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The photocatalytic behaviour of TiO2 prepared from titanium (IV) ethoxide was determined with regard to the decomposition of methyl orange (MO) and methylene blue (MB) dyes, respectively. In addition, we compared the behaviour of TiO2 photocatalysts prepared in a similar fashion but which were (1) doped with different amounts of zirconium, (2) mixed with active carbon and (3) doped with different amounts of zirconium and mixed with active carbon. All of the TiO2 samples were found to be mesoporous with some microporosity having an average particle size between 200 and 500 nm and with anatase crystallographic modification. The kinetics of the MO and MB dyes' photocatalytic degradation fitted well with the Langmuir-Hinshelwood model and were found to follow pseudo-first-order kinetics. The rates were highest for the TiO2 samples doped with both Zr and mixed with the activated carbon. Characterization of these TiO2 photocatalysts was carried out by X-ray diffraction, scanning electron microscopy and adsorpti...

Cobalt aluminate spinels were prepared from cobalt and aluminium nitrate solutions using sol-gel synthesis route by ammonium hydroxide precipitation. The gels were dried at 75°C, doped with different amounts of magnesium nitrate, and then calcined for 3 h at 650°C. Sample characterization was carried out by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, nitrogen adsorption studies, thermogravimetry and by determining acid-base properties. This was carried out with the objective of elucidating the effect, if any, of the presence of the dopant on the spinel structure and properties. The spinel structure was clearly exhibited in all of the prepared samples which were predominantly mesoporous. None of the samples showed any acidic properties, i.e. they exhibited only basic properties. We found that doping with Mg resulted in a slightly increased disorder of cation distribution for those samples doped with higher amounts of Mg. Doping also led to a general increase in surface areas and...

TiO2 obtained from the hydrolysis of titanium ethoxide was impregnated with different amounts of ammonium hydrogen phosphate, and subjected to heat treatment at different temperatures. Textural and acidic properties were determined. It was found that the presence of increasing amounts of phosphate groups within the TiO2 reduces surface area and total pore volume. The development of the bidentate state of ligation of the phosphate, starting at 400 °C is associated with enhanced surface acidity. Although, the bidendate phosphate groups persist till 800 °C, a significant decrease in surface acidity is observed at this temperature, believed to result from the elimination of water from the structure. The presence of the phosphate groups delays the anatase to rutile phase transformation. Moreover, bidentate phosphate groups appear to play a role in stabilizing the pore structure of TiO2.

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.

Mixed titanium and zirconium oxides with different sulfate ion contents were prepared from the oxysulfate and sulfate salts, respectively, using ammonium hydroxide as a precipitating agent. These oxides were subjected to heat treatment at different temperatures, then characterized by nitrogen adsorption studies and infrared spectroscopy. Their surface acidity was determined volumetrically by the adsorption of sodium hydroxide from solution, and was found to depend on both the amount of sulfate ions present as well as their state of ligation within the oxide matrix. Surface acidity varied with heat treatment, reaching maximum values within the temperature range of 380–600 °C, corresponding with the appearance of the chelated sulfato groups. This is corroborated by infrared spectroscopy results. A corresponding decreasing trend in surface area suggests that the increase in sulfate ligation results in pore blocking.

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.

Magnesium oxalate dihydrate was used as a “generator” to produce active magnesium oxide by heating both in vacuo and in presence of constant water vapour pressure. Results indicate that sintering is accelerated in presence of water vapour and probably takes place by a different mechanism than by heating in vacuo. Sintering in vacuo is accompanied by widening of pores, whereas in presence of water vapour it is accompanied by narrowing of pores. The role played by water vapour in accelerating the sintering of magnesia is discussed and possible explanations are offered. Dual effects of water vapour might lead to the sintering acceleration of magnesia; chemisorption of OH groups which create cation vacancy on the surface leading to activated surface diffusion, and oxygen bridging between two adjacent/or opposite OH groups, particularly in narrow pores, leading to their narrowing.

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.

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.

Zirconium oxide superacids with different sulphate ion contents were prepared from Zr(SO4)2 using urea as precipitating agent. These oxides were subjected to different heating temperatures. Characterization was carried out by means of infrared spectroscopy, X-ray diffraction and nitrogen adsorption studies. The surface acidity was determined by the method described by Boehm [1]. Infrared results confirmed the presence of the sulphate ions and suggested the gradual lowering through heat-treatment of the symmetry of the sulphate ions by complex formation. Surface acidity was favored when the sulphate ions were in a bidentate state of ligation. The latter ligands seemed in turn to be stabilized by water. The strongest acidity was displayed in systems where a high concentration of bidentated sulphate ions was present in conjunction with high surface areas and micropore volumes.

Sample Controlled Thermal Analysis is used to highlight the role of the experimental pressure on the thermolysis of hexahydrated nickel nitrate to nickel oxide. At 5 × 10 −2 mbar, dehydration occurs before denitration begins. Formation of an amorphous material occurs, corresponding to the composition of the monohydrate. At 5 mbar, a basic salt is formed. Both these thermal decompositions occur in the solid state whereas at 100 mbar melting occurs. The nature of the nickel oxide formed depends strongly on the experimental pressure. Increasing this pressure increases the temperature of nickel oxide formation. At 5 × 10 −2 mbar an oxide of 80 m 2 g −1 is obtained whereas at 5 mbar and 100 mbar no significant surface area accessible to nitrogen is observed.

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 study has been made of the uptake of the cations Cr 3+ , Co 2+ , Ni 2+ , Cu 2+ and Ca 2+ by zirconia gels prepared at pH values of 3.75, 7.45 and 9.00 using zirconyl chloride as starting material and ammonia solution as precipitating agent. The base exchange capacities of the gels as measured by the uptake of Na + and Cl − ions were found to depend on the preparative pH. The anionic capacity decreases and the cationic capacity increases when precipitation occurs in a basic medium. Before the isoelectric point (≈5.0), the uptake of Cu 2+ , Co 2+ , and Ni 2+ seems to involve complex formation by exchange of water molecules of the aquo ion with gel OH groups. The K d values appear to depend not only on the first hydrolysis constant but also may be affected by the textural characteristics of the gels brought about by differences in preparative pH values. The uptake of Cr 3+ is suggested to follow a different mechanism mainly involving electrostatic attraction between negatively charged anions on the surface and the aquo chromium ion as well as any other hydrolyzed species formed in solution. The uptake of Ca 2+ appears to involve electrostatic interaction. After the isoelectric point, the uptake involves a simple ion-exchange mechanism. The effect of equilibrium pH as well as the preparative pH on the distribution ratio K d has been discussed.

Titanium oxides, with moderately high surface areas exhibiting a mixed mesoporous/microporous texture, were prepared from titanium ethoxide. The porosity seemed to stem from the loss of volatile components from the inner coordination sphere of the titanium ions. After impregnation with sulphate groups, a general decrease in surface area was observed. This decrease was more drastic at higher temperatures when the sulphate ions are in a bidentate state of ligation. A high sulphate concentration led to a distinctive decrease in the total pore volume and to the loss of the microporous texture. Micropore blocking appeared to be due to the presence of the bidentate sulphate groups. The latter are responsible for the higher surface acidities displayed by the sulphated oxides.

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 comparison of different methods to characterise the porosity of Egyptian mortars presented. The results obtained using adsorption manometry, mercury porosimetry and thermoporometry are complementary and overlap in certain regions of pore size.