Surface Modification Of Silica Gel Research Articles

Springback effect and structural features during the drying of silica aerogels tracked by in-situ synchrotron X-ray scattering

The springback effect during ambient pressure drying of aerogels is an interesting structural phenomenon, consisting of a severe shrinkage followed by almost complete re-expansion. The drying of gels causes shrinkage, whereas re-expansion is believed to be linked to repelling forces on the nanoscale. A multi-scale structural characterization of this significant volume change is key in controlling aerogel processing and properties. In this work, hydrophobic, monolithic silica aerogels with high specific surface areas were synthesized by modification with trimethylchlorosilane and ambient pressure drying. Here, we report a multi-method approach focusing on in-situ X-ray scattering to observe alterations of the nanostructured material during the drying of surface-modified and unmodified silica gels. Both show a porous fractal nanostructure, which partially collapses during drying and only recovers in surface-modified samples during the springback effect. Distinct changes of the X-ray scattering data were reproducibly associated with the shrinkage, re-expansion and drying of the gel network. Our findings may contribute to tailor aerogels with specific functionality, as the springback effect has a direct influence on properties (e.g., porosity, pore size distribution), which is directly affected by the degree of re-expansion.

Design and evaluation of polar-embedded stationary phases containing triacontyl group for liquid chromatography

The present work described two triacontyl-bonded silica adsorbents containing different polar embedded groups (i.e. amide- and carbamate-type) for high performance liquid chromatography, which were prepared by covalent surface modification of silica gel with respective pre-synthesized polar-embedded triacontyl (C30) silane. The acylimidazole-mediated method was used for the first time for the synthesis of amide-type alkyl silane, while the carbamate-type silane was obtained via an improved solvent-free procedure. A conventional C30 stationary phase was also developed on the same silica substrate in the similar manner, which was used as a reference column for comparison of the unique mechanisms facilitated and/or furnished by the polar groups. The successful immobilization of the designed C30 species was confirmed by infrared spectroscopy and elemental analysis. In further comparison with an amide-embedded octadecyl (C18) two other conventional C18 stationary phases of different surface chemistry, detailed chromatographic characterization of the C30 series stationary phases was performed in terms of surface density, hydrophobicity, aromatic selectivity, shape selectivity and water tolerance using a diversified range of analytes, including homologous alkylbenzenes, isomeric polycyclic aromatic hydrocarbons, carotenes, congeners of polychlorobiphenyls, aromatic amines, phenolic compounds, estrogens and nucleosides. A high resemblance between the chromatographic behaviors of the two polar-modified C30 stationary phases was observed, meanwhile they demonstrated noticeable differences from non-polar C30 stationary phase. The polar-embedded C30 phases showed satisfactory performance towards the solutes of interest in the studied conditions. The beneficial synergy of the polar groups and the triacontyl chains enabled these polar-enhanced C30 stationary phases to address challenging separation tasks with high selectivity.

Silica functionalized by pyridinecarboximidamides as a novel sorbent of heavy metals ions

ABSTRACT Two novel sorbents, obtained as a result of surface modification of silica gel for the Cu(II), Co(II) and Ni(II) removal from aqueous solutions were proposed. For the modification, 3-chloropropyltrimethoxysilane, N’-hydroxy-N,N-dioctylpyridine-3-carboximidamide and N’-hydroxy-N,N-dioctylpyridine-4-carboximidamides were used. A series of basic tests on the sorption of Cu(II), Co(II) and Ni(II) were carried out and the presented results indicated that the novel sorbents were able to remove all tested metals ions from the aqueous solutions, and the removal efficiency was dependent on the functionalised agent structure, dosage, metal ions concentration and pH. The Langmuir model also assumed that a monolayer sorption occurred.

Modified silica gel surface with chelating ligand for effective mercury ions adsorption

The electron-donating group dithiocarbamate functionalized silica gel (SG-PDC) was prepared and used for adsorption of metal ions from aqueous solution. The modified silica gel was characterized by fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA) and scanning electron microscopy (SEM). It showed excellent adsorption selectivity for Hg(II) ions over other metal ions, such as Cu(II), Cd(II), Pb(II). Kinetics and equilibrium isotherms of Hg (II) sorption were determined in batch equilibrium experiments. The adsorption capacity for Hg (II) of SG-PDC was more than five times as much as that of unmodified silica gel. X-ray photoelectron spectroscopy (XPS) was applied to study the adsorption mechanism and it confirmed that the improvement in mercury adsorption was related to the ligand groups containing S and N atoms anchored on the surface of silica gel. The adsorbent had high reusability after several adsorption–desorption cycles. This study provided a feasible strategy to develop the effective sorbent for Hg (II) ions by covalently modification of silica gel with ligand containing multiple coordination sites.

The estimation of posibility of stearic and oleic acids' TLC-separation with eluents containing surfactants

The possibility of separation of oleic and stearic acids with mobile phases on the basis of surfactants was estimated by the method of a thin-layer chromatography. The influence of surfactant's type and concentration on the retention parameters of the studied acids when using of normal-phase plates for a thin-layer chromatography of Sorbfil UV-254 is investigated in the work. The influence on mobility of oleic and stearic acids of the anionic sodium n-dodecylsulphate, cationic cetylpyridinium chloride and non-ionic Tween-80 in the range of concentration from 1·10-5 mol/l to 0.1 mol/l is estimated. The mixed mobile phases on the basis of two last surfactants taken in various concentrations are also investigated. The рН of eluents was varied in the range from 1 to 9. The addition of 2-propanol into the mobile phase containing surfactant didn't lead to improvement of acids' distribution efficiency. The best results have been received with the eluent, containing 1·10-5 mol/l of cetylpyridinium chloride and boric buffer solution with pH 9. Preliminary modification of silica gel surface with cetylpyridinium chloride did not change the results of chromatography. For clarification of relation of acids' retention with a length of a hydrophobic fragment, and, therefore, a contribution of hydrophobic interactions, in system with the mixed mobile phase on the basis of cetylpyridinium chloride and Tween-80 at pH 3 formic acid, acetic acid, propionic acid, hexanoic acid and myristic acid were analyzed. The smallest mobility was observed for myristic acid (lgPo/w=6.09±0.19) that indicates very strong hydrophobic interactions of acid with the surface of silica gel modified by surfactants. Such interactions are the main reason of bad mobility of studied oleic (lgPo/w=7.7±0.2) and stearic (lgPo/w=8.22±0.19) acids in system with the surfactant-containing eluents. For the manifestation of acidic zones after chromatography, a solution of phosphomolybdic acid, a solution of rhodamine B, a solution of sulfuric acid and an iodine chamber were tested. The best visualization of TLC-сhromatogram is obtained after sprinkle the plates by 6% solution of sulfuric acid in ethanol with their subsequent heating at 110 °C.

Immobilization of cellulase on a silica gel substrate modified using a 3-APTES self-assembled monolayer.

Cellulase was immobilized onto silica gel surfaces pretreated with (3-aminopropyl) triethoxy-silane (3-APTES), and glutaraldehyde (GA) was used as a cross-linker. A carboxymethyl cellulose sodium salt (CMC) solution was used for activity experiments. Protein assay was performed to determine the mass immobilized and compare with free enzyme. Cellulase was successfully demonstrated to be immobilized on the modified silica gel surface, and no detectable amount of enzyme was stripped off during the hydrolysis of the CMC solution. The specific activity of the immobilized cellulase is 7 ± 2 % compared to the similar amount of free cellulase. Significant activity over multiple reuses was observed. The seventh batch achieved 82 % activity of the initial batch, and the fifteenth batch retained 31 %. It was observed that the immobilized cellulase retained 48 % of its initial activity after 4 days, and 22 % even after 14 days.

表面修飾シリカゲルにおける重金属イオンの分配・放出過程の解析

Distribution and release processes of heavy-metal ions between spherical surface-modified silica gel microparticles and water were analyzed by microcapillary manipulation and absorption microspectroscopy. Silica gel modified with triamine (QuadraSil-TA, Q-TA) or thiol groups (QuadraSil-MP, Q-MP) was used as a surface-modified silica gel. A single microparticle was injected into an aqueous HAuCl4 or CuSO4 solution containing 0.01 M KCl (pH = 6), and the distribution rate of the metal ion from water into the microparticle was measured. The rate of release of Au(III) or Cu(II) from Q-TA into water (pH = 6) was much smaller than that of the distribution of the metal. The microparticle radius dependence of the absorbance of the metal in the microparticle and distribution of the metal by cross-sectional SEM-EDS analysis at the distribution equilibrium indicate that Au(III) and Cu(II) distribute into the microparticle interior for Q-TA, while Au(III) distributes at the outer layer in the spherical microparticle for Q-MP. The distribution processes were analyzed as the intraparticle diffusion, and the diffusion coefficient (Dp) observed in the present systems was compared with that calculated from the theoretical pore and surface diffusion model. We consider that the rate-determining step of the distribution of Au(III) in the Q-TA (pore diameter = 5.9 nm) system is the intraparticle diffusion of AuCl4−. On the other hand, the distribution of Cu(II) into Q-TA was much slower than the intraparticle diffusion.

Preparation and preliminary application of 5-HMF@SiO2 micro-particles

We report an organic–inorganic hybrid composite of surface-modified silica gel with 5-hydroxymethylfurfural, which provided a new promising stationary phase for protein separation.

Surface modification of silica gel for adsorptive removal of Ni2+and Cd2+from water

AbstractIn this study, surface of silica gel was functionalized with 1,2-ethylenediamine. The synthesized materials were characterized by Fourier transform infrared spectroscopy, scanning electron microscope, and elemental analysis. Batch adsorption studies were carried out to analyze the adsorption of nickel and cadmium ions from aqueous solutions. The factors influencing % adsorptive removal of Ni2+ and Cd2+ onto the silica gel and functionalized silica gel, such as initial pH value of the Ni2+ and Cd2+ ion solutions, adsorbent dose, initial Ni2+ and Cd2+ ion concentration, contact time, and temperature were investigated. Langmuir and Freundlich isotherm models were used to determine the isotherm parameters associated with the adsorption process. The monolayer adsorption capacity of ASG for Ni2+ and Cd2+ increased from 4.69 to 19.6 and 7.63 to 27 mg/g, respectively, after modification of activated silica gel (ASG) surface with 1,2-ethylenediamine. Kinetic data were analyzed considering pseudo-first-orde...

Synergistic Effect of Polyaniline Modified Silica Gel for Highly Efficient Separation of Non Resolvable Amino Acids

Herein, we present a comparative study for the analysis of amino acids on silica gel (SIG) and polyaniline (Pani) modified SIG as stationary phases using 1% ethanolic solution of boric acid as mobile phase. The separation studies revealed that in the case of modified SIG, improved separations of two component mixtures of amino acids were achieved. Some new combinations of binary separations were achieved on Pani modified SIG layer, which were not efficiently separated in the case of pure SIG. Thus, by the modification of SIG surface with Pani, sorbent with enhanced chromatographic performance can be achieved.

Effect of various structure directing agents on the physicochemical properties of the silica aerogels prepared at an ambient pressure

We studied the effects of various surfactants on the textural properties (BET surface area, pore size, and pore volume) of the silica aerogels prepared at an ambient pressure. A simple surface modification of silica gel prepared at an ambient pressure through hydrolysis and polycondensation of TEOS as a silica precursor was conducted using various structure directing agents. The treatment was found to induce a significant difference in the porosity of the silica aerogel. Highly porous silica aerogels with bimodal porous structures were prepared by modifying the surface of the silica wet-gel (alcogel) with trimethylchlorosilane (TMCS) in order to preserve its porosity. The samples were analyzed by small-angle X-ray scattering and nitrogen adsorption. In this work, a possible new type of highly porous hydrophobic silica aerogel with a bimodal porous structure is presented. A hydrophilic extremely porous (high surface area and large pore volume) silica aerogel was obtained by heating the as-synthesized hydrophobic silica aerogel at 400°C for 1h. There was a significant effect of structure directing agent on the textural properties, such as specific surface area, pore size distribution and cumulative pore volume of the silica aerogels.

Near-Stoichiometric Adsorption of Phosphate by Silica Gel Supported Nanosized Hematite

Decreasing the size of oxide particles to nanoscale enables one to ensure maximal reaction rates and depths in the solid due to the enhancement of the specific surface area and the increase of the diffusion rate caused by shortening diffusion paths. For that reason, one may suggest that in the case of adsorption onto nanoparticles, the complete conversion of sorbents to stoichiometric compounds would become possible. Adsorption of phosphate ions onto nanosized hematite supported on silica gel surface has been studied. Modification of silica gel surface by hematite in the quantity of 0.62 and 1.25 mass% has been carried out by means of a citric acid aided method. The morphology of the samples obtained has been characterized using DTA, XRD, SEM, and low temperature desorption of nitrogen. It has been found in batch experiments that unlike natural and synthetic hematites, for which the limiting adsorption values do not exceed 14 mg/g, silica gel supported nanosized hematite adsorbs 400–2000 mg of the phosphate ions per gram, thus forming near-stoichiometric iron phosphates on the surface of the support. The degree of conversion of hematite to iron phosphates is greater in acidic media and at a lower surface coverage, when hematite crystallites are small and better accessible by adsorbate.

Preparation of Arsenate Anion Surface-Imprinted Material IIP-PDMC/SiO2 and Study on Its Ion Recognition Property

By molecular design, a new ion surface-imprinting technique was set up based on surface-initiated graft-polymerization, and arsenate anion surface-imprinted material with high performance was prepared for the first time. A redox initiating system was constituted by the amino groups on the surface-modified silica gel particles and the ammonium persulphate in the solution. The cationic monomer 2-methacryloyloxyethyl-trimethyl ammonium chloride (DMC) was used as functional monomer and N,N′-methylenebisacrylamide (MBA) was used as cross-linker. In the solution, the monomer molecules were arranged around the template ion, arsenate anion, via ion exchange action, and then the arsenate anion surface-imprinting was carried out along with the surface-initiated graft-polymerization of DMC and MBA, forming arsenate anion surface-imprinted material IIP-PDMC/SiO₂. The experimental results show IIP-PDMC/SiO₂ possesses specific recognition selectivity and excellent binding affinity for arsenate anion. The selectivity coefficients of IIP-PDMC/SiO₂ for arsenate anion are 8.814 and 7.898 relative to chromate and nitrate ions, respectively.

Synthesis, characterization, and catalytic activity for thioanisole oxidation of homogeneous and heterogeneous binuclear manganese(II) complexes with amino acid-based ligands

A binuclear Mn(II) complex [Mn2(HL)2(H2O)4], HL = 2-[(2-Hydroxy-benzylidene)-amino]-3-(4-hydroxy-phenyl)-propionic acid, has been prepared and characterized by physico-chemical and spectroscopic methods. The results suggest that the amino acid Shiff base ligand is coordinated as a bivalent anion with a tridentate NO2 donor set involving the phenolic and carboxylic acid oxygens and azomethine nitrogen. A heterogenized binuclear manganese catalyst was synthesized by the covalent anchoring of [Mn2(HL)2(H2O)4] onto a modified silica gel surface, through the reactive (3-chloropropyl)-trimethoxysilane group. The surface properties of the functionalized catalyst were analyzed by physico-chemical and spectroscopic methods. The silica-supported metal complex, ([Mn2L(HL)(H2O)4]/SiO2), catalyzes the oxidation of thioanisole with H2O2, to give the sulfoxide and sulfone. [Mn2L(HL) (H2O)4]/SiO2 shows lower catalytic activity and turnover number compared to the homogeneous catalyst [Mn 2 II –(HL)2(H2O)4]. However, the activity of the immobilized catalyst remains nearly unchanged after five cycles, indicating that it is truly heterogeneous.

Silica Gel Supported Hydrophobic Ionic Liquid for Selective Extraction and Determination of Coumarin

In this study, a modified silica gel surface with a hydrophobic ionic liquid (SG-1,10-PhenanNTf2) was used as an adsorbent for a selective extraction of coumarin prior to its determination by use of high performance liquid chromatography. Results demonstrated that SG-1,10-PhenanNTf2 phase had a good adsorption capacity up to 85.29 mg?g?1, high selectivity, good site accessibility and fast binding kinetics toward coumarin. The adsorption capacity for coumarin was improved by 62.33% with the SG-1,10-PhenanNTf2 phase as compared to activated silica gel. Adsorption isotherm data displayed that the adsorption process was mainly monolayer on a homogeneous adsorbent surface, confirming the validity of Langmuir adsorption isotherm model. The adsorption of coumarin on the SG-1,10-PhenanNTf2 phase was accomplished after only 60 min contact time. Results of kinetic models showed that the adsorption of coumarin on the SG-1,10-PhenanNTf2 phase obeyed a pseudo second-order kinetic model. Finally, the efficiency of this methodology was confirmed by applying it to real water samples.

Immobilization of lipases from Rhizomucor miehei and Thermomyces lanuginosus by adsorption on variously grafted silica gels

Twenty variously surface-modified mesoporous silica gels were studied as carriers for immobilization by hydrophobic adsorption of the lipases from Rhizomucor miehei (RmL) and Thermomyces lanuginosus (TlL). Several of the surfacemodified silica gels studied proved to be advantageous supports for RmL and TlL resulting in novel biocatalysts of high activity and enantioselectivity in the kinetic resolution of racemic 1-phenylethanol rac-1. The fact that it were different grafting methods which led to the most efficient supports for RmL and TlL indicated that the selection of optimal support for the immobilization of a particular lipase cannot be predicted.

Alkali Metal Modification of Silica Gel-Based Stationary Phase in Gas Chromatography

Modification of the precipitated silica gel was done by treatment with alkali metal (NaCl) before and after calcination. The silica surfaces before and after modification were confirmed by infrared spectroscopy in order to observe the strength and abundance of the acidic surface OH group bands which play an important role in the adsorption properties of polar and nonpolar solutes. The surface-modified silica gels were tested as GC solid stationary phases in terms of the separation efficiency for various groups of non-polar and polar solutes. Also, thermodynamic parameters (<svg style="vertical-align:-0.0pt;width:25.924999px;" id="M1" height="11.425" version="1.1" viewBox="0 0 25.924999 11.425" width="25.924999" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.363)"><path id="x394" d="M600 0h-557v24l268 633l28 8l261 -641v-24zM497 50l-194 489l-196 -489h390z" /></g><g transform="matrix(.017,-0,0,-.017,10.959,11.363)"><path id="x1D43B" d="M865 650q-1 -4 -4 -14t-4 -14q-62 -5 -77 -19.5t-29 -82.5l-74 -394q-12 -61 -0.5 -77t75.5 -21l-6 -28h-273l8 28q64 5 82 21t29 76l36 198h-380l-37 -197q-11 -64 0.5 -78.5t79.5 -19.5l-6 -28h-268l6 28q60 6 75.5 21.5t26.5 76.5l75 394q13 66 2 81.5t-77 20.5l8 28&#xA;h263l-6 -28q-58 -5 -75.5 -21t-30.5 -81l-26 -153h377l29 153q12 67 2 81t-74 21l5 28h268z" /></g> </svg>, <svg style="vertical-align:-0.23206pt;width:23.325001px;" id="M2" height="11.75" version="1.1" viewBox="0 0 23.325001 11.75" width="23.325001" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.4)"><use xlink:href="#x394"/></g><g transform="matrix(.017,-0,0,-.017,10.959,11.4)"><path id="x1D43A" d="M713 296l-5 -25q-47 -7 -59 -20t-23 -72l-15 -79q-9 -48 -3 -74q-15 -3 -55 -13t-63 -15t-59.5 -10t-70.5 -5q-149 0 -243 80t-94 220q0 169 127.5 276.5t336.5 107.5q91 0 206 -36l-10 -165l-29 -1q1 85 -47.5 126t-146.5 41q-153 0 -243.5 -97t-90.5 -242&#xA;q0 -122 68.5 -198.5t188.5 -76.5q121 0 139 75l20 86q13 58 -1.5 70.5t-99.5 20.5l5 26h267z" /></g> </svg>, and <svg style="vertical-align:-0.23206pt;width:19.174999px;" id="M3" height="11.75" version="1.1" viewBox="0 0 19.174999 11.75" width="19.174999" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.4)"><use xlink:href="#x394"/></g><g transform="matrix(.017,-0,0,-.017,10.959,11.4)"><path id="x1D446" d="M457 488l-30 -3q-17 148 -131 148q-53 0 -84.5 -34.5t-31.5 -82.5q0 -42 25.5 -72t74.5 -62l33 -22q63 -42 95 -85t32 -102q0 -84 -67 -137t-163 -53q-58 0 -113 22t-70 43l-4 152l27 4q4 -32 15 -62.5t31 -59.5t53.5 -47t76.5 -18q56 0 92 35t36 96q0 39 -25 70t-78 68&#xA;l-31 22q-32 23 -53.5 41.5t-45 57t-23.5 77.5q0 82 58 132.5t156 50.5q46 0 101 -17l18.5 -6t17 -6t8.5 -3q-4 -55 0 -147z" /></g> </svg>) were determined using <i >n</i>-hexane as a probe in order to show the adsorbate-adsorbent interaction. It was observed that the non-polar solutes could be separated Independent on the reactivity and porosity of the silica surfaces. The efficiency of the surface-modified silica gels to separate the aromatic hydrocarbons seemed to be strongly influenced by the density of the surface hydroxyls.

Use of Surface Modified Silica gel factory Waste for Removal of 2,4-D Pesticide from Agricultural Wastewater: A case study

The silica gel waste (SGW), after its collection from a local factory (Kolkata, India) was modified with cationic surfactant and was utilized as an adsorbing media for the removal of 2,4- dichlorophenoxyacetic acid (2,4-D) from agricultural runoff of a tea garden. Characterization of base adsorbent and modified adsorbent was carried out. The efficacy of the adsorbent was evaluated through both batch and fixed bed mode. Kinetics and isotherm study were conducted and the parameters were compared with 2,4-D bearing distilled water samples. The values of diffusion coefficients were determined. Presence of electrolyte and solution pH was found to affect the performance of the adsorbent significantly. The removal efficiency of surfactant modified silica gel waste (SMSGW) in case of wastewater was found to be lower than the 2,4-D bearing distilled water sample. The data of column run was analyzed using Logit model. Batch desorption study was carried out using ethanol and acetone. The studies revealed surfactant coated SGW to be an efficient adsorbing media for 2,4-D removal.

Chromatographic behavior and separation of pesticides on thin silica gel layers impregnated with cationic micelles

The chromatographic behavior of eight pesticides has been examined on cationic-micelles impregnated silica layers using mixed organic solvent (different combinations of hexane-acetone, v/v) systems. The chromatographic system constituting 0.01% CTAB (N-cetyl-N,N,N-trimethyl ammonium bromide) impregnated silica gel as stationary phase, and hexane-acetone in 1:1 ratio (v/v) as mobile phase was most favorable for on-plate identification of pesticides with preliminary separation. Surface modification of silica gel on impregnation, as indicated by SEM and FTIR studies was responsible for improved chromatographic performance. The results obtained on 0.01% CTAB impregnated silica layers were compared with those achieved on 0.01% CTAB impregnated kieselguhr, cellulose, or alumina layers. With selected chromatographic system, fivecomponent mixtures of pesticides (glyphosate, acephate, chlorpyrifos, malathion/methyl parathion, and isoproturon) were successfully resolved. The interference of metal cations as impurit...

Chiral Separation of Amino Acid Derivatives by Molecular Imprinting Technique

Molecularly imprinted polymers, based on the surface-modified silica gel, were prepared with silylanized silica gel as a carrier, acrylamide as functional monomer, ethylene dimethacrylate (EDMA) as crosslinker and Boc-L-phenylalanine as the template molecule. The results of HPLC shows that the imprinted polymers have good specific recognition of Boc-L-phenylalanine. The baseline separation of Boc-phenylalanine enantiomer was achieved in 20 min, the resolution was 1.84 and the maximum adsorption capacity was 6788 mg g-1.