The manipulation of lamellar photocatalysts for the conversion of visible light into hydrogen fuel.

摘要

Visible light energy was converted and stored as chemical energy in the form of hydrogen gas and triiodide (I3-) using an improved photocatalyst in acidic iodide solutions. The catalyst is composed of the internally platinized wide-bandgap semiconductor K4Nb 6O17, with a visible light sensitizer adsorbed on the surface. The sensitizer is a new phosphonated ruthenium tris(bipyridyl) molecule that forms a strong bond to the surface of the niobate crystallites. Monolayers of [TiNbO5]nn- and poly(styrene sulfonate) that were applied over the sensitizer layer enhanced the system performance.; A study was done on nanoscale tubules that form with the exfoliation of acid exchanged K4Nb6O17 with tetra( n-butyl)ammonium hydroxide, TBA+OH-. The tubes were examined by transmission electron microscopy (TEM), atomic force microscopy (AFM), BET surface area analysis, and flame atomic absorption spectroscopy. The tubes were found to be 15 to 30 nm in diameter and 0.1 to 1 mum in length, and they have hollow interiors. It is suggested that potassium is incorporated into the tube walls during the transformation from bilayers to single sheet tubes. The observed curling tendency, preferential folding, and cleavage angles of the individual sheets are interpreted in terms of the crystal structure of the parent solid, K4Nb6O17 .; A third part of this work investigated the growing of high dielectric thin film materials using a layer by layer technique from metal oxide lamellar colloids. The acid-base chemistry of polycation/polyanion adsorption was studied in detail for PAH/HTiNbO5. The pKa of PAH, defined as the pH at which it is half protonated, is 8.7. Titanoniobate colloids, prepared by reaction of HTiNbO5 with TBA+OH- , are unilamellar at pH ≥ 8.5 and re-stack below pH 7.0. At pH 8.5, high quality multilayer films can be grown by sequentially adsorbing PAH with either the titanoniobate or niobate colloid. Thermal gravimetric analysis and differential thermal analysis studies of bulk PAH/titanoniobate intercalation compounds show that they decompose oxidatively to form HTiNbO 5 at 310--350°C, and that this decomposition is followed by interlayer condensation to make Ti2Nb2O9. A similar process occurs in the PAH/titanioniobate multilayer films at 350°C. (Abstract shortened by UMI.)