Abstract
Mono-dispersed and smaller sized TiO2 nanospheres (˜8nm and ˜20nm) exhibited superior photo-reductive efficiency for few aromatic aldehydes under UV light. It has been found that p-nitrobenzaldehyde and benzaldehyde are efficiently reduced to p-aminobenzyl alcohol (80% and 61%) and benzyl alcohol (59% and 38%) by 8nm and 20nm particles respectively, relative to negligible reduction by TiO2 (P25) under same experimental conditions. However, the successful photo-reduction of p-nitrotoluene (97%) was observed with P25 whose reduction potential (−0.5eV) lies below the conduction band (CB, −0.85eV vs NHE) of the catalyst. These findings can be explained on the basis of unsuitable and mismatched CB of P25 with respect to the lowest unoccupied molecular orbital of −CHO group to access its photo-activity. However, this hydrogenation occurred by synthesized smaller sized TiO2 particles (˜8nm and ˜20nm) due to their favorable band gap (3.85eV and 3.62eV) and conduction band edge (−0.61eV and −0.50eV). Moreover, the other physio-chemical characteristics of 8nm and 20nm sized particles such as surface area (323m2g−1 and 297m2g−1), higher charge carrier relaxation time (61μs and 40μs) are also co-related for ease of photo-activity relative to TiO2 (P25).
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