TY - JOUR T1 - FTIR study of the adsorption of the capping material to different platinum nanoparticle shapes JF - The Journal of Physical Chemistry A Y1 - 2003 A1 - Petroski, J. M. A1 - El-Sayed, Mostafa A AB - FTIR spectroscopy has been used to study the binding geometry of polyacrylate capping material on cubic and tetrahedral platinum nanoparticles. It is proposed that the capping material forms an ester-like linkage to the Pt surface on the tetrahedral shapes through the hydroxyl oxygen atom of the carboxylic acid moiety of the polyacrylate (linear adsorption configuration). On the cubic particle the adsorption is through both of the carboxylic oxygen atoms (bridge adsorption configuration). These shaped nanoparticles are synthesized by changing the starting ratio of the capping material to that of the Pt salt. The results are discussed in terms of the effect of changing the concentration of the polyacrylate capping material on the mode of bonding to the surface. This might be a factor in determining the final shape formed. PB - ACS Publications VL - 107 SN - 1089-5639 UR - http://dx.doi.org/10.1021/jp0300694 CP - 40 M3 - 10.1021/jp0300694 ER - TY - JOUR T1 - Self-assembly of platinum nanoparticles of various size and shape JF - Journal of Physical Chemistry A Y1 - 2001 A1 - Petroski, J. M. A1 - Green, T.C. A1 - El-Sayed, Mostafa A AB - The addition of dodecanethiol to a polydisperse platinum colloidal aqueous solution capped with acrylic acid leads to self-assembled monolayers which not only contain various sizes, but also various shapes of nanoparticles. Assembled monolayers arranged in hcp arrays are achieved for mixed shape-samples. In;the case of the assembly of cubic nanoparticles, cubic closest packing is achieved when the size difference between the nanoparticles is less than 25% (or between 6 and 8 nm). The ccp array is disrupted when the size difference is between 25 and 60% or there is a mixture of shapes. Finally, size segregation is seen in regions where the size difference is more than 60% with the resultant assembly being hcp no matter what the shape. VL - 105 SN - 1089-5639 N1 - Petroski, JM Green, TC El-Sayed, MA M3 - 10.1021/jp0019207 ER - TY - JOUR T1 - Activation energy of the reaction between hexacyanoferrate(III) and thiosulfate ions catalyzed by platinum nanoparticles JF - Journal of Physical Chemistry B Y1 - 2000 A1 - Li, Y. A1 - Petroski, J. M. A1 - El-Sayed, Mostafa A AB - A temperature-dependent study was carried out for the platinum-nanoparticle-catalyzed electron-transfer reaction between hexacyanoferrate(III) and thiosulfate ions in the temperature range of 20-70 degreesC. The Pt nanoparticles are dominantly truncated octahedral in shape and have an average particle size of 7.0 +/- 0.8 nm. The catalyzed reaction is compared with the uncatalyzed reaction in the same temperature range. The activation energy of the reaction is found to be 38.3 +/- 2.0 kJ/mol for the uncatalyzed reaction and 17.6 +/- 0.9 kJ/mol for the catalyzed reaction in the lower temperature range (20-50 degreesC). In the higher temperature range (50-70 degreesC), the rate remains nearly constant. This behavior is attributed to the cancellation of two effects: the temperature dependence of the catalytic reaction and the decrease in the catalyst surface area due to the increase of nanoparticle aggregation. VL - 104 SN - 1089-5647 N1 - Li, Y Petroski, J El-Sayed, MA M3 - 10.1021/jp002569s ER - TY - JOUR T1 - Kinetically controlled growth and shape formation mechanism of platinum nanoparticles JF - Abstracts of Papers of the American Chemical Society Y1 - 1998 A1 - Petroski, J. M. A1 - Wang, Z.L. A1 - Green, T.C. A1 - El-Sayed, Mostafa A VL - 215 SN - 0065-7727 N1 - Petroski, JM Wang, ZL Green, TC El-Sayed, MAPart 2 ER - TY - JOUR T1 - Shape transformation and surface melting of cubic and tetrahedral platinum nanocrystals JF - Journal of Physical Chemistry B Y1 - 1998 A1 - Wang, Z.L. A1 - Petroski, J. M. A1 - Green, T.C. A1 - El-Sayed, Mostafa A AB - We report transmission electron microscopic studies of in-situ temperature-induced shape transformation and melting behavior of polymer-capped cubic and tetrahedral nanocrystals. Our results indicate that the surface-capping polymer is removed by annealing the specimen at temperatures between 180 and 250 degrees C. The particle shapes show no change up to similar to 350 degrees C. In the temperature range between 350 and 450 degrees C, a small truncation occurs in the particle shapes but no major shape transformation is observed. The particle shapes experience a dramatic transformation into spherical-like shapes when the temperature is raised above similar to 500 degrees C, where surface diffusion or surface premelting (softening) takes place. Above 600 degrees C, surface melting becomes obvious leading to coalescence of the surfaces of neighboring nanocrystals and a decrease in the volume occupied by the assembled nanocrystals. The surface melting forms a liquid layer a few atomic layers deep around the still solid core of the nanocrystal. This temperature is much lower than the melting point of bulk metallic platinum (1769 degrees C). The reduction in the melting temperature is discussed in terms of the surface tension of the solid-liquid interface (gamma(SL)). For an 8 nm diameter Pt nanocrystal, gamma(SL) is calculated to be 2.0 N m(-1) at 650 degrees C, which is smaller than that of the bulk solid-vapor metal surface tension (gamma(sv)). This reduction is proposed to be due to the compensation of the increase in gamma(sv) of the nanocrystal by the wetting effect at the solid-liquid interface. VL - 102 SN - 1089-5647 N1 - Wang, ZL Petroski, JM Green, TC El-Sayed, MA M3 - 10.1021/jp981594j ER -