S-scheme heterojunctions based on novel Sm 2 CeMnO 6 double perovskite oxide and g-C 3 N 4 with excellent photocatalytic dye degradation performances.

It has become of utmost importance to preserve marine life and human health by protecting aquatic environments from contaminants. Therefore, using photocatalytic materials in treatment of contaminated water is a promising and innovative technique. Novel double perovskite Sm 2 CeMnO 6 was synthesized through a modified Pechini sol-gel method. Also, urea and melamine were utilized to synthesize graphitic carbon nitride (g-C 3 N 4 ). Combination of Sm 2 CeMnO 6 and g-C 3 N 4 produced several S-scheme heterojunction materials in diverse components ratios. Average crystallite sizes of Sm 2 CeMnO 6 and Sm 2 CeMnO 6 /g-C 3 N 4 (20:80) samples were calculated by Debye-Scherrer and Williamson-Hall methods to be 19.77, 22.72 nm and 42.01, 43.73 nm, respectively. The coexistence of g-C 3 N 4 (002) with a d-spacing of 0.325 nm and Sm 2 CeMnO 6 planes of (222), (111), and (400) with spacing values of 0.314, 0.302, and 0.294 nm, respectively, was depicted in the HR-TEM image of the Sm 2 CeMnO 6 /g-C 3 N 4 (20:80). The estimated bandgaps for the g-C 3 N 4 , Sm 2 CeMnO 6 , and Sm 2 CeMnO 6 /g-C 3 N 4 (20:80) were 2.70, 2.60, and 2.65 eV, respectively. Their application was investigated in photocatalytic degradation of methylene blue (MB) dye as typical pollutant. The estimated degradation pathway of MB was also provided through LC-MS analysis. Under the identical conditions, the best photocatalytic performance was found for Sm 2 CeMnO 6 /g-C 3 N 4 (20:80) composite. Using response surface methodology (RSM), operational parameters of the photocatalytic degradation were modeled and optimized by the best composite through central composite design approach. Applying optimized parameters led to 96% degradation of MB (8 mg/L) at pH 10 under 120 min visible light irradiation (λ > 365 nm) using 0.15 g of Sm 2 CeMnO 6 /g-C 3 N 4 (20:80) composite in 100 mL aqueous solution. Due to low intrinsic charge transfer resistance, modified E g , and good performance in e ‒ /h + pairs production, Sm 2 CeMnO 6 /g-C 3 N 4 (20:80) nanocomposite was introduced as a promising S-scheme photocatalyst.