ADSORPTION OF ANIONIC DYES ON CORN STALKS MODIFIED BY POLYANILINE: KINETICS AND THERMODYNAMIC STUDIES

Abstract

Extensive use of synthetic dyes in different industries has created a major pollution problem. Among \nvarious treatments, adsorption has been considered as an effective method due to its simplicity, \navailability and effectiveness in removing o f dyes from wastewaters. In the current work, the composite \n“corn stalks-polyaniline” (CS-PAN) is proposed to be used as alternative adsorbent to expensive \nactivated carbons. We have synthesized the new composite by the chemical polymerization o f aniline on \nthe surface o f corn stalks using (NH4) 2S2O8 as an oxidation agent and H3PO4 as a dopant. The composite \nwas characterized by using Fourier infrared spectroscopy, specific surface area analysis, pH o f point zero \ncharge, bulk density, and total pore volume. In comparison with corn stalks, the composite CS-PAN had a \nhigh adsorption capacity and efficiency toward anionic dyes (Acid Red and Acid Orange) in the aqueous \nmedium. The adsorption process attains equilibrium within 120-150 min. The adsorption o f the acid dyes \nincreased on CS-PAN composite with increase in temperature. It indicates that the adsorption is an \nendothermic process. Kinetic studies revealed the adsorption process was best described by the reaction \nmodel ofpseudo-second order than pseudo-first order. The activation energy o f adsorption was calculated \nas 13.1 and 7.8 kJ/mol fo r Acid Red and Acid Orange, respectively. Equilibrium adsorption studies o f the \nanionic dyes on CS-PAN indicated the Langmuir equation f it better than the Freundlich equation. \nMaximum adsorption capacity CS-PAN was calculated at different temperatures (303, 313, and 328 K) as \n7.010-5, 8.310-5, 10.7-10-5 and 9.810-5, 12.2-10-5, 16.010-5 mol/g toward Acid Red and Acid Orange, \nrespectively. The values o f the standard free energy change have been calculated as -29.6, -30.7, -32.6 \nfo r Acid Red and -30.1, -31.1, -32.7 kJ/mol fo r Acid Orange at 303, 313, and 323 K, respectively, which \nindicating that a spontaneous process occurred. Calculations indicated that the enthalpy changes o f \nadsorption were 6.7 and 1.3 kJ/mol for Acid Red and Acid Orange, respectively. Besides, the calculated \nstandard entropy changes o f adsorption were 107 and 85 J/mol K for Acid Red and Acid Orange, \nrespectively. Consequently, the composite CS-PAN, an inexpensive, easily synthesized, and efficient \nadsorbent, could be an alternative fo r more costly adsorbents used fo r removal o f anionic dyes in \nwastewater treatment.