F. Del Rey-Bueno

REMOVAL OF DIQUAT AND DEISOPROPYLATRAZINE FROM WATER BY MONTMORILLONITE-(Ce or Zr) PHOSPHATE CROSSLINKED COMPOUNDS

Abstract The adsorption of diquat (1,1′-ethylene-2,2′-dipyridilium dibromide) and one intermediate compound of the degradation of atrazine in water, deisopropylatrazine, on two montmorillonite-(Ce or Zr) phosphate crosslinked compounds from aqueous solution under conditions of varied temperature (288 K and 308 K) has been studied. The experimental adsorption isotherms obtained for diquat on both adsorbents may be classified as H-type of the Giles classification which suggests that diquat molecules are strongly adsorbed on the samples. For the deisopropylatrazine, L-type isotherms were obtained for both montmorillonite-(Ce or Zr) phosphate compounds, which suggests a moderate affinity of this metabolite by the active sites of the adsorbents. The increase of temperature from 288 K to 308 K does not clearly affect the adsorption process of diquat on both adsorbents whereas the deisopropylatrazine adsorption decreases slightly as temperature increases possibly due to a mainly physical process. Fourier transform infrared (FTIR) spectroscopic studies reveal that at the pH generated by the adsorbents, the cationic herbicide interacts to a greater extent with the negative charged surface of the adsorbents than deisopropylatrazine. For both model compounds, the ceriummontmorillonite adsorbent shows the higher capacity of adsorption compared with zirconiummontmorillonite adsorbent.

Surface properties and porous texture of montmorillonite-(Ce or Zr) phosphate cross-linked compounds

In this work, pore texture characteristics of a series of Ce(IV) or Zr(IV) montmorillonite phosphate cross-linked compounds obtained by precipitation of cerium or zirconium phosphate with dilute H3PO4 on the micelles of an aqueous montmorillonite suspension, previously submitted to ion-exchange processes to replace its exchange ions with Ce(IV) or Zr(IV), are studied. Surface areas and pore volumes of the different materials prepared are determined by N2 adsorption at 77 K and mercury porosimetry techniques. Analysis of the N2 adsorption isotherms by the t-De Boer and Dubinin-Radushkevich methods, revealed the presence of a certain degree of microporosity in all the materials studied. Moreover, analysis of the Hg intrusion data permitted to determine the contribution of the macro- and mesopores to the total surface area and pore volume of the prepared compounds. The results reveal a greater specific surface area for these compounds than for montmorillonite and the evolution of this parameter with thermal treatment is related to the nature and content of phosphate in the different samples. However, the changes recorded in the Vp and S/Vp parameters during the thermal process suggest that surface diffusion is the dominant transport mechanism in the sintering 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.

Surface properties of fibrous cerium (IV) and thorium (IV) phosphates

Abstract The evolution of some properties of cerium (IV) phosphate and thorium (IV) phosphate with temperature (range 110°C–600°C) has been studied. The original samples as well as the thermally actived ones were characterized by TG, DSC, IR spectroscopy and X-ray diffraction. Surface properties (surface area accessible to N 2 at 77.4 K, acid surface centers and porosity) are also studied. Isosteric heats and differential entropies of the adsorption processes, for the samples dried at 110°C, were calculated from the N 2 adsorption istherms at 77.4 K and 90.1 K.

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.

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.

Syntheses and surface properties determination of the ammonium, methylamine and ethilamine phases of cerium (IV) and thorium (IV) phosphates

Abstract The characterization of solid phases formed by Sorption of ammonia, methylamine and ethylamine on cerium (IV) and thorium (IV) hydrogen phosphates is reported in this paper. Separate samples of both phosphates, dried at 110°C and evacuated under a dynamic vacuum, were allowed to adsorb NH 3 , CH 3 -NH 2 and CH 3 -CH 2 -NH 2 into a gravimetric adsorption device until equilibrium was reached. X-ray diffraction patterns of the treated samples showed that retention of methylamine and ethylamine by cerium and thorium phosphates causes the interlayer spacing to expand. At the same time, in the corresponding IR spectra bands appear characteristic of the NH + 4 and R-NH + 3 groups formed by protonation of ammonia and alkilamines sorbed molecules. N 2 adsorption isotherms of the materials show that surface area available for the N 2 molecules is not sensitive to amine retention, while the surface acidity decreases strongly.