Platinum, colloidal solution

Dendrimer-protected colloids are capable of adsorbing carbon monoxide while suspended in solution, but upon removal from solution and support on a high surface area metal oxide, CO adsorption was nil presumably due to the collapse of the dendrimer [25]. It is proposed that a similar phenomena occurs on PVP-protected Pt colloids because removal of solvent molecules from the void space in between polymer chains most likely causes them to collapse on each other. Titration of the exposed surface area of colloid solution PVP-protected platinum nanoparticles demonstrated 50% of the total metal surface area was available for reaction, and this exposed area was present as... 

Electrophoresis. Electrophoresis, the movement of charged particles in response to an electric potential, has become very important in biochemistry and colloid chemistry. In the present study an apparatus similar to that described by Burton( M2-M5) was used. A U-tube with an inlet at the bottom and removable electrodes at the two upper ends was half filled with acetone. The a Au-acetone colloidal solution was carefully introduced from the bottom so that a sharp boundary was maintained between the clear acetone and the dark purple colloid solution. Next, platinum electrodes were placed in the top ends of the U-tube, and a DC potential applied. The movement of the boundary toward the positive pole was measured with time. Several Au-acetone colloids were studied, and electrophoretic velocities determined as 0.76-1.40 cm/h averaging 1.08 cm/h. 

Tire electrical method, commonly applied to the preparation of colloidal metals, can also be extended to selenium. When an electric discharge is made to pass under pure water between a platinum anode and a cathode prepared by fusing a small piece of selenium on to platinum foil, colloidal selenium is slowly formed.6 When a dilute solution of selenious anhydride is electrolysed using platinum electrodes, a colloidal solution of selenium and a black cathodic deposit of selenium... 

The reaction mixture is then treated with hydrogen in presence of 70 ml of a 1% colloidal solution of platinum. The reduction product was isolated as hydrochloride. The hydrochloride of L-phenyl-2-methyl-amino-propanol-l crystallizes from alcohol in the form of coarse prisms. MP 214°-216°C. The free base melts at 40°C. 

We have already studied the effect of temperature change on reversible reactions under Le-Chatelier s principle. Some catalysts are, however, physically altered by a rise in temperature and hence their catalytic activity may be decreased. This is particularly true with colloidal solutions like that of platinum, since a rise in temperature may cause their coagulation. In such a case, the rate of reaction increases up to a certain point and then gradually decreases. The rate of reaction is maximum at a particular temperature which is known as the optimum temperature. 

Platinum Hydrosol or Colloidal Platinum.—A solution of platinum hydrosol or colloidal platinum in water is easily prepared by sparking between platinum electrodes immersed in ice-cooled water,8 a current of about 10 amperes and 40 volts being employed. The electrodes consist of thick platinum wire, and, when placed from 1 to 2 mm. apart, sparking takes place, particles of the metal being tom off and suspended in the water. The liquid thus obtained is allowed to stand overnight, and decanted from any sediment. It has a dark colour, but the individual metallic particles cannot be distinguished even with the aid of a microscope. 

Solid Platinum Hycbrosol.—The hydrosol may be obtained in the solid state, completely soluble in warm water. This is most readily accomplished1 by concentration over sulphuric acid in vacuo of the colloidal solution obtained by reducing a platinum salt with hydrazine hydrate in the presence of a protective colloid, such as gum acacia. 

Although platinum is not attacked by nitric acid, yet it dissolves slightly when its alloys with silver are so treated, yielding a colloidal solution which is dark brown in colour. This is particularly the case with alloys containing about 20 per cent, of platinum. On standing for several days the platinum flocculates, and deposits as a black powder in a high state of subdivision, the solution becoming decolorised. 

In our process we make use of a 10% solution of hydrochloroplatinic acid for preparation of our colloidal metal, and precipitate the activated metal in aU aqueous solution of gum arabic by reduction with hydrogen gas without first introducing any colloidal metal to promote the reduction of the platinum chloride solution. Skita used in many cases a promoter to stimulate the formation of colloidal metal (Impfmethode). This was prepared by reducing platinum solution with formaldehyde in alkaline solution. 

The linear CO stretching frequency for the carbonylated platinum colloid while lower than that found for surface bound CO, is in the range reported for the platinum carbonyl clusters [Pt 3 (CO) 6 ] n / sind we find that the carbonylated colloid is easily transformed into the molecular cluster [Pt 12 (CO) 24 ] (10) reaction with water. The cluster was isolated in 50 yield based on platinum content of the precipitate by extraction with tetraethylammonium bromide in methanol from the aluminum hydroxide precipitated when water is added to the aluminoxane solution. The isolation of the platinum carbonyl cluster reveals nothing about the size or structure of the colloidal platinum particles, but merely emphasizes the high reactivity of metals in this highly dispersed state. The cluster isolated is presumably more a reflection of the stability of the [Pt3(CO)6]n family of clusters than a clue to the nuclearity of the colloidal metal particles - in a similar series of experiments with colloidal cobalt with a mean particle size of 20A carbonylation results in the direct formation of Co2(CO)8. 

Narayanan R, El-Sayed MA (2004) Shape-dependent catalytic activity of platinum nanoparticles in colloidal solution. Nano Lett 4 1343... 

Karstedt solution, a complex compound of H2PtCl6 (H20)6) and vinyl-substituted disiloxanes are well known and very active catalysts [19]. Several other catalytic systems, e.g., Pt(cod)2, leading to the formation of platinum colloids have been examined [20]. More recently, hydrosilylation with the Speier catalyst has been tested both under single- and two-phase conditions. The hydrosilylation reaction was thereby optimized for technical realization [21]. 

Figure 1 Scheme of the heterogenization procedure for chirally stabilized platinum colloids 1) mixing the solutions, 2) dropping the mixed solutions on a suitable surftice e. g. a PE film, and drying the droplets afterwaids. 

A combination of AFM, STM and XPS has revealed [14,96] the interaction of platinum hydrosols with oxide (sapphire, quartz) and graphite single crystal substrates. The metal core is immediately adsorbed e.g. on the HOPG surface when dipped into aqueous Pt colloid solutions at 20 °C. As shown in Fig. 2.17, the protecting shell (composed of either residual surfactants or al-organic residues) forms a carpetlike coat which cannot... 

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