Synthesis of Silokhrom S-120 grafted with transition-metal acetylacetonate layers and its acid-base and chromatographic properties

We have synthesized sorbents based on Silokhrom S-120 silica gel grafted with Ni2+, Co2+, and Cu2+ acetylacetonate layers. Using pH measurements and a Hammett indicator method, we have studied the acid-base properties and composition of donor-acceptor centers on silica gel surfaces before and after modification. We have determined chromatographic retention parameters for test compounds and evaluated the polarity and selectivity of the sorbents. Modification with acetylacetone chelates has been shown to increase the surface acidity of Silokhrom S-120, leading to changes in various types of intermolecular interaction

Physicochemical properties of sorbents based on silica gel modified by 1-phenylazo-2-naphtholic complexes of transition metals

Gas chromatography sorbents based on Silokhrom C80 and modified by 1-phenylazo-2-naphtholic complexes of 3d metals (Co(II), Ni(II), Cu(II)) are obtained. Their structural, chromatographic, and sorption characteristics are investigated. It is found that modifying them with 1-phenylazo-2-naphthols of transition metals has a considerable effect on the chromatographic polarity and selectivity of sorption materials. The prospects for the practical application of the obtained sorbents are demonstrated by experiments on the gas chromatographic separation of mixtures of different classes of organic compounds

Adsorption properties of Silochrom chemically modified with nickel acetylacetonate

One of the areas of development of gas chromatography is the creation of new chromatographic materials that have improved sorption and analytical characteristics. In this work, for the first time, a new sorbent based on Silochrom C-120 modified with nickel acetylacetonate was studied using a complex of physico-chemical methods. It has been established that due to chemical modification of silica gel surface with nickel acetylacetonate the surface area of the specific surface decreases from 112 to 98 m2/g and surface acidity diminishes by 1.2 pH units. Using the thermogravimetric analysis it has been revealed that the obtained sorbent can be used in gas chromatography up to 290°C. Gas chromatography method was used to investigate the adsorption properties of the modified materials. According to the retention data of adsorbates: n-alkanes (C6-C9), benzene, ethanol, nitropropane and butanone-2 the differential molar adsorption energy q̄dif, 1, Henry adsorption constants К1,С, the differential molar entropy ΔS̄S1 and Δ q̄dif, 1 (special) of adsorbates in dispersion and specific interactions were calculated. The influence of the modifying additive on the changings in the thermodynamic retention characteristics of all sorbates because of the manifestation of specific sorbate-sorbent interactions has been shown. The highest values of the thermodynamic parameters were indicative for sorbates forming hydrogen bonds and capable of donor-acceptor interaction

Synthesis and study of the composition and properties of chelate complexes of benzoyl acetonates of rare-earth elements and use of these in gas chromatography

Chelate complex cerium [Ce(BA)3)] and europium [Eu(BA)3] benzoyl acetonates were synthesized. According to IR spectroscopic data and elemental analyses, the composition of the complexes is described by the empirical formulas M(BA)3·2H2O. Sorbents based on a mesoporous silica gel modified with cerium and europium benzoyl acetonates were obtained. The nitrogen porosimetry demonstrated that, as the complexes are deposited onto the surface of the starting support, the specific surface area and the pore volume become smaller. The polarity of the sorbents Chromaton N-AW + SiO2 + M(BA)3 with respect to all classes of test compounds decreases in the order CeIII > EuIII. According to the data obtained for the capacity factors, the sorbent modified with cerium benzoyl acetonate selectively separates alcohols, and Chromaton N-AW + SiO2 with deposited chelates Eu(BA)3 shows the best separating capacity for alkanes and alcohols. It was shown that the sorbents can be used in practice for separating gaseous mixtures of light hydrocarbons

Effect of solution pH on the surface morphology of sol-gel derived silica gel

We have examined the effect of solution acidity on the textural characteristics of silica gels prepared by sol–gel synthesis using tetraethyl orthosilicate (TEOS) as a silica precursor and cetyltrimethylammonium bromide (CTAB) as a template. Using IR spectroscopy, we have studied micellar TEOS solutions and the synthesized silica gel samples. The results demonstrate that, in an alkaline medium in a water–ethanol solution, SiO2 experiences short-range ordering on the surface of micelles formed by CTAB molecules, whereas in an acid medium the process is not influenced by the presence of CTAB. Nitrogen porosimetry and electron microscopy data indicate that the silica gel obtained at pH 2 is microporous, with an average pore size of 2 nm. In an alkaline medium at pH 10, we obtained mesoporous SiO2 (18 nm) with a narrow pore size distribution and a specific surface area of 110 m2/g

Use of silochrome with grafted layers of transition metal acetonates for sorption concentration of volatile organic substances from aqueous media

Sorbents based on silica of Silochrome S-120 brand with covalently attached layers of transition metal acetylacetonates were synthesized. The sorption properties of the resulting chelate-containing materials were studied and the analytical potential of their application for rapid sorption concentration of volatile organic compounds from water bodies was evaluated

Determination of aliphatic acids in natural waters using distillation and solid-phase extraction

A procedure is developed and conditions are optimized for the pretreatment of natural water using distillation with no prefiltration of acidified water in combination with preconcentration by solid-phase extraction (SPE) on a Strata-X polymeric adsorbent followed by derivatization for the determination of trace concentrations of C3–C18 aliphatic carboxylic acids by gas chromatography with mass spectrometric detection. It is shown that, at the distillation stage, 90% of free carboxylic acids of the homologous series are transferred to the distillate, which greatly facilitates the procedure of the analysis of natural water containing impurity particles and humic substances and ensures the achievement of the limit of detection for the analytes about 0.05 μg/L. It is found that, at the SPE stage, the adsorbents based on copolymers of styrene, divinylbenzene, and N-vinylpyrrolidone in plastic cartridges may serve as sources of additional pollution with benzoic, palmitic, and stearic acids in the eluates under investigation

Electro-Fenton-like reactions of transition metal ions with electrogenerated hydrogen peroxide

We evaluated and compared the hydroxyl radical-generating ability of chromium, iron, cobalt, nickel, copper, lanthanum, and cerium ions when reacted with electrogenerated hydrogen peroxide by usage the voltammetry. There was reproduced an electro-Fenton-like reaction in electrochemical cell when metal salt added. The nature of metal ions determined the appearance and increasing of current of hydroxyl radicals cathodic reduction due to individual rate of the redox cycling of metal ions with ongoing cathodic regeneration of Fenton-active metal ions oxidation state. The approximated current magnitude growth in relation to metal ions concentration was calculated for each tested metal. It expressed in μA·ml·μmol−1 and is equal to HO•-generating ability of metal ions. Results are usable for improvement of advanced oxidation processes (AOPs) through enhancement of exploitation of electro-Fenton-like processes with selecting metals that are more active. Besides, in accordance with concept of metal-induced hydroxyl radical stress in biological systems, the hydroxyl radical-generating ability of metal ions is equal to their pro-oxidant capacity

Nitrate-citrate sol-gel synthesis of hydrated calcium aluminate and sorption materials on its basis

Sol-gel technique was used to develop a method for synthesis of hydrated tricalcium aluminate Ca3[Al(OH)6]2 and surface-layered gas-chromatographic sorbents on its basis. The materials obtained were examined by X-ray diffraction analysis, scanning electron microscopy, X-ray fluorescence microanalysis, adsorption porosimetry, and gas chromatography. It was found that cubic Ca3[Al(OH)6]2 is the main phase in the surface layer of the sorption materials. The Hammett indicator method was used to examine the acid-base properties and the variation of the content of active centers between sorbents obtained in different ways. The chromatographic retention parameters were determined for test compounds, and the polarity and selectivity of the sorbents under study was evaluated. It was shown that Chromaton N-AW modified with hydrated calcium aluminate can be used, with addition of SE-30 stationary liquid phase, to separate complex mixtures of organic compounds

Physicochemical properties of sorbents based on silica gel modified by 1-phenylazo-2-naphtholic complexes of transition metals

Gas chromatography sorbents based on Silokhrom C80 and modified by 1-phenylazo-2-naphtholic complexes of 3d metals (Co(II), Ni(II), Cu(II)) are obtained. Their structural, chromatographic, and sorption characteristics are investigated. It is found that modifying them with 1-phenylazo-2-naphthols of transition metals has a considerable effect on the chromatographic polarity and selectivity of sorption materials. The prospects for the practical application of the obtained sorbents are demonstrated by experiments on the gas chromatographic separation of mixtures of different classes of organic compounds