A comparative study of hydrogels based on GO-Cu composites for potential applications in water treatment

Abstract

In this study, hydrogels composed of self-assembled graphene oxide (GOH) sheets reinforced with copper particles (Cu-GOH) were synthesized via hydrothermal treatment of a graphene oxide (GO) solution. The metallic copper particles (CuP) were obtained by a green method using a plant extract as reducing agent (Spinacia oleracea). Scanning electron microscopy (SEM) characterization revealed a porous structure in both GOH and Cu-GOH, with effective integration of CuP into the Cu-GOH structure. Energy-dispersive X-ray spectroscopy (EDS) confirmed the presence of C, O, and Cu as primary elements, while X-ray diffraction (XRD) patterns indicated slight oxidation of CuP after the hydrothermal reaction (17 wt% of Cu2O), evidenced by weak Cu2O diffraction peaks. X-ray photoelectron spectroscopy (XPS) analysis indicated a mean chemical reduction in GOHs and Cu-GOHs compared to GO, resulting in alterations in the composition of oxygenated functional groups. Specifically, there were mean reductions in the C–OH/C–O (87%), C=O (68%), and COOH/COO– (72%) bonds. Ultraviolet–visible (UV–Vis) spectroscopy assessed the methylene blue (MB) adsorption capacity and performance of the GOH and Cu-GOH samples, while water loading/unloading cycles evaluated the hydrogels’ resistance. Cu-GOH composites demonstrated enhanced resistance to water loading/unloading cycles compared to GOH, enduring more cycles before structural disintegration. Regarding MB adsorption, Cu50 and Cu100-GOH samples reached a removal rate of 95% within the studied time range, whereas GOH only absorbed around 85% in the same time, highlighting the beneficial role of CuP inclusion in the GOH structure and achieved complete removal of MB from water (95%) within the studied time range, whereas GOH absorbed approximately 85% of MB, highlighting the beneficial role of CuP inclusion in the GOH structure.