Functionalization of mesostructured silica–carbon composites

A strategy for synthesizing highly functionalized porous silica–carbon composites made up of a sulphur- or nitrogen-doped carbon layer coating the pores of two mesostructured silica samples (i.e. SBA-15 and KIT-6) is presented. The synthesis scheme involves several steps: a) infiltration of the silica pores by sulphur-rich (thiophene) or nitrogen-rich (pyrrole) monomers, b) in situ polymerization of these precursors to form polythiophene or polypyrrole, and c) carbonization of the polymers. The resulting silica–carbon composites contain ∼25 wt % of carbonaceous matter and a large number of nitrogen and sulphur functional groups attached to the deposited carbon (up to 4.2 wt % of nitrogen and 6.1 wt % of sulphur). The structural characteristics of the parent silica are retained in the composite materials, which exhibit high surface area, large pore volume and a well-ordered porosity made up of uniform mesopores.     

γ-radiation-induced thermoluminescence of Fe-doped silica gels

Silica gels were prepared by the sol-gel method containing varying amounts of Fe. The gels were irradiated with -ray doses in the range from 0.3 to 11.5 kGy. The thermoluminescent response was characterized before and after irradiation. When the samples were irradiated in the range 0.3 to 1.0 kGy, no thermoluminescent response was detected. However, when the samples were irradiated in the range from 1.0 to 11.5 kGy, they showed a clear thermoluminescent behavior and a linear dose–response relationship over the whole irradiation range, opening up the possibility of employing this system as a radiation dosimeter.     

Mechanism of formation and nanostructure of Stöber silica particles

The formation of silica nano-?and microparticles has been studied during growth by the modified St?ber-Fink-Bohn (SFB) method. It has been experimentally found that the density and fractal structure of particles vary with size as they grow from 70 to 2200?nm. We propose a model of particle structure which is a dense primary particle core and is composed of concentric secondary particle shells terminating in dense primary particle layers.     

Assessment of alkali–silica reaction damage through quantification of concrete nonlinearity

A newly developed nondestructive evaluation technique, Nonlinear Impact Resonance Acoustic Spectroscopy (NIRAS), is applied to concrete specimens in an ongoing assessment of aggregate alkali reactivity during standard concrete prism testing. NIRAS measures the nonlinearity in a specimen caused by the inception and growth of microcracks throughout the sample and debonding at the aggregate/cement interface. NIRAS is used to exploit the nonlinear effect of excitation amplitude dependent resonance frequency changes, which are related to nonlinearity measurements of concrete samples cast with aggregates of varying reactivity. To relate microstructural changes to changes in nonlinearity and expansion, sample characterization is performed with uranyl-acetate staining. The results demonstrate the utility of NIRAS for not only assessing the potential for ASR under standardized test conditions, but for more general damage characterization in concrete and assessment of “job mixtures.” NIRAS can distinguish reactive from nonreactive aggregates without ambiguity, as supported by sample characterization results.     

Electrodeposition of zinc–silica composite coatings: challenges in incorporating functionalized silica particles into a zinc matrix

Abstract

Zinc is a well-known sacrificial coating material for iron and co-deposition of suitable particles is of interest for further improving its corrosion protection performance. However, incorporation of particles that are well dispersible in aqueous electrolytes, such as silica particles, is extremely difficult. Here, we report a detailed study of Zn–SiO₂ nanocomposite coatings deposited from a zinc sulfate solution at pH 3. The effect of functionalization of the silica particles on the electro-codeposition was investigated. The best incorporation was achieved for particles modified with SiO₂–SH, dithiooxamide or cysteamine; these particles have functional groups that can strongly interact with zinc and therefore incorporate well into the metal matrix. Other modifications (SiO₂–NH₃⁺, SiO₂–Cl and N,N-dimethyldodecylamine) of the silica particles lead to adsorption and entrapment only.     

Steric stabilization of Stöber silica dispersions using organosilanes

Organosilanes of the general formula R _x Si(OR)_4–x (where R is an alkyl group and R = CH₃ or CH₂CH₃) were used to sterically stabilize hexane dispersions of submicrometre silica spheres. The dispersions were characterized according to sediment volume results. For 0.5m silica particles, the sediment density increased by more than a factor of three up to 50 to 55% of theoretical in the presence of organosilanes with 12 or more carbons in the R group. Solid-state¹³C nuclear magnetic resonance was used to characterize the powder-dispersant interaction; this technique can distinguish between carbons in the R group of the organosilane and residual organic groups in the silica. Scanning electron micrographs of filter compacts were used to further characterize the dispersions and indicated the presence of primary particles as well as small agglomerates.     

Microstructural investigation of a silica fume–cement–lime mortar

Several additions, minerals and organic, are used in mortars, such as pozzolanic materials, cementicious materials and polymers. Literature about the use of additions in masonry mortars (cement/lime/sand mixes) is scarce; usually, studies are about concrete mortars. The purpose of this work is to study the microstructural effects of the substitution of 10% of Portland cement by silica fume in a 1:1:6 (cement/lime/sand mix proportion by volume) masonry mortar. Scanning electron microscopy with energy dispersive X-rays analysis (SEM/EDX) shows that, with silica fume, the C–S–H formed is type III at early ages and that type III and type I coexist at later ages. Silica fume lowers the total porosity and increases compressive strength only at later age and, as expected, the pore structure of mortar with silica fume is found to be finer than of non-silica fume mortar.     

Preparation and complex characterization of silica holmium sol–gel monoliths

Amorphous, sol–gel derived SiO₂ are known to biocompatible and bioresorbable materials. Biodegradable and inert materials containing radioactive isotopes have potential application as delivery vehicles of the beta radiation to the cancer tumors inside the body. Incorporation of holmium in the sol–gel derived SiO₂ could lead to the formation of a biodegradable material which could be used as carrier biomaterial for the radiation of radioactive holmium to the various cancer sites. The homogeneity of the prepared sol–gel silica holmium monoliths was investigated by Back Scattered Electron Imaging of Scanning Electron Microscope equipped with Energy Dispersive X-ray Analysis, X-ray Induced Photoelectron Spectroscopy and Nuclear Magnetic Resonance Spectroscopy. The biodegradation of the monoliths was investigated in Simulated Body Fluid and TRIS (Trizma pre-set Crystals) solution. The results show that by suitable tailoring of the sol–gel processing parameters holmium can be homogeneously incorporated in the silica matrix with a controlled biodegradation rate.     

Review and discussion of polymer action on alkali–silica reaction

This paper compares the factors known to influence the deleterious alkali–silica reaction in concrete with the properties that polymers tend to modify in cementitious materials. A discussion on the potential ASR-influencing mechanisms of polymer additions is provided, along with a critical review of the existing literature on the subject. The influence of the potentially significant differences in mechanical properties and sorptivity between polymer-modified and unmodified cementitious materials on the expansion results of alkali reactivity tests is also discussed. According to the available results, the influence of polymers on ASR-related expansion seems to depend on both polymer type and dosage, suggesting the existence of concurrent, not yet well understood mechanisms by which polymers may influence ASR-related expansion. As polymer modification of cementitious materials can lead to significantly lower modulus of elasticity, higher tensile strength and resistance to microcracking, it is suggested that further research on the subject includes not only expansion tests but also an assessment of the resistance of polymer-modified cementitious materials to ASR-related damage, the main concern due to this deleterious phenomena.     

Preparation and magnetic characteristics of mesoporous nickel oxide–silica composites

Mesoporous NiO–SiO₂ (MCM-41) silica-matrix composites with various nickel oxide concentrations (NiO : SiO₂ = 0.025 : 1 to 0.2 : 1) have been produced by oxide cocondensation under hydrothermal synthesis conditions in the presence of cetyltrimethylammonium bromide as a template and (2-cyanoethyl) triethoxysilane as an organosubstituted trialkoxysilane additive. X-ray diffraction data have been used to evaluate the maximum nickel(II) oxide concentration (NiO : SiO₂ = 0.1 : 1) that allows the ordered mesopore structure of MCM-41 to persist in the silica-matrix composites. We have studied the magnetic properties of this material as functions of temperature and magnetic field. The results demonstrate that the magnetic properties of the nanocomposite with NiO : SiO₂ = 0.1 : 1 at low temperatures (T < 20 K) are determined by incomplete spin compensation in the matrix and on the surface of the NiO nanoparticles.     

Fabrication of optimized oil–water separation devices through the targeted treatment of silica meshes

Abstract

Efficient oil–water separation is achieved using an optimized superhydrophobic material, generated by the zeolitic roughening and subsequent hydrophobic surface treatment of silica filter membranes. The material is both highly rough and intrinsically hydrophobic, resulting in superhydrophobic membranes which show a substantial affinity for hydrophobic solvents and oils. The membranes are syringe-mounted, suction pressure is applied and the selective collection of oil is achieved. The membranes are extremely robust, which is a result of the zeolitic roughening process, they possess small pores (0.7 μm), as a result these devices can perform complete separation and operate at a range of suction pressures. The devices could be readily used in a range of real-world applications, including oil spill clean-up and industrial filters.     

Transformation of tridymite to cristobalite below 1470° C in silica refractories

Because silica refractory has good volume stability and creep properties at high temperature, it has been used in several furnaces. However, silica has three polymorphs (quartz, tridymite and cristobalite) and each polymorph has an- type transformation. It is known that cristobalite is the stable phase of silica between 1470° C and the melting point of silica refractories. However, sometimes cristobalite was found in silica refractories used in the stable temperature region of tridymite. Therefore, the cause and mechanism of this tridymite-to-cristobalite transformation below 1470° C was studied. Although the transformation temperature of tridymite to cristobalite was also 1470° C in the sample used in this research, it decreased on addition of Al₂O₃. The apparent activation energy of the tridymite-to-cristobalite transformation was found to be 787 kJ mol^–1 above 1470° C and 176 kJ mol^–1 below 1470° C with Al₂O₃ by measuring the transformation rate. It was also observed using EPIVIA that the tridymite included CaO; however, CaO and Al₂O₃ were located on the outside of the cristobalite which was produced below 1470°C. Therefore, it is supposed that the liquid phase was produced by the penetration of Al₂O₃, and impurities in the tridymite crystal diffused outside and then silica was precipitated as cristobalite.     

Characterization of hollow silica–polyelectrolyte composite nanoparticles by small-angle X-ray scattering

Hollow silica–polyelectrolyte composite nanoparticles were prepared using templates of spherical polyelectrolyte brushes which consist of a polystyrene (PS) core and a densely grafted linear poly(acrylic acid) shell. The obtained hollow particles were systematically studied by small-angle X-ray scattering (SAXS) in combination with other characterization methods such as transmission electron microscopy and dynamic light scattering. The hollow structure formed by dissolving the PS core was confirmed by the reduction of electron density to zero in the cavity through fitting SAXS data. SAXS revealed both the inward and outward expansions of the hollow silica–polyelectrolyte composite particles upon increasing pH from 3 to 9, while further increasing pH led to the partial dissolution of silica layer and even destruction of the hollow structure. SAXS was confirmed to be a unique and powerful characterization method to observe hollow silica nanoparticles, which should be ideal candidates for controlled drug delivery.     

Effect of solution pH on the surface morphology of sol–gel derived silica gel

We have examined the effect of solution acidity on the textural characteristics of silica gels prepared by sol–gel synthesis using tetraethyl orthosilicate (TEOS) as a silica precursor and cetyltrimethylammonium bromide (CTAB) as a template. Using IR spectroscopy, we have studied micellar TEOS solutions and the synthesized silica gel samples. The results demonstrate that, in an alkaline medium in a water–ethanol solution, SiO₂ experiences short-range ordering on the surface of micelles formed by CTAB molecules, whereas in an acid medium the process is not influenced by the presence of CTAB. Nitrogen porosimetry and electron microscopy data indicate that the silica gel obtained at pH 2 is microporous, with an average pore size of 2 nm. In an alkaline medium at pH 10, we obtained mesoporous SiO₂ (18 nm) with a narrow pore size distribution and a specific surface area of 110 m²/g.     

Microstructural properties of lithium-added cement mortars subjected to alkali–silica reactions

Little comparative research has been done on the efficiency of lithium additives to reduce the alkali–silica reaction (ASR) expansion. To reduce the ASR effects of reactive aggregate, different mortar bars were obtained by adding lithium additives (Li₂SO₄, LiNO₃, Li₂CO₃, LiBr and LiF) to the mixing water by the following mass percentages of cement: 0%, 0.5%, 1%, 1.5%, 2%, 2.5% and 3%. The ASR expansions of the mortar bars at 2, 7 and 14 days were identified according to ASTM C 1260-14. The morphology of the specimens subject to the ASR effect was analysed using a scanning electron microscope, and their chemical composition was analysed by electron dispersion spectroscopy. Among all specimens, the lowest level of 14-day ASR expansion was obtained in mortar bars with 3% Li₂CO₃ additive.     

Microwave-assisted sol–gel process for production of spherical mesoporous silica materials

Spherical mesoporous SiO₂ and SiO₂–TiO₂ particles were synthesized by sol–gel method using W/O emulsion under microwave irradiation. In SiO₂ system, W/O emulsion was prepared by mixing partially hydrolyzed Si(OC₂H₅)₄ aqueous solution including C₁₈TAC as template with n-hexane solution including polyglycerol polyricinalate as emulsifier. In SiO₂–TiO₂ system, Ti(OC₂H₅)₄ capped by acetylacetone was added to the aqueous phase. In both cases, spherical products were synthesized by heating of W/O emulsion for 30 min under microwave irradiation. The specific surface area and pore size of spherical products were 800 m²/g and 1.6 nm, respectively, which indicates that the spherical products are mesoporous. These results suggest that sol–gel reaction in water phase proceeds rapidly because microwave quickly and selectively heats up the aqueous solution.     

Monodisperse core–shell particles composed of magnetite and dye-functionalized mesoporous silica

Hybrid particles with a core–shell structure have been obtained in the form of monodisperse spherical mesoporous silica particles filled with magnetite and covered with a mesoporous silica shell functionalized with a luminescent dye. The particles have a small root-mean-square size deviation (at most 10%), possess a specific surface area and specific pore volume of up to 250 m²/g and 0.15 cm³/g, respectively, and exhibit visible luminescence peaked at a wavelength of 530 nm. The particles can be used in diagnostics of cancerous diseases, serving simultaneously for therapeutic (magnetic hyperthermia and targeted drug delivery) and diagnostic (contrast agent for magnetic-resonance tomography and luminescent marker) purposes.