| Abstract
| - Most photocatalytic degradation (PCD) reactions ofaquatic pollutants require the presence of dissolved oxygenand hence do not occur in anoxic suspensions. Weinvestigated the PCD reactions of alkylamines in anoxicwater using TiO2 deposited with Pt nanoparticles. Unliketypical PCD reactions, the absence of dissolved oxygenincreases the PCD rates of alkylamines on Pt/TiO2and generates products that are different from thoseformed on pure TiO2. In particular, N-alkylated amines (e.g.,(CH3)3N produced from (CH3)2NH) as well as dealkylatedamines are generated in a deaerated Pt/TiO2 suspension.This anoxic N-alkylation pathway is enabled only in thepresence of Pt deposits on TiO2 and is applicable only toneutral alkylamines and not to alkylammonium cations.The Pt surface appears to interact with the lone-pair electronon the N atom and catalyze the anoxic degradation ofalkylamines mainly through a radical mechanism. Methylradicals generated on Pt participate in the N-methylationreaction. The presence of intermediate methyl radicals onthe Pt surface was verified by the detection of CH4 andCH3CH3 gases evolved during the PCD of (CH3)3N in an anoxicPt/TiO2 suspension, whereas no such products wereobserved in a pure TiO2 suspension. The anoxic PCD ofN-methylethylamine on Pt/TiO2 also produces both N-ethylatedand N-methylated amines as byproducts, which indicatesthat both methyl and ethyl radicals are generated duringthe anoxic degradation process. From a practical point ofview, the present finding that undesirable alkylatedamines can be produced on Pt/TiO2 in anoxic conditionsindicates that caution is necessary when applying Pt/TiO2photocatalyst to the treatment of water that containsamines.
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