| Abstract
| - The photocatalytic degradation (PCD) reaction of N-nitrosodimethylamine (NDMA) in water was investigated usingpure and surface-modified TiO2. The PCD products ofNDMA were methylamine (MA), dimethylamine (DMA),nitrite, nitrate, and ammonium, and their distribution couldbe changed by modifying the surface of TiO2. The PCDreaction of NDMA seems to be initiated mostly by OH radicals,not valence band holes, because the addition of excessoxalates (hole scavengers) only moderately retarded thePCD rate. The presence of oxalate, however, enabled a newreductive transformation path in which the CO2-• radicalsgenerated from the oxalate converted NDMA into DMA.In acidic suspensions of pure TiO2, the formation of MA washighly favored over DMA and NH3, whereas all degradationproducts (MA, DMA, and NH3) were generated atcomparable concentrations at basic pH. It is suggestedthat there are three parallel paths depending on the positionof the initial attack of OH radical on NDMA and theproduct distribution is closely related with which path isfavored under a specific condition. DMA production is relatedto the OH radical attack on the nitrosyl nitrogen. Platinumdeposition, silica loading, Nafion coating, and surfacefluorination were tested to investigate the effects of TiO2surface modification on the product distribution. The surfaceplatinization of TiO2 had little effect on the PCD reactionof NDMA under air-equilibrated conditions but acceleratedthe PCD reaction under deaerated conditions. An enhancedPCD reaction of NDMA was achieved with the silica-loaded TiO2 and Nafion-coated TiO2, both of which favoredthe formation of DMA over MA. The PCD of NDMA onsurface-fluorinated TiO2 was also highly enhanced but favoredthe formation of MA over the formation of DMA.
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