The synthesis and characterisation of novel dimethyl- and diphenyl-silanediolates

Dimethyl- and diphenylsilanediolates are key intermediates in the preparation of dimethyl- and diphenyl-siloxane polymers. Both dimethyl- and diphenylsilanediolates R₂Si(OM)₂, where R = Me or Ph, and M = Li, Na and K were synthesised by the reaction between dimethyl- and diphenylsilanediol and a metal or metal hydride (M/MH where M = Li, Na and K). The silanediolates were characterised by ²⁹Si, ¹³C and ¹H NMR, FTIR and mass spectroscopy.     

Enhanced removal of hydrogen sulfide from a gas stream by 3-aminopropyltriethoxysilane-surface-functionalized activated carbon

A commercial activated carbon was functionally modified by silylation with 3-aminopropyltriethoxysilane (APTES). The silylation led to the fixation of weakly basic functional groups, –NH₂, on the surface as indicated by pH titration, Boehm titration, N $_{2^{-}}$ BET analysis and X-ray photoelectron spectroscopic (XPS) analysis. Despite reducing the specific BET area and the pore volume, silylation improved the H₂S removal capacity so that APTES modified activated carbon (APTES-AC) was 3.55 times more effective than the original activated carbon. XPS results indicate that H₂S removal may be associated with the amino (–NH₂) group and the presence of sulfur in the four oxidation states S^2?, S⁰, S⁴⁺ and S⁶⁺. The effects of moisture, oxygen content and temperature on the performance of APTES-AC for H₂S removal were investigated. The presence of moisture in the gas stream was found to have an adverse effect on the H₂S removal, whilst the presence of oxygen favored the removal of H₂S by APTES-AC. The higher removal capacity of APTES-AC relative to the original activated carbon indicates that APTES-AC is a potential candidate for the removal of H₂S from gas streams. The H₂S removal efficiency of APTES-AC was proved be superior to that of Na₂CO₃-impregnated AC by the pilot-scale test of purification H₂S containing industrial waste gas, yellow phosphorus off-gas.     

Gas adsorption process in activated carbon over a wide temperature range above the critical point. Part 2: conservation of mass and energy

Simulations of the thermal effects during adsorption cycles are a valuable tool for the design of efficient adsorption-based systems such as gas storage, gas separation and adsorption-based heat pumps. In this paper, we present simulations of the thermal phenomena associated with hydrogen, nitrogen and methane adsorption on activated carbon for supercritical temperatures and high pressures. The analytical expressions of adsorption and of the internal energy of the adsorbed phase are calculated from a Dubinin-Astakhov adsorption model using solution thermodynamics. A constant adsorption volume is assumed. The isosteric heat is also calculated and discussed. Finally, the mass and energy rate balance equations for an adsorbate/adsorbent pair are presented and are shown to be in agreement with desorption experiments.     

Thermal and quality evaluation of vegetable oils used in ruminant feed

Dairies add fat supplements to the diets of small ruminants to increase energy production and consequently the production and quality nutritional and sensorial of the milk. This study investigated the thermal and oxidative stability of babassu, castor, faveleira, and sesame oils by TG/DTA and PDSC. The profile of the fatty oils studied was determined by GC–MS as well as physicochemical characteristics. The thermogravimetric profile of the oils indicated that mass loss was caused by the decomposition or volatility of the triacylglycerides. Faveleira and sesame oils showed a high percentage of polyunsaturated fatty acids, especially C18:2. From a nutritional standpoint, unsaturated oils are more suitable supplements for animals because they promote biochemical changes beneficial to human health.     

Modeling breakthrough curves of volatile organic compounds on activated carbon fibers

Granular activated carbon (GAC) and more recently activated carbon fibers (ACF) are used for the treatment of volatile organic compounds (VOC) in industrial processes. The purpose of this study was to investigate the adsorption kinetics of ACF to eliminate VOC from polluted air. This approach is carried out by modeling experimental breakthrough curves with two kinds of models: an equilibrium model and a mass transfer model based on a linear driving force (LDF) in conjunction with the Langmuir equilibrium model. The results show the influence of the intraparticle diffusion on the adsorption kinetics of ACF, in spite of their small fiber diameter. Moreover, external diffusion kinetics is fast because of the influence of the large external surface area of ACF on the VOC mass transfer.     

The removal and kinetic study of Mn,Fe, Ni and Cu ions from wastewater onto activated carbon from coconut shells

Activated carbon from coconut shells (ACCS) was synthesised and used for the removal of metal ions (manganese, iron, nickel and copper) from aqueous solutions. Two different adsorption models were used for analysing the data. Adsorption capacities were determined: copper ions exhibited the greatest adsorption on activated carbon obtained from coconut shells because of their size and pH conditions. Adsorption capacity varied as a function of the pH. Adsorption isotherms from aqueous solutions of heavy metals on ACCS were determined and were found to be consistent with Langmuir’s adsorption model. Adsorbent quantity and immersion enthalpy were studied. The results were compared with other adsorbents used in a prior study.     

Gas adsorption process in activated carbon over a wide temperature range above the critical point. Part 1: modified Dubinin-Astakhov model

Simulations of the thermal effects during adsorption cycles are valuable tools for the design of efficient adsorption-based systems such as gas storage, gas separation and adsorption-based heat pumps. An analytical representation of the measured adsorption data over the wide operating pressure and temperature swing of the system is necessary for the calculation of complete mass and energy conservation equations. In Part 1, the Dubinin-Astakhov (D-A) model is adapted to model hydrogen, nitrogen, and methane adsorption isotherms on activated carbon at high pressures and supercritical temperatures assuming a constant microporous adsorption volume. The five parameter D-A type adsorption model is shown to fit the experimental data for hydrogen (30 to 293 K, up to 6 MPa), nitrogen (93 to 298 K, up to 6 MPa), and for methane (243 to 333 K, up to 9 MPa). The quality of the fit of the multiple experimental adsorption isotherms is excellent over the large temperature and pressure ranges involved. The model’s parameters could be determined as well from only the 77 K and 298 K hydrogen isotherms without much reducing the quality of the fit.     

Electrochemical determination of acetaminophen at a carbon electrode modified in the presence of β-cyclodextrin: role of the activated glassy carbon and the electropolymerised β-cyclodextrin

Acetaminophen is a well-known drug commonly used to provide pain relief, but it can also lead to acute liver failure at high concentrations. Therefore, there is considerable interest in monitoring its concentrations. Sensitive and selective acetaminophen electrochemical sensors were designed by cycling a glassy carbon electrode (GCE) to high potentials in the presence of β-CD in a phosphate electrolyte, or by simply activating the GCE electrode in the phosphate solution. Using cyclic voltammetry, adsorption-like voltammograms were recorded. The acetaminophen oxidation product, N-acetyl benzoquinone imine, was protected from hydrolysis, and this was attributed to the adsorption of acetaminophen at the modified GCE. The rate constants for the oxidation of acetaminophen were estimated as 4.3 × 10^–3 cm² s^–1 and 3.4 × 10^–3 cm² s^–1 for the β-CD-modified and -activated electrodes, respectively. Using differential pulse voltammetry, the limit of detection was calculated as 9.7 × 10^–8 M with a linear concentration range extending from 0.1 to 80 μM. Furthermore, good selectivity was achieved in the presence of caffeine, ascorbic acid and aspirin, enabling the determination of acetaminophen in a commercial tablet. Similar electrochemical data were obtained for both the β-CD-modified and activated GCE surfaces, suggesting that the enhanced detection of acetaminophen is connected mainly to the activation and oxidation of the GCE. Using SEM, EDX and FTIR, no evidence was obtained to indicate that the β-CD was electropolymerised at the GCE.

     

High resolution N2 adsorption isotherms at 77.4 K and 87.3 K by carbon blacks and activated carbon fibers--analysis of porous texture of activated carbon fibers by αs-method

The standard α(s)-data of N(2) at 87.3 K by graphitized and nongraphitized carbon black samples (GCB-I and NGCB) (cf.Figs. 3 and 4) have been determined on the basis of the high resolution adsorption isotherms of N(2) at 87.3 K, which were repeatedly measured in the pressure range of p/p(o)=5×10(-8)-0.4. The high resolution adsorption isotherms of N(2) by two kinds of activated carbon fibers (ACF-I and ACF-II) were measured from p/p(o)=10(-7) to p/p(o)=0.995 at 77.4 K and from p/p(o)=10(-7) to p/p(o)=0.4 at 87.3 K. Combination of the adsorption isotherms by ACF-I and ACF-II with the standard α(s)-data by NGCB at 77.4 K and 87.3 K make it possible to construct the high resolution α(s)-plots from very low filling (1%) to complete filling (100%). The high resolution α(s)-plots of N(2) at 77.4 K and 87.3 K were analyzed. On the basis of the analyzed result, the porous textures of ACF-I and ACF-II will be discussed.     

The Volumetric and Thermochemical Properties of Dipropylsulfoxide in Water

Volumetric and thermal properties of aqueous solutions of dipropylsulfoxide (DPSO) have been studied. Densities of binary mixtures of DPSO with water were measured over the full range of compositions at temperatures from 298.15 K to 338.15 K by means of a vibrating-tube densimeter. We also investigated the thermal properties of the [DPSO + water] system using differential scanning calorimetry at a low heating/cooling rate (2 K⋅min⁻¹). The results obtained are compared with those of dimethylsulfoxide (DMSO) and diethylsulfoxide (DESO) aqueous solutions.     

Osmotic and Activity Coefficients of Trimethyloctylammonium Bromide and Decyltrimethylammonium Bromide in Aqueous Solutions as a Function of Temperature

Osmotic coefficients of aqueous solutions of trimethyloctylammonium bromide and decyltrimethylammonium bromide were measured by the isopiestic method at the following temperatures: 298.15, 293.15, 288.15 and 283.15 K. Activity coefficients of the solutes were calculated from the osmotic coefficients. The results were compared with the Debye-Hückel limiting law and analyzed according to their variation with the alkyl chain length of the cation and with the change in temperature.     

Kinetics and adsorption equilibrium in the system aqueous solution of copper ions—granulated activated carbon

The feasibility of using granulated activated carbon for adsorption removal of copper from aqueous solution was studied. The influence of pH, amount of the adsorbent, contact time, and copper concentration on adsorption of copper was investigated. The single-component equilibrium data on copper adsorption were analyzed using the Langmuir, Freundlich, Redlich—Peterson, Temkin, and Toth adsorption isotherms. The adsorption process was followed by two simplified kinetic models including pseudo-first- and pseudo-second-order equations. Kinetic parameters, rate constants, equilibrium sorption capacities, and the corresponding correlation coefficients were calculated and examined for each kinetic model. It was shown that copper adsorption can be described by the pseudo-second-order equation.     

The SML pump of carbon cycles in oceans

1 Introduction Recently the concepts and models of “pump” are used frequently in studying global cycles and varieties of elements in marine chemistry and marine biogeo-chemistry. For example, there are many “pump” con-cepts including the concepts of s…     

Textural and surface chemistry of activated bagasse and its role in the removal of chromium ions from solution

The role of the surface chemical and physical properties of activated carbon in the removal of chromium was investigated. This was conducted by fitting the chromium removal by adsorption and reduction to Cr(III) to the physical properties including total surface and pore size of the carbon and its chemical property globally measured using carbon pH. The role of heteroatoms—sulfur, nitrogen, hydrogen and oxygen, to chromium removal was also investigated. This study showed that the structural and chemical properties displayed dual and conflicting properties in removing chromium. As such efficiencies gained in controlling the structure of the carbon are minimal. Optimal carbon properties which exhibited high chromium adsorption included high surface area, large pore size, high quantities of sulfur and nitrogen and minimal hydrogen and oxygen contents.     

Adsorption of CO2 as a method for the characterisation of the structure of alumina-pillared clay catalysts

The aim of this work was to study the effect of the metal loading on the structure of two series of cobalt and manganese pillared clay-supported catalysts. For this purpose, equilibrium data for CO₂ adsorption at 273 K were analysed using Freundlich, Langmuir and Toth isotherm models, in order to estimate the adsorption parameters and to relate them with the metal loading of the catalysts. The metal distributions on the porous structure of the catalysts were studied using the temperature programmed reduction results combined with information from the nitrogen physisorption data. Comparison of all results reveals that up to a certain metal loading, about 0.5 wt% of Co and 2 wt% of Mn, the metal oxide is well dispersed into the porous structure of the pillared clay. At higher metal loadings, bulk-metal oxide particles are formed on the external surface.     

Adsorption of lead(II) from aqueous solution onto several types of activated carbon fibers

In this work, the adsorption of Pb(II) from aqueous solution was investigated on various types of activated carbon fibers (ACFs) manufactured from polyacrylonitrile and phenolic resin. The textural and physicochemical properties of the ACFs were determined by the N₂-BET method and acid-base titration. The experimental adsorption equilibrium data of Pb(II) on the ACFs were obtained in a batch adsorber, and the Langmuir isotherm model better fitted the experimental data. The effects of the type of ACF and precursor of ACF, solution pH and temperature upon the adsorption of Pb(II) on the ACFs were examined in detail. The adsorption capacity was highly dependent upon the precursor of ACF. The Pb(II) adsorption capacity of the ACFs augmented when the solution pH and temperature were increased from 2 to 4 and from 288 to 308 K, respectively. The effect of the pH was attributed to the interactions between the surface of the ACF and Pb²⁺ ions present in the water solution. The Pb(II) adsorption capacity of the ACFs was enhanced by oxidation with HNO₃ solution and the enhancement factor was between 1.1 and 1.4. The reversibility of the adsorption of Pb(II) was investigated by first adsorbing Pb(II) on an ACF and then desorbing the Pb(II). It was noticed that Pb(II) was substantially desorbed from ACF while reducing the solution pH to 2. It was concluded that the Pb(II) was mainly adsorbed on the ACFs by chemisorption, electrostatic interactions and ion exchange.     

The safety assessment of herbals with a new and ethical approach

The increasing use of plant medicines (herbals) in Europe needs a shared methodology to determine the toxicity and the daily exposure level to these drugs. For this reason, the European regulatory agencies have undertaken a study that could meet popular uses and toxicological research in different countries of the Union. Here we list some examples of the most used herbal drug classes and we propose a decision-making process based on their characteristics, their content in active principles and on the basis of the present scientific pharmacological and toxicological literature. The proposed decision tree actually makes easier for the assessor to quickly and accurately evaluate the accredited indexes for risk and toxicity assessment based on the preclinical literature data and using the correct classification that some of them may have because they are already present in medicinal products or used as food.     

Photosolvolysis of a carboncarbon bond. The photolysis of n,n-dimethyl- 2,2-diphenylethylamine in methanol.1

The title compound is photolyzed in methanol to give good yields (ca. 50%) of diphenylmethane indicating that the CC bond undergoes a formal heterolytic cleavage from the excited state as predicted from the measured redox potentials of the two ions.