Efficient and rapid degradation of Congo red dye with TiO2 based nano-photocatalysts

Abstract

Degradation of Congo red (CR) dye with TiO2 based nano-photocatalyst (NPC) loaded with Nd3+ and Er3+ ions is reported. The chemical route of synthesis through co-precipitation/hydrolysis (CPH) was employed to produce NPCs with general composition TiO2[R2O3]x, {x = 0.1, 0.2; R □ Nd, Er} and particle size within 12 − 16 nm. Photocatalytic degradation under visible light was measured in terms of the percent degradation of CR in 180 min , time taken to degrade to half of the initial CR concentration (t1/2) and apparent rate constant (kobs). For both doping types, values of close to 100% were obtained with x = 0.2 NPCs, indicating complete removal of the dye. For the same NPCs, very high values of kobs were found; 2.91 × 10−2 min−1 and 2.36 × 10−2 min−1, for Nd3+ and Er3+ loaded NPCs, respectively, suggesting very rapid degradation. Other NPCs with x = 0.1, also showed reasonably good and fast degradation of CR. The observations may be attributed to the small particle size of the NPCs. Moreover, from the DRS results it is observed that the addition of Nd3+ and Er3+ ions apparently introduces intermediate energy levels within the band gap of TiO2. Such new levels seem to support photocatalysis because they act as electron traps leading to effective suppression of the undesired e−/h+ recombination. To some meaningful extent they also facilitate the absorption of visible irradiations required in the process.