Folic Acid-Polyaniline Hybrid Hydrogel for Adsorption/Reduction of Chromium(VI) and Selective Adsorption of Anionic Dye from Water

A porous 3D folic acid (F)-polyaniline (PANI) hybrid hydrogel (F-PANI), produced by in situ polymerization of aniline, exhibit highest compressive stress (15.1 kPa), 3D hierarchical network morphology with BET surface area 236 m2/g. Here, PANI is present in emeraldine salt (ES) state, which facilitates excellent adsorption of anionic pollutants. It exhibits an extremely high adsorption capacity for Cr(VI) and during adsorption Cr(VI) is reduced to Cr(III).The electrical impedance spectra of the Cr(VI) adsorbed xerogel, support the conversion of PANI chains from ES to pernigraniline base(PB) making the xerogel more resistive. It also selectively adsorbs anionic dyes, the adsorption capacity increases with decrease of pH. Both the adsorption data are found to be well explained through pseudo-second-order kinetic model, and they obey Langmuir adsorption isotherm. F-PANI2 showed high adsorption capacities selectively toward anionic pollutants, for example, Cr(VI), eosine yellow, rose bengal, methyl orange, and low adsorption capacities for Hg(II), Pb(II), rhodamineB, bismark brownY methylene blue, and neutral red. The removal of Cr(VI) and anionic dyes are very much effective at neutral and acidic pH. After dye/Cr(VI) adsorption the Nyquist plot indicate significant decrease in the capacitance of xerogels. Cyclic experiments show that, F-PANI xerogels can be effectively reused to remove Cr(VI) from different contaminated water.