One-pot construction of Cu and O co-doped porous g-C3N4 with enhanced photocatalytic performance towards the degradation of levofloxacin

Abstract

Low visible light response and rapid recombination of photogeneration charge carriers have always been the main factors limiting the advanced application of g-C₃N₄ (CN). Element doping has been confirmed to be an efficient method to improve the photocatalytic performance of CN. Here, a series of Cu and O co-doped porous g-C₃N₄ (Cu/O-PCN) nanomaterials were successfully fabricated by a facile one-pot thermal polymerization approach for the first time. Compared to pure CN, the resulting Cu/O-PCN exhibited remarkably enhanced visible-light-driven photocatalytic activity towards levofloxacin (LEVO) degradation. The optimized sample of 0.5% Cu doped (Cu/O-PCN-3) presented the highest degradation rate constant of 0.0676 min^-1, which was about 6.2 times higher than that of CN. Furthermore, a substantial decrease in the residual toxicity against E. coli was observed after photocatalytic degradation treatment. The superior photocatalytic performance of Cu/O-PCN was mainly attributed to the synergistic advantages of stronger visible light response, larger specific surface area, and the more effective separation and transfer of photogenerated charge carriers. Moreover, according to the trapping experiments, ·O₂ ^- and h⁺ were the major oxygen active species in the photocatalytic degradation process. Finally, the possible enhanced photocatalytic mechanism over Cu/O-PCN was proposed.

Fig. 1. (a) XRD patterns of as-prepared nanomaterials. XPS spectra of Cu/O-PCN-3: (b) survey spectrum and the corresponding high-resolution of (c) C 1s, (d) N 1s, (e) O 1s, and (f) Cu 2p.

Fig. 2. (a and b) SEM and (c and d) TEM images of Cu/O-PCN-3, (e) STEM image of Cu/O-PCN-3 and its corresponding EDS mappings for (f) C, (g) N, (h) O, and (i) Cu.

Fig. 3. (a) Nitrogen adsorption–desorption isotherms and (b) BJH pore size distribution of as-prepared nanomaterials.

Fig. 4. (a) UV-vis diffuse reflectance spectra, (b) Kubelka–Munk spectra and (c) the estimated band positions of as-prepared nanomaterials.

Fig. 5. (a) Photocatalytic degradation of LEVO, (b) pseudo first-order kinetic plots of −ln(C_t/C₀) for LEVO as a function of visible light irradiation time with as-prepared nanomaterials and (c) the change in the antibacterial activity of LEVO solution during the photocatalytic process by Cu/O-PCN-3.

Fig. 6. (a) Recycling stability experiments for Cu/O-PCN-3 and (b) active species trapping experiments of Cu/O-PCN-3 during degradation of LEVO.

Fig. 7. (a) Photoluminescence spectra, (b) time-resolved fluorescence spectra, (c) photo-current response and (d) EIS Nyquist plots for as-prepared nanomaterials.

Fig. 8. Illustration of the possible charge transfer and separation processes of Cu/O-PCN-3 under visible light irradiation.