Facet-dependent performance of BiOBr for photocatalytic reduction of Cr(vi)

Abstract

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...

Recent bioreduction of hexavalent chromium in wastewater treatment: A review

“…Recent developments in the understanding of the conventional process emphasize various methods such as thermal treatment [27], desalination [28], direct reduction [29,30], resin adsorption [31,32,214,217], electrolysis [33,34], electrocoagulation [35,36], activated carbon adsorption [212,213], composite ceramic adsorption [37,215,218], carbon nano fibers adsorption [211,216], nano materials catalyzed reduction [38,39], and catalytic reduction [40,41]. The conventional processes are complex due to the different intensive sub-processes and use of large amounts of chemicals and generation of toxic sludges.…”

The synthesis of a BiOClxBr1−x nanostructure photocatalyst with high surface area for the enhanced visible-light photocatalytic reduction of Cr(vi)

“…11 However, the efficiency of solar energy conversion is limited by its large band gap (3.2 eV). [12][13][14] To resolve this issue, many visible-light active photocatalysts, including BiOBr, 15 UiO-66-NH 2 , 5 NH 2 -MIIL-125(Ti), 16 MIL-88(B)-NH 2 , 17 ZIF-67, 18 and BiVO 4 , 19 have been well reported; however, their poor photocatalytic activities and slow photocatalytic reduction rates do not meet the required standards for large scale water treatments. 20 Therefore, the development of highly effective and stable visible light dynamic photocatalysts for the reduction of Cr(VI) is immediately needed.…”

Oxygen Vacancy Enhanced Photoreduction Cr(VI) on Few-Layers BiOBr Nanosheets

“…Compared with the above procedures, the photocatalytic reduction has been considered as a low-cost technique with the merits of the low energy consumption and non-secondary pollution [43]. BiOX(X = Cl, Br, I) photocatalysts have been the comprehensive application in the degradation of organic dyes and pollutants, and recently, it is proved that BiOX photocatalysts also display great potential to the photoreduction of Cr(VI) ions [44][45][46][47][48][49][50][51][52]. However, these obtained BiOX materials have poor ability to photoreduce Cr(VI) ions.…”