Quaternary-Ammonium-Based Gels with Varied Alkyl Chains for the Efficient Removal of Toxic Acid Orange 7

We report the design and synthesis of thiol-norbornene based ingenious gels with pendent quaternary ammonium substituents on the norbornene backbone that are conducive to remove toxic anionic azo dye acid orange 7 (AO7) from wastewater. Three different alkyl side chains on the dangling quaternary ammonium moiety were chosen prudently and their performance towards removal of azo dye was scrutinised. The characterisation of all the precursor monomers and the ensuing gels were accomplished by(1)H,C-13 NMR and Mass spectrometry. The influence of extent of crosslinking on the solvent uptake ability was investigated and the swelling nature of the gels were correlated with the solubility parameter of different solvents. The surface morphology of the gels as visualised by FE-SEM analysis, revealed macropores in the range 4-12 mu m. The relationship between the composition of quaternary ammonium moiety on the gels and their viscoelastic properties was realised. The dye removal kinetics as observed from UV-Vis spectra were best correlated with the pseudo-second-order model and the adsorption isotherm of dye removal process was best fitted with the Langmuir isotherm model with high correlation coefficient. The material was found to be fairly recyclable up to 10(th)cycles with loss of only 8% efficiency. To the best of our knowledge, this is the first ever report on the removal of anionic dye based on thiol-norbornene photo crosslinked network. We believe that this design and composition-property relationship will enthuse the researchers to develop efficient chemical adsorbents based on environmentally benign systems.