BiOBr samples with different facets were prepared and used for photocatalytic reduction of hexavalent chromium under visible light.The results reveal that BiOBr dominated with {110} facets giving a specific rate constant 3 times as high as BiOBr with {001} facets, and its much stronger internal electric field was believed to be the main reason.Hexavalent chromium Cr(VI) is one of the forms of chromium that poses a health risk to humans because of its high acute toxicity and carcinogenic activity. Trivalent chromium Cr(III) is much less toxic and could be easily removed from wastewater as a solid by alkalinication and precipitation. Thus, developing effective technologies capable of reducing Cr(VI) to Cr(III) is of great importance for the treatment of wastewater. Visible light driven photocatalytic reduction as a promising method to achieve this purpose has attracted extensive attention worldwide. 1 Bismuth oxybromide BiOBr has proven itself as a kind of novel visible-light photocatalyst because the separation of photoinduced electrons and holes could be promoted by its internal static electric elds between the positive [Bi 2 O 2 ] slabs and the anionic bromine layers. 2 Li synthesized 3D owerlike BiOBr nanostructures with an excellent removal capacity and fast adsorption rate for Cr(VI). 3 Lin obtained BiOBr nanocrystals with {001} and {010} dominant facets by hydrothermal method for degrading 2,4-dichlorophenol under UV light. 4 Zhang prepared nanosheets dominated with {102} as well as with {001} facets and compared their catalytic performance for the degradation of rhodamine B (RhB) under visible light irradiation. 5 Chen reported ultrathin BiOBr nanosheets with the {001} facet percentage of 98% showing higher photocatalytic activity than BiOBr nanoplates (63% {001}). 6 In this work, the facetdependent photocatalytic activities of BiOBr with {001} and {110} dominant facets are systematically evaluated in the reduction of Cr(VI) ions under visible-light.All of the chemical reagents were of analytical grade and used without further purication. BiOBr with {001} facets, named as BOB-001, was obtained by a hydrolysis process at 90 C for 3 h using deionized water and ethanol (the volume ratio of 3 : 4) as the reaction media. 7 BiOBr dominated by the {110} facets was synthesized by treating the Bi(NO 3 ) 3 -KBr-PVPethylene glycol system at 120 C for 12 h, named as BOB-110. 8 The photocatalytic performance of as-prepared samples was evaluated by the reduction of Cr(VI) under visible-light irradiation at room temperature. Typically, 40 mg of BiOBr was suspended in 40 mL of 20 mg L À1 Cr(VI) solution, and the pH value was regulated to 3.0 by a dilute H 2 SO 4 solution; aer being kept in the dark for 30 min to reach the adsorption-desorption balance, the suspension with 0.5 vol% formic acid was irradiated with white 18 W-LEDs; a portion of reaction solutions, withdrawn every 10 min, was centrifuged and analyzed by 1,5-diphenylcarbazide method on a spectrophotometer (Tianjin UV-752B).The SEM images in Fig. 1 clearly...

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Bi2WO6 samples with different morphologies were hydrothermally synthesized and applied to the photoreduction of hexavalent chromium under visible-light irradiation. It was found that nanosheets with high exposure of {100} facets and crystallinity exhibited the best photocatalytic performance: two times as active as nanoparticles based on specific rate constant.

Rod-shaped rutile TiO2 nanocrystals with various aspect ratios were prepared by a two-step wet-chemical method, and their photocatalytic performance for the reduction of uranyl ions under UV irradiation was investigated. Results show that there is an obvious difference between their specific activities based on equal surface area; rutile TiO2 nanorods with a moderate aspect ratio exhibited the best activity. Different occupation of {111} and {110} facets and a synergistic effect between them are proposed to explain the activity order.

Ionic liquid ([Bmim]OH, [Bmim]Br, [Bmim]BF4) modified TiO2 catalysts were prepared by hydrothrmal method. XRD and UV-visible spectra were used to characterize the prepared composite materials. Ionic liquid modification did not change the crystalline structure of TiO2 particles but reduced the particle size. [Bmim]OH modified TiO2 shows the obviously enhanced visible light absorption. The influence of ionic liquid types, modification amount, reactant concentration and pH value on the photocatalytic activity of TiO2 catalyst under visible light were investigated.