A ternary CdS/AgBr/Ag3PO4 nanocomposite: characterization and the kinetics of its photocatalytic activity

A ternary CdS/AgBr/Ag3PO4 coupled system was prepared, characterized by different techniques, and used for the photodegradation of methylene blue (MB). The hexagonal (wurtzite) CdS, the cubic AgBr, and the Ag3PO4 body-centered cubic crystallite phases were detected by XRD patterns. The Scherer equation showed the crystallite sizes of 3, 26.3, 28, and 27.9 nm for CdS, Ag3PO4, AgBr NPs, and the ternary CdS/AgBr/Ag3PO4 sample, while the Williamson-Hall model got the values of 1.8, 46.2, 62.12, and 92.44 nm, respectively. The diffuse reflectance spectra (DRS) showed that the ternary catalyst could absorb the whole range of visible light photons. The photoluminescence (PL) spectra significantly depended on the solvent nature, and the sharp scattering peaks appeared in the water, while these were absent in acetone as solvent. The ternary catalyst also showed a lower PL intensity and a higher photocatalytic activity concerning the individual NPs. When the moles of CdS were three times greater than the other components, the resulted ternary catalyst showed the lowest PL intensity and the highest degradation activity. The MB mineralization was also studied by the COD technique and compared with MB photodegradation kinetically. The MB photodegradation rate constant of about 0.0276 min(-1) (correspond to t(1/2) 25.1 min) was 1.75 times greater than the MB mineralization rate constant (about 0.0158 min(-1) correspond to t(1/2) value of 43.9 min).

Automated summary

The ternary CdS/AgBr/Ag3PO4 coupled system shows efficient absorption of visible light photons with low photoluminescence intensity and high photocatalytic activity. The photodegradation rate constant of MB is significantly higher than the mineralization rate constant.