Photoreductive dehalogenation of halogenated benzene derivatives using ZnSor CdS nanocrystallites as photocatalysts

ZnS nanocrystallites (nc-ZnS) prepared in N,N-dimethylformamide (DMF) photo catalyze dehalogenation of halogenated benzenes to benzene as the final pro duct from chlorinated benzenes and to difluorobenzenes from fluorinated ben zenes in the presence of triethylamine (TEA) as an electron donor under UV light irradiation (lambda > 300 nm). When CdS nanocrystallites (nc-CdS) are used as a photocatalyst (lambda > 400 nm), halogenated benzenes are photor eductively dehalogenated, yielding trichlorobenzene from hexachlorobenzene and tetrafluorobenzene isomers from hexafluorobenzene as the final products . Photoformed electrons on nc-ZnS and nc-CdS have such negative reduction p otentials that these electrons reduce polyhalogenated benzenes, leading to the successive dehalogenation. nc-ZnS exhibits higher photocatalytic activi ty than nc-CdS due to the more negative potential of the electrons on nc-Zn S than that on nc-CdS. The higher activities of nc-ZnS and nc-CdS compared to their bulk forms are explained as being due to their quantum size effect s and the adsorptive interaction between the substrates and the nanosized p hotocatalysts.