Polymer Hydrogels Based on Acrylic Acid and Acrylamide and Their Applications to Remove Cationic Dye of Basic Red 46 (BR 46) from Aqueous Solutions

Hypothesis: The removal of dyes using polymers with different functional groups is of great concern in environmental applications. Polymeric adsorbents, particularly hydrogels, through formation of polymer complexes by electrostatic attraction and hydrogen bonding have the ability to remove dyes. The hydrogels of polyacrylic acid (PAA), polyacrylamide (PAM) and poly(acrylic acid-co-acrylamide) (poly(AA-co-AM)) were used as adsorbents for basic red 46 (BR 46) dye removal from wastewater.
All three hydrogels were prepared through radical polymerization mechanism by N'-N-methylene-bis(acrylamide) in water. Hydrogel adsorbents were investigated using SEM, FTIR spectroscopy, and TGA-DTG analysis. In order to study the bleaching characteristics of adsorbent, the factors affecting bleaching process such as pH, adsorbent dosage, dye concentration, and contact time were investigated.
Findings: The results showed that pH increase, adsorbent dosage, and contact time had direct impact on bleaching and the concentration of dye had a reverse relationship with it. In addition, the physical and chemical properties in removal of cationic dye of BR46 conformed well to Langmuir isotherm model and the experimental data followed the pseudo-second-order kinetic model well. In evaluation of the reusability of the adsorbent it was shown that after 5 cycles of the absorption/desorption test, the hydrogel absorption capacity decreased from 94.4% to 63.3%. The swelling test of poly(AA-co-AM) hydrogel and its dependence on pH changes revealed its highest percentage of swelling in alkaline environment at pH value of 8.