Abstract

Cadmium selenide/graphene quantum dots (CdSe/GQDs) nanocatalyst with small band gap energy and a large specific surface area was produced via a facile three-step sonochemical-hydrothermal process. The features of the as-prepared CdSe, GQDs and CdSe/GQDs samples were characterized by photoluminescence spectroscopy (PL), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier transformed infrared (FT-IR), diffuse-reflectance spectrophotometer (DRS), and Brunauer-Emmett-Teller (BET) analysis. The sonocatalytic activity of the synthesized CdSe/GQDs was effectively accelerated compared with that of pure CdSe nanoparticles in degradation of methylene blue (MB). The influence of the CdSe/GQDs dosage (0.25-1.25 g/L), initial MB concentration (20-30 mg/L), initial solution pH (3-12), and ultrasonic output power (200-600 W/L) were examined on the sonocatalytic treatment of MB aqueous solutions. The degradation efficiency (DE) of 99 attained at 1 g/L of CdSe/GQDs, 20 mg/L of MB, pH of 9, and an output power of 200 W/L at 90 min of ultrasonic irradiation. Furthermore, DE increased with addition of K2S2O8 and H2O2 as the enhancers via producing more free radicals. However, addition of sulfate, carbonate, and chloride as radical sweeper decreased DE. Furthermore, well-reusability of the CdSe/GQDs sonocatalyst was demonstrated for 5 successive runs and some of the sonocatalytic generated intermediates were indicated by GC-MS analysis.