Visible light-driven photocatalytic degradation of rhodamine B and 5-fluorouracil using ZIF-8/GO: unveiling mechanisms

Abstract

The removal of pharmaceutical and organic contaminants from wastewater remains a pressing challenge for conventional treatment technologies. In this study, a novel photocatalyst composed of Zeolitic Imidazolate Framework-8 (ZIF-8) nanocrystals integrated with a graphene oxide (GO) matrix was developed via a facile interfacial synthesis approach. The structural and morphological properties of the resulting ZIF-8/GO composite were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The composite's photocatalytic efficiency was assessed through the degradation of Rhodamine B (Rho-B), a representative dye pollutant, and 5-fluorouracil (5-Flu), a widely used pharmaceutical, under visible light irradiation. The ZIF-8/GO catalyst achieved near-complete degradation of Rho-B (100%) and 5-Flu (97.4%) within 100 minutes. This high performance is attributed to the synergistic effects of ZIF-8 and GO, which enhance surface area, improve light absorption, and promote charge separation. Moreover, the catalyst retained considerable activity over five cycles, with only a 12.8% decrease in Rho-B degradation due to minor material loss. The findings demonstrate that the ZIF-8/GO composite is a highly efficient, recyclable, and sustainable photocatalyst, showing great promise for the removal of complex pollutants from wastewater and contributing to environmentally friendly water purification technologies.

Scheme 1. Synthesis illustration of the ZIF-8 nanocrystals on GO matrix.

Fig. 1. TEM micrographs of (a–c) ZIF-8/GO composite at 200, 100 and 50 nm of magnifications, (d) ZIF-8/GO FESEM image for EdX, (e–h) EdX elemental mapping; C, O, N, Zn, respectively and (i and j) EDX plots and XRD pattern of the ZIF-8/GO composite.

Fig. 2. BET analysis including (a and b) isothermal and BJH profiles for GO, ZIF-8 and ZIF-8/GO composite.

Fig. 3. High-resolution XPS spectra of pristine GO, ZIF-8 and the ZIF-8/GO composite: (a–c) C 1s and (d–f) N 1s spectra of GO, ZIF-8 and GO@ZIF-8, correspondingly; (g and h) Zn 2p spectra for ZIF-8 and GO@ZIF-8, correspondingly.

Fig. 4. Photocatalytic performance under visible light irradiation for approximately 100 min: (a) photolysis of Rho-B without the occurrence of photocatalysts, (b–d) time-dependent absorbance spectra of Rho-B in the presence of ZIF-8, GO, and ZIF-8/GO, respectively, (e and f) degradation efficiency and pseudo-1st-order fitted equations with respect to the visible time for ZIF-8, GO and ZIF-8/GO, (g) recycling runs of ZIF-8/GO catalyst towards the Rho-B degradation during the photocatalysis reaction, (h) weight loss against the runs during washing of the ZIF-8/GO and (i) TEM images before and after cycling the ZIF-8/GO with EDX mapping.

Fig. 5. Photocatalytic performance under visible light irradiation for approximately 100 min: (a) photolysis of 5-Flu without the occurrence of photocatalysts, (b–d) time-dependent absorbance spectra of 5-Flu in the occurrence of ZIF-8, GO and ZIF-8/GO at given interval of time and (e and f) degradation efficiency and pseudo-1st-order fitted equations with respect to the visible time for ZIF-8, GO and ZIF-8/GO.

Fig. 6. Influence of the various operation conditions using the Rho-B and 5-Flu; (a and b) degradation efficiencies of Rho-B and 5-Flu in the occurrence of the ZIF-8/GO with respect of the irradiation time under visible light and such as 0.25, 0.30, 0.35 g L⁻¹, respectively, (c and d) degradation efficiency of Rho-B and 5-Flu in the presence of the ZIF-8/GO at various pH values including 3, 7 and 9.

Fig. 7. Impacts of the scavengers including K₂Cr₂O₇, AO, p-BQ and FFA, respectively, on the photocatalytic degradation in the presence of ZIF-8/GO; (a) summary of the degradation efficiency of Rho-B with respect to the time, (b) summary of the degradation efficiency of 5-Flu with respect to the time, (c) CV profile for the ZIF-8, GO and their composite, and (d) Nyquist plot for the ZIF-8, GO and their composite.