Although progress has recently been made toward understanding the health and environmental consequences of these materials, challenges ramain for future research.

http://pubs.acs.org/doi/pdf/10.1021/es062726m

Assessing the risks of manufactured nanomaterials.

Composite Photocatalysts Nan Zhang,†,‡ Min-Quan Yang,†,‡ Siqi Liu,†,‡ Yugang Sun,* and Yi-Jun Xu*,†,‡ †State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University, Fuzhou 350002, P.R. China ‡College of Chemistry, New Campus, Fuzhou University, Fuzhou 350108, P.R. China Center for Nanoscale Materials, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States

Waltzing with the Versatile Platform of Graphene to Synthesize Composite Photocatalysts.

Concerns with the environmental and health risk of widely distributed, commonly used nanoparticles are increasing. Nanosize titanium dioxide (TiO2) is used in air and water remediation and in numerous products designed for direct human use and consumption. Its effectiveness in deactivating pollutants and killing microorganisms relates to photoactivation and the resulting free radical activity. This property, coupled with its multiple potential exposure routes, indicates that nanosize TiO2 could pose a risk to biological targets that are sensitive to oxidative stress damage (e.g., brain). In this study, brain microglia (BV2) were exposed to a physicochemically characterized (i.e., dispersion stability, particle size distribution, and zeta potential) nanomaterial, Degussa P25, and cellular expressions of reactive oxygen species were measured with fluorescent probes. P25's zeta potentials, measured in cell culture media and physiological buffer were -11.6 +/- 1.2 mV and -9.25 +/- 0.73 mV, respectively. P25 aggregation was rapid in both media and buffer with the hydrodynamic diameter of stable P25 aggregates ranging from 826 nm to 2368 nm depending on the concentration. The biological response of BV2 microglia to noncytotoxic (2.5-120 ppm) concentrations of P25 was a rapid (<5 min) and sustained (120 min) release of reactive oxygen species. The time course of this release suggested that P25 not only stimulated the immediate "oxidative burst" response in microglia but also interfered with mitochondrial energy production. Transmission electron microscopy indicated that small groups of nanosized particles and micron-sized aggregates were engulfed bythe microglia and sequestered as intracytoplasmic aggregates after 6 and 18 h exposure to P25 (2.5 ppm). Cell viability was maintained at all test concentrations (2.5-120 ppm) over the 18 h exposure period. These data indicate that mouse microglia respond to Degussa P25 with cellular and morphological expressions of free radical formation.

Titanium Dioxide (P25) Produces Reactive Oxygen Species in Immortalized Brain Microglia (BV2): Implications for Nanoparticle Neurotoxicity†

Toxicity and bioaccumulation of TiO2 nanoparticle aggregates in Daphnia magna.

A review on photocatalysis for air treatment: from catalyst development to reactor design

In a previous article, the modeling and experimental verification of the radiation field inside a reactor made of several TiO2 coated, parallel, flat glass fiber meshes, bilaterally UV irradiated was accomplished. The degradation of trichloroethylene (TCE) in an air stream is studied using different values of the pollutant feed concentration, relative humidity and light intensity under operating conditions where kinetic control of the process is established. A kinetic model based on a reaction scheme that involves atomic chlorine as an active reaction intermediate is developed for describing concentration dependencies. It includes, explicitly, the effect of the absorbed light intensity on the rate. The interaction of the existing radiation field with the solid semiconductor to generate electrons, and holes in the reaction catalyst activation step is also modeled. All kinetic parameters are estimated from experiments. The obtained kinetic expression gives a first-order dependence with respect to the TCE concentration and accounts for a competitive effect of water vapor and TCE for the catalyst active sites. An additional important feature of the derived expression is its ability to represent both limiting cases concerning the dependence of the reaction rate with the irradiation rate; that is, order 1 or order 0.5, as well as all possible intermediate values. In fact, the equivalent dependence obtained in this work was 0.6, a value closer to the second case. The results show good agreement between predictions derived from the proposed kinetic expression and TCE experimental concentration data at the reactor's exit. The proposed reactor design provides a practical device for the treatment of contaminated air; it permits a fairly uniform irradiation of the catalytic meshes and a good ratio of the irradiated surface area with respect to the volume of the gaseous reacting mixture. With these features, rather high TCE conversions can be obtained. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Air pollution remediation in a fixed bed photocatalytic reactor coated with TiO2

Fil: Esterkin, Carlos. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto de Desarrollo Tecnologico para la Industria Quimica. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnologico para la Industria Quimica; Argentina

Carlos Esterkin

Papers

Air pollution remediation in a fixed bed photocatalytic reactor coated with TiO2

Radiation field inside a reactor of glass-fiber meshes coated with TiO2