Graphene-based metal/metal sulphide nanocomposites: Fabrication, characterization and its applications / Amir Moradi Golsheikh

Golsheikh, Amir Moradi (2014) Graphene-based metal/metal sulphide nanocomposites: Fabrication, characterization and its applications / Amir Moradi Golsheikh. PhD thesis, University of Malaya.

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Abstract

Graphene, a one-atom-thick planar sheet of sp2-bonded carbon atoms, has attracted tremendous attention due to its unique electronic, mechanical, thermal, and optical properties. Graphene’s high electrical conductivity, large surface-to-volume ratio, and excellent chemical tolerance make it a distinguishable matrix for nanocomposites. Therefore, incorporation of graphene with inorganic materials such as metal, metal oxides and metal sulfides has been the focus of research in recent years for their multifunctional abilities. In order to obtain some graphene-based nanocomposites with controlling the morphology of composite and properties, several synthesis approaches have been designed and carried out. First, silver-nanoparticles-decorated reduced graphene oxide (rGO) have been electrodeposited on indium tin oxide (ITO) by a cyclic voltammetry method. It was established that the silver ammonia complex (Ag(NH3)2OH) was the key component to achieving well-distributed AgNPs with small and narrow size distribution decorated on reduced graphene sheets. The composite deposited on ITO exhibited notable electrocatalytic activity for the reduction of H2O2, leading to an enzymeless electrochemical sensor with a fast amperometric response time less than 2s. The corresponding calibration curve of the current response showed a linear detection range of 0.1 mM to 100 mM (with regression value of R2 = 0.9992) while the limit of detection was estimated to be 5 μM. Second, reduced graphene oxide (rGO) uniformly decorated with silver nanoparticles (AgNPs) have been synthesized through a simple ultrasonic irradiation of the aqueous solution containing silver ammonia complex (Ag(NH3)2OH) and graphene oxide (GO). The size of the nanoparticles could be tuned by adjusting the volume ratio of the precursors and the ultrasonic irradiation time. The average particle size of the silver with the narrowest size distribution was 4.57 nm. The prepared AgNPs-rGO modified glassy carbon electrode exhibited notable electrocatalytic activity toward the non-enzymatic detection of H2O2 with a wide linear range of 0.1–70 mM (R2= 0.9984) and a detection limit of 4.3 μM. Furthermore, the prepared AgNPs-rGO composite was employed for the spectral detection of Hg2+ ions and showed a detection limit of 20 nM. Third, the hydrothermal conditions such as reaction temperature, reaction time, pH of the solution and the amount of gelatin have been optimized for preparing FeS2 nanoparticles and subsequently the optimum hydrothermal conditions have been utilized for preparation of FeS2/graphene nanocomposites with different loading amount of graphene. At the optimum concentration of GO (1 mg/mL), a photocurrent intensity of about 1.01 μA is obtained, which is about 2.6 time higher than that obtained on the pure FeS2 electrode. Finally, reduced graphene oxide decorated with hierarchical ZnS nanoparticles have been synthesized by one-pot sonochemical method. The resultant composites have been characterized by x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), raman spectroscopy, field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and photoluminescence spectroscopy. A significant enhancement in the photocatalytic degradation of methylene blue (MB) was observed with ZnS/rGO nanocomposite as compared to that of the bare ZnS particles. It is worth to notice that all the samples were synthesized for the first time by the mentioned methods. The samples AgNPs/rGO/ITO, AgNPs/rGO and ZnS/rGO were prepared without using any reducing or stabilizing agents and FeS2/rGO was prepared for the first time by using gelatin as a nontoxic reducing and capping agent.

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