Adsorption studies of organic azo dyes from their aqueous solutions by a pH sensitive sodium alginate‐cl‐poly (N‐hydroxyethyl acrylamide‐co‐methacrylic acid) @Au/ montmorillonite nanocomposite hydrogel

Abstract

AbstractA pH responsive monometallic‐clay nanocomposite hydrogel, sodium alginate‐cl‐poly (N‐hydroxy ethyl acrylamide‐co‐methacrylic acid) @ Au/ montmorillonite clay (SANCHG@Au/MMT) is synthesized in situ using sodium alginate (SA) as a polysaccharide. Two other nano composite hydrogels namely sodium alginate‐cl‐poly (N‐hydroxy ethyl acrylamide‐co‐methacrylic acid) @ Au (SANCHG@Au) and sodium alginate‐cl‐poly (N‐hydroxy ethyl acrylamide‐co‐methacrylic acid) @ montmorillonite clay (SANCHG@MMT) are also prepared. All the synthesized nano composite hydrogels are characterized using various techniques. Water swelling of the three hydrogels along with their textile dye adsorption properties is evaluated in congo red (CR), benzopurpurin (BP) and tartrazine (TZ) from their aqueous solutions. Among the three hydrogels the % water swelling of SANCHG@Au/MMT is superior (396% at pH = 8) and also the adsorption capacity over the other two. The dye adsorption property of SANCHG@Au/MMT is found to be pH sensitive. Adsorption follows both the Langmuir adsorption isotherm with Qmax values 512.19 mg.g−1 for CR at pH = 4, 476.09 mg.g−1 at pH = 4 for BP and 454.79 mg.g−1 at pH = 6 for TZ respectively and Dubinin–Radushkevich isotherm model. The kinetic data fit with pseudo second order kinetic model. Thermodynamic parameters like negative and positive values suggest that the adsorption process is spontaneous and endothermic in nature.