Synthesis Of Black Titanium Dioxide And Effect Of Calcination Conditions And Reducing Agent On Photocatalytic Degradation Of Methyl Orange

Abstract

This research studied the synthesis and application of black titanium dioxide in the photocatalytic degradation of methyl orange (MO). First, titanium dioxide was prepared via a sol-gel method. Then sodium borohydride was used as the reducing agent in order to synthesize black titanium dioxide. Thus, a 2x2x3 factorial experimental design was employed to assess the significance of the following three factors: (A) calcination temperature (400 and 500 °C); (B) calcination time (5 and 10 h); and (C) the molar ratio of NaBH4 to TiO2 used (0:1, 0.5:1, and 1:1). The removal of MO under UV and visible light were the responses for the analysis of variance. Prior to the photocatalytic experiment, the catalyst was stirred in the dark for one hour before irradiation by either UV or visible light bulbs for three hours. The concentration of MO was measured by UV-Vis spectrophotometer. The highest conversion of MO (82.17% under UV irradiation and 71.92% under visible irradiation) was obtained by black titanium dioxide that was calcined at 500 °C, 10 h, molar ratio of NaBH4 to TiO2 of 1:1. The catalyst contained the largest amount of surface defect, which trapped photoexcited electrons on the surface and prevent the recombination of electrons and holes. Moreover, the band gap of black TiO2 was narrower and the light absorption in the visible region was enhanced, leading to more photogeneration of charge carriers. From statistical analysis, three main effects and their interactions between factors A and C and factors B and C in the synthesis of white and black TiO2 catalysts were significant for both photocatalytic degradation of MO under UV and visible light.