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Herein, we report a green synthetic strategy for the preparation of ZnO@rGO nanocomposites. Bioinspired synthesis of ZnO nanoarchitectures has been done using a series of biotemplates such as dextrose, sucrose, soluble starch, and carboxy methyl cellulose. The as-prepared morphologically tuned ZnO nanoarchitectures are homogeneously distributed over the surface of rGO sheets, resulting in the formation of ZnO@rGO nanocomposites. For the first time, zinc (Zn) dust, a waste byproduct from industry (Binani Zinc Limited, Kerala, India), is employed for the chemical reduction of GO. ZnO@rGO nanocomposite based nonenzymatic urea and glucose sensors have been developed over a glassy carbon electrode, and the electrochemical performance of the nanocomposite for the detection of urea and glucose are investigated. The biosensor electrode is sensitive to urea in the concentration range of 0.02 × 10−3 mM to 7.2 × 10−3 mM with a detection limit of 0.012 μM. When used for glucose detection, the linear range is 0.02 × 10−3 mM to 18 × 10−3 mM, with a detection limit of 0.008 μM. The developed sensor exhibits an ultra-high sensitivity of 682.8 μA mM−1 cm−2 towards urea and 481 μA mM−1 cm−2 towards glucose.

This study investigated the role of poly-ethylene glycol (PEG) in the microwave synthesis of ZnO (ZPMx) nanorods. The molecular weight of PEG was found to strongly influence the aspect ratio of the synthesized material. The as-prepared ZPMx nanorods were post-grafted onto the surface of GO sheets using 3-amino propyl trimethoxy silane (APTMS) as a cross-linking agent to obtain ZPMx-Si@GO hybrid nanocomposites. Microscopic observations showed that ZPMx nanorods with different aspect ratios were evenly distributed on the surface of the GO sheets. It also showed enhanced thermal and chemical properties. The dependence of the antibacterial behavior on the aspect ratio of the ZPMx nanorods and GO was also investigated. An antibacterial assay was carried out using both the Gram-positive bacteria Staphylococcus aureus (S. aureus) and Gram-negative bacteria Escherichia coli (E. coli), and Klebsiella pneumonia (K. pneumonia). The results showed that the ZPMx-Si@GO hybrid nanocomposite had an excellent antibacterial property toward the test bacteria compared to pure ZPMx and GO. The synergistic effect of ZPMx and GO resulted in a superior antibacterial activity in ZPMx-Si@GO. Interestingly, the hybrid nanocomposite with a higher ZPMx aspect ratio (ZPM6000-Si@GO) showed excellent inhibition zones with diameters of ∼3.7, 3.1, and 2.4 cm corresponding to S. aureus, E. coli, and K. pneumonia, respectively. An optical density measurement, as well as the morphological changes in the bacteria, again confirmed the excellent bacterial growth inhibition of ZPM6000-Si@GO. The studies indicated that the ZPMx-Si@GO hybrid nanocomposite is a promising candidate for use in real waste-water disinfection.

Exfoliated graphene oxide (GO) is catalytically activated via in situ growth of nanocrystalline ZnO crosslinked with 3-aminopropyltrimethoxy silane (APTMS) to result in ZnO/Si@rGO hybrid nanocomposite architectures. Structural and morphological features are systematically ascertained using XRD, SEM, TEM, TGA, UV-vis, FTIR and BET techniques. ZnO/Si@rGO hybrid nanocomposites exhibit a high surface area (78 m2 g−1). It is significantly large compared to phase pure nano-ZnO where the surface area is only 18 m2 g−1. Hybrid nanocomposite also shows ∼55% photocatalytic activity and ∼59% adsorption of dye from aqueous system containing 340 μM methylene blue (MB) dye. It was compared with pure ZnO, which shows only ∼0% adsorption and ∼31% photocatalytic activity. In the similar way, ZnO@rGO nanocomposites in the absence of a crosslinking agent were prepared and characterized. The adsorption and photocatalytic degradation property of both ZnO@rGO and ZnO/Si@rGO against the adsorption and photodegradation of a series of cationic organic dyes were compared for the first time. Interestingly, when ZnO/Si@rGO hybrid nanocomposite is deposited onto the surface of a cotton textile, it showed an excellent hydrophobic surface with a contact angle of 113.7°. Cotton textile modified with hybrid nanocomposite was explored further for the selective pick-up of engine oil contaminants from the aqueous media. The combined properties of dye adsorption, photodegradation and oil sorption properties of ZnO/Si@rGO hybrid nanocomposite enable the design of novel self-regenerative catalytically active cotton textile filters. A facile UV bleaching retrieves the cotton substrate for continuous use. In addition to this, ZnO–rGO composites were also prepared by a physical blending method and compared with ZnO/Si@rGO hybrid nanocomposite and ZnO@rGO nanocomposite.