Evolution of graphene oxide (GO)-based nanohybrid materials with diverse compositions: an overview

The discovery of the 2D nanostructure of graphene was in fact the beginning of a new generation of materials. Graphene itself, its oxidized form graphene oxide (GO), the reduced form of GO (RGO) and their numerous composites are associates of this generation. Out of this spectrum of materials, the development of GO and related hybrid materials has been reviewed in the present article. GO can be functionalized with metals (Ag and Mg) and metal oxides (CuO, MgO, Fe₂O₃, Ag₂O, etc.) nanoparticles (NPs), organic ligands (chitosan and EDTA) and can also be dispersed in different polymeric matrices (PVA, PMMA, PPy, and PAn). All these combinations give rise to nanohybrid materials with improved functionality. An updated report on the chronological development of such nanohybrid materials of diverse nature has been delivered in the present context. Modifications in synthesis methodologies as well as performances and applications of individual materials are addressed accordingly. The functional properties of GO were synergistically modified by photoactive semiconductor NPs; as a result, the GO–MO hybrids acquired excellent photocatalytic ability and were able to degrade a large variety of organic dyes (MB, RhB, MO, MR, etc.) and pathogens. The large surface area of GO was successfully complemented by the NPs so that high and selective adsorption capacity towards metal ions and organic molecules as well as improved charge separation properties could be achieved. As a result, GO–MO hybrids have been considered effective materials in water purification, energy storage and antibacterial applications. GO–MO hybrids with magnetic particles have exhibited selective destruction of cancerous cells and controlled drug release properties, extremely important in the pharmaceutical field. Chitosan and EDTA-modified GO could form 3D network-like structures with strong efficiency in removing heavy metal ions and organic pollutants. GO as a filler enhanced the strength, flexibility and functional properties of common polymers, such as PVA and PVC, to a large extent while, GO–CP composites with polyaniline and polypyrrole are considered suitable for the fabrication of biosensors, supercapacitors, and MEMS as well as efficient photothermal therapy agents. In summary, GO-based hybrids with inorganic and organic counterparts have been designed, the unique properties of which are exploited in versatile fields of applications.

GO undergoes synergistic interaction with MO nanoparticles and the hybrid can be used as a heterogeneous catalyst for the photocatalytic degradation of dyes.

Facile synthesis of an Ag@AgBr nanoparticle-decorated K4Nb6O17 photocatalyst with improved photocatalytic properties

An Ag@AgBr nanoparticle-decorated K₄Nb₆O₁₇ (Ag@AgBr/K₄Nb₆O₁₇) photocatalyst was prepared via the oil-in-water self-assembly method. The Ag@AgBr nanoparticles, with average diameters of 20 nm, were uniformly deposited on the K₄Nb₆O₁₇ surface. The as-prepared Ag@AgBr/K₄Nb₆O₁₇ composites exhibited high visible light absorption, high photocurrent intensity, and high charge transfer efficiency, thus enhancing the photocatalytic performance for methyl-blue (MB) dye degradation. The Ag@AgBr (20 wt%)/K₄Nb₆O₁₇ composite displayed the highest photocatalytic activity, degrading 96% of the MB solution under visible light irradiation for 60 min, which was 2.3-times and 8.5-times that of the bulk Ag@AgBr and K₄Nb₆O₁₇, respectively. The excellent photocatalytic activity of the Ag@AgBr/K₄Nb₆O₁₇ composites is due to the synergistic effect between Ag@AgBr and K₄Nb₆O₁₇, where the Ag@AgBr nanoparticles not only enhanced visible light absorption efficiency due to the Ag nanoparticles' SPR, but also greatly accelerated the separation of the photogenerated electron–hole pairs. From the UV-vis spectra, the Ag@AgBr nanoparticles greatly extend the composites' visible light absorption. The data collected from photoluminescence (PL), photocurrent and electrochemical impedance spectra (EIS) were consistent and confirmed the rapid separation of charge carriers. Moreover, the composite exhibited a larger specific surface area, which was also beneficial for the photocatalytic activity. In addition, the roles of the radical species were investigated, and the holes and ·O₂⁻ radicals were hypothesized to dominate the photocatalytic process. Based on the characterization analysis and experimental results, a possible photocatalytic mechanism for the enhancement of photocatalytic activity is proposed.

The characteristic diffraction peaks of K₄Nb₆O₁₇ and AgBr were detected instead of Ag@AgBr.