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/H2O2 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 (center dot OH), we first observed hydrated electron (e(aq)center dot(-)) formation by electron paramagnetic resonance (EPR) analysis in the presence of an excessive amount of tertiary butanol (t-BuOH), center dot OH scavenger, during the UV-LED/H2O2 reaction. However, the contribution of e(aq)center dot(-) on TMAH degradation was negligible compared to center dot OH which played a major role in TMAH degradation. The calculated reaction rate constant of TMAH with center dot OH was 7.5 x 10(7) M-1 s(-1). From competitive kinetics, [center dot OH]ss and k center dot OH, TMAH value was found to be 7.1 x 10(-13) M and 7.5 x 10(7) M-1 s(-1), respectively. The optimum pH and tem-perature for TMAH degradation were pH 7 and 35 ?C. Three demethylated amines (trimethylamine, dimethyl-amine, and methylamine), along with NH4+ and NO3- ions, were detected as the byproducts, implying that the main degradation mechanism of TMAH in this reaction is H abstraction by center dot OH-induced oxidation and hydrolysis resulting from the center dot OH-induced oxidation, and demethylation. Our result implies that the UV-LED/H2O2 reaction

Automated summary

This study investigated the degradation mechanism of tetramethylammonium hydroxide (TMAH) during the UV-LED/H2O2 reaction under initial nitrogen purging conditions. The results showed that the hydroxyl radical (center dot OH) played a major role in the degradation of TMAH.