Semiconductor wastewater usually has low dissolved oxygen levels because ultra-pure water and solvents underwent a rigorous degassing process. In this study, we investigated the effect of dissolved oxygen on the degradation of tetramethylammonium hydroxide (TMAH), one of the most problematic compounds in semiconductor manufacturing. Radical chain reaction usually takes place after the initial attack of OH radicals. In the absence of dissolved oxygen, kinetics and degradation mechanisms can be changed. However, there were no significant differences in TMAH degradation between anaerobic and aerobic UV-LED/H2O2 reactions. This phenomenon might be derived from the O2 generation followed by hydroperoxyl radical and superoxide radical. The reaction rate constant of OH radicals with TMAH in UV-LED/H2O2 reaction was 7.5 X 107 M-1 s-1. The optimum TMAH degradation pH and temperature were 7 and 35°C. We observed the formation of hydrated electrons under the anaerobic condition by using electron paramagnetic resonance. However, the contribution of hydrated electrons on TMAH degradation was negligible. Three demethylated amines (trimethylamine, dimethylamine, and monomethylamine) along with NH4+ and NO3- ions were detected as byproducts. The main degradation mechanisms of TMAH in UV-LED/H2O2 reaction were hydrogen abstraction by OH radicals-induced oxidation and hydrolysis reactions. Further anaerobic advanced oxidation/reduction processes studies using different radical sources are required to understand the oxidative or reductive radical formation and its application.

Degradation mechanism of tetramethylammonium hydroxide (TMAH) during the anaerobic UV-LED/H2O2 reaction

ACS Spring 2022

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