Adsorption of polyprotic acid at the water/air interface Effect of counter ion and pH on surface activity of Fe-III-EDTA complex

作者：Villeneuve Masumi^*; Tanaka Mihoko; Abe Mayuko; Sakamoto Hiroyasu; Hayami Yoshiteru

来源：Colloid and Polymer Science, 2014, 292(9): 2335-2348.

DOI：10.1007/s00396-014-3203-2

• Adsorption of polyprotic metal complex
• Structure maker counterion
• Structure breaker counterion
• Ions near interface
• Thermodynamic equations
• Surface tension

A rigorous thermodynamic treatment appropriate for surface adsorption from mixed aqueous solution of alkali and polyprotic acid was derived. Those equations were applied to mixed aqueous solution/air systems of alkali metal hydroxide and Fe-III complex with ethylenediamine- N, N, N%26apos;,N%26apos;-tetraacetate (Fe-EDTA). Surface density of each species arising from Fe-EDTA was separately evaluated, and thus, surface activity of Fe-EDTA was studied, especially its dependence on pH and how it is influenced by the counter cations. Fe-EDTA was positively adsorbed at the water/air interface at very low pHs and negatively at high pHs. The pH range of positive adsorption of Fe-EDTA with potassium ion, as a counter ion, was wider than that with sodium ion. Thus, potassium ion, a structure breaker, tended to smooth surface adsorption of Fe-EDTA at the water/air interface, whereas sodium ion, a structure maker, tended to withdraw Fe-EDTA from the interfacial region.

• 出版日期2014-9