Condensation Of Tetraethyl Orthosilicate Research Articles

Transport and retention of silica nanoparticles in glass-bead columns: effects of particle size, type, and concentration of ionic species

Silica nanoparticles (SiO2 NPs) have garnered substantial attention as versatile additives in saline fluids, finding application in areas like environmental remediation, wastewater treatment, enhanced oil recovery, and carbon geo-sequestration. Despite their potential, the intricate interaction between electrolyzed nanoparticles and porous media remains inadequately researched in these contexts. This study delves into the pivotal yet underexplored aspect of silica nanoparticle absorption behavior within porous media, a key determinant of their practical effectiveness. The research focuses on silica particles with dimensions of 10 nm and 50 nm, synthesized via hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in methanol. Employing packed glass bead columns as a surrogate for porous media, the study unravels the complex mechanisms governing nanoparticle transport and deposition. Comprehensive investigations encompass variations in particle sizes, ionic strength, and ionic species, resulting in the examination of 48 distinct flooding scenarios. UV/Vis spectrophotometry is used to quantify nanoparticle concentrations in effluents, elucidating their transport behavior within the porous media. Concurrently, pressure drop alterations across the media serve as indicators of particle plugging and changes in permeability. Intriguingly, specific conditions involving a nanofluid comprising 50 nm silica nanoparticles and 10,000 ppm of magnesium chloride exhibit pronounced permeability reduction, offering potential insights for optimizing applications. Particularly noteworthy is the unique reduction in silica particle retention on glass bead surfaces as salinity increases, especially in the presence of magnesium sulfate. A concentration of 5000 ppm magnesium sulfate induces a log-jamming mechanism, resulting in an amplified final-to-intermediate permeability ratio. Experimental outcomes align with observations from scanning electron microscopy, improving understanding of porous media retention mechanisms. This study contributes to a deeper understanding of interactions between nanoparticles and porous media, paving the way for enhanced application strategies.

The effect of silica nanoparticles obtained from different sources on mechanical properties of polyurethane nanocomposites

Spherical silica particles were synthesized from two different sources, tetraethyl orthosilicate (TEOS) and sodium sili-cate obtained from wheat straw ash, respectively. In the first case, monodispersed and microporous silica particles with average particle size of 400 nm were prepared by hydrolysis and condensation of TEOS. In the second case, the silica particles were generated from supersaturated sodium silicate solution. The extraction of silicate solution from wheat straw ash (WSA) was performed by the multi-step sequential extraction using 2,5 mol/L NaOH. WSA silica particles were polydispersed and contain the primary silica particles with average size of ~250 nm and agglomerates obtained by aggregation of primary silica particles, with average size of ~1.5 mm and 5 mm. The silica particles obtained from WSA have the average pore size of 28.3 nm, total pore volume of 0.1638 cm 3 /g and average surface area of 23.131 m 2 /g. Flexible polyurethane/silica composites with my(TEOS silica and WSA silica) and different filler concentration were synthesized. Dispersion of silica fillers in polyol system preceded the mixing with isocyanate resulted in formation of cavities in polyurethane-silica composite. On the other hand, dispersion of TEOS silica filler into isocyanate which preceded the mixing with polyol system resulted in homogenous and compact composite. The application of silica filler obtained from TEOS at filler concentration of 4 wt.% increased Young's modulus for 20% relative to that of polyurethane without filler. On the other side, the application of WSA silica filler resulted in reduced Young' s modulus probably due to large silica aggregates.

Network–Polymer–Modified Superparamagnetic Magnetic Silica Nanoparticles for the Adsorption and Regeneration of Heavy Metal Ions

Superparamagnetic magnetic nanoparticles (MNPs, Fe3O4) were first synthesized based on a chemical co–precipitation method, and the core–shell magnetic silica nanoparticles (MSNPs, Fe3O4@SiO2) were obtained via hydrolysis and the condensation of tetraethyl orthosilicate onto Fe3O4 seed using a sol–gel process. Following that, MSNPs were immobilized using a three–step grafting strategy, where 8-hloroacetyl–aminoquinoline (CAAQ) was employed as a metal ion affinity ligand for trapping specific heavy metal ions, and a macromolecular polymer (polyethylenimine (PEI)) was selected as a bridge between the surface hydroxyl group and CAAQ to fabricate a network of organic networks onto the MSNPs’ surface. The as–synthesized MSNPs–CAAQ nanocomposites possessed abundant active functional groups and thus contained excellent removal features for heavy metal ions. Specifically, the maximum adsorption capacities at room temperature and without adjusting pH were 324.7, 306.8, and 293.3 mg/g for Fe3+, Cu2+, and Cr3+ ions, respectively, according to Langmuir linear fitting. The adsorption–desorption experiment results indicated that Na2EDTA proved to be more suitable as a desorbing agent for Cr3+ desorption on the MSNPs–CAAQ surface than HCl and HNO3. MSNPs–CAAQ exhibited a satisfactory adsorption capacity toward Cr3+ ions even after six consecutive adsorption–desorption cycles; the adsorption efficiency for Cr3+ ions was still 88.8% with 0.1 mol/L Na2EDTA as the desorbing agent. Furthermore, the MSNPs–CAAQ nanosorbent displayed a strong magnetic response with a saturated magnetization of 24.0 emu/g, and they could be easily separated from the aqueous medium under the attraction of a magnet, which could facilitate the sustainable removal of Cr3+ ions in practical applications.

In Ukrainian

Regulation of enterohepatic circulation of bile acids in human body is actual task to overcome cardiovascular diseases. The aim of this work was to create biocompatible sorbents with improved sorption ability in relation to bile acids. Mesoporous organosilicas of MCM‑41 type with chemically grafted 3‑aminopropyl and steroid groups were obtained by sol‑gel condensation of tetraethyl orthosilicate and functional silanes in the presence of template cetyltrimethylammonium bromide. Porous structure of synthesized organosilicas was characterized by low‑temperature nitrogen adsorption–desorption and X‑ray diffraction analysis. Formation of typical for MCM‑41 hexagonal arrangement of cylindrical mesopores was confirmed. Structural parameters of synthesized silica materials were calculated. The influence of surface steroid groups on sorption ability of organosilicas was studied on example of bile salts (sodium cholate and taurocholate) in dependence of duration of contact, acidity of medium, and equilibrium concentration. Analysis of kinetic parameters of sorption estimated by Lagergren and Ho-McKey models confirms the proceeding of pseudo-second order process. The most effective sorption of sodium cholate and taurocholate was observed at pH ~ 5 and pH ~ 2, respectively, where the ovterlapping of pH regions of 3‑aminopropyl groups protonation and bile acids dissociation takes place. Analysis of experimentally obtained isotherms by use of Freundlich, Redlich‑Peterson, and BET models was carried out. It has been found that protonated amino groups are the main sorption centers of bile acids protolytic forms by synthesized aminosilica in pH range from 1 to 8. Introduction of steroid groups in surface layer at sol-gel synthesis leads to the increase of bile salts sorption due to the cooperative interactions with formation of supramolecular structures in the surface layer of organosilica. Obtained results prove prospects of usage of organosilica sorbents with surface steroid groups for regulation of bile acids content in human body.

Fe3O4@C@MCM41-guanidine core–shell nanostructures as a powerful and recyclable nanocatalyst with high performance for synthesis of Knoevenagel reaction

In this study, preparation, characterization and catalytic application of a novel core–shell structured magnetic with carbon and mesoporous silica shells supported guanidine (Fe3O4@C@MCM41-guanidine) are developed. The Fe3O4@C@MCM41-guanidine was prepared via surfactant directed hydrolysis and condensation of tetraethyl orthosilicate around Fe3O4@C NPs followed by treatment with guanidinium chloride. This nanocomposite was characterized by using Fourier transform infrared spectroscopy, vibrating sample magnetometry, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, thermal gravimetric analysis, wide-angle X-ray diffraction and low-angle X-ray diffraction techniques. This nanocomposite have high thermal, chemical stability, and uniform size. Fe3O4@C@MCM41-guanidine catalyst demonstrated high yield (91–98%) to prepare of Knoevenagel derivatives under the solvent free conditions at room temperature in the shortest time. Also, this catalyst was recovered and reused 10 times without significant decrease in efficiency and stability. Fortunately, an excellent level of yield (98–82%) was observed in the 10 consecutive catalyst cycles.

Thermodynamics of Azo Dye Adsorption on a Newly Synthesized Titania-Doped Silica Aerogel by Cogelation: A Comparative Investigation with Silica Aerogels and Activated Charcoal.

The adsorption isotherms of azo dyes on a newly synthesized titania-doped silica (TdS) aerogel compared to silica aerogels and activated charcoal (AC) are systematically investigated. Monolithic TdS aerogels were synthesized by the cogelation process followed by supercritical drying of tetraethyl orthosilicate (TEOS) as a gel precursor and titanium(IV) isopropoxide (TTIP) as a metal complex precursor for co-polymerization in ethanol solvent. An acid-base catalyst was used for the hydrolysis and condensation of TEOS and TTIP. The effect of Ti4+ doping in a silica aerogel on the mesoporous structure and the adsorption capacity of methylene blue (MB) and crystal violet (CV) dyes were evaluated from the UV-vis absorption spectra. In order to compare the adsorption isotherms, the surface areas of silica and TdS aerogels were first normalized with respect to AC, as adsorption is a surface phenomenon. The azo dye equilibrium adsorption data were analyzed using different isotherm equations and found to follow the Langmuir adsorption isotherm. The maximum monolayer adsorption capacities for the adsorbent TdS aerogel normalized with the AC of the Langmuir isotherm are 131.58 and 159.89 mg/g for MB and CV dyes, respectively. From the Langmuir curve fitting, the Q max value of the TdS aerogel was found to increase by 1.22-fold compared to AC, while it increased 1.25-1.53-fold compared to the silica aerogel. After four cycles, regeneration efficiency values for MB and CV dyes are about 84 and 80%, respectively. The study demonstrates the excellent potential and recovery rate of silica and TdS aerogel adsorbents in removing dyes from wastewater. The pore volume and average pore size of the new aerogel, TdS, were found to be lower than those of the silica aerogel. Thus, a new TdS aerogel with a high capacity of adsorption of azo dyes is successfully achieved.

Synthesis of Patchy Nanoparticles with Symmetry Resembling Polar Small Molecules.

Patchy nanoparticles (NPs) show many important applications, especially for constructing structurally complex colloidal materials, but existing synthetic strategies generate patchy NPs with limited types of symmetry. This article describes a versatile copolymer ligand-based strategy for the scalable synthesis of uniform Au-(SiO2 )x patchy NPs (x is the patch number and 1 ≤ x≤ 5) with unusual symmetry at high yield. The hydrolysis and condensation of tetraethyl orthosilicate on block-random copolymer ligands induces the segregation of copolymers on gold NPs (AuNPs) and hence governs the structure and distribution of silica patches formed on the AuNPs. The resulting patchy NPs possess unique configurations where the silica patches are symmetrically arranged at one side of the core NP, resembling the geometry of polar small molecules. The number, size, and morphology of silica patches, as well as the spacing between the patches and the AuNP can be precisely tuned by tailoring copolymer architectures, grafting density of copolymers, and the size of AuNPs. Furthermore, it is demonstrated that the Au-(SiO2 )x patchy NPs can assemble into more complex superstructures through directional interaction between the exposed Au surfaces. This work offers new opportunities of designing next-generation complex patchy NPs for applications in such as biomedicines, self-assembly, and catalysis.

Physicochemical and Morphological Properties of Hybrid Films Containing Silver-Based Silica Materials Deposited on Glass Substrates

The main goal of this study was to present a facile and inexpensive approach for the preparation of hybrid coatings by the deposition under ambient air conditions of silver-based silica materials on glass substrates, which can be used to improve solar cells’ performance. The silica materials containing silver nanoparticles (AgNPs) were synthesized by the hydrolytic condensation of tetraethylorthosilicate (TEOS), triethoxymethylsilane (MTES), and trimethoxyhexadecylsilane (HDTMES), under acidic conditions, at room temperature (25 ± 2 °C). The silver nitrate solution (AgNO3, 0.1 wt. %) was used as a source of Ag+ ions. The final samples were investigated through Fourier Transform Infrared Spectroscopy–Attenuated Total Reflectance (FTIR–ATR), Transmission Electron Microscopy equipped with energy dispersive X–ray (TEM–EDX), UV–Vis spectroscopy, Atomic Force Microscopy (AFM), and Raman Spectroscopy (RS). The TEM images confirmed the formation of AgNPs and were found to be around 3 nm. It was observed that AgNPs were embedded in the silica matrix. EDX also confirmed the presence of the resulting AgNPs within the silica material. AFM images demonstrated that the morphology of the hybrid films’ surfaces can be changed as a function of sol–gel composition. RS analysis indicated that silanol groups were significantly present on the silver-based silica film surface. The UV–Vis spectra revealed that the hybrid coatings presented a reflectance of ~8%, at 550 nm. This study will enhance the value of nanocoating technology in optoelectronics, particularly in the development of nanostructures that improve the performance in thin-film solar cells.

Constructing efficient and recyclable composite absorbent based on the modification of polymer skeleton with in situ assembled mesoporous silica/graphene oxide nanohybrid

Polymers functionalized with hybrid nanoparticles are very popular for the preparation of composite absorbents with large surface area and good absorption capacity. However, the weak physical interactions between different nanoparticles allow for the easy destruction of the hybrid structure, which will greatly reduce the advantages of the hybrid nanoparticles as building blocks for the composite absorbent and decrease the stability of the composite absorbent in practical use. Here, in situ chemically boned mesoporous SiO2 (mSiO2)/graphene oxide (GO) nanohybrid (GO-mSiO2) was first synthesized by hydrolysis and condensation of tetraethylorthosilicate on the GO sheets, on which mSiO2 with the diameter of ca. 5 nm was uniformly distributed. Subsequently, a ternary absorbent with large surface area and very good water repellency was constructed by first impregnating commercial poly(melamine-formaldehyde) (MF) foam into GO-mSiO2 and then into polydimethylsiloxane (as cement and low surface energy source) solution. Because of the dually roughened skeleton surface with hybrid nanoparticles and the channel structure of mSiO2, the GO-mSiO2 modified hydrophobic MF (m-MF) foam possessed large surface area and high selective absorption ability for different oils and organic solvents from water, showing an absorption capacity that was up to 172 times its own weight. Moreover, m-MF can be recycled via the continued extrusion/sorption method. Taken together, these results suggest that the thus-prepared ternary absorbent can be applied as a potential candidate for the cleanup of oil spillage and toxic chemical leakage.

Hydrolysis and Condensation of Tetraethyl Orthosilicate at the Air–Aqueous Interface: Implications for Silica Nanoparticle Formation

The silica (SiO2) nanoparticles of a well-known silica precursor tetraethyl orthosilicate (TEOS) are generally synthesized via a promising solution-gelation inorganic polymerization process. The monodisperse silica nanoparticles have potential applications ranging from the formation of dental nanocomposites to antireflective coatings. In the present study, we have systematically investigated the in situ interfacial molecular structure of TEOS and its impact on the interfacial water structure during the processes of hydrolysis and condensation at the air–aqueous interface using sum-frequency generation (SFG) vibrational spectroscopy. With the presence of water, a gradual decrease in the SFG intensity in the CH-stretch region for each concentration of TEOS with time reflects the elimination of ethoxy groups, which is a signature of the hydrolysis process. Further, the impact of the hydrolysis process is revealed from the significant enhancement in the SFG signal in the OH-stretch region. The hydrolysis of TEOS is then followed by condensation in which the ≡Si─O– charged species are replaced by forming the ≡Si─O─Si≡ bridging network. The signature of the condensation process is reflected with the gradual decrease in the observed enhanced SFG signal in the OH-stretch region. The formation of monodispersed silica nanoparticles as an end product of size variation from 1.75 to 4.67 nm with the increase in TEOS concentration is confirmed with the DLS measurements. We have also probed the pH-dependent SFG studies at three different pH values (2.0, 5.8, and 9.0). The dominant pH-dependent hydrolysis process is revealed from the observed molecular structure of TEOS at the air–aqueous interface.

Water‐Stable Sulfide Solid Electrolyte Membranes Directly Applicable in All‐Solid‐State Batteries Enabled by Superhydrophobic Li+‐Conducting Protection Layer

AbstractSulfide solid electrolytes (SEs) represent one most promising technical routes to realize all‐solid‐state batteries (ASSBs) due to their high ionic conductivity and low mechanical stiffness. However, the poor air/moisture/water stability of sulfide SEs leads to completely destroyed structure/composition, reduced Li+ conductivity, and toxic H2S release, limiting their practical application in ASSBs. To solve this problem, a universal method applicable to all types of sulfide SEs is developed to realize water‐stable sulfide SE membranes, by spray coating a Li+‐conductive superhydrophobic protection layer with Li1.4Al0.4Ti1.6(PO4)3 (LATP) nanoparticles and fluorinated polysiloxane (F‐POS) via hydrolysis and condensation of tetraethyl orthosilicate and 1H,1H,2H,2H‐perfluorodecyltriethoxysilane molecules. The F‐POS@LATP coating layer exhibits excellent superhydrophobicity (water static contact angles > 160°) to resist extreme exposure (direct water jetting), because of its micro‐/nanoscale roughness and low surface energy. Moreover, ASSBs using the extreme‐condition‐exposed modified Li6PS5Cl membrane exhibit a reversible capacity of 147.3 mAh g‐1, comparable with the ASSBs using pristine sulfide membranes. The superhydrophobic Li+‐conducting layer is demonstrated to be an effective protection method for sulfide membranes so that they remain stable and functionable in extreme water exposure conditions, providing a new approach to protect all types of sulfide SEs and other air/moisture/water‐sensitive materials without sacrificing electrochemical performance.

TS-1 zeolite with homogeneous distribution of Ti atoms in the framework: synthesis, crystallization mechanism and its catalytic performance

The distribution of titanium (Ti) active sites in the framework of TS-1 zeolite is one of the critical factors affecting its catalytic performance, since it can influence accessibility of the Ti active sites and the catalytic utilization of Ti atoms. Here, TS-1 zeolite with homogeneous distribution of titanium atoms in the framework (named BUS-TS-1) is successfully synthesized via bottom-up strategy at high basicity conditions, and BUS-TS-1 zeolite exhibits better catalytic performance for both olefin and alkane oxidation. The comprehensive explorations on the crystallization behavior of BUS-TS-1 zeolite show that, the gripper-like silicon species, as condensed matter in Q2 and Q3 states (detected by 29Si NMR), can be obtained by the condensation of tetraethyl orthosilicate (TEOS) at high alkalinity conditions. The gripper-like silicon species can condense with Ti-OH to form stable and isolated Si-O-Ti species, so that the phase transfer rates of Si and Ti species match during the entire crystallization process, resulting in the homogeneous distribution of Ti atoms. This work offers a useful strategy for the synthesis of high-performance catalysts by regulating the distribution of Ti active-site within TS-1 framework.

Well-Defined Hexagonal Platy Particles of Brucite, Brucite/Silica Core Shell, and Hollow Silica Particle

Abstract Well-defined Mg(OH)2 (brucite) hexagonal platy particles with the lateral size of 80 nm were prepared by precipitation from an aqueous solution of magnesium chloride using a flow reactor with controlled pressure injection. The brucite particles were coated with a thin silica layer by hydrolysis and condensation of tetraethyl orthosilicate (TEOS) catalyzed by ammonium hydroxide to obtain Mg(OH)2@SiO2 core-shell nanoparticle. The heat treatment of the Mg(OH)2@SiO2 in air at 500 °C resulted in the transformation of brucite to periclase MgO. The Mg(OH)2 and MgO cores were removed from Mg(OH)2@SiO2 and MgO@SiO2 core-shell particles by etching with hydrochloric acid to obtain hollow silica particles with a lateral size range of 6 to 12 nm. Meanwhile, heat treatment of the Mg(OH)2@SiO2 at 1000 °C resulted in the transformation of brucite to periclase and forsterite.

Preparation and Characterization of Silica-Coated Iron Oxide Nanoparticles (Fe3O4@SiO2 NPs)

In this study, this SiO2 has been coated on the surface of Fe3O4 (Fe3O4@SiO2) by hydrolysis and condensation of tetraethyl orthosilicate (TEOS) under alkaline medium at 80oC. It was found that only 500 mL TEOS is required to obtain the best coated Fe3O4 core structures which has been confirmed from its TEM micrograph. FTIR analyses revealed the formation of Si-O-Si bonds at 1084.2–1101.4 cm-1 hence confirmed that SiO2 has been successfully coated the Fe3O4 core. From the FESEM analyses, the average size of silica was ~ 50 -70 nm. EDX of the Fe3O4@SiO2 showed that silica had been effectively bonded onto the surface of Fe3O4. The VSM measurements confirmed the superparamagnetic properties of Fe3O4@SiO2 that is desirable for biomedical applications.

Suppressing the Photocatalytic Activity of Titania by Precisely Controlled Silica Coating.

A homogeneous thin silica layer with the thickness of a few nanometers was successfully deposited on an anatase particle by the hydrolysis and condensation of tetraethyl orthosilicate. The heat treatment of the titania/silica hybrid at 1000 °C led to the densification of the silica layer on the anatase particles. The anatase particle after the silica coating did not transform to rutile, and no change in the crystallite size was seen by the heat treatment at 1000 °C. The coating and subsequent heating were repeated to vary the thickness of the silica layer to obtain each coating with similar thickness by each coating procedure (ca. 3 and 2 nm, before and after the heat treatment). The samples were evaluated for the photocatalytic decomposition of methylene blue by the UV irradiation to find that the decomposition became slower after the coating and subsequent heat treatment, and the repeated procedures led to further suppression of the photocatalytic decomposition of methylene blue. The quite small decomposition rate constant (0.01 h-1) was successfully achieved by the coating and subsequent heating for three times (the thickness of the dense silica layer was ca. 7 nm).

Mesoporous amine functionalized SiO2 supported Cu nanocatalyst and a kinetic-mechanistic degradation study of azo dyes

The preparation of stable copper nanoparticles (CuNPs) has remained a challenge for colloid chemists. In this investigation, mesoporous amine functionalized silica (NH2-SiO2) particles have been used as platform to host copper nanoparticles (CuNPs) for preventing their agglomeration. Mesoporous NH2-SiO2 particles are first prepared in one pot by diethyl amine (DEA) catalyzed hydrolysis and condensation of tetraethyl orthosilicate (TEOS) precursor in presence of hexamethylene diamine (HMDA) and cetyltrimethylammonium bromide (CTAB). In the second step, sequential adsorption and chemical reduction of Cu ions are carried out to obtain NH2-SiO2/Cu catalyst nanocomposites. The morphology and structural composition of NH2-SiO2/Cu catalyst nanocomposite particles confirmed the anchoring of evenly distributed ~ 28 nm sized Cu particles. The catalytic activity of nanocomposite particles for reductive degradation of Congo red (CR) and Eriochrome Black-T (EBT) showed maximum degradation at pH values of 7 and 4, respectively. The degradation efficiency increased with the increase in catalyst dose and a maximum degradation of ~ 92% is achieved for CR when 2 mg of catalyst nanocomposite particles is used. Comparatively, the degradation percent for EBT is low (~ 83%). Degradation kinetics of CR preferably followed a pseudo-first-order rate model, but, for EBT degradation hardly any particular kinetic rate model could be preferentially ascertained. The improved stability and increased surface-to-volume ratio of anchored CuNPs enhanced the degradation efficiency of catalyst nanocomposite particles.

Combing three-dimensional water channels and ultra-thin skin layer enable high flux and stability of loose polyimide/SiO2 nanofiltration membranes at low operating pressure via one step in-situ modification

Desalination of brackish water and purification of drinking water still pose several challenges. Combination of in-situ hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in polyamic acid (PAA) solution along with imidization reaction provide a novel polyimide/SiO2 (PI/SiO2) membrane. This is the first synthesis of a PI nanofiltration (NF) membrane with three-dimensional (3D) water channels, ultra-thin skin layer (30 ± 2 nm), and high flux at low operating pressure, by one-step phase inversion method. There was no additional requirement of an acid, since PAA served as a catalyst. The SiO2 cross-linked network provided the skeletal support, due to hydrogen bonding between PAA-PI and silicon hydroxyl groups. The fabricated PI/SiO2 membrane demonstrated a water contact angle of 45°, pore size of 1.05 ± 0.15 nm, Zeta potential of −30 mV, and tensile strength of 2.24 MPa when under optimized conditions. The loose PI/SiO2 NF membrane exhibited salt rejection in the sequence of Na2SO4 (87%)>MgSO4 (67%)>NaCl (41%)>MgCl2 (37%), which was consistent with size exclusion and Donnan exclusion effects. In particular, the water flux of 20.4 L/(m2 h bar) was about 4–15 times higher than that of universal PI-NF membranes. The membrane also exhibited excellent stability for over six days when used for separation. Furthermore, the membrane showed excellent dye (Rose Bengal (RB), Brilliant Blue G (BBG), Amido Black (AB)) rejection of over 90%. To conclude, this work paves a new pathway for the fabrication of PI-NF membranes for efficient NF separation.

Robust siloxane/graphene oxide thin film membranes: Siloxane size adjustment for improved separation performance and flux recovery

Siloxane/graphene oxide (GO) nanocomposites were synthesized by hydrolysis and condensation of tetraethyl orthosilicate in the presence of GO nanosheets through a sol-gel process. The influence of synthesis parameters on the properties of the siloxane/GO samples was studied and their structural, morphological and physicochemical characteristics were compared using various techniques. Polyether sulfone-supported GO and siloxane/GO thin film membranes were prepared using a pressure-assisted self-assembly method using a dead-end cell, and their separation performance and antifouling ability were evaluated. Siloxane/GOs appeared to have higher interlayer spacing, higher zeta potential and thus higher dispersion stability in aqueous media compared to GO. This gave rise to slower and more uniform sedimentation of the siloxane/GOs during the filtration process and formation of thin film membranes possessing denser and smoother morphology. The porosity, mean pore radius, water contact angle and pure water flux of the prepared membranes were compared. The separation performance of the prepared membranes to remove methylene blue (MB) and penicillin G-procaine (PG-P) from water was evaluated as a function of used GO solution concentration. The antifouling ability of membranes was studied by determining reversible fouling (Rr), irreversible fouling (Rir) resistances and flux recovery ratio (FRR). The siloxane/GO thin film membranes containing larger siloxane network exhibited the highest rejection percentage for MB (∼99%) and PG-P (∼88%), which were about 40% and 90% higher than that achieved for GO thin film membranes, while the water flux remained as high as 78.1 l·m−2h−1. Furthermore, these membranes exhibited the highest chlorine resistance, stability under ultrasonication, FRR (89%) and Rr (57%) values, implying higher chemical and mechanical stability, flux recovery capacity and antifouling ability.

The assembly of silica species with alkylamines: Mechanism of wastewater-free synthesis and the application of gel as a catalyst

Silica species generated by the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) could assemble with alkylamines to form silica gel. Herein, it was evidenced that part of the added amines, including butylamine (BA), octylamine (OA) or dodecylamine (DA), was protonated in the mixture of water and ethanol. Therefore, besides the hydrogen bonding between neutral silica species and the micelles composed of the non-protonated amines (Tanev and Pinnavaia, 1995), there existed strong electrostatic attraction between negatively charged silica species and the micelles composed of the protonated amines. This coexisting assembly mechanism could explain why the uncalcined BA- and OA-gels were millimeter-sized small blocks with large porosities and synthesized without waste water emission, while the uncalcined DA-gel was almost non-porous and formed via precipitation from its reaction medium. The uncalcined BA gel was proved to be efficient as a solid basic catalyst, replacing the commonly used ammonia solution which is easily volatilized and has a pungent smell, for the hydrolysis and condensation of TEOS to prepare silica microspheres.

Nanostructured octadecylsilica chemically coated stainless-steel fiber for vacuum-assisted HS-SPME sampling of PAHs in soil

An efficient and robust solid-phase microextraction (SPME) fiber was developed for vacuum-assisted sampling of polycyclic aromatic hydrocarbons (PAHs) in solid samples. The surface of a stainless-steel fiber was first oxidized and then coated with nanostructured n-octadecylsilica using the Stöber method, by hydrolysis and condensation of tetraethylorthosilicate in the presence of octadecyltrichlorosilane through a sol–gel strategy. The synthesized sorbent was characterized using scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX) and Fourier transform infrared spectroscopy (FT-IR). The developed vacuum-assisted headspace SPME (VA-HS-SPME) procedure was coupled with GC-FID and optimized for the analysis of PAHs in soil, using multivariate statistical analysis, based on Box-Behnken design. The calibration graphs for seven PAHs were linear (R2 > 0.995) over 0.001–4000 ng g−1. The limits of detection were found to be 0.1–0.9 pg g−1. The relative standard deviations for six repeated analyses of 100 ng g−1 of the PAHs (using a single fiber) were calculated 3.2–8.7% and fiber-to-fiber reproducibility (n = 6) obtained 5.2–12.34%. The nanostructured octadecylsilica was shown to be substantially robust and durable. It was utilized for ultrasensitive VA-HS-SPME/GC analysis of the PAHs in different polluted soil samples and satisfactory results were obtained, with low matrix effects.