Preconcentration of Se(IV) with Silica Gel Chemically Modified with Sulfur-Containing Groups

Для концентрирования Se(IV) предложены сорбенты на основе силикагеля с привитыми серосодержащими группами различной природы. Количественное извлечение Se(IV) достигается в диапазоне 0,5 М HCl – pH 7 силикагелем с тиольными и тетрасульфидными группами и рН 1–4 силикагелем с дитиокарбаминатными и тиомочевинными группами с временем установления сорбционного равновесия, не превышающим 5 мин. В исследованных диапазонах кислотности на сорбентах МПС, МФС и ТСС отсутствует сорбция Se(VI), что позволяет осуществить разделение Se(IV) и Se(VI) с использованием данных сорбентов. Сорбционная емкость по Se(IV) составляет 0,11; 0,035 и 0,087 ммоль/г для МПС, МФС и ТСС соответственно. Изотермы сорбции удовлетворительно описываются моделью ЛенгмюраAdsorbents based on silica gel with grafted sulfur-containing groups of various nature were proposed for preconcentrating Se(IV). The quantitative extraction of Se(IV) is achieved in the range of 0.5 M HCl – pH 7 by silica gel with thiol and tetrasulfide groups and pH 1–4 by silica gel with dithiocarbamate and thiourea groups with a sorption equilibrium time not exceeding 5 min. In the studied ranges of acidity, there is no sorption of Se(VI) on MPS, MFS, and TSS adsorbents, which makes it possible to separate Se(IV) and Se(VI) using these sorbents. The adsorption capacity for Se(IV) is 0.11; 0.035 and 0.087 mmol/g for MPS, MFS and TSS, respectivel

Comprehensive Study of the Ammonium Sulfamate–Urea Binary System

The physicochemical properties of binary systems are of great importance for the application of the latter. We report on the investigation of an ammonium sulfamate–urea binary system with different component ratios using a combination of experimental (FTIR, XRD, TGA/DSC, and melting point) and theoretical (DFT, QTAIM, ELF, RDG, ADMP, etc.) techniques. It is shown that, at a temperature of 100 °C, the system under study remains thermally and chemically stable for up to 30 min. It was established using X-ray diffraction analysis that the heating time barely affects the X-ray characteristics of the system. Data on the aggregate states in specified temperature ranges were obtained with thermal analysis and determination of the melting point. The structures of the ammonium sulfamate–urea system with different component ratios were optimized within the density functional theory. The atom-centered density matrix propagation calculation of the ammonium sulfamate–urea system with different component ratios was performed at temperatures of 100, 300, and 500 K. Regardless of the component ratio, a regular increase in the potential energy variation (curve amplitude) with an increase in temperature from 100 to 500 K was found

Food Xanthan Polysaccharide Sulfation Process with Sulfamic Acid

Xanthan is an important polysaccharide with many beneficial properties. Sulfated xanthan derivatives have anticoagulant and antithrombotic activity. This work proposes a new method for the synthesis of xanthan sulfates using sulfamic acid. Various N-substituted ureas have been investigated as process activators. It was found that urea has the greatest activating ability. BBD of xanthan sulfation process with sulfamic acid in 1,4-dioxane has been carried out. It was shown that the optimal conditions for the sulfation of xanthan (13.1 wt% sulfur content) are: the amount of sulfating complex per 1 g of xanthan is 3.5 mmol, temperature 90 °C, duration 2.3 h. Sulfated xanthan with the maximum sulfur content was analyzed by physicochemical methods. Thus, in the FTIR spectrum of xanthan sulfate, in comparison with the initial xanthanum, absorption bands appear at 1247 cm−1, which corresponds to the vibrations of the sulfate group. It was shown by GPC chromatography that the starting xanthan gum has a bimodal molecular weight distribution of particles, including a high molecular weight fraction with Mw > 1000 kDa and an LMW fraction with Mw < 600 kDa. It was found that the Mw of sulfated xanthan gum has a lower value (~612 kDa) in comparison with the original xanthan gum, and a narrower molecular weight distribution and is characterized by lower PD values. It was shown by thermal analysis that the main decomposition of xanthan sulfate, in contrast to the initial xanthan, occurs in two stages. The DTG curve has two pronounced peaks, with maxima at 226 and 286 °C