Electrochemical And In Situ FTIR Studies Of The Interaction Of CTAB And HBr With Pt Single Crystal Surfaces

CTAB is widely used as shape tuning agents in nanomaterials shape controlled synthesis, the facet selective adsorption of Br and the steric block of the crystal nuclei by alkylammonium cation are believed to be the key factor for shape control. In this study, the single crystal electrodes with well-defined surface structure were used as working electrode to study the interaction of CTAB and HBr with Pt(100)、Pt(111) and Pt(110) through electrochemical and in-situ FTIR methods. The main results are summarized below:1. The Br" and alkylammonium cation of CTAB are coadsorbed on Pt surface, bromide acts as a bridging center between Pt surface and the quaternary ammonium head group of the surfactant. The coverage of CTAB on platinum was ranked in an order of (100)>(111)>(110), this may support the hypothesis that preferential adsorption of CTAB on (100) facets of metal nuclei promote the anisotropic growth of nanoparticle. CTAB is completely desorbed from the Pt(111) and Pt(100) surface at1.1V, while on Pt(110) surface CTAB is completely desorbed at0.8V.2. Between-0.25V and0.1V, H and Br compete for surface sites. When the upper potential (EU) of CV was below0.9V, the adsorption of OH" was totally compressed by the competitive adsorption of Br-. The oxidation peak at0.98V involves the oxidation of Br-and Pt surface, when the upper limit potential is positive than0.9V the Pt oxidation content is largely compressed by Br-adsorption.3. The adsorption of Br-has no impact on the ordered Pt(100) and Pt(111) surface. Since in HBr solution below0.9V the adsorption of OH-was completely compressed, the transformation of (100) long range order to (100) short range order was totally hindered. Beyond0.9V, the Pt surface oxidation was reduced by Br adsorption, as a result the transformation of (100) and (111) long range order to (100) short range order and (110) steps are reduced correspondingly.4. The compression of CTAB to Pt oxidation is larger than Br", to the most positive potential studied(1.2V) CTAB can totally block the destruction of long range order (100). For Pt(111) electrode, CTAB could not block the destruction of long rnage order (111) sites but reduce the content of long range order (111) to (110) steps and short range order (100).5. The band at1800cm-1correspond to the binding of N+to surface H, the intensity of the N-H deformation follow the order of polycrystaline Pt> Pt(110)≈Pt(111)>Pt(100). When the electrode potential is positive than0.5V, CTAB starts to oxdize and CO2was produced.