Photocatalytic decomposition of l-serine and l-aspartic acid over bare and silver-deposited TiO2

The photocatalytic degradation of l-serine and l-aspartic acid was investigated over bare and silver-deposited TiO2 photocatalysts suspended into aqueous solutions of various pH. The conversion of the model compounds was followed by measuring the loss of the amine function and the formation of nitrogen containing ions, such as NH4+, NO2− and NO3−. In addition, the total organic carbon content (TOC), the total nitrogen content (TN) and the pH were also monitored. It is demonstrated that the initial rate of the photodegradation and the concentration of the surface complexes of amino acids increase with pH in that pH range where the zwitterionic form of amino acids is the principal species. The replacement of bare TiO2 particles with silver-deposited TiO2 particles results in an enhancement in the efficiency of the photocatalytic reaction. The increase in the initial rate has been found to be significant for serine and moderate for aspartic acid. The results of competitive kinetic measurements used oxalic acid as scavenger for photogenerated holes and that of the diffuse reflection Fourier transformed infrared (DRIFT) spectroscopy demonstrated the disappearance of model compounds on the surface of semiconductor particles of the UV irradiated samples have also been exploited for discussing the mechanism of photocatalytic decomposition of the amino acids.