied in the photocatalytic degradation of methylene blue

Full text: Degradation of hazardous pollutants in water has been extensively studied, mainly heterogeneous photocatalysis in presence of TiO₂. Several techniques can be used to prepare advanced photocatalytic materials and the modified sol-gel method allows modulation of the oxides properties by controlling preparation variables such as temperature and calcination time, and even molar ratios between the metal precursor, chelating agent and polymerizer. In this way, the aim of this work was to synthesize TiO₂ particles using the Pechini method [1] and to study the influence of the synthesis variables: temperature (400, 450 and 500°C) and calcination time (4, 6 and 8 h) to the morphological and catalytic properties of the oxides formed. X-ray diffraction patterns of the samples showed characteristic peaks of the anatase and rutile phases, and for the materials calcined at 500°C (T1 and T2), the predominant formation of the rutile phase and increase of its proportion in the sample were observed, as indicated by the data obtained by Rietveld refinement. The photocatalytic activity of the TiO₂ particles against photodegradation of the methylene blue dye under UVC and Vis-IR light was evaluated according to the variables determined by the factorial design. Sample T1 (500°C/8h) was the most efficient under both UVC light with about 90% degradation and Vis-IR with 8 % removal after 90 minutes of irradiation. In contrast, T3 (400°C/8h) had the lowest degradation rate under UV and T5 (450°C/6h) under Vis-IR. The efficiency of the T1 sample can be attributed to higher crystallite diameters of the rutile phase and, consequently, the increase of the mobility of the electron pair with less recombination, even under Vis-IR radiation, due to the decrease of E_gap [2]. (author)