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Pore-size distribution studies were carried out employing nitrogen adsorption, mercury porosimetry and thermoporometry techniques on two titania gels prepared from titanous chloride and ammonia using oxygen gas as the oxidizing agent. These gels were also characterized by scanning electron microscopy and X-ray diffraction. After heat-treatment at 340 °C and 520 °C, the gels were found to possess the anatase structure, being predominantly mesoporous in nature as indicated by nitrogen adsorption studies and α S -plots. Very good agreement was observed between the BJH pore-size distribution analysis data and the thermoporometry pore-size determinations. Comparable results were also obtained by mercury porosimetry. The validity of thermoporometry as a viable and reliable technique for pore structure analysis was ascertained.

The surface characteristics of mixed zirconium and titanium oxides prepared from different starting materials are investigated. One mode of preparation entailed the use of zirconium sulfate and titanium oxysulfate as starting materials and ammonium hydroxide as precipitating agent. The produced oxides were washed to different extents to obtain samples with different sulfate content. A second preparative mode used zirconium oxychloride and titanous chloride as starting materials also with ammonium hydroxide as precipitating agent. The oxidation of the titanous to the titanic form for these oxides was carried out by means of oxygen gas. Resulting samples were heat treated at 400 °C and 600 °C, and textural characteristics determined from the adsorption of N2 at 77 K, complemented by infrared and thermal studies.

Titania gels were prepared by oxidation of precipitates of hydrous TiIII oxide obtained at different pH values from aqueous titanous chloride by the addition of ammonia. The gels were dried at 110–120°C (383–393 K) and their surface properties were characterised by nitrogen adsorption at 196°C (77 K). The nitrogen isotherms have been analysed by the BET and αs-methods. Gels prepared at pH values of 3.30, 5.01, 6.20 and 7.10 were all mesoporous; the pore volume increasing with increase of pH, over the range studied. The gel prepared at pH 2.30 had a small micropore volume, whereas the gel prepared at pH 5.01 and aged for 6 months in water had a much larger micropore volume. The formation of the mesopore structure appears to be due to a condensation-polymerisation process associated with the creation of hydroxo and oxo bridges between neighbouring Ti3+ ions. If stabilising ligands (H2O or NH3) are allowed to remain attached to the cations, the condensation-polymerisation process is retarded and microporosity results.

Hydrous titania gels, precipitated from titanous chloride and aged in different aqueous media have different textural, thermal and structural properties as demonstrated by nitrogen adsorption, differential thermal analysis, X-ray diffraction and scanning electron microscopy studies. Ageing in ammonia leads to the development of microporosity, whereas ageing in water causes an extension of the pore system in the primary particles with little change in the surface texture. Heat-treatment of the precipitated gels prior to ageing seems to afford a certain stability to the primary particle by allowing hydroxo and oxo bridges to be formed, thus leading to the formation of a more rigid structure. The nature of the ageing medium and its effect on the inner coordination sphere of the titanium ions are important parameters affecting the textural and thermal behaviours of the titania gels.

Titania gels were prepared from a master batch of hydrous titanous oxide, which was obtained by the addition of ammonium carbonate solution to aqueous titanous chloride. After oxidation of the Ti3+ to the Ti4+ oxide, the precipitate was divided into various parts for the study of the changes in surface properties produced by storage under ammonia and water and by heat treatment. The outgassed sample having the largest BET surface area and pore volume (as determined by nitrogen adsorption) was obtained by calcination in air for 4 h at a temperature of 493 K. Analysis of the nitrogen isotherm indicates that this sample was both mesoporous and microporous (BET area 284 m2 g−1; pore volume, 0.234 cm3 g−1). Increase in the calcination temperature to 613 K led to removal of the microporosity and a drastic reduction in surface area. The generation of the large surface area appears to be dependent on the formation and decomposition of a carbonato complex.

Infrared studies were carried out on a number of titania gels prepared from titanous chloride under various conditions of pH and oxidizing agents. Oxygen oxidized gels display, below 1200 cm−1, two bands at 1080 cm−1 and 970 cm−1 which are related to the formation of hydroxo complexes of titanium. Heat treatment at 110°C and ageing in water led to successive small shifts of these bands towards higher energies. In the case of hydrogen peroxide oxidized samples, prepared at a low pH, two significant bands appear at 1045 cm−1 and 1389 cm−1 and are attributed to O−2 and HO2 free radicals, respectively. The same kind of gels prepared under neutral or alkaline conditions are shown to incorporate hydroxo complexes of titanium; however, ageing in water leads to the reappearance in these gels of the 1045 cm−1 band attributable to O−2 free radicals. All gels exhibit two sharp bands at around 1400 cm−1 and 1630 cm−1, characteristic of NH+4 ions and molecular water, respectively.

The thermal properties of a number of titania gels prepared from titanous chloride under various conditions of pH and oxidizing agents, have been studied by simultaneous thermogravimetry, differential thermal analysis and differential thermogravimetry. The results obtained suggest that ligands incorporated in the precipitated gels play a crucial role as far as establishing the dehydration characteristics of these gels. Ageing in water leads, in most cases, to the elimination of coordinatively bound water and to a marked decrease in the final weight loss. In the case of hydrogen peroxide oxidized samples, free radicals incorporated in the inner coordination sphere of titanium control, in most cases, the low temperature behavior.

The present investigation deals with the surface properties of titania gels prepared from titanous chloride and ammonium carbonate under acidic and alkaline conditions of pH. The dehydration characteristics of such hydrous oxides are also investigated by means of simultaneous differential thermal analysis, thermogravimetric analysis and differential thermogravimetric analysis. Contrary to hydroxide-precipitated gels, even at a low pH of precipitation, very little ‘coordinated’ water remains in these gels. It is suggested that it is the concomitant presence of ammonium and carbonate ions in the precipitating agent, acting together, that provide the conditions favorable for the development of microporosity and high surface area in the gels.

A study was carried out of the uptake of Cu2+, Ni2+, Co2+ and Ca2+ cations by hydrous titanium oxides prepared at different pH values using titanous chloride as the starting material and hydrogen peroxide as the oxidizing agent. Characterization of the oxides was carried out by nitrogen adsorption and infrared studies. The oxides were found to be amphoteric in nature and exhibited an isoelectric point of 6.6. An attempt was made to elucidate the mechanism of cation uptake which does not entail a simple ion-exchange mechanism.

A study of the various parameters affecting the crystallographic transformation of amorphous titania gels (prepared from TiCl3) to anatase and rutile has been conducted. Analysis of the effect of the preparative pH (3.0, 7.5 and 11.0) and of the ageing media (HCl, H2O, air and NH4OH) suggests that coordinated water as well as the presence of chloride ions (bulk or surface) play an important role in the transformation of amorphous titania gels to the anatase and rutile modifications. The formation or depletion of anion vacancies as well as the presence of interstitial ions seem to be the crucial parameters controlling the rate of transformation of anatase to rutile. A higher heating temperature as well as a higher preparative pH generally lead to an accelerated conversion. In most cases first-order kinetics are followed. A nucleation process with high kn predominates with NH4OH and H2O as ageing media, whereas with air a propagation-growth process in general controls the kinetics of the transformation. Ageing in HCl gives ill-defined kinetic curves. A notably low activation energy for nucleation (≈52 kcal mol−1) was observed in the case of the low pH gels aged in ammonia.

A comparative study of the uptake of the cations, Cu 2+ , Ni 2+ , Co 2+ and Ca 2+ by hydrous titanium oxides unheated and heat-treated at 400°C was carried out. The hydrous oxides were prepared at different pH values, using titanous chloride as starting material and hydrogen peroxide as oxidizing agent. Similarly to the unheated oxides, the heat-treated samples were found to be amphoteric in nature and exhibited an isolelectric point of ∼6.6. The total ion exchange capacity was found to generally decrease with heat treatment, so did the selectivity to a number of cations. Characterization of the samples by infrared and nitrogen adsorption studies were also carried out.

A series of titanium dioxide gels has been prepared by the oxidation of precipitated hydrous Ti(III) oxide, obtained by the addition of aqueous ammonia or ammonium carbonate to aqueous solutions of titanous chloride. The gels were dried in air at 110°C and their structures and surface properties studied with the aid of DTA, X-ray diffraction, nitrogen adsorption, and spectrophotometry. Analysis of the nitrogen isotherms has revealed that the gels exhibited a wide range of different pore structures, extending from narrow micropores to wide mesopores. The development of the gel porosity appears to have been largely controlled by the mode of removal of water ligands from the hydration sphere of the cations, enlargement of the micropore volume being obtained by the replacement of water by carbonato ligands and pore widening by increase in the pH of precipitation (over the pH range 2.3–7.1). All the gels were X-ray amorphous in their original state: some were converted directly to rutile at 500°C while others underwent the more usual transformation into the intermediate anatase form. It is postulated that the rapid removal of the water ligands can result in the formation of a defect structure which controls the development of the pore structure and also the behavior of the gels on heat treatment.