Lara Leardini

Regeneration of high-silica zeolites after sulfamethoxazole antibiotic adsorption: a combined in situ high-temperature synchrotron X-ray powder diffraction and thermal degradation study

Abstract The thermal regeneration of sulfamethoxazole (SMX)-loaded Y and ZSM-5 zeolites was studied using a combined in situ high-temperature synchrotron X-ray powder diffraction and thermal degradation study. The evolution of the structural features was monitored in real time in the 30-575°C temperature range by full-profile Rietveld analysis. SMX thermal degradation pathways into high-silica zeolite antibiotic adducts, as well as the release of evolved species are similar to those for pure SMX. The adsorption/desorption process occurs without any significant loss of zeolite crystallinity, though slight deformations to the channel apertures are observed. Regenerated zeolites regain almost perfectly ‘bare’ (i.e. unloaded) material unit-cell parameters and only a slight memory effect, in terms of structural deformations induced by the process, is registered in the channel geometry. Interestingly, these changes do not affect the adsorption properties of the regenerated samples, which are able to re-adsorb comparable amounts of antibiotic molecules as in the first adsorption cycle.

Removal of emerging organic contaminants from aqueous systems: adsorption and location of methyl-tertiary-butyl-ether on synthetic ferrierite

Abstract This study reports on experimental results concerning methyl-tert-butyl-ether (MTBE, C5H12O) adsorption from water into the pores of siliceous zeolite ferrierite (FER) by combining powder X-ray diffraction analyses and chromatography techniques. Rietveld structure refinement (Immm space group) highlighted the presence of two crystallographically independent MTBE sites located in the 10-ring channel parallel to the [001] direction (MTBE1) and in the ferrierite cage (MTBE2), respectively. On the whole, Rietveld refinement revealed clearly the incorporation of ~1.8 MTBE molecules per unit cell, in very good agreement with the weight loss given by thermogravimetric analyses, and saturation capacity as determined by adsorption isotherms. Rapid kinetics combined with good adsorption suggests that FER can be used beneficially as an adsorbent medium in removing this emerging organic contaminant from water.

Compressibility of microporous materials with CHA topology: 2. ALPO-34

Abstract The HP behavior of ALPO-34 as-synthesized was investigated by means of in-situ synchrotron X-ray powder diffraction, in the frame of a wider project aimed at understanding the role of the framework/extraframework content in the P-induced deformation mechanisms of natural and synthetic microporous materials with CHA framework topology. ALPO-34 compressibility under non-penetrating P-transmitting medium was determined up to 6.0 GPa and upon decompression to Pamb. After an initial large structure deformation at P < 0.4 GPa, a regular volume reduction was observed up to about 3 GPa. Above 3.1 GPa, an abrupt change in the behavior of all cell parameters was observed, accompanied by an evident decrease in compressibility. The isothermal Equation of State (EoS), refined with a II-order Birch–Murnaghan EoS from 0.4 to 3.1 GPa, yielded the following parameters: V0 = 755(1) Å3, K0 = 54(3) GPa. No complete X-ray amorphization was achieved up to the highest investigated P value. A complete reversibility of the unit cell parameters was observed upon P release. The compressibility behavior of ALPO-34 was compared with that of the other CHA-type zeolites. The volume reduction observed for natural chabazite, and for SAPO-34 and ALPO-34 as-synthesized, was 6.2%, 9.4%, and 6.0%, respectively. Notwithstanding the presence of morpholine molecules, as a structure directing agent, in the two as-synthesized phases, they exhibited significantly different compressibility. This can be interpreted as due to the octahedral coordination of part of the ALPO-34 framework aluminum, leading to a more rigid framework compared to that of SAPO-34, which contains only tetrahedral aluminum.

HP-induced penetration of guest molecules in high-Si mordenite

A high-Si mordenite (HS-MOR, SiO2/Al2O3 ~ 200, s.g. Cmcm) was investigated by in-situ synchrotron XRPD under HP using silicone oil (s.o.) as non-penetrating pressure transmitting medium (PTM), and the following penetrating PTM: (16:3:1) methanol: ethanol:water (m.e.w), (3:1) water:ethanol (w:e), ethylene glycol (e.g.) and resorcinol (res). The experiments were performed in DAC at SNBL1 (ESRF, Grenoble). The evolution of the structural features was followed by full profile Rietveld refinements. In the Pamb-1.2 GPa range, the volume contraction of HS-MOR compressed in s.o. (Tab. 1) is the highest found among the HS zeolites studied up to now in the same P range [1-2]. Above this P value, a rapid and irreversible loss of long range order is observed in the diffraction patterns. These findings suggest a gradual P-induced amorphization. The main results of the experiments with penetrating PTM are the following (Tab. 1 and Fig. 1): i) no complete X-ray amorphization and phase transitions achieved up to the highest investigated P; ii) penetration of additional guest species into the channels, even at very low P; iii) lower cell-volume reduction with respect to that found in s.o. in the same P range; iv) partial reversibility of the P-induced effects upon decompression. The lower compressibility of HS-MOR in penetrating PTM with respect to s.o. is due to the entrapping of additional guest molecules, which contributes to sustaining the mordenite framework and stiffening the material.