Preparation Of Graphene / Inorganic Nanocomposites And Its Application In Catalytic Sensing

Carbon nanomaterials regarded as important materials in the21th century is a significant research branch of nanomaterials. Carbon nanomaterials consist of fullerene, carbon nanotube, diamond, graphite and graphene. Graphene, is a new-style two-dimensional (2D) crystal, composed of a planar single sheet with sp2-bonded carbon atoms arranged in honeycomb lattice. Its basal structural unit with six-membered benzene rings is stablest in the organic materials. Graphene is an ideal2D nanomaterial. Because of its large specific surface area, excellent and unique mechanical, electronic, thermal, optical properties and its quantum hall effect, graphene recently has been become the hot research topic in chemical and biological sensor, new catalyst, supercapacitor, lithium battery, solar cell, etc.Graphene/inorganic nanocomposites with different structures can be formed by many synthesis methods, which consist of in-situ and ex-situ techniques. In situ approach includes solution chemical reduction, electrochemical deposition, sol-gel procession, hydrothermal/solvothermal method, gas-phase deposition. Graphene/inorganic nanocomposites can not only keep the characteristics of graphene and inorganic nanomaterials, but also strongly enhance their intrinsic properties, which widens the applications of graphene or inorganic nanomaterials in the catalysis, sensing, energy storage and transfer. In this thesis, graphene oxide used as precursor or3D graphene prepared by chemical vapor deposition as growth template, we synthesized reduced graphene oxide/Ag nanoparticles nanocomposite (RGO/Ag NPs), reduced graphene oxide/TiO2nanoclusters nanocomposite (RGO/TiO2NCs), reduced graphene oxide/branched platinum nanowires (RGO/BPtNW),3D graphene/platinum nanoflowers (3DG/PtNF) with microwave hydrothermal method, microwave and two-phase method, low-temperature solution chemical reduction method. The formed graphene/inorganic nanocomposites were applied in the direct methanol electrochemical oxidation and glucose sensing. The main research contents are as follows:1. A facile wet-chemical approach for the synthesis of branched platinum nanowires (BPtNW) on reduced graphene oxide (RGO) was demonstrated. Formic acid (HCOOH) was used as the reductant for preparing BPtNW and synchronously reducing graphene oxide (GO) under the catalysis of the as-prepared BPtNW. The whole synthetic procedure was carried out easily in one pot under room temperature without any surfactant. The BPtNW/RGO hybrids exhibit higher electrocatalytic activity and stability towards the methanol oxidation reaction than commercial Pt/C catalysts (Hispec4000). The specific methanol oxidation reaction (MOR) activity of the BPtNW/RGO hybrids was1.154mA cm-2at0.700V, which was nearly3.94times higher specific activity than that of Pt/C (Hispec4000).2. Three-dimensional (3D) graphene foam was synthesized throught chemical vapor deposition using nickel foam as the template and ethanol as precursor, Then highly dispersive platinum nanoflowers were prepared uniformly on the3D graphene as growing template by the aqueous-phase method. The as-prepared3D graphene/platinum nanoflowers nanocomposites (3D-graphene/PtNF) were used as electrochemical catalyst for electrooxidation of methanol, which shows better electrochemical catalytic property than commercial40%Pt/C catalyst (Hispec4000). The peak current density of methanol electrooxidation on the3D-graphene/PtNF is0.641mA cm-2, which is higher than that of Pt/C catalyst (Hispec4000)(0.293mA cm-2). The If/Ib ratio for3D-graphene/PtNF is about1.10, which is higher than the If/Ib ratio of commercial Pt/C (Hispec4000), suggesting that3D-graphene/PtNF generates a more complete oxidation of methanol to carbon dioxide and have a superior tolerance to CO and other carbonaceous species. Amperometric experiment confirms that3D-graphene/PtNF has better electrocatalytic stability in the oxidation of methanol than Pt/C catalyst (Hispec4000).3. Reduced graphene oxide/PAMAM-silver nanoparticles nanocomposite (RGO-PAMAM-Ag) was synthesized successfully by self-assembly of carboxyl-terminated PAMAM dendrimer (PAMAM-G3.5) on graphene oxide (GO) as growing template, and in-situ reduction of both AgNO3and GO under microwave irradiation. RGO-PAMAM-Ag nanocomposite was used to modify glassy carbon electrode (GCE), which provided a good microenvironment for immobilizing glucose oxidase (GOD) and keeping the bioactivity of GOD. The modified GCE exhibited excellent direct electron transfer (DET) properties for GOD with the DET rate constant (Ks) of8.59s-1. The fabricated glucose biosensor based on GOD electrode modified with RGO-PAMAM-Ag nanocomposite displayed satisfactory analytical performance including an acceptable linear range (0.032-1.89mM), high sensitivity (75.72μA mM-1cm2), low detection limit (4.5μM), and also preventing the effect of some interfering species usually coexisted with glucose in human blood at the work potential of-0.25V. These results indicated that RGO-PAMAM-Ag nanocomposite could act as a promising candidate material for the development of the third-generation glucose biosensor.4. Highly dispersive titanium dioxide nanocluster (TDN) was synthesized successfully on reduced graphene oxide (RGO) in a toluene-water system under microwave irradiation. The as-prepared RGO/TDN nanocomposite was used to modify glassy carbon electrode (GCE) for loading glucose oxidase (GOD) and constructing the glucose biosensor. RGO/TDN nanocomposite is biocompatible with GOD and can efficiently keep the catalytic activity of GOD. Michaelis-Menten constant (Km) is0.81mM. The fabricated glucose biosensor exhibits excellent performance for glucose sensing including lower work potential (-0.7V), high sensitivity (35.8μA mM-1cm-2), low detection limit (4.8μM), wide linear range from0.032mM to1.67mM.