Chemical Properties Of Solid Surfaces Research Articles

Molecular insights into the microstructure of ethanol/water binary mixtures confined within typical 2D nanoslits: The role of the adsorbed layers induced by different solid surfaces

With the emergence of membrane separation and heterogeneous catalysis applications that are associated with confined ethanol/water binary mixture in the pores of two-dimensional (2D) nanomaterials, understanding their confined microstructures is the first step for further relevant applications. In this work, molecular dynamics was performed to investigate the microstructure of ethanol/water binary mixture of 5% mole fraction confined within the four typical 2-nm width 2D-nanoslits (i.e. hBN, GO-0.2, GO-0.4 and Ti3C2(OH)2). Results demonstrated that different chemical properties of solid surfaces can induce distinctive microstructures of mixed fluid within the interfacial contact (adsorbed) layer and thus can result in different mobility of water molecules within the subcontact layer. The residence times of water molecules in the subcontact layer were found in the sequence of Ti3C2(OH)2 > hBN > GO-0.4 > GO-0.2, whereas their sequence of diffusion coefficient within the x-z plane was Ti3C2(OH)2 > hBN > GO-0.2 > GO-0.4. Detailed hydrogen bond (HB) microstructure analysis showed that a high average number of HBs (between fluid molecules of the interfacial contact layer and water molecules of the subcontact layer) induced by solid surfaces could facilitate water molecules to reside in the subcontact layer. Moreover, the small average number of HBs between the water molecules themselves in the subcontact layer could lead to high in-plane diffusion coefficients.

Model studies in heterogeneous catalysis at the microscopic level: from the structure and composition of surfaces to reaction kinetics

Heterogeneous catalysis is one of the fields of modern technology, in which a characterization of structural and chemical properties of solid surfaces at the microscopic level is of enormous importance. For a long time, such insights have been precluded by the complexity of most catalytically active materials. Recently, substantial progress has been made, however, toward a microscopic-level understanding of complex catalyst surfaces. We discuss the driving factors for these advancements, which are based on the development of new well-defined model systems as well as on advances in experimental technology and theory. Scrutinizing the example of planar model catalysts, we identify the process of linking structural and chemical information to microscopic reaction kinetics as a particular challenging aspect of today’s work. We review the kinetic effects which may have an influence on the reaction kinetics on complex surfaces. As an example how structural and kinetic information can be correlated at the microscopic level we discuss the case of surface oxidation and oxygen induced restructuring of Pd nanoparticles as studied by molecular beam methods.

Characterization of the surfaces of treated glass fibres with different methods of investigation

In the present work four different methods of investigation were used to characterize the surfaces of treated glass fibres. The capillary rise technique and the inverse gas chromatography (IGC) are methods to determine the surface free energy of solids. The zeta potential measurement gives information about the chemical properties of solid surfaces. In addition, the coating homogenity was investigated by field-emission scanning electron microscopy (FE-SEM). Glass fibres with four different treatments were used in this work: polyethylene-(PE)-dispersion treated fibres, polyurethane/aminosilane-dispersion treated fibres, fibres treated with an epoxy resin/ aminosilane-dispersion and fibres with a cationic silane treatment. FE-SEM has shown that the surfaces of the glass fibres were completely covered by the polyethylene and the cationic silane. The polyurethane and the epoxy-resin covered only a part of the glass fibre surface. A statement about the distribution of the aminosilane cannot be made, because the thickness of the monolayer is less than the resolution of the FE-SEM. Zeta potential, IGC and capillary rise technique measurements lead to comparable results about the different chemical properties of the glass fibres.

Effects of Pressure on the Chemical Properties of Solid Surfaces. VII. Surface Basicities of Some Compressed Carbonates and Related Compounds

Abstract In order to investigate the effect of the compacting pressure on the surface basicities of solids, experiments were carried out by employing various carbonates, hydroxides, and oxides of alkali metals and alkaline earth metals as samples. That is, compacting pressures ranging from 0 to 15000 kg/cm2 were applied to these samples, and the changes in the surface basicities were observed using an indicator method. It was observed that the surface basicities of various solid vary on compression. Further, the respective basicity change in cadmium carbonate, calcite, and aragonite could be explained by the change in the surface area of each of these samples. On the other hand, the basicity changes of both strontium carbonate and barium carbonate could be explained thus only with difficulty. From the results of the X-ray-diffraction study and the electron-diffraction study, the changes in the crystal structures of these samples were suspected of causing the basicity changes due to compressions. According to the results of infrared spectroscopic studies, changes in the symmetry around carbonate ions in the sample crystals were considered to be the cause of the basicity changes in strontium cabonate and barium carbonate.

Effects of Pressure on the Chemical Properties of Solid Surface. VI. The Surface Acidity of the Compressed Zinc Sulfate

Abstract In order to clarify the mechanism of the acidity change due to compression, zinc sulfate was compressed under various pressures, ranging from 0 to 7000 kg/cm2, and the surface acidity was measured and compared with the data of the structural change in the sample. According to the experimental results, the surface acidity varied on compression. At lower compacting pressures (P∼2500 kg/cm2), the content of weak acid (H0=1.5–3.3) was high and that of the strong acid was poor. These facts were explained by the higher content of anion-water, or heptahydrate, in the sample. In the pressure region of P=2500<5500 kg/cm2, the acidity-pressure curve showed a maximum at 4500 kg/cm2. Further, in this pressure range, the acidity-pressure curve paralleled well the respective curves of the X-ray peak width of hexahydrate pressure, the relative intensity of the IR v1(SO42−)-pressure, and the half width of the IR v3(SO42−)-pressure. It was considered that the acidity change in this pressure range is caused by the change in the content of the distorted structural unit of hexahydrate in the sample. In the highest pressure range, the content of weak acid was found to increase, whereas the content of strong acid was found to decrease. These results were discussed by considering the increased inclusion of tetrahydrate in the sample.

Effects of Pressure on the Chemical Properties of Solid Surface, VIII. The Surface Acidity of the Compressed Magnesium Sulfate

Abstract In order to clarify the mechanism of the acidity change due to compression, magnesium sulfate was compressed under various pressures ranging from 0 to 12000 kg/cm2, the surface acidities, the powder X-ray diffraction patterns, the DTA data, and infrared spectra of the compressed samples were thus obtained. According to the experimental results, the surface acidity of the sample did not vary upon the compression of low pressures (0–6000 kg/cm2), and a further increase in the compacting pressure resulted in an increase in the surface acidity. From the results of the X-ray diffraction studies, infrared, and far infrared absorption studies and the DTA studies, the relations between the acidity change and the structural changes of the samples were discussed. As a result of this work, the observed acidity change was explained in terms of the distortion of the structural unit of magnesium sulfate.

Surface structure analysis by LEED and RHEED

Chemical analysis and structure determination by X-ray diffraction are two crucial preliminaries to any attempt at relating the properties of a solid to the type and arrangement of atoms that it contains. Although the interpretation of X-ray diffraction patterns is complicated by the loss of all phase information in the scattered waves, because of the experimental necessity of measuring intensity rather than amplitude, the number of structures which have now been solved is very large and relationships between the structure and other properties of bulk solids form a rich and complex pattern. A corresponding attempt to relate the electrical, magnetic, mechanical and chemical properties of solid surfaces to the arrangement and types of atoms present must depend in an equally significant way upon the answer to the question: Where are the atoms at the surface with respect to those in the bulk ? Electron diffraction has played a useful, if subsidiary, role in the determination of bulk structures (e.g. Vainshtein 1) but, because atoms and ions have much larger scattering cross-sections for electrons than for X-rays, electron diffraction offers, at least in principle, the possibility of making surface structure determinations. It is the purpose of this paper to describe briefly the progress that has been made in this direction with both low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED).

Effects of Pressure on the Chemical Properties of Solid Surfaces. V. The Surface Acidity of the Compressed Aluminum Sulfate

Abstract In order to clarify the mechanism of the acidity change due to compression, aluminum sulfate was compressed under various pressures ranging from 0 to 4200 kg/cm2 and at a temperature of 20, 65, or 80°C, and the surface acidity and the structure of these samples were measured. It was found that the acidity change due to compression was proportionate to the protonic acid. Lewis acid was made to appear only by heating the sample at temperatures higher than 90°C. Further, for the purpose of increasing the surface acidity, the compression of the sample at lower temperatures was found to be more effective than the compression at higher temperatures. In addition to the spectroscopic data, the results of DTA and TGA experiments supported the idea that the observed acidity change resulted from the distortion of the structural unit of aluminum sulfate.