Adsorption of nitrobenzene andn-pentanol from aqueous solution on hydrophilic and hydrophobic clay minerals

The sorption of nitrobenzene andn-pentanol from dilute aqueous solution on swelling clay minerals and their organophilized derivatives (organo clays) was studied. Adsorption excess isotherms were obtained by the immersion method. The basal spacings of the clay minerals were determined by X-ray diffraction measurements. By combining these two independent methods, composition and structure of the interlamellar space could be calculated. On the hydrophilic surface of montmorillonite negative adsorption of the organic component was observed at low molar fractions of nitrobenzene or pentanol, i.e., water was preferentially adsorbed. On organophilized montmorillonite and vermiculite adsorption of nitrobenzene and pentanol was positive over the whole range of liquid composition. The amount of interlamellar alkyl chains which is determined by the surface charge of clay mineral inversely affected the adsorption of both solutes.     

Effect of dissolved organic matter from Guangzhou landfill leachate on sorption of phenanthrene by montmorillonite

To investigate the effect of dissolved organic matter (DOM) on the adsorption of phenanthrene (PHE) by montmorillonite (MMT), organic clay complex was prepared by associating montmorillonite with DOM extracted from landfill leachate. Both the raw MMT, DOM, and MMT complex (DOM-MMT) were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photo-emission spectroscopy (XPS), and scanning electron microscope (SEM). Batch adsorption studies were carried out on the adsorption of PHE as a function of contact time, temperature, and adsorbent dose. The sorption of PHE on complex was rapid, and the kinetics could be described well by the Pseudo-first-order model (R(2)>0.99), with an equilibrium time of 120 min. The adsorption isotherm was in good agreement with the Henry equation and Freundlich equation. Also, thermodynamic studies showed that the adsorption process was exothermic and spontaneous in nature. Compared with MMT, the adsorption capacity of DOM-MMT complex for PHE was greatly enhanced. The effects of DOM on PHE sorption by MMT may be attributed to the changes in the surface structure, the specific surface area, the hydrophobic property, and the average pore size of MMT. A series of atomistic simulations were performed to capture the structural and functional qualities observed experimentally.     

Effects of exchanged surfactant cations on the pore structure and adsorption characteristics of montmorillonite

Ca-montmorillonite (Ca-Mont) was exchanged with two quaternary amines, tetramethylammonium (TMA) chloride and hexadecyltrimethylammonium (HDTMA) bromide, to study the surfactant ion exchange effect on the pore structure, surface characteristics, and adsorption properties of montmorillonite. The revolution of both the surface area and pore structure of montmorillonite was characterized based on classical and fractal analyses of the nitrogen isotherms as well as the XRD patterns. The change of surface characteristics was identified from FTIR patterns and zeta-potential plots. The adsorption isotherms of acid dye, Amido Naphthol Red G (AR1), were then measured to identify the effects of the ion-exchange process on the adsorption properties of montmorillonite. It was found that the exchange processes might induce an increase or decrease in the surface area, pore size, pore volume, and surface fractal dimension D of montmorillonite, depending on the size, the molecular arrangement, and the degree of hydration of the exchanged ion in the clay. On the other hand, it was also found that the hydrophobic bonding by conglomeration of large C(16) alkyl groups associated with HDTMA could cause positive charge development on the surface of montmorillonite, which was not observed for TMA-modified montmorillonite (TMM). The effects of the alteration of the surface characteristics of montmorillonites on their adsorption selectivity for acid dye were discussed.     

Nickel Sorption Mechanisms in a Pyrophyllite-Montmorillonite Mixture

Nickel sorption on pyrophyllite, montmorillonite and a 1:1 pyrophyllite-montmorillonite mixture was studied at pH 7.5 and a reaction time of 40 min. The main modes of Ni uptake under these reaction conditions are adsorption on montmorillonite and surface precipitation on pyrophyllite. For the clay mixture, where adsorption on the montmorillonite component and surface precipitation on the pyrophyllite component compete for Ni uptake, X-ray absorption fine structure spectroscopy (XAFS) was used to estimate the distribution of Ni over the mixture components. This was done by comparison to pyrophyllite-montmorillonite mixtures with known Ni distributions over the mixture components. Nickel uptake on singly reacted pyrophyllite was slightly higher than on singly reacted montmorillonite. This was consistent with the XAFS results for the clay mixture, which suggested that the pyrophyllite component sorbed slightly more Ni than the montmorillonite component. Our findings suggested that both adsorption and surface precipitation were important mechanisms in the overall Ni uptake in the clay mixture, and that neither sorption mechanism truly out-competed the other in the reaction time of 40 min employed. Therefore, both mechanisms should be considered when modeling Ni sorption in similar systems. Copyright 1999 Academic Press.     

Surface fractal and structural properties of layered clay minerals monitored by small-angle X-ray scattering and low-temperature nitrogen adsorption experiments

Small-angle X-ray scattering of the clay minerals kaolinite, montmorillonite and illite was studied with a compact Kratky camera. From the scattering function, the correlation length, the Porod constant and the specific surface area were determined. The scattering functions also led to the surface fractal dimension. The pore volume distribution, the adsorption/desorption hysteresis, the specific surface area and the surface fractal dimension of the same samples were also determined by nitrogen adsorption at 77 K.     

Synthesis and Characterizations of Hydroxy-aluminum Cross-Linked Montmorillonite

Cross-linked montmorillonite was prepared by reacting homoionic sodium form of bentonite (Na-M) from Istenmezeje (Hungary) with high molecular weight polyhydroxy-aluminum complex. The complex was prepared by controlled hydrolysis of alumina macrocation. The intercalated clay (Na-Al-M) was thermally treated to convert the hydroxy cations to oxide pillars. The pillared products were characterized by X-ray powder diffraction (XRD), Fourie transform infrared spectroscopy (FTIR), (thermogravimetry (TG), differential thermal analysis (DTA) and thermal analysis-mass spectrometry (TA-MS) methods. The specific surface area as well as pore size and pore structure distribution of samples were measured by nitrogen, water and carbon tetrachloride adsorption, and the heat of immersion was also determined. The pillared products were characterized by d(001) reflections of 19 Å, which is stable even at 500°C. The interaction of polymer alumina caused several changes in the obtained FTIR spectra due to the formation of different new bonds. The rate of dehydroxylation of the pillared product is very moderate, the water release occurred in different temperature ranges according to TA-MS results. Dehydration starts at interfaces and at the wall of pores, occurring nearly with uniform rate at 250-500°C. DTA curve indicates the formation of a new phase at 950°C. The obtained surface area of the pillared product by nitrogen adsorption becomes larger (208 m2 g-1) with respect to the non pillared clay, which decreases less than 10% upto 700°C. The pillared sample has a definite pore structure, the quantity of micropores (0-40 Å) decreased with increasing of macropores (>1000 Å). The obtained domestic pillared montmorillonite possesses a high degree of thermal stability and may be used as adsorbent.     

Synergism of the Bacillus thuringiensis Cry1, Cry2, and Vip3 Proteins in Spodoptera frugiperda Control

The polyphagous caterpillar, Spodoptera frugiperda, has been controlled with either chemical insecticides or transgenic plants such as Bt maize that expresses the cry and/or vip genes of the Bacillus thuringiensis (Bt) bacterium. Despite the efficiency of Bt toxins in lepidopteran control, populations resistant to Bt plants have emerged in different locations around the world. Thus, understanding how combined proteins interact against pests can assist resistance control and management. This work demonstrated the toxicity of Cry1Ab, Cry1Ac, Cry1Ca, Cry1Ea, Cry2Aa, Cry2Ab, Vip3Aa, and Vip3Ca in single and combined assays against S. frugiperda neonatal larvae. All protein mixtures had synergistic action in the control of the larvae. The Vip3Aa + Cry1Ab mixture had the highest toxicity, sequentially followed by Vip3Aa + Cry2Ab, Cry1Ab + Cry2Ab + Vip3Aa, Cry1Ea + Cry1Ca, Cry1Ab + Cry2Ab, Vip3Ca + Cry1Ea, and Vip3Ca + Cry1Ca. Cry1Ab, Cry1Ac, Cry2Ab, and Vip3Aa bound to more than one site on the brush border membrane vesicles (BBMV) of S. frugiperda. The Cry1Ab and Cry1Ac proteins share binding site, while Cry1Ab does not share binding site with the Cry2Aa and Cry2Ab proteins. The Vip3Aa protein does not share receptors with the tested Cry1 and Cry2. The results suggest that combination these tested proteins may increase toxicity against S. frugiperda neonates.

     

苏云金芽孢杆菌毒素Cry1Aa、Cry2Aa、Cry3Aa和Cry4Aa结构的计算机对比分析

运用生物信息学软件对苏云金芽孢杆菌毒素Cry1Aa、Cry2Aa、Cry3Aa和Cry4Aa的 序列和基本参数、二级结构、三级结构、跨膜区和表面电势进行了预测比较。它们在一级 结构上有较大差异,但二级结构和跨膜区相似,三级结构中各毒素的结构域Ⅰ之间基本相 似,结构域Ⅱ之间差异较大,其中Cry2Aa为差异最大成员。4种毒素的表面电势分布不同。 毒素之间的结构相似性和差异性与其作用机理和杀虫特异性有关。     

Theoretical study of the atrazine pesticide interaction with pyrophyllite and Ca2+‐montmorillonite clay surfaces

Atrazine, a pesticide belonging to the s‐triazine family, is one of the most employed pesticides. Due to its negative impact on the environment, it has been forbidden within the European Union since 2004 but remains abundant in soils. For these reasons, its behavior in soils and water at the atomic scale is of great interest. In this article, we have investigated, using DFT, the adsorption of atrazine onto two different clay surfaces: a pyrophyllite clay and an Mg‐substituted clay named montmorillonite, with Ca²⁺ compensating cations on its surface. The calculations show that the atrazine molecule is physisorbed on the pyrophyllite surface, evidencing the necessity to use dispersion‐corrected computational methods. The adsorption energies of atrazine on montmorillonite are two to three times larger than on pyrophyllite, depending on the adsorption pattern. The computed adsorption energy is of about −30 kcal mol⁻¹ for the two most stable montmorillonite‐atrazine studied isomers. For these complexes, the large adsorption energy is related to the strong interaction between the chlorine atom of the atrazine molecule and one of the Ca²⁺ compensating cations of the clay surface. The structural modifications induced by the adsorption are localized: for the surface, close to substitutions and particularly below the Ca²⁺ cations; in the molecule, around the chlorine atom when Ca²⁺ interacts strongly with this basic site in a monodentate mode. This study shows the important role of the alkaline earth cations on the adsorption of atrazine on clays, suggesting that the atrazine pesticide retention will be significant in Ca²⁺‐montmorillonite clays. © 2016 Wiley Periodicals, Inc.     

Adsorption of phenanthrene on organoclays from distilled and saline water

Isotherms of phenanthrene adsorption on different organoclay complexes were obtained using the HPLC technique to understand the adsorption behavior and to characterize the effect of sodium chloride (NaCl) on the adsorption. The adsorbed amounts of phenanthrene on montmorillonite exchanged by organic cations such as tetraheptylammonium, benzyltrimethylammonium, hexadecyltrimethylammonium, or tetraphenylphosphonium were several times higher than those obtained using montmorillonite clay without surface modification. At the same equilibrium concentration, the adsorbed amount of phenanthrene is higher on clay modified with benzyltrimethylammonium than on clay modified with hexadecyltrimethylammonium or other cations. Adsorption of phenanthrene on clay modified with benzyltrimethylammonium increased dramatically as the concentration of NaCl increased up to 150 g/l in the aqueous solution. The shape of the curves obtained can be classified as S-type. The adsorption data obtained from salinity experiments support a mathematical model that links the Langmuir constant with the salinity constant. This model may be useful to predict the equilibrium concentration of a contaminant in saline solution. FTIR studies showed strong interactions between the aromatic rings of phenanthrene and the preadsorbed benzyltrimethylammonium on clay surfaces.     

Interaction of Pseudomonas putida with kaolinite and montmorillonite: a combination study by equilibrium adsorption, ITC, SEM and FTIR

Equilibrium adsorption along with isothermal titration calorimetry (ITC), Fourier transform infrared spectra (FTIR) and scanning electron microscopy (SEM) techniques were employed to investigate the adsorption of Pseudomonas putida on kaolinite and montmorillonite. A higher affinity as well as larger amounts of adsorption of P. putida was found on kaolinite. The majority of sorbed bacterial cells (88.7%) could be released by water from montmorillonite, while only a small proportion (9.3%) of bacteria desorbed from kaolinite surface. More bacterial cells were observed to form aggregates with kaolinite, while fewer cells were within the larger bacteria–montmorillonite particles. The sorption of bacteria on kaolinite was enthalpically more favorable than that on montmorillonite. Based on our findings, it is proposed that the non-electrostatic forces other than electrostatic force play a more important role in bacterial adsorption by kaolinite and montmorillonite. Adsorption of bacteria on clay minerals resulted in obvious shifts of infrared absorption bands of water molecules, showing the importance of hydrogen bonding in bacteria–clay mineral adsorption. The enthalpies of −4.1 ± 2.1 × 10⁻⁸ and −2.5 ± 1.4 × 10⁻⁸ mJ cell⁻¹ for the adsorption of bacteria on kaolinite and montmorillonite, respectively, at 25 °C and pH 7.0 were firstly reported in this paper. The enthalpy of bacteria–mineral adsorption was higher than that reported previously for bacteria–biomolecule interaction but lower than that of bacterial coaggregation. The bacteria–mineral adsorption enthalpies increased at higher temperature, suggesting that the enthalpy–entropy compensation mechanism could be involved in the adsorption of P. putida on clay minerals. Data obtained in this study would provide valuable information for a better understanding of the mechanisms of mineral–microorganism interactions in soil and associated environments.     

The characterization of prepared organomontmorillonite (DEDMAM) and sorption of phenoxyalkanoic acid herbicides from aqueous solution

The montmorillonite has been subjected to modification through ion-exchange reaction by N,N'-didodecyl-N,N'-tetramethylethanediammoniumdiiodide (DEDMAI). The modified sample was studied by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). The basal spacing of modified montmorillonite was determined as 28.72 A. The IR spectra of organomontmorillonite showed changes in C-H vibrations. The characterization of N,N'-didodecyl-N,N'-tetramethylethanediammonium montmorillonite (DEDMAM) and the adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4-dichlorophenoxybutyric acid (2,4-DB), 4-chloro-2-methylphenoxyacetic acid (MCPA), and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) on organomontmorillonite was studied as a function of the solution concentration. The adsorption energy (E) and adsorption capacity (qm) for phenoxyalkanoic acid herbicides adsorbing on organomontmorillonite (DEDMAM) were estimated using the Dubinin-Radushkevic (D-R) equation. These isotherms were modeled according to Freundlich and Dubinin-Radushkevic adsorption isotherms. The sorption of the herbicides on DEDMAM increased in order of MCPA<2,4-D<2,4-DB<2,4,5-T.     

Preferential adsorption of extracellular polymeric substances from bacteria on clay minerals and iron oxide

The adsorption of extracellular polymeric substances (EPS) from Bacillus subtilis on montmorillonite, kaolinite and goethite was investigated as a function of pH and ionic strength using batch studies coupled with Fourier transform infrared (FTIR) spectroscopy. The adsorption isotherms of EPS on minerals conformed to the Langmuir equation. The amount of EPS-C and -N adsorbed followed the sequence of montmorillonite>goethite>kaolinite. However, EPS-P adsorption was in the order of goethite>montmorillonite>kaolinite. A marked decrease in the mass fraction of EPS adsorption on minerals was observed with the increase of final pH from 3.1 to 8.3. Calcium ion was more efficient than sodium ion in promoting EPS adsorption on minerals. At various pH values and ionic strength, the mass fraction of EPS-N was higher than those of EPS-C and -P on montmorillonite and kaolinite, while the mass fraction of EPS-P was the highest on goethite. These results suggest that proteinaceous constituents were adsorbed preferentially on montmorillonite and kaolinite, and phosphorylated macromolecules were absorbed preferentially on goethite. Adsorption of EPS on clay minerals resulted in obvious shifts of infrared absorption bands of adsorbed water molecules, showing the importance of hydrogen bonding in EPS adsorption. The highest K values in equilibrium adsorption and FTIR are consistent with ligand exchange of EPS phosphate groups for goethite surface. The information obtained is of fundamental significance for understanding interfacial reactions between microorganisms and minerals.     

Changes in the characteristics of acid‐treated clay after the inclusion of proteins

The aim of this work is to study the difference in the characteristics of commercial clay after the inclusion of two proteins. Bovine serum albumin and egg white lysozyme were immobilized on the structure of commercial montmorillonite, which was previously treated with a hydrochloric acid solution. Studies were carried out at two different concentrations, fixing the pH to ensure the charge of biomolecules and clay surface. Acid‐treated clay containing proteins was characterized by X‐ray diffraction, Fourier transformed infrared spectroscopy, thermogravimetric analysis, and nitrogen adsorption at 77 K. The powders showed similar thermal behavior after the inclusion of proteins but with variations in the amount of mass loss in each sample. Moreover, changes in the surface characteristics of the final solid were observed, depending on both the concentration and the nature of the incorporated protein. The differences observed in the acid‐treated clay characteristics after the inclusion of each type of protein are discussed. The characterization of materials after the inclusion of protein molecules can be useful to understand the adsorption mechanism of biomolecules on solid surfaces. Copyright © 2014 John Wiley & Sons, Ltd.     

W544F定点突变提高苏云金杆菌Cry1Ac蛋白的稳定性

W544是Cry1Ac蛋白上独特于其它Cry类蛋白的一个氨基酸, 它与F578和F604一起组成一个“螺旋桨状”的疏水簇, 通过疏水相互作用维持蛋白的三维结构稳定. 本研究通过定点突变将W544保守地替换为苯丙氨酸, SDS-PAGE分析结果表明其纯化的原毒素对紫外照射、胰蛋白酶处理和室温存贮的稳定性相对于野生Cry1Ac都有一定程度的提高; 经原子力显微镜观察, 发现W544F产生的晶体两个顶点间的垂直距离比野生型Cry1Ac约长0.6 μm, 且晶体表面不及野生型光滑; 此外, W544F与野生Cry1Ac的杀虫活性相似, 但经过紫外光照射9 h后, 其保留的杀虫活性比野生型高4倍以上. W544F突变较好地解决了Cry1Ac毒素蛋白田间应用不持久的问题, 具有重要的应用价值.     

Adsorption of benzene vapor on sodium and pyridinium montmorillonites

The adsorption properties of sodium and pyridinium montmorillonites are studied. It is shown that, in the temperature range 293–773 K, the limiting value of benzene adsorption on sodium montmorillonite slightly decreases and the specific surface area changes insignificantly, while these parameters for pyridinium montmorillonite increase by 1.3 and 1.6 times, respectively, within the interval 293–423 K. The dependences of the heat of adsorption on the amount of adsorbed benzene are determined from the isosteres of benzene adsorption and desorption on montmorillonite samples dehydrated at 373 K.     

Preparative Purification and Bioassay of Bt Toxin from Cry1Ab Transgenic Rice

IntroductionSince the first report of transgenic plants ap-peared in1 984[1] ,there has been a rapid progressdirecting toward using this new technique to im-prove crops. Protecting crops from insect pestsquickly became a major goal ofgenetic engineering.By far,the greatest research effort in developingpest- resistant transgenic crops has been devoted tothe expression of Bacillus thuringiensis( Bt) toxinin plants.The formulations based on bacterium Bacillusthuringiensis as a biopesticide for …     

An infrared study of adsorption of para-nitrophenol on mono-, di- and tri-alkyl surfactant intercalated organoclays

Infrared spectroscopy has been used to study the adsorption of para-nitrophenol on mono-, di- and tri-alkyl surfactant intercalated montmorillonite. Organoclays were obtained by the cationic exchange of mono-, di- and tri-alkyl chain surfactants for sodium ions [hexadecyltrimethylammonium bromide (HDTMAB), dimethyldioctadecylammonium bromide (DDOAB), methyltrioctadecylammonium bromide (MTOAB)] in an aqueous solution with Na-montmorillonite. Upon formation of the organoclay, the properties change from strongly hydrophilic to strongly hydrophobic. This change in surface properties is observed by a decrease in intensity of the OH stretching vibrations assigned to water in the cation hydration sphere of the montmorillonite. As the cation is replaced by the surfactant molecules, the para-nitrophenol replaces the surfactant molecules in the clay interlayer. Bands attributed to CH stretching and bending vibrations change for the surfactant intercalated montmorillonite. Strong changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane surface of the montmorillonite. Such a concept is supported by changes in the SiO stretching bands of the montmorillonite siloxane surface. This study demonstrates that para-nitrophenol will penetrate into the untreated clay interlayer and replace the intercalated surfactant in surfactant modified clay, resulting in the change of the arrangement of the intercalated surfactant.     

Influence of the intercalated cations on the surface energy of montmorillonites: consequences for the morphology and gas barrier properties of polyethylene/montmorillonites nanocomposites

Organically modified montmorillonites obtained by cation exchange from the same natural layered silicate were studied. The surface properties of the pristine and a series of organically modified clays were determined by inverse gas chromatography and the water adsorption mechanisms were studied by a gravimetric technique coupled with a microcalorimeter. A significant increase of the specific surface area, a decrease of the water adsorption, and a decrease of the dispersive component of the surface energy were observed when the sodium cations of the natural montmorillonite were exchanged for a quaternary ammonium. Slighter differences in surface properties were observed, on the other hand, between the different types of organically modified montmorillonites. Indeed, similar dispersive components of the surface energy were determined on the organoclays. Nevertheless, the specific surface area increased in the range 48-80 m(2)/g with increasing d-spacing values and the presence of specific groups attached to the quaternary ammonium, such as phenyl rings or hydroxyl groups, led to some specific behaviors, i.e., a more pronounced base character and a higher water adsorption at high activity, respectively. Differences in interlayer cation chain organization, denoted as crystallinity, were also observed as a function of the nature of the chains borne by the quaternary ammonium. In a later step, polyethylene-based nanocomposites were prepared with those organically modified montmorillonites. The clay dispersion and the barrier properties of the nanocomposites were discussed as a function of the montmorillonite characteristics and of the matrix/montmorillonite interactions expected from surface energy characterization.     

Montmorillonite intercalated with SiO2, SiO2-Al2O3 or SiO2-TiO2 pillars by surfactant-directed method as catalytic supports for DeNOx process

The intercalation of natural montmorillonite with SiO₂, SiO₂-Al₂O₃ or SiO₂-TiO₂ pillars by the surfactant-directed method resulted in the formation of high surface area porous materials; these were tested as catalytic supports for the process of selective catalytic reduction of NO (DeNOx). The incorporation of titanium or aluminium into the structure of the silica pillars significantly increased the surface acidity of the clay samples. Iron and copper were deposited onto the surface of the pillared clays mainly in the form of monomeric isolated cations and oligomeric metal oxide species. The contribution of the latter species was higher in the clay intercalated with SiO₂-TiO₂ pillars than in the samples modified with SiO₂ and SiO₂-Al₂O₃ pillars. The pillared clay-based catalysts were active in the DeNOx process but, in this group, the best results were obtained for the clay intercalated with SiO₂-TiO₂ pillars and doped with iron and copper. The catalytic performance of the samples is discussed in respect of their surface acidity and active forms of transition metal species deposited.