Fabricating pentaazatetraethylene modified sulfonated polyacrylamide for dye adsorption from aqueous media: isotherms...

In this study, pentaazatetraethylene-modified sulfonated polyacrylamide (PAm-SO₃-N₅) was synthesized and used as a novel efficient adsorbent to remove calmagite from aqueous media. To this end, a central composite design (CCD) was applied to reduce the number of reaction variables (i.e., adsorbent concentration, temperature, initial concentration, and pH) on calmagite removal. The results showed that calmagite was entirely adsorbed by the PAm-SO₃-N₅ within 30 min. In addition, a pseudo-second-order (PSO) model was prepared as the optimum formula to fit the kinetics information. The modeling results revealed that film diffusion and adsorption are rate-limiting stages to remove the dyes. Using a Langmuir isotherm to fit the equilibrium data, the highest equilibrium adsorption was calculated to be 1732.5 mg/g. In the present study, the ΔH value indicates that the adsorption is of chemical type. Also, the negative sign of ΔS° shows that PAm-SO₃-N₅ removes calmagite during a relatively stable process with randomness in the system. The increase in ΔG° values with increasing temperature indicates a descending trend in the feasibility degree of calmagite adsorption. Eventually, recycling the adsorbent for 7 cycles to adsorb calmagite dye showed no remarkable activity loss.