Metal ion-TiO2 nanocomposites for the selective photooxidation of benzene to phenol and cycloalkanol to cycloalkanone

TiO2 has attracted a great deal of research attention for photochemical redox combined transformation of organic functional groups into useful products. In this context, various transition metal ions impregnated-TiO2 catalysts are prepared and characterised by SEM surface morphology, TEM size and shape analysis, magnetic susceptibility measurement and tested for benzene and cycloalkanol oxidation. The highest yield (14.8 mu mol) and selectivity (80%-86%) of phenol as compared to hydroquinone (yield = 2%-8%) is achieved during 1-2-h irradiation (125W Hg arc lamp, 10.4 mW/cm(2)) of aqueous suspension of 5wt% Fe+3-TiO2 and 20mM benzene solution. The co-catalytic activity of metal ions imparted to TiO2 during benzene oxidation was highly enhanced in the order Fe+3 > Ag+ > Au+3 > Cu+2 as compared to very low reactive elemental metal loading. Metal/metal ion deposition onto TiO2 highly reduces the cycloketone yield whereas bare TiO2 exhibits the maximum amount of cyclohexanone (60%) and cycloheptanone (50%) formation from respective cycloalkanol photooxidation up to 4-h irradiation.