The photooxidative degradation of N-methylpyrrolidinone in the presence of Cs3PW12O40 and TiO2 colloid photocatalysts

The mechanisms of the heterogeneous photocatalytic behavior of TiO2 and Cs3PW12O40 for the oxidative destruction of N-methylpyrrolidinone (NMP) in water are discussed. Both photocatalysts generate N-methylsuccinimide (NMS) and succinimide as the main intermediates from oxidation at the a-carbon and methyl positions. 2-Pyrrolidinone (2P) and 5-hydroxy-N-methylpyrrolidinone (5-HNMP) have also been identified as primary intermediates. These intermediates are all broken down under further photooxidation. However, differences in product distribution indicate the possibility of several mechanistic pathways. Hydroxyl radical-like attack predominates for TiO2-photocatalyzed degradation, whereas the polyoxotungstate appears to oxidatively destroy NMP by both OH radical attack and direct oxidation. For TiO2, the relative quantum yields for NMP oxidation (0.5 g L-1 TiO2, pH 3, 254 nm, 7 x 10(-6) ein sec(-1)) increase from <0.01 at 10 ppm NMP to near 0.03 at 60-100 ppm. For Cs3PW12O40 under the same conditions, the apparent quantum yield is nearly invariant (0.005-0.009) over the concentration range 10-1000 ppm.