Investigation of Mono/Competitive Adsorption of Environmentally Relevant Ionized Weak Acids on Graphite: Impact of Molecular Properties and Thermodynamics

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• 作者：Ahmed M. A. Moustafa ; Kerry N. McPhedran ; Jes煤s Moreira ; Mohamed Gamal El-Din
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：December 16, 2014
• 年：2014
• 卷：48
• 期：24
• 页码：14472-14480
• 全文大小：467K
• ISSN：1520-5851

文摘

The thermodynamics of adsorption and competitive interactions of five weak acids on a graphite surface was assessed in alkaline solutions. Adsorption of the acids in mono- and multicompound solutions followed their Freundlich isotherms which suggest a diversity of graphite adsorption sites as confirmed by the presence of carboxylic and phenolic groups observed on graphite surfaces. Thermodynamic calculations assigned the formation of the negatively charged assisted hydrogen bond (鈭扖AHB) between ionized solutes and adsorbent surface groups as the possible adsorption mechanism. However, the similar pK_a values of current acids resulted in comparable free energies for 鈭扖AHB formation (螖G^鈥揅AHB) being less than solvation free energies (螖G_Solv). Thus, additional 螖G is supplemented by increased hydrophobicity due to proton exchange of ionized acids with water (螖螖G_{Hydrophobicity}). Adsorption capacities and competition coefficients indicated that 螖螖G_{Hydrophobicity} values depend on the neutral and ionized acid K_ow. Competitive adsorption implies that multilayer adsorption may occur via hydrophobic bonding with the CH₃ ends of the self-assembled layer which affects the acid adsorption capacities in mixtures as compared to monocompound solutions. The determination of adsorption mechanisms will assist in understanding of the fate and bioavailability of emerging and classical weak acids released into natural waters.