Degradation of tetramethylammonium hydroxide (TMAH) during UV-LED/H2O2 reaction: Degassing effect, radical contribution, and degradation mechanism

Semiconductor wastewater usually has a low level of dissolved oxygen and alcohol because ultra-pure water used in the process undergoes rigorous degassing and wafer development, respectively. In this study, we investigated the degradation mechanism of tetramethylammonium hydroxide (TMAH), a compound of concern in the semiconductor manufacturing process, during the UV-LED/H 2 O 2 under initial nitrogen purging conditions to remove dissolved oxygen. The effect of the initial degassing was negligible due to the in-situ O 2 production during the reaction. Along with hydroxyl radical (•OH), we first observed hydrated electron (e aq •-) formation by electron paramagnetic resonance (EPR) analysis in the presence of an excessive amount of tertiary butanol (t-BuOH), •OH scavenger, during the UV-LED/H 2 O 2 reaction. However, the contribution of e aq • - on TMAH degradation was negligible compared to •OH which played a major role in TMAH degradation. The calculated reaction rate constant of TMAH with •OH was 7.5 × 10 7 M −1 s −1 . From competitive kinetics, [•OH] ss and k •OH, TMAH value was found to be 7.1 × 10 −13 M and 7.5 × 10 7 M −1 s −1 , respectively. The optimum pH and temperature for TMAH degradation were pH 7 and 35 °C. Three demethylated amines (trimethylamine, dimethylamine, and methylamine), along with NH 4 + and NO 3 - ions, were detected as the byproducts, implying that the main degradation mechanism of TMAH in this reaction is H abstraction by •OH-induced oxidation and hydrolysis resulting from the •OH-induced oxidation, and demethylation. Our result implies that the UV-LED/H 2 O 2 reaction can be one of the options to treat TMAH contaminated water by recycling H 2 O 2 produced in the semiconductor manufacturing process and lowering the energy consumption by using UV-LED. • OH radical played a major role in the TMAH degradation in the UV-LED/H 2 O 2 reaction. • Hydrated electron (e aq •-) was observed, but the contribution can be neglected. • Neutral pH and higher temperature favored TMAH degradation. • Demethylated amines, ammonium, and nitrate were identified as major byproducts. • H abstraction by •OH oxidation and hydrolysis were the main degradation reactions.