Synthesis and characterization of bismuth gadolinium oxide/g-C3N4 heterojunction nano photocatalyst for efficient sunlight-driven purification of wastewater containing malachite green dye

• Synthesis of BiGdO 3 /g-C 3 N 4 (BGO/CN) nanocomposites for the first time by auto-combustion route. • Investigation of various synthesis conditions on the dimensional properties of nanostructures. • Investigation of different contents of g-C 3 N 4 on the size and morphology of BGO/CN nanocomposite. • The best degradation percentage was obtained in the presence of BGO/CN over malachite green (MG). • •OH active radicals are the prominent active species in the degradation of MG. In this research, considering the problem of water pollution, efficient bismuthate nanostructures have been designed to destroy organic pollutants; and in the following, suitable strategies to improve the photocatalytic efficiency have been presented and analyzed. In this regard, BiGdO 3 nanoparticles were prepared by auto-combustion route using sucrose as fuel. A series of techniques including X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared Spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET), Diffuse Reflectance Spectroscopy (DRS) to analyze the morphology, phase purity and optical properties of BiGdO 3 (BGO) samples are employed. Then, the obtained bismuthate nanostructures with an average size of 34.84 nm are used to form BiGdO 3 /g-C 3 N 4 (BGO/CN) nanocomposites with different content. According to BET analysis, the specific surface area of BGO/CN nanocomposites was found as 5.18 m 2 g −1 . According to DRS data, the BGO band gap (2.78 eV) decreases to 2.45 eV with CN incorporation. The obtained pure BGO nanostructures are studied in malachite green (MG) decomposition. Under optimal conditions , 0.10 g BGO degrades 97.27 % of 20 ppm MG. To investigate the photocatalytic ability of nanocomposites and to improve the use of sunlight, a comparative study is conducted between the light sources. Experimental results show that BGO/CN nanocomposites show higher pho tocatalytic activity (98.36 %) than pure BiGdO 3 and g-C 3 N 4 . In addition, the photodegradation mechanism of BGO/CN by scavenging experiments introduces •OH active radicals as the main factor in the photocatalytic process.