Abstract
Graphene oxide (GO) was synthesized and exfoliated into fewer layers in various solvents, including ethanol, ether, and water, as well as in mixtures of these solvents. The exfoliated GO was fully characterized utilizing various techniques, and it also exhibited enhanced physicochemical properties compared to the pristine GO (unexfoliated). For example, the surface area and lateral size of the GO exfoliated in water are 233.28 m2.g-1 and 22.0 micrometers (μm), respectively. This is a significant enhancement compared to the pristine GO, with a surface area and lateral size of 131.50 m2.g-1 and 4.6 μm, respectively. The Raman spectra, through the decrease in Id/Ig ratios, indicated the aromatic structure of the exfoliated GO nanosheets were in better standing compared to the pristine GO. Shift in d-spacing was also observed in the X-ray diffraction (XRD) analyses for the exfoliated GO, which serve as an indication that fewer layers of GO sheets with larger interlayer spacing were prepared via polar solvent exfoliation. The exfoliation exercise generally indicated that polar solvents like ethanol, ether, and water and their mixtures played an indispensable role in promoting the synthesis of defect-free graphitic sheets, since the impact of exfoliating GO in various polar solvents showed significant enhancement on the physicochemical properties of GO. The exfoliated GO sheets were further modified in two steps. Firstly, by grafting the modified ZnOFe3O4 composites to the GO substrate through the epoxy groups, thereby transforming the fZnOFe3O4 into the fZnOFe3O4@GO composites. Secondly, in order to increase the quantity of the ZnOFe3O4 composites grafted to the GO substrate, more grafting sites needed to be created across the surface of the GO substrate. To this effect, the exfoliated GO sheets were treated with poly(ethylene glycol) diglycidyl ether
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(PDGDE), which resulted in a quantitative increase of the epoxy groups as well as other relevant oxygen functionalities of the GO substrate (as anticipated). The product obtained was named ‘oxygen rich GO sheets (fGO)’. The ZnOFe3O4 composites were thereafter grafted to the synthesized fGO, transforming them into the ZnOFe3O4@fGO composites. The ZnOFe3O4@fGO composites were thereafter planted into the polyamide thin film (PA-TFC) layer atop the surface of a porous support, viz interfacial polymerization. The physicochemical properties of the synthesized GO, Zinc oxide (ZnO), fZnOFe3O4, fZnOFe3O4@GO, and ZnOFe3O4f@GO composites were confirmed via various techniques, including Raman spectroscopy (RS), XRD, Brunauer–Emmett–Teller (BET), Fourier transform infrared (FTIR), Thermogravimetric analysis (TGA), Scanning electron microscope (SEM), Transmission Electron Microscope (TEM), Zeta potential (ZP), X-ray photoelectron spectroscopy (XPS) measurement, Diffuse reflectance spectroscopy (DRS), UV-visible spectroscopy (UV−vis), Fluorescence spectroscopy, Inductively coupled plasma-optical emission spectrometer (ICP-OES), and photocatalystis application. The synthesized membranes were characterized by: atomic force microscope (AFM), water contact angle (WCA), dead-end filtration (pure water flux, antifouling studies, and solute rejection, cross section (SEM), chlorine resistivity, and surface charge analysis (zeta potential). From the analysis, the FTIR and XPS molecular fingerprints were used to affirm the successful coupling of the fZnOFe3O4 nanoparticles (NPs) to the epoxy groups of the GO substrate. The DRS studies indicated a successful reduction in band gap energy of the fZnOFe3O4@GO (1.34 eV) composites compared to baseline materials (GO: 2.5eV, ZnO: 3.3eV, and fZnOFe3O4: 1.88eV), an indication that the optical band gap of GO can be improved
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without subjecting GO to high thermal or harsh chemical treatment. The photoluminescence studies indicated multiple light emission channels exist in the fZnOFe3O4 and fZnOFe3O4@GO composites within the UV and visible regions, this is not present in the GO. These characteristics make the modified nanocomposites suitable candidates for ultraviolet (UV) and visible light photocatalysis application. The fZnOFe3O4 and fZnOFe3O4@GO catalystts exhibited good adsorption and photo-degradation efficiency for methylene blue (MB) and Congo red (CR) under UV and visible light irradiation. When tested on real industrial textile wastewater (TWS), the fZnOFe3O4@GO catalystt showed improved photo-degradation efficiency compared to the fZnOFe3O4 catalystt. The PA-TFC membrane displayed a decrease in WCA values (less than 46%), improved antifouling properties with a flux recovery ratio of 84%, improved chlorine tolerance, and pure water flux when compared to the pristine PA-TFC membranes. In terms of general membrane performance, implanting the ZnOFe3O4@fGO composites into the PA-TFC layer amounted to a performance gain for the TFC membranes.