Sorption Mechanism of Interaction of the Oxide–Graphene Composite TiO2||C and of Titanium Oxide Derived from It with La(III), Ce(III) Ions in Ultradilute Solutions

Abstract

Methods of physicochemical analysis, thermodynamics, and kinetics were used to interpret the sorption interaction of the new graphene oxide composite TiO₂||C and of TiO₂ derived from it with La(III) and Ce(III) ions in the Henry region. The variance analysis of experimental sorption isotherms showed the identity of the sorption characteristics of TiO₂||C and TiO₂ in the framework of the Langmuir model. The sorption equilibrium in the systems under consideration was proved by the coincidence of the experimental and literature values of the La(III) and Ce(III) ion hydrolysis constants and the data of sorption kinetics. The presence of surface terminal and bridging OH groups in TiO₂, according to ¹H NMR data, allowed using a model of surface complexation with the participation of functional groups {≡TiOH⁰} and {≡TiO^–} to describe the sorption. Varietal Henry’s constants of sorption of hydroxy and carbonate complexes of La(III) and Ce(III) within the framework of the two-K_a model were found. The pH region of extremely high values of logK_d [mL/g] = 6 in the region of predominance of hydroxo and carbonate complexes was experimentally established.