The inevitable occurrence of Br– in natural water affects the degradation kinetics of micropollutants in the UV/chlorine process, the radical chemistry of which, however, is largely unclear. As Br– in the UV/chlorine process first forms free bromine (HOBr/OBr–), this study investigated the radical chemistry of the UV/bromine process for the degradation of selected micropollutants resistant to bromine, i.e., ibuprofen and benzoate, to focus on the roles of radicals. The actual quantum yields of HOBr and OBr– by UV photolysis at 254 nm are 0.43 (±0.025) and 0.26 (±0.025) mol Einstein–1, respectively. Br• and HO• are generated first, and then, Br2 •– is formed, with the signal detectable at 360 nm by laser flash photolysis. Compared with Cl• in the UV/chlorine system, Br• exists at higher concentrations (∼10–12 M) in the UV/bromine system while HO• exists at similar concentrations. In the UV/bromine process, reactive bromine species (RBS) dominates the degradation of ibuprofen, while HO• dominates the degradation of benzoate. Br• and Br2 •– are reactive toward ibuprofen which second-order rate constants (k) were determined to be 2.2 × 109 and 5.3 × 107 M–1 s–1, respectively, by laser flash photolysis. Br• was the major RBS for ibuprofen degradation by the UV/bromine treatment, whereas Br2 •– increasingly contributed to ibuprofen degradation with increasing free bromine or Br– concentrations. Br• could be scavenged by HCO3 – and natural organic matter (NOM), and the k with NOM was determined to be 2.6 × 104 (mg/L)−1 s–1. Both Br• and Br2 •– prefer to react with ibuprofen via electron transfer with activation energy barriers (Δ‡ G 0 SET) of 1.35 and 7.78 kcal mol–1, respectively. RBS promoted the formation of hydroxylated products. Then free bromine, rather than RBS, was responsible for the formation of brominated products, increasing the total organic bromine (TOBr) and tribromomethane yields in the UV/bromine system. This study demonstrates for the first time the roles of RBS and HO• in micropollutant degradation in the UV/bromine process.

Photocatalytic materials are pivotal for the implementation of disruptive clean energy applications such as conversion of H2O and CO2 into fuels and chemicals driven by solar energy. However, efficient and cost-effective materials able to catalyze the chemical reactions of interest when exposed to visible light are scarce due to the stringent electronic conditions that they must satisfy. Chemical and nanostructuring approaches are capable of improving the catalytic performance of known photoactive compounds however the complexity of the synthesized nanomaterials and sophistication of the employed methods make systematic design of photocatalysts difficult. Here, we show by means of first-principles simulation methods that application of biaxial stress, η, on semiconductor oxide thin films can modify their optoelectronic and catalytic properties in a significant and predictable manner. In particular, we show that upon moderate tensile strains CeO2 and TiO2 thin films become suitable materials for photocatalytic conversion of H2O into H2 and CO2 into CH4 under sunlight. The band gap shifts induced by η are reproduced qualitatively by a simple analytical model that depends only on structural and dielectric susceptibility changes. Thus, epitaxial strain represents a promising route for methodical screening and rational design of photocatalytic materials.

Ceria (CeO2) nanorods have been prepared by simple short-term precipitation at room temperature for the first time.

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