Atomic layer deposition of TiO2 on mesoporous silica

Ultra-thin layers of titanium dioxide are conformally grown within the pores of an ordered mesoporous silica, SBA-15, using atomic layer deposition, reducing the pore size from the original value of 67 Å to a final value of 32 Å. Analysis of the nitrogen isotherms indicated a conformal growth process in which both the internal surface area of the mesoporous material and the external surface was coated.     

Preparation of multi-amine-grafted mesoporous silicas and their application to heavy metal ions adsorption

Single amine-, double amine- and trinal amine-grafted mesoporous silica SBA-15 (denoted as 1N-SBA-15, 2N-SBA-15 and 3N-SBA-15) have been synthesized by refluxing SBA-15 and γ-aminopropyltriethoxysilane (APTS), N-[3-(trimethoxysilyl)-propylethylene]diamine (TPED) and trimethoxysilyl propyl diethylenetriamine (TPDT), respectively, in dry toluene under nitrogen atmosphere. These adsorbents could remove the metal ions of Pb²⁺, Cu²⁺, Cd²⁺, Zn²⁺ as well as Hg²⁺ rather completely. Thus these adsorbents will be a better choice when more than one kind of metal ions needs to be removed. From 1N-SBA-15 to 3N-SBA-15, their adsorption capacities for Hg²⁺ increase from 382 mg/g to 726 mg/g , which can be attributed to not only the large content of amino groups but also the rather increased steric freedom and accessibility of the functional groups in the large pore channels of SBA-15. The Hg/N ratio decreases with the increase of N numbers. A decrease about 20–47% of adsorption capacity of regenerated samples has been obtained and could be attributed to the N loss in concentrated acid. In addition, the fresh dry samples were found to show much higher adsorption capacity than the aged ones due to the competitive adsorption between atmosphere moisture and the metal ions on the amino groups.     

Preparation of mesoporous silicas using food grade emulsifiers and its application for enzyme supports

A novel mesoporous silica (TMPS) was synthesized via self-assembly using a myristic acid ester of pentaglycerol. The ester is obtained from catalytic esterification and it is commercially available as a food grade emulsifier. TMPS material was employed for preparation of a biocatalyst in order to examine the ability as an enzyme support in comparison with the other mesoporous silica materials having a channel or a cage-like pore system. The used TMPS materials possessed the interconnected channel-like pore system with the pore sizes of 9.2, 12, and 16 nm. The materials successfully entrapped lipase into their mesopores with the high loadings. The resultant lipase/TMPS conjugates functioned as the biocatalyst for hydrolysis of p-nitrophenyl propionate (p-NPP), having the higher activity than those of the used mesoporous silica conjugates. The high activities were ascribed to the textural properties such as the small particle length, large pore size and the three-dimensional pore connectivity that permit the accessibility of p-NPP to the immobilized lipases during the reactions. Consequently, we concluded that TMPS materials are of the suitable mesoporous support for the enzymes.     

The effect of acidity on the structural and textural evolution of titania in the presence of primary amine and inorganic precursor

Titania was synthesized from laurylamine hydrochloride (LAHC) and Ti(SO₄)₂ under different acidic conditions. The effect of acidity on the structural and textural evolution of titania has been investigated by X-ray diffraction (XRD), nitrogen adsorption–desorption, transmission electron micrographs (TEM), FTIR spectroscopy and thermogravimetric analysis (TGA). With increasing the pH value in the initial mixture, the obtained samples transformed from nanoparticles with intra-particle mesostructures (pH 0.6 and 2.0) to nanoparticles with nonporous structure (pH 3.7), and finally to worm-like porous materials with inter-particle mesostructures (pH 4.2) resulted from the aggregates of nanoparticles. The obtained mesoporous nanoparticles (pH 0.6 and 2.0) have mean diameter of ca. 25 nm, and the pore size distributions are bimodal with fine intra-particle pores and larger inter-particle pores. The intra-particle mesostructure not only retard the growth of nanocrystallites, but also prevent phase transition of anatase to rutile at high temperature. The BET surface area of the TiO₂ calcined at 300 °C decreased from 212 to 74 m²/g with pH increasing from 0.6 to 4.2.     

Effect of uni-axial loading on the nanostructure of silica aerogels

Aerogels are unique materials offering a combination of remarkable properties that make them useful in a wide range of applications. However, aerogel materials can be difficult to work with because they are fragile. The intent of the work presented here was to study the relationship between axial loading and pore structure in aerogel material. Silica aerogel samples with a bulk density of 0.1 g/mL were compressed by uni-axial force loads from 1 to 5 kN which resulted in stress levels up to 23 MPa. The resulting change in the pore distribution was observed using nitrogen desorption analysis and scanning electron microscopy. Uncompressed aerogel samples exhibit peak pore volume at diameters of about 20 nm. As the aerogels are subjected to increased loading, the location of the peak volume moves to smaller diameters with a reduced volume of pores occurring above this diameter. The peak diameter, the average pore diameter and pore volume all decrease and scale with increasing maximum stress while the surface area of the aerogel samples remains unaffected at about 520 m²/g. When combined with data from the literature, the relation between maximum pore diameter and applied stress suggests a failure mechanism dominated by bending induced fracture.     

Influence of synthesis temperature on the structural characteristics of mesoporous silica

The characteristics of mesoporous silica prepared at different temperatures and the behavior of this system relating to the microencapsulation of a model drug were investigated. The preparation of mesoporous materials was initiated with the dissolution of a surfactant in distilled water and strong acid medium. After this, tetraethyl orthosilicate was added under agitation. The mixture was heated for 24 h at the synthesis temperature (60 °C, 80 °C, 100 °C and 130 °C) under static conditions. The surfactant was removed by calcination, which was carried out by increasing the temperature to 550 °C for 5 h. Atenolol was used as a model drug to study the kinetics of drug delivery. It could be observed that aging materials at higher temperatures presents no microporosity, and this influences the control of the release of the model drug.     

Photoluminescence characterization of aged and regenerated mesoporous silica

The investigation of the photoluminescence features of aged and regenerated mesoporous silica is reported. The emission spectrum of aged samples displays a blue band peaked at about 450 nm at room temperature with excitation channels at 250 and 200 nm. No UV emission band is detected. The regenerated samples recover the optical transparency of the samples, the vibrational properties in the 3000–3800 cm^? 1 but for the isolated silanols band and the UV-blue emission features. Indeed beside the blue band peaked around 450 nm a UV band centred at 340 nm is reported whose relative contribution depends on the excitation wavelength. The aging and regeneration processes are discussed in view of the attribution of the observed emission features to specific surface defects.     

Adjusting the porous and structural properties of mesoporous silica by the addition of organic modifiers

The effects of the organic modifiers 2-cyanoethyltriethoxysilane and 3-aminopropyltriethoxysilane on the porous properties of silicates synthesised by co-condensation with tetraethyl orthosilicate were investigated. Materials were synthesised in aqueous solutions of cetyltrimethylammonium bromide or n-dodecylamine surfactants. Preparations using cetyltrimethylammonium bromide and sodium hydroxide gave MCM-48, with an average pore diameter of 25 Å, while addition of 10 mol% (of total silica) 2-cyanoethyltriethoxysilane improved the mesoporosity characteristics; the modified preparation gave a more intense X-ray diffraction pattern confirming a more ordered structure with a greater volume of regular mesopores. Disordered materials with pores 145 Å in diameter were formed using 2-cyanoethyltriethoxysilane modifier and ammonia as base. All preparations incorporating 3-aminopropyltriethoxysilane modifier were disordered and microporous. For silicates synthesised using n-dodecylamine surfactant, mesopores with diameter 118 Å were formed using 2-cyanoethyltriethoxysilane while preparations with 3-aminopropyltriethoxysilane and in the absence of a modifier were microporous. The particle sizes of the silicates displayed a clear correlation with the pore diameters: microporous silicates were 0.5–1 μm in particle diameter, MCM-48 phase (25/27 Å) were 1–2 μm, while relatively large mesoporous materials (>100 Å) had particle dimensions 10–100 μm.     

Synthesis and structural characterization of potato starch sponges

Materials with hierarchical porous structures have attracted great attention over the past years since they have been widely used in many industrial applications. Starch stands out among the materials commonly used as sacrificial templates in environmentally friendly applications. In addition, starch is inexpensive, easy to process, and readily available. In this work we present a structural characterization of sponges prepared by freezing and thawing of a starch gel. Samples obtained in this study were examined by scanning electron microscopy (SEM) and X-ray microtomography (μ-CT). SEM tests revealed that these samples show an open macroporous framework with continuous walls. μ-CT tests revealed that it is possible to tailor the pore structure of these materials by changing the starch concentration in gels used in their processing. We noticed that increasing starch concentration from 15 wt.% to 60 wt.% leads to sponges with porosities ranging from about 28% to over 65%. It was also observed that the higher the starch concentration, the greater the mean pore size of the prepared sponge.     

Positronium study of porous structure of sol–gel prepared SiO2: influence of pH

Positron annihilation lifetime and Doppler broadening of annihilation line techniques have been used to obtain information about the small-pore structure of SiO₂ prepared by the alkoxide method in different experimental conditions. Samples prepared in strong acidic environment (pH = 2) contain only small pores with mean radius R∼5 Å, while those prepared at pH = 6 and pH = 9 contain pores of two sizes, R∼5 and R∼17–26 Å. The influence of pH, water/alkoxide molar ratio and temperature of heat-treatment of the samples on their pore structure has been studied.     

Polymer nano-encapsulation of templated mesoporous silica monoliths with improved mechanical properties

Macroporous (1–5 μm) monolithic silica aerogels consisting of both random but also ordered mesoporous walls have been synthesized via an acid-catalyzed sol–gel process from tetramethoxysilane (TMOS) using a triblock co-polymer (Pluronic P123) as a structure-directing agent and 1,3,5-trimethylbenzene (TMB) as a micelle-swelling reagent. Pluronic P123 was removed by Soxhlet extraction, and materials in monolithic form were obtained by extracting the pore filling solvent with liquid CO₂, which eventually was taken out supercritically. Although these monoliths are more robust than base-catalyzed silica aerogels of similar density, nevertheless, the mechanical properties can be improved dramatically by letting an aliphatic di-isocyanate (Desmodur N3200) react with the silanols on the macro- and mesoporous surfaces. As it turns out, the polymer fills the mesopores and coats conformally the macropores of templated samples, so that BET surface areas decrease dramatically, from 550–620 m² g^?1 to <5 m² g^?1. By comparison, polymer nano-encapsulation of non-templated acid-catalyzed aerogels preserves a large fraction of their mesoporous surface area, and BET values decrease from 714 m² g^?1 to 109 m² g^?1. Finally, since polymer nano-encapsulation preserves the macroscopic physical dimensions of the monoliths before drying, comparative analysis of the physical dimensions against XRD data of native versus polymer nano-encapsulated samples provides evidence that upon drying macropores (micron size regime) shrink less than mesopores (nanometer size regime).     

Synthesis of hybrid mesoporous spheres using the chitosan as template

Hybrid mesoporous spheres of Al and Si oxides were synthesized for the mixture of organic material (chitosan) with inorganic material (aluminum and silicon hydroxide). It was observed that chitosan with larger polymerization degree, resulted in a larger mechanical resistance of the spheres. The oxides were characterized by the following: Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC), as well as, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and adsorption isotherms of N₂ (BET). Highly uniform oxide sphere diameters were obtained (average of 1.0 mm). The results of the adsorption isotherms indicated that the material is mesoporous. The surface area of the materials ranged between 620 and 245 m²/g, and the pore volume varied between 0.82 and 0.28 cm³/g, depending on the molar ratio of the organic and inorganic materials.     

SBA-15-collagen hybrid material for drug delivery applications

The development of mesoporous materials offers new possibilities for incorporating biological agents into silica structures and controlling the release kinetics from the matrix due to its well-arranged pore architecture. Indeed, the introduction of appropriate organic compounds into these ceramics has presented excellent results regarding drug release control. In this paper, two types of materials were used to evaluate drug delivery: SBA-15 and a hybrid SBA-15-collagen. The samples were charged with atenolol as a model drug and in vitro release assays were carried out. Significant differences were observed between the release patterns of the different materials, and the release rate was influenced by the presence of collagen in the mesopores.     

Synthesis and characterization of SBA-15 with titania clusters entrapped in micropores

Titania-containing SBA-15s were synthesized by impregnation of titanium isopropoxide in iso-propanol. X-ray diffraction, transmission electron microscopy, and N₂ sorption measurements showed that the mesostructures are intact after impregnations. Raman and UV–vis DRS spectra proved the existence of small anatase TiO₂ clusters (∼1.3 nm) after three loading cycles. Disappeared micropores and unchanged mesopore volumes after three loading cycles demonstrated that majority of micropores were consumed to immobilize these small titania clusters, which could provide a new way for the development mesoporous silica-supported titania.     

Synthesis of Pt-containing mesoporous silica using Pt precursor as a pore-forming agent

We synthesized Pt nanoparticle-containing mesoporous silica in a one-pot process using tetraammineplatinum(II) hydroxide (TPH) precursor as a pore-forming agent and silica nanospheres as a silica source. The TPH precursor was added into as-prepared colloidal silica sol with silica nanospheres (SN) of about 8 nm in particle diameter, to obtain the SN–TPH sol. During drying process of the SN–TPH sol, an amorphous SN–TPH nanocomposite was formed via hydrogen-bonding interaction between silanol groups and amine groups of the TPH precursor. The hydrogen-bonding interaction was confirmed by thermal gravimetry and differential thermal analysis (TG–DTA) profiles and Fourier transform infrared (FTIR) spectra. Using the TPH precursor as a pore-forming agent, incorporation of the Pt nanoparticles into the mesoporous silica can be simultaneously achieved with the synthesis of the mesoporous silica in a one-pot process. In addition, Pt nanoparticle size and pore diameter of the mesoporous Pt/silica were simultaneously controlled by simply varying the concentration of the TPH precursor. The pore diameter of the mesoporous silica was easily controlled from 3.2 nm to 6.5 nm with an increase in the TPH concentration.     

Synthesis and bioactive properties of macroporous nanoscale SiO2–CaO–P2O5 bioactive glass

A macroporous nanoscale bulk bioactive glass (SiO₂–CaO–P₂O₅ system) was prepared by sol–gel co-template method. Porosimeter analysis showed that the as-synthesized bioactive glasses (BGs) had a porosity of 85% and exhibited a multimodal pore size distribution, nanopores (10–40 nm) and macropores (100 nm–10 μm). Morphological and structural characterizations showed the pores were interconnected with pore walls of about 250 nm in width and 1 μm in length. In vitro bioactivity test indicated that the as-synthesized bulk BGs exhibited faster apatite layer formation capability than the conventional sol–gel BGs. Additionally, the deposited layer was identified as hydroxycarbonate apatite, which is similar to the inorganic part of human bone.     

Microstructural and photocatalytic properties of sol–gel-derived vanadium-doped mesoporous titanium dioxide nanoparticles

The vanadium (V)-doped mesoporous titanium dioxide (TiO₂) nanoparticles at low V/Ti ratios ranging from 0 to 2 wt% were prepared using hydrolytic sol–gel method in the presence of tri-block copolymer Pluronic F127. The microstructures of TiO₂ in terms of morphology, crystallization, chemical states of species, surface area, and band gap were characterized by SEM, TEM, XRPD, XPS, surface area analyzer, and UV–Vis spectrophotometer, respectively. SEM images showed that the V-doped TiO₂ nanoparticles were porous structures, and the surface areas and pore sizes ranged from 86 ± 9 to 96 ± 15 m²/g and from 12 ± 4 to 15 ± 2 nm, respectively. The XRPD patterns indicated that V-doped mesoporous TiO₂ after calcination at 500 °C was mainly anatase phase, and the crystallite sizes were in the range 14–16 nm, which are consistent with the results obtained from SEM images. XPS spectra and HRTEM images showed that vanadia was doped both on the surface and in the lattice of anatase TiO₂. A slight red-shift in wavelength absorption was observed when V/Ti ratio increased from 0 to 2 wt%. Methylene blue (MB) was further used as the target compound to examine the photocatalytic activity of V-doped mesoporous TiO₂ nanocatalysts under illumination of solar simulator or UV light. Addition of vanadium ions slightly decreased the photocatalytic activity of TiO₂ toward the decolorization of MB under the illumination of UV light at 305 nm. However, a 1.6–1.8 times increase in rate constants for MB photodegradation was observed when 0.5–1.0 wt% V-doped TiO₂ was illuminated with sunlight at AM 1.5.     

Synthesis and characterization of high nickel-containing mesoporous silica via a modified direct synthesis method

A method by modifying tetraethyl orthosilicate (TEOS) with nickel species has been developed for the synthesis of mesoporous silica with high nickel content (up to 14.7 wt% of Ni). Using the method, nickel-containing mesoporous materials were obtained with high BET surface area and pore volume. The materials were characterized by means of X-ray powder diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, N₂ adsorption, Fourier transform infrared. Nickel species were incorporated into the silica frameworks. Formation of nickel phyllosilicates was also confirmed. After activation, mesostructures are still intact. Small nickel clusters embedded in the silica walls were found.     

Ag-doped antibacterial porous materials with slow release of silver ions

The inorganic–organic hybrids of polyethyleneglycol (PEG), tetraethoxysilane (TEOS) and triethylphosphate (TEP) doped by silver ions were prepared by sol–gel method. After molding and heating at 600 °C to remove organic components, porous Ag–P₂O₅–SiO₂ monoliths were obtained. Thermogravimetry (TG), differential thermal analysis (DTA), infrared spectra, ultraviolet–visible (UV–vis) spectra and pore structure of the samples were measured to show that organic components and residual water could be removed by a heat-treatment up to 600 °C and the mesopores with 6 nm pore diameter were formed. Specific surface area and pore volume of the samples were adjusted with different contents of TEP in the starting composition. Ag⁺ ions could be stably released into water at 30 °C up to 28 days. Antibacterial experiment showed that such materials treated at 600 °C could restrain Escherichia coli effectively.     

Physical aging effects in selenide glasses accelerated by highly energetic γ-irradiation

Effect of ⁶⁰Co γ-irradiation on As–Se glasses stored for 20 years and subjected to saturated natural physical aging is studied using differential scanning calorimetry. It is shown that γ-irradiation activates further physical aging, which leads to an increase in glass transition temperature and endothermic peak area near glass transition region for As_xSe_100−x samples with x < 30. The observed changes are associated with additional structural relaxation of radiation-modified glass network.