Composite Xerogel Research Articles

Optical Fiber Oxygen Sensor Based on Ru (II) Complex and Porous Silica Nanoparticles Embedded in Sol-Gel Matrix

This paper presents a high-sensitivity oxygen sensor that comprises an optical fibre coated at one end with tris (4, 7-diphenyl-1, 10-phenanthroline) ruthenium (II) ([Ru (dpp)3]2+) and porous silica nanoparticles embedded in an n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio IN2/IO2, where IN2 and IO2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results show that the oxygen sensor has a sensitivity of 26. The experimental results show that compared to oxygen sensor based on Ru (II) complex immobilized in the sol-gel matrix, the proposed optical fibre oxygen sensor has higher sensitivity. In addition to the increased surface area per unit mass of the sensing surface, the porous silica nanoparticles increase the sensitivity because a substantial number of aerial oxygen molecules penetrate the porous silica shell. The proposed optical sensor has the advantages of easy fabrication, low cost, fast response and high sensitivity for oxygen monitoring using a cheap LED as a light source.

Sol–Gel Synthesis and Characterization of Silica Polyamine Composites: Applications to Metal Ion Capture

A sol-gel method has been developed for the synthesis of composite materials analogous to the previously reported and commercialized silica polyamine composite (SPC) materials made from amorphous silica. Monolithic xerogels were formed using a two-step procedure with no templating agent using acid catalyzed followed by base catalyzed hydrolysis. This reaction was followed by (1)H NMR. Initial sol-gels were formed using a methyltrimethoxysilane (MTMOS) and 3-chloropropyltrimethoxysilane (CPTMOS) mixture. Elemental analyses and (13)C CPMAS NMR confirmed incorporation of both monomeric units into the surface structure. Some control over surface morphology was achieved by adjusting synthetic conditions. The resulting xerogels were reacted with poly(allylamine) (PAA) to give composite materials which showed much lower metal ion capacities than the commercially available amorphous silica analogs. The low degree of reaction of the chloropropyl groups indicated they were not surface-available to the polyamine. Addition of tetramethoxysilane (TMOS) produced a structural matrix and resulted in higher chloride utilization (reaction of surface chloropropyl groups with the polyamine). The ratio of the three siloxane monomeric components was varied until the resulting polyamine composite xerogels had metal capacities comparable with the commercialized SPC materials. These composites had narrower average pore size distributions and fewer small pores. Further modification of these composites with metal selective ligands showed material characteristics similar to those of commercially available SPC materials. Subjecting a composite made by the sol-gel route to one thousand load-strip cycles with Cu(2+) shows essentially no loss in metal capacity, and this robustness compares favorably with that observed for the SPC made from amorphous silica gels.

Improvement of the cycle life of composite xerogel V2O5/C in aqueous LiNO3 solution by addition of vinylene carbonate

The xerogel V2O5/C composite was synthesized by a sol-gel method, using the suspension of carbon black in the solution of crystalline V2O5 in hydrogen peroxide as the precursor solution. The Li+ intercalation/deintercalation reactions of the xerogel V2O5/C composite, used as an anode material of a two-electrode cell with an aqueous LiNO3 solution as the electrolyte, was studied before and after the addition of vinylene carbonate (VC). Upon addition of vinylene carbonate in an amount of only l wt %, the coulombic capacity during galvanostatic cycling, instead of commonly observed permanent fade, displayed an initial increase and then a stable plateau.

Possibilities and limitations of preparing silica/collagen/hydroxyapatite composite xerogels as load-bearing biomaterials

The combination of silica and collagen was identified in natural composites and recently recognized to be a valuable system for the preparation of innovative biomaterials for bone substitution applications. The present study reports on the development of silica/collagen composites, investigation of the underlying formation processes as well as further interactions with hydroxyapatite as a third phase. The possibilities and limitations of the material concept based on the sol–gel strategy were screened and characteristic composition ranges were identified. The gelation determining the processing time is strongly linked to the pH of silicic acid and collagen suspension mixtures as well as the buffer used and collagen concentration. The templating activity of collagen for silica formation is driven by primary amine groups as suggested by biochemical analysis and scanning electron microscopy. A high solid concentration in the initial hydrogels is essential in order to maintain the sample shape during transformation into monolithic and compact xerogels. The presence of fibrillar collagen significantly enhances the compressive strength of the xerogels up to 200 MPa and strain to fracture of up to 11%. The modular concept of the composite xerogel formation process allows incorporation of further phases such as calcium phosphate phases or prospectively drugs for the treatment of local or systemic diseases, opening large perspectives for the development of multifunctional bone implants.

Rare earth (Eu 3+, Tb 3+) centered composite gels Si–O–M (M = B, Ti) through hexafluoroacetyl-acetone building block: Sol–gel preparation, characterization and photoluminescence

This report focuses on the syntheses of a series of novel photoactive composite xerogels materials in which the functionalized hexafluoroacetylacetone (HFAASi) organic components are grafted into the different inorganic networks (SiO 2–B 2O 3 or SiO 2–TiO 2) via covalent bonds through a sol–gel process. Subsequently, the physical characterization and especially photoluminescent properties of the resulting xerogel materials are studied in detail. Except for composite xerogels linked to SiO 2–TiO 2 networks, all of these composite xerogels exhibit homogeneous microstructures and morphologies, suggesting that molecular-based materials are obtained with strong covalent bonds between the organic β-diketone ligand and inorganic matrices. In addition, the ternary rare earth composite gels present stronger luminescent intensities, longer lifetimes, and higher luminescent quantum efficiencies than the binary ones, indicating that the introduction of the second ligands (phen) can sensitize the luminescent emission of the rare earth ions in the ternary hybrid systems. It should be especially noted that these composite xerogels based on Si–O–B networks possess not only higher thermal stability but also stronger luminescent intensities than the other systems linked to different inorganic networks.

Optical oxygen sensing properties of Ru(II) complex and porous silica nanoparticles embedded in solgel matrix

This paper presents a high-sensitivity oxygen sensor that comprises an optical fiber coated at one end with tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) ([Ru(dpp)3]2+) and porous silica nanoparticles embedded in an n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio IN2 /IO2 , where IN2 and IO2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results show that the oxygen sensor has a sensitivity of 26. The response time was 2 s when switching from pure nitrogen to pure oxygen, and 7.7 s when switching in the reverse direction. The experimental results show that compared to an oxygen sensor based on Ru(II) complex immobilized in the solgel matrix, the proposed optical fiber oxygen sensor has higher sensitivity. In addition to the increased surface area per unit mass of the sensing surface, the porous silica nanoparticles increase the sensitivity because a substantial number of aerial oxygen molecules penetrate the porous silica shell. The proposed optical sensor has the advantages of easy fabrication, low cost, fast response, and high sensitivity for oxygen monitoring using a cheap LED as a light source.

Review on recent developments of fluorescent oxygen and carbon dioxide optical fiber sensors

Oxygen and carbon dioxide sensors are involved in many chemical and biochemical reactions. Consequently, considerable efforts over years have been devoted to discover and improve suitable techniques for measuring gas concentrations by optical fiber sensors. Optical gas sensors consist of a gas-sensitive dye entrapped in a matrix with a high permeability to gas. With such sensors, gas concentration is evaluated based upon the reduction in luminescence intensity caused by gas quenching of the emitting state. However, the luminescence quenching effect of oxygen is highly sensitive to temperature. Thus, a simple, low-cost plastic optical fiber sensor for dual sensing of temperature and oxygen is presented. Also, a modified Stern-Volmer model is introduced to compensate for the temperature drift while the temperature is obtained by above dual sensor. Recently, we presented highly-sensitive oxygen and dissolved oxygen sensors comprising an optical fiber coated at one end with platinum (II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and PtTFPP entrapped core-shell silica nanoparticles embedded in an n-octyltriethoxysilane(Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. Also, two-dimensional gas measurement for the distribution of chemical parameters in non-homogeneous samples is developed and is of interest in medical and biological researches.

Development of an osteoblast/osteoclast co-culture derived by human bone marrow stromal cells and human monocytes for biomaterials testing

The communication of bone-forming osteoblasts and bone-resorbing osteoclasts is a fundamental requirement for balanced bone remodelling. For biomaterial research, development of in vitro models is necessary to investigate this communication. In the present study human bone marrow stromal cells and human monocytes were cultivated in order to differentiate into osteoblasts and osteoclasts, respectively. Finally, a cultivation regime was identified which firstly induces the differentiation of the human bone marrow stromal cells followed by the induction of osteoclastogenesis through the osteoblasts formed--without the external addition of the factors RANKL and M-CSF. As a feedback on osteoblasts enhanced gene expression of BSP II was detected for modifications which facilitated the formation of large multinuclear osteoclasts. Phenotype characterization was performed by biochemical methods (DNA, LDH, ALP, TRAP 5b), gene expression analysis (ALP, BSP II, RANKL, IL-6, VTNR, CTSK, TRAP, OSCAR, CALCR) as well as light microscopy, confocal laser scanning microscopy, and scanning electron microscopy. After establishing this model on polystyrene, similar positive results were obtained for cultivation on a relevant bone substitution material--a composite xerogel of silica, collagen, and calcium phosphate.

Heterogeneous integration of Polymer Porous Photonic Bandgap Structure with Xerogel based Biochemical Sensors

ABSTRACTWe report the heterogeneous integration of a multifunctional sensor based on polymer porous photonic bandgap (P3BG) structure and xerogel based luminescence sensor technology. The P3BG structure was fabricated using holographic interferometry. Initially, holographic interferometry of a photo-activated prepolymer syrup that included a volatile solvent as well as monomer, photoinitiator, and co-initiator was used to initiate photopolymerization. Subsequent UV curing resulted in well defined lamellae of the polymer separated by porous polymer regions that created a high quality photonic bandgap structure. The resulting P3BG structure was then integrated with the xerogel based luminescence element to produce a luminescence sensor with a selective narrow band reflector. The prototype xerogel based luminescence sensor element consisted of an O2 sensing material based on spin coated tetraethylorthosilane (TEOS) composite xerogel films containing tris (4,7-diphenyl-1,10-phenanthroline) ruthenium (II) ([Ru(dpp)3]2+) luminophore. We demonstrated enhancement of the signal-to-noise ratio (SNR) of this integrated multifunctional sensor while maintaining the same sensitivity to O2 sensing of the xerogel based element. The resulting advantages and enhanced SNR of this integrated sensor will provide a template for other luminescence based assays to support highly sensitive and cost-effective sensor systems for biomedical applications.

Highly sensitive and linear calibration optical fiber oxygen sensor based on Pt(II) complex embedded in sol–gel matrix

A simple, low-cost technique for fabrication of high performance optical fiber oxygen sensor is described. An organically modified silicate (ORMOSIL) as a matrix for the fabrication of oxygen sensing film was produced. The technique is based on coating the end of an optical fiber with ORMOSIL composite xerogel films film sequestered with luminophore platinum (II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) prepared by a sol–gel process. The composite xerogels studied are 3,3,3-trifluoropropyltrimethoxysliane (TFP-TriMOS) or n-propyltrimethoxysilane ( n-propyl-TriMOS)/tetraethylorthosilane (TEOS)/ n-octyltriethoxysilane (Octyl-triEOS). Results show that, expect for PtTFPP-doped TFP-TriMOS or n-propyl-TriMOS/TEOS/Octyl-triEOS composite xerogels show the high sensitivity and linear Stern–Volmer relationship which indicate the homogenous environment of the luminophore. The sensitivities of the two oxygen sensors are quantified in terms of the ratio I N2/ I O2, where I N2 and I O2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results reveal that the PtTFPP-doped TFP-TriMOS/TEOS/Octyl-triEOS and n-propyl-TriMOS/TEOS/Octyl-triEOS oxygen sensors have sensitivities of 101 and 155, respectively. The experimental results confirm that the current oxygen sensors exhibit the linear Stern–Volmer plots and high-sensitive based on the oxygen indicator embedded in TFP-TriMOS or n-propyl-TriMOS/TEOS/Octyl-triEOS composite xerogels.

Optical fiber dissolved oxygen sensor based on Pt(II) complex and core-shell silica nanoparticles incorporated with sol–gel matrix

This paper presents a highly sensitive dissolved oxygen sensor comprising an optical fiber coated at one end with core-shell silica nanoparticles and platinum(II) meso-tetrakis (pentafluorophenyl) porphyrin (PtTFPP) embedded in an n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. The sensitivity of optical fiber dissolved oxygen sensor is quantified in terms of the ratio I 0/ I 100, where I 0 and I 100 represent the detected fluorescence intensities in fully deoxygenated and fully oxygenated water, respectively. The experimental results show that the optical fiber dissolved oxygen sensor has a sensitivity of approximately 117 in the range 0–40 mg/L of dissolved oxygen concentrations. The experimental results show that as compared to the other optical dissolved oxygen sensors based on Pt(II) or Ru(II) complexes, the proposed optical fiber dissolved oxygen sensor has the highest sensitivity. In addition to the increased surface area per unit mass in the sensing surface, the dye entrapped in the core of silica nanoparticles also play an important role in the increased sensitivity because of the penetration of substantial amount oxygen molecules through the porous silica shell.

Enhanced oxygen sensing properties of Pt(II) complex and dye entrapped core–shell silica nanoparticles embedded in sol–gel matrix

This paper presents a highly sensitive oxygen sensor that comprises an optical fiber coated at one end with platinum(II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and PtTFPP entrapped core–shell silica nanoparticles embedded in an n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio I 0/ I 100, where I 0 and I 100 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results show that the oxygen sensor has a sensitivity ( I 0/ I 100) of 166. The response time was 1.3 s when switching from pure nitrogen to pure oxygen, and 18.6 s when switching in the reverse direction. The experimental results show that compared to oxygen sensors based on PtTFPP, PtOEP, or Ru(dpp) 3 2+ dyes, the proposed optical fiber oxygen sensor has the highest sensitivity. In addition to the increased surface area per unit mass of the sensing surface, the dye entrapped in the core of silica nanoparticles also increases the sensitivity because a substantial number of aerial oxygen molecules penetrate the porous silica shell. The dye entrapped core–shell nanoparticles is more prone to oxygen quenching.

Preparation and IR Characterization of Li<SUB>2</SUB>O-B<SUB>2</SUB>O<SUB>3</SUB>-Al<SUB>2</SUB>O<SUB>3</SUB> Composite Xerogel

以甲醇锂和金属醇盐为原料,利用溶胶-凝胶法制备了Li2O-B2O3-Al2O3三元复合干凝胶.采用FTIR以及XRD对干凝胶结构随Al2O3含量和温度的变化进行了表征.结果表明：在干凝胶中随着Al2O3含量的增加,四配位态B原子的相对含量在降低,处于非对称态的三配位B原子的相对含量在增加,处于对称态的三配位B原子相对含量在降低,三配位态B原子总的相对含量在增加.含10mol%Al2O3的干凝胶经过550℃热处理1h,其结构由非晶态转变为晶态,主晶相是Li2AlB5O10.

Optical oxygen sensors based on platinum porphyrin dyes encapsulated in ORMOSILS

A strategic approach to develop an “ideal” sensor platform is addressed. Novel quenchometric O 2 sensing materials with 100-fold adjustable sensitivity ( I N 2 / I O 2 from 3 to over 300), reverse and fast response (1 s), linear calibration, and long-term stability are developed. These materials are spin-casted composite ORMOSILs (organically modified silicates) xerogel films sequestered with luminophore Pt(II) octaethylporphine (PtOEP) and Pt(II) meso-tetra(N-methyl-4-pyridyl)porphyrin tetrachloride (PtTMP). The composite xerogels studied are pentafluorophenylpropyltrimethoxysilane (PFTMOS)/ n-octyltrimethoxysilane (C 8TMOS)/tetramethoxysilane (TMOS) and 3,3,3-trifluoropropyltrimethoxysilane (TFTMOS)/ n-propyltrimethoxysilane (C3TMOS). Luminescence spectroscopy (steady state and time resolved) have been used to investigate their analytical figures of merit for gaseous O 2 sensing and to determine the underlying reasons for the observed performance. Results show that, except for PtTMP-doped PFTMOS/C8TMOS/TMOS, all other xerogel composites show linear Stern–Volmer relationship and the single exponential time-resolved intensity decay, which indicate the homogeneous environment of the luminophore. For PtTMP-doped PFTMOS/C8TMOS/TMOS xerogels, the Stern–Volmer plots are non-linear and the time-resolved intensity decay profiles are best fitted by double exponential decay model, which are resulted from the heterogeneous environment of the luminophore. The sensitivity of the sensing materials can be tuned by adjusting the xerogel composition and luminophore. For PtOEP-doped PFTMOS/C8TMOS/TMOS, while keeping C8TMOS and TMOS at the same mol ratio, sensitivity ( I N 2 / I O 2 ) decreases from 333 to 246 with increased PFTMOS% from 0 to 30%, which is due to the decreased bimolecular quenching constant ( k q ). However, I N 2 / I O 2 = 3 was observed from PtTMP-doped PFTMOS/C8TMOS/TMOS. For PtTMP-doped TFTMOS/C3TMOS, sensitivity increases with increased TFTMOS% from 0 to 50% and decreases with further increased TFTMOS% from 50 to 100%, which is mainly due to corresponding increase and decrease of k q . An optimized composition with high sensitivity is observed at 10 PFTMOS/45C8TMOS/45 C8TMOS with I N 2 / I O 2 = 330 .

Bioactive silica–collagen composite xerogels modified by calcium phosphate phases with adjustable mechanical properties for bone replacement

The development of composites has been recognized as a promising strategy to fulfil the complex requirements of biomaterials. The present study reports on the modification of a novel silica–collagen composite material by varying the inorganic/organic mass ratio and introducing calcium phosphate cement (CPC) as a third component. The sol–gel technique is used for processing, followed by xerogel formation under specific temperature and relative humidity conditions. Cylindrical monolithic samples up to 400 mm 3 were obtained without any sintering processes. Various hierarchical phases of the organic component were applied, ranging from tropocollagen and collagen fibrils up to collagen fibers, each characterized by atomic force microscopy. Focusing on the application of fibrils, various inorganic/organic mass ratios were used: 100/0, 85/15 and 70/30; their influence on the structure of the composite material was demonstrated by scanning electron microscopy. The composition was extended by the addition of 25 wt.% CPC which led to increased bioactivity by accelerating the formation of bone apatite layers in simulated body fluid. Synchrotron microcomputed tomography demonstrated the homogeneous distribution of the cement particles in the silica–collagen matrix. Compressive strength tests showed that the mechanical properties of the brittle pure silica gel are changed significantly due to collagen addition. The highest ultimate strength of about 115 MPa at about 18% total strain was registered for the 70/30 silica–collagen composite xerogels. Incorporation of CPC lowered the gel’s strength. By demonstrating differentiation of human monocytes into osteoclast-like cells, an important feature of the composite material regarding successful bone remodeling is fulfilled.

Luminescence and oxygen sensing properties of ORMOSILs covalently grafted with a novel ruthenium(II) complex

A series of VTES/TEOS composite xerogels covalently grafted with a novel complex Ru(phen)2(Dppz-Si)Cl2 were prepared, using the alkoxysilane-modified dipyrido[3,2-a:2′,3′-c]phenazine compound (denoted as Dppz-Si) as the second ligand of the Ru(phen)2Cl2 (phen = 1,10-phenanthroline) complex and a precursor of the sol–gel process. Bulk xerogels were obtained by co-hydrolyzing and co-condensation from a mixture of triethoxysilane (TEOS), Ru(phen)2(Dppz-Si)Cl2 and Vinyltriethoxysilane (VTES). The luminescence intensity of composite xerogels is enhanced by 18.2 times, and the sensitivity is improved from 1.1 to 3.1 by optimizing the molar ratio of VTES to TEOS. The composite xerogel containing 80% VTES in precursor was optimal, exhibiting the maximum luminescence intensity and sensitivity. These results indicate that the complex Ru(phen)2(Dppz-Si)Cl2 is sensitive to oxygen concentration, VTES is a kind of excellent organic modifier and can greatly improved photoluminescent (PL) and oxygen sensing performances.

Engineering Silica Particles as Oral Drug Delivery Vehicles

Porous silica particles are emerging as complementary systems to polyester microspheres for the encapsulation and controlled delivery of small-organic drugs. Their recent application in pharmaceutics is strengthened by well-established characterization and synthetic routes from the chemical engineering sciences. Silica is an interesting scaffold material for the encapsulation of organic molecules. It can be formed into hierarchical structures over a wide range of length scales and interconnectivities. Encapsulation can therefore be tailored not only to the drug but the desired release properties. In addition to surfactant-templating of hierarchical silica structures, polypeptides from marine organisms may offer biological routes to novel silica materials. Silica sol-gels have also been evaluated as delivery vehicles, particularly with regard to generating hybrid systems with mesoporous silica or composite xerogels. This review will first focus on the detailed characterisation of pore size and structure of mesoporous silica with regards water penetration and drug diffusion. We then describe the pharmaceutical applications of silica materials with regard to improving oral bioavailability, multiparticulate systems for gastroretention or sustained release, composite xerogels and in vivo biocompatibility.

Changes in the structure of composite colloid-polymer xerogels after cold isostatic pressing

Monolithic gels, prepared from different mixtures of colloidal silica in a sol solution containing tetraethoxysilane under powerful ultrasonic agitation (sonosols), were compacted at an isostatic pressure of 390 MPa. Then N2 adsorption-desorption data were used to construct structural models of the gels using Monte-Carlo calculations on the basis of random close-packing (RCP) premises. Structural information on these composites obtained before compaction indicates that the characteristic uniform structure of silica colloid gel undergoes profound modification when it is mixed with silica sonogel. From a structural point of view, the behaviour under compaction of the sonogel phase, which exhibits a significant degree of microporosity, depends on the relative concentration of the colloidal phase. Two hierarchic levels of micropores were discerned. After compression, the size of the elementary particles—and their aggregates—of the sonogel phase increases from 1.6 to 2.1 nm radius when the colloidal phase content is increased from 30 to 82% by weight. For an intermediate content, 50% of the volume reduction is caused by compression of the sonogel phase at the micropore level.

Preparation of silica microspheres coated with V 2O 5 xerogel and V 2O 5/WO 3 composite xerogel via adapted Stöber process

In the present study, we have synthesized spherical silica particles covered with either layered V 2O 5 xerogel or V 2O 5/WO 3 mixed xerogel via an adapted Stöber method using an ammonia solution of methyltriethoxysilane (MTES). The SEM images revealed the presence of a lamellar V 2O 5 xerogel layer coating the silica particles, as evidenced by the (0 0 1) diffraction lines. Both materials have voltammetric behavior that is quite similar to that of the V 2O 5 xerogel. The catalytic activity of the silica particles coated with the V 2O 5/WO 3 mixed xerogel was evaluated in the epoxidation of styrene using iodosylbenzene as an oxidant.

Preparation, characterization and catalytic studies of V2O5–SiO2 xerogel composite

In this work, we report the synthesis, characterization and catalytic properties of a vanadium oxide–silicon oxide composite xerogel prepared by a soft chemistry approach. In order to obtain such material, we submitted a vanadium pentoxide gel previously synthesized via protonation of metavanadate species to an “in situ” progressive polycondensation into silica gel. The material has been characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. Further, the catalytic activity of this material was evaluated for the epoxidation of styrene and cyclooctene using iodosylbenzene, hydrogen peroxide and m-chloroperbenzoic acid as the oxidizing agent.