Inorganic Silica Gel Research Articles

Silica-Based 1,3-Diphenyl-1,3-Propanedione Composites: Efficient Uranium Capture for Environmental Remediation

Introduction:: This study synthesizes and characterizes a novel hybrid composite, SGdpm, to capture UO2 2+ ions from water. The composite has successfully formed by hosting covalently diphenylmethane-1,3-dione (dpm) within an inorganic silica gel matrix, showing promising potential for environmental remediation and nuclear waste management. Methods:: The preparation involved the reaction of tetraethylorthosilicate (TEOS) with diphenylmethane- 1,3-dione (dpm) under acidic conditions, resulting in white solids. The doped composite was characterized by Fourier Transform Infrared Spectroscopy (FTIR), revealing the presence of siloxane and Si-O-C bonds. The application of SG-dpm for capturing UO2 2+ ions from water was investigated, showing a shift in FTIR peaks and confirming the formation of SG-dpm-UO2 2+ as inner-sphere complexes. Scanning Electron Microscopy (SEM) revealed a non-uniform distribution of particles, essential for consistent behavior in applications such as adsorption. Results and Discussion:: Batch sorption experiments demonstrated temperature-dependent sorption behavior with increased efficiency at higher temperatures (T = 55°C). The study also explored the influence of pH and initial concentration on UO2 2+ sorption, revealing optimal conditions at pH 5 and lower initial concentrations (1.0 mg L-1). Kinetic studies using pseudo-second-order models indicated a high efficiency of UO2 2+ ion removal (99%) as a chemisorption process. Intraparticle diffusion models highlighted three distinct sorption stages. Sorption isotherm studies favored the Langmuir model, emphasizing monolayer adsorption. The thermodynamic analysis suggested an endothermic (ΔH = + 16.120 kJ mol-1) and spontaneous (ΔG = −25.113 to − 29.2449 kJ mol-1) sorption process. Selectivity studies demonstrated high efficiency in capturing Cu2+, Co2+, and Cr3+ ions, high degree selectivity of UO2 2+ ions (74%), moderate efficiency for Fe3+ and Zn2+, and lower efficiency for Pb2+, Ni2+, and Cd2+, and poor efficiency for Mn2+ ions. Conclusion: SG-dpm exhibits promising potential for selective UO2 2+ ion removal, demonstrating favorable characteristics for various applications, including environmental remediation and nuclear waste management.

Preparation and properties evaluation of novel silica gel-based fracturing fluid with temperature tolerance and salt resistance for geoenergy development

Various polymers are the most widely used product to provide rheology for water-based fracturing fluid, however, they have weaknesses in terms of temperature resistance and salt resistance. The change from organic-based to inorganic thickeners may be a meaningful attempt. Inorganic silica gel is a potentially alternative viscosifier with high temperature resistance, excellent proppant carrying capacity, and can even be used to prepare fracturing fluids with high salinity of produced water. In this paper, the silica gel viscosifier was firstly prepared using sol–gel method. Then, the gelation time under different influencing factors and rheological properties of the silica gel viscosifier were studied in detail. Subsequently, the silica gel-based fracturing fluid was prepared by adding the desired amount of drag reducer to the silica sol solution, and the properties of novel fracturing fluid were systematically evaluated with regard to the temperature and shearing resistance, drag reduction, and static proppant suspension. The potential mechanism of gelation process by syneresis of silica gel was revealed at last. Results showed that the microstructure of silica gel is synthetic, amorphous and consists of a three-dimensional network of SiO2 particles. The effect of SiO2 concentration on the gelation time is more pronounced than other factors such as temperature and pH level. In addition, the silica gel viscosifier exhibits strong salt resistance, whether monovalent ions (Na+, K+) or divalent ions (Ca2+, Mg2+), and the gelation time decreased significantly with the increase of salt concentration. The shear viscosity of the silica gel viscosifier increased with an increase of SiO2 concentration, showing shear thinning behavior as well. Meanwhile, the silica gel-based fracturing fluid prepared by adding drag reducer into silica sol solution also presented excellent thermal stability and shear resistance, drag reduction and proppant suspension performances. The retained viscosity can be maintained above 50 mPa·s after shearing at 180 °C for 60 mins; the drag reduction rate shows a declining trend at high displacement due to the gelation process; the settling rate of 40/70 mesh sand proppant with 35 % sand ratio is less than 30 % after standing at 90 °C for 4 h. In addition, the gelation process is essentially the formation of Si-O-Si linkage by dehydration between SiO2 particles, which is gradually extended at both ends and sides of the chain, and eventually forms a rigid, highly porous, entangled network. Findings found in this study provide a research basis for the popularization and application of silica gel-based fracturing fluid.

Design of CDs/SiO2 Composite Phosphors via a Double Hydrolysis Reaction and their Expectable Luminescence Performance

Carbon dots (CDs), as an emerging carbon material, have attracted considerable interest for their promising luminescent properties. However, the inevitable aggregation of CDs in solid-state results in some bottleneck problems such as aggregation-induced quenching and foster resonance energy transfer. Therefore, developing solid-sate CDs with good luminescent performance is still a challenge. Herein, a simple and low-cost approach is presented to prepare the solid-state CDs/SiO2 composite in which the CDs were well dispersed and embedded in inorganic silica gel, hence restraining the natural issues of the solid-state CDs. As expected, the CDs/SiO2 composite phosphors showed higher fluorescence intensity about twice than the CDs aqueous solution, and a high photoluminescence quantum yield of 21%. This work would be of significance for the preparation of CDs and even their practical applications.

The Gel Growth Technique—A Neglected Yet Effective Tool to Prepare Crystals of Oxysalts and Supergene Minerals

The technique of crystal growth in gels has nowadays become somewhat neglected in the scope of earth sciences, to the disadvantage of the experimental mineralogist. Even preparing an inorganic silica gel can prove a challenge to many, let alone successfully configure the entire experiment. Based not only on previous literature but also on our extensive experience, crystals of many substances, including supergene minerals as reference standards, can be successfully grown in gel, aiding in accomplishing various research goals in earth sciences. Instead of providing the reader with an overwhelming compendium of historical information and theoretical knowledge of the subject which can be found elsewhere, we presented herein a comprehensive, practically oriented guide to the understanding and successful use of the technique of crystal growth in gels, mentioning, in addition to the general principle, the numerous pitfalls which we encountered during our own use of the method, and the ways to overcome them. Despite that the procedure is nowadays used mainly for the laboratory synthesis of organic or metal-organic compounds, we believe it to be a valuable asset to any mineralogist, and often, the only way to obtain inorganic reference material of a particular mineral of interest.

Evaluation of pro-angiogenic properties of an inorganic silica gel fibre fleece.

Hard-to-heal wounds represent an increasing health and economic burden on society. At present, therapy options for hard-to-heal wounds are often unsatisfactory, and the development of more effective wound treatments is urgently needed. We have shown that orthosilicic acid-releasing silica fibre fleece (SIFIB), via its pronounced anti-inflammatory properties, exhibited a significantly enhanced effect on wound closure kinetics in a porcine wound model in vivo. In this present study, we have examined in vitro the impact of the pro-angiogenic potential of SIFIB. Using an in vitro angiogenesis assay we describe for the first time how an inorganic biodegradable silica-based material significantly improved endothelial microvessel-like structure formation. We further demonstrate that the molecular mechanism of this pro-angiogenic activity of SIFIB is based on a significantly increased and tumour necrosis factor (TNF)α-dependent VEGF protein expression. In conclusion, due to its positive effects on angiogenesis, our results further indicate that decomposition products of silica-based biodegradable inorganic materials might represent very relevant therapeutic components of modern wound dressings for the treatment of hard-to-heal wounds.

Geopolymerization of soil by sodium silicate as an approach to control wind erosion

Transportation of fugitive dust over long distances because of wind erosion is a severe environmental threat. Different approaches are experienced to control wind erosion, but durability and costs are the main drawbacks of existing techniques. This study hereby investigates sodium silicate usage as an alkaline additive to bind soil particles and control wind erosion. Sodium silicate is an environmentally safe material and the precipitated inorganic silica gel from which has the affinity with soil texture that makes the overall geopolymerization materials and method clean and environmentally friendly. The neutral condition of natural soils can reduce the alkalinity of sodium silicate’s alkalinity upon contact to the silica gel formation and soil geopolymerization. Different water-diluted solutions containing 50, 35, 20 wt% sodium silicate were prepared and sprayed over the soil surface while various specifications of the stabilized part were evaluated. It was found that interparticle cohesion, shear strength, and wind erosion were affected by sodium silicate content, as explained through a series of immersion, direct shear, and wind tunnel tests. A combination of mechanical and chemical forces can explain the interparticle cohesion since no chemical bonding was established between silica gel and soil particles, as described in Fourier-transform infrared spectroscopy analysis. Scanning electron microscopy coupled with energy-dispersive spectroscopy and thermogravimetric experiment displayed soil particles’ aggregation without mineralogical alteration. The achieved results implicate sodium silicate’s promising role as a stabilizer to bind the soil particles and control wind erosion.

Novel sodium silicate/polymer composite gels for the prevention of spontaneous combustion of coal.

Novel gel materials are proposed for fire prevention and extinction in coal mines, where spontaneous combustion of coal continues to pose a significant risk. Cationic polyacrylamide (CPAM), anionic polyacrylamide (HPAM), and carboxymethyl cellulose (CMC) were each introduced separately into a sodium silicate (WG) gel, to obtain three gels labeled as CPAM/WG, HPAM/WG, and CMC/WG. A crosslinking agent, aluminum citrate, was subsequently added to the HPAM/WG and CMC/WG gels to afford two novel interpenetrating network hydrogels, HPAM-Al3+/WG and CMC-Al3+/WG, respectively. Among the various gels, the HPAM-Al3+/WG hydrogel exhibits the best seepage capacity, water retention capacity, compressive strength, and inhibition characteristics, which effectively resolve the post-water-loss cracking and pulverization problems commonly associated with inorganic consolidated silica gels. The microstructures of all the gels were investigated by scanning electron microscopy and their inhibitory effects on the oxidation of hydroxyl and methylene groups in coal at high temperatures were analyzed by Fourier transform infrared spectroscopy. Elemental mapping by energy dispersive X-ray spectroscopy indicated that the inorganic silica gel blends uniformly with the polymeric gel. Fire extinction experiments indicated that the HPAM-Al3+/WG gel reduces the fire-source temperature, heat radiation, and CO generation. Thus, the HPAM-Al3+/WG gel is an ideal fire prevention and extinction material.

Missing Iron-Oxidizing Acidophiles Highly Sensitive to Organic Compounds.

The genus Acidithiobacillus includes iron-oxidizing lithoautotrophs that thrive in acidic mine environments. Acidithiobacillus ferrooxidans is a representative species and has been extensively studied for its application to the bioleaching of precious metals. In our attempts to cultivate the type strain of A. ferrooxidans (ATCC 23270T), repeated transfers to fresh inorganic media resulted in the emergence of cultures with improved growth traits. Strains were isolated from the resultant culture by forming colonies on inorganic silica-gel plates. A representative isolate (strain NU-1) was unable to form colonies on agarose plates and was more sensitive to organics, such as glucose, than the type strain of A. ferrooxidans. Strain NU-1 exhibited superior growth traits in inorganic iron media to those of other iron-oxidizing acidithiobacilli, suggesting its potential for industrial applications. A draft genome of NU-1 uncovered unique features in catabolic enzymes, indicating that this strain is not a mutant of the A. ferrooxidans type strain. Our results indicate that the use of inorganic silica-gel plates facilitates the isolation of as-yet-unexamined iron-oxidizing acidithiobacilli from environmental samples and enrichment cultures.

Physisorption data for methyl-hybrid silica gels

The porous structure of inorganic silica and methyl-ormosil gels were studied using nitrogen adsorption at 77 K. Organically, modified silica gels were produced from mixtures of tetraethoxysilane (TEOS) and triethoxy(methyl)silane (MTES), under basic and acid sol–gel catalysis. Starting from pure TEOS, mixtures of increasing MTES content have been prepared. Although not new, silica-based surface morphology is still a challenging subject, particularly when related to silica functionalise systems. N2 adsorption isotherms were used, and the validity of BET model has been discussed for ormosil systems. The pore size distribution of inorganic and hybrid sol–gel silica materials were calculated by using the adsorption branch of the N2 isotherm. Compared with inorganic silica gel, the microstructure of the resulting hybrid gel has been modified—sorption capacities and average pore radius have intensely increased. Acid and basic catalyst determine the type of gel microstructure. Further, the presence of the more flexible ≡Si–CH3 bonds is the responsible for the increasing mobility during gelation, and for the presence of not energetically equivalent terminal groups, which will affect the final pore structure by the suppleness capacity. The rigid and regular pore shape assumption is no more valid. For MTES content higher than 2 mol%, the N2 isotherms reached no more the equilibrium. N2 adsorption isotherms are though not very suitable for surface characterisation of hybrid silica gels, over a limit organic moiety concentration.

Perfluoro-tagged rhodium and ruthenium nanoparticles immobilized on silica gel as highly active catalysts for hydrogenation of arenes under mild conditions

Perfluoro-tagged rhodium and ruthenium nanoparticles have been stabilized on highly fluorinated hybrid organic–inorganic silica gel. The method for preparation of these nanoparticles is highly reproducible and the new materials were robust, recoverable and active catalysts for arene hydrogenation under very mild conditions.

Synthesis, structural and optical characterization of nanocrystalline ZnS:Cu embedded in silica matrix

The synthesis of Cu doped ZnS nanoparticles inside the pore of an inorganic silica gel matrix is presented. The synthesized nanoparticles were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). X-ray diffraction pattern reveals the crystalline wurtzite phase of ZnS. The existence of silica gel in modeling morphologies of the nanoparticles was characterized using Fourier transform infrared (FTIR) spectrometer. Thickness of the silica shell was also calculated. UV- absorption spectrum shows the appearance of an absorption peak at 273 nm which confirms the blue shift as compared to that of bulk ZnS. The photoluminescence (PL) emission spectrum of the sample showed a broad band in the range 465–510 nm due to the transition from the conduction band edge of ZnS nanocrystals to the acceptor like t2 state of Cu.

Effect of Cross-Linking and Organic Groups on the Visible Photoluminescence Characteristics of n-Octadecylsiloxanes

The photoluminescence (PL) properties of properly annealed n-octadecylsiloxanes, which are newly recognized highly emissive hybrid materials reported recently by us (Nishimura, A.; Sagawa, N.; Uchino, T. J. Phys. Chem. C 2009, 113, 4260), with different cross-linking structures are investigated using steady-state and time-resolved PL spectroscopy. We find that the observed PL intensity and the PL decay dynamics are strongly dependent on the degree of cross-linking of the organic−inorganic hybrid materials. We attribute these changes to the initial concentration of the residual silanol groups, which can be converted into emission and electron-trapping centers through the condensation reaction during annealing. These PL features are then compared with those of purely inorganic silica gels to evaluate the effect of organic groups on the PL characteristics of the n-octadecylsiloxanes. It has been found that organic groups contribute to the PL decay component in the time scale of ∼70 to ∼100 ns. Also, organic ...

RETRACTED: Preparation and thermal properties of form-stable paraffin phase change material encapsulation

Form-stable paraffin phase change materials (PCMs), in which the paraffin as a latent heat storage material and the polyolefins as a supporting material, have to be encapsulated because of the paraffin leakage and lipophilicity. A novel microencapsulated PCM in which form-stable paraffin is encapsulated into inorganic silica gel polymer is prepared successfully by in situ polymerization. A differential scanning calorimeter (DSC) is used to measure the thermal properties of the PCM. Moreover, the Washburn equation associated with the wetting properties of powder materials, is used to test the hydrophilic-lipophilic properties of PCM. The results indicate that the optimum microencapsulated PCM is endowed with good hydrophilicity, and its specific enthalpy maintains 123.78 J g -1 .

Drug Release from Self-Assembled Inorganic−Organic Hybrid Gels and Gated Porosity Detected by Positron Annihilation Lifetime Spectroscopy

Self-assembled silica and hybrid organo−silica sol−gel materials have been prepared in the presence of the pharmaceutically active guest molecule Persantin. The dissolution of the drug molecule and the matrix porosities are related to the synthesis parameters, compositions, and pH values. Whereas larger pores and faster release times are observed at weakly acidic sol−gel reactions (pH 5.6), more dense materials and slower drug-release kinetics are found at values down to pH 2−3. It is shown that organically functionalized host gels can control drug release, depending on the organic functionality. All self-assembled systems show controlled-release profiles compared to the direct-release profile for impregnated silica. Gels with acetoxypropyl-group functionalization show faster release kinetics with an increasing number density of these organic moieties, whereas hybrid gels functionalized with an increasing number of methyl, propyl, phenyl, or benzyl groups inhibit release. Positron annihilation lifetime spectroscopy shows a bimodal pore system for gels prepared at weakly acidic pH values. Only the larger pores are accessible to N2 adsorption for inorganic silica gels or hybrid gels with methyl or propyl groups. N2 adsorption for hybrid gels with acetoxypropyl groups is prevented by the organic side chains that gate the pores.

Structure and Dynamics of Silica and Acrylamide Gels

Abstract The structure and dynamics of silica and acrylamide gels were studied using a probe diffusion technique of dynamic light scattering (DLS). Latex particles, diameter = 0.05 μm, embedded in the gel network serve as a probe through their diffusion behavior within the network. A quantitative analysis of the homogeneity of the gel is introduced based on a shift of the correlation function of the dynamic light scattering. The lag time of the particles' correlation function in a completed inorganic silica gel is increased by increasing the contents of the gel network; but the particles' diffusion coefficient in a viscoelastic (acrylamide) gel lowers the f(A)max, the maximum value of the y-axis in the correlation function. The silica gel makes a more homogeneous and compact structure than that of a PAA gel, which has partial heterodyning, by increasing the solid contents of the network density.

Synthesis of Monophasic Hybrid Organic−Inorganic Solids Containing [η6-(Organosilyl)arene]chromium Tricarbonyl Moieties

Silica gel containing benzenechromium tricarbonyl units have been obtained from molecular organosilicon precursors. The hydrolytic sol−gel polymerization of [η6-C6H5Si(OMe)3]Cr(CO)3 (1), [η6-1,4-C6H4RR‘]Cr(CO)3 [R = R‘ = Si(OMe)3 (2), R = R‘ = CH2Si(OMe)3 (3), R = R‘ = CH2CH2Si(OMe)3 (4)], {η6-1,3,5-C6H3[Si(OMe)3]3}Cr(CO)3 (5), under nucleophilic catalysis by fluoride ion (NH4F), have led quantitatively to new monophasic hybrid organic−inorganic silica gels. The derived xerogels X were characterized by FT IR, 13C and 29Si solid state CP MAS NMR spectroscopies. The silicon−carbon bond and the tricarbonylchromium ligand were retained within the gel. The major environment of the Si atoms corresponded to a T2:CSi(OR)(OSi)2 substructure for X2−X4, a T3:CSi(OSi)3 one for X1 and a Ts:CSi(OR)2(OSi) in the case of X5. In most cases, these were amorphous materials that exhibited low specific surface areas (∼10 m2 g-1). Upon heating the xerogels X1, X2, and X4 at 400 °C under an argon flow, weight losses corresponding to complete carbon monoxide elimination were obtained, leading to chromium in a low oxidation state within the solid.