Dynamics and isotherms of water vapor sorption on mesoporous silica gels modified by different salts

The mesoporous silica gels impregnated with different metal salts were prepared and studied. The pore structure and specific surface area of adsorbents were evaluated using nitrogen adsorption. Then, the sorption isotherms and dynamics of water vapor were carried out at 303 K and different relative humidity (RH). The temperature programmed desorption experiments were conducted to estimate the activation energy (E _d) of water desorption on the silica gels. The results showed that the sorption capacity for water decreased with the increase of the ionic radius (except the calcium ion) and that CaCl₂ and LiCl were particularly suitable for use in modification of the mesoporous silica gel to improve their sorption rates and capacities for water vapor at the lower and medium RH (RH < 80%). The larger the average pore diameter and pore volume of the initial silica gels, higher the accrual rates of the water vapor sorption rate and capacity were after modification with hygroscopic salts. The activation energy of the water desorption on the mesoporous silica gel modified by CaCl₂ were much higher than that on the silica gel modified by LiCl, because the polarizability of the Ca²⁺ was higher than that of Li⁺.     

Heavy metal adsorption ability of a new composite material based on starch strengthened with chemically modified cellulose

Adsorption of heavy metals (Pb, Zn, and Cu) on a new bioadsorbent based on starch reinforced with modified cellulose with toluene‐diisocyanate has been studied using batch‐adsorption technology. The study was carried out in order to find if this bio material, designed for seedling pots manufacture, is able to act like a barrier between soil pollutants and plants. The influence of contact time, pH, adsorbent dose, and salt concentrations was also evaluated. The obtained data were examined using the Langmuir and Freundlich adsorption models. Optimal results were obtained at pH 5.0, temperature of 25°C, contact time of 120 minutes, and an adsorbent dose of 4 mg/mL. Experimental data along with computed Langmuir parameters show that the adsorption process is favorable, and the maximum adsorption capacity of the adsorbent for lead, zinc, and copper was 66.66, 58.82, and 47.61 mg/g, respectively.     

Characterization of the hydrophobicity of mesoporous silicas and clays with silica pillars by water adsorption and DRIFT

The hydrophobic-hydrophilic properties of a solid are related to the material chemistry and, often, these properties are relevant to the applications of a particular material. Contrarily to what happens with other properties, such as specific surface areas or pore volumes, the methodologies to ascertain on the hydrophilicity of a porous material are not well defined. In this work, we discuss and relate the information on the hydrophobicity degree obtained from water adsorption isotherms and from diffuse reflectance infrared Fourier transform (DRIFT), in a set of porous materials. The studied materials were mainly mesoporous solids, namely of MCM-41 and SBA-15 types, two xerogels and also different porous clays heterostructures. Both techniques were informative on the hydrophobic-hydrophilic properties of the studied samples, but the correlation between the information obtained by each technique was not straightforward. Water adsorption isotherms are much more sensitive to the differences of the studied materials than the DRIFT spectra. For silica-based mesoporous materials with similar surface chemistry, the water adsorption process and hence, the hydrophobic-hydrophilic properties, is mainly dependent on the pore diameters. However, water adsorption is much more sensitive to changes in the nature of the adsorbent surface than to changes in the pore diameter.     

Phosphorylated cellulose for water purification: a promising material with outstanding adsorption capacity towards methylene blue

Cellulose - Enhancing the sorption properties of cellulose is a prerequisite for its efficient use in water purification as an alternative to costly activated carbon. Here, solvent-free...     

Kinetic features of the adsorption of water vapor by copper and nickel ammine complexes with polyoxometallate anions

The rate of adsorption of water vapor by compounds obtained from cationic copper(II) and nickel(II) ammine complexes and polyoxometallate anions may be described by the linear driving force mass transfer model as one or two parallel processes. The differences observed were attributed to differences in the crystal structure of the adsorbents. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 112–117, March–April, 2007.     

新试剂光度法测定废水中氯化十六烷基吡啶的研究

研究了新试剂4,4′-二[3-(4-苯基-2-噻唑基)三氮烯基]联苯(BPTTBP)与氯化十六烷基吡啶(CPC)的显色反应。在NaOH碱性介质中,试剂与CPC发生显色反应,形成紫色离子缔合物,最大吸收波长592 nm。试剂BPTTBP与CPC的缔合比为1∶1,其表观摩尔吸光系数为2.84×104L.mol-1.cm-1,CPC量在0~1.0×10-5mol/L范围内服从比尔定律。方法可直接用于废水中微量CPC的测定。     

Phosphazenium chloride catalysts immobilized on SBA-15 mesoporous material and silica gel: new exceptionally active catalysts for the chlorination of organic acids

Novel reusable phosphazenium chloride catalysts immobilized on SBA-15 mesoporous material and silica gel show exceptional activities and selectivities even in the continuous chlorination reaction of organic acids with thionyl chloride or phosgene.     

电厂废气中饱和水蒸气对活性炭变压吸附捕集CO2的影响

由于热电厂废气中含有高湿饱和水蒸气,选用疏水材料活性炭为吸附剂,利用真空变压吸附技术研究了活性炭分离电厂废气中水蒸气和二氧化碳的可行性和优越性,研究了水对CO₂捕集的影响。实验分析表明,水在活性炭上的“S”型等温吸附曲线有利于真空条件下被解吸。同时,圆锥模型描述了水蒸气在吸附床内的浓度分布。结果表明,即使水蒸气可以被活性炭吸附,但它的存在不影响CO₂的捕集。每个循环操作可在相对较短的解吸时间和较高的解吸压力下完成。实验中单床三步变压吸附工艺可以使CO₂回收率高达80%,CO₂纯度达43%。     

The development of a new LDF mass transfer correlation for adsorption in fixed beds

In this study, a general LDF model has been introduced to predict mass transfer rate through adsorbents with the macropore diffusion as the controlling step. Using this relation eliminates the need for solving the time-consuming diffusion equation to find mass transfer rate through the porous adsorbent. The proposed relation was successfully applied in the general mathematical model for an adsorption fixed bed. This correlation was adjusted to be capable of predicting the mass transfer rate in a wide range of gas adsorption systems reported in the literature. This correlation was used in 21 different adsorbent and adsorbate systems. The results demonstrated an excellent agreement between the correlation results and those obtained using Fickian diffusion equation. By applying the developed LDF model instead of diffusion model, a great deal of CPU time can be saved. The latter characteristic will be very important when this model is employed in commercial software such as Aspen Adsorption or Prosim Dynamic Adsorption Column.     

Zinc-containing mesoporous silicas as a catalyst for the benzylation of benzene and other aromatics by benzyl chloride

The benzylation of benzene and the substituted benzenes reaction employing benzyl chloride as the alkylating agent over a series of zinc-containing mesoporous silicas with different Zn contents have been investigated. These materials (Zn-HMS-n) have been characterized by chemical analysis, BET, and XRD. The mesoporous zinc-containing materials showed both high activity and high selectivity for benzylation of benzene. The activity of these catalysts for the benzylation of different aromatic compounds is in the following order: benzene > toluene > p-xylene > anisole. The kinetics of the benzene benzylation over these catalysts has also been investigated. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 3, pp. 421–425.     

Solid ink-printed filter paper as a green adsorbent material for the solid-phase extraction of UV filters from water samples

This work describes the development of a new green solid-phase extraction approach, which is based on the use of low-cost extraction discs composed of plain filter papers that are covered with a synthetic wax-like coating. The filter papers are printed in a commercial solid ink printer, which dispenses a synthetic wax-like ink on the surface of the paper, to cover the hydrophilic cellulose fibre matrix with an interface of lipophilic domains where non-polar analytes can partition through hydrophobic interactions. The modified paper filters were used to extract hydrophobic organic compounds from water samples following the customary procedure of solid-phase extraction without sorbent preconditioning and needless of high-vacuum sources. As a proof-of-concept application, a series of non-polar organic UV filters were used as model analytes to optimise the extraction parameters and evaluate the performance of the method in spiked water samples. Based on this principle, a new sample preparation platform with low environmental footprint has been developed that enables extraction to be carried out using low-cost, environmental benign and non-toxic conventional materials. The advantages and disadvantages of the method, alongside with its future prospects towards the development of custom-made ‘printed extraction kits’, are envisioned and discussed.     

Chitosan impregnated Ca-alginate: a new hybrid material for removal of uranium from potable water

Novel sorbent, chitosan impregnated calcium alginate (Cal-Alg-Chi) bead was developed to sorb uranium from potable water without compromising water quality parameters. The uptake study in batch mode, showed more than 98% sorption of uranium in the concentration range of 0.1–50 µg mL⁻¹. Cal-Alg-Chi beads, reduced the concentration of uranium below 15 ng mL⁻¹ from 100 to 450 ng mL⁻¹ in groundwater collected from effected regions in India. Sorption isotherm followed Langmuir model and maximum sorption capacity was evaluated as 36.04 mg g⁻¹. The sorption was endothermic with ΔG ⁰ value of −9.76 kJ mol⁻¹ and kinetics followed pseudo-second order rate law.

     

Evaluation of a new electrolytic cold vapor generation system for mercury determination by AFS

In this study we firstly report a new electrolytic cold vapor generation system for mercury determination on Pt/Ti cathode in the presence of organic acid catholyte. Comparing with the traditional inorganic acid, formic acid increased the signal intensity of Hg vapor from electrolytic generation on Pt cathode and reduced the impact of cathode erosion on the stability of signal intensity. Moreover, formic acid has better interference tolerance. The introduction location for carrier gas is probably the most important factor that influences the signal intensity of Hg from electrolytic vapor generation. The effects of the electrolytic conditions and interference ions on the ECVG have been studied. Under the optimized conditions, the detection limit (3σ) of Hg (II) in aqueous solutions is 1.4 ng L⁻¹; a relative standard deviation of 2.3% for 1 μg L⁻¹ Hg was obtained. The accuracy of this method was verified by the determination of mercury in the certified reference materials. This system has been applied satisfactorily to the determination of Hg in Traditional Chinese Medicines samples.     

Polymerization of vinyl chloride and copolymerization with carbon monoxide by a new initiator

The system comprising the ethoxydized product of triethylaluminum, cuprous chloride, and carbon tetrachloride was used as an initiator for polymerization of vinyl chloride, and the polymerization kinetics was studied. From plots of the molar number of number-average polymer chain Y/P? versus yield Y, the two parameters a ( = ∫ R_idt ? 1/2 ∫ R_tdt) and b ( = ∫ R_trdt/∫ R_pdt) were estimated to be 6 × 10^?3 mole/l. and 6.6 × 10^?4 respectively. Studies of the tacticity of the poly(vinyl chloride) showed isotactic = 49.3% and syndiotactic = 50.7%. The present initiator also permitted copolymerization of vinyl chloride with carbon monoxide; the monomer reactivity ratios were r₁ = 0.40 (vinyl chloride) and r₂ = 0.01 (carbon monoxide).     

A new analytical methodology for a fast evaluation of semi-volatile polycyclic aromatic hydrocarbons in the vapor phase downstream of a diesel engine particulate filter

A new sampling method was developed to collect vapor-phase polycyclic aromatic compounds (PAHs) downstream of a diesel engine equipped with a diesel particulate filter (DPF). This configuration allowed us to collect separately the particulate phase, which was trapped inside the DPF, and the vapor phase, which was sampled downstream of the DPF. PAHs, which were not predominantly absorbed into the poor organic fraction of the diesel soot, but were rather physically sorbed on high energetic adsorption sites, should be extracted using very drastic extraction conditions Microwave-assisted extraction using solvent mixtures composed of pyridine and diethylamine were used to desorb particulate PAHs, and the total PAH amounts corresponded to a very low value, i.e., 8 μg g⁻¹ or 0.24 μg km⁻¹, with a predominance of low weight PAHs. For collection of the vapor phase, gas bubbling in an aqueous medium was preferred to conventional methods, e.g., trapping on solid sorbents, for several reasons: aqueous trapping allowed us to use a solid phase enrichment process (SPE) that permitted PAH sampling at the sub-picogram levels. Consequently, low volume sampling was possible even if the sampling duration was very short (20 min). Additionally, the amount of time saved for the analysis was considerable when coupling SPE to the analytical system (liquid chromatography with fluorimetric detection). Solvent consumption for the overall sampling and analytical processes was also drastically reduced. Experiments on a diesel engine showed that vapor phase samples collected downstream of the DPF contained all of the 15 target priority PAHs, even the heaviest ones. The total vapor-phase PAH amount was 6.88 μg N m⁻³ or 10.02 μg km⁻¹, which showed that the gaseous fraction contains more PAHs than the particulate fraction. Partitioning coefficients (K_p) were estimated showing the predominance in the vapor phase of all the PAHs. However, the DPF technology effects a considerable decrease in the total PAH emission when compared to non-equipped diesel vehicles.     

A new method for preparation of organocalcium halides by cocondensation of calcium vapor with solvents

Calcium vapor (atom) when cocondensed with various solvents at 77 K was found to be very reactive toward alkyl and aryl halides. A series of organocalcium halides was prepared in good yields by addition of alkyl or aryl halides to the resultant calcium atom-solvent slurries at ambient temperatures.     

A filter paper coated with phenylboronic acid-modified mesoporous silica for enrichment of intracellular nucleosides prior to their quantitation by HPLC

Microchimica Acta - The authors describe a filter paper modified with mesoporous silica that carries phenylboronic acid on its surface. The material possesses the advantages of the flexibility of...     

Simultaneous determination of nitroaromatic compounds in water using capillary electrophoresis with amperometric detection on an electrode modified with a mesoporous nano‐structured carbon material

In this article, a carbon disk electrode modified with mesoporous carbon material (CMK‐3) was used in CE with amperometric detection system for the simultaneous determination of four types of important nitroaromatic compounds, including 2,4,6‐trinitrotoluene (TNT), 1,3,5‐trinitrobenzene (TNB), 2,4‐dinitrotoluene (DNT) and 1,3‐dinitrobenzene (DNB). Compared with the bare carbon electrode, the CMK‐3 modified electrode greatly improved the sensitivity at a relatively positive detection potential due to its excellent electrocatalytic activities, high conductivity and large effective surface area. The four analytes could be well separated and detected within 480 s. A good linear response was obtained for TNB, DNB, TNT and DNT from 8.4 to 5.0×10³ μg/L, with correlation coefficients higher than 0.9992. And the detection limits were established between 3.0 and 4.7 μg/L for the four investigated nitroaromatic compounds (S/N=3). The CMK‐3‐modified electrode was successfully employed to analyze coking wastewater, tap water and river samples with recoveries in the range of 94.8–109.0%, and RSDs less than 5.0%. The presented results demonstrated that the CMK‐3‐modified carbon electrode used in CE with amperometric detection was of convenient preparation, high sensitivity and good repeatability, which could be employed in the rapid determination of practical samples.