Modified Silica Gel Research Articles

Removal of Th(IV) from aqueous solution with modified silica gel by 4-hydroxy-N ′ - ((thiophen-2-yl) methylene)benzohydrazide schiff base

ABSTRACT In this study, SiCPMS@L solid adsorbent was prepared using 4-Hydroxy-N ′- ((Thiophen-2-yl)methylene)benzohydrazide Schiff base for thorium(IV) removal from aqueous solution, and the structure of the solid adsorbent was characterized by FTIR, SEM, elemental analysis, and BET surface analysis methods. Solution pH, initial thorium concentration, contact time, adsorbent dose, and temperature parameters affecting the adsorption of Th(IV) ions with SiCPMS@L adsorbent were examined, and optimum uptake conditions were determined. The effective initial pH for adsorption was found to be 4.0. The binding sites on SiCPMS@L solid adsorbent were saturated using an initial Th(IV) concentration of 16.0 mg/L. 30 minutes was determined as the optimum contact time when the adsorption equilibrium was established. The optimum adsorbent dose for SiCPMS@L was determined as 1.0 g/L. At optimum conditions, adsorption efficiency and adsorption capacity values for SiCPMS@L adsorbent were respectively; 97.4% ± 0.1 and 15.6 ± 0.1 mg/g were obtained. The calculated thermodynamic parameters ∆S°, ∆G° and ∆H° showed that the Th(IV) sorption process is thermodynamically advantageous, spontaneous and endothermic. Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms for removal of Th(IV) ions with SiCPMS@L solid adsorbent were investigated and found to be compatible with Langmuir isotherm.

Carbonation behavior of calcium silicate hydrate (C-S-H): Its potential for CO2 capture

Calcium silicate hydrate (C-S-H), as the main component of cementitious materials, is susceptible to carbonation presenting a potential to capture CO2. Although some researches paid attentions to the carbonation behaviors of C-S-H given the durability of concrete structure, the kinetics of C-S-H carbonation as well as changes of C-S-H itself under carbonation have not been fully addressed. In this study, the carbonation kinetics of C-S-H with various calcium to silica ratio (Ca/Si) were investigated and the evolution of carbonation products in terms of compositions and micro-mechanical properties was quantitatively characterized by quantitative X-ray diffraction (QXRD), energy dispersive spectroscopy (EDS), and nuclear magnetic resonance (NMR). Three distinct periods are found in the course of C-S-H carbonation, encompassing dissolution period, diffusion period and slowly ongoing reaction period. A progressive decrease in Ca/Si and pH is observed in dissolution period with the formation of calcium carbonate, the reaction rate of which is strongly dependent on the initial Ca/Si of C-S-H. In the diffusion period, a small proportion of crosslinking occurs in C-S-H structure before producing a large amount of calcium modified silica gel, during when the Ca/Si and pH remain unchanged due to the incongruent dissolution of C-S-H as revealed by thermodynamic modellings. In the slowly ongoing reaction period, C-S-H decomposed completely and the mixture of microcrystalline calcium carbonate and calcium modified silica gel becomes the final product. The micro-mechanical property of C-S-H was significantly weakened by the change of phase assemblage. Our findings do not only advance our understandings on the deterioration of cementitious material under carbonation but also provides new insights into the CO2 capture using C-S-H widely existing in cementitious materials.

The enrichment of rare earth from magnesium salt leaching solution of ion-adsorbed type deposit: A waste-free process for removing impurities

Due to the complex composition of ion-adsorbed type rare earth ore leaching solution, there are challenges in the process of rare earth (RE) separation, such as large RE loss rate, low product purity, radioactive residue and so on. In this article, 8-hydroxyquinoline modified silica gel (HQ-SiO2) and 2,2′-(1,4-phenylenebis(oxy)) dioctanoic acid (PPBOA) were used to form an efficient process for impurities removal and RE enrichment. Solid phase extraction successfully intercepted 96.7% of the radioactive element thorium. The concentration of aluminium was reduced to 2.14 ppm by frank chromatography. Rare earth elements were enriched from 336.35 mg/L to 237.75 g/L by extraction-precipitation, that is, the enrichment multiple reached more than 700 and the proportion of RE was increased from 21.85% to 96.62%. The loss rate of RE was controlled below 1.59%. Moreover, the magnesium salt leaching solution could be recycled for the leaching of RE ores. Although some liquid waste need to be treated in the processes of HQ-SiO2 production and regeneration, the integrated process helps to decrease volatile organic solvent, acid-base consumption, wastewater and waste residue. It is an environment-friendly RE enrichment and impurity removal process, which shows application potential in the production field of ion-adsorbed type rare earth mineral products.

Carbonation behaviors of calcium silicate hydrate (C-S-H): Effects of aluminum

The cement systems containing supplementary cementitious materials (SCMs) usually present lower resistance to carbonation compared with ordinary Portland cement (OPC) systems. However, the contribution of the main component in these systems, calcium aluminum silicate hydrate (C-A-S-H), to carbonation still remains unclear. In this study, the carbonation behaviors of C-S-H and C-A-S-H were compared by accelerated carbonation experiments. FTIR, XRD, TGA, NMR, and electron microscope were integrated to reveal the kinetics and thermodynamics of C-(A)-S-H carbonation. It is concluded that the carbonation of C-(A)-S-H experiences three periods including dissolution, diffusion, and stationary period, turning into calcium carbonate with different polymorphs, calcium and aluminum modified silica gel. In the end product of carbonation, aluminum modified silica gel is observed to have a similar Al/Si to the initial C-A-S-H. But such small incorporation of aluminum into C-S-H structure (maximum Al/Si ∼ 0.1) can hardly have a significant effect on its resistance to carbonation.

Adsorption water vapor characteristics on modified silica gel for desalination application

Adsorption water vapor characteristics on modified silica gel for desalination application

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.

Silica gel-assisted synthesis of benzo[b]thiophenes from o-(alkylsulfanyl)(ethynyl)benzenes

A variety of 2-substituted benzo[b]thiophenes were prepared from o-(alkylsulfanyl)(ethynyl)benzenes in the presence of silica gel under thermal conditions. Tertiary alkyl-substituted sulfanyl derivatives gave good results. Methylsulfanyl-substituted precursors also afforded benzo[b]thiophenes at higher temperature. Effect of modified silica gel was evaluated and the mechanism of this method was discussed. This method was also applied to preparation of 2-substituted thieno[3,2-b]thiophenes, which gave moderate yields.

Silica gels grafting with upper rim tetraphosphorylated tetrahydroxy(thia)calixarenes. Europium(III) sorption

Sequential treatment of silica gel with tetrachlorosilane and cone-shaped tetraphosphorylated tetrahydroxy(thia)calixarenes yielded porous organo-inorganic sorbents, the surface of which is covered by spatially ordered phosphonate, phosphinate and phosphine oxide groups capable of co-operative binding of metal cations. Sorption of europium(III) by the modified silica gels was studied.

Application of iPDMS protein microarray in screening of tumor-associated antigen autoantibodies

The rapid screening of tumor markers is a challenging task for early diagnosis of cancer. This study aims to use highly sensitive chemiluminescent protein microarray technology to efficiently screen a variety of low abundance tumor related markers. A new material, termed integrated polydimethylsiloxane modified silica gel (iPDMS), was obtained by adding a surface polymerization initiator with olefin end to the conventional polydimethylsiloxane, and fixing into the three-dimensional structure of polydimethylsiloxane by thermal crosslinking through silicon hydrogen bonding. In order to make the iPDMS material resistant to non-specific protein adsorption, a poly(OEGMA) polymer brush was synthesized by surface-initiated atom transfer radical polymerization at the active initiation site. Finally, 20 tumor-related antigens were printed into the specific areas of the microarray by high-throughput spray printing technology, and assembled into 48-well detection microtiterplates of the iPDMS microarray. It was found the VEGFR and VEGF121 autoantibodies that obtained from 8 common tumors (breast cancer, lung cancer, colon cancer, gastric cancer, liver cancer, leukemia, lymphoma and ovarian cancer) can be used as potential tumor markers. The chemiluminescence labeled iPDMS protein microarray can be used for the screening of tumor autoantibodies at early stage.

SORPTION OF ERYTHROSINE ONTO SILICA GEL MODIFIED BY CETYLPYRIDINIUM BROMIDE

In the current paper, adsorbent based on silica gel L 40/100 modified with cetylpyridinium bromide was obtained. The presence of cetylpyridinium cations on the silica gel surface was confirmed by the diffuse reflectance infrared fourier transform spectroscopy method. The sorption conditions of erythrosine from dilute aqueous solutions with the proposed sorbent were studied and optimized. It is shown that the use of modified silica gel allows efficient (>95%) extraction of erythrosine from aqueous solutions. Under optimal sorption conditions (pH 7, sorbent dosage 0.1 g and sorption time is 15 min), the sorption capacity of modified erythrosine sorbents was determined. It is shown that, with increasing temperature, a change in the isotherm type from the H‑type to the L‑type is observed. This change can be explained by the aggregation of erythrosin in solution, which is a competitive sorption process. It was shown that adsorption isotherms were well described by the Langmuir equation. Thermodynamic studies have made it possible to establish the spontaneous sorption. The desorption of erythrosine from the surface of silica gel modified with cetylpyridinium bromide was studied. It is shown that when using solutions of sulfuric acid, sodium hydroxide and distilled water, desorption does not occur. It was shown that the most effective eluent is solution of sodium dodecylsulfate in alkaline medium, and desorption of erythrosine occurs due to the destruction of ion pairs of dye anions with cetylpyridinium cations fixed on the surface. The data obtained can then be used to develop a test system for determination of erythrosine via corresponding colorimetric scales or for quantitative solid phase extraction and adsorption-spectroscopic quantification of erythrosine in some real samples.

Study of flavonoids and phenolic acids in green tea leaves

The aim of work is study qualitative composition and quantitative content of flavonoids and phenolic acids in green tea leaves. Material and methods. The object of the study was green tea leaves, which were collected in Anhui Province, China. The analysis of 60 % ethanolic extract from green tea leaves was performed by high-performance liquid chromatography using a Prominence LC-20 Shimadzu chromatographic system (Japan) with an SPD-20AV spectrophotometric detector, an Agilent Technologies Microsorb-MV-150 column (reversed-phase, C18 modified silica gel, length – 250 mm, diameter – 4.6 mm, particles size – 5 μm). Identification of substances in the extract was carried out by comparing the retention time and the spectral characteristics of the test substances with the same characteristics of the reference standards. Results. 13 compounds were identified and determined by high-performance liquid chromatography. Among flavonoid aglycones quantitatively dominated by quercetin (0.35 %), in the case of flavonoid glycosides, it was luteolin-6-C-glycoside (1.30 %) and among phenolic acids, it was gallic acid (5.21 %). Conclusions. The qualitative composition, quantitative content of flavonoids and phenolic acids in the green tea leaves were determined by high-performance liquid chromatography. According to HPLC, the content of flavonoids in green tea leaves was higher than the content of phenolic acids.

Determination of catechins in green tea leaves by HPLC compared to spectrophotometry

Aim. To study the qualitative composition, the quantitative content of catechins in green tea leaves and compare the data obtained with those evaluated by spectrophotometry.Materials and methods. Green tea leaves used for the analysis were collected in Anhui Province, China. The extract for the HPLC analysis was obtained by the maceration method with 60 % ethanol twice in the raw material/extractant ratio of 1 : 20. In the case of the spectrophotometric analysis, green tea leaves were extracted with 70 % ethanol twice by the maceration method in the raw material/extractant ratio of 1 : 20. The analysis of the extract from green tea leaves was performed by high performance liquid chromatography using a Prominence LC-20 Shimadzu chromatographic system (Japan) with a SPD-20AV spectrophotometric detector, an Agilent Technologies Microsorb-MV-150 column (reversed phase, C18 modified silica gel, length – 150 mm, diameter – 4.6 mm, particles size – 5 μm). Substances in the extract were identified by comparing the retention time and the spectral characteristics of the test substances with the same characteristics of the reference standards. Spectrophotometric measurements were carried out using a UV-1000 single beam spectrophotometer (China) with the pair of S90-309Q quartz square cells.Results and discussion. Using high performance liquid chromatography 5 catechins were identified. Among them epigallocatechin-3-O-gallate (10.85 %) predominated, while catechin (0.61 %) had the lowest concentration. The total amount of catechins in green tea leaves was 30.56 and 24.79 % by HPLC and spectrophotometry, respectively. The F- and t-tests showed that there was no significant difference between the results of HPLC and spectrophotometry.Conclusions. The qualitative composition and the quantitative content of catechins have been determined in the extract from green tea leaves by high performance liquid chromatography and spectrophotometry. Both HPLC and spectrophotometric methods can be used to determine the total catechin content in green tea leaves. The high content of catechins makes the extract promising for further study and creation of new herbal medicinal products and dietary supplements. The results obtained will be used for standardization of green tea leaves and for future pharmacological research of its extract.

Assessment of compositional changes of carbonated cement pastes subjected to high temperatures using in-situ Raman mapping and XPS

This paper presents a new method for assessing the compositional changes of carbonated cement pastes subjected to high temperatures. In this new method, in-situ Raman mapping combined with X-ray photoelectron spectroscopy (XPS) was used to monitor the phase transformation in carbonated cement pastes subjected to various high temperatures from 30 to 950 °C. Two kinds of carbonated areas, i.e., vaterite dominated and calcite dominated, were found in the in-situ Raman measurements. With the elevation in temperature, most of the vaterite was converted to calcite at 500 °C and completely decomposed at 600 °C, while the decomposition of calcite started at 600 °C and finished at 720 °C. Meanwhile, the depolymerization of the calcium modified silica gel to the silicate phases with a lower degree of polymerization was initiated at 500 °C, which led to the crystallization of β-C2S at 600 °C. The generation of β-C2S was found to increase with the elevation in temperature and became the dominant phase at 950 °C. In conclusion, the high temperature could affect the stability of carbonated cement pastes at 500 °C and above. The in-situ Raman mapping measurement has provided an extraordinary view of the spatial distribution of interesting phases subjected to high temperatures in a non-destructive way, which should be more consistent with the true condition in the material.

β-Cyclodextrin Derivative Grafted on Silica Gel Represents a New Polymeric Sorbent for Extracting Nitisinone from Model Physiological Fluids.

Nitisinone (NTBC) is used in the treatment of disorders affecting the tyrosine pathway, including hereditary tyrosinemia type I, alkaptonuria, and neuroblastoma. An inappropriate dosage of this therapeutic drug causes side effects; therefore, it is necessary to develop a rapid and sensitive method to monitor the content of NTBC in patients’ blood. This study aimed to develop anew polymeric sorbent containing β-cyclodextrin (β-CD) derivatives grafted on silica gel to effectively extract NTBC from model physiological fluids. The inclusion complex formed between β-CD and NTBC was examined by proton nuclear magnetic resonance spectroscopy. The novel sorbents with derivatives of β-CD were prepared on modified silica gel using styrene as a comonomer, ethylene glycol dimethacrylate as a crosslinking agent, and 2,2′-azo-bis-isobutyronitrile as a polymerization initiator. The obtained products were characterized via Fourier transform infrared spectroscopy and then used as sorbents as part of a solid phase extraction technique. High NTBC recovery (70%indicated that the developed polymeric sorbent may be suitable for extracting this compound from patients’ blood samples.

Development and Validation of QuEChERS Followed by UHPLC-ToF-MS Method for Determination of Multi-Mycotoxins in Pistachio Nuts.

Pistachios are one of the types of tree nut fruits with the highest mycotoxin contamination, especially of aflatoxins, worldwide. This study developed a Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method that was followed by Ultra-High Performance Liquid Chromatography combined with Time-of-Flight Mass Spectrometry (UHPLC–ToF-MS) for the determination of mycotoxins in pistachios. Different approaches to dispersive solid phase extraction as a clean-up method for high lipid matrices were evaluated. For this, classic sorbents such as C18 (octadecyl-modified silica) and PSA (primary secondary amine), and new classes of sorbents, namely EMR-Lipid (enhanced matrix removal-lipid) and Z-Sep (modified silica gel with zirconium oxide), were used. The QuEChERS method, followed by Z-Sep d-SPE clean-up, provided the best analytical performance for aflatoxins (AFB1, AFB2, AFG1 and AFG2), ochratoxin A (OTA), zearalenone (ZEA), toxin T2 (T2) and toxin HT-2 (HT2) in pistachios. The method was validated in terms of linearity, sensitivity, repeatability, interday precision and recovery; it achieved good results according to criteria imposed by Commission Regulation (EC) no. 401/2006. The method was applied to real samples and the results show that pistachios that are available in Portuguese markets are safe from mycotoxins that are of concern to human health.

Methoxy terminated poly dimethylsiloxane bonded stationary phase for reversed-phase liquid chromatography

In this work, a methoxy terminated poly dimethylsiloxane modified silica gel material was proposed as a novel stationary phase for reversed-phase liquid chromatography. With 5 μm silica gel as matrix, methoxy terminated poly dimethylsiloxane polymer was grafted by one step chemical bonding reaction. The obtained stationary phase was characterized by scanning electron microscopy, fourier transform infrared spectroscopy and element analysis. To our knowledge, this is the novel methoxy terminated poly dimethylsiloxane bonded stationary phase with good separation efficiency (42107-46988 plates/m for benzene homologues) and high stability (RSD is 0.08-5.09%). Comparing to other traditional columns of the same type, the proposed stationary phase has a wider polarity separation scale and shorter analysis time. In addition to the rapid separation of hydrophobic compound, such column also exhibited great potential in the separation of hydrophilic analytes.

Polyaniline modified silica gel coupled with green solvent as eco favourable mobile phase in thin layer chromatographic analysis of organic dyes

This article studies a new green eco-friendly TLC (thin layer chromatography) using silica gel and polyaniline modified silica gel as stationary phase in combination with ethyl acetate (EA), n-butyl acetate (BA) and butane-1-ol (BO) solutions as mobile phase for the comparative study of migration behaviour of organic dyes to identify the most suitable thin layer chromatographic system for the resolution of co-existing dyes. Better separation efficiency was observed by modifying silica gel with polyaniline as compared to pure silica stationary phase. Densitogrpahic presentation of separations achieved on polyaniline modified silica gel Pani@SG-EB1 was also presented. The thin layer chromatographic system comprising of polyaniline modified silica gel Pani@SG-EB1 as stationary phase and n-butyl acetate:DDW, 5:5 as green mobile phase was observed to be the most favourable for the separation of various combinations of three or four-component mixtures of organic dyes viz. methyl thymol blue, tartrazine, carmoisine, rose bengal, amidoblack 10B, bromopyrogallol red and 4-nitrobenzene dizonium tetrafluoroborate. The effect of presence of cations and anions on separation trend was also examined and the limits of detection of the separated organic dyes were estimated. Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron micrograph (TEM) studies were undertaken to characterize silica gel and modified silica gel (stationary phase). The developed method has been successfully applied for the identification of carmoisine in Solvin cold DS syrup and tartrazine in MefastTM syrup.

Sequestered uptake of chromium(VI) by Irvingia gabonensis stem bark extract anchored silica gel

In this research, the mechanism and efficiency of Cr(VI) uptake onto Irvingia gabonensis stem bark extract modified silica gel (IGMS) was reported for the first time. The pristine silica gel (PS) and IGMS adsorbents were characterized by the XRD, FTIR, FESEM, EDX, BET, and TGA techniques. The characterizations proved the successful coating of the plant extract onto silica gel. The FTIR spectra showed the Si–O–Si bands present on the silica gel materials. The FESEM revealed an increase in surface roughness of IGMS after coating with the plant extract, while TGA showed a high thermal stability of both PS and IGMS with over 65% of the initial weight retained at 800 °C. The batch Cr(VI) adsorption revealed optimum uptake at pH 2.0, with a maximum monolayer uptake capacity of 23.26–26.18 mg/g for IGMS at temperatures of 295 to 318 K. The kinetic modeling of Cr(VI) uptake onto PS and IGMS was best fitted by the Elovich model in comparison to the pseudo-second-order, pseudo-first-order, and intraparticle diffusion model. The Langmuir and Freundlich isotherms gave the best fit to the adsorption of Cr(VI) onto IGMS and PS, respectively. Adsorption thermodynamics revealed endothermic, increased randomness and spontaneous removal of Cr(VI) onto IGMS and PS adsorbents. The results revealed that Irvingia gabonensis stem bark extract modified silica gel is a viable and highly efficient adsorbent for the removal of Cr(VI) from Cr(VI)-contaminated effluents.

Adsorption and Separation of Carbon Dioxide/Methane in Landfill Gas with Barium Ion–Modified Silica Gel

Environmental issues caused by greenhouse gases are becoming more and more severe. The main components of landfill gas, carbon dioxide (CO2) and methane (CH4), are greenhouse gases, and the separation and recovery of them are a popular research topic. In order to improve the adsorption capacity of the silica gel adsorbent for landfill gas, a method such as modify silica gel with alkali metal ions is often used. It is to improve the selective adsorption capacity of CO2 by adjusting the polarizability and charge distribution of the silica gel surface while improving the separation effect of the mixed gas. In this study, the adsorption performance of a silica gel adsorbent modified or not with alkali metal ions was measured in terms of the adsorption and separation of a CO2/CH4 mixture (simulating landfill gas). The N2 adsorption and desorption curve of the silica gel adsorbent at 77 K was plotted by determining the specific surface area and pore-size distribution. The results indicated that the unmodified silica gel adsorbent had a large micropore volume and specific surface area and exhibited a high capacity to adsorb gas. After potassium chloride, calcium chloride, magnesium chloride, or barium chloride solution was used to modify the silica gel adsorbent, the adsorption performance of the modified silica gels was ranked as barium chloride > potassium chloride > calcium chloride > magnesium chloride. The best-performing concentration of barium chloride solution was 0.1 mol/L. The research results will provide certain reference for the fields of chemistry and environmental science.

Solid-Phase Reagents on the Modified Silica Gel Base for the Rapid Determination of Nickel(II) Ions

The new solid-phase reagent is synthesized by previous modifying the surface of silica gel with l-(4-sulfophenyl)-3-methyl-5-(benzoxazol-2-yl)formazan for Ni(II) ions determination in water. The high effective colour change (Δλ = 200 nm) is observed due to complex-formation reaction reagent with nickel (II) ions. Increasing toxicant concentration is accompanied by growth the colour intensity of the solid-phase sorbent, which form the basis of colour scale development for the Ni(II) ions determination in the range 10-100 mkg/ml. Ni(II) ions determination can’t be disturbed by the presence of Co(II) ions, alkali or alkali-earth metal ions. Proposed technique is high rapid (its max duration is 2-3 min), ordinary (it is required neither expensive equipment nor qualified staff to use the technique) and ecological friendly.