Behaviour of pure water and water mixture with benzene or chloroform adsorbed onto ordered mesoporous silicas

Abstract

Structural characteristics of synthesized ordered mesoporous silicas MCM-41, MCM-48 and SBA-15 were studied using XRD, nitrogen adsorption and FTIR methods. Pure water and mixtures with water/benzene and water/chloroform-d adsorbed onto silicas were studied by 1 H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial liquids. Concentrated aqueous suspensions of MCM-48 and SBA-15 were studied by thermally stimulated depolarization current (TSDC) method. Benzene and chloroform−d can displace a portion of water to broad pores from the pore walls and from narrower pores, especially in the case of a large excess of an organic solvent. This process is accompanied by diminution of both interaction energy of water with an adsorbent surface and freezing temperature depression of adsorbed water. The effect of nonpolar benzene on pore water is much stronger than that of weakly polar chloroform-d. Modifications of the Gibbs-Thomson relation to describe the freezing point depression of mixtures of immiscible liquids confined in pores allow us to determine distribution functions of sizes of structures with unfrozen pore water and benzene.

Application of nmr spectroscopy to determine the thermodynamic characteristics of water bound to OX-50 nanosilica

“…For chloroform molecules (having higher molar refraction than methane), this effect is more pronounced and accordingly, clusters of adsorbed water in chloroform medium become less strongly bound to the silica surface. The effect described has also been observed in other microporous and mesoporous silica and carbon adsorbents [17][18][19]. It is probably general for processes involving co-adsorption of water and nonpolar/low-polarity organic substances.…”

Heating effects on morphological and textural characteristics of individual and composite nanooxides

“…with low and high content of alumina) and Al 2 O 3 /SiO 2 /TiO 2 (AST with high content of alumina and low content of silica and titania) ( Table 1) were analyzed here. Another set of fumed oxides (A-50, A-100, A-200, A-300, A-400, A-500, Al 2 O 3 , TiO 2 , SA1, SA3, SA23, SA30, ST9, ST14, ST20, ST29, AST50) (pilot plant at the Institute of Surface Chemistry, Kalush, Ukraine) described in detail previously (Gun'ko et al , 2003(Gun'ko et al , 2005(Gun'ko et al , 2007a(Gun'ko et al , 2007b(Gun'ko et al , 2007c, silica gels Si-40, Si-60 and Si-100 (Merck) (Gun'ko et al 2002), mesoporous ordered silicas (Gun'ko et al 2007b) were used for comparative characterization. Chemical composition of mixed fumed oxides (Table 1) was analyzed using a XRF (Canberra, USA) spectrophotometer with a 55 Fe (or 109 Cd) radioactive source and an amplitude analyzer (Canberra) coupled with a computer with the AXIL program.…”

“…Before the XRF measurements all samples were heated at 723 K for 8 h to remove adsorbed compounds and residual HCl and MCl groups remaining after pyrogenic synthesis in the O 2 /H 2 /N 2 flame using precursors MCl n (M = Si, Al, Ti). The synthesis of similar individual and composite nanooxides was described previously (Basic Characteristics of Aerosil 1997;Gun'ko et al , 2005Gun'ko et al , 2007aGun'ko et al , 2007bGun'ko et al , 2007c.…”

“…(1-2 nm), primary (5-100 nm), secondary (<0.1-1 μm), ternary (1-10 μm) and quaternary (>10 μm) particles depend on flame synthesis conditions (flame temperature, its gradient, flame length, flow velocity and turbulence, ratio of reactant concentrations), phase distributions for composite oxides, amount of adsorbed water, and sample history (Iler 1979;Legrand 1998;Basic Characteristics of Aerosil 1997;Gun'ko et al 2003Gun'ko et al , 2004Gun'ko et al , 2005Gun'ko et al , 2007aGun'ko et al , 2007bGun'ko et al , 2007c. These characteristics are of importance to control the adsorption of various adsorbates (water, metal ions, low-molecular organics, polymers, proteins, etc.…”

NSAID naproxen in mesoporous matrix MCM-41: drug uptake and release properties

“…In the recent years, ordered mesoporous materials were investigated as materials for applications in many areas, such as catalysis [1,2], sorption [3], separation [4], drug delivery or controlled release [5,6]. The drug delivery systems are of special interest since controlled and prolonged release of the drug could lead to prolonged efficiency, less frequent doses and consequently to minimalization of the side, negative effects of the drugs.…”