Polypyrrole-coated gum ghatti-grafted poly(acrylamide) composite for the selective removal of hexavalent chromium from waste water

The aim of this study was to synthesize a gum ghatti-g-poly(acrylamide)/polypyrrole composite using a multi-step aqueous polymerization method, in which the pyrrole monomer was absorbed into the network of the gum ghatti-acrylamide graft copolymer followed by the polymerization of the pyrrole monomers, and use it for the removal of Cr(VI) from water. The prepared was characterized using FT-IR, SEM, BET, XPS and XRD. The effects of the pH, adsorbent dose, contact time, concentration of Cr(VI), and temperature on the adsorption performance of the composite were investigated systematically. The adsorption of Cr(VI) on the composite depended strongly on the pH, and a Cr(VI) removal of 99.6% was attained at pH 2.0, initial concentration of Cr(VI) of 100 mg/L, and adsorbent dosage of 0.035 g. The kinetics of the adsorption followed a pseudo-second order model and the adsorption data fitted well the Langmuir isotherm model. The maximum adsorption capacity of the adsorbent at 298, 308, and 318 K was determined to be 321.5, 357, and 416 mg/g, respectively. The presence of coexisting ions in the solution did not affect the adsorption of Cr(VI) significantly. Adsorption–desorption experiments revealed that the synthesized polymer composite could be used for up to four consecutive cycles.