Thioureas methyl-derivatives photo-induced transformation on titanium dioxide

Thiourea methyl-derivatives photocatalytic degradation has been studied by adopting titanium dioxide as a photocatalyst. A combined study has been performed and had involved: (1) the study of (methyl)thioureas degradation rate; (2) the identification of intermediate compounds, obtained by HPLC tandem mass spectrometry and (3) the assessment of the mineralization process.Thiourea is mainly transformed into cyanamide and urea and then (very slowly) mineralized (up to 24 h of irradiation are required). For its methyl derivatives, the formation of the corresponding methylureas is realized; in addition, several dimeric compounds have been identified. Methyl thiourea gives the formation of CH3NHC(NH)CH2NHCONHCH3 and methylcyanamide dimeric form, while dimethylthiourea forms NCNHCH(OH)CH2NHCONHCH3, but no cyano derivatives are observed.The rate of mineralization gets higher at the increasing of the number of the methyl groups. Sulphur is easily released as sulphate ions in all cases. The nitrogen is preferentially released as ammonium ions, with a ratio ammonium versus nitrate ions of 2:1, observed in all cases but with dimethylthiourea, where instead an initial major formation of ammonium ions, at the increasing of the irradiation time a slight inversion between nitrate and ammonium formation is seen.