[Show abstract][Hide abstract] ABSTRACT: The Langmuir-Blodgett technique was utilized and optimized to produce closed monolayers of cobalt-platinum nanoparticles over vast areas. It is shown that sample preparation, "dipping angle", and subphase type have a strong impact on the quality of the produced films. The amount of ligands on the nanoparticle's surface must be minimized, the dipping angle must be around 105 degrees , while the glycol subphase is necessary to obtain nanoparticle monolayers. The achieved films were characterized by scanning electron microscopy (SEM) and grazing incidence X-ray scattering (GISAXS). The electrical properties of the deposited films were studied by direct current (DC) measurements, showing a discrepancy to the variable range hopping transport from the granular metal model and favoring the simple thermal activated charge transport. SEM, GISAXS, as well as DC measurements confirm a narrow size distribution and high ordering of the deposited films.
[Show abstract][Hide abstract] ABSTRACT: We report an alternative procedure to incorporate gold nanoparticles into 3D ordered colloidal crystal film. The size of gold nanoparticles within the films can be controlled from about 10 nm to about 60 nm by simply varying the gold plating time. The application of the as-prepared films in surface-enhanced Raman spectroscopy (SERS) is investigated by using Rhodamine 6G (R6G) as probe molecules. It is found that the resultant gold-coated 3D ordered colloidal crystal films can be used as SERS substrates, exhibiting excellent enhancement ability.
Chemistry of Materials 10/2005; 17(23):5731. · 8.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A forced-flow catalytic membrane reactor was applied for dimerisation of isobutene to isooctene. Several catalysts, such as silica supported Nafion(R) (Nalion(R) SAC-13), Nafion(R) NR50, Amberlyst(TM) 15, and silica supported phosphotungstic acid were mixed in solution with a polymeric binder. Teflon(R) AF, Hyflon(R) AD, polytrimethylsilylpropyne, and polydimethylsiloxane (PDMS) were applied as binder to form a porous, reactive layer on top of a porous, polymeric, supporting membrane. An optional intermediate PDMS film acted as flow regulator and enabled selective product removal. Isobutene was fed to the reactive membrane, the reaction started immediately and a pressure of around 4 bar built-up on the feed side. Liquid product was collected on the permeate side in an iced trap. Depending on the type of binder high conversions up to 98% at 22% selectivity to isooctene (binder = Hyflon(R) AD) and space velocity of 530 g(i-C4)/g(cat) h, or high selectivities of >80% at 45% conversion of isobutene and space velocity of 275 g(i-C4)/g(cat) h (binder = Teflon(R) AF) were achieved. Catalyst poisoning was not observed during operation for at least 1 week. (C) 2004 Elsevier B.V. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Dimerisation of isobutene is of increasing interest to substitute oxygenated products such as MTBE or the like as fuel additives. Catalysts applied in commercial alkylation plants,e.g., hydrofluoric and sulfuric acid may be replaced by less harmful solid catalysts, for example by solid heteropolyacids ("super" acids) or polymeric sulfonic acids. To overcome decrease in catalyst performance by time and to increase product selectivity a membrane reactor approach is suggested and first successful results are presented.