Effect of Ag and Mn doping for methylene blue photodegradation performance

Currently, wastewater management is ineffective, operationally expensive, and difficult to be implemented in Indonesia. The photocatalyst is a technology that may answer this problem. Titania (TiO2) is a high-activity, inexpensive, stable, and non-toxic photocatalyst material. However, TiO2 has large band-gap energy and rapid recombination. In this research, TiO2 was doped by Ag (a noble metal) and Mn (a transition metal) to compare the performance of photocatalysts in organic pollutant degradation, using methylene blue. Ag/TiO2 catalyst was synthesized by Photo Assisted Deposition (PAD) method, while Mn/TiO2 was synthesized by impregnation method. The physicochemical properties of both catalysts were assessed by SEM-EDX and UV-Vis DRS. SEM-EDX indicated that both methods successfully doped Ag and Mn into TiO2. Besides, UV-Vis DRS confirmed the presence of metal dopants that caused the narrowing of the bandgap. Ag/TiO2 catalyst increased the degradation of methylene blue by up to 97% in 30 minutes. Meanwhile, the Mn/TiO2 catalyst inhibited the degradation of methylene blue. The increased activity by Ag dopants is due to the Localized Electromagnetic Field (LEMF) and Schottky barrier phenomena which increase charge separation. Meanwhile, decreased activity by Mn dopants is due to the shading effect and Mn electronic structure that can facilitate recombination at high loading. Ag/TiO2 catalyst also improved photodegradation performance of TiO2 when irradiated by visible light.