Iranian Journal of Materials Science and Engineering

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In this paper we have investigated the physical properties of reduced graphene oxide (RGO) thin films prepared at various substrate temperatures of 230, 260, 290, 320 and 350 ^oC using spray pyrolysis technique. We have compared these films from various viewpoints, including structural, morphological, optical, electrical and thermos-electrical properties. XRD analysis showed a phase shift from graphene oxide (GO) to RGO due to elevate the substrate temperature from 200 ^oC to higher temperatures. FESEM images of RGO thin films reveal that a stacked image of irregular and folding nanosheets, and rod-like features at temperatures below and above 290 ^oC; respectively. Optical studies showed that the layers have a relatively high absorption coefficient (∼0.8×10⁴ to 1.7×10⁴ cm⁻¹) in the visible range, with an optical band gap of 1.67–1.88 eV. The Hall effect data showed that all samples have a p-type conductivity with a hole concentration of ∼10¹⁵ cm⁻³, and sheet resistance values of about 10⁶ Ω/sq, in agreement with previous reports. The thermoelectric measurements revealed that with increasing applied temperature gradient between the two ends of the samples, the thermoelectric electromotive force (emf) of the prepared RGO thin films increases.

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The graphene oxide -TiO₂ (GO-TiO₂) and pre-reduced graphene oxide -TiO₂ (rGO-TiO₂) nanocomposites were fabricated successfully by hydrothermal method. The microstructure of synthesized nanocomposites was investigated using field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS) analysis. Moreover, galvanostatic charge/discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) methods in three electrode system were applied to evaluate electrochemical properties. The results revealed that nanoparticles distributed more uniformly on graphene sheets, at lower concentrations of TiO₂. The rGO-TiO₂ and GO-TiO₂ nanocomposites showed 224 and 32 F/g specific capacitance at 5 mV s^-1 scan rate in 1 M KOH aqueous electrolyte, respectively. The pre-reduction of graphene oxide is the main reason for the better electrochemical performance of rGO-TiO₂ nanocomposite compared to GO-TiO₂ nanocomposite.

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Researchers have increasingly investigated hybrid nanocomposites that mix physical and chemical properties of carbonaceous materials and metal/metal oxides. In this work, a nanocomposite composed of reduced graphene oxide and silver (I) oxide, rGO@Ag₂O, was prepared using ascorbic acid as a green reducing agent. The Ag₂O nanoparticles were synthesized by means of a controlled precipitation process in water. The carbonaceous material of rGO was obtained through a modified Hummers' approach. After being combined with a solvent, the Ag₂O and rGO in ethanol were dried with heat. The resultant nanocomposite was structurally and optically examined using different characterization techniques.  
The results showed that GO has been successfully reduced, Ag₂O revealed a crystalline structure, and Ag₂O nanostructures were found on the surface of rGO sheets. Disk diffusion assay was adopted in order to evaluate antibacterial activity of nanocomposite against both Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) bacteria. The Ag₂O nanostructures in the composite form exhibited inhibition zone with higher diameter compared to their uncomposited counterparts. Higher antibacterial activity of rGO@Ag₂O was attributed to the role of negatively charged oxygen-containing groups present on the surface of rGO in slightly improvement in the stability of Ag₂O nanostructures.
Our findings show that rGO@Ag₂O could be a useful antimicrobial material for biomedical surfaces, as a coating, and in systems that clean water. It could be a good option for future research in nano-enabled antimicrobial technology because it can destroy bacteria, is made in an environmentally benign way, and could be made on a larger scale.