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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.

Metal to bulk metal oxide nanoparticles have been successfully processed via a sustainable, facile, and ecofriendly (green) approach, namely, aqueous mechanical-oxidation. Micron-sized zinc (Zn) dust (∼45 μm) was directly wet-milled using ceramic milling media for 72 h, resulting in the production of bulk monocrystalline ZnO nanorods (aspect ratio ∼5.2, hydrodynamic diameter of 315 nm) and voluminous H2 gas by catalyst-free water-splitting reaction. The mill-induced surface oxidation and the chemical purity of the synthesized nano ZnO were carefully studied using the XPS analysis. Other standard analytical tools were also employed to understand the crystallinity, phase purity, morphology, and surface area of the final artifact. The photocatalytic activities of these mechanically grown ZnO nanorods were ascertained from two cationic dye-degradation experiments, using the dyes methylene blue and rhodamine 6G. In a nutshell, the study throws a new insight into a cost-effective, zero-effluent, single-step, an...

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.

Photoactive zinc based nanoplates were developed through a rapid microwave synthesis. A low temperature thermolysis reaction in a surfactant medium was initially performed for producing microwave active zinc based polar precursors. Using these precursors, the zinc oxide nanopowder having platelet morphologies were prepared. The nanoplatelets exhibited random growth with non-polar (1 0 1) surface as the major growth plane. The structural and functional features of the resultant zinc oxide samples were monitored using XRD, FTIR, TEM and PL. The photocatalytic activities of the samples were investigated through the standard photoreduction kinetics using the methylene blue dye. The catalytic efficiencies of the samples were checked both under UV and sunlight. A comparative study was also performed with the standard TiO 2 sample. The analyses revealed that the microwave derived zinc oxide have higher catalytic efficiency, than the standard titania samples, both under UV and sunlight illuminations. The unique nature of the zinc oxide non-polar surfaces can be attributed due to the presence of more active two dimensional open surfaces and the higher content of oxygen defect concentrations.

A facile aqueous synthesis has been reported for the preparation of organosilane treated ZnO nano architectures (Si@ZnO) via microwave strategy. An in-situ addition of 3-aminopropyl trimethoxy silane (APTMS) resulted in the formation of polysiloxane network that effectively controlled the exaggerated growth of ZnO finally produced high surface area, mesoporous Si@ZnO nano clusters. The formation of a polysiloxane network was confirmed from the FTIR analysis. Reduction in the crystallite size was verified from the powder X-ray diffraction and TEM analyses. Silane treated ZnO shows highly stable dispersion, in aqueous medium. The quantum confinement effect of size controlled Si@ZnO was confirmed from the blue shift in UV–vis absorption spectra. As a function of APTMS concentration both surface charge and surface area was found to enhance from (−12) to (+35.5) mV and 18 to 80 m2 g−1, respectively. Such positively charged Si@ZnO nano architectures showed property highly receptive to anionic dyes for the adsorption as well as photodegradation. In this study, size controlled, surface engineered, dual-functional photoactive adsorbent is successfully designed which is potentially useful for the recovery and recycling of dye contaminated water.

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.