A. Garcia-Rodriguez

Lithium adsorption by acid and sodium amberlite

In this paper we used a previously reported model for examining the adsorption of nonelectrolytes in solution by solid adsorbents to study the adsorption of lithium(I) cations by acid and sodium amberlites, which is an ion-exchange process. Based on the results, both are equilibrium processes and obey a kinetic law with a unity partial order in the Li+ concentration. The kinetic results were used to calculate the specific rate constants and thermodynamic activation functions involved. Also, equilibrium isotherms were used to determine the corresponding ion-exchange capacities, the individual equilibrium constants, and the thermodynamic functions for the overall process.

Synthesis and characterization of montmorillonite-(Ce or Zr) phosphate crosslinked compounds

Abstract A series of montmorillonite-(Ce or Zr) phosphate crosslinked compounds has been synthesized by reaction of a cerium or zirconium cation exchanged montmorillonite (diameter ⩽ 2 μm) with phosphoric acid under appropriate conditions of concentration, addition rate and temperature. The materials thus obtained were characterized by chemical and thermal analyses, X-ray diffraction, IR spectroscopy and SEM-EDX. The results show that tetravalent metal phosphate acts as a cement among the clay particles, hindering material dispersion in aqueous media. At the same time, this framework limits the cerium or zirconium hydrolysis. The surface area of the metal(IV) phosphate crosslinked montmorillonite obtained increases, relative to that reported for the individual precursors. On the other hand, micrographs and microanalyses of the samples show that a fraction of the Ce(IV) or Zr(IV) ions remain as exchange cations in the clay particles.

Adsorption of ammonia over halloysite activated at different temperatures

Abstract The evolution of some properties of halloysite with heat treatment (temperature range 110°C–1000°C) has been studied. The original samples as well as the thermally active ones were characterized by TG, DSC, IR spectroscopy and X-ray diffraction. The influence of the temperature on the surface properties (surface area, acid surface centres and porosity) are also studied. The surface area available to N2at 77.4K ranged between 42 m2.g−1 and 126 m2.g−1 and the number of surface acid centres ranged from 4.9 × 1019 c.a.g−1 to 10.3 × 1019 c.a.g−1. Once the properties accounting for the surface activity of halloysite and hence for its potential use as adsorbent had been determined, the adsorption of ammonia gas at 273K on samples activated between 110°C and 1000°C was studied. The surface area accessible to NH3 molecules a 273K ranged between 47 m2.g−1 and 132 m2.g−1.

Synthesis and structure of a 1:2 addition compound of mercuric chloride with 6-amino-1,3-dimethyl-5-formyluracil

Abstract Crystals of the adduct belong to the monoclinic P 2 1 / c space group with a=10.606(1), b =14.829(1), c =13.498(1) A, β=111.63(1)° and Z =4. The structure was refined on 1539 observed Mo K α reflections to R =0.026. The unit cell contains ligands and linear HgCl 2 molecules packed in an arrangement optimizing interligand van der Waals contacts and HgO secondary binding. The HgCl 2 molecule deviates slightly from linearity (ClHgCl=175.5°) with a mean bond length of 2.292 A. Both independent ligands have their formyl oxygen retained on the side of the NH 2 group by hydrogen bonding. Near the plane perpendicular to the HgCl bonds are found, around each Hg, one carbonyl O2 and three formyl oxygens with Hg···O distances ranging from 2.716 to 3.011 A. The compound dissociates into HgCl 2 and free ligand when dissolved in Me 2 SO.

ACIDITY OF MONTMORILLONITE-(Ce OR Zr) PHOSPHATE CROSS-LINKED COMPOUNDS

The nature and number of acid sites per unit weight on a series of materials obtained by interaction of a montmorillonite with zirconium or cerium hydrogenphosphates precipitated in situ by reaction between their precursors have been investigated.The quantitative determination of the surface acidity has been carried out by three different methods: titration with triethanolamine in aqueous media; TG analysis of the samples after n-butylamine treatment and vacuum desorption; and chemisorption of NH3 at 239.8 K. Additional information about the nature of the surface acid sites has been obtained from the IR spectra of the samples with bases adsorbed.Results show that the acid site density on the montmorillonite-cerium or zirconium phosphate cross-linked compounds is greater than on the parent montmorillonite and increases as the content in tetravalent metal phosphate rises throughout the different series. Also the number of acid sites for the cerium phosphate-montmorillonite materials is lower than for zirconium ones and the characteristics obtained depend on the bases used for their evaluation.The presence of two IR adsorption bands at 1400 and 3145 cm−1, assigned to the NH4+ ion, and the absence of the 1170–1361 cm−1 bands, characteristic of the NH3 adsorbed on a Lewis site, strongly suggest the Brönsted character of the acidity of these compounds.

Characterization of a fibrous thorium phosphate containing Co(II) and Ni(II) as exchange ions

Abstract The influence of the temperature (range 110–600°C) on the surface properties of two samples of fibrous thorium phosphate with Co(II) and Ni(II) as exchange ions respectively has been studied. The original samples as well as the thermally activated ones have been characterized using the following techniques: TG, DSC, IR and X-ray diffraction. The surface area accessible to N2 at 77.4 K ranged between 15 and 21 m2g−1 for Co-ThP samples and between 18 and 23 m2g−1 for Ni-ThP ones. The number of surface acid centres ranged from 1.11×1020 to 1.64×1020 a.c.g−1 for Co-ThP samples and from 1.04×l020 to 1.79×l020 a.c.g −1for Ni-ThP ones.

Thermal studies on Ni(II), Cu(II) and Pd(II) complexes of 6-amino-5-formyluracil and its N-methyl derivatives

The thermal behaviour of 6-amino-5-formyluracil (HFU), 6-amino-1-methyl-5-formyluracil (1-MFU), 6-amino-3-methyl-5-formyluracil (3-HFU) and 6-amino-1,3-dimethyl-5-formyluracil (HDFU) is described. Only HDFU is shown to contain crystallization water. Dehydration and fusion enthalpy values have been calculated from the DSC curves. Likewise, the thermal behaviour of new complexes obtained by reaction between the above pyrimidine derivatives and Ni(II), Cu(II) and Pd(II) ions is reported.ZusammenfassungDas thermische Verhalten von 6-Amino-5-formyluracil (HFU), 6-Amino-1-methyl-5-formyluracil (1-HFU), 6-Amino-3-methyl-5-formyluracil (3-HFU) und 6-Amino-1,3-dimethyl-5-formyluracil (HDFU) wird beschrieben. Nur HDFU enthält Kristallwasser. Dehydratisierungs- und Schmelzenthalpiewerte wurden aus den DSC-Kurven berechnet. Auch über das thermische Verhalten neuer, durch Reaktion der obigen Pyrimidin-Derivate mit Ni(II)-, Cu(II)- und Pd(II)-Ionen erhaltenen Komplexe wird berichtet.РезюмеОписано термическое поведение 6-амино-5-форм ил-, 6-амино-1-метил-5-формил-, 6а мино-З-метил-5-формили 6-амино-1,3-диметил-5-форми лурацилов. Показано, ч то только последнее соединени е содержит кристалли зационную воду. На основе кривых ДСК вычислены значения энтальпии д егидратации и плавле ния. Подобным образом изу чено также термическ ое разложение комплекс ов вышеприведенных п роизводных пиримидина с двухвал ентными никелем, медью и палла дием.