Low-Temperature Elimination of Organic Components from Mesostructured Organic−Inorganic Composite Films Using Vacuum Ultraviolet Light

Abstract

A novel and simple procedure named photocalcination has been developed for removing organic components from mesostructured organic−inorganic composite films. This procedure employs an excimer lamp radiating vacuum ultraviolet (VUV) light of 172 nm in wavelength. Organic molecules are removed through two distinct photochemical reactions proceeding simultaneously at room temperature: the photocleavage of C−H and C−C bonds in the organic molecules by direct photoexcitation and their subsequent oxidation with activated oxygen species generated by the photoexcitation of atmospheric oxygen molecules. In this study, a composite of cetyltrimethylammonium chloride−silica (CTAC−silica) was used. Thin films of this organic−inorganic composite were prepared on Si substrates coated with a self-assembled monolayer of octadecyltrimethoxysilane. The films were irradiated with VUV light under pressures of 10, 102, 103, or 105 Pa. Although, in each case, the CTAC molecules in the composite films were completely oxidized and removed, the elimination rate increased with an increase in the photocalcination pressure. While 3 h of irradiation was necessary to completely remove the CTAC molecules at 10 Pa, only 0.5 h was required at 105 Pa. However, the periodic mesostructures of the film photocalcined at 105 Pa distorted significantly because of the rapid photooxidation. As a control experiment, identical CTAC−silica mesocomposite films were calcined thermally. The films were heated in air at temperatures from 373 to 773 K. Although the CTAC molecules could be eliminated completely at temperatures higher than 573 K, the periodic mesostructures of the thermocalcined films were much more distorted than those of the photocalcined films.

An energy-efficient route to the rapid synthesis of organically-modified SBA-15 via ultrasonic template removal

“…Ultrasonication offers an extremely rapid and energy-efficient route to the extraction of P123 surfactant template employed in the widespread synthesis of SBA-15 materials, and specifically the preparation of sulfonic acid-functionalised 15 SBA-15 via a co-condensation route for heterogeneous catalysis applications. Around 90 % of P123 can be removed from SBA-15 via 5 min ultrasonication in 10 ml methanol at room temperature, comparable to that achievable after a conventional 48 h reflux using ten times the methanol volume.…”

“…The past two decades have seen a host of new applications for 15 silica-derived materials following the discovery of the MCM family of ordered mesoporous silicas 1 and subsequent HMS, 2 SBA 3 and KIT 4 families. Amongst the most widely exploited of all mesoporous silicas is the hexagonal close-packed SBA-15, first reported by Zhao et al in 1998, 5 which possesses 20 large pore diameters spanning 5-30 nm, coupled with excellent thermal, mechanical and chemical resistance properties which underpin its application in catalysis, [6][7][8][9][10][11] enzyme immobilisation 12 and separation science.…”

“…10 A key step in the synthesis of mesoporous SBA-15 materials is removal of the organic surfactant template. This has been explored via several approaches, including 45 photocalcination by vacuum UV, 15 ozone treatment 16 and oxidation by acidified KMnO 4 , 17 however by far the most common routes are high temperature calcination (typically around 550 o C) and solvent extraction. Calcination, and extraction by reflux under acidic solvents (e.g.…”

“…Reflux is commonly employed to remove Pluronic templates from mesoporous frameworks, 10 however the success of extraction depends heavily on the solvent (cm 3 ):material (g) ratio. Our finished PrSO 3 H-SBA-15 materials were thus obtained from the preceding dried (organic-inorganic) solid following either (i) literature reflux methods using 50 (or 100) cm 3 of solvent per 100 mg of solid 15 material at 60 ºC for 24 (or 48) h, or (ii) ultrasonic extraction employing either 10 cm 3 or 50 cm 3 methanol (ethanol) per 100 mg of solid, whereby the crushed slurry was placed in a polypropylene bottle immersed in an Elma Ultrasound bath (50 Hz) at room temperature. The water temperature was 20 constant during 5 min treatments.…”

The effect of surfactant removal on continuous mesoporous ultra-thin silica films—A study by X-ray reflectivity, X-ray diffraction and Kr adsorption

“…Conventional calcination at 400-550°C may induce film cracks and structural distortion and cannot be used on thermally unstable supports. Several treatments have been developed to remove the organic templates under moderate temperature conditions, such as room temperature UV-ozone (UV-O 3 ) [5][6][7][8], ozone ashing at~200°C [9] or solvent extraction including supercritical CO 2 extraction at ≤100°C [10][11][12][13][14]. The Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) investigations have shown that the UV-O 3 treatment could remove completely nonionic surfactant template, such as Brij®56 (C 16 H 33 (OCH 2 CH 2 ) 10-OH), and gave a highly hydrophilic silica film [5].…”