A bipyridinium-based polyhydrazone adsorbent that exhibits ultrahigh adsorption capacity for the anionic azo dye, direct blue 71

A novel alkyl-functionalized polyviologen-based polymer, 6.nBr, was synthesized via step-growth polymerization of water soluble bipyridinium dialdehyde 5.2Br with an alkyl-substituted aryl dihydrazide 4 in aqueous acidic medium. The chemical structure of the new polymer was verified by 1H NMR and Fourier-transform infrared (FT-IR) spectroscopy techniques and the molecular weight distribution (MWD) was determined using high temperature gel permeation chromatography (HT GPC). Investigation of the surface morphology of 6.nBr was conducted by SEM analysis, which revealed that the material self-assembled to form a porous supramolecular material. The adsorption properties of the polymer, as an insoluble heterogeneous adsorbent towards the uptake of Direct Blue 71 (DB71), were evaluated. Following a detailed investigation of the adsorption kinetics and isotherms for the adsorbent, it was revealed that polymer 6.nBr can be used to efficiently remove DB71 at varied pH values from water. The adsorption process was fast, and occurred via both chemi- and physisorption, with the primary driving force being ionic interactions. The material 6.nBr outperformed many reported adsorbents in terms of Langmuir maximum adsorption capacity (3767 mg/g) and equilibration time for the sequestration of DB71. Polymer 6.nBr is easily synthesized, scalable, and a very promising adsorbent for the removal of anionic pollutants from water.