Development of a free radical-based kinetics model for the oxidative degradation of chlorazol black in aqueous solution using periodate photoactivated process

This paper presents the first modeling study on UV/periodate (IO4-) advanced oxidation process. A reaction mechanism consisting in 45 chemical reactions including a number of radicals (IO3 center dot, IO4 center dot, (OH)-O-center dot, O center dot-, HO2 center dot, O-2(center dot-), O-3(center dot-)) and non-radical intermediates/products (O(P-3), O-3, IO3-, H2O2, HO2-,I2O6 and I2O8) has been developed to assess the reactive species generation, use and distribution during the oxidation of one model azo dye, chlorazol black (CB), by the periodate photoactivated process. The model fitted excellently the CB degradation data over a wide range of solution pH and initial IO4- concentration. Unavailable second-order rate constants of several important reactions were optimized using the genetic algorithm. Those include O-3 + IO3 center dot -> IO4 center dot + O-2 (k =1 x 10(8) M(-1)s(-1)), 2IO(4)(center dot) -> I2O8 (k = 4.68 x 10(8) M(-1)s(-1)), reaction of CB with (OH)-O-center dot (k = 1 x 10(9) M(-1)s(-1)), IO3 center dot (k = 2.63 x 10(8) M(-1)s(-1)), IO4 center dot (k = 0 M(-1)s(-1)), O((3) P) (k = 0 M(-1)s(-1)) and O-3 (k = 0.574 M(-1)s(-1)). Besides, the first order kinetic constant of periodate photolysis, IO4- + hv -> IO3 center dot + O center dot- and IO4- + hv -> IO3- + O((3) P), were respectively (0.5-4.16)x10(-3) s(-1) and similar to 2 x 10(-4) s(-1), indicating that the radical pathway for IO4- photolysis is predominately the IO3--releasing path. (OH)-O-center dot and IO3 center dot were found to play the key role in the CB degradation. The concentration of radicals increased with pH decrease and initial periodate concentration rise, favoring higher degradation rate at acidic conditions and higher IO4- dosages. The selectivity analysis showed that the contribution of these species is similar to 79 % for (OH)-O-center dot and similar to 21 % for IO3 center dot, under various conditions of pH and [IO4-](0). This study would helpfully provide some practical indications for the application of UV/periodate AOP

Automated summary

This study presents a modeling study on the UV/periodate (IO4-) advanced oxidation process, evaluating the generation and distribution of reactive species. The research found that (OH)-O-center dot and IO3 center dot play a key role in the degradation of chlorazol black, with radical concentration increasing with decreasing pH and rising periodate concentration.