Highly efficient photodegradation of raw landfill leachate using cost-effective and optimized g-C3N4/SnO2/WO3 quantum dots under Vis–NIR light

Abstract In this study, photodegradation of raw landfill leachate under Vis–NIR irradiation and sunlight has been investigated using optimized g-C 3 N 4 /SnO 2 /WO 3 quantum dots as a novel nanocomposite. g-C 3 N 4 /SnO 2 /WO 3 QDs was successfully synthesized and characterized using various analyses. The best mixing ratios of the nanocomposite components were obtained by response surface methodology (RSM). The morphology and the surface area characteristics of the photocatalyst were investigated by scanning and transmission electron microscopy (SEM and TEM) and Brunauer, Emmett and Teller (BET) analysis. Results of UV–Visible diffuse reflectance spectroscopy (UV–Vis DRS) and photoluminescence (PL) spectrum revealed that the nanocomposite has a great light absorption capacity and improved separation of charge carriers. Using the optimized nanocomposite with the best mixing ratios of urea, SnO 2 , and WO 3 QDs solution, obtained from the central composite design (CCD), the chemical oxygen demand (COD) of the leachate (4575 mg/L) was reduced by 74% and 47% in 4 h under visible-NIR and sunlight irradiations, respectively. Gas chromatography–mass spectrometry (GC–MS) analysis also revealed that a significant reduction of aromatic compounds of the raw leachate occurred after the photodegradation process with g-C 3 N 4 /SnO 2 /WO 3 QDs nanocomposite. Moreover, the stability and recyclability of the photocatalyst were evaluated, and it was observed that after five experimental cycles of leachate degradation, no significant loss of nanocomposite performance could be seen. Financial analysis was also performed, and the feasibility of this process was investigated.