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CuO-reduced graphene oxide (rGO) composite is the potential candidate in the fields of optoelectronics and sensor applications. In the present work, we synthesized CuO nanosheets-rGO composites (CG) by a simple room-temperature preparation method. The prepared composites were named as CG1 (without any surfactant), CG2 (with polyethyleneglycol-400), and CG3 (polyvinylpyrrolidone). The equal intensity of (002,111)/(200,111) patterns in XRD (monoclinic CuO), double absorption peaks in UV–Vis spectra at 263 nm and 294 nm, and the FE-SEM images are evidenced for the sheet-like morphology of CuO. The FT-IR bands appeared at 547 and 596 cm−1 for the Cu–O vibrations. Micro-Raman studies also evidenced the formation of CuO-rGO structures. CG3 has larger sheets compared to others due to the interaction of long-chain PVP with rGO as well as CuO. The peak at 933.5 eV in XPS spectrum of CG1 confirms the presence of CuO in the sample.

Three different ionic liquids based on 1-butyl-3-methylimidazolium were prepared and used to synthesize Ag/AgX (X = Cl, Br, & F) nanoparticles-decorated reduced graphene oxide (rGO). The formation of the Ag/AgX-rGO composites were confirmed from the powder XRD patterns of the samples and the absorption peaks at 220 nm, 280 nm, and 352 nm in UV–visible spectroscopy. The functional groups in rGO and decoration of Ag/AgX on rGO sheets were established by the peaks in FT-IR at 1192 cm−1, 1270 cm−1, and 1569 cm−1. The ID/IG ratios in micro-Raman analysis, and FE-SEM images witness the above observation. The endothermic peak at 956 °C in DSC analysis indicates the presence of silver in the samples. The natural visible light photocatalytic properties of these materials were studied with the degradation of methylene blue (MB) dye. The samples with Ag/AgX structures have better photocatalytic properties than AgX and rGO. This is due to the increased utilization of sunlight by the plasmonic Ag in the Ag/AgX-rGO samples and the fast charge separation by rGO. The samples GIA1 and GIA3 are showing better dye degradation efficiency, these samples degrade 97% and 97.5% of MB dye, respectively. The formation of AgX was dependent on the type of ionic liquids used in the synthesis which is highly reflected in the photocatalytic behavior.

Physical properties of graphene-related materials can be tuned by doing chemical modifications in its structure through covalent and non-covalent functionalization. Covalent functionalization of ionic salts on rGO structures changes it’s optical and electronic properties. In this work, pyrrolidone and imidazolium-based ionic liquids namely N-methyl-2-pyrrolidone hydrogensulfate (H-NMP+.HSO4ˉ), 1-butyl-3-methyl imidazoliumtetrafluoroborate (BMIM BF4), 1-butyl-3-methyl imidazoliumtrifluoroacetate (BMIM TFA) and 1-butyl-3-methyl imidazoliummethylsulfate (BMIM MeSO4) were covalently functionalized on reduced graphene oxide through microwave assisted process. Presence of (002) peak in the XRD pattern indicates the reduction of GO and fluorination of rGO prepared by functionalzation with BMIM BF4 was confirmed by a peak (001) appeared at 2θ of 12.73⁰. Red shift of π-π* and blue shift of n-π* transitions in UV-Vis spectrum were due to chemical modification in rGO sheets through IL functionalization. The peaks corresponding to IL were observed in FTIR spectra of synthesized samples. The increase in ID/IG ratio in micro-Raman analysis shows more sp3 bonds were formed during IL functionalization.