**5.1. Bactericidal activity of MNPs**

Among the currently known nanomaterials, it is well-known that AgNPs have unique antimicrobial properties.[69] Textiles, keyboards, wound dressings, and biomedical devices now contain AgNPs that continuously release a low level of Ag ions to provide protection against bacteria. Even if Ag has been known to be a bactericidal element for at least 1200 years, considering the unusual properties of nanometric scale materials, largely different from those of their bulk counterparts[70], it is not surprising that AgNPs have been found significantly more efficient than Ag+ ions in mediating their antimicrobial activities.[71-75] All in all, the exact antibacterial action of AgNPs is still under debate.

Conversely, in many countries the microbial contamination of potable water sources poses a major threat to public health and the emergence of microorganisms resistant to multiple antimicrobial agents increases the demand for improved disinfection methods.[76] The importance of potable water for people in some countries dictates the need for the development of innovative technologies and materials for the production of safe potable water. This type of application can be a perfect niche for nanomaterials containing AgNPs. However, it is necessary to develop ecologically-safe nanomaterials that prevent the postcontamination of the used samples.[77] In this sense and as it has been already stated, functionalized polymers are currently acquiring a prominent role as NPs stabilizers for their excellent performance.[78, 79]

It is worthy to note here that ion-exchange materials are already widely used for various water treatment processes, mainly to eliminate undesired or toxic ionic impurities including hardness ions, iron, heavy metals, and others. The stabilization and immobilization of Ag-NPs in such matrices is very promising since using this approach, two complementary water treatment steps could be performed with a single material and the safety of the nanocomposites could be increased.

In our research group, the surface modification of ion-exchange materials used for traditional water treatment has been undertaken and promising results have been patented.[80] Such modification included the incorporation of either Ag or Ag@Co NPs.

As an example of the obtained results, Table 3 shows the synthetic conditions and the corresponding compositions of some nanocomposites of this family, probing the feasibility of the synthesis of both pure and core-shell nanoparticles.

To evaluate the efficiency of these nanocomposites for disinfection procedures, an increasing amount of nanocomposites beads was added to individual wells containing 105 CFU/mL of *E. coli* suspension in LB medium. After overnight incubation, bacterial proliferation was evaluated by measuring the optical density of each well at 550 nm (this wavelength is indicative of bacterial proliferation). The bactericidal activity of the Ag, Co and Ag@Co nanocomposites (in all the polymeric granulated matrices studied) was determined and raw materials were used as control (results are shown in Figure 22).

As it was expected, Ag and Ag@Co NPs containing sulfonated granulted materials increased their activity due to the presence NPs, but the enhancement was slightly higher for modified Ag@Co NPs. Anyhow, this proof of concept demonstrates the rightness of the approach.


**Table 3.** Metal content in granulated nanocomposites containing Ag- or Ag@Co-NPs and, analyzed by ICP-MS.

**Figure 22.** Variation of the absorbance at 550 nm with the number of polymer beads for ( ) the raw material, (□) Ag- and, (▲ ) Ag@Co-nanocomposites (3 replicates).

#### **5.2. Nanocatalysts for organic synthesis**

62 Ion Exchange Technologies

**5.1. Bactericidal activity of MNPs** 

excellent performance.[78, 79]

nanocomposites could be increased.

of the synthesis of both pure and core-shell nanoparticles.

materials were used as control (results are shown in Figure 22).

Among the currently known nanomaterials, it is well-known that AgNPs have unique antimicrobial properties.[69] Textiles, keyboards, wound dressings, and biomedical devices now contain AgNPs that continuously release a low level of Ag ions to provide protection against bacteria. Even if Ag has been known to be a bactericidal element for at least 1200 years, considering the unusual properties of nanometric scale materials, largely different from those of their bulk counterparts[70], it is not surprising that AgNPs have been found significantly more efficient than Ag+ ions in mediating their antimicrobial activities.[71-75]

Conversely, in many countries the microbial contamination of potable water sources poses a major threat to public health and the emergence of microorganisms resistant to multiple antimicrobial agents increases the demand for improved disinfection methods.[76] The importance of potable water for people in some countries dictates the need for the development of innovative technologies and materials for the production of safe potable water. This type of application can be a perfect niche for nanomaterials containing AgNPs. However, it is necessary to develop ecologically-safe nanomaterials that prevent the postcontamination of the used samples.[77] In this sense and as it has been already stated, functionalized polymers are currently acquiring a prominent role as NPs stabilizers for their

It is worthy to note here that ion-exchange materials are already widely used for various water treatment processes, mainly to eliminate undesired or toxic ionic impurities including hardness ions, iron, heavy metals, and others. The stabilization and immobilization of Ag-NPs in such matrices is very promising since using this approach, two complementary water treatment steps could be performed with a single material and the safety of the

In our research group, the surface modification of ion-exchange materials used for traditional water treatment has been undertaken and promising results have been patented.[80] Such modification included the incorporation of either Ag or Ag@Co NPs.

As an example of the obtained results, Table 3 shows the synthetic conditions and the corresponding compositions of some nanocomposites of this family, probing the feasibility

To evaluate the efficiency of these nanocomposites for disinfection procedures, an increasing amount of nanocomposites beads was added to individual wells containing 105 CFU/mL of *E. coli* suspension in LB medium. After overnight incubation, bacterial proliferation was evaluated by measuring the optical density of each well at 550 nm (this wavelength is indicative of bacterial proliferation). The bactericidal activity of the Ag, Co and Ag@Co nanocomposites (in all the polymeric granulated matrices studied) was determined and raw

As it was expected, Ag and Ag@Co NPs containing sulfonated granulted materials increased their activity due to the presence NPs, but the enhancement was slightly higher for modified Ag@Co NPs. Anyhow, this proof of concept demonstrates the rightness of the approach.

All in all, the exact antibacterial action of AgNPs is still under debate.

Nanoparticles are increasingly used in catalysis, where the large surface area per unit volume of the catalyst may enhance reactions. This enhanced reactivity significantly reduces the quantity of catalytic materials required to carry out the reactions. Particular industries, including the oil and the automobile ones, are interested in this area for the use of NPs in catalytic converters.[81] As a prove of their industrial potentiality, many big companies, including BASF, Johnson Matthey and 3M, have interests in developing commercial applications for AuNPs catalysts.

In the last decade, heterogeneous catalysts have attracted much interest because of their general advantages that have been boosted thanks to the use of nanomaterials.[82, 83] One crucial property for catalysts is their recovery and, in this sense, magnetic nanocatalysts present some outstanding advantages because they can be conveniently recovered by using an external magnetic field.[84]

On the one hand, Platinum Group Metals (PGMs) are well-known as highly selective catalysts and are widely used in organic synthesis, chemical industry and other areas like dehalogenation, hydrodechlorination, carbonylation or oxidation.[85-87] Concerning the potential applications, Pd, Pt, Rh, and Au-NPs have proven to be very versatile as they are 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 properties of the bare Fe oxides or other catalytic materials (*e.g.,* Co).[93, 94]

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 magnetic field (Figure 23).[96]

**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 consecutive runs.

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 industry is big enough to pay attention on it. Further research is needed to successfully increase the amount of immobilised metals what, very probably will provide better catalytic nanocomposites.


**Table 4.** Suzuki reaction yields (in %) for the Pd- and Pd@Co-nanocomposites
