Introduction to Nanoscience and Nanotechnology. Chris Binns

Introduction to Nanoscience and Nanotechnology - Chris Binns


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in water, an applied magnetic field gradient will move all the particles through the water in the same direction to a point where they can be collected. On the laboratory scale, this is easy to demonstrate with a simple bar magnet as shown for the case of the removal of lead (Pb) contamination from water [28]. In this experiment, the nZVI nanoparticles were coated with a shell of graphene (see Chapter 4) to increase their effectiveness at adsorbing the Pb ions and the magnetic separation is demonstrated in Figure 2.17. The left image shows a suspension of the grapheme‐coated nZVI particles (labeled G‐nVZI) at a density of 1mg/ml and the right image demonstrates their separation with a bar magnet. Graphene alone is sometimes used as an adsorbent to filter Pb from water and it was found that the G‐nVZI particles are twice as effective in removing the contaminant as it is able to remove the Pb in both the neutral and ionic states. The ability to then separate the magnetic nanoparticles is a bonus.

      Magnetic separation of contaminants has only been demonstrated in the laboratory and is much more difficult in field applications. One issue is that it is difficult to apply sufficiently high field gradients over the distance scales required to produce magnetic separation on a workable timescale. In addition, if the particles are carried in a flow, the viscous drag will overcome the magnetic field gradients that can be applied in practice in even slow flows (see Chapter 8, Advanced Reading Box 8.1).

      

      2.7.2 Conversion of Waste Plastics to High‐Grade Materials (Upcycling)

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      The properties of the solid polymer are highly controllable by changing the chain length, introducing other atoms and branching the polymer chains. This happens naturally to some extent and can be encouraged to form a low‐density light material (LDPE) or discouraged, which allows the linear chains to pack tightly and form a high‐density strong material (HDPE). This controllability coupled with the low cost of production has made plastic something of a wonder material that has become ubiquitous in modern society. Currently, around 400 million tons of plastic are produced every year by manufacturers and 75% of this goes into single‐use products.

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      Source: Reproduced with the permission of the American Chemical Society from [29].

      Other recent innovations in upcycling have been to use waste plastic feedstock to produce carbon nanotubes and graphene [30, 31]. These materials are described in Chapters 3 and 4 and are destined to find applications in a range of emerging nanotechnologies described in those chapters. The processes to extract them from waste are described in Chapter 5, Section 5.1.12. Producing such a high‐value product from waste plastic is a further step toward encouraging recycling.

      This chapter has by far the widest scope in this book and each topic introduced here could easily occupy a book of its own. The treatment, therefore, has necessarily been superficial but a number of references are given for a more in‐depth study of various topics. The aim has been to give a flavor of the importance of nanoparticles in shaping our environment and also in addressing environmental issues. In the next chapter, we will bring our attention back to the research laboratory and discuss the fascinating world of carbon nanoparticles.

      1 1 In a volcanic eruption most of the mass of volcanic ash is distributed in


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