**3. Environmental and safety concerns**

52 Ion Exchange Technologies

groups).

membranes as:

2. perfluorocarbon membranes 3. inorganic membranes

**Figure 12.** Typical Sulfonated polymers.

ii. anion exchange membranes (with cationic charged groups)

membrane layer and an anion exchange membrane layer)

random throughout the membrane

iii. amphoteric ion exchange membranes (with both cation and anion exchange groups at

iv. bipolar exchange membranes (bilayer membranes composed by a cation exchange

v. mosaic ion exchange membranes (which have certain domains that may be separated with an isolator of cation-exchange groups and also domains with anion-exchange

On the other hand, a classification based on the constituent materials allows grouping such

4. composite membranes of inorganic ion exchanger and organic polymer (e.g., hybrids). Nowadays, one of the most employed commercial ion exchange membranes is Nafion, a cation exchange homogenous perfluorinated membrane. It is an excellent proton conductor: it has excellent chemical stability, high ionic conductivity, good mechanical strength, good thermal stability, etc. ideal for performance in fuel cells. The main drawback of these membranes and of those containing Fluor in their structure (i.e. Selemion) are their high cost and, specially, the absence of pores that limits their application to the transport of ions in solution or vapour (pervaporation). Thus, the search of new homogeneous cation exchange membranes has been focussing much of efforts. In these sense, sulfonated polymers open a new window to the ion

1. membranes composed of hydrocarbons or partially halogenated hydrocarbons

exchange membranes field. Some typical sulfonated polymers are shown in Figure 12.

One of the polymers that fulfils the properties to be casted as an ion exchange membrane is sulfonated poly(ether-ether ketone) (SPEEK) which is nowadays attracting great interest regarding the fabrication of membranes for fuel cells, due to its thermoplastic properties, its

high chemical strength, its high stability towards oxidation and its low cost.[44, 45]

Perception and knowledge are important parts of public understanding of nanotechnology. They can be influential, for an achievable benefit obtained and the possible risks and hazard which it could imply.

The use of engineered nanoparticles (ENPs) in the environment, as a consequence of the development of nanotechnology, is a serious case of worldwide concern. However, a few studies have already demonstrated the toxic effects of nanoparticles on various organisms, including mammals. Nanotechnology is still in a discovery phase in which novel materials are first synthesized in small scale in order to identify new properties and further applications.

Therefore, detail understanding of their sources, release interaction with environment, and possible risk assessment would provide a basis for safer use of ENPs with minimal or no hazardous impact on environment

In order to do that, future directions such as the inclusion of regulatory and knowledge gaps within the risk identification framework should be designed and applied.

Thus, the evaluation of potential health impact as well as an enhanced design of the production of higher performance nanomaterials is mandatory; as well as defining criteria that distinguish between technologies and products more or less likely to present a health risk to avoid inappropriate and possibly deleterious sweeping conclusions regarding potential impact.

It is required to study their release, uptake, and mode of toxicity in the organisms. Furthermore, to understand the long-term effect of ENPs on the ecosystem, substantial information is required regarding their persistence and bioaccumulation.

### **3.1. Safe polymer-metal nanocomposites**

A massive industrial production of nanomaterials in the near future may result in the appearance of both NPs and the waste generated during their production in various

environments, yielding the possibility that humans could be exposed to these NPs through inhalation, dermal contact or ingestion and absorption through the digestive tract. Nowadays, there is claim for more restrictive legislation that would allow a better protection for both human beings and the global environment.

In this sense, for a comprehensive knowledge of properties of these materials (both physical and chemical), it is important to find standards and control materials to work with as reference models (such those from the British Standards Institute and International Standards Organisation).[49]

An investigation into nanomaterials toxicity involves: a determination of the inherent toxicity of the material, their interaction with living cells and the effect of exposure time.[50] It should be noted that the doses or exposure concentrations used for in vitro and in vivo toxicological studies are most often extraordinarily high in comparison with possible accidental human exposure.[51, 52]

Consequently, more research is needed before generalized statements can be made regarding NPs ecotoxicology.

Unfortunately, only few initiatives in this direction have been started so far. For instance, the German Federal Ministry for Education and Research, together with industry, has established the research programme NanoCare. This programme has a budget of €7.6 million and aims to assess and communicate new scientific knowledge of the effects of NPs on health and the environment.[53]

Scientists and technologists in this area have to deal with NPs presence in the environment but very often they do not have the appropriate tools and analytical methods for NPs detection and quantification to guarantee a satisfactory detection.[4]

Thus, it is of vital relevance to dedicate those efforts towards this direction, as we have not yet invented a so-called "Geiger counter" for NPs.

**Figure 13.** Schema describing the concepts involved in the design of safe polymer-metal nanocomposites.

As a consequence, the prevention of NPs escape into the environment is currently most likely the best approach that can be considered. In this regard, a possible solution appeared through the development of this project, which describes the results obtained by developing environmentally safe polymer–metal nanocomposite materials exhibiting magnetic properties. These materials prevent NPs escape by profiting of the embedding of NPs into organic matrices and the use of magnetism. [54] As a result, NPs reduce their mobility and, in case of leakage, NPs could be easily recovered by using simple magnetic traps.[13, 55-57]
