CdS–Ag3PO4 nano-catalyst: A brief characterization and kinetic study towards methylene blue photodegradation

Abstract

CdS and Ag3PO4 NPs were synthesized by the sol-gel method and coupled mechanically. The XRD analysis showed the hexagonal (wurtzite) CdS and the body-centered cubic of Ag3PO4 crystallite phases in the resulted nano-catalyst (NC). The average crystallite sizes of 2.07, 25.36, and 20.83 nm were respectively obtained for the as-synthesized CdS, Ag3PO4, and CdS–Ag3PO4 samples by the Scherrer equation which varied to 1.25, 49.52 and 55.46 nm based on the Williamson-Hall equation. The samples were also characterized by scanning electron microscope (SEM), UV–Vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) techniques. A boosted photocatalytic activity for the coupled system was observed due to the better charge carrier's separation that occurred in this system. The lowest PL intensity and the highest photodegradation activity were obtained for the NC with a CdS:Ag3PO4 mole ratio of 2. The mineralization extent of the MB photodegraded solutions was studied by the COD method. The rate constants of 0.0108 and 0.0132 min−1 were obtained for the MB-photodegradation and mineralization processes by applying the results in the Hinshelwood apparent first-order kinetic model, respectively. These values correspond to t1/2 values of 64.2 min and 22.2 min, respectively. The k-values of 0.0095, 0.0086, 0.0075 and 0.0075 min−1 (average: 0.0083 ± 0.0009 min−1) with a RSD of 12% were obtained for 4 successive reusing runs for the NC.