Ultrasonic spray pyrolysis synthesis of reduced graphene oxide/anatase TiO₂ composite and its application in the photocatalytic degradation of methylene blue in water

Reduced graphene oxide (RGO)/anatase TiO₂ composite was prepared using a simple one-step technique—ultrasonic spray pyrolysis—in order to inhibit the aggregation of TiO₂ nanoparticles and to improve the photocatalytic performance for degradation of methylene blue (MB). Different proportions (0–5 wt%) of RGO/TiO₂ composites were characterized by scanning electronic microscopy (SEM), dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area, X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD), Raman spectroscopy, UV–vis spectroscopy, and electrochemical impedance spectroscopy (EIS) to verify mechanism. From these analysis, TiO₂ nanoparticles are distributed uniformly on the RGO sheets with crumpled shape during ultrasonic spray pyrolysis and surface area is increasing by increasing portion of RGO. Band gap of RGO₅/TiO₂ (5 wt% of RGO) composite is 2.72 eV and band gap was reduced by increasing portion of RGO in RGO/TiO₂ composites. The RGO₅/TiO₂ composite was superior to other lower content of RGO/TiO₂ composites with a rapid transport of charge carriers and an effective charge separation. The highest removal efficiency of MB was obtained at the RGO₅/TiO₂ composite under UVC irradiation, which coincided with the EIS, and the optimal dose of the composite was determined to be 0.5 g/L. The RGO₅/TiO₂ composite improve the photocatalytic degradation rate of MB over the TiO₂ due to a retardation of electron-hole recombination. The MB adsorption capacity and photocatalytic degradation efficiency were greatly affected by pH changes and increased with increasing pH due to electrostatic interactions and generation of more hydroxyl radicals. The reusability of RGO₅/TiO₂ composite was examined during 3 cycles.