Preparation, Surface Assembly Of Pt Nanoparticles With Different Agglomeration States And Investigation Of Their Electrochemical And Particular IR Properties

As a new rising discipline, nanomaterial has attracted multidisciplinary interests from material science, chemistry, physics, biology and engineering, etc. because of their unusual properties that could not possessed by corresponding bulk materials. Nanomaterial is the core subject of nano- science and technology. Platinum group metals are widely used in energy conversion and green synthesis duo to their high electrocatalytic activity and stability. The research and preparation of metal electrocatalyst at nanometer scale is one of the key subjects in electrocatalysis.In this paper, Pt nanoparticles (Ptn) were prepared by chemical reduction method. The results of UV-vis and TEM showed that Ptn are formed mainly at the initial stage of refluxing. The prepared Pt nanoparticles were then self-assembled on Au substrate using dithiol as cross-linkers. The ability of electronic transfer during the self-assembly of dithiol and Ptn was studied in the presence of redox active probe Fe (CN) 64-/3- couple. The result indicates that the dithiol monolayer serves as a large barrier for the electron transfer. The redox current is increased significantly when Pt nanoparticles are self-assembled on the top of the dithiol monolayer assembly electrode. The surface morphology and composition of assembly electrode were analyzed by AFM and XPS. In situ FTIRS results illustrated that CO adsorbed on Ptn exhibit enhanced IR absorption, and exhibited more adsorption states in comparison with COad on bulk platinum. Electrochemical CV results illustrated that COad oxidized at higher potential because of the surface structural effect and nano-size effect of Pt nanoparticles.In this paper, for the first time, we have revealed that dispersed Pt nanoparticles for CO adsorption display enhanced IR absorption at either solid | electrolyte or solid | gas interface. However abnormal infrared effects (AIREs) was observed for CO adsorbed on agglomerates of Pt nanoparticles. In order to investigate the origin of the AIREs of nanomaterials, transmission IR spectroscopy was applied to study CO adsorption on Pt nanoparticles with different agglomeration states. The results illustrated that along with the increase of the degree of agglomeration of Pt nanoparticles, the IR spectral patterns of CO adsorbates were transformed from enhanced IR absorption bands to Fano-like spectral line shapes, and further to abnormal anti-absorption IR features. It was demonstrated that the AIREs is a general phenomena of nanomaterials and it is closely related to the size and agglomeration state of nanomaterials. The agglomerates of Pt nanoparticles have also been found to exhibit significant electrocatalytic activity for the oxidation of methanol.The investigation in the current paper has contributed to understand deeply the nature of the metal nanomaterials, and is of significant importance in understanding the origin of special optical properties of nanometer materials.