Photosensitization of TiO2 by ZnS and bromo thymol blue and its application in photodegradation of para-nitrophenol

Controlled precipitation method was used to prepare of TiO2/ZnS/BTB photocatalyst. The ZnS and bromo thymol blue (BTB) dye were used as modifier and sensitizer agents, respectively. The composition of TiO2/ZnS/BTB photocatalyst was characterized by EDX spectra, FT-IR spectra and SEM images. The XRD patterns showed the phases of routile and cubic for TiO2 and ZnS, respectively, in composite of TiO2/ZnS/BTB. The diffuse reflectance UV/VIS spectra were used to estimate of band-gap energies of samples. The band-gap energies of TiO2, TiO2/ZnS and TiO2/ZnS/BTB were obtained as 3.03, 2.76 and 2.68 eV, respectively. The TiO2/ZnS/BTB photocatalyst was used in photodegradation process of para-nitrophenol (PNP). The order of photocatalytic activity was obtained as: TiO2/ZnS/BTB > TiO2/ZnS > TiO2 that matched with the band-gap energies. The degradation efficiency of >95 % was obtained at optimized conditions of pH 6, 1.0 g/L of photocatalyst, 10 mg/L of PNP in time 180 min. The kinetic rate constants of Langmuir–Hinshelwood were decreased with increasing of initial concentration of PNP. Furthermore, the TOC result indicated the degradation of 90 % PNP in photodegradation reaction.