The photocatalytic degradation of 3-nitrobenzenesulfonic acid in the presence of solar radiation and artificial UV radiation with suspended TiO2 was studied in a batch and continuous annular reactor, respectively. The effects of catalyst loading, pH, presence of anions and cations and initial concentration on the rate of photocatalytic degradation were investigated. Concentration-time data were correlated with the rate equation d[C-t=0]/dt = k(r)K[C-t=0]l(1 + K[C-t=0]). Studies were carried out to compare the photolytic, photochemical and photocatalytic methods of degradation. (c) 2005 Society of Chemical Industry