Enrique Jaimez

Formation of crystalline titanium(IV) phosphates from titanium(III) solutions

Crystalline phases of titanium (IV) phosphate have been obtained from titanium(III) chloride in phosphoric acid solutions. The {alpha}-titanium phosphate synthesis is possible at low temperature (60--80 C). {gamma}-Titanium phosphate is obtained by reflux with very concentrated phosphoric acid in 3--5 hours by oxidation with O{sub 2}. The influence in these reactions of several factors (concentration of reagents, molar ratio P:Ti in the reaction mixture, temperature and reaction) was studied. The {alpha}-titanium phosphate formation takes place in several steps through the sequential formation of amorphous titanium(IV) phosphate, {gamma}-titanium phosphate and/or a semicrystalline titanium(IV) hydroxophosphate, Ti(OH){sub 2}(HPO{sub 4}){center_dot}H{sub 2}O.

Synthesis and characterization of a novel layered Tin(IV) phosphate with ion exchange properties

A novel layered tin(IV) phosphate, Sn(NH{sub 4}PO{sub 4})(HPO{sub 4}){center_dot}2H{sub 2}O ({delta}-SnP-NH{sub 4}), was synthesized under mild hydrothermal conditions (190 C) in the presence of urea. The treatment of this compound with mineral acids gave a new phase of tin(IV) bis(monohydrogenphosphate), Sn(HPO{sub 4}){sub 2}{center_dot}3H{sub 2}O ({delta}-SnP-H). The layered nature of the solid was confirmed from amine intercalation, exfoliation in alkaline media, and the ion exchange behavior towards alkali and alkaline earth ions. High affinity (K{sub d}{sup Cs} {approximately} 5 {times} 10{sup 4} to 2 {times} 10{sup 5} mL g{sup {minus}1}) and capacity (160--200 mg Cs{sup +} per g of exchanger) for Cs{sup +} makes these materials promising for selective radioactive cesium removal from contaminated groundwater and nuclear waste.

Synthesis of phosphate–phenylphosphonates of titanium(IV) and their n-butylamine intercalates

Layered compounds of general formula Ti(PhPO3)x(HOPO3)2 –x·yH2O have been synthesized and characterized by X-ray powder diffraction, IR spectroscopy, TG and 31P magic angle spinning NMR spectroscopy. Different sources for the tetravalent metal in the synthetic process have been studied. The overall α-layered structure type is maintained while the ratio of phosphate to phenylphosphonate incorporated into the mixed derivative varies. The intercalation behaviour of mixed derivatives toward n-butylamine was also studied. The synthetic process shows kinetic control as a function of the tetravalent metal source; at low titanium(IV) concentration a mixture of products is obtained (phosphate + phosphonate) rather than a phosphate–phenylphosphonate single phase.

Intercalation of α,ω-Alkyldiamines into Layered α-Titanium Phosphate from Aqueous Solutions

Abstract This paper reports a study on the mechanism of intercalation of α,ω-alkyldiamines, NH 2 (CH 2 ) n NH 2 (n = 2–9), into layered α-titanium phosphate, α-Ti(HPO 4 ) 2 ·H 2 O. The intercalates synthesis was performed by titrating the host with aqueous solutions of alkyldiamine at 25%C. Crystalline phases showing a general formula α-Ti(HPO 4 ) 2 ·xNH 2 (CH 2 ) n NH 2 ·H 2 O (x ≤ 1) have been obtained. In every case, a monolayered arrangement of α,ω-alkyldiamine molecules into the host layers is formed. The average inclination angle of the alkyldiamine molecules to the phosphate layer and the intercalates packing density have been determined.

Effect of the method of preparation on the surface area and porosity of titanium(IV) phenylphosphonate

By using three synthetic procedures we have prepared layered α-titanium phenylphosphonate samples with different degrees of crystallinity and distinct textural parameters. The solids were prepared by reacting phenylphosphonic acid with different titanium compounds used as precursors. The materials obtained have a high thermal stability as shown by TGA measurements.An analysis of nitrogen adsorption-desorption isotherms on the resulting materials allowed determination of the corresponding specific surface area and porous texture. The N2-isotherms correspond to type IV of the BDDT classification with hysteresis loops of the type H-1. The materials are essentially mesoporous and it was not detected any mensurable microporosity. Crystallinity, BET surface areas and porosity are markedly dependent on the preparation procedure.

The titanium(I) salt ofN,N-(diphosphonomethyl)glycine: synthesis,characterisation, porosity and proton conduction

A new diphosphonic acid,N,N -(diphosphonomethyl)glycine, has been prepared. The titanium(iv) salt [Ti(dpmg)] of this acid has been characterised by X-ray powder diffraction, thermogravimetry, 31 P MAS NMR spectroscopy, isothermal N 2 adsorption–desorption and ac conductivity measurements. Phosphorus is present in a mixture of bonded phosphonate and free phosphonic acid groups. The material is both amorphous and porous (BET specific surface area=119 m 2 g -1 ), and its water content is relative humidity (RH)-dependent. Ti(dpmg) is a protonic conductor (at 90% RH and 90 °C, σ=3×10 -2 S cm -1 ), with conductivity exhibiting Arrhenius-type behaviour at constant RH. Conductivity and Arrhenius parameters are strongly dependent on the water content.

Survival cryopreservation of hop shoot tips monitored by differential scanning calorimetry

Differential scanning calorimetry is used for monitoring the survival conditions of hop (Humulus lupulus L.) shoot tips under cryopreservation. The survival is related to the absence of formation and growing of ice crystals during the cooling process as shown by the absence of heat effect from ice formation. Samples with different degrees of humidity were obtained through a controlled process of dehydration.

Thermal behaviour of α-titanium phosphate/n-alkylamine intercalation compounds

Abstract The thermal decomposition of the intercalation compounds α-Ti(OPO 3 ) 2 · 2C n H 2n+1 NH 3 · H 2 O ( n = 1–6) is studied. Decomposition takes place in seven steps. The crystallization water is lost in the first step and the condensation of the hydrogenphosphate groups into pyrophosphate takes place in the last step. In the remaining five steps, the intercalated amine is desorbed, the last product being TiP 2 O 7 in every case. Materials of formula TiH 2−y (OPO 3 ) 2 ·yC n H 2n+1 NH 3 (y = 2.0, 1.7, 1.3, 1.0) have been characterized. When y =2.0, 1.7 or 1.3 the n -alkylamines form a bimolecular film. The interlayer distance of the intercalates decreases with decreasing amine content of the solids. Likewise, the inclination angle of the alkyl chains with respect to the phosphate layer decreases. When y = 1.0 the n -alkylamines form a monomolecular film.

Intercalation of Cyclic Amines into α-Titanium Phosphate

The intercalation of some amines (aniline, benzylamine, cyclohexylamine,piperidine, pyridine, pyrazine and piperazine) into α-titaniumphosphate, Ti(HPO4)2×H2O,has been investigated by the batch method and/or by exposing the host to thevapour of the amines. The changes in the interlayer distance of the solidduring the intercalation process was followed by X-ray powder diffraction.The new intercalates were characterised by chemical and thermal analysis.Materials with a monolaminar and/or bilaminar arrangement of amine moleculesin the phosphate interlayer region are obtained depending on the nature ofthe amine. Due to steric hindrance, saturated phases are not obtained forall amines studied. The thermal decomposition of the intercalates (nitrogenatmosphere), takes place in three stages: dehydration, removal of amines andcondensation of the hydrogenphosphate to pyrophosphate groups.

Dihydroxotitanium( IV ) phosphate: characterisation and studies of n-alkylamine intercalation, ion-exchange properties, and proton conduction

The thermal behaviour and porosity of the dihydroxotitanium(IV) phosphate Ti(OH) 2 (HPO 4 )·H 2 O have been investigated. The intercalation of n-alkylamines, ion-exchange behaviour, and near-ambient-temperature proton conduction have also been studied and are discussed in comparison with the behaviour of layered crystalline titanium(IV) phosphates.