Selective photocatalytic oxidation of 4-substituted aromatic alcohols in water with rutile TiO2 prepared at room temperature

Home-prepared (HP) rutile TiO2 catalysts were prepared at room temperature by using H2O and TiCl4 in different ratios and without addition of additives. The catalysts were used for carrying out the selective photocatalytic oxidation of 4-methoxybenzyl alcohol to 4-methoxybenzaldehyde in aqueous suspension, free from any organic co-solvent. The selectivities showed by the home prepared catalysts were in the 45-74% range, up to four times higher than that of a commercial rutile TiO2 sample, the reaction rates being comparable. By using the most selective photocatalyst, the oxidation of benzyl, 4-methylbenzyl, and 4-nitrobenzyl alcohols was also carried out in order to investigate the influence of the substituent group on the oxidation rate and selectivity. The presence of an -OCH3 group positively influenced the selectivity whereas a -NO2 group showed to have a detrimental effect. The Hammett relationship effectively describes the influence of substituent group on the kinetic constant of partial oxidation of aromatic alcohols to aldehydes.