Metal-ion-exchanger nanocomposites in redox sorption processes

Abstract

Metal‐ion-exchanger nanocomposites were produced by redox sorption. For the first time, conditions were substantiated for the stabilization of metal (Ag, Cu) particles by an ion-exchange matrix through the limitation of recrystallization via matrix isolation of particles and reduction of the mobility of metal counterions. A model was proposed for the redox sorption of molecular oxygen from water in the nanocomposites, given a metal particle size distribution function. This model was used to calculate the particle size at which the kinetic control of the process is replaced by the optimal control by internal diffusion. Metal‐ion-exchanger nanocomposites are nanostructured heterogeneous systems consisting of particles of a metal or its slightly soluble compounds that are distributed throughout the bulk of an ion-exchange polymer matrix. Owing to the excess Gibbs energy of nanodispersed metal particles and the ability of the matrix to exchange ions, the nanocomposites can be used as highly efficient catalysts, sorbents, and chemical reagents. The kinetics of metal deposition into the ion exchanger, the chemical activity of the obtained nanocomposites with respect to molecular oxygen dissolved in water, and the laws of reaching quasi-equilibrium were studied previously [1‐3]. The creation and use of nanocomposites as reagents include the same processes, namely, ion-exchange or molecular sorption and redox reaction. The overall process involving simultaneous reaction steps can be called redox sorption. The specific feature of this process for the metal‐ion-exchanger nanocomposites is that the redox reaction is particle-size-dependent [4]. To develop the concepts of particle-size-dependent processes, it is important to determine the conditions for the aggregation stability of metal particles in the ionexchange matrix and to investigate the effect of the particle size on the kinetic laws of processes involving nanocomposites. The purpose of this work was to reveal the role of the ion-exchange matrix in maintaining the aggregation stability of metal nanoparticles and determine the effect of their size on the macrokinetics of redox sorption of molecular oxygen from water. Metal (Ag, Cu) is deposited into macroporous and gel sulfo cation exchange matrices (KU-23 and KU-2). A metal salt solution is brought into contact with the ion exchanger under static or dynamic conditions. Metal ions enter the matrix by an ion-exchange mechanism and are held as counterions near charged ionogenic groups; e.g.,