pH-tunable hydrogelators for water purification: structural optimisation and evaluation

Wood, D. M., Greenland, B. W., Acton, A. L., Rodríguez-Llansola, F., Murray, C. A., Cardin, C. J. ORCID: https://orcid.org/0000-0002-2556-9995, Miravet, J. F., Escuder, B., Hamley, I. W. ORCID: https://orcid.org/0000-0002-4549-0926 and Hayes, W. ORCID: https://orcid.org/0000-0003-0047-2991 (2012) pH-tunable hydrogelators for water purification: structural optimisation and evaluation. Chemistry - A European Journal, 18 (9). pp. 2692-2699. ISSN 0947-6539 doi: 10.1002/chem.201102137

Abstract/Summary

A focused library of potential hydrogelators each containing two substituted aromatic residues separated by a urea or thiourea linkage have been synthesised and characterized. Six of these novel compounds are highly efficient hydrogelators, forming gels in aqueous solution at low concentrations (0.03–0.60 wt %). Gels were formed through a pH switching methodology, by acidification of a basic solution (pH 14 to ≈4) either by addition of HCl or via the slow hydrolysis of glucono-δ-lactone. Frequently, gelation was accompanied by a dramatic switch in the absorption spectra of the gelators, resulting in a significant change in colour, typically from a vibrant orange to pale yellow. Each of the gels was capable of sequestering significant quantities of the aromatic cationic dye, methylene blue, from aqueous solution (up to 1.02 g of dye per gram of dry gelator). Cryo-transmission electron microscopy of two of the gels revealed an extensive network of high aspect ratio fibers. The structure of the fibers altered dramatically upon addition of 20 wt % of the dye, resulting in aggregation and significant shortening of the fibrils. This study demonstrates the feasibility for these novel gels finding application as inexpensive and effective water purification platforms.