Removal of anionic dyes from aqueous solutions using polyacrylamide and polyacrylic acid hydrogels

This study deals with the application of polyacrylamide (PAM) and polyacrylic acid (PAA) hydrogels in the removal of anionic dyes such as reactive orange-20 (RO-20) and direct red-31(DR-31) from aqueous solutions. The adsorption efficiency of as-prepared hydrogels was compared with each other and the suitable hydrogel for adsorption of RO-20 and DR-31 dyes was identified. Adsorption experiments were performed as function of pH, PAM or PAA dosage, contact time and initial dyes concentration. Langmuir and Freundlich isotherm models were used to describe the equilibrium adsorption data. The results displayed that the adsorption data fitted with Langmuir model more than Freundlich model for DR-31 and fitted well with Freundlich model for RO-20. The kinetic studies showed that the experimental data fitted well with the pseudo-second order kinetic model. This study showed that PAM could be used as effective adsorbent for removal of anionic dyes in comparison with PAA.