Antonios T. Sdoukos

Preparation of hydroxyapatite via microemulsion route.

Hydroxyapatite (HAp) was prepared using a microemulsion route in combination with the pH-shock wave method. The samples as received consisted of amorphous aggregated particles, which had remarkable mesoporosity with a narrow pore size distribution. After being heated at 650 degrees C, the A-type carbonate hydroxyapatite was crystallized at 635 degrees C in particles of similar size (40--120 nm) with no internal porosity. At a higher temperature (900 degrees C) a sintering process took place, resulting in network of a larger particles, consisting of HAp and beta-tricalcium phosphate (beta-TCP). The crystallization of HAp occurs at 635 degrees C with an activation energy of 62.7--72.2 kcalmol(-1).

Seasonal fluctuations of organochlorine and triazines pesticides in the aquatic system of Ioannina basin (Greece)

Abstract For the period September 1984 to November 1985 water samples from the aquatic system of Ioannina basin were analyzed every second month for organochlorine and triazines pesticides. The detected compounds were found to follow a seasonal pattern, with an increment during summer followed by a decrease during winter and an increase again during late spring. This pattern was apparent for Ioannina lake as well as for the Kalamas river connected to it through the Lapsistas canal and tunnel. The results are discussed in terms of the amounts of the detected pesticides used for farming in the vicinity of the Ioannina basin and the seasonal rainfall.

Influence of the structure of alumina–aluminium phosphate (AAP) catalysts containing Fe3+ and Cr3+ on their catalytic activity for isopropyl alcohol decomposition

Phosphate catalysts of the general formula Al100PxM20, where M = Al, Cr, Fe and x= 0, 4.5, 9, 18, 36, 72 and 144, have been prepared by coprecipitation of the corresponding nitrate salts and phosphoric acid with ammonia at pH 9.5. The resulting solids, after characterization by surface area and XRD measurements, were checked for their total surface acidity (Bronsted and Lewis) by pyridine titration and also tested for their catalytic activity towards the isopropanol dehydration. It was found that for the Al100PxAl20 solids the surface density of the acid sites increases on addition of phosphorus in a fairly regular manner. Substitution of some Al by Cr or Fe blurrs the picture of increasing acidity described above. The catalytic activity for isopropyl alcohol dehydration, calculated as the number of molecules decomposed per acid site per second, shows a minimum at x= 18–36 for Al100PxAl20 and Al100PxFe20, while for Al100PxCr20 a continuous increment with x is observed. The activity minima of the first two sets of solids coincide with the total absence of crystallinity as detected by XRD measurements. On the contrary, the continuous increment of activity for the Cr-containing catalysts is related to the presence of crystalline α-Cr2O3. This behaviour is attributed to competition between the diffusional and chemical steps controlling the reactions process. On the amorphous solids, where high values of activation energy and decreased activity are observed, the chemical reaction seems to be the slow and rate-determining step, while diffusion is fast because of the large porosity of the solids. The other samples show activation energies that are half those of the amorphous solids and larger activities. The controlling step in these cases seems to be diffusion, a fact related either to smaller pores or larger rate constants.

Influence of Cr3+ and Fe3+ cations on the structure of alumina–aluminium phosphate solids and their catalytic activity for N2O decomposition

Phosphate salts of the metals Al, Fe and Cr supported on alumina were prepared by co-precipitation with NH3 from solutions containing calculated amounts of the metal nitrates and phosphoric acid. The atomic ratio of the elements participating in the solids was Al : P : M = 100 : x : 20 where M = Al, Fe, Cr and x= 0, 4.5, 9, 18, 36, 72 and 144. The parent compounds Al100PxAl20 are formed by an endothermic decomposition of NH4NO3, which exists in the dried precipitant, to NH3 and HNO3. The resulting solids for x= 0 contain just γ-Al2O3, for x= 144 AlPO4 plus an amorphous phase, while for intermediate values of x a totally amorphous phase is formed. Substitution of 20 % Al by Fe alters slightly the route of decomposition, the endo-effect noticed above is followed by a small exothermic one, meaning probably the decomposition of part of the resulting nitric acid through anion breakdown to N2, H2O and O2. The structure of the resulting solids corresponds to α-M2O3 for x= 0 and MPO4 for x= 144, while for intermediate values amorphous materials are formed. An addition of Cr instead of Fe alters completely the route of decomposition of NH4NO3 to N2, H2O and O2 for reasons similar to those noticed for Fe. For x= 0 the resulting solids contain α-M2O3 oxides alone, for x= 144 they are totally amorphous and for intermediate values of x an amorphous phase plus crystalline Cr2O3 is formed. The behaviour of these systems for a simple redox reaction, namely N2O decomposition, shows a continuous drop of activity with phosphorous content. An analysis of the results according to the kinetic theory of poisoning indicates an order of deactivation between one and two, depending on the catalyst and the temperature. A mechanism which may explain this result is proposed. Thiele modulus and effectiveness factors which have been calculated show that for AlPAl an AlPCr species internal diffusion is the rate-determining step and the reaction occurs mainly on the external surface. For the AlPFe catalysts the rate of diffusion is almost equal to that of reaction.

Movement of methyl parathion, lindane and atrazine through lysimeters in field conditions

The movement of pesticides methyl parathion, lindane and atrazine due to leaching by rainfall was studied in lysimeters containing different types of soil from the loannina area of Greece. For a period between October 1985 to June 1986 the amount of pesticides was analysed in water samples from rainfall concentrated after filtration through the soils to a depth of 100 cm. The total amounts of each pesticide transported in this way were 0.15–0.26% for methyl parathion, 0.15–0.19% for lindane and 0.54–0.66% for atrazine of the initial amounts.

Low-temperature synthesis of perovskite solids LaMO3(M = Ni, Co, Mn)via binuclear complexes of compartmental ligand N,N′-bis(3-carboxysalicylidene)ethylenediamine

A new method has been developed for the low-temperature synthesis of perovskite solids LaMO3 where M = Ni, Co, Mn, using binuclear complexes of the ligand N,N′-bis(3-carboxysalicylidene)ethylenediamine (H4fsaen). The thermal decomposition of such complexes was studied using a thermobalance. The solids that formed after thermal treatment from 400 to 1000 °C were characterized by X-ray diffraction. Using this method perovskites LaNiO3, LaCoO3 and LaMnO3 have been synthesized at temperatures of ca. 500–600 °C. The above procedure yields solids with specific surface areas substantially higher than those obtained from ordinary ceramic methods, such as citrate and the nitrate routes.

Synthesis and properties of some mesoporous aluminophosphates with acidic surface sites

Mesoporous solids of the general formula Al100PxFe5-y[x= 0, 15, 60, and y(the final firing temperature in °C)= 400 or 600] have been prepared and characterised by surface area and porosity measurements, X-ray diffraction (XRD), Mossbauer spectroscopy and solid-state NMR (27Al and 31P). The surface acidities of the solids were also determined by ammonia adsorption, and the ζ-potential of the particles was measured. The gradual incorporation of phosphate groups into the alumina results in an increase of the surface area. The materials possess a pore-size distribution approximated by a mixed Gaussian and Lorentzian component which varies in a controllable manner according to the elemental composition. The material Al100P15Fe5 corresponds to that with the maximum surface area and pore volume. The XRD analysis showed that the materials without phosphorus possess the γ-Al2O3 structure, but they become amorphous upon addition of 15% P. A further increase in the amount of phosphorous to 60% initiates the transformation of the solids to AlPO4. The Mossbauer spectra suggest that, in the samples without phosphorus, the iron species are segregated, but the addition of phosphorus results in a dispersion of the iron into the aluminium phosphate matrix. The 27Al MAS NMR spectra indicate that the aluminium atoms are predominately in octahedral environments in the samples Al100P0Fe5-600 and Al100P15Fe5-600 but they become equally distributed between octahedral and tetrahedral sites in Al100P60Fe5-600. The ζ-potential of the particles in aquatic suspension indicates that this parameter is sensitive to the temperature of thermal treatment. The surfaces of the solids showed increased acidity which is linearly related to the phosphorus content.

Effect of the first row transition metal cations on the mode of decomposition of ammonium nitrate supported on alumina-aluminum phosphate and the final products obtained

Abstract The mode of decomposition of ammonium nitrate in mixtures with 80% Al 2 O 3 and 20% of first row transition metal oxides MOx (M = Mn, Cr, Fe, Co, Ni, Cu, Zn) and containing different amounts of phosphorus (Al:M:P = 100:20:18 and 100:20:144) has been examined under non-isothermal conditions in a thermogravimetric balance. Pure ammonium nitrate is decomposed endothermically while addition of Al 2 O 3 shows a stabilizing action of this endo effect. Substitution of 20% of aluminum by a first row transition metal (M = Mn, Cr, Fe, Co, Ni, Cu and Zn) shows that zinc does not alter the route of decomposition while the rest show a tendency to decompose ammonium nitrate exothermically. The catalytic action of the cations toward such an exothermic route is Fe = Ni 4 NO 3 are primarily related to electrochemical Gibbs free energy Δ G = − nFE of the process M oxidized /M reduced . On top of this the crystal field stabilization effect for each particular cation should be taken into account. The extent of exothermic decomposition of the ammonium nitrate seems to influence the specific surface area of the final product in a positive manner in the absence of phosphorus but in a negative manner in its presence. The reasons underlying this effect should be attributed to the stabilizing action of phosphorus on the decomposition route.

De-sintering action of phosphorus in alumina–aluminium phosphates (AAP) containing transition-metal ions (M = Cr, Mn, Fe, Co, Ni, Cu, Zn)

The de-sintering action of phosphorus added in different amounts to alumina containing 20% of a second cation M (M = Cr, Mn, Fe, Co, Ni, Cu, Zn) has been quantified from measurements of the surface areas of the solids. The solids were prepared by co-precipitation with NH3 from solutions containing calculated amounts of metal nitrates and phosphoric acid and by heating at 600 °C. The atomic ratio of the elements in the obtained solids was Al : P : M = 100 : x : 20 where x= 0, 4.5, 9, 18, 36, 72 and 144. The surface areas of the solids were measured by the B.E.T. method. The results showed that the maximum de-sintering action of phosphorus, as estimated from the change of the surface area of the solids, appeared at x= 9. Thereafter the surface area decreased, at a different pace for each cation, and at x= 36 it returned to the original value at x= 0. Further addition of phosphorus decreased the surface area even further and at x= 144 it fell almost to zero, depending on the second cation. The strongest sintering ability was exhibited by Cu and Mn and the smallest by Cr, Fe and Ni, with the rest occupying intermediate positions. An explanation of the results is attempted by taking into account the enthalpies of formation of the corresponding metal phosphates and aluminates formed in each case.

Describing movement of three pesticides in soil using a cstr in series model

The movement of methyl parathion, lindane, and atrazine in two successive soil layers has been described by a Continuously Stirred Tank Reactor (CSTR) model. In the first layer the concentration of each pesticide continuously decreased with time. In the second layer, a peak maxima appeared, whose position might be dependent on the water solubility of each pesticide and their adsorption by soil components. The physical process of transfer with the precipitating rainfall could be the main factor governing the transfer of pesticides, while the chemical, photochemical and biological processes of degradation acted uniformly on top of this process.