Search results for " Silica"
showing 10 items of 418 documents
Borate-driven gatelike scaffolding using mesoporous materials functionalised with saccharides.
2009
We report the development of an MCM-41 mesoporous support that is functionalised with saccharides at the pore outlets and contains the dye [Ru(bipy)(3)](2+) in the pores (solid S1; bipy = 2,2'-bipyridyl). For this hybrid system, the inhibition of mass transport of the dye from the pore voids to the bulk solution in the presence of borate is demonstrated in water at neutral pH. The formation of the corresponding boroester derivative is related to the selective reaction of borate with the appended saccharides. This control is selective and only anion borate, among several anions and cations, can act as a molecular tap and inhibit the delivery of the entrapped guest. Additionally, the S1-borat…
Selective Antimicrobial Effects of Curcumin@Halloysite Nanoformulation: A Caenorhabditis elegans Study
2019
Alterations in the normal gastrointestinal microbial community caused by unhealthy diet, environmental factors, and antibiotic overuse may severely affect human health and well-being. Novel antimicrobial drug formulations targeting pathogenic microflora while not affecting or even supporting symbiotic microflora are urgently needed. Here we report fabrication of a novel antimicrobial nanocontainer based on halloysite nanotubes loaded with curcumin and protected with a dextrin outer layer (HNTs+Curc/DX) and its effective use to suppress the overgrowth of pathogenic bacteria in Caenorhabditis elegans nematodes. Nanocontainers have been obtained using vacuum-facilitated loading of hydrophobic …
Solubility of Zn(II) in Association with Calcium Silicate Hydrates in Alkaline Solutions
1999
The binding of Zn(II) to the cement mineral calcium silicate hydrate (CSH) was investigated in a well-defined laboratory system. CSH (Ca:Si = 1:1) was synthesized by coprecipitation with varying contents of Zn(II). Zn(II) was added in the proportions 0, 0.1, 1.0, 5.0, and 10% in exchange for Ca. The resulting CSH was characterized by X-ray diffraction. The solid phases were then equilibrated in aqueous suspensions, and the solubilities of Ca, Si, and of Zn(II) were determined as a function of pH and Zn(II) content in the solid phase. The solubility of Ca and Si in equilibrium with the CSH phases was in agreement with that predicted by thermodynamic calculations. Dissolved Zn(II) concentrati…
Triple-Quantum Two-Dimensional 27Al Magic Angle Nuclear Magnetic Resonance Study of the Aluminum Incorporation in Calcium Silicate Hydrates
1998
Triple-quantum two-dimensional 27Al magic angle spinning nuclear magnetic resonance (27Al 3Q-MAS NMR) was used to characterize the substitution of Si4+ by Al3+ into the Te−Oc−Te structure of calcium silicate hydrates (C−S−H). This substitution was studied with C−S−H having an Oc/Te ratio of 1 and in equilibrium with Al(OH)3 in aqueous suspensions. In the absence of NaOH, no substitution into the C−S−H structure occurred. Addition of NaOH in the preparation increased the concentration of Al(OH)4- and favored substitution. The deficit of charge resulting from this substitution was compensated by the accommodation of sodium in the interlayer space of the C−S−H. Increasing levels of substituted…
Zeta-Potential Study of Calcium Silicate Hydrates Interacting with Alkaline Cations
2001
An investigation into the interaction between alkaline cations and calcium silicate hydrates (CSH) was conducted by electrokinetic measurements, which provided information on the nature of the interface between the solid and its equilibrium solution. Calcium constitutes for the CSH surface a potential-determining cation. A model of the CSH surface could be proposed, accounting for the experimental evolution of the CSH zeta potential. The necessity of studying the zeta-potential evolution of the system as a function of the calcium activity, instead of its concentration, was underlined. The results obtained suggest a specific interaction between cesium and the CSH surface, whereas sodium and …
Electrochemical Fingerprint of Archeological Lead Silicate Glasses Using the Voltammetry of Microparticles Approach
2016
9 págs.; 14 figs.; 1 tab.
Irradiation induced Germanium Lone Pair Centers in Ge-doped Sol-gel SiO2: luminescence lifetime and temperature dependence
2010
We studied the temperature dependence of the emission profile and of the lifetime, measured at 4.3 eV, related to the germanium lone pair centers (GLPC) induced by gamma ray at 5 MGy in a Ge-doped silica sample and in an analogous sample irradiated at 10 MGy, in which by a successive thermal treatment up to 415 °C the induced GLPC has been modified (named residual GLPC in the following). The measurements were recorded in the temperature range 10-300 K using an excitation of ∼5.2 eV. The data show that the energy level scheme of the induced and the residual GLPC is very similar to that of the native defects generated during the synthesis, and the intersystem crossing process (ISC) of the ind…
Investigation of the He solubility in H2O-CO2 bearing silicate liquids at moderate pressure: a new experimental method
2000
We have designed the first available experimental method capable to investigate the solubility of inert gases in H2O–CO2 bearing silicate melts in a large range of pressures. The method overcomes the difficulties imposed by the physical state of volatiles at room conditions. Experiments were done by using an internally heated pressure vessel, where sealed capsules containing the sample are introduced. The peculiarity of the method consists in the capability of loading, in accurately known proportions (even lower than ppm), volatiles in a gaseous state at room conditions. Gas is loaded as a weighed amount of a gas-bearing glass, which was previously prepared by using the same gas as a pressu…
Development of controlled release systems of biocides for the conservation of cultural heritage
2017
Abstract The presence of microorganisms is one of the main causes of monument deterioration. Biocides are usually applied after or before restoration in order to prevent or slow down microbial growth. Frequent applications are necessary leading to increased costs and high risks to humans and the environment. The aim of this study is the design of novel controlled release systems comprising a biocide loaded into a mesoporous silica. Pristine MCM41 as well as MCM41 functionalised with carboxy- (MCM41-COOH) and amino-groups (MCM41-NH2) were used. Biotin T and New Des 50, two commercial formulations, were chosen as biocides. The biocide encapsulation was performed adding the mesoporous silica t…
Formulation of Mesoporous Silica Nanoparticles for Controlled Release of Antimicrobials for Stone Preventive Conservation
2020
The biotic deterioration of artifacts of archaeological and artistic interest mostly relies on the action of microorganisms capable of thriving under the most disparate environmental conditions. Thus, to attenuate biodeterioration phenomena, biocides can be used by the restorers to prevent or slow down the microbial growth. However, several factors such as biocide half-life, its wash-out because of environmental conditions, and its limited time of action make necessary its application repeatedly, leading to negative economic implications. Sound and successful treatments are represented by controlled release systems (CRSs) based on porous materials. Here, we report on the design and developm…