Significant enhancement of bromate removal in drinking water: Implications for the mechanism of sonocatalytic reduction

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>Bromate (BrO<SUB>3</SUB> <SUP>−</SUP>) is a potential carcinogenic compound that can form during the disinfection of drinking water. For the first time, the sonocatalytic reduction of BrO<SUB>3</SUB> <SUP>−</SUP> were studied through examining the effect of the important operational parameters such as ultrasound (US) frequency, TiO<SUB>2</SUB> loading, pH, temperature and other anions. By observing sonoluminescence (SL) at various frequencies and measuring H<SUB>2</SUB> production rates, a new reduction mechanism for BrO<SUB>3</SUB> <SUP>−</SUP> is also proposed. The kinetic results presented that the BrO<SUB>3</SUB> <SUP>−</SUP> reduction rates enlarged as the measured H<SUB>2</SUB> production rate increased for all parameters, and the slopes between the BrO<SUB>3</SUB> <SUP>−</SUP> reduction and H<SUB>2</SUB> production rates for sonocatalysis were much higher than those for sonolysis. Interestingly, sonolysis could be limited by the amount of H<SUB>2</SUB> production, but sonocatalysis could increase the BrO<SUB>3</SUB> <SUP>−</SUP> reduction rate because of additional electrons (e<SUP>−</SUP>) from the surface of TiO<SUB>2</SUB> via SL. The highest SL intensities for H<SUB>2</SUB> production and BrO<SUB>3</SUB> <SUP>−</SUP> reduction rates occurred at an ultrasound frequency of 500kHz, implying that an increase in SL intensity caused by ultrasound cavitation enhanced H<SUB>2</SUB> production and increased the e<SUP>-</SUP> released to the conduction band of TiO<SUB>2</SUB>. At 500kHz, BrO<SUB>3</SUB> <SUP>−</SUP> reduction rate (6.84×10<SUP>−2</SUP> min<SUP>−1</SUP>) by sonophotocatalysis was 5.2 times higher than that (1.32×10<SUP>−2</SUP> min<SUP>−1</SUP>) of sonolysis. Investigation into the effect of anion species showed that BrO<SUB>3</SUB> <SUP>−</SUP> reduction was inhibited or enhanced depending on the type of anions present. In real application, sonocatalytic reduction of BrO<SUB>3</SUB> <SUP>−</SUP> could be advantageous, as it has higher reduction rates than those reported for photocatalysis.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sonocatalytic BrO<SUB>3</SUB> <SUP>−</SUP> reduction was studied at various parameters and H<SUB>2</SUB> production. </LI> <LI> A new reduction mechanism is proposed by interpreting experimental results. </LI> <LI> Sonocatalytic reduction rates of BrO<SUB>3</SUB> <SUP>−</SUP> is much higher than sonolysis or photocatalysis. </LI> <LI> Other anions do not affect the sonocatalytic removal of BrO<SUB>3</SUB> <SUP>−</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>