An infrared spectroscopic study on the influence of water on alcohols

Summary The influence of the water content on absorption bands in FTIR spectra of monohydric alcohols was studied and the effects were compared to changes in spectra of absolute solvents at various temperatures. The FTIR spectra were recorded by the ATR technique in order to distinguish the weak bands of the solvents from the intensive water bands more easily. By addition of water to anhydrous alcohols both OH stretching and bending bands increased in intensity and width. Similar changes in spectra of anhydrous alcohols can be obtained by decreasing the temperature. Addition of water to monohydric alcohols causes the lengthening of the intramolecular OH bonds to a smaller extent than the shortening of the intermolecular OH bonds. This contraction of the liquid structure is also reflected in other physical and chemical properties.

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Eine infrarotspektroskopische Untersuchung über den Einfluß von Wasser auf Alkohole

Zusammenfassung Der Einfluß des Wassergehalts auf die Absorptionsbanden in den FTIR-Spektren einwertiger Alkohole wurde untersucht und die Effekte mit den Veränderungen der Spektren der absoluten Lösungsmittel bei Temperaturvariationen verglichen. Die FTIR-Spektren wurden mit Hilfe der ATR-Technik aufgenommen, um die meist nur schwachen Banden der Lösungsmittel neben den intensiven Wasserbanden besser erkennen zu können. Es zeigte sich, daß durch Zugabe von Wasser zu absoluten Alkoholen sowohl die OH-Streckschwingungs- als auch die Deformationsschwingungsbande an Intensität und Breite zunehmen. Ähnliche Veränderungen der Banden lassen sich auch in den Spektren von absoluten Alkoholen bei Temperaturerniedrigung feststellen. Diese spektroskopischen Veränderungen werden in folgender Weise interpretiert. Die Zugabe von Wasser zu einwertigen Alkoholen bewirkt die Verlängerung der intramolekularen O-H-Bindungen in schwächerem Ausmaß als die Verkürzung der Intermolekularen O...H-Bindungen, d.h. sie bewirkt eine Erhöhung der Symmetrie der H-Brückenbindungen und eine Verstärkung der O...O-Wechselwirkungen. Diese Verdichtung der Flüssigkeitsstruktur spiegelt sich auch in anderen physikalischen und chemischen Eigenschaften wider.

     

An environment-friendly electrochemical detachment method for porous anodic alumina

This paper describes an improved one-step voltage pulse detachment method by using perchloric acid and ethanol mixture as detaching solution for the preparation of through-hole porous anodic alumina (PAA) membranes. The detachment of PAA from aluminum substrate and the dissolution of the barrier layer can be completed simultaneously in the detachment solution by applying a pulse voltage in situ after the anodization process. The influence of voltage pulse height and nature of the detachment solution on the efficiency of detachment have been systematically investigated. The present procedure is more environmental friendly and efficient as compared to the conventional electrochemical detachment methods and is promising for the preparation of freestanding PAA films with through-hole morphology which are important for nanomaterials synthesis and nanoscale separation.     

Physicochemical features of formation of silicate porous mesophases

Silicate mesoporous mesophases analogous to SBA-3 or MCM-41 with the hexagonal (honeycomb) structure can be synthesized in a moderately acidic region (pH ∼2.5—5). The synthesis was carried out using aqueous solutions of sodium silicate and a surfactant of the alkyltrimethylammonium bromide type as the starting precursors. For Part 4, see Ref. 1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 29–34, January, 2008.     

The dehydroxylation of basic aluminum sulfate: An infrared emission spectroscopic study

The tridecameric aluminum polymer [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ was prepared by forced hydrolysis of Al³⁺ up to an OH/Al molar ratio of 2.2. Upon addition of sulfate, the tridecamer crystallized as the monoclinic basic aluminum sulfate Na_0.1[AlO₄Al₁₂(OH)₂₄(H₂O)₁₂](SO₄)_3.55. The dehydroxylation of the basic aluminum sulfate has been studied by Fourier transform in-situ infrared emission spectroscopy over a temperature range of 200° to 750°C at 50°C intervals. The spectrum is characterized by the sulfate ν₁ (1024 cm⁻¹), ν₃ doublet (1117 and 1168 cm⁻¹) and the ν₄ doublet (568 and 611 cm⁻¹) modes. Furthermore, minor bands assigned to nitrate are observed. Upon heating from ≈350° to 400°C major changes are observed, especially in the bandwidth and band intensities. The bands in the hydroxyl stretching region due to the Al₁₃ group disappear, whereas the bands around 1050 cm⁻¹ display various changes in bandwidths, intensities and positions associated with the dehydration and dehydroxylation of the basic sulfate and the changing of the structure into an aluminum oxosulfate. The nitrate bands diminish upon heating.     

An FTIR study of the adsorption of surfactants on silica

The absorption of cetyltrimethyl ammonium bromide onto silica was studied by FTIR as an example of the interaction of cationic surfactants with surfaces of medium polarity. It was found that the free silanol groups of the silica interacted strongly with the surfactant and that the methylene group adsorption bands varied with coverage in both frequency and width. These results could be interpreted in terms of chemisorption of a first layer of surfactant followed by physisorption of subsequent layers, or in terms of the inhomogeneity of the silica surface.     

Preparation of sodium borosilicates using sodium silicate and boric acid

The gelling behaviour of an aqueous sodium silicate solution with boric acid was investigated for different initial compositions and solid sodium borosilicate samples were obtained by drying the gels at 100°C, 225°C and 450°C. The chemical composition, dissolution, pH, loose-packed bulk density, B.E.T. surface area, moisture, size distribution and XRD/IR patterns of the sodium borosilicate particles were determined. The minimum gelling times were observed at pH values between 9–10 and although no gels were obtained using HCl at pH = 11, the silicate solution was gelled with boric acid suggesting borate ions promote the formation of siloxane network and behave as a crosslinking agent.     

An infrared spectroscopic study of changes in unsaturation resulting from irradiation of isotropic and uniaxially oriented polyethylene films in the presence of acetylene

Interchain bridges of unsaturated double bonds have been proposed to form in amorphous regions, when polyethylene is irradiated in the presence of acetylene. We have corroborated the formation of these bridges by infrared spectroscopic studies. The double bonds are composed mainly of trans-olefin and vinyl end groups, formed as a result of competing radical-radical termination and hydrogen atom abstraction reactions. The hydrogen atom abstraction reaction becomes insignificant in uniaxially oriented high-density polyethylene having a draw ratio of 7.5, because of the alignment and positioning of the initiating radical pairs. During in vacuo irradiation and annealing only in-chain trans-olefins are usually formed. © 1994 John Wiley & Sons, Inc.     

Diffuse reflectance fourier transform infrared spectroscopic study of the thermal degradation of barley protein

Diffuse reflectance infrared spectroscopy was used to study isothermal degradation of crude barley protein, that was obtained as a side product of alcohol production. The isothermal temperatures used were in the range 50–150° C. Before analysis the protein fraction was dried either by lyophilization or spray drying. The drying method did not have a major effect on the subsequent isothermal degradation of the material. The main reactions observed in the spectra were oxidation indicated by the appearance of a broad composite carbonyl band and degradation of both proteins and starch. The reactions were visible already in the spectra taken at 70° C and there rates gradually increased as the temperature was raised to 150° C.     

Oxygen evolution: the mechanism of formation of porous anodic alumina

Abstract  Aluminium anodization behavior in ammonium sebacate solution (w = 4%) in ethylene glycol, and in several H₃PO₄-containing electrolytes, has been investigated. A new mechanism is proposed for the formation of porous anodic films. The model emphasizes the close relationship between pore generation and oxygen evolution. PO₄ ³⁻ ions incorporated in the anodic films behave as the primary source of avalanche electrons. It is the avalanche electronic current through the barrier film that causes oxygen evolution during anodization. When growth of anodic oxide and oxygen evolution occur simultaneously at the aluminium anode, cavities or pores are formed in the resulting films. Accordingly, the mechanisms of growth of barrier and porous films are not very different in nature. These findings are a decisive new step towards full understanding of the nature of anodic alumina films. Graphical abstract        

Removal of residual nitrate ion from bioactive calcium silicate through soaking

Bioactive calcium silicates prepared by sol–gel routes mainly use calcium nitrate as the calcium precursor. However, the toxic nitrate ions are usually removed by calcination(i.e. 550 8C or over), which poses great challenge for the in situ preparation of inorganic/polymer composites, as polymer moieties could not survive such temperatures. In this study, we prepared 70Si30Ca(70 mol% Si O_2 and 30 mol%Ca O) bioactive glass at low temperatures where polymer could survive(i.e. 200 8C and 350 8C), and proposed to remove the residual nitrate ions through soaking. Deionized water and simulated body fluid(SBF) were employed as the soaking medium. The results showed that the residual nitrate ions could be removed as quickly as 0.5 h while maintain the bioactivity of the samples. This technique may open the possibility of preparing sol–gel derived bioactive glass/polymer hybrids in situ with reduced potential toxicity.     

An infrared study of CO adsorption on silica-supported Ru-Sn catalysts

CO adsorption on Ru-Sn/SiO(2) catalysts of various Sn/(Ru+Sn) ratios was examined by Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS). The catalysts were prepared by the incipient wetness impregnation method. Catalysts were activated by H(2) reduction at 773 K. CO adsorbed on the catalysts shows spectra whose band frequencies are divided into three groups: (i) High Frequency Region (HFR), containing a band at 2065 cm(-1), (ii) Low Frequency Region 1 (LFR(1)), containing bands at 2040-2015 cm(-1), (iii) Low Frequency Region 2 (LFR(2)), containing bands at 1990 and 1945 cm(-1). The types of adsorbed CO species formed strongly depend on the ratio Sn/(Ru+Sn) in the catalyst, CO pressure and temperature of adsorption. Adsorption of CO on Ru sites in the Ru/SiO(2) catalyst results in LFR(1) bands at 2040-2015 cm(-1), which are independent of the CO pressure but the adsorption complexes are easily destroyed by raising the temperature. The addition of Sn to the catalyst creates new sites for CO adsorption. After adsorption at 298 K, the HFR band at 2065 cm(-1) and LFR(2) bands at 1990-1950 cm(-1) are observed. The relative intensities of these bands increase with increasing Sn-content in the samples. The LFR bands are thermally stable while the HFR band is not. The formation of the corresponding species is favored by increasing the CO pressure. Adsorbed CO species giving LFR(1) bands are assigned to linearly-adsorbed CO on the Ru(0) and/or on the Ru-Sn alloy sites. Adsorbed CO species giving HFR bands are assigned to CO adsorption on Ru(delta+)-O-Sn sites. After low temperature CO adsorption on samples with high Sn-content, only species that show bands at 1990 and 1945 cm(-1) in LFR(2) are observed.     

Evolution of standing mesochannels on porous anodic alumina substrates with designed conical holes

We report the formation of standing mesochannels simply by spin-coating a precursor solution onto a PAA (porous anodic alumina) substrate with designed conical holes, utilizing exactly the same precursors and reaction conditions that form two-dimensional (2D) hexagonal mesoporous SBA-15-type films. When the aspect ratios of the conical holes are lower, the sponge-like mesopores are generated within the conical holes. Such a formation of sponge-like mesostructures truly acts as a trigger for the evolution of perpendicularly oriented and tilted mesochannels. On the other hand, when the PAA substrates with high-aspect cones are used, the mesochannels are stacked like a doughnut within the conical holes, which leads to parallel orientations of the mesochannels in the continuous film region.     

18O distributions in porous anodic alumina by plasma profiling time‐of‐flight mass spectrometry and nuclear reaction analysis

A comparison is made between plasma profiling time‐of‐flight mass spectrometry (PP‐TOFMS) and nuclear reaction analysis (NRA) for depth profiling of ¹⁸O tracer in porous anodic oxide films on aluminum. The films were formed galvanostatically, for a range of times, using phosphoric acid electrolytes that were either enriched in ¹⁸O or of the natural isotopic concentration. The morphologies of the films were determined by electron microscopy. The findings from PP‐TOFMS and NRA reveal a partitioning of the tracer between the surface regions and buried layers of the films. However, a relatively high background of ¹⁶O in PP‐TOFMS prevents a reliable quantification of the concentration of ¹⁸O. Copyright © 2012 John Wiley & Sons, Ltd.     

Infrared study of nitrogen adsorption on alumina

Good agreement of the results of numerical calculations with experimental data shows that the simple representation of a Lewis acid site of an alumina surface as a positive point charge plus van der Waals interaction can describe some characteristics of its interaction with a nitrogen molecule.     

Inelastic neutron scattering and infrared spectroscopic study of furan adsorption on alkali-metal cation-exchanged faujasites.

Inelastic neutron scattering (INS) as well as infrared (IR) transmission and diffuse reflection infrared Fourier transform (DRIFT) spectra of furan adsorbed on Li-LSX, NaY, NaX, K-LSX, and CsNaX zeolites have been measured in the range 2000-200 and 4000-1300 cm(-1), respectively. On the basis of an assignment of normal modes of furan taken from the literature and our own quantum chemical calculations of vibrational frequencies, the observed frequency shifts between bulk furan and furan adsorbed on the zeolites mentioned above have been interpreted in view of the interactions between furan and zeolite. For an explanation of frequency shifts of CH out-of-plane bendings, CH stretchings and some ring vibrations, it has to be assumed that in addition to the interaction between furan and the corresponding cation of the zeolite, a further interaction between the CH bonds and lattice oxygen atoms exists.     

Zeolite basicity characterized by chloroform chemisorption. An infrared study

The basicity of alkali-exchanged zeolites has been characterized by chloroform adsorption using FTIR spectroscopy. The chloroform is adsorbed on the basic oxygen site through its hydrogen atom, while a weak interaction also exists between the adjacent cation and the chlorine atom of chloroform. The charge on the oxygen atoms (basic sites) was calculated using the electronegativity equivalence method. The CH stretching frequency of chloroform adsorbed on basic sites is well correlated with this oxygen charge.     

An infrared study of adsorption of N2O on ZnO

The adsorption of N₂O on finely divided ZnO at room temperature shows two principal infrared absorption bands at 2237 cm⁻¹ (strong) and 1255 cm⁻¹ (weak), corresponding to the reversible adsorption of an N₂O surface species. The N₂O is postulated to be coordinated to Zn²⁺ cations by the oxygen atom. Water pre-treatment of the ZnO surface gives only weak bands from adsorbed N₂O, indicating that the latter's adsorption site is taken up by adsorbed water. Spectroscopic experiments on ‘reduced’ surfaces of ZnO at 200°C show that limited reaction of N₂O with the surface has occurred, presumably through decomposition to nitrogen and adsorbed oxygen. New adsorptions on the ZnO surface itself, and a reduced amount of reversibly adsorbed N₂O, implied a reduction in pressure of the adsorbate. Such effects were not observed appreciably over ‘oxidised’ ZnO.     

Novel electrodeposition behavior of Ni on porous anodic alumina templates without a conductive interlayer

During template-assisted electrodeposition, single-crystalline metallic nanowires could be obtained only when the overpotential is low. However, an unusual electrodeposition behavior on the PAA/Si substrate without a conductive interlayer between the template and Si is described in the present study. Through the electrical breakdown of the template, Ni nanodots, nanowires and nanotubes could be obtained by only changing the electrodeposition voltage on the same substrate. The mechanisms leading to the formation of various nanostructures are described in detail and compared with those for the conventional template-assisted electrodeposition process. The electrodeposition first occurred on the pore wall instead of from the underlying substrate, leading to the formation of some Ni nanotubes at a more negative voltage. Besides, single-crystalline Ni nanowires could also be formed even when the electrodeposition voltage was as negative as -40 V, indicating that the formation of single-crystalline metallic nanowires under a large overpotential is possible.