Charis R. Theocharis

A study of the infrared absorption spectra of thin amorphous films of molybdenum trioxide

The spectra of thin amorphous films of MoO3 deposited by vacuum evaporation have been studied within the spectral range 4000–400 cm−1 by the Fourier transform infrared technique. Some samples in the thickness range 100 to 400 nm were investigated at room temperature. Four samples were investigated in the substrate deposition temperature range 293 to 543 K. Some samples were annealed in vacuum in the temperature range 473 to 673 K and their IR spectra were recorded as soon as the samples were cooled to room temperature. It has been observed that annealing of the samples at 473 K or above and also heating the substrates in the temperature range 473 K or above, results in the formation of molybdenum species of lower oxidation state than the normal Mo(VI), i.e. Mo(V). This new oxidation state is formed by electron transfer from the oxygen 2p to the molybdenum 4d level.

The Adsorption of Water Vapour by Microporous Solids

Summary The adsorption of water vapour has been studied with a range of microporous carbons, zeolites and aluminophosphates in order to elucidate the relative influence of surface chemistry, pore size and pore shape upon the form of the water isotherm. It was possible to separate the adsorbents into three groups on the basis of their affinity and capacity for water vapour. The porous carbons were further examined using the BET and Dubinin-Serpinsky equations. The results show that the adsorption of water vapour at low p/po is largely dependent upon specific adsorbent-adsorbate interactions whilst at higher relative pressures the micropore size and shape control the extent of adsorption. It is proposed that hydrogen-bonded layers of water can be more readily accommodated in the narrow slit shaped pores (∼0.5nm) of molecular sieve carbons than in tubular pores of similar width (e.g. Silicalite/ZSM-5).

Adsorptive properties and stability of VPI-5, a large-pore molecular sieve

The unusual adsorptive properties and the reported instability of VPI-5 have been investigated in some detail. The VPI-5 framework was found to undergo an irreversible but incomplete phase transformation to AlPO4-8 during the removal of the zeolitic water. Furthermore, ill-defined constrictions are believed to be introduced into the framework during the course of this transformation. These have a great effect on the resulting adsorptive properties of dehydrated VPI-5. The adsorptive properties of the dehydrated material are dependent on factors such as the outgassing conditions, the sample history, the concentration of intracrystalline P—OH and other defect sites and the method of sample synthesis.

Modified aluminophosphate molecular sieves: preparation and characterisation

Abstract Crystalline microporous aluminium phosphate has been prepared in a variety of ways. The influence of the preparative conditions affecting the solid state properties of the resultant solids were studied. Quencg cooling of the reaction mixture led to a change of crystal morphology, but not in structure. Incorporation of zinc also affected the crystal morphology, but the pore structure was essentially unaltered for both systems.

Investigation of infrared absorption spectra of copper phosphate glasses containing some rare earth oxides

The spectra of copper-lutetium-phosphate and copper-erbium-phosphate glasses have been studied within the spectral range 4000 to 400 cm− by Fourier transform infrared spectroscopy. Incorporation of a small amount of lutetium or erbium influences some band positions compared with binary copper phosphate glasses. The additional bands in the range 491 to 576 cm−1 are attributed to the presence of Lu-O and Er-O groups. It has been observed that annealing of the samples at 500 ° C leads to a slight shift in the peak positions.

Infrared spectra of some thin amorphous films of MoO3-In2O3 deposited by vacuum evaporation

The infrared absorption spectra of vacuum-evaporated MoO3-In2O3 thin films are reported for a series of films of varying compositions within the spectral range 4000 to 400 cm−1 and interpreted in relation to the spectrum of the pure MoO3 films. The affects of changes in composition, film thickness, substrate deposition temperature and annealing on the absorption bands are observed. In some cases a shift in band frequency is also observed. The gradual increase in ordering and decrease in valency state with increase of annealing temperature is observed in the infrared curves. Some new peaks appear which reveal the presence of a lower valency state in MoO3. The shift in band frequency may be attributed to the incorporation of Mo(VI) ions in the indium interstitial positions.

Changes in the surface properties of calcium hydroxide upon ageing A spectroscopic and gas sorption study

Abstract The surface chemistry of commercial grade calcium hydroxide was studied by sorption methods, thermal analysis and spectroscopy. In this paper, the effect of exposure to the atmosphere (moisture and carbon dioxide) upon the surface chemistry of calcium hydroxide is discussed. This ageing process appears to involve the partial conversion of the hydroxide to calcium carbonate, for which reaction the presence of water is essential. The reaction proceeds beyond the monolayer stage, and results in the destruction of the mechanical integrity of the particles, and the subsequent aggregation, to form agglomerates of about 40 μm diameter.

An infrared spectroscopic study of vacuum evaporated amorphous thin films of MoO3-SiO

A series of amorphous MoO3-SiO thin films of varying compositions were investigated by infrared spectroscopy. In some cases a shift in band frequency was observed. Some new peaks appeared when SiO was mixed in MoO3. These new peaks are due to bond-rocking vibrations of the bridging oxygen atoms (430 to 440 cm−1), bending motion of the same oxygen atom (800 to 810 cm−1), stretching vibration of non-bridging oxygen atoms (876 cm−1) and bond-stretching vibrations of oxygen atoms (1040 to 1060 cm−1) in SiO. The band of 940 cm−1 is attributed to the absorption of oxygen atoms in its two-fold-coordinated bridging Si-O-Si bond at an isolated site indicating that there is no oxygen atom as a second-nearest neighbour to any other oxygen atom.

Sorption of Water Vapour by Partially Decomposed Calcium Hydroxide

Abstract The surface chemistry of commercial grade calcium hydroxide was studied by sorption methods, thermal analysis and spectroscopy. Part of this investigation was the study of the sorption of water vapour by the partially thermally decomposed calcium hydroxide. It was found that when the decomposition takes place in the absence of air, the result is a high surface-area, porous solid. The pores are slit-shaped. Complete rehydroxylation takes place upon exposure to water vapour. The whole process is reversible, and reproducible.

Solid state reactions of metals complexes of substituted cyclopentanones: An infrared spectroscopic study

Abstract The solid state reactivity of a family of substituted benzylidene cyclopentanones has been studied extensively. The effect of complexation to metal ions onto their crystal structure and solid state reactivity has ben studied. Complexation was possible because of the incorporation either of pairs of ortho hydroxyl substituents on the phenyl rings, or of a malonic group at the 3-position of the five member ring. Coordination polymers with extended conjugation systems have been prepared in some cases, and the effect of varying the metal: ligand ration on photoreactivity was studied. Types of light-induced solid state reactivity which have been encountered, are [2+2] topochemical cycloaddition, decarboxylation and dehydration, whilst some compounds were found to be photostable. The main technique used in these investigations was FTIR.