Composite of cellulosic agricultural waste coated with semiconducting polypyrrole as potential dye remover

A composite was obtained from cellulosic agricultural waste material (Sorghum vulgare) coated with conducting polypyrrole by in situ polymerization using potassium persulfate as chemical oxidant. The composite was characterized by Raman spectroscopy, FTIR spectroscopy, scanning electron microscopy (SEM), and cyclic voltammetry. Aqueous adsorption experiments of methylene blue dye onto the obtained materials at different pH values were conducted. The results showed that this composite is an efficient sorbent for dye removal. The adsorption mechanism was well described by the Langmuir isotherm. The adsorption capacity at neutral pH for uncoated sorghum at an equilibrium concentration (C_e) of methylene blue dye of 10 mg/l was 41.6 mg of dye/g of sorghum and for sorghum/PPy composite was 68.4 mg of dye/gram of composite, which is 1.6 times higher; however, the maxima adsorption capacities were 86.2 and 94.4 mg/g, respectively (only 9.5% more than the uncoated sorghum). It was also observed that at acidic pH for a C_e of 10 mg/l the adsorption capacity of composite was 79.2 mg of dye/gram of composite and the maximum adsorption capacity was 143.5 mg/g (66.4% more than the uncoated sorghum). SEM analysis showed homogeneous coating of cellulosic sorghum material with PPy. Conductivity value of composite was 13.0 × 10⁻³ S/m. Fabrication of this composite should significantly diminish the cost of dye removal from aqueous solutions with respect to some commercial adsorbents. POLYM. COMPOS., 35:186–193, 2014. © 2013 Society of Plastics Engineers