M. Sookhakian

Effects of graphene oxide concentration on optical properties of ZnO/RGO nanocomposites and their application to photocurrent generation

The effects of different concentrations of graphene oxide (GO) on the structure and optical properties of ZnO nanoparticles (NPs) were investigated. The nanocomposites were synthesized via the sol-gel method in a gelatin medium. X-ray diffraction patterns (XRD) and Fourier transform infrared spectroscopy indicated that the GO sheets were reduced and changed to reduced GO (RGO) during the calcination of the nanocomposites at 400 °C. In addition, the XRD patterns of the NPs indicated a hexagonal (wurtzite) structure for all the products. Microscopic studies showed that the NPs were decorated and dispersed on the RGO sheets very well. However, these studies revealed that the RGO concentration had an effect on the crystal growth process for the ZnO NPs. Furthermore, these studies showed that the NPs could be grown with a single crystal quality in an optimum RGO concentration. According to the XRD results that were obtained from pure ZnO NPs, the calcinations temperature was decreased by the RGO. UV–vis and room temperature photoluminescence studies showed that the optical properties of the ZnO/RGO nanocomposite were affected by the RGO concentration. Finally, the obtained ZnO/RGO nanocomposite was used to generate a photocurrent. Observations showed that the photocurrent intensity of the nanocomposite was significantly increased by increasing the RGO, with an optimum RGO concentration.

Characterization of nickel-doped biphasic calcium phosphate/graphene nanoplatelet composites for biomedical application

The effect of the addition of an ionic dopant to calcium phosphates for biomedical applications requires specific research due to the essential roles played in such processes. In the present study, the mechanical and biological properties of Ni-doped hydroxyapatite (HA) and Ni-doped HA mixed with graphene nanoplatelets (GNPs) were evaluated. Ni (3wt.% and 6wt.%)-doped HA was synthesized using a continuous precipitation method and calcined at 900°C for 1h. The GNP (0.5-2wt.%)-reinforced 6% Ni-doped HA (Ni6) composite was prepared using rotary ball milling for 15h. The sintering process was performed using hot isostatic pressing at processing conditions of 1150°C and 160MPa with a 1-h holding time. The results indicated that the phase compositions and structural features of the products were noticeably affected by the Ni and GNPs. The mechanical properties of Ni6 and 1.5Ni6 were increased by 55% and 75% in hardness, 59% and 163% in fracture toughness and 120% and 85% in elastic modulus compared with monolithic HA, respectively. The in-vitro biological behavior was investigated using h-FOB osteoblast cells in 1, 3 and 5days of culture. Based on the osteoblast results, the cytotoxicity of the products was indeed affected by the Ni doping. In addition, the effect of GNPs on the growth and proliferation of osteoblast cells was investigated in Ni6 composites containing different ratios of GNPs, where 1.5wt.% was the optimum value.

Spongy nitrogen-doped activated carbonaceous hybrid derived from biomass material/graphene oxide for supercapacitor electrodes

Carbon derived from low cost agricultural waste material was used as a precursor for the preparation of a spongy-like nitrogen doped activated composite from carbon/graphene oxide via a one-step thermal treatment. N-doping and activation of the carbon/graphene oxide mixture were achieved simultaneously by the treatment of urea and potassium hydroxide at 800 °C. The nitrogen content and ratio between the nitrogen species was controlled by the mass ratio of KOH : carbon. The composite was prepared with a KOH : carbon ratio of 1 which resulted in a moderate surface area (1712.4 m2 g−1) and a high nitrogen content (14.51%). The hybrid material gave high specific capacitance (267 F g−1 at 5 mV s−1) and good cycling stability (92.3% capacitance retention after 5000 cycles) in 6 M KOH electrolyte. Hence, the new composite presented in this work can be used as an advanced material for supercapacitor applications.

Synthesis and characterization of Co3O4 ultra-nanosheets and Co3O4 ultra-nanosheet-Ni(OH)2 as non-enzymatic electrochemical sensors for glucose detection.

The present study examines the synthesis of Co3O4 ultra-nanosheets (Co3O4 UNSs) and Co3O4 ultra-nanosheet-Ni(OH)2 (Co3O4 UNS-Ni(OH)2) via solvothermal process and their application as non-enzymatic electrochemical sensors for glucose detection. X-ray diffraction and transmission electron microscopy results confirmed the Co3O4 UNS deposition on Ni(OH)2 surface. The presence of Co3O4 UNSs on Ni (OH) 2 surface improved the sensitivity of glucose detection, from the increase of glucose oxidation peak current at the Co3O4 UNS-Ni(OH)2/glassy carbon electrode (current density: 2000μA·cm(-2)), compared to the Co3O4 UNSs. These results confirmed that Ni(OH)2 on glassy carbon electrode is a sensitive material for glucose detection, moreover the Co3O4 UNSs can increase the interaction and detection of glucose due to their high surface area. The estimated limit of detection (S/N=3) and limit of quantification (S/N=10) of the linear segment (5-40μM) are 1.08μM and 3.60μM respectively. The reproducibility experiments confirmed the feasibility of Co3O4 UNS-Ni(OH)2 for the quantitative detection of certain concentration ranges of glucose.

Solid-phase electrochemical reduction of graphene oxide films in alkaline solution

Graphene oxide (GO) film was evaporated onto graphite and used as an electrode to produce electrochemically reduced graphene oxide (ERGO) films by electrochemical reduction in 6 M KOH solution through voltammetric cycling. Fourier transformed infrared and Raman spectroscopy confirmed the presence of ERGO. Electrochemical impedance spectroscopy characterization of ERGO and GO films in ferrocyanide/ferricyanide redox couple with 0.1 M KCl supporting electrolyte gave results that are in accordance with previous reports. Based on the EIS results, ERGO shows higher capacitance and lower charge transfer resistance compared to GO.

Graphene oxide electrocatalyst on MnO2 air cathode as an efficient electron pump for enhanced oxygen reduction in alkaline solution

Graphene oxide (GO) was deposited on the surface of a MnO2 air cathode by thermal evaporation at 50°C from a GO colloidal suspension. Fourier transformed infrared spectroscopy and field emission scanning electron microscopy confirmed the presence of GO on the MnO2 air cathode (GO-MnO2). Voltammetry and chrono-amperometry showed increased currents for the oxygen reduction reaction (ORR) in 6 M KOH solution for GO-MnO2 compared to the MnO2 cathode. The GO-MnO2 was used as an air cathode in an alkaline tin-air cell and produced a maximum power density of 13 mW cm−2, in contrast to MnO2, which produced a maximum power density of 9.2 mW cm−2. The electrochemical impedance spectroscopy results suggest that the chemical step for the ORR is the rate determining step, as proposed earlier by different researchers. It is suggested that the presence of GO and electrochemically reduced graphene oxide (ERGO) on the MnO2 surface are responsible for the increased rate of this step, whereby GO and ERGO accelerate the process of electron donation to the MnO2 and to adsorbed oxygen atoms.

Crystalline quality assessment, photocurrent response and optical properties of reduced graphene oxide uniformly decorated zinc oxide nanoparticles based on the graphene oxide concentration

Zinc oxide-nanoparticles (ZnONPs)–reduced graphene oxide (rGO) composites with a high degree of crystallinity and a high dispersity were successfully synthesized via a one-pot, facile sol–gel method in a starch environment, during which the formation of zinc oxide nanoparticles, the reduction of graphene oxide and the loading of the ZnONPs onto the rGO surface occur simultaneously. Starch, as a natural capping agent, plays a significant role in controlling the degree of dispersion and coverage of the ZnONPs. The effect of rGO on the crystalline structure and optical properties of the ZnONPs was determined via X-ray diffraction, UV-visible diffused reflectance spectroscopy and photoluminescence spectroscopy. The ZnONPs+rGO composites exhibit excellent potential for photocurrent generation compared with pure ZnONPs under visible light irradiation, provided that efficient photo-induced charge separation and transportation can be achieved at the interface. The maximum photocurrent response, crystalline quality and factor optical properties (NBE/DLE ratio) were obtained for the ZnONPs+rGO composite with a 1.7% mass fraction of rGO, which is twice that achieved on pure ZnONPs.

The synthesis and characterization of a hexanuclear copper yttrium complex for deposition of semiconducting CuYO2 0.5Cu2O composite thin films

The copper–yttrium hexanuclear complex [Cu4Y2(dmae)6(OAc)7.85(OH)0.15(H2O)2]·2CH3C6H5 (1) (where dmae = dimethylaminoethanoato, OAc = acetato) has been synthesized and characterized by its melting point, elemental analysis, and FT-IR, thermogravimetric/differential thermogravimetric (TG/DTG) and single crystal X-ray diffraction analyses. The complex crystallizes in the triclinic space group P with cell parameters a = 9.4934(3) A, b = 13.2045(4) A, c = 14.6990(5) A, α = 76.486(2)°, β = 85.811(2)° and γ = 83.394(2)°. A thin film of a CuYO2–0.5Cu2O composite has been deposited on a FTO glass substrate by implementation of the complex (1) at 400 °C under an argon atmosphere via aerosol assisted chemical vapour deposition (AACVD). XRPD, SEM and EDX analyses reveal the formation of impurity-free crystalline mixtures of the CuYO2–0.5Cu2O composite with well-defined evenly distributed rods of Cu2O in the size range of 0.85–1.05 μm and granules of CuYO2 in the size range of 110–125 nm. UV-Vis spectrophotometric measurements and photoelectrochemical (PEC) results show an optical band gap energy of 2.6 eV and a photocurrent density of 81 μA cm−2 under illumination using a 150 W halogen lamp at a potential of 1.0 V vs. SCE.