Adsorption characteristics of various organic substances on the surfaces of tantalum, titanium, and zirconium

Adsorption characteristics of carboxylic acids, amines, an octapeptide composed of four l-alanine and four l-aspartic acid residues (Peptide-A4D4), and β-lactoglobulin (β-Lg) on tantalum (Ta), titanium (Ti), and zirconium (Zr) particles were examined at 30 °C and in some case, were compared with their adsorption onto SUS316L stainless steel particles (S6L). The adsorption isotherms on the Ta, Ti, and Zr particles could usually be expressed either by a Langmuir-type equation for reversible adsorption or by a modified Langmuir-type adsorption equation including terms for both reversible and irreversible adsorption. The adsorption equilibrium of benzoic acid, benzylamine, and m-xylylenediamine on all the metal surfaces followed a Langmuir-type equation, while those of phthalic acid, mellitic acid, and Peptide-A4D4 could be fitted to the modified Langmuir-type adsorption equation. The adsorption characteristics of different adsorbates on the different surfaces were discussed particularly with reference to the pH dependencies of the qirrev, qrev, and K values and the electrostatic properties of the oxidized surface of the metal particles. Fourier transform infrared spectroscopic analyses using a reflection/absorption technique (RA-IR) indicated that phthalic acid and mellitic acid are adsorbed in similar adsorption states irrespective of the type of metal. β-Lg was adsorbed onto the surfaces principally in an irreversible manner. The desorption behavior of β-Lg from Ta, Ti, and S6L surfaces was examined, in order to evaluate the extent of interaction between β-Lg and the metals.