Claudiu C. Pavel

Synthesis and characterization of the microporous titanosilicates ETS-4 and ETS-10

In the last years the interest in new zeolitic structures has increased. Some of these materials possess improved catalytic and adsorptive properties in comparison with the classical aluminosilicates. Among these materials are the AlPOs which opened new roads in the study of zeotypes. Subsequently, the study of titanium- and silicon-based molecular sieves was deepened. Among the numerous synthesized structures ETS-10 is a totally synthetic one while ETS-4 is the synthetic counterpart of the mineral zorite. In this paper a complete study is devoted to the ETS-10 and ETS-4 crystallization fields as a function of the quantities of Na2O and TiO2 in the initial gel. The influence of the initial pH on the two phases was also studied. The crystallization curves as a function of time for ETS-10 and ETS-4 with different initial Na and Ti contents were determined and analyzed. The SEM pictures allowed one to determine the morphology of the two ETS phases. Their compositions were determined by chemical analysis, and local structural characteristics were derived from NMR analysis.

The sorption of some radiocations on microporous titanosilicate ETS-10

The microporous titanosilicate ETS-10 synthesized from gel with following molar composition: 1.0 Na2O: 1.49 SiO2 : 0.2 TiO2 : 0.6 KF : 1.28 HCl : 39.5 H2O was subjected to sorption of radioactive cations 115Cd2+, 204Hg2+, 60Co2+ and 137Cs+ (M) from aqueous solution, in the absence of ionic competition. The uptake of these cations on the ETS-10 was compared by means of the distribution coefficient (Kd) versus contact time and sorption capacity (R) at equilibrium. The FT-IR spectra of M-ETS-10 sorption products exhibit a modification of the absorption band, principally at 381 cm-1.

Contrasting immobilization behavior of Cs+ and Sr2+ cations in a titanosilicate matrix

ETS-10 titanosilicate was tested as an adsorbent for the removal of Cs+ and Sr2+ cations from radioactive waters, considering both the ion exchange and the behaviour of the loaded adsorbent during thermal conditioning. The studies indicate that ETS-10 has a high and similar affinity for both Cs+ and Sr2+ cations reaching the ion exchange capacity of ETS-10 at a concentration of about 50 milliequivalents gram per liter. Thermal treatment of Cs+- and Sr2+-exchanged ETS-10 materials results in melting at approximately 700 °C. The melting temperature increases with the initial Cs+ and Sr2+ concentration and is higher for Sr2+ than for Cs+ exchanged ETS-10. Recrystallisation occurs only in the presence of Sr2+ as evidenced by the exothermic effects between 800 and 900 °C. After calcination of Cs+- and Sr2+-exchanged ETS-10 in air at 800 °C, two types of materials were obtained: an amorphous glass material with homogeneous Cs+ distribution and a strontium fresnoites glass–ceramic material.

Improvement of retention capacity of ETS-10 for uranyl ions by porosity modification and their immobilization into a titanosilicate matrix

The retention capacity of ETS-10 titanosilicate for uranyl ions was improved by generation of additional intra-crystalline porosity with formation of an extended silica-rich surface area. Chemical bonds between uranyl groups and [SiO4] tetrahedra were found. By calcination at 800 °C, the uranium-loaded ETS-10 transforms into a inert titanosilicate matrix that encapsulates uranium.

Study of the thermal dehydration of metal-exchange ETS-10 titanosilicate

The ion exchange of nickel, cobalt and copper on ETS-10 and the dehydration kinetics of metal-exchanged ETS-10 titanosilicate were studied by means of X-ray diffraction, scanning electron microscopy and thermal analyses. The number of water molecules in the metal-exchaned ETS-10 is higher than in parent ETS-10 and the activation energies for dehydration vary in the sequence: ETS-10> Ni-ETS-10 >Co-ETS-10 >Cu-ETS-10. A part of copper cations precipitate on the strong basic surface of ETS-10 as claringbullite (Cu4Cl(OH)7·0.5H2O). The differential thermogravimetry (DTG) curves show that the maxima of dehydration temperature are shifted towards lower temperature as the metal concentration increases.

Influence of zirconium on the crystallisation kinetics of ETS-4 molecular sieves

The scope of the paper is to synthesize and characteirze ETS-4 molecular sieve starting from gels containing titanium and zirconium: xNa2O-0.2TiO2-0.6KF-yZrO2-1.28xHCl-1.49SiO2-39.5H2O with 0.5≤x≤1.5 and 0.0≤y≤0.2. The study is based on the physicochemical characterization of the various products and on the determination of the kinetic parameters.

Synthesis of microporous titanosilicates ETS-10 and AM-2 using Ti2(SO4)3

Abstract The microporous titanosilicates ETS-10 (Engelhard Titanium Silicate−10) and AM-2 (Aveiro—Manchester−2) were synthesized using titanium (III) sulphate as the titanium source without the organic additive. This reagent is not sensitive to moisture in the air, and therefore, its use makes the preparation of the synthesis gels more convenient and simpler than TiCl 4 . Pure ETS-10 and AM-2 were obtained from gels of composition: x(1.28Na 2 O-K 2 O)-yTiO 2 -5.0SiO 2 -350H 2 O with 2.5≤x≤5.5 and 0.75≤y≤2.0.

Study of ETS-10 crystallization in the presence of TAABr salts

Abstract ETS-10 zeolites were synthesized under hydrothermal conditions from gels of composition 1.0Na 2 O-0.2TiO 2 -0.6KF-1.28HC1-0.2TAABr-1.49SiO 2 -39.5H 2 O with TAA=tetramethyl(TMA)-, tetraethyl(TEA)-, tetrapropyl (TPA)- and tetrabutyl(TBA)-ammonium ions. The samples were characterized by XRD, thermal analysis (DTG, DSC), SEM and multinuclear 13 C- and 29 Si-NMR. The reaction kinetics were determined together with the energy of activation. The following sequence was found for E a : ETS-10>TMA-ETS-10∼ TEA-ETS-10>TPA-ETS-10>TBA-ETS-10. The chemical shifts of the organic cations showed clearly that the TAA + ions are quite hydrated in the ETS-10 channels.