Effects of TiO 2 coating dosage and operational parameters on a TiO 2/Ag photocatalysis system for decolorizing Procion red MX-5B

Abstract

In this study, titanium dioxide (TiO 2) powder was coated onto the surface of a dendritic silver (Ag) carrier to synthesize TiO 2/Ag for decolorizing Procion red MX-5B (MX-5B), and related operation factors were also studied. The results showed that even without ultraviolet-A (UVA) irradiation, the Ag carrier from the TiO 2/Ag catalyst had oxidizing ability, which could effectively degrade MX-5B color, but TiO 2 was ineffective. In addition, TiO 2 from TiO 2/Ag demonstrated photocatalysis performance when irradiated, and the Ag carrier further showed an electron-scavenging ability to mitigate electron–hole pair recombination, which can improve the photocatalytic efficacy. With the oxidization and electron-scavenging ability of Ag and the photocatalysis ability of TiO 2, TiO 2/Ag can decolor MX-5B more efficiently than TiO 2. The heavier Ag carrier also improves the solid–liquid separation of nano-TiO 2, making TiO 2/Ag more suitable for application in slurry systems of photocatalytic water treatment. When the TiO 2/Ag coating ratio was 50% by weight, there was a sufficient amount of TiO 2 on Ag's surface with a good distribution, and it exhibited a good photocatalysis decolorizing effect. In a study of how operational factors impact the decolorizing of MX-5B in the TiO 2/Ag photocatalysis system with UVA irradiation (UVA-TiO 2/Ag), the decolorization efficiency was optimal when the solution was maintained at pH 6.35. The addition of 0.01 M hydrogen peroxide (H 2O 2) aided the photocatalysis decolorization efficiency, although excessive H 2O 2 reacted with hydroxyl free radicals and decreased the active groups in the system, thereby reducing the photocatalysis activity. An operating temperature of 40 °C was conducive to MX-5B decolorization, which was better than operating at room temperature.