Enhanced photocatalytic reduction of concentrated bromate in the presence of alcohols

• TiO2 + UV + alcohol is used as a more efficient photocatalytic method to reduce bromate.
• Alcohols act as sacrificial reagents to scavenge holes from the valence band.
• TiO2 + UV + alcohol is remarkably more efficient than TiO2 + UV for reducing bromate.
• Effects of alcohol species and fraction, temperature, pH, anions were examined.
• TiO2 + UV + alcohol is re-used many times to reduce bromate without refilling alcohol.

Membrane separation of bromate can continuously treat bromate-containing water; however concentrated bromate solutions would be an inevitable waste which requires proper treatments before discharge. In addition to hydrogenation of bromate using transitional metallic catalysts and hydrogen gas, chemical reduction of bromate can be also achieved by photo-catalysis. While chemically-doped photocatalysts are extensively studied to improve photocatalytic reduction of bromate, another strategy for enhancing photocatalytic efficiency of bromate reduction by adding hole-scavengers (e.g., alcohols) has not been investigated. Thus, in this study, we aim to evaluate photocatalytic reduction of bromate in the presence of alcohols. As TiO2 + UV was selected as a model photocatalytical process, TiO2 + UV + alcohol exhibited remarkably higher reduction efficiency and faster reduction kinetics than TiO2 + UV, possibly owing to suppressed recombination of electron-hole pair as alcohols act sacrificial reagents. A higher fraction of methanol (MeOH) also increased the reduction kinetics. The elevated temperature improved the reduction kinetics, whereas lowering pH of bromate solution substantially accelerated bromate reduction. TiO2 + UV + MeOH remained effective to reduce bromate in the presence of other anions; it exhibited a significantly high selectivity toward the bromate reduction over the nitrate reduction. TiO2 + UV + MeOH can be re-used for multiple cycles without loss of conversion efficiency even though no MeOH was refilled and bromide was accumulated within the reactor. These features reveal that TiO2 + UV + MeOH is a highly effective and promising approach to treat concentrated bromate in water.

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