Functionalized Silica Gel Research Articles

Schiff base functionalized silica gel for simultaneous separation and preconcentration of Cu(II), Ni(II), and Cd(II) in pharmaceuticals and water samples

A method for separation and preconcentration of Cu(II), Ni(II), and Cd(II) using N-N'-bis(5-methoxsalicylidene)-2-hydroxy-1,3-propanediamine modified silica gel was improved for aqueous samples and pharmaceuticals. Determination of the analytes was achieved by inductively coupled plasma optic emission spectrometry. The experimental conditions including pH value, sample volume, eluent type and volume, sorbent mass, sample, and eluent flow rates were optimized with univariate and multivariate optimization tools. The relative standard deviations of the method were 2.9% for Cu(II), 3.0% for Ni(II), and 3.3% for Cd(II) with recovery values between 98.8 ± 3.2-101.5 ± 3.0%. The limits of detection were found to be 62.4, 39.5, and 28.2 ng L-1 for Cu(II), Ni(II), and Cd(II), respectively. The accuracy of the suggested procedure was tested with the certified reference material (Certipur ICP multi-element standard solution IV) and addition-recovery experiments. The method was successfully applied to eye drop, anesthetic, serum, tap water, mineral water, and spring water samples.

Immobilization of xylanase on differently functionalized silica gel supports for orange juice clarification

The immobilization of xylanase from Trichoderma longibrachiatum via ion exchange on 3-propylsulfonic acid (Xyl/Si-SO3) and 3-aminopropyl (Xyl/Si-NH3) functionalized silica gel and covalently on 3-carboxypropyl (Xyl/Si−COOH) and silica gel functionalized with 3-aminopropyl and modified with glutaraldehyde (Xyl/Si-Glu) were performed and the prepared biocatalysts were used for clarification of orange juice. The supports and immobilized biocatalysts were characterized by scanning electron microscopy, and thermal gravimetric analysis. Free and all immobilized xylanase samples showed maximal catalytic activity at pH 6.0. The free xylanase and Xyl/Si-NH3 had a maximal catalytic activity at 50 °C, while Xyl/Si-Glu, Xyl/Si−COOH and Xyl/Si-SO3 exhibited their maximal catalytic activities at 60 °C. The Xyl/Si-Glu showed 4.2-fold higher thermal stability than the free xylanase at 50 °C and pH 6.0. The clarity of orange juice was increased by 74.7, 73.6, 59.3, 60.3, and 78.8 % respectively by using free xylanase, Xyl/Si-Glu, Xyl/Si−COOH, Xyl/Si-SO3 and Xyl/Si-NH3 at 50 °C after 180 min treatment time. The reusability studies showed that Xyl/Si-Glu, Xyl/Si−COOH, Xyl/Si-SO3 and Xyl/Si-NH3 retained 77, 71, 11 and 16 %, respectively, of their initial activities after 10 reuses. These results show that Xyl/Si-Glu and Xyl/Si−COOH are better potential candidates than Xyl/Si-SO3 and Xyl/Si-NH3 in fruit juice clarifying processes.

Adsorption Separation of Arsenic(III) and Arsenic(V) using Functionalized Silica Gels

A method for the adsorption separation of inorganic arsenic species (As(III)/As(V)) using sequentially connected preconcentrating columns filled with functionalized silica gels and their determination by inductively coupled plasma optical emission spectrometry was proposed. As(V) was effectively retained at pH 3.5–6.5 by an adsorbent containing groups of quaternary phosphonium bases on the surface and exhibiting the properties of an anion exchanger. In this pH range, As(III) was not extracted, which made it possible to separate As(V) from As(III). As(III) was retained in a wide pH range of 1–6 by a complexing adsorbent containing mercapto groups on the surface. Adsorbed As(V) was quantitatively eluted from the surface with 1M HNO3, and As(III) – with 5 % unithiol solution in 2M HCl. The use of «non-aggressive» eluents allows us to reuse adsorbents for preconcentration of As(III) and As(V) at least 5 times. The separation efficiency was confirmed by the analysis of model solutions

Different interactions of gaseous CH3I with both Ag nanoparticles and Ag+ ions included in mercaptopropyl functionalized silica gels

Mercaptopropyl functionalized silica gels were prepared and interacted with Ag0 nanoparticles and Ag+ ions. After that, these gels were all exposed to gaseous CH3I. To investigate the silver oxidation states and interactions with the surrounding gels, peak shifts were observed using X-ray photoelectron spectroscopy. The cleavage of mercaptopropyl during the electron-beam irradiation applied for Ag0 nanoparticle production was also discussed. The produced Ag nanoparticles formed covalent bonds with the mercaptopropyls. However, in this study, decomposition of the gaseous CH3I was not observed, and the CH3I remained on the surfaces of the Ag nanoparticles. On the other hand, Ag+ ions formed ionic bonds with the mercaptopropyls, and the physisorption of gaseous CH3I on the Ag+ ions occurred. Thereafter, the gaseous CH3I was decomposed by UV light, and the Ag+ ions and iodide interacted to form AgI. Different reactions of gaseous CH3I were observed depending on the oxidation states of the silver.

Diethylenetriamine functionalized silica gel for adsorption of uranium from aqueous solution and seawater

Diethylenetriamine functionalized silica gel for adsorption of uranium from aqueous solution and seawater

4-Hydroxypyridinium Antimony Tetrachloride-Functionalized Silica Gel Nanoparticles-Catalyzed One-Pot Synthesis of Naphtho-Bis-[1,3]-Oxazin-3-One/Thione

A novel method for the synthesis of diarylylnaphtho bis([1,3]oxazine) dione/thione derivatives is established by employing one-pot three-component reaction of naphthalene-1,8-diol/naphthalene-1,5-diol, aromatic aldehydes, and urea or thoiurea using a catalytic amount of 4-hydroxypyridinium antimony tetrachloride functionalized silica gel in methanol in excellent yields. The FTIR, 1H NMR, and 13C NMR confirm the structures of the products. After synthesis of the compounds, their potential antibacterial and antifungal activities were evaluated, and result showed significant antibacterial activities.

Silver (I)-dimercaptotriazine functionalized silica: A highly selective liquid chromatography stationary phase targeting unsaturated molecules

Silver(I)-mercaptopropyl (Ag-MP) functionalized silica gel has demonstrated its effectiveness in separating various unsaturated organic compounds including unsaturated fatty acid ethyl esters (FAEEs), triglycerols (TAGs) and long-chain alkyl ketones (alkenones). While Ag-MP stationary phase displays many advantages over the conventional silver ion-impregnated silica gel (e.g., stability, high recovery, etc.), potential drawbacks of Ag-MP include relatively low retentions for unsaturated molecules, which could limit chromatographic resolutions under certain circumstances. In this study, we evaluate a new silver-thiolate stationary phase: silver(I)-dimercaptotriazine (Ag-DMT) functionalized silica gel targeting the separation of unsaturated compounds. We show Ag-DMT affords substantially higher retention factors, peak resolutions and capacities for TAGs and FAEEs than Ag-MP does. Ag-DMT also yields higher purity eicosapentaenoic acid (EPA) from fish oil FAEE mixtures than Ag-MP. In addition, Ag-DMT resolves double bond positional and cis/trans-isomers of C18:1 fatty acid methyl esters (FAMEs) as well as unsaturated methyl/ethyl alkenones with different number of double bonds. Based on van't Hoff plots, enthalpy changes during the adsorption of unsaturated FAEEs onto Ag-DMT are ~2 times higher than those on Ag-MP. Such difference may be attributed to the stronger electron-withdrawing effect of the thiol group on DMT, which results in more positively charged silver ions hence greater interactions with unsaturated molecules. The stronger interaction between double bonds and Ag-DMT is further corroborated by density-functional theory (DFT) calculations. Ag-DMT shows its high stability for repeated uses in the separation of TAGs over 319 runs, with peak resolutions decreasing by < 3%. Collectively, our data demonstrate the exceptionally high efficiency of Ag-DMT column for separating unsaturated molecules.

Microwave Assisted Oxidation of Benzyl Halides to Aldehydes and Ketones with 4-Hydroxypyridinium Nitrate Functionalized Silica Gel in Aqueous Media

Aldehydes and ketones, available by numerous methods and from plentiful starting materials, are vital classes of chemicals which serve as precursors and intermediates for the preparation of such di...

Enhanced Stability Designs of Cell Membrane Chromatography for Screening Drug Leads

Cell membrane chromatography (CMC) is an effective method to screen bioactive components acting on specific receptor from complex systems. CMC keeps the biological activity of the membrane receptors and improves the efficiency of screening. However, the traditional CMC suffered from poor stability, resulting in limited life span and low reproducibility. Which greatly limits the application of this method, especially limit the application of precious cell materials. To solve this problem, cyanuric chloride (TCT)-functionalized silica gel was used for covalent immobilization of cell membranes. TCT reacts with amino groups on the cell membrane to form covalent bonds. In this way, the cell membranes are not easy to fall off. The column life of the TCT-decorated epidermal growth factor receptor (EGFR)/CMC column was extended to more than 8 days, while the normal CMC column of the control group dropped sharply in the first 3 days. TCT-decorated EGFR/CMC online HPLC-IT-TOF-MSn system was successfully applied for potential screening of drug leads from Trifolium pratense L.. One potential drug lead acts on the EGFR receptor as formononetin was screened. Such immobilization method owing to the properties of mild conditions, fast reaction speed, high yield and small loss of membrane protein activity. In a word, our strategy of covalent immobilization of cell membrane receptors improves the stability of CMC.

Schiff base functionalized silica gel for simultaneous separation and preconcentration of Cu(II), Ni(II), and Cd(II) in pharmaceuticals and water samples.

A method for separation and preconcentration of Cu(II), Ni(II), and Cd(II) using N-N'-bis(5-methoxsalicylidene)-2-hydroxy-1,3-propanediamine modified silica gel was improved for aqueous samples and pharmaceuticals. Determination of the analytes was achieved by inductively coupled plasma optic emission spectrometry. The experimental conditions including pH value, sample volume, eluent type and volume, sorbent mass, sample, and eluent flow rates were optimized with univariate and multivariate optimization tools. The relative standard deviations of the method were 2.9% for Cu(II), 3.0% for Ni(II), and 3.3% for Cd(II) with recovery values between 98.8 ± 3.2-101.5 ± 3.0%. The limits of detection were found to be 62.4, 39.5, and 28.2 ng L-1 for Cu(II), Ni(II), and Cd(II), respectively. The accuracy of the suggested procedure was tested with the certified reference material (Certipur ICP multi-element standard solution IV) and addition-recovery experiments. The method was successfully applied to eye drop, anesthetic, serum, tap water, mineral water, and spring water samples.

Improvement of biodiesel production from palm oil by co-immobilization of Thermomyces lanuginosa lipase and Candida antarctica lipase B: Optimization using response surface methodology

Candida antarctica lipase B (CALB) and Thermomyces lanuginose lipase (TLL) were co-immobilized on epoxy functionalized silica gel via an isocyanide-based multicomponent reaction. The immobilization process was carried out in water (pH 7) at 25 °C, rapidly (3 h) resulting in high immobilization yields (100%) with a loading of 10 mg enzyme/g support. The immobilized preparations were used to produce biodiesel by transesterification of palm oil. In an optimization study, response surface methodology (RSM) and central composite rotatable design (CCRD) methods were used to study the effect of five independent factors including temperature, methanol to oil ratio, t-butanol concentration and CALB:TLL ratio on the yield of biodiesel production. The optimum combinations for the reaction were CALB:TLL ratio (2.1:1), t-butanol (45 wt%), temperature (47 °C), methanol: oil ratio (2.3). This resulted in a FAME yield of 94%, very close to the predicted value of 98%.

Synthesis and characterization of novel polystyrene-silica composites containing azomethine

Herein, four novel polystyrene / silica composites containing azomethine (Si-PSNO2, Si-PSH, Si-PSCl, Si-PSCH3) were reported. For this purpose, polymers including azomethine (PSNO2, PSH, PSCl, PSCH3), one of which is novel (PSNO2) were obtained from condensation reaction between 4-benzyloxybenzaldehyde with 2-aminophenol and its derivatives. Then, these polymers were immobilized on 3-chloropropyl functionalized silica gel to obtain polymer / silica composites. The structures of novel composites were characterized by various spectroscopic techniques (IR, GPC, TG-DTA, SEM-EDX, EA, ICP-MS, optical profilometer).

Supported metalloporphyrins as reusable catalysts for the degradation of antibiotics: Synthesis, characterization, activity and ecotoxicity studies

The preparation of covalently linked manganese(III) meso-tetrakis(2,6-dichlorophenyl)porphyrin acetate to aminopropyl functionalized silica gel and its full characterization by standard spectroscopic methods including Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and scanning electronic microscopy (SEM) is described. The supported metalloporphyrin was evaluated as catalyst in the degradation of trimethoprim (TMP), using hydrogen peroxide as green oxidant. Catalyst was reused for five consecutive cycles without significant loss of activity or catalyst degradation/leaching. Degradation products were identified by UHPLC-MS, allowing to propose a plausible degradation pathway. Furthermore, ecotoxicity (EC50 and EC20) of TMP-based solutions (before and after degradation) were evaluated towards the bacterium V. fischeri, the microalgae R. subcapitata and the invertebrate B. calyciflorus.

Facile synthesis of thiosalicylic acid functionalized silica gel for effective removal of Cr(III): Equilibrium modeling, kinetic and thermodynamic studies

Thiosalicylic acid functionalized silica gel (SiO2-APS-TSA) was prepared after modification of silica with 3-aminopropyltrimethoxysilane. The adsorption of Cr (III) onto SiO2-APS-TSA was carried out in batch experiments and result shows high removal efficiency (99.90 %) of Cr (III). The characterization of SiO2-APS-TSA was done using FTIR, TGA, DTA, and SEM with EDX. The adsorption of Cr (III) onto SiO2-APS-TSA was optimized by response surface methodology. Central composite design of three factors was undertaken to examine the process parameters, namely pH (0.64–7.36), adsorbent dose (15.0–385.0 mg) and contact time (9.55–110.45 min). The goodness of fit of the experimental data to the second-order polynomial model was revealed with R2 of 0.9999. The results showed that 0.2 g of SiO2-APS-TSA was sufficient to remove 99.90 % Cr (III) from aqueous solution (20 mL; 20 mg L−1) at pH 4.0 in 60 min. Linear and nonlinear fitting of Freundlich isotherm model to adsorption data revealed the multilayer coverage of Cr (III) onto SiO2-APS-TSA. Pseudo second order kinetic model fitted well to the kinetic data. Negative values of ΔG° suggested the spontaneity of the adsorption of Cr (III). The sorption/desorption study demonstrated the potential of SiO2-APS-TSA as an adsorbent to remove Cr (III) from wastewater.

Cu(II)-Hydrazide Coordination Compound Supported on Silica Gel as an Efficient and Recyclable Heterogeneous Catalyst for Green Click Synthesis of β-Hydroxy-1,2,3-triazoles in Water.

A hydrazone ligand, (E)-6-(2-((2-hydroxynaphthalen-1-yl)methylene)hydrazinyl)nicotinohydrazide (H2L), was synthesized and characterized by spectroscopic methods. The reaction of H2L with CuCl2·2H2O in methanol gave Cu(II) coordination compound, [Cu(HL′)(Cl)]·CH3OH (1), which was characterized by elemental analysis and spectroscopic methods (Fourier transform infrared (FT-IR) and UV–vis). The structure of 1 was also determined by single-crystal X-ray analysis. Structural studies confirmed the formation of esteric group during the synthesis of 1. Compound 1 was immobilized on 3-aminopropyltriethoxysilane (APTS)-functionalized silica gel through the amidification reaction and the obtained heterogeneous coordination compound was utilized as a catalyst for the three-component azide–epoxide–alkyne cycloaddition reaction in water as a green solvent. The structural properties of the heterogeneous catalyst were characterized by a combination of FT-IR, UV–vis, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) analyses. The effect of the amount of catalyst and temperature on the cycloaddition reaction was studied, and the obtained 1,2,3-triazoles were characterized by spectroscopic studies and single-crystal X-ray analysis. The catalytic investigations revealed that this catalytic system has high activity in the synthesis of β-hydroxy-1,2,3-triazoles. It was also found that the aromatic and aliphatic substituents on the alkyne and epoxide together with the reaction temperature have considerable effects on the activity and regioselectivity of this catalytic system.

In Russian

The aim of this work is to study the influence of the chemical nature of grafted β-cyclodextrins side functional groups on chemically modified silica gels sorption affinity for cadmium, lead, and copper cations as the most typical water pollutants. Two organo-inorganic sorbents that differ only in the chemical nature of side functional groups of grafted β-cyclodextrin molecules wide edge were synthesized by chemical immobilization of mono-(6-O-(toluenesulfonyl))-β-cyclodextrins on the granular mesoporous silica gel surface. The obtained functionalized silica gels were characterized by IR and UV spectroscopy, chemical, elemental and derivatographic analysis, pH-metry, low-temperature nitrogen adsorption-desorption as well as sorption measurements. The results of studying the sorption of cadmium, lead, and copper cations from nitrate buffer solutions with pH = 2.0 were analyzed using the Lagergren kinetic model for pseudo-first and pseudo-second order processes, and the equilibrium sorption results were analyzed using the Langmuir and Freindlich models for homogeneous and heterogeneous surfaces. It has been found that only β-cyclodextrin-containing surface centers of chemically modified silica gels participate in the sorption of metal cations. The simultaneous formation of inclusion complexes of grafted β-cyclodextrin molecules with nitrate anions of the solution and mixed complexes of metal cations with side functional groups of the wide edge of immobilized cyclic oligosaccharides occurs during the interaction of synthesized silica gels with buffer solutions of cadmium, lead and copper nitrates. The sorption affinity of β-cyclodextrin-containing silica gel with secondary alcohol groups in the structure increases in the order Cd 2+ < Pb 2+ < Cu 2+ . The cation sorption sequence is opposite – Cu 2+ < Pb 2+ < Cd 2+ – for β-cyclodextrin-containing silica gel with side thiosemicarbazidoethyl groups. The change in the sorption specificity of functionalized silica gels to metal cations is interpreted from the standpoint of the theory of “soft” and “hard” acids and bases. The formation of “β-cyclodextrin ‒ nitrate-anion” inclusion complexes with a composition of 1:1 on the surface of chemically modified silica gels promotes metal cations sorption. The results obtained make it possible to predict the sorption specificity of β-cyclodextrin-containing silica materials and its directed change using various functional derivatives of β-cyclodextrin.

A crosslinked, low pH-stable, mixed-mode cation-exchange like stationary phase made using the thiol-yne click reaction

Mixed-mode cation-exchange stationary phases are useful for the separation of mixtures containing hydrophobic, acidic, and basic molecules. To ensure that weak organic bases are protonated and carboxylic acids are neutral low pH mobile phases are required. Mixed-mode stationary phases that are stable at pH < 3 are needed. We synthesized a crosslinked structure along the surface of thiol functionalized silica gel particles using the thiol-yne click reaction. The alkyne, 1,7-octadiyne, was added to the 3-mercaptopropyl silica gel, then crosslinked using 1,6-hexanedithiol. Elemental analysis showed low octadiyne ligand surface coverage, but, stoichiometrically, three sulfurs were added to each octadiyne ligand during the crosslinking step, indicating that crosslinking occurred. The effect of the crosslinking on the stability was tested with a 50:50 (v/v) pH 0.50 5% TFA aqueous:acetonitrile mobile phase at 70 °C for six days, over 35,000 column volumes. The stationary phase showed good stability with the retention of triphenylene decreasing only 20% during that time. The Tanaka test showed that the phase has a methylene selectivity of 1.20 ± 0.04, a high shape selectivity of 2.71 ± 0.03, and a 3.98 ± 0.05 cation-exchange factor at pH 2.70. The phase has a selectivity factor for nitrobenzene and benzene of 1.41 ± 0.01, indicating the electron donating charge transfer characteristic of the phase. The mixed-mode characteristics of the phase were investigated using a mixture of the monoamine neurotransmitters norepinephrine, dopamine, and serotonin. Baseline resolution of the monoamines could be obtained using a simple 20 mM potassium phosphate (pH 2.70)/methanol mobile phase. Altering both the methanol content and the potassium ion concentration altered the retention of the monoamines indicating mixed-mode cation exchange characteristic of the crosslinked stationary phase.

Enhanced adsorption and separation of zirconium and hafnium under mild conditions by phosphoric acid based ligand functionalized silica gels: Insights from experimental and theoretical investigations

Separation of zirconium and hafnium is one of the challenging problems due to their similar chemical behaviors and in general, their separation has been carried out under very high acidic conditions. Herein, we have proposed novel synthesis and application of modified phosphoric acid based ligands, viz., mono-phosphate functionalized silica gel (MPFSG), bi-phosphate functionalized silica gel (BPFSG) and amine, amido pyridyl phosphate functionalized silica gel (AAPPFSG). Important outcome of the present work is that there is a significant enhancement of adsorption and separation of the ions Zr and Hf by employing the above ligands and more importantly, we can achieve the above separation process under mild conditions (pH 0.5–3.0) which is in contrary to the usage of very harsh conditions followed in the existing solid phase extraction based methods. The kinetics of the adsorption is found to be fast and takes place within 10 min with the adsorbent dose 1gL−1 while the selectivity for zirconium over hafnium increases in the order, MPFSG < BPFSG < AAPPFSG under mild conditions. The results based on the quantum chemical calculations reveal that the enhanced separation process is manifested by the differences in the electronic properties (dipole moment and polarizability) of the metal ion complexes and functionalized phosphate ligands.

Solvent-free, microwave assisted oxidation of alcohols with 4-hydroxypyridinium chlorochromate functionalized silica gel

Solvent-free, microwave assisted oxidation of alcohols with 4-hydroxypyridinium chlorochromate functionalized silica gel

Synthesis of Silica Gel Supported Amidoxime Ligand for Adsorption of Copper and Iron from Aqueous Media

Organic-inorganic hybrid polymers have been demonstrated to be an efficient technique for the adsorption of pollutants present in water. Silica gel adsorbent has been applied in this field due to promising characters, such as thermally stable, reusability and high metal ion adsorption capacities. Here, silica gel supported acrylonitrile functional group (silica-APTS-DPN) was reacted with hydroxylamine to yield silica gel supported amidoxime ligand (SBA). All the functionalized silica gel adsorbents were characterized by FTIR. In terms of metal ions adsorption, SBA revealed good absorption capacities towards both copper (Cu2+) (172 mg g-1) and iron (Fe3+) (168 mg g-1) ions at pH 6 and followed the order of Cu2+ &gt; Fe3+. Increased pH condition was beneficial for both metal ions adsorption. The adsorption kinetics of both ions followed the pseudo-first-order model within 0-60 min of adsorption time. Langmuir and Freundlich isotherm models were both applied to study the adsorption behaviour, Freundlich isotherm model (R2 &gt; 0.99) proved to be a better fit, which propose that multilayer adsorption occurred on the silica gel grafted with amidoxime ligand. Finally, this study proved that the silica gel supported amidoxime ligand was successfully applied as an absorbent for the removal of both copper and iron from aqueous media.