Abstract
Iodide ( I − ) could promote ultraviolet-activated S(IV) processes (UV/S(IV)) and degrade aqueous halogenated organic compounds and hazardous oxoanions. With the interest of promoting use of this technology, this study investigated the feasibility of using bismuth oxyiodide (BiOI) as an I − source to enhance UV/S(IV) where monochloroacetic acid (MCAA) was selected as a testing model compound. Degradation of MCAA by UV/S(IV) increased by 50% in presence of BiOI. Results of competitive kinetics indicated that the promotion effect brought by BiOI mainly originated from its sustainable release of I − , and subsequent enhanced generation of hydrated electrons. Electron spin resonance detection and fluorescence characterization proved increased formation of sulfite radical, resulting from sulfite oxidation by UV-excited BiOI. However, the sulfite radical only made a small contribution (9%) to MCAA degradation due to its moderate reactivity toward MCAA (4.2 × 105 M−1·s−1). UV/S(IV) combined with BiOI significantly decreasing the biotoxicity of MCAA solution. BiOI can be regenerated using I − -containing solution. Our findings provide evidence that BiOI is a promising I − source and photocatalyst, which progresses the I − -assisted UV/S(IV) process towards practical application.
Highlights
Efficient degradation of some halogenated organic compounds (HOCs) and hazardous oxoanions was achieved through UV-activatedsulfite (S(IV)) reduction (abbreviated as UV/S(IV)) [1,2,3], which is classified as a hydrated electron (e−aq )-based advanced reduction process −(eaq -ARP)
This study examined the promotion effect of bismuth oxyiodide (BiOI) on the UV/S(IV) process using monochloroacetic acid (MCAA) as model compound
The results of this research indicated that the presence of BiOI can greatly increase MCAA
Summary
Efficient degradation of some halogenated organic compounds (HOCs) and hazardous oxoanions was achieved through UV-activated (bi)sulfite (S(IV)) reduction (abbreviated as UV/S(IV)) [1,2,3], which is classified as a hydrated electron (e−aq )-based advanced reduction process −(eaq -ARP). Efficient degradation of some halogenated organic compounds (HOCs) and hazardous oxoanions was achieved through UV-activated (bi)sulfite (S(IV)) reduction (abbreviated as UV/S(IV)) [1,2,3], which is classified as a hydrated electron Aq ), UV photon absorbance by S(IV) dominates the production efficiency of e−. For this reduction process [4]. The aq UV sources currently used in water treatment are the low-pressure mercury lamp (UV-L) and medium-pressure mercury lamp (UV-M). Aq and a low energy utilization rate are expected when UV-L and UV-M are used to activate S(IV) due to its relatively low absorptivity at wavelength >250 nm (Figure 1). High S(IV) dosage, high pH (to decrease the proportion of bisulfite), and high power of UV lamp are usually needed to increase e−
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