Synthesis of polyacrylamide-bound hydroquinone via a homolytic pathway: Application to the removal of heavy metals

Polyacrylamide (PAAm) was chemically modified with hydroquinone (HQ) via a homolytic route. A degree of modification of approximately 58% was obtained under optimal reaction conditions: time of 6 h, and modifier]/acrylamide] molar ratio of 5. PAAm and its modified form HQ–PAAm were characterized by UV–visible spectroscopy, FT–IR spectroscopy, ¹³C NMR spectroscopy, DSC, TGA, XRD, and SEM. A relatively lower molecular weight of the corresponding hydroquinone-functionalized form was measured. The glass transition temperature of the modified polymeric material was lower than that of the pristine one: 78.82 °C for HQ–PAAm versus 161.19 °C for PAAm. A study of Cu(II) adsorption by the cross-linked PAAm and HQ–PAAm resins was conducted by varying the following parameters: pH, time, temperature, ionic strength, sorbent mass, and initial Cu(II) concentration. The adsorption capacity of Pb(II) and Cd(II) by the different resins and their corresponding extents of desorption were estimated. The optimal conditions for metal ion uptake by polyacrylamide and its modified resin were: pH = 5.4, time = 120 min, temperature = 45 °C. The sorption extent by the modified resin was in the order Pb(II) > Cu(II) > Cd(II). The desorption of the experimented metallic ions from the resins exceeded 97%. A new way of cross-linking PAAm and its modified form is described herein.