Polypyrrole-coated granules for humic acid removal

Granules with positive surface charges were prepared by coating glass beads with polypyrrole (PPy). The coated glass beads were found to possess high positive zeta potentials over a wide range of pH values. Batch and fixed be d humic acid adsorption experiments using the coated glass beads as adsorbe nts were conducted. Scanning electron microscope (SEM) was used to examine the surface morphology of the coated glass beads before and after humic aci d adsorption. X-ray photoelectron spectroscopy (XPS) was applied to assess the protonation and charge transfer of the PPy coating with and without ads orbed humic acid. SEM images showed that the PPy coating considerably incre ased the surface roughness of the granules and a significant amount of humi c acid was adsorbed on the PPy coating. From XPS analysis, it was found tha t 28% of the nitrogen atoms in the PPy coating were protonated, leading to a highly positively charged surface at pH < 10.5. The results also showed t hat the amount of protonated nitrogen atoms decreased by up to 25% due to h umic acid adsorption, suggesting that humic acid uptake by the PPy-coated g lass beads was affected at least partly by charge neutralization. Humic aci d adsorption also resulted in a reverse of the positive zeta potential of t he PPy coating, indicating the importance of macromolecular adsorption in t he process. The adsorption equilibrium data can be fitted with either the L angmuir or the Freundlich expression. Both pH and ionic concentration were found to affect the extent of humic acid adsorption by the PPy-coated granu les. (C) 2001 Academic Press.