Tailoring the porous texture of activated carbons by CO<Subscript>2</Subscript> reactivation to produce electrodes for organic electrolyte-based EDLCs

Highly microporous carbon obtained by KOH etching of carbohydrates exhibited enhanced specific capacitance due to the increased adsorption of electrolyte ions on its large surface, which renders it a promising electrode material. However, the KOH-activated carbon electrode did not achieve its optimum charge capacity in organic electrolytes due to the limited accessibility of the electrolyte ions to the micropores, which hindered the adsorption of ions. The electrode performance was enhanced by enlarging the micropores of KOH-activated carbon to mesopores via reactivation in a stream of CO₂, which allowed the mesopore/micropore ratio to be increased without compromising the originally high specific surface area. The extended amount of mesopores increased the charge capacity of the electrode by enabling the large organic electrolyte ions to access the porous surface, as compared to untreated KOH-activated carbon.     

对氨基苯甲酸分子在银表面多相吸附及氯离子影响的SERS研究

研究对氨基苯甲酸(PABA)在银表面上的吸附动力学过程以及氯离子对其的影响,发现PABA在银表面上呈多相吸附。与匀相吸附的情况相似,表面形态的差异较大地改变吸附速率常数,而对多相因子的影响不明显。氯离子的竞争吸附改变PABA吸附的多相性质,随着氯离子浓度的增加,PABA分子从多相吸附逐渐转变为匀相吸附。根据吸附等温线估算了PABA的吸附能,U≈-9.6kJ/mol。结果分析进一步证实:化学吸附时多相吸附意味着表面上存在非单一的吸附形式。 关键词：     

Functionalized SBA-15 organosilicas as sorbents of zinc(II) ions

SBA-15 nanoporous silicas functionalized with amine-, thiol-, vinyl-, phenyl- and cyano surface groups were synthesized by using the amphiphilic block copolymer P123 as the structure-directing agent. The obtained materials have a well-developed porous structure - the values of specific surface area are in the range 800-950 m²/g and the sizes of cylindrical mesopores are in the range 7.4-8.6 nm. It was established that the size of the mesopores strongly depends even on small amounts of co-monomers co-condensing with TEOS. Adsorption of Zn(II) ions at the SBA-15/NaCl interface was investigated by means of the radioactive isotope tracer technique over the pH range of 3-11. Surface charge density, adsorption density, pH_50% and ΔpH_10-90% parameters for different concentrations of the carrying electrolyte were evaluated and discussed.     

Novel surface tension isotherm for surfactants based on local density functional theory

In this Letter we report a new general method for calculating of surface tension isotherms in the presence of surfactants, based on a local density functional. We illustrate this method by deriving the interfacial tension isotherm for nonionic surfactants at an air-water or oil-water interface by using the self-consistent field theory of polymer brushes. We consider a particular case of local density functional to calculate explicitly how the interfacial tension and the surfactant adsorption depend on the surfactant bulk concentration. Experimental data for the surface tension and the surfactant adsorption isotherm for nonionic surfactants were interpreted with the help of the new isotherm. Very good agreement between the adsorption of n-dodecyl pentaoxyethylene glycol ether (C12E5) at an air-water interface, calculated from the surface tension isotherm and small-angle neutron-scattering is obtained.     

Passivation at semiconductor/electrolyte interface: Role of adsorbate solvation and reactivity in surface atomic and electronic structure modification of III-V semiconductor

These studies are focused on understanding the role played by a solvent in chemical and electronic processes occurred in the course of semiconductor surface passivation at semiconductor/electrolyte interface. It is shown that the chemical reactivity of the ionic adsorbate at a semiconductor/electrolyte interface can be changed considerably through interaction with solvent molecules. The reactivity of anions depends essentially on the solvating solvent: hydrated ions could be either slightly electrophilic or slightly nucleophilic, whereas the ions solvated by alcohol molecules are always strongly nucleophilic. Mechanism of interaction of such solvated ions with the semiconductor surface atoms depends on the solvent, as is demonstrated by the example of processes occurred at GaAs(1 0 0)/sulfide solution interfaces. It is found that on adsorption of HS⁻ ions from different solvents the AsS bonds with solvent-dependent ionic character are formed on a GaAs(1 0 0) surface. The surface obtained in such a way possesses different ionization energy and exhibit different electronic properties dependent on the solvent.     

电解质浓度对胶体粒子表面有效电荷的影响

胶体粒子的表面有效电荷是决定胶体性质的重要物理量,但溶液环境(如电解质溶液浓度)是否影响其数值至今尚无统一认识,近年来的一些研究工作给出了存在争议的不同结果和假设.在直接实验测量方面,由于电解质离子和胶体表面吸附离子的置换,粒子表面基团的不完全电离和胶体粒子对离子吸附的共同作用,使得对这类粒子在不同溶液环境下的表面有效电荷的测量和变化机理的认识极为困难.针对该问题,本文测定了羧基和磺酸基修饰的聚苯乙烯胶体颗粒在不同粒子浓度和HCl浓度下的电导率,由于两种粒子与HCl电离产生的阳离子相同(均为H+),可根据电导率-数密度法(迁移法)得到胶体颗粒表面有效电荷数.通过实验结果分析,明确了HCl浓度以及粒子数密度对胶体粒子表面电荷的影响规律以及表面电荷随HCl浓度增大的原因.除此之外,羧基修饰颗粒比磺酸基修饰颗粒的表面电荷随HCl浓度变化更快;对于同一HCl浓度,磺酸基修饰胶体表面电荷不受粒子数密度影响,而羧基修饰胶体颗粒却与之相关.基于粒子表面电荷的理论模型,对这些问题都给出了相应的解释.     

Generalized Poisson-Boltzmann Equation Taking into Account Ionic Interaction and Steric Effects

Generalized Poisson-Boltzmann equation which takes into account both ionic interaction in bulk solution and steric effects of adsorbed ions has been suggested.We found that,for inorganic cations adsorption on negatively charged surface,the steric effect is not significant for surface charge density 0.0032 Cdm 2,while the ionic interaction is an important effect for electrolyte concentration 0.15 moll in bulk solution.We conclude that for most actual cases the original PB equation can give reliable result in describing inorganic cation adsorption.     

Adsorption of propylene carbonate on the Li Mn_2O_4 (100) surface investigated by DFT+U calculations

Understanding the mechanism of the interfacial reaction between the cathode material and the electrolyte is a significant work because the interfacial reaction is an important factor affecting the stability,capacity,and cycling performance of Li-ion batteries.In this work,spin-polarized density functional theory calculations with on-site Coulomb energy have been employed to study the adsorption of electrolyte components propylene carbonate(PC)on the LiMn2O4(100)surface.The findings show that the PC molecule prefers to interact with the Mn atom on the LiMn2O4(100)surface via the carbonyl oxygen(Oc),with the adsorption energy of?1.16 eV,which is an exothermic reaction.As the adsorption of organic molecule PC increases the Mn atoms coordination with O atoms on the(100)surface,the Mn3+ions on the surface lose charge and the reactivity is substantially decreased,which improves the stability of the surface and benefits the cycling performance.     

Influence of oxygen adsorption on the surface potential of a metal oxide semiconductor

Analytical expressions describing dependences of the surface density of adsorbed oxygen ions and energy band bending in the subsurface region of a metal oxide semiconductor on the oxygen concentration that consider not only the process of neutral gas particle adsorption, but also their charge transfer at the expense of electron capture from the conduction band are presented. It is demonstrated that the heat of oxygen ion absorption is equal to the sum of the heat of neutral particle adsorption and the energy gap between the Fermi level and the level of the oxygen ion on the semiconductor surface. When the adsorption equilibrium is established, an analytical expression describing the time dependence of the energy band bending can be obtained only for small change of the oxygen concentration in the gas mixture.     

The role of polarization of Xe by di- and monovalent cations in Xe NMR studies in zeolite A

We consider the role of polarization in the adsorption of Xe in zeolites of type A by direct comparative analysis of the adsorption isotherms, distributions of occupancies, and ¹²⁹Xe NMR chemical shifts of Xe_n in cages containing Ca_xNa_{12 −2x} ions per alpha cage (x = 0, 1, 2, 3, 5). We find that the qualitative trends in the adsorption isotherms, and in the progressions of Xe_n chemical shifts (for n = 0–8 in cages with x = 0, 1 Ca²⁺ ions and for n = 0–5 in cages with x = 2, 3 Ca²⁺ ions) upon increasing the level of Ca²⁺ ion for Na⁺ ion substitution could only be accounted for by including polarization of the Xe atom by the zeolite framework and its ions. This system, which permits observation of individual Xe_n peaks and of directly comparable adsorption isotherms in several cage types, provides a good model system for the interpretation of the more general case in which only the overall average ¹²⁹Xe NMR chemical shift is observed in open network zeolites, arising from free exchange of Xe among cavities of variable occupancy and variable cation distribution.     

The lithiation studies of nanostructured tungsten oxide film prepared via electrochemical precipitation

In this work, nanostructured tungsten oxide was electrodeposited by cyclic voltammetric technique onto a stainless steel surface. The structure and surface morphology of the resulting oxide film were characterized by means of X-ray diffraction, scanning probe microscopy, and scanning electron microscopy. The electrochemical intercalation of lithium into the nanostructured tungsten oxide was studied using cyclic voltammetry, galvanostatic charge–discharge curves, and electrochemical impedance spectroscopy in a liquid electrolyte consisting of 1 M LiClO₄ in propylene carbonate. The as-deposited tungsten oxide indicated the capacity for electrochemical lithium insertion. The specific capacitance of 108.05 F?g^?1 was obtained at the constant discharge density of 0.07 mA?cm^?2.     

Interactions of water,methanol and diethyl ether molecules with the surface of oxidized activated carbon

Two samples of oxidized activated carbon of wood origin were used as adsorbents of water, methanol, and diethyl ether. Structural and chemical characteristics of the samples' surfaces were obtained using adsorption of nitrogen and Boehm titration. The adsorption isotherms of water and methanol were measured using a volumetric apparatus whereas the adsorption of diethyl ether was studied by means of inverse gas chromatography at finite concentration. Then the isotherms at three different temperatures were used to calculate the isosteric heats of adsorption. The results showed that the strength of interaction depends on the porosity of the sample and its surface chemistry. The effect of surface chemistry and the presence of oxygenated groups are predominant in the case of water and the least important in the case of diethyl ether. This is the result of the chemical nature of the molecules, their sizes, and the relative strengths of the dispersive interactions in small pores in comparison with hydrogen bonding to surface functional groups.     

Generalized Poisson-Boltzmann Equation Taking into Account Ionic Interaction and Steric Effects

Generalized Poisson-Boltzmann equation which takes into account both ionic interaction in bulk solution and steric effects of adsorbed ions has been suggested. We found that, for inorganic cations adsorption on negatively charged surface, the steric effect is not significant for surface charge density <0.0032 C/dm², while the ionic interaction is an important effect for electrolyte concentration >0.15 mol/l in bulk solution. We conclude that for most actual cases the original PB equation can give reliable result in describing inorganic cation adsorption.     

Rigid rod adsorption including long-range dispersion interactions

The Caillé-Ågren analysis of rigid rod adsorption is extended by applying the van Kampen theory of condensation to include long-range dispersion interactions between the adsorbed rods. We discuss in greater detail the characteristics of the phase transition predicted by Caillé and Ågren between states having an isotropic and anisotropic distribution of rods adsorbed parallel to the surface. The maximum density range over which the anisotropic adsorbed phase is stable is determined as a function of the length-to-breadth ratio x of the rigid rods and the strength of the anisotropic dispersion energy. Critical surface adhesion and anisotropic dispersion energies necessary for anisotropic adsorption are also obtained as a function of x. In agreement with Caillé and Ågren the isotropic-anisotropic transition for rigid rod adsorption with attractive forces present is found to be second order. We also discuss the spreading pressure-density or area per molecule isotherms obtained for adsorbed rods having various values of x and surface adhesion and dispersion energies. Whenever feasible we compare our results with the spreading pressure isotherms obtained for monolayers of lyotropic molecules on either aqueous or mercury subphases and obtain qualitative agreement. In particular, the critical density and pressure associated with the two dimensional adsorbed gas-liquid condensation for rigid rods with x = 10 gives reasonable agreement with the critical constants observed by Hawkins and Benedek and Kim and Cannell for the corresponding condensation of pentadecanoic acid monolayers on neutral and acidified aqueous subphases. This agreement suggests that considerable dimerization of the pentadecanoic acid molecules may occur on aqueous surfaces.     

Adsorption of Al on the Si(0 0 1) surface

The first-principles calculations have been presented to study the adsorption of aluminum (Al) on the Si(0 0 1)(2×1) surface. We have investigated the optimized geometries and electronic structures of the adatom-substrate system. The adsorption energy of the system has been calculated. The most stable adsorption sites were consequently determined to be HH site and T3+T4. It is shown that the Si-Si dimer is asymmetric on the reconstructed bare surface and become symmetric upon Al adsorption. In addition, the bond length of Si-Si was found to be considerably elongated in the adsorption system. It is found that the work function change obtained in our work is different from other previous results on the adsorption of alkali metals on the Si(0 0 1) surface. In order to investigate the relative stability of phases at different coverages, the surface formation energy of the adsorption system was calculated. To shed light on the nature of the Al-Si bond and the character of silicon surface, the density of states (DOS) and difference charge density of the system were evaluated.     

基于TaCl5的Ta2O2气凝胶制备工艺

 主要介绍了以TaCl₅为前驱体,低分子醇类为溶剂,分别采用环氧丙烷和环氧氯丙烷作为凝胶促进剂制备Ta₂O₂湿凝胶,湿凝胶经过CO₂超临界干燥而获得白色Ta₂O₂气凝胶。透射电镜图谱表明气凝胶是由粒度为10～20 nm的颗粒堆积而成。N₂等温吸附-脱附分析表明,气凝胶的比表面积为800～900 m²/g。     

Hydrothermal synthesis of graphene oxide/multiwalled carbon nanotube/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> ternary nanocomposite for removal of Cu (II) and methylene blue

In this work, highly activated graphene oxide/multiwalled carbon nanotube/Fe₃O₄ ternary nanocomposite adsorbent was prepared from a simple hydrothermal route by using ferrous sulfate as precursor. For this purpose, the graphene oxide/multiwalled carbon nanotube architectures were formed through the π-π attractions between them, followed by attaching Fe₃O₄ nanoparticles onto their surface. The structure and composition of as-prepared ternary nanocomposite were characterized by XRD, FTIR, XPS, SEM, TEM, Raman, TGA, and BET. It was found that the resultant porous graphene oxide/multiwalled carbon nanotube/Fe₃O₄ ternary nanocomposite with large surface area could effectively prevent the π-π stacking interactions between graphene oxide nanosheets and greatly improve sorption sites on the surfaces. Thus, owing to the unique ternary nanocomposite architecture and synergistic effect among various components, as-prepared ternary nanocomposite exhibited high separation efficiency when they were used to remove the Cu (II) and methylene blue from aqueous solutions. Furthermore, the adsorption isotherms of ternary nanocomposite structures for Cu (II) and methylene blue removal fitted the Langmuir isotherm model. This work demonstrated that the graphene oxide/multiwalled carbon nanotube/Fe₃O₄ ternary nanocomposite was promising as an efficient adsorbent for heavy metal ions and organic dye removal from wastewater in low concentration.     

Ion transport and battery discharge characteristics of polymer electrolyte based on PEO complexed with NaFeF4 salt

Ion-conducting solvent-free solid polymer electrolytes based on polyethylene oxide (PEO) complexed with sodium ferric tetrafluoride (NaFeF₄) were prepared using a solution casting technique. The complexation of the films was investigated through X-ray diffraction and Fourier transform infrared spectroscopic studies. Measurements of DC conductivity in the temperature range 300–370 K and the transference numbers were carried out to investigate the nature of charge transport in the polymer electrolyte system. Transference number data shows that the charge transport in this system is found to be predominantly due to ions. Using these polymer electrolytes, electrochemical cells were fabricated with the configuration of Na/(PEO+NaFeF₄)/(I₂+C+electrolyte). Various cell parameters, such as open circuit voltage, short circuit current, power density, and energy density of the device were evaluated and reported.     

水合金属氧化物对氟的吸附机理研究

通过碱沉淀法制备了Ce,Al,Ni,Cu的水合氧化物,研究了它们的Langmuir吸附等温线,并利用BET法通过吸附-脱附氮气测定了其比表面积,同时对其吸附氟离子前后的变化进行了IR谱图的表征.结果表明不同水合金属氧化物具有不同的比表面积,其孔径分布也不尽相同,吸附量与比表面积之间没有直接相关的正比关系.吸附等温线均符...