Al Azhar University
Faculty of Science
Chemistry Department
Nanotechnology and Its Applications
Submitted By
Mahmoud Ahmed...
Contents
Introduction
1.1 Definition 1
1.2 Origins
2
Characterization of Nanotechnology 5
2.1 Observing with photons 5
2.1...
3.2.5 Nanocrystals of Semiconductors and Other
Materials by Arrested Precipitation
20
3.2.6 Thermolysis Routes 21
3.2.7 So...
1
Introduction
1.1 Nanotechnology:
It is defined as the study and use of structures between 1 nanometer
and 100 nanometers...
2
such as physics, biology, engineering, chemistry, computer science and
more, nano science is rapidly expanding. Nanotech...
3
developed and popularized a conceptual framework for nanotechnology,
and high-visibility experimental advances that drew...
4
which culminated in a public debate between Drexler and Smalley in
2001 and 2003.
Meanwhile, commercialization of produc...
5
Characterization of Nanoparticles
What is characterization?
-Characterization refers to study of materials features such...
6
can, for example, selectively view certain reactions. The fluorescent
signals are detected by electronic
2.1.2 X-ray mac...
7
transmitted. The data is processed by a computer which reconstructs
cross- sections of the object, in other words 3-D im...
8
– The different elements of electronic optics, such as electromagnetic
lenses (equivalent to traditional optic lenses) w...
9
2.2.2 Scanning Electron Microscope (SEM):
-Operation: Generates image by scanning the surface of the sample in a
raster ...
11
Synthesis of Nanocrystals
Modern materials science is characterized by a close interplay with
physics, chemistry, and b...
11
carbides, and nitrides can be prepared by carrying out the discharge in a
suitable
gas medium or by loading the electro...
12
3.1.6 Spray Pyrolysis
In spray pyrolysis, small droplets of a solution containing a desired
precursor are injected into...
13
Fig. 2.1. TEM image of Cr nanocrystals synthesized by borohydride reduction. The scale bar
corresponds to 20nm (reprodu...
14
Alcohol Reduction
This reaction is further catalyzed by a base and requires the
presence of α-hydrogen in the alcohol. ...
15
3.2.2 Solvothermal Synthesis
The solvothermal method provides a means of using solvents at
temperatures well above thei...
16
slow release of sulphide or selenide ions. Nanocrystal dispersions are
often obtained even without a capping agent. In ...
17
Metals such as Cd and Tl have been obtained by photolysis. PVP-
covered Au nanocrystals are produced by the reduction o...
18
Fig. 2.11. Schematic illustration of the steps involved in the electrochemical reduction
of metal nanocrystals by the R...
19
Bimetallic particles could be prepared by using two ions, one of which
was from the anode and the other from the metal ...
21
3.2.5 Nanocrystals of Semiconductors and Other Materials
by Arrested Precipitation
Nanocrystals can be obtained from so...
21
Fig. 2.12. TEM images of thioglycerol–capped CdSe nanocrystals prepared by
arrested precipitation reaction. Insets show...
22
Metal and Metal Oxide Nanocrystals
Various metal nanoparticles have been prepared by decomposition
of low-valent comple...
23
Semiconductor Nanocrystals
The synthesis of some of the semiconducting metal chalcogenide
nanocrystals was discussed in...
24
Single Molecule Precursors
Decomposition of single molecular precursors provides convenient
and effective routes for th...
25
3.2.7 Sonochemical Routes
The effect of ultrasound on a colloidal system has been known for
sometime although its use f...
26
products are usually obtained. The collapse of the bubble does not signal
the end of the reaction. The collapse is freq...
27
Biological Methods
Of the templates and systems used for the synthesis of nanocrystals,
microbes offer an interesting p...
28
correspond to 50 nm. A high-resolution image of an individual particle is
shown in the center (reproduced with permissi...
29
shown to yield CdS nanoparticles. Kowshik . have identified the ability of
yeast Torulopsis sp. to produce nanoscale Pb...
31
Application of Nanotechnology
4.1 History:
The 2000s have seen the beginnings of the applications of
nanotechnology in ...
31
Different fields of nanotechnology application
4.2 Nano-medicine:
Nanomedicine is the medical application of nanotechno...
32
Nanomedicine seeks to deliver a valuable set of research tools and
clinically useful devices in the near future. The Na...
33
particle and if the particle is metal, energy from the light will heat the
particle and surrounding tissue. Light may a...
34
4.3 Nano-biotechnology:
Nanobiotechnology, bionanotechnology, and nanobiology are
terms that refer to the intersection ...
35
application of nanophotonics for manipulating molecular processes in
living cells.
Recently, the use of microorganisms ...
36
4.4 Green nanotechnology:
Green nanotechnology refers to the use of nanotechnology to enhance
the environmental sustain...
37
Nanoremediation and water treatment:
Nanotechnology offers the potential of novel nanomaterials for the
treatment of su...
38
down-time and labour. Work is in progress to develop enzyme
treatments that may be able to break down such biofilms.
Po...
39
opens many doors for the development of new ways to capture, store, and
transfer energy. The inherent level of control ...
41
promising potential especially in the field of cosmetics. Nanotechnology
also has numerous potential applications in he...
41
Another way nanotechnology can improve soldiers’ uniforms is by
creating a better form of camouflage. Mobile pigment na...
42
Medical system:
A medical surveillance system for soldiers to wear can be made
using nanotechnology. This system would ...
43
Nanotechnology is an active research area that encompasses a
number of disciplines such as electronics, bio-mechanics a...
44
instruments to study the nanoscale in general, but the understanding of
the structure and behavior of concrete at the f...
45
Steel:
Steel is a widely available material that has a major role in the
construction industry. The use of nanotechnolo...
46
makes the HAZ grains finer in plate steel. This nanoparticle addition
leads to an increase in weld strength. The increa...
47
hydrophobic polymers. Mechanical studies of bones have been adapted to
model wood, for instance in the drying process.
...
48
of the desired protective or functional properties. The coatings should
have self-healing capabilities through a proces...
49
temperature, humidity, and airborne toxins, which needs nanotech-based
improved batteries. The building components will...
51
References
1. A.P. Weber, M. Seipenbusch, G. Kasper: J. Phys. Chem. A105 8958 (2001) A.
Ghezelbash, B.A. Korgel: Langmu...
51
33. X. Li, Y. He, M.T. Swihart: Langmuir 20 4720 (2004) A. Watanabe, M. Unno, F.
Hojo et al.: Mater. Lett. 57 3043 (200...
of 54

Nanotechnology And Its Application

Published on: Mar 3, 2016
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Transcripts - Nanotechnology And Its Application

  • 1. Al Azhar University Faculty of Science Chemistry Department Nanotechnology and Its Applications Submitted By Mahmoud Ahmed Abd El-Maabud Abo Omar 4th Year Special Chemistry Under Supervision of Dr. Essam Shawky Abd El Hady Khattab Doctor of Medical Biochemistry And Molecular Biology 2014 - 2015
  • 2. Contents Introduction 1.1 Definition 1 1.2 Origins 2 Characterization of Nanotechnology 5 2.1 Observing with photons 5 2.1.1 The optical microscope in visible light 5 2.1.2 X-ray machines. 6 2.2 Observing with electrons: 7 2.2.1 The transmission electron microscope (TEM). 8 2.2.2 The scanning electron microscope (SEM). 9 Synthesis of Nanocrystals 10 3.1 Physical Methods 10 3.1.1 Inert Gas Condensation 10 3.1.2 Arc Discharge 10 3.1.3 Ion Sputtering 11 3.1.4 Laser Ablation 11 3.1.5 Pyrolysis and Other Methods 11 3.1.6 Spray Pyrolysis 12 3.2 Chemical Methods 12 3.2.1 Metal Nanocrystals by Reduction 12 3.2.2 Solvothermal Synthesis 15 3.2.3 Photochemical Synthesis 16 3.2.4 Electrochemical Synthesis 17
  • 3. 3.2.5 Nanocrystals of Semiconductors and Other Materials by Arrested Precipitation 20 3.2.6 Thermolysis Routes 21 3.2.7 Sonochemical Routes 25 3.2.8 The Liquid–Liquid Interface 26 3.3 Biological Methods 27 APPLICATIONS OF NANOTECHNOLOGY 4.1 History 30 4.2 Nano-medicine 31 4.2.1 Cancer treatment 32 4.3 Nano-biotechnology 34 4.4 Green nanotechnology 36 4.4.1 Current research 36 4.5 Energy applications 38 4.6 Industrial applications 39 4.6.1 Military 40 4.6.2 Construction 42 5 References 51
  • 4. 1 Introduction 1.1 Nanotechnology: It is defined as the study and use of structures between 1 nanometer and 100 nanometers in size. To get an idea of how small that is, it would take eight hundred 100 nanometer particles side by side to match the width of a human hair. A nanometer is one billionth of a meter (10-9 m) and is the unit of length that is generally most appropriate for describing the size of single molecules. The nanoscale marks the nebulous boundary between the classical and quantum mechanical worlds; thus, realization of nanotechnology promises to bring revolutionary capabilities. Fabrication of nanomachines, nanoelectronics and other nanodevices will undoubtedly solve an enormous amount of the problems faced by mankind today. If one looks at current forecasts for nanotechnology, often reads outstanding sentences such as “Small is Big”, “Big Plans for the Tiny World”, “Nanotechnology: It’s a small, small, small world” etc. Several countries have been steadily allocating more resources for nanotechnology R&D studies. The reason behind is that forecasters have already projected that expertise in nanotechnology will be a key factor of the economical leadership in the 21st century. Nanoscience is an interdisciplinary field that seeks to bring about mature nanotechnology. Focusing on the nanoscale intersection of fields
  • 5. 2 such as physics, biology, engineering, chemistry, computer science and more, nano science is rapidly expanding. Nanotechnology centers are popping up around the world as more funding is provided and nanotechnology market share increases. The rapid progress is apparent by the increasing appearance of the prefix "nano" in scientific journals and the news. Thus, as we increase our ability to fabricate computer chips with smaller features and improve our ability to cure disease at the molecular level, nanotechnology is here. 1.2 Origins: The concepts that seeded nanotechnology were first discussed in 1959 by renowned physicist Richard Feynman in his talk There's Plenty of Room at the Bottom, in which he described the possibility of synthesis via direct manipulation of atoms. The term "nano-technology" was first used by Norio Taniguchi in 1974, though it was not widely known. Inspired by Feynman's concepts, K. Eric Drexler used the term "nanotechnology" in his 1986 book Engines of Creation: The Coming Era of Nanotechnology, which proposed the idea of a nanoscale "assembler" which would be able to build a copy of itself and of other items of arbitrary complexity with atomic control. Also in 1986, Drexler co- founded The Foresight Institute (with which he is no longer affiliated) to help increase public awareness and understanding of nanotechnology concepts and implications. Thus, emergence of nanotechnology as a field in the 1980s occurred through convergence of Drexler's theoretical and public work, which
  • 6. 3 developed and popularized a conceptual framework for nanotechnology, and high-visibility experimental advances that drew additional wide-scale attention to the prospects of atomic control of matter. In 1980s two major breakthroughs incepted the growth of nanotechnology in modern era. First, the invention of the scanning tunneling microscope in 1981 which provided unprecedented visualization of individual atoms and bonds, and was successfully used to manipulate individual atoms in 1989. The microscope's developers Gerd Binnig and Heinrich Rohrer at IBM Zurich Research Laboratory received a Nobel Prize in Physics in 1986. Binnig, Quate and Gerber also invented the analogous atomic force microscope that year. Second, Fullerenes were discovered in 1985 by Harry Kroto, Richard Smalley, and Robert Curl, who together won the 1996 Nobel Prize in Chemistry. C60 was not initially described as nanotechnology; the term was used regarding subsequent work with related graphene tubes (called carbon nanotubes and sometimes called Bucky tubes) which suggested potential applications for nanoscale electronics and devices. In the early 2000s, the field garnered increased scientific, political, and commercial attention that led to both controversy and progress. Controversies emerged regarding the definitions and potential implications of nanotechnologies, exemplified by the Royal Society's report on nanotechnology.Challenges were raised regarding the feasibility of applications envisioned by advocates of molecular nanotechnology,
  • 7. 4 which culminated in a public debate between Drexler and Smalley in 2001 and 2003. Meanwhile, commercialization of products based on advancements in nanoscale technologies began emerging. These products are limited to bulk applications of nanomaterials and do not involve atomic control of matter. Some examples include the Silver Nano platform for using silver nanoparticles as an antibacterial agent, nanoparticle-based transparent sunscreens, and carbon nanotubes for stain-resistant textiles. Governments moved to promote and fund research into nanotechnology, beginning in the U.S. with the National Nanotechnology Initiative, which formalized a size-based definition of nanotechnology and established funding for research on the nanoscale. By the mid-2000s new and serious scientific attention began to flourish. Projects emerged to produce nanotechnology roadmaps which center on atomically precise manipulation of matter and discuss existing and projected capabilities, goals, and applications.
  • 8. 5 Characterization of Nanoparticles What is characterization? -Characterization refers to study of materials features such as its composition, structure, and various properties like physical, electrical, magnetic, etc. Why is characterization of nanoparticles important? -Nanoparticle properties vary significantly with size and shape -Accurate measurement of nanoparticles size and shape is, therefore, critical to its applications 2.1 Observing with photon: 2.1.1 The optical microscope in visible light The optical microscope was the first instrument that enabled man to observe objects normally invisible to the naked eye. As the microscope is subject to the laws of optics, its resolution is limited to several tenths of a micron. In order to study samples from living organisms, the samples must be prepared with coloration techniques A new generation of microscope which uses laser light appeared in the 1980s. It has enabled scientists to create three dimensional images at different levels of depth of the matter being studied by using focalization and laser beam scanning. This type of microscope is known as a confocal microscope1 and is particularly adapted for use in the natural world One very interesting use of these microscopes corresponds to their ability to work with fluorescent markers. The laser beam excites a fluorescent substance which has been added to the sample, for which we know the affinity for certain molecular sites. Thanks to these markers we
  • 9. 6 can, for example, selectively view certain reactions. The fluorescent signals are detected by electronic 2.1.2 X-ray machines X-rays are photons with a wavelength that is much shorter than the wavelength of ultraviolet light. X-rays are produced from an accelerated shock of electrons against a metallic target. One of the first applications of machines using X-rays was in the macroscopic domain. The X-rays benefit from the fact that this radiation has a strong penetrating power in materials with the rate of absorption depending on the density of the material. Radiation transmitted through a body coated with a phosphorescent or photosensitive substance is commonly known as radio waves. A sophisticated version of this type of machine is the X-ray scanner. The transmitter turns around the object at the same time as the receptor does, measuring the intensity of the X-rays
  • 10. 7 transmitted. The data is processed by a computer which reconstructs cross- sections of the object, in other words 3-D imagery. The resolution is determined by the quality of the X-ray beam used. This type of machine is used in many applications, especially in medical imagery . Another type of machine, which uses the interactive properties of X-rays with crystalline structures, is used in X-ray spectroscopy. These machines enable scientists to investigate objects in the nanoworld. Their operation rests on the following principle: a crystal is made up of identical patterns of atoms following a particular lattice whose chain is the same size as the wavelength of the X-ray. The X-rays are realigned by selective reflection in predetermined directions and then form diffraction figures. The information contained in the diffraction figures clearly deals with the structure of the lattice and, more specifically, the rather complex three-dimensional structures of atomic patterns. This analysis is possible, firstly, due to the quality of today’s machines and, secondly, because of the sophisticated calculation techniques used. This type of machine is an essential tool for chemists who want to assemble molecules in crystalline form in order to study their atomic pattern. This method enabled the discovery of the double helix by Francis Crick and James Watson in 19532 2.2 Observing with electrons Electron microscopy uses the wave properties of electrons. However, as particles they need a vacuum in order to travel. Microscopes are in the form of a metal vacuum enclosure in which the following can be found: – The electron gun, such as in cathode ray tubes used in television sets.
  • 11. 8 – The different elements of electronic optics, such as electromagnetic lenses (equivalent to traditional optic lenses) which control the trajectories of the electrons as well as the support of the object to be studied . There are two types of electron microscope The transmission electron microscope (TEM) The scanning electron microscope (SEM) 2.2.1 Transmission Electron Microscope(TEM): -Operation: Image is generated based on the interaction pattern of electrons that transmit through the specimen -Variation: Scanning Transmission Electron Microscope -Advantages: Additional analysis techniques like X-ray spectrometry are possible with the STEM, high-resolution , 3-D image construction possible but aberrant -Limitations: Needs high-vacuum chamber, sample preparation necessary, mostly used for 2-D images
  • 12. 9 2.2.2 Scanning Electron Microscope (SEM): -Operation: Generates image by scanning the surface of the sample in a raster pattern, using an electron beam -Modes of operation: -i. Secondary electrons -ii. Back-scattered electrons (BSE) -iii. X-rays -Advantages: Bulk-samples can be observed and larger sample area can be viewed, generates photo-like images, very high-resolution images are possible -Disadvantages: Samples must have surface electrical conductivity, non- conductive samples need to be coated with a conductive layer
  • 13. 11 Synthesis of Nanocrystals Modern materials science is characterized by a close interplay with physics, chemistry, and biology. This is especially true of nanomaterials, as vividly demonstrated by the methods of synthesis employed for these materials. On the one hand, are the top-down methods which rely on continuous breakup of bulk matter while on the other are the bottom-up methods that build up nanomaterials from their constituent atoms. The top-down and bottom-up approaches can also be considered as physical and chemical methods, respectively. A variety of hybrid methods have since come into being. 3.1- Physical Methods 3.1.1 Inert Gas Condensation This method is most widely used and provides straightforward means to prepare nanosized clusters, especially of metals. A metal foil or ingot is heated in a ceramic crucible placed in a chamber filled with an inert gas, typically a few torr of argon. Thme etal vapor cools rapidly losing energy on collision with argon atoms, thereby producing nanoparticles. 3.1.2 Arc Discharge Another means of vaporizing metals is to strike an arc between metal electrodes in the presence of an inert gas. Weber used this method to prepare Ni nanoparticles and studied the in situ catalytic properties without interference from a substrate. Nanoparticles of metal oxides,
  • 14. 11 carbides, and nitrides can be prepared by carrying out the discharge in a suitable gas medium or by loading the electrodes with suitable precursor 3.1.3 Ion Sputtering In this method, accelerated ions such as Ar+ are directed toward the surface of a target to eject atoms and small clusters from its surface. The ions are carried to the substrate under a relatively high pressure (∼1mTorr) of an inert gas, causing aggregation of the species. Nanoparticles of metals and alloys as well as semiconductors have been prepared using this method 3.1.4 Laser Ablation A variant of the method is the supersonic expansion method where the plume produced by the laser pulse is carried by an inert gas pulse through a narrow orifice to cause adiabatic expansion. This results in the formation of nanoclusters. Harfenist prepared mass-selected Ag nanoparticles from this method and collected them in the form of a sol outside the preparation chamber. Because of spatial and temporal confinement of the gaseous species with supersonic speeds, the method calls for extreme sophistication in instrumentation. 3.1.5 Pyrolysis and Other Methods In laser pyrolysis, a precursor in the gaseous form is mixed with an inert gas and heated with CO2 infrared laser (continuous or pulsed), whose energy is either absorbed by the precursor or by an inert photosensitizer such as SF6.
  • 15. 12 3.1.6 Spray Pyrolysis In spray pyrolysis, small droplets of a solution containing a desired precursor are injected into the hot zone of a furnace to obtain nanoparticles. The droplets are generated by using a nebulizer, generally by making use of a transducer. By controlling the nebulizer energy, the relative vapor pressures of the gases and the temperature of the furnace, the particle size is controlled 3.2 Chemical Method 3.2.1 Metal Nanocrystals by Reduction A variety of reducing agents are used to reduce soluble metal salts to obtain the corresponding metals. By terminating the growth with appropriate surfactants or ions, metal nanoparticles are produced. We shall discuss the use of a few representative reducing agents in this section. Some of the older methods of preparing nanoparticles were reviewed by Turkevich in 1951 Borohydride Reduction The basic reaction involves the hydrolysis of the borohydride accompanied by the evolution of hydrogen. BH− 4 + 2H2 O −→ BO− 2 + 4H2 (2.1)
  • 16. 13 Fig. 2.1. TEM image of Cr nanocrystals synthesized by borohydride reduction. The scale bar corresponds to 20nm (reproduced with permission from [150]) Nanocrystals of a variety of metals have been made by borohydride reduction. Thus, Pt nanocrystals with mean diameter 2.8nm were prepared by the reduction of chloroplatinic acid with sodium borohydride. Homiyama and coworkers made Cu sols by the borohydride reduction of Cu salts. Green and O’Brien prepared Cr and Ni nanoparticles by carrying out the reduction with Li or Na borohydride at high temperatures in coordinating solvents (see Fig. 2.3). Citrate Reduction Synthesis by the citrate method involves the addition of chloroauric acid to a boiling solution of sodium citrate. A wine red color indicates the onset of reduction. The average diameter of the nanoparticles can be varied over a range of 10–100nm by varying the concentration ratio between chloroauric acid and sodium citrate (see Fig. 2.3). Fig. 2.3. TEM image of Au nanocrystals synthesized by citrate reduction. The magnification is 50,000 (reproduced with permission from [144])
  • 17. 14 Alcohol Reduction This reaction is further catalyzed by a base and requires the presence of α-hydrogen in the alcohol. By making use of polymeric capping agents such as PVP, the growth of metal particles can be arrested. The polyol method of Figlarz and coworkers [183, 184] involves the reduction of metal salts with high boiling polyols such as ethylene glycol. The polyol serves both as the reducing agent and the stabilizing agent. Particles of Co, Ni, Cu, Au, Ag, and their alloys in the size range of 100nm to a few microns have been obtained by this method (see Fig. 2.4) . Fig. 2.4. TEM image of large Ag nanocrystals synthesized by the polyol method (reproduced with permis [185])
  • 18. 15 3.2.2 Solvothermal Synthesis The solvothermal method provides a means of using solvents at temperatures well above their boiling points, by carrying out the reaction in a sealed vessel. The pressure generated in the vessel due to the solvent vapors elevates the boiling point of the solvent. Typically, solvothermal methods make use of solvents such as ethanol, toluene, and water, and are widely used to synthesize zeolites, inorganic open-framework structures, and other solid materials. Due to the high-pressures employed, one often obtains high-pressure phases of the materials. In the past few years, solvothermal synthesis has emerged to become the chosen method to synthesize nanocrystals of inorganic materials. Numerous solvothermal schemes have been employed to produce nanocrystalline powders as well as nanocrystals dispersible in a liquid. Qian and coworkers have reported several solvothermal routes to chalcogenide nanocrystals. CdS nanocrystals of 6nm diameter have been made using cadmium sulphate/nitrate as the Cd source, thiourea as the S source and ethyleneglycol as the solvent. The reaction was carried out for 12 h at 180◦C. Chen and Fan have prepared transition metal dichalcogenides (MS2; M = Fe, Co, Ni, Mo; S = S or Se) with diameters in the range 4– 200nm by a hydrothermal route (water as solvent). Fe, Co, and Ni chalcogenides were obtained by treating the corresponding halide with Na2S2O3 (sodium thiosulphate) or Na2SeSO3 (sodium selenosulphate) for 12 h at 140–150◦C. Mo chalcogenides were prepared starting from Na2MoO4, sodium thio or seleno sulphate and hydrazine. By employing a metal salt, elemental Se or S and a reducing agent (to reduce Se or S), it is possible to produce metal chalcogenide nanocrystals (see Table 2.3). Control over size is rendered possible by the
  • 19. 16 slow release of sulphide or selenide ions. Nanocrystal dispersions are often obtained even without a capping agent. In some cases, S or Se can be caused to disproptionate, making the reducing agent redundant. Thus, CdSe nanocrystals have been prepared solvothermally by reacting Cd stearate with elemental Se in toluene in the presence of tetralin (see Fig. 2.5) Fig. 2.5. TEM image of CdSe nanocrystals synthesized by solvothermal method. The scale bar corresponds to 50 nm. The inset shows a histogram of particle size distribution (reproduced with permission from) 3.2.3 Photochemical Synthesis Photochemical synthesis of nanoparticles is carried out by the light-induced decomposition of a metal complex or the reduction of a metal salt by photogenerated reducing agents such as solvated electrons. The former is called photolysis and the latter radiolysis. The formation of photographic images on a AgBr film is a familiar photolysis reaction. Henglein, Belloni, and their coworkers have pioneered the use of photolysis and radiolysis for the preparation of nanoscale metals.
  • 20. 17 Metals such as Cd and Tl have been obtained by photolysis. PVP- covered Au nanocrystals are produced by the reduction of HAuCl4 in formamide by UV-irradiation. The reaction is free radical mediated, with the radicals being generated by photodegradation of formamide. This provides a route to ion-free reduction of HAuCl4. Radiolysis of Ag salts in the presence of polyphosphates produces extremely small clusters that are stable in solution for several hours. Effective control can be exercised over the reduction process by controlling the radiation dosage. Marandi et al. have shown that the size of CdS nanocrystals could be controlled photochemically in the reaction of CdSO4 and Na2S2O3. Radiolysis also provides a means for the simultaneous generation of a larger number of metal nuclei at the start of the reaction, thereby yielding a fine dispersion of nanocrystals. Studies of the reduction pathways by radiolysis have been carried out. 3.2.4 Electrochemical Synthesis Reetz and coworkers have pioneered the electrochemical synthesis of metal nanocrystals. Their method represents a refinement of the classical electrorefining process and consists of six elementary steps they are oxidative dissolution of anode, migration of metal ions to the cathodes, reduction of ions to zero-valent state, formation of particles by nucleation and growth, arrest of growth by capping agents, and precipitation of particles.
  • 21. 18 Fig. 2.11. Schematic illustration of the steps involved in the electrochemical reduction of metal nanocrystals by the Reetz method (reproduced with permission from [265]) The steps are schematically illustrated in Fig. 2.11. The capping agents are typically quaternary ammonium salts containing long-chain alkanes such as tetraoctylammonium bromide. The size of the nanocrystals could be tuned by altering the current density, the distance between the electrodes, the reaction time, the temperature, and the polarity of the solvent. Thus, using tetraoctylammonium bromide as stabilizer, Pd nanocrystals in the size range of 1–5nm have been obtained. Low current densities yield larger particles (∼4.8 nm) while large current densities yield smaller particles (∼1.4 nm). Larger Pd nanoparticles stabilized by the solvent (propylene carbonate) have also been obtained [259]. This method has been used to synthesize Ni, Co, Fe, Ti, Ag, and nanoparticles. Bimetallic colloids such as Pd–Ni, Fe–Co, and Fe–Ni have been prepared using two anodes consisting of either metals [260]. Mono and bimetallic particles consisting of Pt, Rh, Ru, and Mo could be prepared by reduction of their salts dissolved in the electrolyte (see Table 2.4) .
  • 22. 19 Bimetallic particles could be prepared by using two ions, one of which was from the anode and the other from the metal salt dissolved in the electrolyte Table 2.4. Metal particles synthesized by the electrochemical reduction of salts Table 2.5. Bimetallic particles synthesized by the combination of anodic oxidation and salt reduction (see Table 2.5). Pascal et al. synthesized maghemite nanocrystals in the size range of 3–8nm by the use of an Fe electrode in an aqueous solution containing DMF and cationic surfactants.
  • 23. 21 3.2.5 Nanocrystals of Semiconductors and Other Materials by Arrested Precipitation Nanocrystals can be obtained from solutions that precipitate the bulk matter under conditions unfavorable for the growth of particulates in the precipitate. For example, the precipitation of metal salts by chalcogens can be arrested by employing a high pH. The groups of Brus, Henglein, and Weller have prepared CdS nanocrystals by adopting this strategy. Typically, CdSO4 is reacted with (NH4)2S in water at high pH to obtain CdS particles of diameter around 5 nm. Other sulfur sources such as H2S and Na2S are also used to obtain CdS. Capping agents (e.g., sodium polyphosphate) stabilize such dispersions. In addition to water, methanol, acetonitrile and such solvents can be used to obtain CdS and ZnS nanocrystals by arrested precipitation. Weller and coworkers have pioneered the use of water soluble thiols, such as 1-thioglycerol, 2- mercaptoethanol, 1-mercapto-2-propanol, 1,2-dimercapto- 3-propanol, thioglycolic acid, thiolactic acid, and cysteamine as capping agents to prepare CdS, CdSe, CdTe, HgSe, HgTe, and CdHgTe nanocrystals. Typically, a solution containing a metal salt (e.g., perchlorate) and the capping agent is treated with NaOH to raise the pH, degassed by bubbling inert gas (to prevent the oxidation of chalcogen source), followed by the introduction of the chalcogen in the form of Na2S, NaHSe, etc. under inert conditions (see Fig. 2.12).
  • 24. 21 Fig. 2.12. TEM images of thioglycerol–capped CdSe nanocrystals prepared by arrested precipitation reaction. Insets show a HRTEM image and a Fourier transform of one of the HRTEM images (reproduced with permission from [272 3.1.6 Thermolysis Routes Thermolys is routes are related to chemical vapor deposition (CVD)-based methods to prepare thin films. By carrying out thermolysis reactions in high boiling solvents in the presence of capping agents, nanocrystals of various materials are obtained. Thermal decomposition provides remarkable control over size and is well suited for scale up to gram quantities.
  • 25. 22 Metal and Metal Oxide Nanocrystals Various metal nanoparticles have been prepared by decomposition of low-valent complexes involving olefinic ligands, such as cyclooctatetraene (COT), cycloocta-1,5-diene (COD), and carbonyls. It has been known since long that colloidal Co can be prepared by the decomposition of Co carbonyls . Bawendi and coworkers [288] carried out a similar reaction with Co2(CO)8, in the presence of tri-n- octylphosphine oxide (TOPO) and obtained Co nanoparticles with an average diameter of 20 nm. By using capping agents such as carboxylic acids and alkyl amines the size of the nanoparticles can be tuned to be in the range of 3–20nm . Decomposition of carbonyls has been used to prepare nanocrystals of Fe Fig. 2.13. TEM image of large Au nanocrystals prepared by decomposition of Au thiolate [C14H29(CH3)3N][Au(SC12H25)2] (reproduced with permission from [300]) FeCo [, FeMo , FePt , CoPt , FePd , and SmCo , as well. Large Au nanoparticles with diameters of tens of nanometers have been prepared by Nakamoto. by the thermolysis of Au(I) thiolate complexes – [R(CH3)3N][Au(SC12H25)2],[R(CH3)3N][Au(SC6H4–p–R_)2] (R=C14H29, C12H25); (R_=C8H17, CH3)(see Fig. 2.13)
  • 26. 23 Semiconductor Nanocrystals The synthesis of some of the semiconducting metal chalcogenide nanocrystals was discussed in an earlier section. Murray and coworkers in a pathbreaking paper described a method for synthesizing CdSe nanocrystals by reacting a metal alkyl (dimethylcadmium) with TOPSe (tri-octylphosphineselenide) in TOP (tri-n-octylphosphine), a coordinating solvent that also acts as the capping agent (see Fig. 2.14). This method readily yields CdS and CdTe nanocrystals as well. The reaction scheme of Murray succeeds to some extent in separating the nucleation and growth steps. When the chalcogen source is injected into the hot solution, explosive nucleation occurs, accompanied by a fall in temperature. Further growth occurs by maintaining the reagents around 100K or lower, the final size depending on the growth temperature. The scheme of Murray has proved to be extraordinarily popular and has received extensive attention from numerous groups. Fig. 2.14. TEM image of CdSe nanocrystals produced by the Murray method. The nanocrystals are elongated along one axis (reproduced with permission from
  • 27. 24 Single Molecule Precursors Decomposition of single molecular precursors provides convenient and effective routes for the synthesis of semiconductor nanocrystals. In this method, a molecular complex consisting of both the metal and the chalcogen is thermally decomposed in a coordinating solvent. Initial attempts with dithio and diselno carbamates, [Cd(E2CNEt2)]2 (E=S,Se) gave nanoparticles of CdS . The nanoparticles were capped with TOPO, the reaction medium. CdSe nanocrystals have been produced starting with compounds of the form RCd(S2CNEt2)(R = neopentyl, methyl)(see Fig. 2.15). Diselenocarbamates with unsymmetrical R groups such as hexyl and methyl (CdSe2CNMeHex)2 were found to be good air stable precursors for CdSe nanoparticles . ZnS and ZnSe nanoparticles were prepared starting from [EtZn(E2NEt2)]2 . Fig. 2.15. TEM image of CdSe nanocrystals produced by the thermal decomposition
  • 28. 25 3.2.7 Sonochemical Routes The effect of ultrasound on a colloidal system has been known for sometime although its use for the preparation of nanosized matter is of relatively recent origin. Numerous methods have been discussed in the literature for the sonochemical synthesis of nanosized particles. However, not all the nanosized particles so obtained have been dispersed in a liquid medium. Progress in sonochemical synthesis made over the last two decades is illustrated by the set of examples discussed later. In order to carry out sonochemical reactions, a mix of reagents dissolved in a solvent is subjected to ultrasound radiation (20 kHz–10 MHz). Acoustic cavitation leads to the creation, growth, and collapse of bubbles in the liquid medium. The creation of bubbles is due to the suspended particulate matter and impurities in the solvent. The growth of a bubble by expansion leads to the creation of a vacuum that induces the diffusion of volatile reagents into the bubble. The growth step is followed by the collapse of the bubble which takes places rapidly accompanied by a temperature change of 5,000–25,000K in about a nanosecond. Collapse of the bubble triggers the decomposition of the matter within the bubble. The rapid cooling rate often hinders crystallization, and amorphous Table2.5. Bimetallic particles synthesized by the combination of anodic oxidation and salt reduction
  • 29. 26 products are usually obtained. The collapse of the bubble does not signal the end of the reaction. The collapse is frequently accompanied by the formation of free radicals that cause further reactions. A few of the sonochemical reactions are, in fact, mediated by free radicals 3.2.7 The Liquid–Liquid Interface Rao and coworkers have used reactions taking place at the interface of two liquids such as toluene and water to produce nanocrystals and films of metals, semiconductors, and oxides. In this method, a suitable organic derivative of the metal taken in the organic layer reacts at the interface with the appropriate reagent present in the aqueous layer to yield the desired product. For example, by reacting Au(PPh3)Cl in toluene with THPC in water, nanocrystals of Au can be obtained at the interface of two liquids. This method has been extended to prepare nanocrystals of Ag and Pd, Au–Ag alloys, semiconducting sulphides such as CdS, ZnS, and CoS, and oxides such as Fe2O3 and CuO (see Fig. 2.17). By an appropriate choice of the reaction parameters, it has been possible to obtain isolated nanocrystals with narrow size distribution or well-formed films of the nanocrystals. By varying parameters such as the reaction temperature, and the reactant concentrations, the size of the nanocrystals and the coverage of the films can be modified. Thus, a change in the reaction temperature from 298 to 348 K, increases the size of Au nanocrystals from 7 to 16nm (see Fig. 2.18). Starting with a mixture of metal precursors, it has been possible using this method to prepare Au–Ag alloy nanocrystalline films of varying compositions
  • 30. 27 Biological Methods Of the templates and systems used for the synthesis of nanocrystals, microbes offer an interesting possibility. The innards of a microorganism can be a tiny Fig. 2.17. Nanocrystals of: (a) Au, (b) CdS, and (c) γ–Fe2O3 formed at the toluenewater interface (reproduced with permission from) Fig. 2.18. Transmission electron micrographs of ultrathin nanocrystalline Au films prepared at the liquid–liquid interface at (a) 303K (b) 318K (c) 333 K, and (d) 348 K. The histograms of particle size distribution are also shown. The scale bars
  • 31. 28 correspond to 50 nm. A high-resolution image of an individual particle is shown in the center (reproduced with permission from) reactor as well as a container. Elementary reactions such as reduction are generally mediated by enzymes. Synthesis can therefore be carried out by simply incubating a solution of metal ions in the right microbial culture. The ability of microbes to accumulate inorganic particles such as Au , CdS , ZnS , and magnetite is well documented in the literature. It is also known that microorganisms put nanoscale particles to use as UV shields (CdS particles) and direction indicators (magnetite). The possibility of harnessing microorganisms for the synthesis of nanocrystals was realized only recently . Nair and Pradeep have utilized Lactobacillus present in yogurt to synthesize Au, Ag, and Au–Ag alloy nanoparticles. The nanoparticles thus produced were in the size range of 15–500 nm. Joerger and coworkers have synthesized Ag nanoparticles in the size range 2–200nm by using Pseudomonas Stutzeri. Klebsiella aerogenes has been used to synthesize CdS nanoparticles in the size range 20–200nm . Roh and coworkers have substituted metal ions such as Co, Cr, and Ni in magnetite nanocrystals synthesized using the iron-reducing bacteria Thermoanaerobacter ethanolium. Enzymes act as catalysts for the growth of metal nanoparticles. Enzyme 58 2 Synthesis of Nanocrystals mediated growth of metallic nanoparticles can be exploited for various purposes in biology involving dip pen lithography . Apart from bacteria, yeast, and fungi have been used to obtain nanoparticles. Yeasts, Candida glabrata and Schizosaccharomyces pombe have been
  • 32. 29 shown to yield CdS nanoparticles. Kowshik . have identified the ability of yeast Torulopsis sp. to produce nanoscale PbS nanoparticles. Sastry and coworkers have identified two fungi species, Fusarium oxysporum and Verticillium sp. to produce Au and Ag nanoparticles. Fusarium oxysporum also reduces CdSO4 to CdS to yield CdS nanoparticles. CdS nanoparticles have been produced in the extracellular space. Highly luminescent, water-soluble and biocompatible CdTe nanocrystals have been prepared by using glutathione as a stabilizer. Quantitum yields in excess of 60% have been observed with these nanoparticles . A novel nature of such biological synthetic schemes is that they produce nanoparticles at room temperature in aqueous medium, although poor size and morphology control also appear to be characteristic of these routes. Besides control over size and morphology, identification of the active biological ingredient that brings about the reaction remains unknown.
  • 33. 31 Application of Nanotechnology 4.1 History: The 2000s have seen the beginnings of the applications of nanotechnology in commercial products, although most applications are limited to the bulk use of passive Nanomaterials. Examples include titanium dioxide and zinc oxide nanoparticles in sunscreen, cosmetics and some food products; silver nanoparticles in food packaging, clothing, disinfectants and household appliances such as Silver Nano; carbon nanotubes for stain-resistant textiles; and cerium oxide as a fuel catalyst. As of March 10, 2011, the Project on Emerging Nanotechnologies estimated that over 1300 manufacturer-identified nanotech products are publicly available, with new ones hitting the market at a pace of 3–4 per week. Nanotechnology is being used in developing countries to help treat disease and prevent health issues. The umbrella term for this kind of nanotechnology is Nano medicine. Nanotechnology is also being applied to or developed for application to a variety of industrial and purification processes. Purification and environmental cleanup applications include the desalination of water, water filtration, wastewater treatment, groundwater treatment, and other Nano remediation. In industry, applications may include construction materials, military goods, and nano-machining of nano-wires, nano-rods, few layers of graphene, etc.
  • 34. 31 Different fields of nanotechnology application 4.2 Nano-medicine: Nanomedicine is the medical application of nanotechnology. Nanomedicine ranges from the medical applications of nanomaterials, to nanoelectronic biosensors, and even possible future applications of molecular nanotechnology. Current problems for nanomedicine involve understanding the issues related to toxicity and environmental impact of nanoscale materials (materials whose structure is on the scale of nanometers, i.e. billionths of a meter). Functionalities can be added to nanomaterials by interfacing them with biological molecules or structures. The size of nanomaterials is similar to that of most biological molecules and structures; therefore, nanomaterials can be useful for both in vivo and in vitro biomedical research and applications. Thus far, the integration of nanomaterials with biology has led to the development of diagnostic devices, contrast agents, analytical tools, physical therapy applications, and drug delivery vehicles.
  • 35. 32 Nanomedicine seeks to deliver a valuable set of research tools and clinically useful devices in the near future. The National Nanotechnology Initiative expects new commercial applications in the pharmaceutical industry that may include advanced drug delivery systems, new therapies, and in vivo imaging. Nanomedicine research is receiving funding from the US National Institutes of Health, including the funding in 2005 of a five-year plan to set up four nanomedicine centers. Nanomedicine is a large industry, with nanomedicine sales reaching $6.8 billion in 2004, and with over 200 companies and 38 products worldwide, a minimum of $3.8 billion in nanotechnology R&D is being invested every year. In April 2006, the journal Nature Materials estimated that 130 nanotech-based drugs and delivery systems were being developed worldwide. As the nanomedicine industry continues to grow, it is expected to have a significant impact on the economy. 2.2.1 Cancer: Another nanoproperty, high surface area to volume ratio, allows many functional groups to be attached to a nanoparticle, which can seek out and bind to certain tumor cells. Additionally, the small size of nanoparticles (10 to 100 nanometers), allows them to preferentially accumulate at tumor sites (because tumors lack an effective lymphatic drainage system). Limitations to conventional cancer chemotherapy include drug resistance, lack of selectivity, and lack of solubility. Nanoparticles have the potential to overcome these problems. In photodynamic therapy, a particle is placed within the body and is illuminated with light from the outside. The light gets absorbed by the
  • 36. 33 particle and if the particle is metal, energy from the light will heat the particle and surrounding tissue. Light may also be used to produce high energy oxygen molecules which will chemically react with and destroy most organic molecules that are next to them (like tumors). This therapy is appealing for many reasons. It does not leave a "toxic trail" of reactive molecules throughout the body (chemotherapy) because it is directed where only the light is shined and the particles exist. Photodynamic therapy has potential for a noninvasive procedure for dealing with diseases, growth and tumors. Kanzius RF therapy is one example of such therapy.[citation needed] Also, gold nanoparticles have the potential to join numerous therapeutic functions into a single platform, by targeting specific tumor cells, tissues and organs. A schematic illustration showing how nanoparticales or other cancer Druges might be used to treat cancer
  • 37. 34 4.3 Nano-biotechnology: Nanobiotechnology, bionanotechnology, and nanobiology are terms that refer to the intersection of nanotechnology and biology. Given that the subject is one that has only emerged very recently, bionanotechnology and nanobiotechnology serve as blanket terms for various related technologies. This discipline helps to indicate the merger of biological research with various fields of nanotechnology. Concepts that are enhanced through nanobiology include: nanodevices, nanoparticles, and nanoscale phenomena that occurs within the discipline of nanotechnology. This technical approach to biology allows scientists to imagine and create systems that can be used for biological research. Biologically inspired nanotechnology uses biological systems as the inspirations for technologies not yet created. However, as with nanotechnology and biotechnology, bionanotechnology does have many potential ethical issues associated with it. The most important objectives that are frequently found in nanobiology involve applying nanotools to relevant medical/biological problems and refining these applications. Developing new tools, such as peptoid nanosheets, for medical and biological purposes is another primary objective in nanotechnology. New nanotools are often made by refining the applications of the nanotools that are already being used. The imaging of native biomolecules, biological membranes, and tissues is also a major topic for the nanobiology researchers. Other topics concerning nanobiology include the use of cantilever array sensors and the
  • 38. 35 application of nanophotonics for manipulating molecular processes in living cells. Recently, the use of microorganisms to synthesize functional nanoparticles has been of great interest. Microorganisms can change the oxidation state of metals. These microbial processes have opened up new opportunities for us to explore novel applications, for example, the biosynthesis of metal nanomaterials. In contrast to chemical and physical methods, microbial processes for synthesizing nanomaterials can be achieved in aqueous phase under gentle and environmentally benign conditions. This approach has become an attractive focus in current green bionanotechnology research towards sustainable development.
  • 39. 36 4.4 Green nanotechnology: Green nanotechnology refers to the use of nanotechnology to enhance the environmental sustainability of processes producing negative externalities. It also refers to the use of the products of nanotechnology to enhance sustainability. It includes making green nano-products and using nano-products in support of sustainability. Green nanotechnology has been described as the development of clean technologies, "to minimize potential environmental and human health risks associated with the manufacture and use of nanotechnology products, and to encourage replacement of existing products with new nano-products that are more environmentally friendly throughout their lifecycle." 2.4.1 Current research: Solar cells: One major project that is being worked on is the development of nanotechnology in solar cells. Solar cells are more efficient as they get tinier and solar energy is a renewable resource. The price per watt of solar energy is lower than one dollar. Nanotechnology is already used to provide improved performance coatings for photovoltaic (PV) and solar thermal panels. Hydrophobic and self-cleaning properties combine to create more efficient solar panels, especially during inclement weather. PV covered with nanotechnology coatings are said to stay cleaner for longer to ensure maximum energy efficiency is maintained.
  • 40. 37 Nanoremediation and water treatment: Nanotechnology offers the potential of novel nanomaterials for the treatment of surface water, groundwater, wastewater, and other environmental materials contaminated by toxic metal ions, organic and inorganic solutes, and microorganisms. Due to their unique activity toward recalcitrant contaminants, many nanomaterials are under active research and development for use in the treatment of water and contaminated sites. The present market of nanotech-based technologies applied in water treatment consists of reverse osmosis, nanofiltration, ultrafiltration membranes. Indeed, among emerging products one can name nanofiber filters, carbon nanotubes and various nanoparticles. Nanotechnology is expected to deal more efficiently with contaminants which convectional water treatment systems struggle to treat, including bacteria, viruses and heavy metals. This efficiency generally stems from the very high specific surface area of nanomaterials which increases dissolution, reactivity and sorption of contaminants. Some potential applications include:  To maintain public health, pathogens in water need to be identified rapidly and reliably. Unfortunately, traditional laboratory culture tests take days to complete. Faster methods involving enzymes, immunological or genetic tests are under development.  Water filtration may be improved with the use of nanofiber membranes and the use of nanobiocides, which appear promisingly effective.  Biofilms are mats of bacteria wrapped in natural polymers. These can be difficult to treat with antimicrobials or other chemicals. They can be cleaned up mechanically, but at the cost of substantial
  • 41. 38 down-time and labour. Work is in progress to develop enzyme treatments that may be able to break down such biofilms. Pollution: Scientists have been researching the capabilities of buckminsterfullerene in controlling pollution, as it may be able to control certain chemical reactions. Buckminsterfullerene has been demonstrated as having the ability of inducing the protection of reactive oxygen species and causing lipid peroxidation. This material may allow for hydrogen fuel to be more accessible to consumers. 2.5 Energy applications of nanotechnology: Over the past few decades, the fields of science and engineering have been seeking to develop new and improved types of energy technologies that have the capability of improving life all over the world. In order to make the next leap forward from the current generation of technology, scientists and engineers have been developing energy applications of nanotechnology. Nanotechnology, a new field in science, is any technology that contains components smaller than 100 nanometers. For scale, a single virus particle is about 100 nanometers in width. An important subfield of nanotechnology related to energy is nanofabrication. Nanofabrication is the process of designing and creating devices on the nanoscale. Creating devices smaller than 100 nanometers
  • 42. 39 opens many doors for the development of new ways to capture, store, and transfer energy. The inherent level of control that nanofabrication could give scientists and engineers would be critical in providing the capability of solving many of the problems that the world is facing today related to the current generation of energy technologies. People in the fields of science and engineering have already begun developing ways of utilizing nanotechnology for the development of consumer products. Benefits already observed from the design of these products are an increased efficiency of lighting and heating, increased electrical storage capacity, and a decrease in the amount of pollution from the use of energy. Benefits such as these make the investment of capital in the research and development of nanotechnology a top priority. 2.6 Industrial applications of nanotechnology: Nanotechnology is impacting the field of consumer goods, providing products with novel functions ranging from easy-to-clean to scratch- resistant. Modern textiles are wrinkle-resistant and stain-repellent; in the mid-term clothes will become "smart", through embedded "wearable electronics". Several products that incorporate nanomaterials are already in use. Nanomaterials are in a variety of items, many of which people do not even realize contain nanoparticles. For example, car bumpers are made lighter, clothing is more stain repellant, sunscreen is more radiation resistant, synthetic bones are stronger, cell phone screens are lighter weight, glass packaging for drinks leads to a longer shelf-life, and balls for various sports are made more durable. Such novel products have a
  • 43. 41 promising potential especially in the field of cosmetics. Nanotechnology also has numerous potential applications in heavy industry. Nanotechnology is predicted to be a main driver of technology and business in this century and holds the promise of higher performance materials, intelligent systems and new production methods with significant impact for all aspects of society. 2.6.1 Military: Biological sensors: Nanotechnology can improve the military’s ability to detect biological agents. By using nanotechnology, the military would be able to create sensor systems that could detect biological agents.[10] The sensor systems are already well developed and will be one of the first forms of nanotechnology that the military will start to use. Uniform material: Nanoparticles can be injected into the material on soldiers’ uniforms to not only make the material more durable, but also to protect soldiers from many different dangers such as high temperatures, impacts and chemicals. The nanoparticles in the material protect soldiers from these dangers by grouping together when something strikes the armor and stiffening the area of impact. This stiffness helps lessen the impact of whatever hit the armor, whether it was extreme heat or a blunt force. By reducing the force of the impact, the nanoparticles protect the soldier wearing the uniform from any injury the impact could have caused.
  • 44. 41 Another way nanotechnology can improve soldiers’ uniforms is by creating a better form of camouflage. Mobile pigment nanoparticles injected into the material can produce a better form of camouflage. These mobile pigment particles would be able to change the color of the uniforms depending upon the area that the soldiers are in. There is still much research being done on this self-changing camouflage. Nanotechnology can improve thermal camouflage. Thermal camouflage helps protect soldiers from people who are using night vision technology. Surfaces of many different military items can be designed in a way that electromagnetic radiation can help lower the infrared signatures of the object that the surface is on. Surfaces of soldiers’ uniforms and surfaces of military vehicle are a few surfaces that can be designed in this way. By lowering the infrared signature of both the soldiers and the military vehicles the soldiers are using, it will provide better protection from infrared guided weapons or infrared surveillance sensors. Communication method: There is a way to use nanoparticles to create coated polymer threads that can be woven into soldiers’ uniforms. These polymer threads could be used as a form of communication between the soldiers. The system of threads in the uniforms could be set to different light wavelengths, eliminating the ability for anyone else to listen in. This would lower the risk of having anything intercepted by unwanted listeners.
  • 45. 42 Medical system: A medical surveillance system for soldiers to wear can be made using nanotechnology. This system would be able to watch over their health and stress levels. The systems would be able to react to medical situations by releasing drugs or compressing wounds as necessary. This means that if the system detected an injury that was bleeding, it would be able to compress around the wound until further medical treatment could be received. The system would also be able to release drugs into the soldier’s body for health reasons, such as pain killers for an injury. The system would be able to inform the medics at base of the soldier’s health status at all times that the soldier is wearing the system. The energy needed to communicate this information back to base would be produced through the soldier’s body movements. Weapons: Nano-weapon is the name given to military technology currently under development which seeks to exploit the power of nanotechnology in the modern battlefield. 2.6.2 Construction: Nanotechnology has the potential to make construction faster, cheaper, safer, and more varied. Automation of nanotechnology construction can allow for the creation of structures from advanced homes to massive skyscrapers much more quickly and at much lower cost. In the near future, Nanotechnology can be used to sense cracks in foundations of architecture and can send nanobots to repair them.
  • 46. 43 Nanotechnology is an active research area that encompasses a number of disciplines such as electronics, bio-mechanics and coatings. These disciplines assist in the areas of civil engineering and construction materials.[25] If nanotechnology is implemented in the construction of homes and infrastructure, such structures will be stronger. If buildings are stronger, then less of them will require reconstruction and less waste will be produced. Nanotechnology in construction involves using nanoparticles such as alumina and silica. Manufacturers are also investigating the methods of producing nano-cement. If cement with nano-size particles can be manufactured and processed, it will open up a large number of opportunities in the fields of ceramics, high strength composites and electronic applications. Nanomaterials still have a high cost relative to conventional materials, meaning that they are not likely to feature in high-volume building materials. The day when this technology slashes the consumption of structural steel has not yet been contemplated. Cement: Much analysis of concrete is being done at the nano-level in order to understand its structure. Such analysis uses various techniques developed for study at that scale such as Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Focused Ion Beam (FIB). This has come about as a side benefit of the development of these
  • 47. 44 instruments to study the nanoscale in general, but the understanding of the structure and behavior of concrete at the fundamental level is an important and very appropriate use of nanotechnology. One of the fundamental aspects of nanotechnology is its interdisciplinary nature and there has already been cross over research between the mechanical modeling of bones for medical engineering to that of concrete which has enabled the study of chloride diffusion in concrete (which causes corrosion of reinforcement). Concrete is, after all, a macro-material strongly influenced by its nano-properties and understanding it at this new level is yielding new avenues for improvement of strength, durability and monitoring as outlined in the following paragraphs Silica (SiO2) is present in conventional concrete as part of the normal mix. However, one of the advancements made by the study of concrete at the nanoscale is that particle packing in concrete can be improved by using nano-silica which leads to a densifying of the micro and nanostructure resulting in improved mechanical properties. Nano- silica addition to cement based materials can also control the degradation of the fundamental C-S-H (calcium-silicatehydrate) reaction of concrete caused by calcium leaching in water as well as block water penetration and therefore lead to improvements in durability. Related to improved particle packing, high energy milling of ordinary Portland cement (OPC) clinker and standard sand, produces a greater particle size diminution with respect to conventional OPC and, as a result, the compressive strength of the refined material is also 3 to 6 times higher (at different ages).
  • 48. 45 Steel: Steel is a widely available material that has a major role in the construction industry. The use of nanotechnology in steel helps to improve the physical properties of steel. Fatigue, or the structural failure of steel, is due to cyclic loading. Current steel designs are based on the reduction in the allowable stress, service life or regular inspection regime. This has a significant impact on the life-cycle costs of structures and limits the effective use of resources. Stress risers are responsible for initiating cracks from which fatigue failure results. The addition of copper nanoparticles reduces the surface un-evenness of steel, which then limits the number of stress risers and hence fatigue cracking. Advancements in this technology through the use of nanoparticles would lead to increased safety, less need for regular inspection, and more efficient materials free from fatigue issues for construction. Steel cables can be strengthened using carbon nanotubes. Stronger cables reduce the costs and period of construction, especially in suspension bridges, as the cables are run from end to end of the span. The use of vanadium and molybdenum nanoparticles improves the delayed fracture problems associated with high strength bolts. This reduces the effects of hydrogen embrittlement and improves steel micro- structure by reducing the effects of the inter-granular cementite phase. Welds and the Heat Affected Zone (HAZ) adjacent to welds can be brittle and fail without warning when subjected to sudden dynamic loading. The addition of nanoparticles such as magnesium and calcium
  • 49. 46 makes the HAZ grains finer in plate steel. This nanoparticle addition leads to an increase in weld strength. The increase in strength results in a smaller resource requirement because less material is required in order to keep stresses within allowable limits. Wood: Nanotechnology represents a major opportunity for the wood industry to develop new products, substantially reduce processing costs, and open new markets for biobased materials. Wood is also composed of nanotubes or “nanofibrils”; namely, lignocellulosic (woody tissue) elements which are twice as strong as steel. Harvesting these nanofibrils would lead to a new paradigm in sustainable construction as both the production and use would be part of a renewable cycle. Some developers have speculated that building functionality onto lignocellulosic surfaces at the nanoscale could open new opportunities for such things as self-sterilizing surfaces, internal self- repair, and electronic lignocellulosic devices. These non-obtrusive active or passive nanoscale sensors would provide feedback on product performance and environmental conditions during service by monitoring structural loads, temperatures, moisture content, decay fungi, heat losses or gains, and loss of conditioned air. Currently, however, research in these areas appears limited. Due to its natural origins, wood is leading the way in cross- disciplinary research and modelling techniques. BASF have developed a highly water repellent coating based on the actions of the lotus leaf as a result of the incorporation of silica and alumina nanoparticles and
  • 50. 47 hydrophobic polymers. Mechanical studies of bones have been adapted to model wood, for instance in the drying process. Glass: Research is being carried out on the application of nanotechnology to glass, another important material in construction. Titanium dioxide (TiO2) nanoparticles are used to coat glazing since it has sterilizing and anti-fouling properties. The particles catalyze powerful reactions that break down organic pollutants, volatile organic compounds and bacterial membranes. TiO2 is hydrophilic (attraction to water), which can attract rain drops that then wash off the dirt particles. Thus the introduction of nanotechnology in the Glass industry, incorporates the self-cleaning property of glass. Fire-protective glass is another application of nanotechnology. This is achieved by using a clear intumescent layer sandwiched between glass panels (an interlayer) formed of silica nanoparticles (SiO2), which turns into a rigid and opaque fire shield when heated. Most of glass in construction is on the exterior surface of buildings. So the light and heat entering the building through glass has to be prevented. The nanotechnology can provide a better solution to block light and heat coming through windows. Coatings: Coatings is an important area in construction coatings are extensively use to paint the walls, doors, and windows. Coatings should provide a protective layer bound to the base material to produce a surface
  • 51. 48 of the desired protective or functional properties. The coatings should have self-healing capabilities through a process of "self-assembly". Nanotechnology is being applied to paints to obtained the coatings having self-healing capabilities and corrosion protection under insulation. Since these coatings are hydrophobic and repel water from the metal pipe and can also protect metal from salt water attack. Nanoparticle based systems can provide better adhesion and transparency. The TiO2 coating captures and breaks down organic and inorganic air pollutants by a photo-catalytic process, which leads to putting roads to good environmental use. Fire Protection and detection: Fire resistance of steel structures is often provided by a coating produced by a spray-on-cementitious process. The nano-cement has the potential to create a new paradigm in this area of application because the resulting material can be used as a tough, durable, high temperature coating. It provides a good method of increasing fire resistance and this is a cheaper option than conventional insulation. Risks in construction: In building construction nanomaterials are widely used from self- cleaning windows to flexible solar panels to wi-fi blocking paint. The self-healing concrete, materials to block ultraviolet and infrared radiation, smog-eating coatings and light-emitting walls and ceilings are the new nanomaterials in construction. Nanotechnology is a promise for making the "smart home" a reality. Nanotech-enabled sensors can monitor
  • 52. 49 temperature, humidity, and airborne toxins, which needs nanotech-based improved batteries. The building components will be intelligent and interactive since the sensor uses wireless components, it can collect the wide range of data. If nanosensors and nanomaterials become an everyday part of the buildings, as with smart homes, what are the consequences of these materials on human beings?  Effect of nanoparticles on health and environment: Nanoparticles may also enter the body if building water supplies are filtered through commercially available nano-filters. Airborne and waterborne nanoparticles enter from building ventilation and wastewater systems.  Effect of nanoparticles on societal issues: As sensors become commonplace, a loss of privacy and autonomy may result from users interacting with increasingly intelligent building com
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