Graphene, an atomically thin two-dimensional carbonaceous material, has attracted tremendous attention in the scientific community, due to its exceptional electronic, electrical, and mechanical properties. Indeed, with the recent explosion of methods for a large-scale synthesis of graphene, the number of publications related to graphene and other graphene based materials has increased exponentially. Particularly the development of easy preparation methods for graphene like materials, such as highly reduced graphene oxide (HRG) via reduction of graphite oxide (GO), offers a wide range of possibilities for the preparation of graphene based inorganic nanocomposites by the incorporation of various functional nanomaterials for a variety of applications. In this review, we discuss the current development of graphene based metal and metal oxide nanocomposites, with a detailed account of their synthesis and properties. Specifically, much attention has been given to their wide range of applications in various fields, including electronics, electrochemical and electrical fields. Overall, by the inclusion of various references, this review covers in detail the aspects of graphene-based inorganic nanocomposites.

Plant-mediated green synthesis of nanomaterials has been increasingly gaining popularity due to its eco-friendly nature and cost-effectiveness. In the present study, we synthesized silver nanoparticles (AgNPs) by using an aqueous solution of Saudi Origanum vulgare L. plant extract as a bioreducing agent. The as-synthesized AgNPs were characterized using various microscopic and spectroscopic techniques. The results indicated the formation of crystalline face-centered cubic (fcc) AgNPs. Additionally, FT-IR study confirmed that the O. vulgare L. extract not only functioned as a bioreductant but also stabilized the surface of the AgNPs by acting as a capping agent. Moreover, the effect of the amount of the plant extract on the size and the antimicrobial activity of the NPs was also assessed. It was found that with increasing amounts of plant extract, the size of the NPs was decreased. Moreover, as-synthesized AgNPs as well as O. vulgare L. plant extract were separately tested to examine their antimicrobial activities. The activities were tested against various bacterial and fungal microorganisms including Shigella sonnei, Micrococcus luteus, Escherichia coli, Aspergillus flavus, Alternaria alternate, Paecilomyces variotii, Phialophora alba, and so on. These results evidently show that the inclusion of O. vulgare L. extracts improves the solubility of AgNPs, which led to a significant enhancement in the toxicity of the NPs against the assessed microorganisms.

Recently, green reduction of graphene oxide (GRO) using various natural materials, including plant extracts, has drawn significant attention among the scientific community. These methods are sustainable, low cost, and are more environmentally friendly than other standard methods of reduction. Herein, we report a facile and eco-friendly method for the bioreduction of GRO usingSalvadora persicaL. (S. persicaL.) roots (miswak) extract as a bioreductant. The as-prepared highly reduced graphene oxide (SP-HRG) was characterized using powder X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron (XPS) spectroscopy, and transmission electron microscopy (TEM). Various results have confirmed that the biomolecules present in the root extract of miswak not only act as a bioreductant but also functionalize the surface of SP-HRG by acting as a capping ligand to stabilize it in water and other solvents. The dispersion quality of SP-HRG in deionized water was investigated in detail by preparing different samples of SP-HRG with increasing concentration of root extract. Furthermore, the dispersibility of SP-HRG was also compared with chemically reduced graphene oxide (CRG). The developed eco-friendly method for the reduction of GRO could provide a better substitute for a large-scale production of dispersant-free graphene and graphene-based materials for various applications in both technological and biological fields such as electronics, nanomedicine, and bionic materials.

The synthesis of Palladium (Pd) nanoparticles by green methods has attracted remarkable attention in recent years because of its superiority above chemical approaches, owing to its low cost and ecological compatibility. In this present work, we describe a facile and environmentally friendly synthesis of Pd nanoparticles (Pd NPs) using an aqueous extract of aerial parts of Origanum vulgare L. (OV) as a bioreductant. This plant is available in many parts of the world as well as in Saudi Arabia and is known to be a rich source of phenolic components, a feature we fruitfully utilized in the synthesis of Pd NPs, using various concentrations of plant extracts. Moreover, the OV extract phytomolecules are not only accountable for the reduction and progression of nanoparticles, but they also act as stabilizing agents, which was confirmed by several characterization methods. The as-synthesized Pd nanoparticles (Pd NPs) were analyzed using ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and thermal gravimetric analysis (TGA). Further, FT-IR study has proven that the OV not merely represents a bioreductant but also functionalizes the nanoparticles. Furthermore, the green synthesized metallic Pd NPs were successfully applied as catalysts for selective oxidation of alcohols.

Water contamination by organic pollutants is a major problem. Secbumeton herbicide is a toxic pollutant and contaminates our water resources. Composite nanoadsorbent was prepared, characterized, and used for the removal of secbumeton from water by adsorption process. Secbumeton in water was analyzed by GC–MS under validated conditions. The optimized adsorption parameters were 30.0 μg/L concentration, contact time 30.0 min, pH 7.0, dose 2.5 g/L, and temperature 20.0°C, with 90% as removal capacity. The adsorbent was selective with respect to secbumeton. The results followed Langmuir, Freundlich, and Temkin models. The values of thermodynamic parameter i.e. ΔG° were −5.89, −5.81, and −5.71 kJ/mol at 20, 25, and 30°C temperatures. The value of ΔH° was −11.08 kJ/mol, indicating exothermic nature of adsorption. ΔS° value was −1.78 × 10⁻² kJ/mol K; an indication of entropy decrease during adsorption. Kinetic modeling showed pseudo-second-order and liquid film diffusion mechanisms. The developed adsorption method was fast, eco-friendly, and economic as may be used at pHs of natural water bodies with low contact time and dose. This method may be used for the removal of secbumeton from any water body at large scale economically.

Palladium (Pd), a noble metal, has unique properties for C-C bond formation in reactions such as the Suzuki and Heck reactions. Besides Pd-based complexes, Pd NPs have also attracted significant attention for applications such as fuel cells, hydrogen storage, and sensors for gases such as H₂ and non-enzymatic glucose, including catalysis. Additionally, Pd NPs are catalysts in environmental treatment to abstract organic and heavy-metal pollutants such as Cr (VI) by converting them to Cr(III). In terms of biological activity, Pd NPs were found to be active against Staphylococcus aureus and Escherichia coli, where 99.99% of bacteria were destroyed, while PVP-Pd NPs displayed anticancer activity against human breast cancer MCF7. Hence, in this review, we attempted to cover recent progress in the various applications of Pd NPs with emphasis on their application as sensors and catalysts for energy-related and other applications.