Introduction to Nanoscience and Nanotechnology. Chris Binns

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Introduction to Nanoscience and Nanotechnology - Chris Binns


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Rosetta spacecraft was launched and 12 years later was installed in orbit around the comet 67P/Churyumov‐Gerasimenko, from where spectacular images of the 4 km wide nucleus like the one in Figure 2.14a were obtained. The orbiter collected pieces of dust from the plumes emerging from the comet on sticky targets and it was the first space mission that had an atomic force microscope (see Chapter 5, Section 5.4.4) onboard that could image the grains with nanometre resolution [23]. Typical dust grains had sizes of a few μm but closer inspection showed that these particles were compact agglomerates of smaller grains as shown in Figure 2.14b. The image displays a single dust grain about 1 μm across but it is composed of at least seven smaller particles smaller than 500 nm across and there is evidence that these are composed of yet smaller particles. This is consistent with current models of protoplanetary growth where the dust is composed of a hierarchy of aggregates with the smallest units being nanoparticles.

      Source: ESA/Rosetta/NAVCAM/CC BY‐SA IGO 3.0. Reproduced under Creative Commons CC BY‐SA 3.0 license.

      (b) Atomic force microscope (AFM) image of a single ~1 μm dust particle from the comet showing that it is composed of smaller particles.

      Source: Reproduced with the permission of the Nature Publishing Group from [23].

      The chapter so far has focused on naturally occurring nanoparticles or those produced as a by‐product of human activity. In this final section, the use of nanoparticle technologies to address environmental issues will be described with reference to two examples, that is, removing toxins from water and recycling of plastics.

      2.7.1 Water Remediation Using Magnetic Nanoparticles

      Soil and groundwater remediation to reduce toxins to safe levels is thus an important activity and traditionally, water is cleaned using filter beds. For severe or toxic contamination, the use of nanoporous filters, which present a very large active surface to remove contaminants per unit volume of filter, is more effective. An issue with these, however, is the slow volume flow rate through them and more recently there has been great interest in an alternative approach, which is to present the large surface area as a dispersal of nanoparticles within the contaminated water.

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      The nZVI removes contaminants by forming compounds with them and bonding them to the surface of the nanoparticles, which is greatly facilitated by the large surface area presented. This is typically 25 m2/g for commercially available nZVI powders but can reach 100 m2/g (see Problem 1, Chapter 1). The freshly synthesized nZVI particles have a thin porous oxide shell that allows contaminants to get very close to the iron/oxygen interface where the reactions take place. As they work, the nanoparticles get coated by a shell of the reaction products and eventually become inactive. The first demonstration of the method was in 1997 where it was used to remove chlorinated organic toxins [26] but since then it has been shown to clear a range of contaminants from groundwater including antibiotics, dyes, solvents, pesticides, metals, and radioactive isotopes. For a comprehensive list of contaminants removed see [27].

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