Preparation, Characterization And Electrocatalysis Application For Multimorphology Silver Composite

Nanocomposites with superior properties have attracted various researchers’ attention. Nanosilver modified electrodes can highly improve the efficiency of the electron transfer, catalytic properties, the sensitivity and selectivity of electrochemical analysis. The catalytic activity of silver relies on its different shape and size. In the work, different materials with high catalyzing activity and good stability were synthesized. The nanocomposites were used to detect analyte and the mechanism of catalytic oxidation was discussed deeply. This research work mainly includes the following three contents:1. The thin graphene oxide which dispersed well in water was synthesised by improved Hummers method. Graphene can accelerate the electron transfer and also anchor nanosilver material. Hexagonal Ag nanoplates (NPs,～36nm) were synthesized by polyvinylpyrrolidone (PVP) and trisodium citrate (TSC) which selectively absorbed to Ag (100) and Ag (111) surfaces, and then were anchored to graphene (GN) to form novel Ag NPs/GN composite. The Ag NPs/GN can not only prevent the stack of graphene, also make the composite with better catalytic properties and large surface area, inducing enough adsorption for vanillin. It turns out that the mechanism of vanillin oxidation is adsorption process. Ag NPs/GN exhibited an excellent electrocatalytic activity and good selectivity toward vanillin. The corresponding linear range was estimated to be from 2 to 100μM (R2=0.998), and the detection limit is 3.32×10-/M (S/N=3).2. The multi-walled carbon nanotubes (MWCNTs) were treated with sulfuric acid, nitric acid and heated in water bath without any other reagent. The introduction of C=O groups helped in unzipping of MWCNTs to form the MWCNT@GNR composite. Silver particles (-6nm) with good dispersibility were anchored on MWCNT@GNR by chemical reduction method. MWCNT@GNR@Ag exhibited good film property, conductivity and excellent catalytic performance. L-cysteine can be adsorbed on Ag (111) to form molecular layers. The low overpotential of L-cys oxidation (+0.3V) is attributed to the loose structure and conductivity of the composite. The results showed that the oxidation of L-cys on electrode governed by a diffusion mechanism is a two-electron transfer reaction. The corresponding linear range was from 0.01 to 15μM (R2=0.9975), and the detection limit is 1.5×10-8 M (S/N=3).3. By combining polyols and hydrothermal process, Ag nanowires (NWs) were synthesized. The FeCl3 was added slowly to control the discharge of silver ions from AgCl. The redox reaction of Fe consumed oxygen in solution which avoided the etching of Ag wires. The Pd nanoparticles (-5 nm) were coated on the surface of Ag wires in suit. When Pd atoms were combined with Ag atoms, the d-band center of Pd shifted up and caused the adsoption ability of the hydroxyl ion stronger, which in turn enhanced the electro-oxidation of ethanol on Ag NWs@Pd. The effective area of modified electrode reached 3.78×105cm2. Under alkaline medium, Ag NWs@Pd/GCE reduced the overpotential of ethanol electro-oxidation which was qualified for a high efficiency, stable and low cost catalyst.