Influence of surfactants on the adsorption and elektrokinetic properties of the system: guar gum/manganese dioxide

The adsorption of non-ionic polysaccharide—guar gum (GG) in the presence or absence of the surfactants: anionic SDS, cationic CTAB, nonionic TX-100 and their equimolar mixtures SDS/TX-100, CTAB/TX-100 from the electrolyte solutions (NaCl, CaCl₂) on the manganese dioxide surface (MnO₂) was studied. The increase of GG adsorption amount in the presence of surfactants was observed in every measured system. This increase results from formation of complexes between the GG and the surfactant molecules. This observation was confirmed by the determination of the influence of GG on surfactants adsorption on the MnO₂ surface. The increase of GG adsorption on MnO₂ was the largest in the presence of the surfactant mixtures (CTAB/TX-100; SDS/TX-100) which is the evidence of the synergetic effect. The smallest amounts of adsorption were obtained in the presence of TX-100, which results from non-ionic character of this surface active agent. In the case of single surfactant solution CTAB has the best efficiency in increasing the amount of GG adsorption on MnO₂ which results from strong interactions with GG and also with the negatively charged surface of the adsorbent. In order to determine the electrokinetic properties of the system, the surface charge density of MnO₂ and the zeta potential measurements were performed in the presence of the GG macromolecules and the above mentioned surfactants and their mixtures. The obtained data showed that the adsorption of GG or GG/surfactants complexes on the manganese dioxide surface strongly influences the diffused part of the electrical double layer (EDL)—MnO₂/electrolyte solution, but has no influence on the compact part of the electric double layer. This is the evidence that the polymers chains are directly bonded with the surface of the solid and the surfactants molecules are present in the upper part of the EDL.     

Adsorption of a double-chain surfactant on an oxide

Adsorption of surfactants on solids is affected by the intermolecular packing in the adsorbed layer besides the driving forces. The adsorption behavior of a double-chain surfactant on silica is studied here along with that of the single-chain one. Comparison of adsorption of these two surfactants is warranted since while the single-chain surfactants form spherical micelles, the double-chain ones form bilayered vesicles in solution. While the adsorption of the single-chain surfactant reaches the plateau in a wide concentration range, the adsorption of the double-chain one increases sharply in a concentration range 10⁻⁵ mol/L up to the plateau. The single chain is found to form 1.5 monolayers under saturation coverage suggesting adsorption with reverse orientation at high concentration. In contrast, the adsorption of the double-chain surfactant under saturation coverage is equivalent to a 0.9 monolayer. Fluorescence tests revealed the hydrophobicity change of the surface with increase in adsorption. However, the hydrophobicity tests show the solid surface to be hydrophilic in this range; the double-chain surfactant is proposed to form a partial bilayer.     

CDG/表面活性剂二元体系性能研究

针对温度70℃、矿化度20794mg/L的油藏,开展了胶态分散凝胶(CDG)/表面活性剂二元体系研究。研究了超支化聚合物浓度、聚交比对新型CDG成胶性能影响,结果表明聚合物浓度为800mg/L、聚交比为20∶1的CDG体系具有较好的成胶性能;扫描电镜实验表明CDG呈胶态分散结构;TGU装置测定CDG的转变压力,聚合物浓度为800mg/L、聚交比为20∶1体系成胶后形成CDG转变压力为52.4KPa。将CDG与表面活性剂SA复配后形成CDG/表面活性剂二元体系,与CDG相比其粘度增大、界面张力降低。岩心驱油实验表明:超支化聚合物浓度为800mg/L CDG与0.2%表面活性剂复配的二元体系的提高采收率程度比CDG提高采收率程度高6.58%。     

Electronic structure and magnetic properties of small manganese oxide clusters

To investigate the electronic structure and magnetic properties of manganese oxide clusters, we carried out first-principles electronic structure calculations for small MnO clusters. Among various structural and magnetic configurations of the clusters, the bulklike [111]-antiferromagnetic ordering is found to be favored energetically, while the surface atoms of the clusters exhibit interesting electronic and magnetic characteristics which are different from their bulk ones. The distinct features of the surface atoms are mainly attributed to the reduction of Mn coordination numbers and the bond-length contractions in the clusters, which may serve as a key factor for the understanding of physical and chemical properties of magnetic oxide nanoparticles.     

Adsorption of protein/surfactant complexes at the air/aqueous interface

We use optical reflectometry and surface pressure techniques to measure co-adsorption of the anionic surfactant sodium dodecyl sulfate (SDS) and the protein lysozyme at the air-aqueous interface. We observe lysozyme/SDS co-adsorption behavior in two different buffers for which solution-phase binding data are available in the literature. The co-adsorption of lysozyme/SDS complexes is controlled by the mode of protein/surfactant binding that occurs in solution. In a pH 5.0 acetate buffer, the extent of co-adsorption is weakly dependent on SDS concentration throughout the specific and transitional binding regimes. In a pH 6.9 phosphate buffer, the extent of co-adsorption is weakly dependent on SDS concentration in the specific binding regime, but it increases dramatically, giving rise to multilayer co-adsorption, in the transitional binding regime. In both buffers, the extent of co-adsorption dramatically decreases in the cooperative binding regime. Lysozyme/SDS co-adsorption is strongly influenced by kinetically trapped non-equilibrium adsorbed layer states, such that adsorbed amounts are markedly path-dependent. Surface pressure measurements by themselves do not capture the variations in adsorption in the different binding regimes, nor do they capture the path-dependency of co-adsorption.     

Behavior of a styrene oxide-ethylene oxide diblock copolymer/surfactant system: a thermodynamic and spectroscopy study

Co-micellization of the diblock copolymer oxyphenylethylene/oxyethylene (S(17)E(65)) with the anionic surfactant sodium dodecyl sulfate (SDS) was investigated in aqueous solution using light scattering, transmission electron microscopy, isothermal titration calorimetry (ITC), and density measurements. Upon the addition of the surfactant, changes in the physicochemical properties of the micellized block copolymer take place due to interactions between the surfactant and the copolymer. Mixed micelles of copolymer and surfactant are formed and the size of the mixed aggregates changes in dependence of the amount of SDS. At a certain limiting concentration of SDS, only small rich-surfactant-copolymer aggregates and free surfactant micelles are observed in solution, as confirmed by the thermodynamic data obtained by ITC and transfer volumes. Thus, it seems that the presence of surfactant can be a tool to control the size and properties of block copolymer aggregates in solution.     

Adsorption properties of GaAs-CdS system

The adsorption properties of GaAs-CdS solid solutions and the constituent binary systems with respect to CO and NH₃ were studies by piezoquartz microweighing, temperature-programmed desorption, and IR spectroscopy. On the basis of an analysis of the measured α _p = f(T), α _T = f(p), and α _T = f(t) dependences, the thermodynamic and kinetic characteristics of adsorption, earlier obtained acid-base and other physicochemical characteristics of adsorbents, and the electronic properties of the adsorbate molecules, the mechanism and regularities of the adsorption processes at various conditions and compositions of the system were established. A comparison of the adsorption properties of the GaAs and CdS individual binary compounds with their (GaAs)_x(CdS)_1?x solutions, multicomponent systems, revealed common and distinctive features. Optimal compositions of adsorbents suitable for manufacturing primary transducers in sensors for medical and environmental purposes were determined.     

Facile synthesis and characterization of copper oxalate/cobalt oxalate/manganese oxalate and copper oxide/cobalt manganese oxide/manganese oxide as new nanocomposites for efficient photocatalytic degradation of malachite green dye

Scientists seek to synthesize new catalysts with simple methods to treat water pollution from organic dyes using photocatalytic degradation technology. In this technology, when light falls on the catalyst, the produced hydroxyl free radicals convert the dye into non-toxic gases such as CO₂ and H₂O. So, in this work, copper oxalate/cobalt oxalate/manganese oxalate (Abbreviated as P₁) and copper oxide/cobalt manganese oxide/manganese oxide (Abbreviated as P₂) new nanocomposites were fabricated via precipitation of Cu²⁺/Co²⁺/Mn²⁺ solution using oxalic acid and ignition of precipitate at 550 °C for 4 hrs, respectively. Some tools, involving X-ray diffraction (XRD), UV–vis spectrophotometer, energy dispersive X-ray spectroscopy (EDX), nitrogen gas sorption analyzer, transmission electron microscope (TEM), and field emission scanning electron microscope (FE-SEM), were used for characterizing the fabricated nanocomposites. The EDX spectra confirmed that the P₁ composite consist of C (26.28 %), oxygen (46.66 %), manganese (7.27 %), cobalt (7.59 %), and copper (12.20 %). Also, the P₂ composite consist of oxygen (8.23 %), manganese (31.34 %), cobalt (27.19 %), and copper (33.24 %). A transmission electron microscope shows that the P₁ and P₂ composites consist of polyhedral and spherical shapes with an average diameter of 28.13 and 14.37 nm, respectively. The BET surface area, average pore size, and total pore volume of the P₁ composite are 29.0725 m²/g, 2.0749 nm, and 0.0302 cc/g, respectively. Besides, the BET surface area, average pore size, and total pore volume of the P₂ composite are 58.1088 m²/g, 1.6087 nm, 0.0467 cc/g, respectively. 60 mg of the synthesized nanocomposites completely decompose 60 mL of 15 mg/L of malachite green dye solution within 20 min in the presence of hydrogen peroxide and UV light. The synthesized catalysts outperformed many other catalysts published in previous studies.     

Gaseous adsorption properties of a silica-pillared layered manganese oxide

Adsorptions of N(2), H(2)O, and organic vapors including CH(2)Cl(2), CCl(4), c-C(6)H(12), C(6)H(6), n-C(6)H(14), and n-C(9)H(20) on a silica-pillared layered manganese oxide (SiHMnO) and nonane-preadsorbed SiHMnO were examined. It is found that SiHMnO has a microporosity with a wide pore width distribution showing different pore wall affinities. Micropores with smaller width preferentially accommodate the nonane preadsorbate while the surface hydrophilicity of pore wall leads to an easier detachment of the adsorbed nonane molecules. H(2)O adsorption influences both the porosity and the surface properties by accelerating a sufficient hydrolysis of the remained TEOS molecules in SiHMnO. Examinations using Dubinin-Radeshkevich (DR) equation and isosteric heat of adsorption of organic molecules provide evidences that the wall surface of micropores with smaller and larger width have less affinity toward nonpolar and polar organic vapors, respectively.     

Adsorption characteristics of uranyl ions by manganese oxide coated sand in batch mode

In this paper, the sorption properties of manganese oxide coated sand (MOCS) towards uranium(VI) from aqueous solutions were studied in a batch adsorption system. Scanning electron microscope (SEM) and infrared (IR) analyses were used to characterize MOCS. Parameters affecting the adsorption of uranium(VI), such as the contact time, salt concentration, competitive ions, temperature and initial uranium(VI) concentration, were investigated. The equilibrium adsorption data were analyzed by Langmuir, Freundlich and Redlich–Peterson models using nonlinear regressive analysis. The results indicated that the Langmuir and Redlich–Peterson models provided the best correlation of experimental data. The kinetic experimental data were analyzed using three kinetic equations including pseudo-first order equation, pseudo-second order equation and intraparticle diffusion model to examine the mechanism of adsorption and potential rate-controlling step. The process mechanism was found to be complex, consisting of both surface adsorption and pore diffusion. The effective diffusion parameter D _i values estimated in the order of 10⁻⁷ cm² s⁻¹ indicated that the intraparticle diffusion was not the rate-controlling step. Thermodynamic study showed that the adsorption was a spontaneous, endothermic process. Adsorbed U(VI) ions were desorbed effectively (about 94.7%) by 0.1 mol L⁻¹ HNO₃. The results indicated that MOCS can be used as an effective adsorbent for the treatment of industrial wastewaters contaminated with U(VI) ions.     

氧化锰团簇粒子在有序多孔氧化锆孔道中的组装及其特殊性能研究

利用醇溶液浸渍法及后续的热处理工艺成功实现了氧化锰团簇粒子在有序多孔氧化锆孔道中的组装，借助XRD，TEM，UV-vis，EPR以及O~2-TPD等分析手段进行样品结构表征及性能分析。研究表明，氧化锰团簇粒子能比较均匀地分散于规则的孔道中；团簇粒子的生长随着热处理温度的提高受到孔道大小的限制；孔道中的氧化锰团簇粒子能显示出与较大尺寸氧化锰粒子完全不同的强顺磁信号，并且还具有优异的表面氧吸附特性。     

Competitive adsorption in the system: carboxymethylcellulose/surfactant/electrolyte/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The adsorption of carboxymethylcellulose (CMC) in the presence or absence of the surfactants: anionic SDS, nonionic Triton X-100 and their mixture SDS/TX-100 from the electrolyte solutions (NaCl, CaCl₂) on the alumina surface (Al₂O₃) was studied. In each measured system the increase of CMC adsorption in the presence of surfactants was observed. This increase was the smallest in the presence of SDS, a bit larger in the presence of Triton X-100 and the largest when the mixture of SDS/Triton X-100 was used. These results are a consequence of formation of complexes between the CMC and the surfactant particles. Moreover, the dependence between the amount of surfactants’ adsorption and the CMC initial concentration was measured. It comes out that the surfactants’ adsorption amount is not dependent on the CMC initial concentration and moreover, it is unchanged in the whole measured concentration range. The influence of kind of electrolyte, its ionic strength as well as pH of a solution on the amount of the CMC adsorption at alumina surface was also measured. The amount of CMC adsorption is larger in the presence of NaCl than in the presence of CaCl₂ as the background electrolyte. It is a result of the complexation reaction between Ca²⁺ ions and the functional groups of CMC belonging to the same macromolecule. As far as the electrolyte ionic strength is concerned the increase of CMC adsorption amount accompanying the increase of electrolyte ionic strength is observed. The reason for that is the ability of electrolyte cations to screen every electrostatic repulsion in the adsorption system. Another observation is that the increase of pH caused the decrease of CMC adsorption. The explanation of this phenomenon is connected with the influence of pH on both dissociation degree of polyelectrolyte and kind and concentration of surface active groups of the adsorbent.     

Adsorption and desorption of polymer/surfactant mixtures at solid-liquid interfaces: substitution experiments

The adsorption of mixtures of aqueous solutions of cationic hydroxyethylcellulose polymer JR400 and anionic surfactant, sodium dodecyl sulfate, using atomic force microscopy (AFM) has been studied. Samples with various compositions from different regions of the ternary phase diagram presented in our previous work were imaged by atomic force microscopy on freshly cleaved mica, and hydrophobically modified mica and silica in soft-contact mode. A series of "washing" (subsequent injection of compositions with gradually decreasing polymer/surfactant ratio) and "scratching" (mechanical agitation of the surface material with an AFM tip) experiments were performed. It was revealed that the morphology of the adsorbed layer altered in a manner following the changes in morphology in the bulk solution. These changes were evidenced in cluster formation in the layer. The results suggest that the influence of the surface was limited to the formation of the adsorbed layer where the local concentrations of polymer and surfactant were higher than those in the bulk. All further modifications were driven by changes in the mixture composition in bulk. Force measurements upon retraction reveal the formation of network structures within the surface aggregates that will greatly slow structural reequilibration.     

Adsorption behavior of hydrophobin and hydrophobin/surfactant mixtures at the solid-solution interface

The adsorption of surface-active protein hydrophobin, HFBII, and HFBII/surfactant mixtures at the solid-solution interface has been studied by neutron reflectivity, NR. At the hydrophilic silicon surface, HFBII adsorbs reversibly in the form of a bilayer at the interface. HFBII adsorption dominates the coadsorption of HFBII with cationic and anionic surfactants hexadecyltrimethyl ammonium bromide, CTAB, and sodium dodecyl sulfate, SDS, at concentrations below the critical micellar concentration, cmc, of conventional cosurfactants. For surfactant concentrations above the cmc, HFBII/surfactant solution complex formation dominates and there is little HFBII adsorption. Above the cmc, CTAB replaces HFBII at the interface, but for SDS, there is no affinity for the anionic silicon surface hence there is no resultant adsorption. HFBII adsorbs onto a hydrophobic surface (established by an octadecyl trimethyl silane, OTS, layer on silicon) irreversibly as a monolayer, similar to what is observed at the air-water interface but with a different orientation at the interface. Below the cmc, SDS and CTAB have little impact upon the adsorbed layer of HFBII. For concentrations above the cmc, conventional surfactants (CTAB and SDS) displace most of the HFBII at the interface. For nonionic surfactant C(12)E(6), the pattern of adsorption is slightly different, and although some coadsorption at the interface takes place, C(12)E(6) has little impact on the HFBII adsorption.     

Adsorption behavior of hydrophobin and hydrophobin/surfactant mixtures at the air-water interface

The adsorption of the surface-active protein hydrophobin, HFBII, and the competitive adsorption of HFBII with the cationic, anionic, and nonionic surfactants hexadecyltrimethylammonium bromide, CTAB, sodium dodecyl sulfate, SDS, and hexaethylene monododecyl ether, C(12)E(6), has been studied using neutron reflectivity, NR. HFBII adsorbs strongly at the air-water interface to form a dense monolayer ～30 ? thick, with a mean area per molecule of ～400 ?(2) and a volume fraction of ～0.7, for concentrations greater than 0.01 g/L, and the adsorption is independent of the solution pH. In competition with the conventional surfactants CTAB, SDS, and C(12)E(6) at pH 7, the HFBII adsorption totally dominates the surface for surfactant concentrations less than the critical micellar concentration, cmc. Above the cmc of the conventional surfactants, HFBII is displaced by the surfactant (CTAB, SDS, or C(12)E(6)). For C(12)E(6) this displacement is only partial, and some HFBII remains at the surface for concentrations greater than the C(12)E(6) cmc. At low pH (pH 3) the patterns of adsorption for HFBII/SDS and HFBII/C(12)E(6) are different. At concentrations just below the surfactant cmc there is now mixed HFBII/surfactant adsorption for both SDS and C(12)E(6). For the HFBII/SDS mixture the structure of the adsorbed layer is more complex in the region immediately below the SDS cmc, resulting from the HFBII/SDS complex formation at the interface.     

Adsorption properties of CdS-CdTe system semiconductors

The adsorption of carbon(II) oxide and ammonia on nanofilms of solid solutions and binary compounds of the CdS-CdTe system is studied by means of piezoquartz microweighing, FTIR IR, and measuring electroconductivity. Allowing for the conditions and composition of semiconductor systems, we determine the mechanisms and principles of adsorption processes by analyzing the α _p = f(T), α _T = f(p), and α _T = f(t) experimental dependences; IR spectra; the thermodynamic and kinetic characteristics of adsorption; the acid-base, electrophysical, and other characteristics of adsorbents; the electron nature of adsorbate molecules; and the obtained acid-base characteristics: the composition and adsorption characteristics and composition state diagrams. Previous statements on the nature and retention of local active centers responsible for adsorption and catalytic processes upon changes in their habitus and composition (as components of systems of the A^IIIB^V-A^IIB^VI and A^IIB^VI-A^IIB^VI types) on the surface of diamond-like semiconductors are confirmed. Specific features of the behavior of (CdS) _x (CdTe)_{1 ? x} solid solutions are identified in addition to general features with binary compounds (CdS, CdTe), as is demonstrated by the presence of critical points on acid-base characteristics-composition and adsorption characteristics-composition diagrams. On the basis of these diagrams, the most active adsorbents (with respect to CO and NH₃) used in designing highly sensitive and selective sensors are identified.     

Rapid evaluation of charge/discharge properties for lithium manganese oxide particles at elevated temperatures

A microelectrode technique was applied to investigate the electrochemical properties of LiMn₂O₄ particles at elevated temperatures. Cyclic voltammograms of LiMn₂O₄ were measured after the particles were exposed to the electrolytes. This technique results in rapid and precise evaluation of the redox behavior of the materials. A significant capacity fading was observed in 1 M LiPF₆/EC+PC electrolytic solution, which indicates that both LiMn₂O₄ and LiPF₆ participate in the reaction to produce an inert material on the particle surface. Next, the capacity fading for two different BET surface area particles were compared using 1 M LiPF₆/EC+PC at 50 °C. The reaction was found not to be controlled by the surface area. Finally, a Li_1.1Mn_1.9O₄ particle was employed. The fading in discharge was ca. 10% for 50 cycles even at 50 °C, which means that the partial substitution of Mn in LiMn₂O₄ by Li substantially enhanced the capacity stability. Electronic Publication     

E-beam radiation synthesis of xanthan-gum/carboxymethylcellulose superabsorbent hydrogels with incorporated graphene oxide

In this study the electron beam (e-beam) radiation synthesis in “paste-like condition” and characterization of the network structure of acrylic acid (AA) sodium salt/xanthan gum (XG)/carboxymethylcellulose (CMC) superabsorbent hydrogels incorporating graphene oxide (GO) was investigated. The effects of the AA concentration on gel fraction, sol-gel analysis, swelling degree and network parameters, as well as the relationship between these parameters and radiation dose was also established.

Gel fraction exceeds 90%, and the p₀/q₀ ratio shows a moderate degradation process. The swelling kinetic data were used to determine, first the swelling degree, second the diffusion characteristics, and third the average molecular weight between crosslinks (Mc), as well as. The diffusion data revealed a Fickian mechanism transport, for each hydrogel compositions. The network parameters (Mc and ξ) increased with absorbed dose, while cross-linking density and the radiation-chemical yields were decreased.     

Adsorption properties of Ni-Pd catalysts supported on aluminum oxide

The surface composition of Ni-Pd/Al₂O₃ catalysts has been studied using XPES and adsorption methods. The bimetallic catalysts differ from the single-metal Ni and Pd catalysts in the dispersivity of the metal phase which depends on the method of preparation and the presence of K⁺ promoter. A catalyst produced by the immersion method is strongly enriched in Pd compared with impregnated catalysts.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1746–1751, August, 1991.