Photochemical reactions of biphenyl and its chlorinated derivatives on the surfaces of γ-alumina and silica–alumina

Photochemical reactions of biphenyl and its chlorine-substituted derivatives on the surfaces of γ-alumina and silica–alumina have been investigated. Diffuse reflectance spectra show that biphenyl molecules adsorbed on activated surfaces (Ta > 350 °C) form chemical products and charge-transfer complexes. The existence of the latter is also confirmed via observation of an EPR signal on photoirradiation into the CT band. Photoirradiation of the adsorbed organic molecules leads to a redox process on the surface, radical cations are formed, and dechlorination takes place. The coadsorption of persulfate and dinitrobenzene significantly influences the electron-transfer processes. The photochemical products on both activated and non-activated surfaces were separated by HPLC, and the collected fractions were studied spectroscopically. The important reaction of radical cations is hydrolysis resulting in hydroxybiphenyl, the radical BP(OH)˙ is suggested as a key intermediate in hydrolysis.