Photocatalytic degradation of different pollutants by the novel gCN-NS/Black-TiO2 heterojunction photocatalyst under visible light: Introducing a photodegradation model and optimization by response surface methodology (RSM)

Abstract A novel binary black TiO2/g–C3N4–nanosheet heterojunction nanocomposite was successfully synthesized. Three strategies were applied: hydrogenation of TiO2 (black TiO2), exfoliation of g-C3N4 (g–C3N4–nanosheet), and further decoration of the black TiO2 nanoparticles on the g–C3N4–nanosheet (black TiO2/g–C3N4–nanosheet). Different analyses like XRD, EDX, XPS, AFM, FESEM, FT-IR, TEM, HRTEM, PL, UV–Vis DRS, DLS, EIS, photocurrent, and BET were used to characterize the photocatalysts. This heterostructured photocatalyst exhibited notably improved photocatalytic ability of 77.5, 9, 84, and 3.7 folds greater than that of g-C3N4, g–C3N4–nanosheet, TiO2, and black TiO2 for rhodamine B (RhB) photodegradation as a model organic dye pollutants under visible light irradiation, respectively. Central composite design (CCD) was utilized to optimize the kinetics of degradation of RhB based on response surface methodology (RSM). The established quadratic model has high reliability and fitness with R2 value of 0.9936. The maximum degradation efficiency of was achieved under the optimum conditions of the initial RhB concentration of 9 ppm, photocatalyst weight of 147.5 mg, and pH of 9.17. A reasonable photocatalytic mechanism based on the Tauc plot, Mott-Schottky curve and scavenging experiment results was proposed. Stability testing predicted that the binary photocatalyst was stable during 4 runs. Also, photocatalytic abilities of the as-obtained photocatalysts were further assessed by degradation of MB, MO, and phenol upon visible light. This work will be helpful for the design and preparation of heterostructured photocatalysts with new architectures for applications in water purification.