Silica Gel Sorbent Research Articles

Chromate surface-imprinted silica gel sorbent for speciation of Cr in surface waters

This study is focused on the synthesis of chromate anion imprinted sorbent supported on silica gel for nonchromatographic Cr speciation in surface waters. The preparation procedure is based on grafting of 3-methyl-1-trimethoxysilylpropylimidazolium, preliminarily coordinated to CrO$_{4}^{2-}$ as a template ion, onto the surface of silica gel. Sorption and desorption characteristics of surface-imprinted sorbent toward Cr(III) and Cr(VI) were examined by batch solid-phase extraction. An excellent separation of Cr(VI), selectively retained on the sorbent, from Cr(III) remained in the solution, was achieved at pH 2-3 for 20 min. A freshly prepared mixture of ascorbic acid and nitric acid was selected as the most efficient eluent for quantitative desorption of the retained Cr(VI). An analytical procedure for Cr speciation in surface waters was developed and validated through analysis of certified reference materials. Detection limits achieved and relative standard deviations for typical concentration levels of Cr(VI) in surface waters matched the requirements of analytical procedures used in monitoring programs.

Asphaltene Adsorption from Hydroconverted Bottoms

The adsorption of asphaltenes from hydroconverted bottoms (HCB) was evaluated using the Asphaltene Determinator to quantify the amount of asphaltenes removed, track the changes in the asphaltene solubility profile, and gauge the selectivity of removing the most aromatic asphaltenes as judged by the 500 nm Coke Index. Adsorption onto a variety of silica gel sorbents was investigated to determine the importance of surface area relative to pore diameter and pore volume. The adsorption behavior of HCB was compared with that of unprocessed bitumen from the Peace River area (PRFR), which contains significantly larger asphaltenes that were more sensitive to sorbent pore properties. Additionally, the optimum adsorption temperature for the unprocessed PRFR asphaltenes was much higher than that for HCB asphaltenes. Adsorption of asphaltenes from HCB improved the quality of the oil by significantly reducing its viscosity, increasing the H/C ratio, decreasing the nitrogen and total basic nitrogen, increasing the P value, removing precoke-type asphaltenes, and reducing Ni and V.

Adsorption behaviors of anionic and cationic dyes on ionic liquid-modified silica gel as sorbent

In this study, adsorption behaviors of typical anionic (red congo (RC)) and cationic (methylene blue (MB)) dyes on new synthesized [C8mim][PF6]-modified silica gel sorbent were examined. Outstanding differences were observed in adsorption behaviors of studied dyes on synthesized sorbent. The most percent adsorption of RC molecules was related to acidic pH values, while basic pH values were more effective than acidic ones for adsorption of MB molecules. Adsorption of RC molecules on sorbent was exothermic, but temperature had no considerable effect on MB adsorption. Thermodynamic parameters such as Gibbs free energy change of dyes partitioning (ΔG0T), their enthalpy change of partitioning (ΔH0T), and also their entropy change of partitioning (ΔS0T) related to partition coefficient (K) of studied dyes between [C8mim][PF6]-modified silica gel and aqueous solution were obtained. Desorption of adsorbed dyes, their preconcentration factors, and adsorption capacity of sorbent for each dye were also studied.

Amine impregnated porous silica gel sorbents synthesized from water–glass precursors for CO2 capturing

In this work, porous silica gel-solid beads have been made from economically affordable water–glass precursors via sol–gel nano casting technique. A stable nanometric silica sol was prepared first from water glass and studied for surface potential and sol to gel transition. A free-flow, injectable gel was obtained upon aging the sol which was then assembled into spherical silica beads in a chemical bath. A surface area of 304.7m2g−1 was obtained for water glass derived silica gel beads. These gel beads were impregnated with 3-aminopropyltrimethoxysilane (APTMS) and polyethylenimine (PEI) active functional groups at different percentages for turning the gel beads as sorbents for CO2 gas adsorption. The effect of amine loading on the thermal stability, morphology as well as porosity was studied and was correlated with CO2 adsorption values. Depending upon the amount of amine loaded in the gel support CO2 uptake was found varied. These amine modified silica gel porous adsorbents showed CO2 adsorption capacity at temperatures as low as 100°C; samples modified with 15wt% PEI had CO2 adsorption capacity of 1.16mmolg−1 at 50°C.

Ultra-trace determination of polycyclic aromatic hydrocarbons using solid-phase extraction coupled with HPLC based on graphene-functionalized silica gel composites

A graphene (Gr) functionalized silica gel (Gr–SiO2) sorbent was prepared and used as a new sorbent for solid-phase extraction (SPE) of polycyclic aromatic hydrocarbons (PAHs) including naphthalene, acenaphthylene, fluorene, phenanthrene, fluoranthene, and pyrene. The analytes were separated and detected by high-performance liquid chromatography (HPLC) with a UV detector. Factors affecting the extraction efficiency including the eluent type and its volume, adsorbent amount, sample volume, sample pH and flow rate were optimized. Under the optimized conditions, the present method showed a wide linear range (0.01–600 μg L−1), acceptable repeatability of the extraction (RSDs of 1.7–8.2%, n = 3) and satisfactory detection limits (0.0029–0.052 μg L−1). The recovery studies using this new sorbent were performed by three consecutive extraction steps of water and milk samples at three spiked levels. The average recoveries of the analytes in environmental water and milk samples were 89.0–115.4%, which demonstrated the applicability of the developed method.

Simultaneous determination of melamine and cyanuric acid in foodstuffs by solid phase extraction-hydrophilic interaction chromatography-tandem mass spectrometry

A method based on solid phase extraction-liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the simultaneous determination of melamine and cyanuric acid in foodstuffs is presented. The melamine and cyanuric acid residues were extracted by acetonitrile and water, degreased by hexane, and the extract was cleaned-up by a mixed-mode solid phase-extraction column (MCT) of hydrophilic functional silica gel sorbent and cation exchange resin. The LC separation was performed on a hydrophilic interaction chromatograph, the melamine and cyanuric acid were determined by MS/MS in positive-negative switched electrospray ionization mode, multiple reaction monitoring (MRM) mode, and quantified by isotope internal standard method. The melamine and cyanuric acid were linear in the range of 10-2 500 microg/L with the correlation coefficients (r) higher than 0.99, and the limits of quantification were 25 microg/kg and 50 microg/kg, respectively. The recoveries of melamine and cyanuric acid spiked in animal-derived foods, plant-derived foods, milk and milk products were in the range of 70.0%-129.6% and 70.0%-128.6%, respectively, with the relative standard deviations (RSD) of 1.4%-23.3% and 2.8%-18.7%, respectively. The method can meet the requirement for the determination of melamine and cyanuric acid in foodstuffs simultaneously.

Solid-Phase Removal of Dissolved Organic Species from Water and Identification by GC-MS

A method is described for the detection and identification of dissolved organic compounds (DOCs) in various water samples. Acid treated active silica gel sorbent (pH 3) was packed into a micro-column and used as a solid-phase extraction medium for adsorption of DOCs. Silica particles-adsorbed-organic species were then divided into equal portions followed by suspension into various organic solvents of different polarities such as methanol, acetone, ethyl acetate, and toluene. Suspended silica-adsorbed-organic species were shaken for 1 h at room temperature and the organic extracts were subjected to GC–MS analysis under temperature programming conditions for qualitative detection and identification of these species. Blank solvents and silica samples were also subjected to the same extraction procedures and GC–MS analysis for comparison. The mass spectrum of each eluted chromatographic peak was library searched or manually interpreted to identify the compound.

Synthesis and evaluation of molecularly imprinted silica gel for 2-hydroxybenzoic Acid in aqueous solution.

A molecularly imprinted silica gel sorbent for selective removal of 2-Hydroxybenzoic acid (2-HA) was prepared by a surface imprinting technique with a sol-gel process. The 2-HA molecularly imprinted silica gel (2-HA-MISG) sorbent was evaluated by various parameters, including the influence of pH, static, kinetic adsorption and selectivity experiments. The optimum adsorption capacity to the 2-HA appeared to be around pH 2 by the polymer. Morevoer, the imprinted sorbent displayed fast uptake kinetics, obtained within 20 min. The adsorption capacity of the 2-HA-MISG (76.2 mg g−1) was higher than that of the non-imprinted silica gel (NISG) (42.58 mg g−1). This indicates that the 2-HA-MISG offers a higher affinity for 2-HA than the NISG. The polymer displays good selectivity and exhibits good reusability. Experimental results show the potential of molecularly imprinted silica sorbent for selective removal of 2-HA.

Preparation and Application of Reversed Phase ChromatorotorTM for the Isolation of Natural Products by Centrifugal Preparative Chromatography

A method of preparation of rotors with a reversed phase (RP) solid silica gel sorbent layer has been developed for centrifugal preparative chromatography (CPC), also known as rotational planar chromatography (RPC). The rotors consist of binder free RP solid SiO2 layers of different thicknesses packed between two supported circular glass discs and can be used in any appropriate device for centrifugal chromatography, like Chromatotron and CycloGraph. Polar and /or semi-polar compounds with close R(f) values, as well as extracts and column fractions were separated and/or purified in a preparative and/or semi-preparative scale using the RP rotors, eluted with mixtures of aqueous-based solvents. We herein report three examples of its application, using RP Chromatorotors, for the isolation of the diastereoisomeric alkaloids banistenosides I and II from Banisteriopsis caapi, saponins III and IV from Fagonia cretica, and the sesquiterpenes artemisinin (V) and artemisinic acid (VI) from Artemisia annua.

Ion-imprinted carboxymethyl chitosan–silica hybrid sorbent for extraction of cadmium from water samples

A new ion-imprinted carboxymethyl chitosan-functionalized silica gel sorbent was synthesized by surface imprinting technique using Cd(II) as the template, carboxymethyl chitosan (CMCS) as the functional monomer and glutaraldehyde as the cross-linking agent for the selective adsorption of Cd(II) from aqueous solution. The optimum batch experimental conditions (pH, amount of adsorbent, contact time) and column experimental conditions (concentration and volume of elution solution) were evaluated. The maximum static adsorption capacity of the ion-imprinted sorbent for Cd(II) was 20.7mg/g. The enrichment factor of Cd(II)-imprinted polymer for Cd(II) was 257. The relative selectivity factor values of Cd(II)/Pb(II), Cd(II)/Co(II) were 5.3 and 1.5, respectively. The recoveries of water samples were about 98.0–104.0% (R.S.D.≤0.8). The proposed method was successfully applied to determination of Cd(II) in water samples with satisfactory.

Synthesis and Characteristics of Al(III)-Imprinted Silica Gel Sorbent

Synthesis and Characteristics of Al(III)-Imprinted Silica Gel Sorbent

Removal of arsenic from ammoniacal etching waste liquor by 3-(2-aminoethylamino)propyltrimethoxysilane functionalized silica gel sorbent

3-(2-Aminoethylamino)propyltrimethoxysilane (AAPTS) functionalized silica gel (AAPTS/SiO2) was synthesized by a sol–gel process and was used for the arsenic removal from ammoniacal etching waste liquor which was oxidized by H2O2. The AAPTS/SiO2 sorbent reached absorption saturation at 20 min and had a substantial binding capacity in the range of pH 4.7–10.2. The maximum static adsorption capacity of AAPTS/SiO2 sorbent for arsenic was 16.1 mg g-1. Equilibrium data fitted perfectly with Langmuir isotherm model compared to Freundlich isotherm model. The removal rate of arsenic by AAPTS/SiO2 sorbent was 95.4% at the optimal conditions from ammoniacal etching waste liquor. Results showed that AAPTS/SiO2 sorbent could be used for the arsenic removal from ammoniacal etching waste liquor.

An ionic liquid-based sorbent for solid phase extraction of trace iron(Ш) from biological and natural water samples

A new ionic liquid modified silica gel sorbent was prepared from the reaction of active silica gel with N-3-(-3-triethoxysilylepropyl)-3-methylimidazolium chloride ([(TESP)MIm]Cl). This sorbent was exploited as solid phase extractant for separation and preconcentration of metal ions prior to their determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). It was found that it can selectively adsorb Fe(Ш). Identification of the surface modification was performed on the basis of FT-IR. Experimental conditions for effective adsorption of trace Fe(Ш) were optimised using both batch and column procedures. At pH 3, Fe(Ш) could be quantitatively adsorbed and completely eluted by using 2 mL of 0.1 mol L−1 of HCl. 150 mL of sample solution was adopted as the maximum sample volume and a high enrichment factor of 75 was obtained. Most common coexisting ions did not interfere with the separation and preconcentration of Fe(Ш) at optimal conditions. The maximum static adsorption capacity of the sorbent was 37.0 mg g−1. The detection limit of the present method was 0.48 µg L−1, and the relative standard deviation (R. S. D.) was lower than 1.7%. The method was successfully applied to the preconcentration of trace Fe(Ш) in biological and natural water samples with satisfactory results.

Selectively removal of Al(III) from Pr(III) and Nd(III) rare earth solution using surface imprinted polymer

Rare earth is a very important strategic resource. But, impurities, such as Al3+, have great influence on the properties of rare earth material. In this paper, an Al3+-ionic imprinted polyamine functionalized silica gel sorbent was prepared by a surface imprinting technique for selectively adsorbing Al3+ from rare earth solution. The adsorption and recognition properties of IIP-PEI/SiO2 for Al3+ were studied in detail. The experimental results showed that IIP-PEI/SiO2 possessed strong adsorption affinity, specific recognition ability, and excellent selectivity for Al3+. The adsorption isotherm data greatly obey the Langmuir model, and the adsorption was typical monolayer. The adsorption capacity could reach to 1.98mmolg−1, and relative selectivity coefficients relative to Pr3+ and Nd3+ are 23.47 and 22.85, respectively. Besides, IIP-PEI/SiO2 was regenerated easily using diluted hydrochloric acid solution as eluent and IIP-PEI/SiO2 possesses better reusability.

Evaluation of solid phase extraction for downstream separation of propane-1,3-diol and butan-1-ol from fermentation broth

Today, glycerol is mainly a by-product of fat splitting and biodiesel production. This study examined the use of chemically modified silica gels for downstream separation of propane-1,3-diol and butan-1-ol from fermentation broths obtained through the glycerol fermentation process. The developed method was found to be simple and efficient for the isolation and purification of butan-1-ol from the other components in the fermentation mixture. However, in the case of the separation of propane-1,3-diol from fermentation broth, the silica gel sorbents were ineffective.

Selective Removal of Arsenic(V) from Aqueous Solution Using A Surface-Ion-Imprinted Amine-Functionalized Silica Gel Sorbent

A new surface-ion-imprinted amino-functionalized silica gel sorbent was prepared by the surface imprinting technique with As(V) as the template, 3-(2-aminoethylamino)propyltrimethoxysilane as the functional monomer, silica gel as the support, and epichlorohydrin as the cross-linking agent and was characterized by FTIR, SEM, nitrogen adsorption, and the static adsorption–desorption experiment method. The results showed that the maximum static adsorption capacity of the imprinted silica gel sorbent was 16.1 mg·g–1, the adsorption equilibrium could be reached in 20 min, there was no influence of pH values on adsorption capacity of the imprinted silica gel sorbent in the range of 3.7–9.2, and the imprinted silica gel sorbent could be used repeatedly and indicated high selectivity even in the presence of the other metal ions. The Langmuir adsorption model was more favorable than the Freundlich adsorption model. Kinetic studies indicated that the adsorption followed a pseudosecond-order model. Various thermodynamic parameters such as ΔGo, ΔHo, and ΔSo were evaluated with results indicating that this system was a spontaneous and endothermic process.

Selective Removal of Iron from Aqueous Solution using Ion Imprinted Cyanato-Functionalized Silica Gel Sorbents

We combined a surface imprinting technique with sol-gel process for preparing a new iron(III)-imprinted cyanato-functionalized silica gel sorbents using (3-cyanatopropyl)triethoxysilane as the functional monomer, and epichlorohydrin as the cross-linking agent for the selective removal of iron(III) from aqueous solution. The iron(III)-imprinted cyanato-functionalized silica gel was characterized by FT-IR spectra and the static adsorption-desorption method. Maximum binding capacity, optimum pH, and equilibrium binding time were found to be 35.6 mg · g−1, pH 3, and 20 min, respectively. The relative selectivity coefficients of ion imprinted cyanato-functionalized silica gel sorbents for Fe(III)/Ni(II), Fe(III)/Co(II), Fe(III)/Cd(II), and Fe(III)/Pb(II) were 8.56, 11.95, 16.96, and 50.71 times greater than the non-imprinted silica gel, respectively. The iron(III)-imprinted cyanato-functionalized silica gel sorbents could be used repeatedly without significantly decreasing their adsorption capacities.

Selective removal of iron from aqueous solution using ion imprinted thiocyanato-functionalized silica gel sorbents

We combined surface imprinting technique with sol-gel process for preparing a new iron(III)-imprinted thiocyanato-functionalized silica gel sorbent using 3-thiocyanatopropyltriethoxysilane as the functional monomer, and epichlorohydrin as the cross-linking agent for the selective removal of iron(III) from aqueous solution. The iron(III)-imprinted thiocyanato-functionalized silica gel was characterized by FT-IR spectra, SEM, and the static adsorptiondesorption method. Maximum binding capacity, optimum pH, and equilibrium binding time were found to be 20.31 mg·g−1, pH 4.2, and 20min, respectively. The relative selectivity coefficients of Fe(III)-imprinted thiocyanato-functionalized silica gel sorbents for Fe(III)/Ni(II), Fe(III)/Co(II), Fe(III)/Cd(II) and Fe(III)/Pb(II) were 11.8, 10.6, 8.2 and 9.1 times greater than the non-imprinted silica gel, respectively. The iron(III)-imprinted thiocyanato-functionalized silica gel sorbents could be used repeatedly without decreasing in their adsorption capacities significantly.

An ion-imprinted amino-functionalized silica gel sorbent prepared by hydrothermal assisted surface imprinting technique for selective removal of cadmium (II) from aqueous solution

A new ion-imprinted amino-functionalized silica gel sorbent was synthesized by the hydrothermal-assisted surface imprinting technique using Cd2+ as the template, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AAAPTS) as the functional monomer, and epichlorohydrin as the cross-linking agent (IIP-AAAPTS/SiO2) for the selective removal of Cd2+ from aqueous solution, and was characterized by FTIR, SEM, nitrogen adsorption and the static adsorption–desorption experiment method. The specific surface area of the IIP-AAAPTS/SiO2 sorbents was found to be 149m2g−1. The results showed that the maximum static adsorption capacities of IIP-AAAPTS/SiO2 sorbents by hydrothermal heating method and by the conventional heating method were 57.4 and 31.6mgg−1, respectively. The IIP-AAAPTS/SiO2 sorbents offered a fast kinetics for the adsorption and desorption of Cd(II). The relative selectivity coefficients of IIP-AAAPTS/SiO2 sorbents for Cd2+/Co2+, Cd2+/Ni2+, Cd2+/Zn2+, Cd2+/Pb2+ and Cd2+/Cu2+ were 30.68, 14.02, 3.00, 3.12 and 6.17, respectively. IIP-AAAPTS/SiO2 sorbents had a substantial binding capacity in the range of pH 4–8 and could be used repeatedly. Equilibrium data fitted perfectly with Langmuir isotherm model compared to Freundlich isotherm model. Kinetic studies indicated that adsorption followed a pseudo-second-order model. Negative values of ΔG° indicated spontaneous adsorption and the degree of spontaneity of the reaction increased with increasing temperature. ΔH° of 26.13kJmol−1 due to the adsorption of Cd2+ on the IIP-AAAPTS/SiO2 sorbents indicated that the adsorption was endothermic in the experimental temperature range.

Highly selective determination of rhodium(III) using silica gel surface-imprinted solid-phase extraction

A novel Rh(III)-imprinted amino-functionalised silica gel sorbent was prepared by a surface imprinting technique for preconcentration and separation of Rh(III) prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Compared with the traditional solid sorbents and non-imprinted polymer particles, the ion-imprinted polymers (IIPs) had higher adsorption capacity and selectivity for Rh(III). The maximum static adsorption capacity of the imprinted and non-imprinted sorbent for Rh(III) was 29.86 mg g−1 and 11.23 mg g−1, respectively. The imprinted Rh(III) was removed with 2 mL of 3% thiourea + 2 mol L−1 HCl. The obtained imprinted particles exhibited excellent selectivity and rapid kinetics process for Rh(III). The relatively selective factor (αr) values of Rh(III)/Ru(III), Rh(III)/Au(III), Rh(III)/Pt(IV), Rh(III)/Ir(IV), Rh(III)/Pd(II) were 26.7, 39.0 29.2, 28.1, 43.7, respectively, which were greater than 1. The detection limit (3σ) of the method was 0.26 µg L−1. The relative standard deviation of the method was 1.79% for eight replicate determination of 10 µg of Rh3+ in 200 mL water sample. The method was validated by analysing standard reference material (GBW 07293), the results obtained is in good agreement with standard values. The developed method was also successfully applied to the determination of trace rhodium(III) in geological samples with satisfactory results.