Silica chemically modified with N-benzoyl- N-phenylhydroxylamine in chemisorption of hydrogen and metal ions

Abstract

New chemically modified silicas – macroporous and pyrogenic – with covalently bonded chelating groups of N-benzoyl- N-phenylhydroxylamine (SiO 2–BPHA) were obtained in three-step surface reaction. From elemental analysis, metal chemisorption and pH titration the concentration of bonded groups was determined as 0.076 and 0.21 mmol g −1 for Silochrome and Aerosil, correspondingly. In both cases about 50% transformation of initial aminopropyl groups to BPHA was achieved. A chemisorption of hydrogen and some metal ions (Fe(III), V(V), Nb(V), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II)) from aqueous and acetonitrile media was investigated. The adequate approximation of interfacial equilibria was only possible if strong lateral interactions between bonded ligands were presumed. From the results of a quantitative physicochemical analysis it was found that dissociation constant of bonded BPHA considerably rose in comparison with the dissociation constants of analogs in solution. Bonded complexes with all studied metals were less stable. Linear correlation between stability of complexes in dioxane–water solution and on the silica surface was found as log β(surf.)=log β(sol.)−2.9. Strong fixation of counter-ions near the surface was concluded from experiments. In aqueous media SiO 2–BPHA demonstrates high selectivity towards Fe(III) and V(V). Linear correlation that was found between concentration of sorbed Fe 3+ and the Kubelka–Munk function for SiO 2–BPHA can be used for ion optical sensoring. Vanadium(V) forms several bonded complexes with different composition instead.