Effects of carboxyl groups on the adsorption behavior of low-molecular-weight substances on a stainless steel surface.
The adsorption isotherms of various carboxylic acids and several amines on a stainless steel surface were taken as a function of pH and the ionic strength of the solution at 30 degrees C. In particular, the effect of the number of carboxyl groups on the adsorption behavior was investigated. Monocarboxylic acids such as benzoic acid and n-butyric acid were reversibly adsorbed on the stainless steel particles and showed a Langmuir-type adsorption isotherm, i.e., Q=KqmC/(1+KC), where Q and C are, respectively, the amount of adsorbate adsorbed and the equilibrium concentration in the bulk solution, qm, the maximum adsorbed amount, and K is the adsorption equilibrium constant. Carboxylic acids having plural carboxyl groups had much higher affinity to the surface and were adsorbed in both reversible and irreversible modes. The adsorption isotherms for the carboxylic acids having plural carboxyl groups could be expressed by a modified Langmuir-type adsorption isotherm, i.e., Q=q(irrev)+Kq(rev)C/(1+KC), where q(irrev) and q(rev) are, respectively, the maximum amounts adsorbed irreversibly and reversibly. The K and q(irrev) values increased with an increase in the number of carboxyl groups except for isophthalic acid and terephthalic acid. On the basis of the pH dependencies of K, qm, q(irrev), and q(rev) as well as the surface properties of the stainless steel, both reversible and irreversible adsorptions were considered to occur through the electrostatic interaction between negatively charged carboxyl groups and the positively charged sites on the surface. The dependency of the q(irrev) value on ionic strength was discussed on the basis of the differences in their adsorbed state with the interaction forces to the surface and repulsive forces among the adsorbed molecules. The adsorption of amine components was quite weak. The RA-IR and molecular dynamics calculation were done to investigate the adsorption states of phthalic acid, trimellitic acid, and mellitic acid.
Nagayasu
Takeshi
T
Department of Bioscience and Biotechnology, Faculty of Engineering, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan.
Yoshioka
Chisato
C
Imamura
Koreyoshi
K
Nakanishi
Kazuhiro
K
D000327:Adsorption; D000588:Amines / Q000737:chemistry; D002264:Carboxylic Acids / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D008970:Molecular Weight; D009994:Osmolar Concentration; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D013193:Stainless Steel / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature
D000588:Amines; D002264:Carboxylic Acids; D013193:Stainless Steel