**6. Conclusions**

64 Ion Exchange Technologies

magnetic field (Figure 23).[96]

consecutive runs.

efficient and selective catalysts for several types of catalytic reactions, including olefin hydrogenation and C-C coupling such as Heck, Suzuki and Sonogashira reactions.[88-90] Among them, Pd-catalyzed cross-coupling has emerged as an effective synthetic methodology that is employed in both academic and industrial sectors.[91] Despite such progress, a number of challenges still remain unknown, including the dilucidation of highly efficient and selective catalysts able to react with multiple reactive C-H or N-H bonds.

On the other hand, several types of magnetic materials have been used, including magnetite, hematite, maghemite, wüstite.[92] Magnetic aggregation and their need for functionalization do still hinder the application of magnetic NPs in industry. Thus, searching for more suitable magnetic materials to overcome these restrictions is still a challenge for realizing practical catalytic applications. Yet, for catalytic purposes, magnetic NPs surface is often chemically functionalized with molecular catalytic complexes because of the poor catalytic

Therefore, and taking into account, the demonstrated efficiency of PGMs and the advantages of magnetic nanoparticles, it has been possible to apply develop Pd@Co-based nanocomposites for a typical C-C coupling reaction: the Suzuki reaction.[95] The preparation of such catalyses has only been possible thanks to the characteristics of IMS procedure, which allows the combination of a magnetic nanocore (made of Co) with the catalytic activity of a shell (Pd). The resulting material can be separated by simple filtration methods and, moreover, NPs can be re-covered and re-used by their retention under a

**Figure 23.** Suzuki reaction by using Pd or Pd@Co nanocomposites with optimized conditions.

Previous results with Pd@Co-NPs incorporated to fibrous materials showed the feasibility of this approach.[37] Differently, as it can be seen in Table 4, the catalytic efficiency of granulated polymers (containing either sulfonic or carboxylic groups) was very scarce, very likely due to the low metal immobilization achieved. However, two interesting results can be withdrawn: a substantial increase of the reaction yield was obtained when using the nanocomposite samples with higher Pd-content and the reaction yield could increase for

Even if low conversions where achieved, this results are not discouraging since granulated polymeric matrices are still interesting for industrial applications because of their mechanical properties. Their high mechanical resistance leads to obtain higher reproducibility in synthesis as well as easier manipulation. Moreover, granulated polymer

properties of the bare Fe oxides or other catalytic materials (*e.g.,* Co).[93, 94]

The conclusions derived from the results presented in this chapter can be briefly formulated as follows:

1. The ion-exchange assisted Intermatrix Synthesis (IMS) technique represents one of the most promising techniques that allows for the production of a large variety of polymer– metal nanocomposites of practical importance for different fields of modern science and technology.

The attractiveness of this technique is basically determined by its relative simplicity in comparison with other methods used for production of nanocomposite materials and also by its flexibility and the possibility of tuning the specific properties of the final nanocomposites to meet the requirements of their final applications. IMS technique gives a unique possibility of production of nanocomposites containing MNPs of various composition and structure (for example, monometallic, bimetallic or polymetallic MNPs with core-shell, core-sandwich and even more complex structures) for the applications of interest.

2. The spectrum of polymers applicable for IMS of PSMNPs is quite wide and includes various functionalized polymers, i.e. those bearing functional groups in the form of granules, fibers or membranes, which are capable to bind either metal or reducer ions prior to the metal reduction inside the polymer matrix (IMS of PSMNPs).

The dissociated ionogenic functional groups of the polymer bearing positive or negative charges provide a possibility to couple IMS technique with Donnan exclusion effect. In case of polymers with negatively charged groups the IMS technique consists of the metal loading stage followed by metal reduction inside the polymer. When polymer bears positively charged groups the IMS procedure starts with the reducer loading followed by the simultaneous metal loading-reduction stage.


The polymer matrix also serves as the MNPs stabilizing media preventing their aggregation and release to the medium under treatment. The functional properties of the nanocomposites (e.g., catalytic or bactericide) are mainly determined by the properties of MNPs immobilized inside the matrix.

