Adsorptive features of polyacrylamide{aluminosilicate composites for methyleneblue

Abstract

Polyacrylamide{montmorillonite (PAAm-Mt) and polyacrylamide{clinoptilolite (PAAm-Z) composites wereprepared by cross-linked polymerization of acrylamide in dispersions of Mt and Z. The composites were characterizedby FT-IR, SEM, XRD, CEC, and PZC analysis. The adsorptive features of PAAm-Mt and PAAm-Z for methylene blue(MB) were investigated by their relevance to initial dye concentration, temperature, contact time, PZC, and pH. Themonolayer adsorption capacities were 0.14 and 0.08 mol kg1for PAAm-Z and PAAm-Mt, respectively. The changesin pH of MB solution had an insigni cant in uence on their adsorption capacities. The values of enthalpy and entropychanges were positive (∆HP AAmMt= 7.6 and ∆HP AAmZ= 17.6 kJ mol1, ∆SP AAmMt= 55.7, and ∆SP AAmZ= 107.2 J mol1K1). The negative free enthalpy change was proof of the spontaneity of adsorption (∆GP AAmMt= {9.0, ∆GP AAmZ= {14.4 kJ mol1). The adsorption kinetics obeyed a pseudo-second order model (kP AAmMt= 11.5 and kP AAmZ= 1.18 mol1kg min1, R2>0.99). The adsorption mechanism was the combination ofchemical and physical adsorption governed by Coulombic forces (liquid lm diffusion) on which the contribution ofintraparticle diffusion was not signi cant. This was consistent with a low value of the adsorption activation energy (Ea= 9.4 kJ mol1). The composites had amphoteric features buffering the pH of the studied adsorption environment toapproximately neutral levels.

Polyacrylamide{montmorillonite (PAAm-Mt) and polyacrylamide{clinoptilolite (PAAm-Z) composites wereprepared by cross-linked polymerization of acrylamide in dispersions of Mt and Z. The composites were characterizedby FT-IR, SEM, XRD, CEC, and PZC analysis. The adsorptive features of PAAm-Mt and PAAm-Z for methylene blue(MB) were investigated by their relevance to initial dye concentration, temperature, contact time, PZC, and pH. Themonolayer adsorption capacities were 0.14 and 0.08 mol kg1for PAAm-Z and PAAm-Mt, respectively. The changesin pH of MB solution had an insigni cant in uence on their adsorption capacities. The values of enthalpy and entropychanges were positive (∆HP AAmMt= 7.6 and ∆HP AAmZ= 17.6 kJ mol1, ∆SP AAmMt= 55.7, and ∆SP AAmZ= 107.2 J mol1K1). The negative free enthalpy change was proof of the spontaneity of adsorption (∆GP AAmMt= {9.0, ∆GP AAmZ= {14.4 kJ mol1). The adsorption kinetics obeyed a pseudo-second order model (kP AAmMt= 11.5 and kP AAmZ= 1.18 mol1kg min1, R2>0.99). The adsorption mechanism was the combination ofchemical and physical adsorption governed by Coulombic forces (liquid lm diffusion) on which the contribution ofintraparticle diffusion was not signi cant. This was consistent with a low value of the adsorption activation energy (Ea= 9.4 kJ mol1). The composites had amphoteric features buffering the pH of the studied adsorption environment toapproximately neutral levels.