A well-defined S-g-C3N4/Cu-NiS heterojunction interface towards enhanced spatial charge separation with excellent photocatalytic ability: synergetic effect, kinetics, antibacterial activity, and mechanism insights

Abstract

A well-defined heterojunction among two dissimilar semiconductors exhibited enhanced photocatalytic performance owing to its capability for boosting the photoinduced electron/hole pair transportation. Therefore, designing and developing such heterojunctions using diverse semiconductor-based materials to enhance the photocatalytic ability employing various approaches have gained research attention. For this objective, g-C₃N₄ is considered as a potential photocatalytic material for organic dye degradation; however, the rapid recombination rate of photoinduced charge carriers restricts the widespread applications of g-C₃N₄. Henceforth, in the current study, we constructed a heterojunction of S-g-C₃N₄/Cu-NiS (SCN/CNS) two-dimensional/one-dimensional (2D/1D) binary nanocomposites (NCs) by a self-assembly approach. XRD results confirm the construction of 22% SCN/7CNS binary NCs. TEM analysis demonstrates that binary NCs comprise Cu-NiS nanorods (NRs) integrated with nanosheets (NSs) such as the morphology of SCN. The observed bandgap value of SCN is 2.69 eV; nevertheless, the SCN/CNS binary NCs shift the bandgap to 2.63 eV. Photoluminescence spectral analysis displays that the electron-hole pair recombination rate in the SCN/CNS binary NCs is excellently reduced owing to the construction of the well-defined heterojunction. The photoelectrochemical observations illustrate that SCN/CNS binary NCs improve the photocurrent to ∼0.66 mA and efficiently suppress the electron-hole pairs when compared with that of undoped NiS, CNS and SCN. Therefore, the 22% SCN/7CNS binary NCs efficiently improved methylene blue (MB) degradation to 99% for 32 min under visible light irradiation.

Fig. 1. XRD patterns of undoped NiS, CuS nanoplates, 7% Cu–NiS, undoped SCN and 22% SCN/7CNS NCs.

Fig. 2. SEM images of (a) undoped SCN, (b) CuS nanoplates and (c) NiS. (d) and (e) Are the SEM images of 22% SCN/7CNS NCs at different magnifications. (f) TEM image of 22% SCN/7CNS NCs. (g) HRTEM image of 22% SCN/7CNS NCs. (h) Shows the EDX of 22% SCN/7CNS NCs.

Fig. 3. High-resolution XPS results of 22% 2D/1D SCN/CNS NCs; (a) Ni 2p, (b) Cu 2p, (c) S 2s and (d) N 1s.

Fig. 4. (a) FT-IR measurements and (b) the BET surface area isotherms estimated from nitrogen adsorption–desorption of undoped NiS, 7CNS, SCN and 22% 2D/1D SCN/CNS heterostructure.

Fig. 5. (a) UV-vis absorption ranges of NiS, 7CNS, SCN and 22% 2D/1D SCN/CNS NCs. Tauc's plots of (b) NiS and 7CNS, (c) SCN, and (d) 22% 2D/1D SCN/CNS heterostructure.

Fig. 6. The measurement of MB degradation in visible light radiation for (a) NiS, Cu–NiS (2, 4, 7, 12 and 20%) NRs, and (b) 22% 2D/1D SCN/CNS NCs. (c) MB photodegradation rate and (d) pseudo-first-order kinetic plots of dye, NiS, 7CNS, and 2D/1D SCN/CNS (4, 12, 22, 32 and 45 wt%) NCs.

Fig. 7. Using a 22% 2D/1D SCN/CNS heterostructure, a possible schematic illustration of the reaction pathways for photocatalytic elimination of MB.

Fig. 8. (a) The 22% 2D/1D SCN/CNS NC photocatalyst demonstrated cycling stability in 7 consecutive MB photodegradation experiments. (b) The structural stability of 2D/1D SCN/CNS NCs was revealed by XRD patterns obtained before the first cycle and after the seven-recycling test. (c) PL spectra of pure 2D SCN and 2D/1D SCN/CNS (4, 12, 22, 32 and 45 wt%) NCs at 320 nm excitation wavelength. (d) Transient photocurrent responses of NiS, 7% Cu–NiS, undoped SCN and 22% 2D/1D SCN/CNS NCs in visible-light irradiation (λ > 420 nm).

Fig. 9. (a) EIS Nyquist plots of NiS NRs, Cu–NiS NRs, S-g-C₃N₄, and 7%, 10% and 22% SCN/7CNS NCs. (b) Effect of scavengers on the photocatalytic activity of 22% 2D/1D SCN/CNS NCs. ESR spectra of 22% 2D/1D SCN/CNS NCs: (c) in aqueous suspension for DMPO⁻˙OH and (d) in methanol suspension for DMPO⁻˙O₂⁻ under visible light irradiation.