Removal of hexavalent chromium from aqueous media using pomegranate peels modified by polymeric coatings: Effects of various composite synthesis parameters

Abstract

In this research, pomegranate peel (PGP) powder modified by polyaniline (PANI) and polypyrrole (PPy) was used to remove Cr (VI) from aqueous media. The effects of various composite synthesis parameters including type of solvents and stabilizers such as polyvinyl alcohol (PVA) and polyethylene glycol (PEG) at various concentrations were first investigated and the best composite capable of removing the highest percentage of chromium was determined. Batch chromium removal experiments were performed and parameters such as pH, contact time, adsorbent dose and adsorption isotherms were studied. According to the results, pomegranate peel–polypyrrole composites (PGP–PPy composites) outperformed pomegranate peel–polyaniline composites (PGP–PANI composites) in terms of chromium removal. Among the synthesized composites, the pomegranate peel composite synthesized in water/butanol (50:50 vol/vol) showed the best performance with a removal efficiency of 47.59% (the concentration of chromium decreased from 50 ppm to 26.20 ppm). To investigate the reason for changes in chromium adsorption capacity by the synthesized composites, some of the adsorbent properties were studied using SEM, XRD, FTIR, BET and FE–SEM analyses. The SEM and FE–SEM micrographs showed deposition of much finer and ordered polypyrrole particles synthesized in water/butanol on the surface of pomegranate peel. According to the BET analysis, the specific surface area of PGP-PPy composite synthesized in water/butanol was 8.026 g/m2, which was higher than that of the PGP–PPy composite synthesized in other solvents. The FTIR and XRD spectra confirmed amorphous structure of the PGP–PPy composite synthesized in water/butanol. Investigation of the parameters influencing the adsorption process for PGP–PPy composite that synthesized in water/butanol indicated that a maximum adsorption percentage of 95.35% (the concentration of chromium decreased from 50 ppm to 2.32 ppm) was obtained at pH = 1 and contact time of 90 min with an adsorbent dose = 10 g/L. The adsorption isotherms also showed that the Freundlich equation exhibited a better goodness of fit than the Langmuir equation for this composite. The desorption results suggested that the PGP–PPy composite synthesized in water/butanol was able to desorb up to 93.75% of the adsorbed chromium to the aqueous media.