How I– alters UV and UV/VUV processes' redox capacities: Evidences from iodine species evolution, hydrogen peroxide formation, and oxyhalides degradation?
Although UV and/or VUV tandem I – are often proposed as advanced reduction processes (ARPs) to eliminate micropollutants by generating e aq – , the fate of I – and its byproducts formation remain to be explored. Therefore, this study investigated the iodine species evolution during UV/I – and UV/VUV/I – processes under different influencing factors. Results show that UV/VUV oxidized most of I – to IO 3 – whereas UV only oxidized a portion of I – to intermediate reactive iodine species (RISs, including I 2 , HOI, and I 3 – ); meanwhile, substantial H 2 O 2 was generated only in UV/VUV/I – process but not in UV/I – process, proving that UV/VUV owns stronger oxidation ability than UV alone. Spiking I – into water exerted triple-sided effects by consuming •OH, generating e aq – , and shielding light, thus complicating the systems. Holistically, increasing pH or decreasing dissolved oxygen converted oxidizing environment into reducing condition and caused less RISs formation, especially for UV/VUV/I – . For oxyhalides , neither UV/I – nor UV/VUV/I – degraded ClO 4 – . While UV/I – cannot remove ClO 3 – , UV/VUV/I – reduced ClO 3 – to Cl – . Expectedly, both UV/I – and UV/VUV/I – reduced BrO 3 – to Br – more efficiently than UV and UV/VUV, confirming that I – can enhance the reduction capacities of UV/VUV and UV technologies .
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