title: UV irradiation induced transformation of TiO2 nanoparticles in water: aggregation and photoreactivity.
abstract: Transformation of nanomaterials in aqueous environment has significant impact on their behavior in engineered application and natural system. In this paper, UV irradiation induced transformation of TiO2 nanoparticles in aqueous solutions was demonstrated, and its effect on the aggregation and photocatalytic reactivity of TiO2 was investigated. UV irradiation of a TiO2 nanoparticle suspension accelerated nanoparticle aggregation that was dependent on the irradiation duration. The aggregation rate increased from <0.001 nm/s before irradiation to 0.027 nm/s after 50 h irradiation, resulting in aggregates with a hydrodynamic diameter of 623 nm. The isoelectric point of the suspension was lowered from 7.0 to 6.4 after irradiation, indicating less positive charges on the surface. ATR-FTIR spectra displayed successive growth of surface hydroxyl groups with UV irradiation which might be responsible for the change of surface charge and aggregation rate. UV irradiation also changed the photocatalytic degradation rate of Rhodamine B by TiO2, which initially increased with irradiation time, then decreased. Based on the photoluminescence decay and photocurrent collection data, the change was attributed to the variation in interparticle charge transfer kinetics. These results highlight the importance of light irradiation on the transformation and reactivity of TiO2 nanomaterials.
authors.affiliation: State Key Laboratory of Environmental Chemistry and Eco-toxicology, Research Centre for Eco-environmental Sciences, Chinese Academy of Sciences , 18 Shuangqing Road, P.O. Box 2871, Beijing 100085, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Sun
authors.forename: Liang-Hong
authors.initials: LH
authors.lastname: Guo
authors.forename: Hui
authors.initials: H
authors.lastname: Zhang
authors.forename: Lixia
authors.initials: L
authors.lastname: Zhao
mesh_terms: D007700:Kinetics; D008027:Light; D053758:Nanoparticles / Q000737:chemistry*; D055668:Photochemical Processes; D012235:Rhodamines / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013535:Suspensions; D014025:Titanium / Q000737:chemistry* / Q000528:radiation effects; D014466:Ultraviolet Rays; D014867:Water; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D012235:Rhodamines; D013535:Suspensions; D014874:Water Pollutants, Chemical; D014867:Water; C009495:titanium dioxide; D014025:Titanium; C029773:rhodamine B