Silica Gel Surface Research Articles

SYNTHESIS AND SIMPLE METHOD OF CHARACTERIZATION OF ALDEHYDE-SILICA GEL

Two approaches to the functionalization of the silica gel surface have been proposed, which make it possible to obtain materials with covalently immobilized highly reactive aldehyde groups. Immobilization of aldehyde groups in the first case is achieved by the click-reaction of azido-alkyne cycloaddition of 4-(prop-2-in-1-yloxy)benzaldehyde and 3-azidopropyl silica gel. In the second case, surface modification is performed by the alkylation reaction of hydroxybenzaldehydes with 3-chloropropyl silica gel. The obtained silica gel samples were characterized by infrared spectroscopy and thermogravimetric analysis data. In IR spectra absorption bands determination of aldehyde groups on the silica gel surface using 2.4 -dinitrophenylhydrazine has been proposed. The proposed method is based on the condensation reaction between the aldehyde groups grafted on the surface and 2.4 -dinitrophenylhydrazine. The quantitative estimation of the grafted aldehyde groups is suggested to be calculated by the difference between the initial amount of 2.4-dinitrophenylhydrazine and the amount remaining in the solution after the reaction. The necessity of maintaining a constant acidity of the medium by adding H2SO4 was established. It is shown that at λ = 315 nm the Bouguer-Beer-Lambert Law is satisfied in the concentration range 2.5∙10-5 to 12.5∙10-5 M. The correctness of the proposed method was checked using the procedure of operative control of the correctness of the results of chemical analysis. This procedure provides the determination of aldehyde groups in the modified material by multiply varying the silica gel weight and using the root-mean-square deviation of the repeatability of measurement results as an error characteristic. The proposed method for determining the aldehyde groups was tested on all silica gel samples. It was shown that by varying the conditions of surface modification it is possible to obtain materials with different functional capacity for aldehyde groups.

A rapid approach to capture the potential bioactive compounds from Rhizoma Drynariae, utilizing disease-associated mutation in calcium sensing receptor to alter the binding affinity for agonists

Rhizoma Drynariae (RD) was used clinically to treat osteoporosis in China due to stimulating bone formation and inhibiting bone resorption, however, the bioactive constituents with the dual effect on bone are still unknown exactly. Disease-causing mutations in calcium sensing receptor (CaSR) can alter parathyroid hormone secretion and affect Ca2+ release from bone and Ca2+ reabsorption from kidney, which gives an indication that CaSR is a potential target for developing therapeutics to manage osteoporosis. Herein, a chromatographic approach was established, by immobilizing the mutant CaSR onto the surface of silica gels as stationary phase in a one-step procedure and then adding the different amino acids into mobile phase as competitors, for exploring the binding features of the known agonists and further screening ligands from RD. The mutant CaSR-coated column was prepared rapidly without the complicated purification and separation of the receptor, which had the large capacity of 13.1 mg CaSR /g silica gels and kept a good stability and specificity for at least 35 days. The CaSR mutation can weaken the binding affinities for three agonists, and the largest decreases occurred on the mutational site Thr151Met for neomycin, on the two sites of Asn118Lys and Glu191Lys for gentamicin-C, and on the site Phe612Ser for kanamycin, which gained new insights into their structure-function relationship. The potential bioactive compounds from RD were screened using the mutant CaSR-coated column and were recognized as coumaric acid 4-O-β-D-glucopyranoside, caffeic acid, and naringin using UPLC-MS. Among them, naringin targeting CaSR gives a possible explanation that RD could manage osteoporosis. These results indicated that, such a rapid and simple method, utilizing disease-associated mutation in CaSR to alter the binding affinity for agonists, can be applied in capturing the potential bioactive compounds efficiently from complex matrices like herb medicines.

The Adsorption of Pb(II) Using Silica Gel Synthesized from Chemical Bottle Waste: Optimization Using Box-Behnken Design

The adsorption of Pb(II) on silica gel synthesized from chemical glass bottle waste has been studied. The effect of independent variables (adsorbent dose, initial concentration of Pb(II), contact time, and pH) on the Pb(II) removal from water was evaluated and optimized using the Response Surface Methodology (RSM). Under optimized conditions (adsorbent dose: 20 mg; contact time: 30 min; initial Pb(II) concentration: 120 mg. L−1 ; and pH: 8), the removal of Pb(II) was 99.77%. The adsorption equilibrium data obtained from the batch experiment were investigated using different isotherm models. The Langmuir isotherm model fits the experimental data. This shows that the surface of the silica gel synthesized from chemical bottles waste was covered by a Pb(II) monolayer. XRF analysis showed that the synthesized silica gel had a SiO2 content of 75.63%. Amorphous silica was observed from XRD analysis. SEM-EDX characterization showed that Pb was adsorbed on the silica gel surface. SEM analysis showed that silica gel has irregular particles with a surface area of 297.08 m2 .g−1 with a pore radius of 15.74 nm calculated from BET analysis.

Benzoyl isothiocyanate modified surface of silica gel as the extraction material for adsorbing steroid hormones in water.

Steroid hormones have been listed as priority pollutants in the environment, and their detection and pollution control deserve our extensive attention. In this study, a modified silica gel adsorbent material was synthesized by benzoyl isothiocyanate reaction with hydroxyl groups on the silica gel surface. The modified silica gel was used as a solid phase extraction filler for the extraction of steroid hormones from water, which was further analyzed by the HPLC-MS/MS method. The FT-IR, TGA, XPS, and SEM analysis indicated that benzoyl isothiocyanate was successfully grafted on the surface of silica gel to form a bond with an isothioamide group and benzene ring as the tail chain. The modified silica gel synthesized at 40 °C showed excellent adsorption and recovery rates for three steroid hormones in water. Methanol at pH 9.0 was selected as the optimal eluent. The adsorption capacity of the modified silica gel for epiandrosterone, progesterone, and megestrol acetate was 6822 ng mg-1, 13 899 ng mg-1, and 14 301 ng mg-1, respectively. Under optimal conditions, the limit of detection (LOD) and limit of quantification (LOQ) for 3 steroid hormones by modified silica gel extraction with HPLC-MS/MS detection were 0.02-0.88 μg L-1 and 0.06-2.22 μg L-1, respectively. The recovery rate of epiandrosterone, progesterone, and megestrol was between 53.7% and 82.9%, respectively. The modified silica gel has been successfully used to analyze steroid hormones in wastewater and surface water.

An Evaluation of Immobilized Poly-(S)-N-(1-phenylethyl)acrylamide Chiral Stationary Phases

In this study, brush type and polymer type stationary phases were prepared based on (S)-N-(1-phenylethyl) acrylamide, and the polymeric stationary phase demonstrated superior chiral recognition ability. The two polymeric stationary phases were synthesized by two strategies, one was the “grafting from” method, which obtained polymer CSP by initiating monomer polymerization on the surface of 3-methacrylatepropyl silica gel, and the other was “grafting to”, which fixed the copolymer of (S)-N-(1-phenylethyl) acrylamide and trimethoxysilylpropyl methacrylate on silica gel. A comparison of these two bonding modes revealed that the stationary phase produced by “grafting to” had higher chiral recognition ability. Further improvement can be achieved by the end-capping of silanol groups with trimethylchlorosilane to reduce non-enantioselective retention caused by residual silanol groups and improve the peak shape of enantiomers. Chiral separation in subcritical fluid chromatography was also studied. Similar enantioselectivity results with higher resolution were observed due to the improvement of peak shape.

The optimization of silica gel synthesis from chemical bottle waste using response surface methodology

To reduce the amount of hazardous chemical bottle waste in the environment, we report the optimization research of silica extraction in chemical bottle waste into silica gel. Alkali fusion and sol–gel process were utilised to prepare silica gel effectively. The alkali fusion process was carried out by adding sodium hydroxide to produce sodium silicate. Afterwards, silica gel was prepared by the sol–gel method using hydrochloric acid. Box-Behnken Design (BBD) was applied to Optimisation factors the poptimiseactors affecting the silica recovery. The factors that optimised mass ratio, particle size, and temperature. The optimum recovery of silica gel was obtained by SiO2: NaOH mass ratio of 1:3, the particle size of 63–74 µm, and a temperature of 800 °C. The purity of silica gel optimum is 63.74% characterised using X-ray fluorescence. The structure of silica gel is the appearance of amorphous peaks at 2θ 20-30° characterised using an x-ray diffractogram. The silica gel surface was characterises using scanning electron microscopy-energy dispersive x-ray. It showed an irregular surface and characteristic showed that silica gel had a radius of 15.74 nm and a specific surface area of 297.08 m2.

Adsorption of Wet Ammonia on the Surface of Vanadium-Containing Silica Gel

Adsorption of Wet Ammonia on the Surface of Vanadium-Containing Silica Gel

Synthesis and sorption properties of organo-mineral sorbents based on poly(styrene-b-4-vinylpyridine) copolymer

New organo-mineral composites SiO2/poly(styrene-b-4-vinylpyridine) were obtained by adsorption of block- copolymers poly(styrene-b-4-vinylpyridine) with molar ratios of styrene (St) and 4-vinylpyridie (4-VP) St:4-VP = 1:4 and St:4-VP = 1:5 from THF solution onto silica gel surface. Block-copolymers were synthesized by controlled radical polymerization of styrene with RAFT agent and further copolymerization with 4-vinylpyridine. Also blok-copolymer with thiol end-group was obtained and has been employed for preparation of the composite. Composition of the block-copolymers and surface morphology of composites obtained were determined using 1H NMR and FT-IR spectroscopy, differential scanning calorimetry, thermogravimetric analysis and scanning electron microscopy. It was established that sorption capacity of the organo-mineral composites toward Pb(ІІ), Fe(ІІІ) and Cu(ІІ) ions is in 2–4 times higher in comparison with parent silica gel.

Studies on the Catalytic Activities of Cp2ZrCl2 in Olefin Polymerizations that was In-Situ Synthesized or Adsorbed on Organosilaneized Surface of Spherical Silica Gel

Studies on the Catalytic Activities of Cp2ZrCl2 in Olefin Polymerizations that was In-Situ Synthesized or Adsorbed on Organosilaneized Surface of Spherical Silica Gel

Exploration of coal tar asphaltene molecules based on high resolution mass spectrometry and advanced extraction separation method

The structure of coal tar asphaltenes has been recognized as one of the most challenging research topics in coal chemistry. In this work, a stepwise extraction subfraction separation method is developed for coal tar asphaltenes to reveal the polar molecule distribution and structure information using (+) ESI FT-ICR MS coupled with collision induced dissociation (CID). It is found that the most easily ionized molecules are preferentially observed in unfractionated asphaltenes, while the strongly polar molecules are suffered with ionization suppression. The heteroatoms are more likely to be present in aromatic cores instead of substituent chains, and this phenomenon grows more significantly with the increase of solvent polarity. The O/C increases with the increase in solvent polarity, and O plays an important role in the adsorption and desorption of asphaltenes on silica gel surface. The “atypical” asphaltenes molecules are rich in N, S and particularly O containing groups with low aromaticity and small aromatic structures, and tending to be island structures. Moreover, the coal tar asphaltenes has a significantly higher island/archipelago ratio than petroleum asphaltenes. The polar driving force has a great impact on archipelago molecules, the proportion of which is high in polar fractions.

In Ukrainian

One of the most important tasks of environmental chemistry is the development of effective methods for the extraction and chemical analysis of highly toxic oxyanions, such as nitrate, phosphate and arsenate. They enter the environment, raw materials and commercial products with waste from chemical and metallurgical industries. This problem can be solved by synthesizing selective materials that absorb anions due to the complementarity of their active centers and ions. The aim of this work is a directed chemical design of silica surface for the construction of sorption active centers with a high affinity for nitrate, orthophosphate, and orthoarsenate anions. Chemical design of β-cyclodextrin-containing supramolecular structures on the surface of granular mesoporous silica gel to obtain sorbents of highly toxic oxyanions was carried out. The structure and surface chemistry of the initial and functionalized silica gels were characterized by means of IR spectroscopy, spectrophotometry, thermogravimetric and chemical analysis, pH metry, low-temperature adsorption-desorption of nitrogen and sorption techniques. The sorption of nitrate, orthophosphate, and orthoarsenate anions from aqueous one- and multicomponent salt solutions was studied as dependent on the time and ion concentration, as well as in the cyclic sorption-desorption mode. The results obtained are interpreted using kinetic models of pseudo-first and pseudo-second order processes and the equilibrium adsorption models of Langmuir and Freundlich. The main characteristics of the specificity and selectivity of the obtained β-cyclodextrin silica gel were calculated. Conclusions are drawn regarding the possibility of using functionalized silica gel for the sorption of oxyanions from water and aqueous solutions, their concentrating, chromatographic separation, and chemical analysis.

TEXTURAL AND CATALYTIC FEATURES OF SILICON SURFACE MODIFIED WITH ZnO IN THE REACTION OF HOMOGENOUS-HETEROGENEOUS ACTIVATION OF PROPANE-OXYGEN MIXTURES AT LOW PRESSURES

The textural and catalytic characteristics of the surface of silica gel modified with zinc oxide by the sol-gel method and by means of a chemical transport reaction (CTR) have been studied. It was found that catalytic activity of the obtained contacts depends on both the nature and the structural and textural characteristics of the supported ZnO. Using the example of the reaction of low-temperature oxidation of propane, it was found that lower limit of the release of radicals from the surface into the volume with the CTR modification method is lower by 15–20 degrees than in the case of the sol-gel method. It was shown that the catalyst obtained by applying the active phase on the surface of the support by the CTR method is more efficient due to the energy homogeneity of its active centers and the texture characteristics of the surface.

Photochemical transformation of hexachlorobenzene (HCB) in solid-water system: Kinetics, mechanism and toxicity evaluation

As one of the first batch of persistent organic pollutants (POPs) included in Stockholm Convention, hexachlorobenzene (HCB) has attracted great attention because of its wide occurrence and great environmental risks. Considering the easy adsorption of HCB on solids and the complexity of natural particles, we systematically investigated the photodegradation of HCB on the surface of silica gel (SG) in aqueous solution in this work to reveal its fate in natural waters. Under mercury lamp irradiation, more than 90% of HCB loaded on SG could be removed after 240 min. Moreover, the effects of solution pH and water constituents were examined, and results showed that the presence of NO2−, NO3−, Fe3+ and humic acid (HA) significantly inhibited the reaction due to the scavenging of ROS and/or competitive absorption of light. According to radical quenching experiments and electron paramagnetic resonance (EPR) spectra, hydroxyl radicals and singlet oxygen generated on the surface of SG could participate in the transformation of HCB, but •OH played a dominant role. Based on products identified by high performance liquid chromatography-mass spectrometry (HPLC-MS) and gas chromatography-mass spectrometry (GC-MS), two main pathways were proposed for the removal of HCB, including dechlorination and hydroxylation which represent direct and indirect photodegradation, respectively, and the occurrence of these two reactions was further supported by density functional theory (DFT) calculations. From the quantitative analysis of penta-chlorobenzene, it was estimated that dechlorination and hydroxylation contributed to approximately 44.4% and 55.6% of initial HCB degradation, respectively. Furthermore, toxicity predictions by the ecological structure–activity relationship model (ECOSAR) suggested that the toxicity of HCB was decreased in the photodegradation process. This study would provide important information for understanding the photochemical transformation mechanism of HCB at the solid/water interface.

Wettability and Stability of Naproxen, Ibuprofen and/or Cyclosporine A/Silica Delivery Systems

The characteristics of the wetting process of the porous surface of silica gel when penetrated by base liquids (water and n-octane), ethanol and stable drug systems (naproxen, ibuprofen and cyclosporine A), as biologically active substances in two ethanol concentrations, were determined by the wetting rate vs. time. The tests were performed for contacted and non-contacted plates with the vapours of the wetting liquid. Thin-layer liquid chromatography was used to determine the penetration rate of the SiO2-coated plates, taking into account the linear dependence consistent with the Washburn equation. Additionally, the changes in the adhesive tension ΔG were determined for the tested drugs. Drug stability tests were conducted using the dynamic light scattering technique and microelectrophoresis. The penetration time of the plate depends on the properties and structure of the wetting liquid droplets. The types of interactions (dispersive, electrostatic and hydrogen bonding) formed between the silanol surface groups of the silica gel and the groups contained in the adsorbate particles are also very important factors. The greater the impact force, the slower the wetting process due to the strong penetration of the liquid into the pores of the substrate. The characteristics of the drug wetting/stability process may contribute to the development of their new forms, creating delivery systems with greater efficiency and lower side effects.

Anchored complexes of rhodium and iridium for the hydrogenation of alkynes and olefins with parahydrogen

Iridium and rhodium complexes anchored on silica gel surface via NH2–(CH2)3– and P(Ph)2–(CH2)2– linker groups achieve high (∼9%) efficiency in pairwise addition of parahydrogen to unsaturated gaseous substrates in heterogeneous hydrogenation processes.

Expeditious base-free solid-state reaction between phenyl boronates and hydrogen peroxide on silica gel

The expeditious base-free reaction between a phenyl boronate film and H2O2 vapor can be realized on a silica gel surface, playing an important role in sensor manufacturing applications and chemical production.

Silica‐Mediated Monohydrolysis of Dicarboxylic Esters

AbstractA new method for the monohydrolysis of dicarboxylic esters is presented, involving as key step a silanolysis at elevated temperatures at the silica gel surface. In the second step, the surface bound silyl esters are cleaved off under mild conditions, giving a straightforward and fast access to half esters. Based on recovered starting material generally yields well above 70 % are achieved, both, with stiff aromatic as well as flexible aliphatic substrates, as long as the ester groups involved are remote enough from each other. Otherwise competing reactions are becoming determinative, anhydride formation in the case of phthalates and decarbonylative fragmentation in the case of malonates. The new method was also successfully tested on a multigram scale with a minimalistic apparatus setup.

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.

ВПЛИВ ПОЖЕЖ В ПРИРОДНИХ ЕКОСИСТЕМАХ НА МІГРАЦІЙНУ ЗДАТНІСТЬ ВАЖКИХ МЕТАЛІВ, МЕТОДИ СОРБЦІЙНО-СПЕКТРОФОТОМЕТРИЧНОГО ЇХ ВИЗНАЧЕННЯ

Purpose. Development of methods for sorption-spectrophotometric and atomic-emission determination of hazardous toxicants in order to increase the reliability of monitoring pollution parameters and assess possible future adverse consequences for humans and the environment. Methodology. Sorption-spectrophotometric and atomic-emission determination of Cu (II), Ni (II), Cd (II), Pb (II), Al (III), Fe (III), in soils degraded due to fires, using sorbents based on silica gel, sequentially modified with polyhexamethylene guanidine and arsenazo-I salts, which can be used for simple and fast methods for the determination of heavy and transition metals. Findings. Identification of chemical pollution by heavy metals in degraded soils as a result of tegogenic activity, fires, climate change for making the necessary management decisions. Originality. Sorbents for the group extraction of heavy metal ions were obtained by the method of non-covalent modification of the silica gel surface with polyhexamethylene guanidine and a triphenylmethane sulfonyl dye. Practical value. Techniques have been developed for the sorption-spectrophotometric and atomic-emission determination of Cu (II), Ni (II), Cd (II), Pb (II), Al (III), Fe (III) using silica gel, sequentially modified with salts of polyhexamethylene guanidine and arsenazo I, which can be used for simple, rapid test methods for determining the migration capacity of heavy and transition metals in technogenically polluted ecosystems and will make it possible to make scientifically based decisions on the priority of the implementation of environmental protection measures. To determine the microquantities of the ions under study, it is advisable to use fine-grained silica gel, and coarse-grained silica gel – to determine higher concentrations of the tested ions. Сonclusions. The paper proposes methods for the group sorption - spectrophotometric determination of Cu (II), Ni (II), Cd (II), Pb (II), Al (III), Fe (III) in the main components of the environment (soil and natural waters) on based on sorbents modified with specific analytical reagents, which is one of the promising directions for increasing the sensitivity and selectivity of analysis. References 15, tables 2, figures 5.

The impact of the silica gel structure and surface chemistry on the melting of aliphatic nanocrystals: Thermodynamic model and experiment

Phase transitions in nano-sized systems are of fundamental importance in a variety of fields, including sustainable energy and the pharmaceutical industries. Here we report the thermal properties of undecylenic acid nanocrystals in silica gel pores of different sizes and the chemical composition of the pores’ surface. The results of N2 absorption at 77 K, thermogravimetric method, powder XRD method, and differential scanning calorimetry were analyzed to gain an insight into the processes accompanying the phase transition. We using a thermodynamic model of nanocrystal melting in an open porous system and analyze temperature dependence of the effective size of pores, as well as the dependence of the specific heat of melting on the effective size of the pores. This model helps us obtain the following properties of the undecylenic acid: the density of nanocrystals, pressure inside the nanocrystal, the relation between the surface tension coefficients and specific entropies on the nanocrystal-porous matrix interface and melt-porous matrix interface. We demonstrate that as the nanocrystals of the undecylenic acid form in the cavities of the porous matrix, the pressure in such nanocrystals, and thus their densities are much lower than pressure and density in bulk crystals of the undecylenic acid. However, when the crystallization of the nanocrystals occurs in the presence of aliphatic chains grafted on the silica gel pore walls, these chains become embedded into nanocrystals. As the result, the character of the change of properties reverses: both the pressure in the undecylenic acid nanocrystals and their density become larger than those for a bulk undecylenic acid crystal. Throughout the paper, we also contrast the behaviour of a polar undecylenic acid in pores with that of nonpolar 1-octadecen molecules.