Preparation Of Precious Metal Nanoparticles Coatings Through In-situ Self-assembly On Nickel Surface And Their Performances

The microemulsion is a thermodynamically stable isotropic transparent ortranslucent system composed of surfactant, cosurfactant, oil and water in a certainproportion. The preparation of nanomaterials in microemulsion is, in essence, usingthe nano pool packed by surfactant and cosurfactant as microreactor, exchangingmaterials by bumping into each other to achieve chemical reaction to preparenanoparticles. The surfactant in microemulsion adsorbing on the particle surface canprevent the coalescence, and the growth of the particles is limited due to the smallmicropool. Therefore, nanoparticles prepared in W/O microemulsion have theadvantages of small particle size, good dispersion, high purity etc. And the particlesize can be effectively controlled in the synthesis process.In this paper, TX-100and CTAB were used as the surfactant, mixed withn-hexane, n-hexanol and chlorine acid to constitute the reverse microemulsion. Aseries of single metallic and bimetallic monolayers were prepared by self-assemblymethod, scanning electron microscopy (SEM) was used to characterize themicroscopic structure and morphology of the membranes. Cyclic voltammetry (CV)and time-current analysis were used to study the performance and application of theself-assembly membranes. The main research results are as follows:Using the reverse microemulsion prepared with octyl polyethylene glycol phenylether (TX-100), n-hexane, n-hexanol and strong acidic aqueous solution containinggold chloride as soft template, Au nano self-assembled monolayer was prepared byself-assembly method at room temperature on the nickel electrode surface. Themorphology and catalytic activity of the nanometer Au assembly membrane wereresearched by SEM and CV. The assembly membranes prepared in reversemicroemulsion consisting of X-100/CTAB dual surfactant or CTAB surfactant,common water solution were also researched for comparison. The results showed thatthe Au nanoparticles in assembly membrane prepared in the TX-100reversemicroemulsion distribute more uniform with the partical size ranged from10to15nmand the particle size increases with the increase of HAuCl4concentration andpreparation time. They also exhibit better catalytic activity and electrochemicalstability for glycerol oxidation. The catalytic activity of the Au nano membrane underalkaline condition increases with the increase of loading of Au nanoparticles. Keep the preparation time constant, the catalytic activity of the membrane increases withthe increase of HAuCl4concentration.TX-100was used as surfactant and butanol was used as cosurfactant, mixed withoil phase and water phase to constitute the reverse microemulsion. N-octane wasserved as the oil phase and the water phase was made up of strong acidic HAuCl4,(NH4)2PdCl6or the mixture of HAuCl4and (NH4)2PdCl6. Pd-Au bimetallicnanoparticles self-assembled monolayers were prepared by self-assembly method atroom temperature on the nickel electrode surface. The morphology and catalyticactivity of the nanometer Au assembly membrane were researched by SEM and CV.The assembly membranes prepared in reverse microemulsion consisting ofX-100/CTAB dual surfactant or CTAB surfactant, common water solution were alsoresearched for comparison. The results showed that the reaction medium andself-assembly method both affect the morphology of the Pd-Au bimetallicnanoparticles. The Pd-Au membrane prepared by self-assembling Pd and then Au inTX-100system has the best morphology. Pd and Au bimetallic nanoparticles haveuniform particle size of about10nm. The dispersion of the particles is good and hasno coalescence. The Pd-Au nanometer film modified electrode prepared in TX-100reverse microemulsion system has the highest catalytic activity under alkalinecondition for oxidation of ethanol and glycerol. Moreover, double metal nanometermembrane prepared by one-step self-assembly has better catalytic activity thantwo-step self-assembly membrane. Double metal nanometer film has better catalyticperformance, anti-poisoning ability and electrochemical stability than single metalnano membrane.