Adsorption and reaction of sulfachloropyridazine sulfonamide antibiotic on a high silica mordenite: A structural and spectroscopic combined study

Owing to their acidic nature, sulfonamide antibiotics concentrate in anionic form in water bodies where they can remain unchanged for long periods of time, accounting for great concern for antibiotic-resistance issues. In this study the removal of sulfachloropyridazine (4-amino-N-(6-Cl-3-pyridazinyl)benzene sulfonamide) antibiotic from water by adsorption on a high silica mordenite with channel window dimension comparable to that of the antibiotic, and with a significant concentration of internal silanol groups due to the dealumination process, was investigated. The adsorption of sulfachloropyridazine by mordenite at room temperature was completed within 4 h with the maximal amount of adsorbed antibiotic of 15.1% zeolite dry weight. The desorption trials elucidated the irreversibility of the adsorption process. The embedding of sulfachloropyridazine into mordenite channels was confirmed by a combined XRPD and FTIR study. Rietveld structure refinement revealed that the incorporation of sulfachloropyridazine molecules caused changes in the dimension of the zeolite channel systems, when compared to the parent zeolite, and a close vicinity of the heterocycle ring nitrogen to the oxygens of mordenite side pocket. FTIR revealed a strong perturbation of the vibrational modes of both the pyridazinyl ring and mordenite silanol groups upon antibiotic adsorption. When the adsorption was conducted at 65 degrees C, an unfavourable temperature effect was highlighted and, interestingly, sulfachloropyridazine transformed with 100% selectivity to 4-amino-N-(6-hydroxyl-3-pyridazinyl)benzene sulfonamide. A nucleophilic aromatic substitution (SNAr) mechanism was suggested for the formation of the reaction product It is proposed that the H-bond between mordenite silanol groups and pyridazine nitrogen atom, clearly detected by FTIR, stabilize in the ring partial positive charges favouring the displacement of the chloride leaving group. (C) 2012 Elsevier Inc. All rights reserved.