Adsorption-energetic and IR spectroscopic studies of NH4 natrolite

The ammonium form of natural zeolite, natrolite, obtained by vapor phase ion exchange is similar to calcium-containing zeolites of the natrolite group in its de- and rehydration characteristics and the heats of immersion in water. The adsorption capacity and the heat of immersion in water are maximum after evacuation of the zeolite at 200 °C. The irreversible sintering of NH₄ natrolite occurs above 200 °C (up to 45% at 500 °C), accompanied by the formation of hydroxyl groups. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 359–361, February, 1998.     

Recent Development of Hypercrosslinked Microporous Organic Polymers

Hypercrosslinked polymers (HCPs) are currently receiving great interest due to their easy preparation, high chemical and thermal stability, and low cost. Combined with the lightweight properties and high surface areas HCPs can be considered as promising materials for gas storage and separation, catalysis, and heavy metal ions removal in wastewater treatment. This Feature Article summarizes strategies for the preparation of HCPs, comprising the post‐crosslinking of “Davankov‐type” resins, direct polycondensation of aromatic chloromethyl (or hydroxymethyl) monomers, and knitting aromatic compound polymers (KAPs). The HCPs applications, such as H₂ storage, CO₂ capture, and heterogeneous catalysis, are also discussed throughout in the article. Finally, the outlook of this research area is given.     

Covalent attachment of trypsin on plasma polymerized allylamine

This paper focuses on the immobilization of a proteolytic enzyme, trypsin, on plasma polymerized allylamine (ppAA) films. The later have been deposited onto silicon substrate by means of radiofrequency glow discharge. The covalent attachment of the enzyme was achieved in three steps: (i) activation of the polymer surface with glutaraldehyde (GA) as a linker, (ii) immobilization of trypsin and (iii) imino groups reduction treatment. The effects and efficiency of each step were investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Fluorescent spectroscopy was used to evaluate the change of the biological activity following the immobilization steps. The results showed that enzyme immobilization on GA-modified substrate increases the enzyme activity by 50% comparing to adsorbed enzymes, while the imino reduction treatment improves the enzyme retention by about 30% comparing to untreated samples. In agreement with XPS and AFM data, UV–vis absorption spectroscopy, used to quantify the amount of immobilized enzyme, showed that allylamine plasma polymer presents a high adsorption yield of trypsin. Although the adsorbed enzymes exhibit a lower activity than that measured for enzymes grafted through GA linkers, the highest catalytic activity obtained was for the enzymes that underwent the three steps of the immobilization process.     

Effect of the interface on separation in multicapillary gas chromatography-based hyphenated techniques for speciation analysis of organometallic compounds

This paper reports the effect of transfer line (TL) internal diameter (i.d.) on gas chromatographic separation characteristics such as efficiency and speed, when a multicapillary (MC) column is used for speciation analysis of mercury. Five different TL consisting of fused-silica capillaries with 0.15, 0.20, 0.25, 0.32, and 0.53 mm i.d. are compared. The separation efficiency and total chromatographic run time are critically affected by the i.d. of the TL. Narrow capillaries (i.d.0.20 mm) produce minimum peak dispersion whereas wide capillaries result in narrow peaks and shorter chromatographic analysis times. A thermodynamic approach is proposed to describe the motion of the analytes through the separation column and TL. The model provides good agreement with the experimental data for high pressures (35 psig) and wide TL (0.25 mm i.d.).Dedicated to the memory of Wilhelm Fresenius     

Arsenic speciation in some environmental samples: a comparative study of HG–GC–QFAAS and HPLC–ICP–MS methods

Some water and soil extracts polluted with arsenic, and a sewage sludge certified for total arsenic have been analysed by high‐performance liquid chromatography–inductively coupled plasma–mass spectrometry (HPLC–ICP–MS) and hydride generation–gas chromatography– quartz furnace atomic absorption spectrometry (HG–GC–QFAAS techniques.) Detection limits in the range of 200–400 and 2–10 ng l⁻¹ respectively allowed the determination of inorganic [As(III), As(V)] and methylated (DMA, MMA, TMAO) arsenic species present in these samples. Results obtained by both methods are well correlated overall, whatever the arsenic chemical form and concentration range (8–10 000 μg l⁻¹). Comparison of these results enabled us to point out features and disadvantages of each analytical method and to reach a conclusion that they are suitable for arsenic speciation in these environmental matrices. Copyright © 2000 John Wiley & Sons, Ltd.     

Mechanistic aspects of magnetic MgAlNi barium-ferrite nanocomposites enhanced adsorptive removal of an anionic dye from aqueous phase

The mechanistic aspects of improved aqueous removal of methyl orange (MO) dyes using high performance novel magnetic MgAlNi barium-ferrite (MgAlNi-BaFe) ternary double layer hydroxide (LDH) nanocomposites is reported in this study. Detailed surface characterization coupled with kinetic, equilibrium, thermodynamics and regeneration studies were undertaken under different operational conditions of temperature (298–318 K), initial concentration (20–100 mg/L), pH (2–6). The kinetic results show that MO sorption was mainly, associated with pseudo-second order and intra-particular diffusion process. The MO adsorption onto the MgAlNi-BaFe nanocomposites suggests a multi-layered sorption process that is endothermic and spontaneous in nature. The MO adsorption mechanism insight taken in cognizance of FTIR, XRD, pKa, zeta potential, the adsorbates surface functional groups and the adsorbate-adsorbent surface charges interactions suggest involvement of hydrogen bonding and n-π interactions, predominantly via physisorption process (ΔG° = −7.406 to −5.69 kJ/mol). The excellent adsorptive performance of the MgAlNi-BaFe adsorbents for removal of MO from water compared with other magnetic LDH nanocomposites was further elucidated via the MgAlNi-BaFe nanomaterials high rates of regeneration and superior performances for three successive desorption-adsorption cycles. This study demonstrates the high potentials of employing MgAlNi-BaFe nanomaterials for removal of dyes from water and wastewater.     

One Singularly Perturbed Problem of Turbulent Gas Dynamics

The problem of the interaction of a Prandtl–Mayer wave with a shear layer is solved using the small parameter method for the case where the flow vorticity in the shear layer is small. A direct expansion is constructed and its inadequacy at large distances from the vortex layer is proved. The strained coordinate method is used to obtain a uniformly adequate expansion. It is shown that for certain velocity distributions in the shear layer, the characteristics in the reflected simple wave resulting from the interaction intersect each other and a shock arises in the flow. There coordinates of the shock origin and the function describing the shock shape are obtained.     

气相色谱法研究聚辛烯-1与不同溶剂的热力学相互作用

用气相色谱法测定了聚辛烯－１与８种溶剂的Ｆｌｏｒｙ－Ｈｕｇｇｉｎｓ相互作用参数χ１和聚辛烯－１的溶解度参数,确定了χ１与温度的数学关系式。测定结果表明聚辛烯－１溶于正辛烷是一个放热过程。     

Single Si atom supported on defective boron nitride nanosheet as a promising metal‐free catalyst for N2O reduction by CO or SO2 molecule: A computational study

The low‐temperature reduction of N₂O plays a significant role for solving the growing environmental and health issues caused by emission of this greenhouse gas. The aim of this study is to investigate the possible reaction pathways for the reduction of N₂O by CO or SO₂ molecule over Si‐doped boron nitride nanosheet (Si‐BNNS). According to our results, a B or N‐vacancy defect in BN sheet could be able to greatly stabilize the single Si adatom. The relatively large diffusion barrier for the Si atom over the defective BN sheet also indicates Si‐BNNS is stable enough to be utilized in catalytic reduction of N₂O. The large charge‐transfer from the surface to N₂O leads to the spontaneous dissociation of this molecule into N₂ molecule and an activated oxygen atom (O_ads). The O_ads moiety is then eliminated by CO or SO₂ molecule. The calculated activation energies and reaction energies reveal that the Si atom located on top of the B‐vacancy site has a large catalytic activity toward the reduction of N₂O by CO or SO₂.