Infrared spectroscopic study of O2 interaction with carbon nanotubes

Infrared reflection-absorption spectroscopic measurements have been performed on single-wall carbon nanotubes (SWNTs), cleaned by heating to approximately 500 degrees C in vacuo, during exposure to pure 16O2 or 18O2 at room temperature and at pressures of up to approximately 630 Torr. No vibrational signature of any form of adsorbed O is detected. However, structure is seen which is very similar to that observed for the adsorption of atomic H or D and which indicates changes in the SWNT vibrational spectrum. The close similarity between the spectra for atomic H and D, on one hand, and O2 on the other is an unexpected result. Changes are also noted in the broad background extending throughout the mid-IR which arises from the Drude contribution to the reflectance. All these effects increase with O2 exposure and are essentially irreversible upon evacuation of the gas. The results are consistent with other data indicating that O2 interacts only weakly with, and does not chemisorb on, pristine regions of the SWNT under these conditions. The small and irreversible effects seen upon O2 exposure are interpreted in terms of enhanced chemisorption, at or near defective regions of the SWNT wall, which saturates at a low O coverage.     

Infrared spectroscopic study of the CO2 adsorption effect on the surface acidity of zinc oxide

Taking account the bands ν_a(O¹²CO) and ν_a(O¹³CO) (in natural abundance) due to linear species, the study by FT-infrared spectroscopy of the CO₂ adsorption on ZnO has shown particular sites which can be described as Zn²⁺ ions with two vacancies, with a reactive oxygen ion in an adjacent position. Using the usual probe molecules (CO, acetonitrile, ammonia, pyridine), we have compared the Lewis acidity of ZnO and ZnO which has been pretreated with CO₂. This preadsorption causes an increase of the Lewis acidity. Moreover we have found that it prevents the dissociative adsorption of acetonitrile, ammonia, pyridine, propene and butenes. The model site described above well accounts for these results. It is concluded that the increase of the acidity due to CO₂ preadsorption is related to the formation of bidentate carbonates.     

Ga2O3-La2O3-Yb2O3-Er2O3(HO2O3)体系光谱性质的研究

根据稀土离子能级的特点,对Ga2O3-La2O3-Yb2O3-Er2O3(HO2O3)体系的光谱性质进行了探讨,发现它们有二类发光性质:Stokes发光和反Stokes发光,研究了发光强度和发射波长与掺杂离子的依赖关系,观察到由能量的共振转移引起的荧光浓度猝灭现象,并取得了最大发光强度时的掺杂离子浓度和一些规律性结果.     

Microcalorimetric and FT-IR spectroscopic study of benzene adsorption on α-Fe2O3 and γ-Al2O3

The adsorption of benzene at room temperature on-Fe₂O₃ and on-Al₂O₃ powders was investigated by heat-flow microcalorimetry and FT-IR spectroscopy.On iron oxide a chemisorption-combustion step is followed by a highly exothermic adsorption step, reversible at r.t.Few combustion centres exist on alumina if reducing pretreatment is not carried out. Two reversible adsorption steps are subsequently observed and were interpreted as due to interaction with two different types of surface hydroxy groups.

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Zusammenfassung Die Adsorption von Benzol an-Fe₂O₃- und-Al₂O₃-Pulvern bei Raumtemperatur wurde mittels Wärmefluß-Kalorimetrie und FT-IR-Spektroskopie untersucht. Beim Eisenoxid folgt auf dem Chemisorptions-Verbrennungs-Schritt ein bei Raumtemperatur reversibler, stark exothermer Adsorptionsschritt. Aluminiumoxid besitzt einige Oxydationszentren, sofern keine reduzierende Vorbehandlung erfolgt. Zwei aufeinanderfolgende reversible Adsorptionsschritte treten auf und werden der Wechselwirkung mit zwei verschiedenen Typen von Oberflächenhydroxylgruppen zugeschrieben.

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-Fe₂O₃ -l₂₃. - , . , , . , .

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This work was supported by the CNR Progetto Finalizzato Chimica Fine e Secondaria. Prof. Vincenzo Lorenzelli is gratefully thanked for the kind loan of instrumental facilities and helpful discussions.     

Effect of Ga2O3 on the spectroscopic properties of erbium-doped boro-bismuth glasses

The spectroscopic properties and thermal stability of Er3+-doped Bi2O3-B2O3-Ga2O3 glasses are investigated experimentally. The effect of Ga2O3 content on absorption spectra, the Judd-Ofelt parameters Omega t (t=2, 4, 6), fluorescence spectra and the lifetimes of Er3+:4I 13/2 level are also investigated, and the stimulated emission cross-section is calculated from McCumber theory. With the increasing of Ga2O3 content in the glass composition, the Omega t (t=2, 4, 6) parameters, fluorescence full width at half maximum (FWHM) and the 4I 13/2 lifetimes of Er3+ first increase, reach its maximum at Ga2O3=8 mol.%, and then decrease. The results show that Er3+-doped 50Bi2O3-42B2O3-8Ga2O3 glass has the broadest FWHM (81nm) and large stimulated emission cross-section (1.03 x1 0(-20)cm2) in these glass samples. Compared with other glass hosts, the gain bandwidth properties of Er+3-doped Bi2O3-B2O3-Ga2O3 glass is better than tellurite, silicate, phosphate and germante glasses. In addition, the lifetime of 4I 13/2 level of Er(3+) in bismuth-based glass, compared with those in other glasses, is relative low due to the high-phonon energy of the B-O bond, the large refractive index of the host and the existence of OH* in the glass. At the same time, the glass thermal stability is improved in which the substitution of Ga2O3 for B2O3 strengthens the network structure. The suitability of bismuth-based glass as a host for a Er3+-doped broadband amplifier and its advantages over other glass hosts are also discussed.     

Fourier transform infrared spectroscopic study of surface acidity by pyridine adsorption on Mo/ZrO2-SiO2(Al2O3) catalysts

Acidity of the oxidic molybdenum catalysts supported on mixed ZrO2-SiO2 and ZrO2-Al2O3 carriers was investigated by Fourier transform infrared spectroscopy of pyridine adsorption. Deposition of molybdenum on ZrO2-SiO2 and ZrO2-Al2O3 supports leads to formation of surface Br?nsted acid sites. The number of the Br?nsted and Lewis acid sites in supported-molybdenum catalysts depends on both the ZrO2 content and the type of the support. With increasing ZrO2 content, the Lewis acid sites increase for both series of catalysts. The Br?nsted acid sites are higher for Mo/ZrO2-SiO2 samples compared to those for Mo/ZrO2-Al2O3 and also increase with zirconia.     

Infrared spectroscopic and density functional theory study on the reactions of lanthanum atoms with carbon dioxide in rare-gas matrices

Reactions of laser-ablated La atoms with CO2 molecules in solid argon and neon have been investigated using matrix-isolation infrared spectroscopy. On the basis of isotopic shifts, mixed isotopic splitting patterns, and CCl4-doping experiments, absorptions at 1839.9 and 753.6 cm-1 in argon and 1855.9 and 771.3 cm-1 in neon are assigned to the C-O and La-O stretching vibrations of the OLaCO molecule, respectively. Ultraviolet-visible photoinduced isomerization of OLaCO to La-(eta2-OC)O and OLa-(eta2-CO) have been observed under different wavelength photolyses in the solid matrix. The neon matrix experiments give the C-O and La-O stretching vibrations of the OLaCO- anion at 1769.5 and 779.3 cm-1, respectively. Density functional theory calculations have been performed on these products, which support the experimental assignments of the infrared spectra. The present study reveals that the C-O stretching vibrational frequencies of OMCO decrease from Sc to La, which indicates an increase in metal d orbital --> CO pi* back-donation in this series.     

IR spectroscopic study of the adsorption of MeOH and H2O on decationized zeolites

The IR spectra of decationized zeolites with adsorbed bases have been analyzed. A correlation between the shift (OH) of the center of gravity of the set of bandsA,B, andC (components of the (OH) vibration) and the strength of the H-bond between the bridging hydroxyl groups and the molecule of a base has been found. This is evidence in support of the Fermi-resonance nature of the perturbations of the (OH) vibration. Spectral data on the adsorption of H₂O and MeOH on decationized zcolitcs that cannot be interpreted in terms of the formation of complexes with strong H-bonds have been obtained. Arguments in favor of the formation of H₃O⁺ and MeOH₂ ⁺ ions linked to the neighboring oxygen atoms in the zeolitc latticevia two identical hydrogen bridges have been presented.Na—Y zeolites were synthesized by N. N. FeoktistovaTranslated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1377–1381, June, 1996.     

First principles study of gallium atom adsorption on the alpha-Al2O3(0001) surface

The adsorption of Ga atoms in low coverage on the Al-terminated alpha-Al(2)O(3)(0001) surface has been studied theoretically by using first principles periodic boundary condition (PBC) calculations within the framework of the generalized gradient approximation (GGA). Eight possible adsorption sites are investigated, but only two are found to correspond to stationary points. Both of these locations are characterized as hollow sites, with three surrounding surface O atoms and an Al atom in the center located deeper within the Al(2)O(3) slab. The slight difference in the stability of these two sites is due to a difference in the chemical interactions between the Ga atom and the surface O atoms. Strong interactions between the Highest Occupied Molecular Orbital (HOMO) of the Ga atom and the surface state of the Al(2)O(3) surface are observed. This interaction promotes charge transfer from the Ga to the surface Al atoms, which in turn causes the surface Al atoms to move up from the surface.     

The adsorption of triethylenediamine on Al(2)O(3)-I: a vibrational spectroscopic and desorption kinetic study of surface bonding

The adsorption of triethylenediamine (TEDA) at 300 K is observed to occur via hydrogen bonding to isolated Al-OH groups on the surface of partially dehydroxylated high area gamma-Al(2)O(3) powder. This form of bonding results in +0.3 to +0.4% blue shifts in the CH(2) scissor modes at 1455 cm(-1) and a -0.4% red shift in the CN skeletal mode at 1060 cm(-1), compared to the gas-phase frequencies. Other modes are red shifted less than 0.1%. The isolated OH modes are red shifted by -200 to -1000 cm(-1) due to the strong hydrogen bonding association of Al-OH groups with an N atom in TEDA. Thermal desorption of adsorbed TEDA from the surface occurs in the range 300-700 K. Mass spectral and infrared studies indicate that the decomposition of TEDA occurs on Al(2)O(3) above 725 K, and that C-H bonds are broken, forming adsorbed species with N-H bonds which are stable to 1000 K or above. In contrast to adsorption at 300 K, adsorption of TEDA at 85 K results in the formation of a condensed ice of TEDA, which covers the outer surface of the porous Al(2)O(3) and which does not interact with Al-OH groups inside the porous powder due to immobility.     

Infrared study of CO2 adsorption on haematite

This work has shown that CO₂ molecules can interact at b.t. with high surface α-Fe₂O₃ obtained by thermal decomposition of goethite giving: a) physisorption, possibly via charge transfer mechanism between the carbon atom and the oxygen of a surface hydroxyl; b) formation of both monodentate and bidentate carbonate ions which can be easily decomposed by degassing even at b.t..More severe conditions of contact allow the progressive formation of Fe₂O₂CO₃ layers thermally stable up to 400°C which can be identified through their characteristic IR absorptions.     

Infrared spectroscopic and density functional theory study on the reactions of rhodium and cobalt atoms with carbon dioxide in rare-gas matrixes

Reactions of laser-ablated rhodium and cobalt atoms with carbon dioxide molecules in solid argon and neon have been investigated using matrix isolation infrared spectroscopy. The OMCO, O2MCO, OMCO(-) (M = Rh, Co), OCo2CO, and OCoCO(+) molecules have been formed and characterized on the basis of isotopic shifts, mixed isotopic splitting patterns, ultraviolet irradiation, CCl4-doping experiments, and the change of laser power. Density functional theory calculations have been performed on these products. The overall agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these products from the matrix infrared spectrum.     

Carbon dioxide adsorption on carbon nanomaterials

The adsorption of CO₂ on a number of activated carbons, thermal carbon black, and oxide materials at 195 K was studied using static and dynamic techniques. The landing surface areas ω(CO₂) ≈ 0.19 nm² on thermal carbon black and the absolute values of sorption for P/P ₀ < 0.4 were determined. The density of adsorbed CO₂ in the micropore volume was estimated at ρ(CO₂) = 0.91 g/cm³. It was demonstrated that the previously found effect of a weakening of the sorption interaction of nitrogen molecules with thin-walled materials (which manifested itself in an analysis of sorption isotherms by a comparative method) was pronounced to a lesser degree for the sorption of CO₂. At the same time, the presence of supermicropores in activated carbon samples resulted in overestimated values of surface areas. A dynamic method was proposed to measure the spectra of CO₂ desorption at 195–260 K using a SORBI-MS system for evaluating the binding energy of sorbate molecules with the surface.     

Cr2O3-Rh/Ga2O3光催化分解水的时间分辨红外光谱研究

研究半导体光催化分解水反应中光生电荷动力学和助催化剂的作用对理解其反应机理至关重要.一般来说,助催化剂不仅可以促进半导体/助催化剂界面处的光生电荷高效分离,而且可以作为反应活性中心来直接催化表面氧化或还原反应.Cr2O3-Rh是一种重要的产氢助催化剂,通过担载Cr2O3-Rh助催化剂来提高光催化分解水的策略被应用到许多...     

Structural, energetic, electronic, bonding, and vibrational properties of Ga3O, Ga3O2, Ga3O3, Ga2O3, and GaO3 clusters

The results of density functional theory based calculations on Ga3O, Ga3O2, Ga3O3, Ga2O3, and GaO3 clusters are reported here. A preference for planar arrangement of the constituent atoms maximizing the ionic interactions is found in the ground state of the clusters considered. The sequential oxidation of the metal-excess clusters increases the binding energy, but the sequential removal of a metal atom from the oxygen-excess clusters decreases the binding energy. The increase in the oxygen to metal ratio in these clusters is accompanied by increase in both electron affinity and ionization potential. The ionization induced structural distortions in the neutral clusters are relatively small, except those for Ga3O2. In anionic (cationic) clusters, the added (ionized) electron is shared by the Ga atoms, except in the case of GaO3. The vibrational frequencies and charge density analysis reveal the importance of the ionic Ga-O bond in stabilizing the gallium oxide clusters considered in this study.     

Infrared spectroscopic identification of species arising from reactive adsorption of carbon oxides on metal oxide surfaces

Published data on the infrared spectra and coordination of carbonate, bicarbonate and formate ions, and of CO₂ in metal complexes are reported. The usual assignments of absorption bands due to products of CO and CO₂ reactive adsorption on metal oxide surfaces are also critically reexamined.     

Infrared study of trapped carbon dioxide in thermally treated apatites

The formation of molecular CO₂ in synthetic apatites (prepared in aqueous systems), dental enamel, dentine, and various apatitic rock phosphates after heating in the range 120–900°C has been investigated by infrared spectroscopy. The CO₂ band at 2340 cm^?1 was observed in the synthetic samples, enamel, and some of the rock phosphates, but not in dentine or bone. It is suggested that the absence of this band in dentine and bone is caused by the small crystal size of their apatites. The CO₂ band at 667 cm^?1 was never observed. The polarized infrared spectrum of heated dental enamel showed that the linear CO₂ molecules were either randomly oriented or oriented so that the length of the molecules made an angle of about 56° with the c axis. It is suggested that, if the latter is correct, the CO₂ originates from a CO^2?₃ ion which occupied the sloping face of the phosphate ion site.