Fast and complete degradation of Congo red under visible light with Er3+ and Nd3+ ions doped TiO2 nanocomposites

We report fast and complete destruction of the\ud dye Congo red (CR) under visible light in the\ud presence of Nd3+ and Er3+ doped TiO2 nanocomposites\ud (NCs). TiO2 NCs with general composition\ud TiO2[R2O3]x, {x=0.1, 0.2; R≡ Nd, Er} and\ud particle size 12-16 nm were synthesized through\ud co-precipitation/hydrolysis (CPH). A set of similar\ud composites was also prepared through solid\ud state reaction (SSR) route, which produced 31-\ud 47 nm particles. After characterization, visible\ud light photocatalytic activity of all the samples\ud was recorded for the degradation of CR. NCs\ud with molar concentration x=0.2 of both doping\ud types produced close to 100% degradation in 180\ud min. The apparent rate constant (kobs) was found\ud to be 2.91×10–2 min–1 and 2.36×10–2 min–1, for\ud these Nd3+ and Er3+ doped NCs, respectively. The\ud other NCs with x=0.1, also showed significant\ud degradation of CR, but the samples prepared\ud through SSR performed worse. The excellent\ud degradation obtained with the NCs may be\ud attributed to their small particle size. Moreover,\ud the doping of Nd3+ and Er3+ ions further supported\ud the photocatalysis through formation of intermediate\ud energy levels within the band gap of\ud TiO2. These new levels not only acted as electron\ud traps for efficient suppression of the undesired\ud e–/h+ recombination, but also facilitated to a certain\ud extent the absorption of visible irradiation