Two-step Sol-gel Process Research Articles

Preparation of SiO2/Fe2O3 composite aerogels for thermal insulation enhancement

Silica aerogel, with a unique nano-network structure, serves as a high-performance thermal insulation material. However, silica aerogel possesses a high infrared wave transmission ratio above 300 °C, whose thermal conductivity increases and thermal insulation performance further decreases with the increasing temperature. Introducing opacifiers to silica aerogel is a crucial strategy for addressing this issue. In this work, the ferric oxide exerted as an opacifier was incorporated into the main-phase silica aerogel to improve its thermal insulation at high temperatures. The SiO2/Fe2O3 composite aerogels were created via the two-step sol-gel process followed by supercritical drying, which involved doping ferric nitrate nonahydrate as a Fe2O3 precursor into the silica sol generated with tetraethoxysilane. In this way, SiO2/Fe2O3 composite aerogels with low density (0.04 g/cm3), high specific surface area (705 cm2/g), and low thermal conductivity (0.026 W/(m K)) were obtained by structural adjustment. The incorporation of Fe2O3 improves the thermal insulating properties of silica aerogels. After heat treatment at 1100 °C, the thermal conductivity of the SiO2/Fe2O3 composite aerogel was 0.167 W/(m K), lower than that of the pure silica aerogel (0.249 W/(m K)). Furthermore, the SiO2/Fe2O3 composite aerogel maintained its amorphous structure and exhibited a specific surface area of approximately 94.56 cm2/g, which was three times that of the pure silica aerogel. When subjected to 5-min heating at 1000 °C, the maximum surface temperature of the heat delivery surface of the SiO2/Fe2O3 composite aerogel reached 280.8 °C, whereas the pure silica aerogel reached 353.8 °C.

Determining the influence mechanism of defects on remarkable room temperature ferromagnetic behavior for C-doped titanium dioxide aided by carboxymethyl cellulose as C source

C-doped titanium dioxide nanoparticles (C–TiO2) were synthesized through a two-step sol-gel process aided by carboxymethyl cellulose (CMC) as C source, following by annealed at different temperature under vacuum. Lattice defects and room temperature ferromagnetism (RTFM) influenced by C doping and annealing temperature are investigated in detail. Correlation between the variation tendency of defects and that of saturation magnetization (Ms) of C–TiO2 is determined, and influence mechanism of defects on RTFM is clarified. Results reveal that influenced by the increase of annealing temperature, C–TiO2 transforms from anatase to rutile phase, followed by some brookite phase and a small amount of elemental carbon precipitate. Three types of defects are introduced in C–TiO2 lattice, namely, substitutional C atoms at titanium sites (CTi), interstitial C defects (Ci) and oxygen vacancies (VOs). Content of CTi shows a gradual increase with increase in annealing temperature from 200 °C to 500 °C, after which a decrement is observed, and that of Ci shows an opposite tendency, while VOs content increases monotonically with increased annealing temperature. Influenced by annealing temperature, Ms shows a similar variation tendency to that of CTi. Joint effect of CTi and VOs promotes the formation of RTFM in C–TiO2, and CTi defects play a major role by inducing ferromagnetic coupling interaction between C 2p and O 2p states. CMC is a more suitable C source than citric acid to induce remarkable room temperature ferromagnetic behavior in C–TiO2 nanoparticles.

Non-fluorinated sol-gel processing of hydrophobic coating on cotton fabric

In this study, the importance of wash durability tests for providing efficient hydrophobic surfaces through non-fluorinated sol-gel processes has been investigated. Various concentrations of methyltriethoxysilane (MTEOS) and trimethylchlorosilane (TMCS) have been used to deposit SiO2 nanoparticles on a cotton fabric in a two-step sol-gel process. The effects of catalyst type on the hydrophobic properties of fabric are investigated by using ammonia or hydrochloric acid in the sol-gel procedure. Surface characteristics, such as morphology and wettability are evaluated by image processing techniques and contact angle measurements. Air permeability, mechanical strength and wash durability tests are also performed to investigate the physical/mechanical properties of the samples. The results show that SiO2 nanoparticles are well dispersed on cotton fabrics with a contact angle of 149o. It is revealed that the fabric coated with 1 mL of MTEOS and ammonia catalyst exhibits the highest breathability and strength. Moreover, the first stage of the sol-gel technique is sufficient to provide super hydrophobicity. However, the results of the durability test indicate that sol-gel technique does not provide suitable wash durability that should be considered in future investigations.

Microstructural properties and heat transfer characteristics of in-situ modified silica aerogels prepared with different organosilanes

• In-situ modified silica aerogels were synthesized in ambient pressure by a facile sol-gel method. • Various organosilanes MTMS, MTES, VTMS, MEMO and GLYMO were utilized as silica precursors. • Heat transfer mechanisms were investigated both theoretically and experimentally. • SA-MTMS had the lowest density (92 kg⁄m 3 ) and high thermal stability (up to 700 °C). • All samples exhibited similar insulation performances (λ in between 42 and 47 mW/mK). • The density was the most decisive parameter for different heat transfer modes in aerogels. • Coupling thermal conductivity term is the key contributor to the total thermal conductivity. Conducting an in-situ modification during the sol-gel reactions, without any post gelation-modification, offers a cost-effective and time-saving strategy in the production of silica aerogels. Therefore, in this study, in-situ modified silica aerogels were synthesized as potential thermal insulation materials via a two-step sol-gel process under ambient pressure. Different organosilanes having methyl (SA-MTMS), ethyl (SA-MTES), vinyl (SA-VTMS), epoxide (SA-GLYMO), and methacrylate functional (SA-MEMO) groups were used as silica sources. According to the selected precursor, the change in the heat transfer properties were investigated both by thermal conductivity measurements and by theoretical models. SA-MTMS possessed the lowest density (92 kg / m 3 ) and high thermal stability (up to 700 °C). Despite the existence of bulk organic groups in its structure, the SA-GLYMO had the highest specific surface area (531 m 2 / g ) . Regardless of their morphology, all samples have exhibited similar insulation performances (λ=42–47 mW/mK). However, the prominent heat transfer mechanisms were directly affected by the bulk density and the underlying microstructure. For low-density samples, gas-contributed thermal conductivities were the key contributor to the total thermal conductivity whereas solid thermal conduction was the dominant mechanism in high-density samples. The coupling thermal conductivity term was also crucial as the total conductivity would have been significantly underestimated without it.

Evaluation of the antibacterial properties and in-vitro cell compatibilities of doped copper oxide/hydroxyapatite composites

Mg, Zn and Ce-doped CuO/HA composites were prepared by a two-step sol-gel and hydrothermal process. SEM images showed a spherical appearance of HA and a needle-like morphology for doped CuO. XRD patterns revealed that all doped CuO/HA composites exhibited a hexagonal crystal structure of HA and a monoclinic crystal structure of CuO with no impurities. ICP analysis indicated that with the increase of loading amount of doped CuO, the concentrations of Cu2+ ions and doping ions released from composites increased. Moreover, CuO/HA composites exhibit improved antibacterial properties against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as compared with HA. When the loading amount of doped CuO in composites increased to 15 wt%, the composites exhibited the best antibacterial activity and complete bacterial growth inhibition effect. Furthermore, the CCK-8 assay revealed that the doped CuO/HA composites are noncytotoxic and can promote the proliferation of osteosarcoma cells. This work highlights the potential of the doped CuO/HA composites with significant antibacterial activity, bioactivity and cell compatibility for potential biomedical applications in dental implants and bone regeneration.

Performance regulation of silica aerogel powder synthesized by a two-step Sol-gel process with a fast ambient pressure drying route

This paper proposed a timesaving route for preparing silica aerogel powder with TEOS as a precursor. Thermal insulating super hydrophobic silica aerogel powder was synthesized by combining two-step Sol-gel reaction with a fast ambient pressure drying process. Silica Sol-gel was formed after catalytic reaction by oxalic acid and NH4OH, and then turned to be hydrophobic aerogel through further surface modification (only three hours with no solvent exchange process) and drying process. By optimizing every tiny trace of synthetic component, the obtained silica aerogel powder exhibits excellent properties, such as low apparent density (0.212 g/cm3) and thermal conductivity (0.053 W/mK), as well as high BET surface area (769.86 m2/g) and water contact angle (149.0 °). This work presents a timesaving method for synthesizing thermal insulating hydrophobic silica aerogel powder.

Study of compositional stability and related optical properties of perovskite CH3NH3PbBr3 films fabricated via two-step sol-gel process using weakly coordinating isopropanol solvent

Compositional stability of perovskites is crucial for perovskite solar cells (PSCs) application because of directly affecting the performance of PSCs. Highly crystallized perovskite MAPbBr3 (MA = CH3NH3) with micronscale crystallites are usually fabricated via the one-step sol-gel process that uses strongly coordinating organic solvents. The two-step sol-gel process using weakly coordinating organic solvent is rarely used to fabricate MAPbBr3 films with relatively small crystallites. However, the two-step sol-gel process is preferred to fabricate PSCs because the residual PbBr2 can prevent the direct contact between electron- and hole-transporting layers. Thus in this work, perovskite MAPbBr3 films are fabricated via two-step sol-gel process using weakly coordinating isopropanol solvent. The compositional stability in dry ambient air and related optical properties of the films are intensively studied by a technique of post-annealing. A compositional transition from MAPbBr3 to PbBr2 occurs with increase of post-annealing temperature (Tpa). The product PbBr2 begins to form in the MAPbBr3 films at approximately 130 °C Tpa, and MAPbBr3 is fully thermally degraded to PbBr2 at 170 °C Tpa. The compositional stability of the films in dry air is inherently determined by instable organic cations (MA)+ and small electronegativity of Br−. The perovskite film initially shows a redshifted and then a blueshifted optical absorption edge with increase of Tpa, which is due to the decrease in film tensile stress and to the enhancement in thermal degradation to PbBr2, respectively. The increase in number of PbBr2 particles and defects in the films remarkably reduces the intensity of the green emission of MAPbBr3.

Superhydrophobic, enhanced strength and thermal insulation silica aerogel/glass fiber felt based on methyltrimethoxysilane precursor and silica gel impregnation

Silica aerogel was often reinforced with glass fiber and changed to hydrophobicity via a surface modification to overcome its fragile and hygroscopic nature for practical application. However, though the mechanical and hydrophobic performances of the silica aerogel were improved, its unique ultra-low thermal conductivity was compromised. In order to prepare the hydrophobic silica aerogel felt while maintaining its excellent mechanical and insulation performances, the tetraethoxysilane and methyltrimethoxysilane (MTMS) as co-precursors, glass fiber as felt, and silica gel as a filling agent were selected to make the felt. An approach of the two-step sol–gel process followed by supercritical CO2 drying was applied. The morphology, structure, and properties of the felt were analyzed by field emission scanning electron microscope, a Fourier transform infrared spectrometer, and a thermal constants analyzer, etc. It was found that the felt showed excellent mechanical, thermally insulating, and hydrophobic performance. Also, it maintained low density and had higher thermal stability, due to the addition of silica gel and MTMS in the felt. The former enhanced the combination of silica aerogel with glass fiber and improved the microstructure of the felt. The latter endowed the felt excellent hydrophobicity, flexibility, and thermal stability.

Hydrophobic granular silica-based aerogels obtained from ambient pressure monoliths

Aiming at obtaining granular silica-based aerogels for incorporating in superinsulating systems, strong monoliths were produced at ambient pressure by a two-step sol–gel process, subsequently crushed and selectively sieved. The key to a strong and stable hybrid network was to use two silica co-precursors, tetraethoxysilane (TEOS) and dimethyldiethoxysilane (DMDES). The role of DMDES is to contribute to a more robust initial network, able to withstand surface modification during aging. To tailor the properties of the final monoliths the DMDES:TEOS and water:precursors molar ratios were varied (0 to 1 and 4 to 10, respectively). Aging in a solution of hexamethyldisilazane in 2-PrOH was essential to improve hydrophobicity and stability to moisture, producing lighter, more open and three-dimensional pore structures, with very high specific surface areas. A well-balanced relationship between density, pore structure, strength and hydrophobicity was achieved. These properties allowed grinding the monoliths without dust release and selective sieving into granulate diameters above 2 mm, in the ranges 1–2 mm, 500 µm-1 mm, 250–500 µm, 125–250 µm and 63–125 µm, and bellow 63 µm. These granules have the advantages of being produced at ambient pressure with minimum amounts of organic co-precursor and hydrofobizing agent, which constitute a substantial fraction of the raw materials cost. Affording well defined granulate ranges opens the possibility of controlling the granulometric curve of the aerogel, and thus the mechanical properties and thermal conductivity of the final aerogel-based product. The hydrophobicity (steady water contact angles from 122–142o) envisages perspective applications not restricted to moisture-protected environments.

Study of perovskite (CH3NH3)xCs1-xPbBr3 films with nanometer crystallites fabricated via two-step sol-gel process: Impact of CH3NH3+ molar content on microstructure and optical properties

Perovskite (MA)xCs1-xPbBr3 (MA = CH3NH3) films have high stability in heat and humidity, which is crucial for perovskite solar cell application. (MA)xCs1-xPbBr3 films are highly crystallized with micrometer crystallites in the one-step sol-gel process. By contrast, the films usually have nanometer crystallites in the two-step sol-gel process using nonpolar or weakly coordinating organic solvent. The related study is rarely reported so far. Herein, we reported the fabrication of perovskite (MA)xCs1-xPbBr3 films with nanometer crystallites via the two-step sol-gel process. The impact of x ((MA)+ molar content) was thoroughly studied on the film's microstructure and optical properties. The admixture of more (MA)+ greatly improves the film crystallization and restricts the production of the intermediate products. The film's photoluminescence (PL) intensity is enhanced with admixture of more (MA)+, inherently due to the increased PL lifetime caused by the improved film crystallization and the reduced film defects. The films initially exhibit a redshifted, and then a blueshifted and then a redshifted optical absorption edge with increased of x. The red shift in optical absorption edge is due to the increased crystal lattice constants, and the blue shift to the transition of the preferred orientation from <110> to <100>.

Fabrication and characterization of all-inorganic halide perovskite CsPbBr3 films via the two–step sol–gel process: Impact of annealing temperature

Organic–inorganic hybrid perovskite solar cells (PSCs) have realized a 23.2% power conversion efficiency (PCE), thereby making the PSC application promising. However, the compositional instability of perovskites and PSCs in high-temperature and/or –humidity ambient air condition has restricted the PSC application. All–inorganic CsPbBr3-based PSCs can deal with the problem due to the high stability in heat and humidity of CsPbBr3. Perovskite CsPbBr3 is highly crystallized with micronscale crystallites by Pb2+ strongly coordinating with organic molecules in the one–step sol–gel process. By contrast, CsPbBr3 crystalizes in nanoscale crystallites in the two-step sol-gel process using nonpolar or weakly coordinating organic solvent. The related study is rarely reported so far. Herein, we reported the fabrication of all–inorganic perovskite CsPbBr3 films via the two–step sol–gel process using weakly coordinating methanol solvent. The impact of annealing temperature (Tanneal) was in particular studied on the film's microstructure and optical properties. The Increased Tanneal restricts the production of byproduct Cs4PbBr6 and greatly improves the film crystallization, thereby increasing the film's photoluminescence intensity and lifetime. A transition from the compressive stress to tensile stress in the films is observed at 250 °C Tanneal. The red shift in optical absorption edge with increased Tanneal is mainly due to the increased compressive stress and reduced tensile stress in the films.

Citric acid functionalized silane coupling versus post-grafting strategy for dual pH and saline responsive delivery of cisplatin by Fe3O4/carboxyl functionalized mesoporous SiO2 hybrid nanoparticles: A-synthesis, physicochemical and biological characterization

Synthesis of monodisperse carboxylic acid-functionalized magnetic mesoporous silica nanoparticles is performed by either two-step sol-gel process or post-grafting using citric acid modified isocyanate silane coupling agent (MMSN-NCO-CA) or succinic anhydride modified magnetic mesoporous silica (MMSN-NH-SA). Morphology, structure and magnetic properties of bare and mesoporous silica coated Fe3O4 core were studied using various techniques such as FTIR, VSM, TEM, FESEM, XRD and N2 adsorption-desorption isotherms (BET). Cisplatin (cis-Pt) adsorption isotherms and its release profile in various media were investigated by ICP-OES. MMSN-NCO-CA with mean particle size 107 nm had lower surface area (87.5 m2/g) and larger pore size (6.9 nm) in comparison with MMSN-NH-SA (respective values of 151.2 m2/g and 3.5 nm). cis-Pt loading into particles followed a saturable adsorption with respect to the drug to particle mass ratios. More sustained release of cis-Pt was observed for MMSN-NCO-CA, though both nanoparticles exhibited a pH- and saline concentration-dependent drug release. In addition, general and cis-Pt specific cytotoxicity were examined by MTT assay in MDA-MB-231 breast cancer cell line, and to further detect apoptosis, acridine orange/ethidium bromide dual cell staining was investigated by fluorescence microscopy. In-vitro anti-tumor efficiency of cis-Pt loaded MMSN-NCO-CA and MMSN-NH-SA were similarly enhanced in comparison to free cis-Pt; however, more specific apoptotic death occurred for cis-Pt loaded MMSN-NCO-CA. Therefore, the as-synthesized citric acid functionalized core-shell magnetic mesoporous hybrid nanoparticles could be used as a promising drug carriers for cancer therapy in-vivo.

Silica aerogel/polyester blankets for efficient sound absorption in buildings

In this paper sound absorption characteristics of silica aerogel/polyester (PET) blankets are investigated. PET fibers were made on an industrial scale compact melt spinning line and then processed on a laboratory scale needling line to produce nonwoven fabrics. The silica aerogel blankets were prepared by in situ synthesis of silica aerogel on the nonwoven fabrics via a two-step sol-gel process of tetraethoxysilane which was followed by drying at ambient pressure. In order to achieve aerogel particles with different pore structure and properties, various synthesis conditions were used. The nonwoven samples were characterized in terms of thickness, fiber diameter, porosity and pore size by X-ray micro-computed tomography and scanning electron microscopy. Moreover, nitrogen adsorption analysis was carried out to determine the specific surface area and pore structure of aerogel particles.The effect of pore structure, physical properties and hydrophobicity of aerogel particles on sound absorption coefficient (SAC) of blankets was investigated using two-microphone transfer function method. Also, the effect of sol volume and nonwoven thickness was investigated. The results indicated that at all frequency levels, silica aerogel/PET blankets enjoy higher SAC than their untreated counterparts. It was found that, SAC is strongly affected by the pore structure of aerogel particles. Silica aerogels with lower bulk densities, larger pore size and higher porosities exhibited better sound absorption performance. The results also indicated that hydrophobic aerogel blankets exhibit higher SAC as compared with hydrophilic blankets. The results also showed that the thickness of nonwoven fabric strongly affects the SAC of aerogel blankets.

Fabrication and characterization of perovskite CH3NH3PbI3 films via two-step sol-gel process: Impact of soaking time of PbI2

Perovskite MAPbI3 (MA = methylammonium, CH3NH3) films and solar cells have thoroughly been studied in recently years. However, the formation mechanism of MAPbI3 in the two-step sol-gel process is not reported and not well understood yet. Thus in this work, the cubic perovskite MAPbI3 films with preferred 〈110〉 orientation were fabricated on the glass substrates via the two-step sol-gel process. Impact of soaking time (tsoaking) of PbI2 in MAI in isopropyl alcohol (IPA) solution was thoroughly studied on the microstructure and the optical properties of the MAPbI3 films. The formation mechanism of MAPbI3 in the two-step sol-gel process was in particular proposed. The blue and red shifts of the absorption edge of the films with increase of tsoaking are attributed to the improved crystallization and to the weakened surface effect of the grains, respectively. An intermediate metal-organic frameworks (MOF) structure of PbI2:MAI:IPA is formed during the soaking due to Pb weakly coordinating with IPA organic molecules. The unstable MOF structure is collapsed during the following annealing, and PbI2 and ions I− from the hydrolyzed MAI form the stable PbI64− cubic frame. Ions (MA)+ diffuse to the interstice positions in the cubic frame structure under the electrostatic force, thus producing the ultimate MAPbI3.

Polypropylene/Silica Aerogel Composite Incorporating a Conformal Coating of Methyltrimethoxysilane-Based Aerogel.

Silica aerogels possess low thermal conductivity but have a brittle nature, while their polymers tend to exhibit enhanced mechanical properties. In this study, we introduce a new approach to overcoming this brittle property of silica aerogels. Polypropylene/silica aerogel composites were prepared by thermally induced phase separation followed by a supercritical CO₂ drying method. Silica aerogel was formed onto a polypropylene scaffold using a two-step sol-gel process with methyltrimethoxysilane as the silica precursor. Enhancement of the mechanical properties of the polypropylene/silica aerogel composite compared with a pristine methyltrimethoxysilane-based silica aerogel was observed. The effects of the latter on the microstructure and physical properties of the polypropylene/silica aerogel (hereafter referred to as the polymer matrix aerogel) composite were investigated. Compared with the polypropylene monolith, the polymer matrix aerogel composite demonstrated enhanced surface-chemical and microporous-structural properties such as higher hydrophobicity (135°), pore volume (0.18 cm³/g), average pore diameter (12.55 nm), and specific surface area (57.2 m²/g). This novel approach of incorporating methyltrimethoxysilane-based silica aerogel onto polypropylene when synthesizing the polymer matrix aerogel composite shows great potential as a durable superhydrophobic and corrosion resistant thermal insulating material.

Hydroxyapatite/tricalcium silicate composites cement derived from novel two-step sol-gel process with good biocompatibility and applications as bone cement and potential coating materials

Tricalcium silicate (C3S) and hydroxyapatite (HAp) composites were fabricated through the sol-gel process. The aim of this research is to improve the biocompatibility of C3S through HAp addition and study the potential of using this as coating materials. The composites (HAp/C3S) were characterised by Fourier transform infrared spectrometry, thermal gravity-differential thermal analysis and X-ray diffraction. The working and setting times of cement pastes were tested using Gillmore needle. Mechanical properties were examined by nanoindentation and material testing system. In vitro biocompatibility of the materials were studied by cell attachment and viability of L929 and MG-63 cells. HAp/C3S as a coating material on gelatin film were measured with the surface roughness and imaged by scanning electron microscope. With the addition of HAp, no undesirable free CaO was detected with the synthesis by the sol-gel preparation. The pH values of HAp added groups were between 7.54 and 8.76, which were much lower than pure C3S group (pH = 11.75). For in vitro studies, the presence of HAp could effectively enhance the cell attachment and viability of both L929 and MG-63 cells grown in the extract or directly on the composites. However, the mechanical properties of the composites were impaired as compared to pure C3S. Lastly, HAp/C3S cement could be evenly coated on gelatin film. HAp is successfully demonstrated to improve C3S biocompatibility with this new composites HAp/C3S. C-75 (75% C3S and 25% HAp), in particular, has good biocompatibility, relatively high compressive strength and can be uniformly coated onto gelatin film. Thus, C-75 is a promising material for further investigation as a coating on other biopolymers.

Enhanced dielectric, electromechanical and hydrophobic behaviors of core-shell AgNWs@SiO2/PDMS composites

This paper reports a feasible method to prepare polymeric nanocomposites with enhanced dielectric, electromechanical and hydrophobic performance by introducing the core-shell AgNWs@SiO2 filler into polydimethylsiloxane (PDMS). The homogenous core-shell AgNWs@SiO2 was firstly synthesized through a two-step sol-gel process. The thicknesses of AgNWs and SiO2 coating layer are approximately 70 nm and 20 nm, respectively. The dielectric constant is improved effectively due to enhanced interfacial polarization, while extremely low dielectric loss and conductivity are achieved by introducing the insulating SiO2 interlayer to moderate the internal surface area of core-shell nanowires and restrict the electron transfer between Ag nanowires. Typically, the PDMS nanocomposites with 20 wt% AgNWs@SiO2 have a dielectric constant of 6.7, nearly 2.7 times larger than that of pure PDMS, and remains a quite low loss of 0.02 at 1 kHz. Meanwhile, nanocomposites also show improved electromechanical and hydrophoic properties. Nanocomposites with 10 wt% AgNWs@SiO2 exhibit the highest electromechanical sensitivity (β=9.04), about 12.6 times higher than that of pure PDMS at 1 kHz. The static contact angle of nanocomposties with 20 wt% AgNWs@SiO2 reaches 129°. All the improved performances show great potential application for dielectric elastomer material and electrowetting devices.

Reinforced silica-carbon nanotube monolithic aerogels synthesised by rapid controlled gelation

This work introduces a new synthesis procedure for obtaining homogeneous silica hybrid aerogels with carbon nanotube contents up to 2.50 wt.%. The inclusion of nanotubes in the highly porous silica matrix was performed by a two-step sol–gel process, resulting in samples with densities below 80 mg/cm3. The structural analyses (N2 physisorption and SEM) revealed the hierarchical structure of the porous matrix formed by nanoparticles arranged in clusters of 100 and 300 nm in size, specific surface areas around 600 m2/g and porous volumes above 4.0 cm3/g. In addition, a relevant increase on the mechanical performance was found, and an increment of 50% for the compressive strength and 90% for the maximum deformation were measured by uniaxial compression. This reinforcement was possible thanks to the outstanding dispersion of the CNT within the silica matrix and the formation of Si–O–C bridges between nanotubes and silica matrix, as suggested by FTIR. Therefore, the original synthesis procedure introduced in this work allows the fabrication of highly porous hybrid materials loaded with carbon nanotubes homogeneously distributed in the space, which remain available for a variety of technological applications.

Highly Efficient Glioma Targeting of Tat Peptide-TTA1 Aptamer-Polyephylene Glycol-Modified Gelatin-Siloxane Nanoparticles.

Gliomas are the most common type of intracranial malignant tumor; however, current treatment approaches are often ineffective due to limited penetration of genes or drugs through the blood-brain barrier (BBB). Here we describe the synthesis of gelatin-siloxane nanoparticles (GS NPs) as candidate gene carriers through a two-step sol-gel process. To increase the efficiency of glioma targeting, human immunodeficiency virus-derived Tat, tumor-targeting aptamer (TTA)1, and polyethylene glycol (PEG) were conjugated to the GS NPs to generate Tat-TTA1-PEG-GS NPs. In vivo imaging revealed that these modified NPs not only evaded capture by the reticulo-endothelial system, but were able to cross the BBB to reach gliomas. Our results suggest that Tat-TTA1-PEG-GS NPs are a new type of non-viral vector that can deliver therapeutic DNA or drugs for highly efficient glioma treatment.

Ambient pressure dried tetrapropoxysilane-based silica aerogels with high specific surface area

In the present paper, we report the synthesis of tetrapropoxysilane (TPOS)-based silica aerogels with high surface area and large pore volume. The silica aerogels were prepared by a two-step sol-gel process followed by surface modification via a simple ambient pressure drying approach. In order to minimize drying shrinkage and obtain hydrophobic aerogels, the surface of the alcogels was modified using trichloromethylsilane as a silylating agent. The effect of the sol-gel compositional parameters on the polymerization of aerogels prepared by TPOS, one of the precursors belonging to the Si(OR)4 family, was reported for the first time. The oxalic acid and NH4OH concentrations were adjusted to achieve good-quality aerogels with high surface area, low density, and high transparency. Controlling the hydrolysis and condensation reactions of the TPOS precursor turned out to be the most important factor to determine the pore characteristics of the aerogel. Highly transparent aerogels with high specific surface area (938 m2/g) and low density (0.047 g/cm3) could be obtained using an optimized TPOS/MeOH molar ratio with appropriate concentrations of oxalic acid and NH4OH.