In English

Abstract

Extensive use of synthetic dyes in different industries has created a major pollution problem. Among various treatments, adsorption has been considered as an effective method due to its simplicity, availability and effectiveness in removing of dyes from wastewaters. In the current work, the composite “corn stalks-рolyaniline” (CS-PAN) is proposed to be used as alternative adsorbent to expensive activated carbons. We have synthesized the new composite by the chemical polymerization of aniline on the surface of corn stalks using (NH 4 ) 2 S 2 O 8 as an oxidation agent and H 3 PO 4 as a dopant. The composite was characterized by using Fourier infrared spectroscopy, specific surface area analysis, pH of point zero charge, bulk density, and total pore volume. In comparison with corn stalks, the composite CS-PAN had a high adsorption capacity and efficiency toward anionic dyes (Acid Red and Acid Orange) in the aqueous medium. The adsorption process attains equilibrium within 120–150 min. The adsorption of the acid dyes increased on CS-PAN composite with increase in temperature. It indicates that the adsorption is an endothermic process. Kinetic studies revealed the adsorption process was best described by the reaction model of pseudo-second order than pseudo-first order. The activation energy of adsorption was calculated as 13.1 and 7.8 kJ/mol for Acid Red and Acid Orange, respectively. Equilibrium adsorption studies of the anionic dyes on CS-PAN indicated the Langmuir equation fit better than the Freundlich equation. Maximum adsorption capacity CS-PAN was calculated at different temperatures (303, 313, and 328 K) as 7.0·10 –5 , 8.3·10 –5 , 10.7·10 –5 and 9.8·10 –5 , 12.2·10 –5 , 16.0·10 –5 mol/g toward Acid Red and Acid Orange, respectively. The values of the standard free energy change have been calculated as -29.6, -30.7, -32.6 for Acid Red and -30.1, -31.1, -32.7 kJ/mol for Acid Orange at 303, 313, and 323 K, respectively, which indicating that a spontaneous process occurred. Calculations indicated that t he enthalpy changes of adsorption were 6.7 and 1.3 kJ/mol for Acid Red and Acid Orange, respectively. Besides, the calculated standard entropy changes of adsorption were 107 and 85 J/mol K for Acid Red and Acid Orange, respectively. Consequently, the composite CS-PAN, an inexpensive, easily synthesized, and efficient adsorbent, could be an alternative for more costly adsorbents used for removal of anionic dyes in wastewater treatment.