PHOTOCATALYTIC DEGRADATION OF METHYLENE BLUE OVER POLYDOPAMINE-AG/TIO2

Abstract

This research investigated the effect of silver and polydopamine (PDA) doping on TiO2 catalysts for the photocatalytic degradation of methylene blue in aqueous phase. Titanium dioxide was synthesized via a sol-gel method and was calcined at 400 °C for two hours. Silver was loaded onto TiO2 by an incipient wetness impregnation method. The amount of Ag was varied from 0.5%wt to 3%wt. Then polydopamine-Ag/TiO2 catalyst was prepared by an impregnation method, using dopamine as a precursor. The amounts of polydopamine were 5%wt and 10%wt. All catalysts were characterized by N2 physisorption, ICP-OES, XRD, FTIR, CO chemisorption, Photoluminescence, and UV-Visible spectrophotometry. The photocatalytic degradation of methylene blue in aqueous phase was conducted under either UV or visible light irradiation. In each experiment the catalyst was dispersed in an aqueous solution of 10 ppm methylene blue. The suspension was stirred in the absence of light for one hour and was then irradiated by either one UV or visible light bulb for a period of two hours. The concentration of methylene blue was measured by a UV-Visible spectrophotometer. Addition of both Ag and polydopamine to TiO2 photocatalyst improved the performance in methylene blue photodegradation under both UV and visible light irradiations. The highest conversion of methylene blue (87.54% under UV irradiation and 78.98% under visible irradiation) was obtained by 10%PDA-2%Ag/TiO2. Addition of Ag improved trapping of electrons and polydopamine transfered electrons to prevent the recombination of photogenerated charge carriers. Moreover, the band gap was narrower and the light absorption in the visible region was enhanced, leading to more photogeneration of electrons and holes.