Organophilic zeolite Y used in PRB technology: regeneration after sulfonamide antibiotics removal from water.

Introduction The large amount of non-biodegradable sulfonamide antibiotics used in hospitals, feedstocks and in fish farming cause their occurrence in the aquatic environment resulting in the dramatic emergence of antibiotic resistance in fish pathogens and in the transfer of these resistance determinants to bacteria in land animals and to human pathogens [1]. Permeable Reactive Barrier (PRB) is an innovative technology for the remediation of aquifers based on reactive materials which capture and remove or break down the contaminants, releasing uncontaminated water. Recently, a cheap and environmentally friendly material with excellent sorbent properties for sulfonamides has been proposed: an hydrophobic high-silica zeolite Y [2,3]. At maximal solubility, it is able to almost completely (>90%) and quickly (t<1 min) remove sulfonamide antibiotics from water media [2, 3]. Other advantage of zeolites as permeable barrier is their stability towards radiative and thermal treatments necessary to induce complete degradation of adsorbates and therefore to regenerate exhausted sorbents. In this work, the regeneration capacity of an hydrophobic high-silica zeolite Y after sulfamethoxazole antibiotic adsorption [3] was investigated by in situ high-temperature synchrotron X-ray powder diffraction to monitor the structural modifications induced by the regeneration treatment. This kind of information is crucial to design and optimize the regeneration treatment of zeolites with a very high potential for application in water remediation technologies. Experimental A powder sample of hydrophobic high-silica (SiO2/Al2O3 ~ 200) zeolite Y (a=24.248(1) and V=14256.7(1), s.g. Fd-3) loaded at room temperature in aqueous solution with sulfamethoxazole sulfonamide antibiotic (C10H11N3O3S, SMX hereafter) [3] was used for this study. The in situ high-temperature X-ray powder diffraction experiments were performed at the GILDA beamline at ESRF (Grenoble), using a fixed wavelength of 0.653 Å. The powder sample was packed in a 0.3 mm diameter quartz glass capillary, open at both ends, and heated in situ using a hot air stream. 45 diffraction patterns were recorded on a flat image-plate detector while heating the sample up to 575 °C (heating rate 10 °C/min) (temperature ramp) and then keeping this temperature for 120 minutes (isotherm mode). A further powder pattern was collected after cooling down the sample up to room conditions for 2 h (reverse). The evolution of the structural features was followed by full profile Rietveld refinements. An ex situ regeneration was also performed on the sample heated up to 550 °C (heating rate 10 °C/min) and kept at this temperature for 4 hours. The corresponding powder pattern was then compared to those collected in situ at the same temperature. Results and discussion 576 Figure 1 shows selected XRPD patterns collected in situ and the reverse and ex-situ patterns. It is evident that the thermal treatment necessary to regenerate the exhausted sorbent does not affect the crystallinity of zeolite Y. Figure. 1. Selected XRPD patterns collected in situ (in black). The reverse and ex situ powder patterns are also reported (grey lines). Figure 2. Normalized unit-cell parameters as a function of time (minutes)/temperature (°C). Figure 3. Number of SMX molecules/u.c. as a function of time (minutes)/temperature (°C). The evolution of the unit-cell parameters upon heating are shown in Figure 2. Between 25- 200°C, the unit-cell parameters slightly increase with increasing T. In this temperature range, the relaxation of the H-bonding interactions between SMX and the framework oxygen atoms induces a slight ditrigonal 6-membered rings (6MRs) regularization and a 12-membered rings (12MR) ellipticity decreasing. Above 200 °C, the degradation and expulsion of SMZ molecules cause a double-six rings (D6Rs) tetrahedra cooperative anti-rotation which results in the flattening of the D6R itself and in a consequent cell volume contraction. At the same time, a regularization of the ditrigonal 6MRs and of the elliptical 12MRs is also observed. Around 400-450 °C, in correspondence with the final degradation of SMX, the unit cell volume is still contracting and no further changes in D6R and 12MR are observed until the isotherm is reached. During the heating in the isotherm mode, the unit-cell parameters evolution reaches a plateaux and the SMX content is reduced to zero. After the complete regeneration, the unit-cell volume increases again. This process is followed by an increase in the D6R thickness, a ditrigonalization of the 6MR and by an expansion of the 12MR which keeps its circular shape. All the features of the pattern and the unit-cell parameters of the starting material [4] are well recovered after cooling down the sample up to room conditions (reverse) and after heating the sample ex situ (ex situ). Conclusions The in situ high-temperature synchrotron X-ray powder diffraction allowed us to demonstrate that the thermal treatment at 575 °C assures a complete regeneration of exhausted Y zeolite. The removal of SMX induces deformations of the framework which do not affect the crystallinity of the sorbing material. These results indicate that high-silica zeolite Y is an affordable material for water clean-up and drug delivery. References [1] B. Hileman, Chem. Eng. News 79 (2001) 31-33. [2] I. Braschi, S. Blasioli, L. Gigli, C.E. Gessa, A. Alberti, A. Martucci, J. Hazard Mater.178 (2010) 218–225. [3] S. Blasioli, C.T. Johnston, A. Martucci, L. Gigli, I. Braschi, A. Alberti, C.E. Gessa, Advances in Zeolites Science and Technology (2011) 49-52, De Frede Eds., Napoli. [4] L. Pasti, A. Martucci, M. Nassi,A. Cavazzini, A. Alberti, R. Bagatin, Micropor. Mesopor. Mat. 160 (2012) 182– 193.