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

A focused library of poten- tial 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-d-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 ca- pable of sequestering significant quan- tities of the aromatic cationic dye, methylene blue, from aqueous solution (upto1.02gofdyepergramofdryge- lator). Cryo-transmission electron mi- croscopy of two of the gels revealed an extensive network of high aspect ratio fibers. The structure of the fibers al- tered dramatically upon addition of 20 wt % of the dye, resulting in aggre- gation and significant shortening of the fibrils. This study demonstrates the fea- sibility for these novel gels finding ap- plication as inexpensive and effective water purification platforms.