Synthesis and characterization of sol-gel-derived xerogel films with antifouling/foul release properties and the preparation, immobilization, and evaluation of a sequestered selenoxide catalyst for brominations with hydrogen peroxide and sodium bromide in an aqueous environment
Bennett, Stephanie M.
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Xerogel films with uniform surface topogrophy, as determined by scanning electron microscopy, atomic force microscopy (AFM), and time-of-flight secondary ion mass spectrometry, were prepared from aminopropylsilyl-, fluorocarbonsilyl-, and hydrocarbonsilyl-containing precursors. Young's modulus was determined from AFM indentation measurements. The xerogel coatings gave reduced settlement of zoospores of the marine fouling alga Ulva compared to a poly(dimethylsiloxane) elastomer (PDMSE) standard. Increased settlement correlated with decreased water wettability as measured by the static water contact angle or with decreased polar contribution to the surface free energy as measured by comprehensive contact angle analysis. The strength of attachment of 7-day sporelings (youngplants) of Ulva on several of the xerogels was similar to that on PDMSE although no overall correlation was observed with either water contact angleor surface energy. For sporelings attached to the fluorocarbon/hydrocarbon-modified xerogels, the strength of attachment increased with increased water wettability. The aminopropyl-modified xerogels did not follow this trend. 4-(Hydroxymethyl)phenyl benzyl selenoxide sequestered in a halide-permeable, Class II xerogel formed from 10/90 (mol/mol) 3-amino-propyltriethoxysilane/tetraethoxysilane catalyzes the bromination of organic substrates (4-pentenoic acid, 3,5-dihydroxybenzoic acid, 1,3,5-trimethoxybenzene, N-phenylmorpholine, and N,N-dimethylaniline) with NaBr and H 2 O. Catalyst performance (reaction rate) when sequestered within the halide-permeable xerogel is 23-fold greater in comparison to xerogel-free catalyst in solution. The catalyst is easily separated from the reaction mixture via filtration and the recovered catalyst can be reused without loss of activity through formation of the first 60 moles of product per mole of catalyst.