Transparent TiO2 sol nanocrystallites mediated homogeneous-like photocatalytic reaction and hydrosol recycling process

Lanthanide metal europium ion modified titanium dioxide (Eu3+-TiO2) sol nanocrystallites was fabricated by the wet-chemical coprecipitation-peptization method under low temperature (80°C). Eu3+-TiO2 sol particles show the anatase-rutile mixed crystal structure and the narrow particles distribution with the mean size of 6 nm. Comparing with pure TiO2 sol, Eu3+-TiO2 sol possesses smaller primary particle size and better particulate dispersion. Transparent sol catalyst could conduct the homogeneous-like photocatalysis rather than heterogeneous one for organic pollutants degradation reaction. This crystallized Eu3+-TiO2 sol particles exhibits better interfacial adsorption effect and electron-transfer efficiency between dye molecules and catalyst particles, which contributed to stronger photocurrent response in the photoelectrochemical process. For photocatalytic degradation of azo dye, fresh Eu3+-TiO2 sol catalyst showed higher photocatalytic activity and photomineralization capability than P25 TiO2 powder and pure TiO2 sol under either ultraviolet light (UV) or visible light (Vis) irradiation. The recycling application of the crystallized sol catalysts was well attempted by taking advantage of its sensitivity to the medium pH value. Although Eu3+-TiO2 recycle sol had better dispersion effect and smaller secondary particles size, the absolute recovery efficiency of Eu3+-TiO2 sol particles was obvious inferior to TiO2 sol due to its poor flocculation-separation effect. For continuous recycle use of hydrosol photocatalysis, pure TiO2 sol demonstrates the better total discolouration efficiency than Eu3+-TiO2 sol although instinctive photochemical reactivity of fresh TiO2 was inferior to fresh Eu3+-TiO2.