Kinetics of photocatalytic degradation of phenols with multiple substituent groups

The photocatalytic degradation of seven phenols, substituted with two of the following groups: chloro, methyl and nitro, was investigated using combustion-synthesized catalyst. The intermediates were analyzed and a possible pathway of degradation was proposed. The first order kinetic rate constants for the degradation of various phenols were determined. The rate of photocatalytic degradation followed the order: 4-chloro,3-methyl phenol > 2-chloro,4-methylphenol > 4-chloro,2-nitrophenol > 4-chloro,2-methyl phenol > 4-chloro,3-nitrophenol ∼ 2-chloro,4-nitrophenol > 4-methyl,2-nitrophenol. The overall degradation rate of 4-chloro,3-methyl phenol was nearly an order of magnitude faster than the degradation rate of 4-methyl,2-nitrophenol. Chloromethylphenols degraded faster than chloronitrophenols due to the ring deactivating characteristic of nitro group for hydroxyl radical attack. The nature of substituent groups plays a more important role than the position of the substituent groups in determining the degradation rate of multi-substituted phenols.