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New imaging technique homes in on electrocatalysis of nanoparticles


By modifying the rate at which chemical reactions take place, nanoparticle catalysts fulfill myriad roles in industry, the biomedical arena and everyday life. They may be used for the production of polymers and biofuels, for improving pollution and emission control devices, to enhance reactions essential for fuel cell technology and for the synthesis of new drugs. Finding new and more effective nanoparticle catalysts to perform these useful functions is therefore vital.

Now Nongjian (NJ) Tao, a researcher at Arizona State University’s Biodesign Institute, has found a clever way to measure catalytical reactions of single nanoparticles and multiple particles printed in arrays, which will help characterize and improve existing nanoparticle catalysts, and advance the search for new ones.

Most catalytic materials synthesized in labs contain particles with different sizes and shapes, each having different electrocatalytical activities, but the conventional methods measure the average properties of many nanoparticles, which smear out the properties of individual nanoparticles.

“The capability of measuring single nanoparticle catalytical reactions allows for determining the relationship between the efficiency of a catalytical reaction and the size, shape and composition of the nanoparticle,” Tao explained. “Such an imaging capability also makes it possible to image arrays of nanoparticle catalytical reactions, which may be used for fast screening of different nanoparticles,” he added.

In the current study, platinum nanoparticles acting as electrochemical catalysts are investigated by means of the new technique, known as plasmonic electrochemical imaging. The method combines the spatial resolution of optical detection with the high sensitivity and selectivity of electrochemical recognition.

Results of the study appear in this week’s advanced online edition of the journal Nature Nanotechnology.

Scanning electrochemical microscopy (SECM) has been used to image electrochemical reactions by mechanically scanning a sample surface using a microelectrode. In this process however, imaging speed is limited and the presence of the microelectrode itself may impinge on the sample and alter results.

The new method relies instead on imaging electrochemical reactions optically based on the phenomenon of surface plasmon resonance. Surface plasmons are oscillations of free electrons in a metal electrode, and can be created and detected with light. Every electrochemical reaction is accompanied by the exchange of electrons between reactants and electrodes, and the conventional electrochemical methods, including SECM, detect the electrons.

“Our approach is to measure electrochemical reactions without directly detecting the electrons,” Tao said. “The trick is to detect the conversion of the reactant into reaction products associated with the exchange of electrons.” Such conversion in the vicinity of the electrode affects the plasmon, causing changes in light reflectivity, which the technique converts to an optical image.

Using plasmonic electrochemical current imaging, Tao’s group examined the electrocatalytic activity of platinum nanoparticles printed in a microarray on a gold thin-film electrode, demonstrating for the first time the feasibility of high-throughput screening of the catalytic activities of nanoparticles.

Additionally, the new study shows that the same method can be used to investigate individual nanoparticles. As an electrical potential is applied to the electrode and cycled through a range of values, nanoparticles clearly appear as spots on the array. The effect can be seen in accompanying videos, where nanoparticle spots ‘develop’ over time as the potential changes, much like a polaroid picture gradually appears. 

Microarrays featuring different surface densities of nanoparticles were also produced for the study. Results showed that electrocatalytic current at a given potential increases proportionally with nanoparticle density. Further, when individual nanoparticles were characterized using SPR microscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM), good agreement was shown between the results, further validating the new technique.

Tao notes that in principle, plasmonic electrochemical imaging – a rapid and non-invasive technique offering the combined benefits of optical and electrochemical detection – may be applied to other phenomena for which conventional electrochemical detection methods are currently used.

Synthesis of Nanoparticles


Nanoparticles may be created using several methods. Some of them may occur in nature as well. The methods of creation include attrition and pyrolysis. While some methods are bottoms up, some are called top down. Top down methods involve braking the larger materials into nanoparticles.

Nanoparticle Synthesis

Top-Down viaBottom-Up via
Attrition / MillingPyrolysis
 Inert gas condensation
 Solvothermal reaction
 Sol-Gel fabrication
 Structured media

Attrition

Attrition methods include methods by which macro or micro scale particles are ground in a ball mill, a planetary ball mill, or other size reducing mechanism. The resulting particles are air classified to recover nanoparticles.
  • Involves mechanical thermal cycles
  • Yields
    • broad size distribution (10-1000 nm)
    • varied particle shape or geometry
    • impurities
  • Application
    • Nanocomposites
    • Nano-grained bulk materials

Bottoms up methods

These are further classified according to phases:
  • Gas (Vapor) Phase Fabrication: Pyrolysis, Inert Gas Condensation
  • Liquid Phase Fabrication: Solvothermal Reaction, Sol-gel, Micellar Structured Media

Pyrolysis

In pyrolysis, a vaporous precursor (liquid or gas) is forced through a hole or opening at high pressure and burned. The resulting solid is air classified to recover oxide particles from by-product gases. Pyrolysis often results in aggregates and agglomerates rather than singleton primary particles.
Instead of gas, thermal plasma can also deliver the energy necessary to cause evaporation of small micrometer size particles. The thermal plasma temperatures are in the order of 10,000 K, so that solid powder easily evaporates. Nanoparticles are formed upon cooling while exiting the plasma region. Examples of plasma used include dc plasma jet, dc arc plasma and radio frequency (RF) induction plasmas.
For example, silica sand can be vaporized with an arc plasma at atmospheric pressure. The resulting mixture of plasma gas and silica vapour can be rapidly cooled by quenching with oxygen, thus ensuring the quality of the fumed silica produced.
The advantages of vapor phase pyrolysis include it being a simple process, cost effective, a continuous operation with high yield.

Liquid phase synthesis methods

The liquid phase fabrication entails a wet chemistry route.
Methods are:
  • Solvothermal Methods (e.g. hydrothermal)
  • Sol-Gel Methods
  • Synthesis in Structure Media (e.g., microemulsion)
Effectiveness of Solvothermal Methods and Sol-gel methods demands a simple process, low cost, continuous operation and high yield.

Solvothermal process

Precursors are dissolved in hot solvents (e.g., n-butyl alcohol) and solvent other than water can provide milder and friendlier reaction conditions If the solvent is water then the process is referred to as  hydrothermal method.

Sol-gel process

The sol-gel process is a wet-chemical technique (also known as chemical solution deposition) widely used recently in the fields of materials science and ceramic engineering.
Steps include:
  • Formation of stable sol solution
  • Gelation via a polycondensation or polyesterification reaction
  • Gel aging into a solid mass. This causes contraction of the gel network, also phase transformations and Ostwald ripening.
  • Drying of the gel to remove liquid phases. This can lead to fundamental changes in the structure of the gel.
  • Dehydrationat temperatures as high as 8000 degree C, used to remove M-OH groups for stabilizing the gel, i.e., to protect it from rehydration.
  • Densification and decomposition of the gels at high temperatures (T > 8000 degree C), i.e., to collapse the pores in the gel network and to drive out remaining organic contaminants
The ultimate microstructure of the final component will clearly be strongly influenced by changes implemented during this phase of processing. The precursor sol can be either deposited on a substrate to form a film (e.g. by dip-coating or spin-coating), cast into a suitable container with the desired shape (e.g. to obtain a monolithic ceramics, glasses, fibers, membranes, aerogels), or used to synthesize powders (e.g. microspheres, nanospheres).

Advantages of the sol-gel process

Advantages of the sol-gel process are that it is a cheap and low-temperature technique that allows for the fine control of the product’s chemical composition. Even small quantities of dopants, such as organic dyes and rare earth metals, can be introduced in the sol and end up uniformly dispersed in the final product.

Properties of Nanoparticles


Nanoparticles are important scientific tools that have been and are being explored in various biotechnological, pharmacological and pure technological uses. They are a link between bulk materials and atomic or molecular structures.

While bulk materials have constant physical properties regardless of its size, among nanoparticles the size often dictates the physical and chemical properties. Thus, the properties of materials change as their size approaches the nanoscale and as the percentage of atoms at the surface of a material becomes significant.

For bulk materials, those larger than one micrometer (or micron), the percentage of atoms at the surface is insignificant in relation to the number of atoms in the bulk of the material.

Physical properties of nanoparticles
Nanoparticles are unique because of their large surface area and this dominates the contributions made by the small bulk of the material. Zinc oxide particles have been found to have superior UV blocking properties compared to its bulk substitute. This is one of the reasons why it is often used in the preparation of sunscreen lotions.

Other examples of the physical properties of nanoparticles:

Color – Nanoparticles of yellow gold and gray silicon are red in color
Gold nanoparticles melt at much lower temperatures (~300 °C for 2.5 nm size) than the gold slabs (1064 °C)
Absorption of solar radiation in photovoltaic cells is much higher in nanoparticles than it is in thin films of continuous sheets of bulk material - since the particles are smaller, they absorb greater amount of solar radiation

Optical properties of nanoparticles
Nanoparticles also often possess unexpected optical properties as they are small enough to confine their electrons and produce quantum effects. One example of this is that gold nanoparticles appear deep red to black in solution.

Formation of suspensions
An important physical property of nanoparticles is their ability to form suspensions. This is possible since the interaction of the particle surface with the solvent is strong enough to overcome density differences. In bulk materials this interactions usually result in a material either sinking or floating in a liquid.

Magnetization and other properties of nanoparticles
Other properties unique among nanoparticles are quantum confinement in semiconductor particles, surface plasmon resonance in some metal particles and superparamagnetism in magnetic materials.

For example, ferroelectric materials smaller than 10 nm can switch their magnetisation direction using room temperature thermal energy, thus making them unsuitable for memory storage. Thus this property is not always desired in nanoparticles.

Diffusion properties of nanoparticles
At elevated temperatures especially, nanoparticles possess the property of diffusion. Sintering can take place at lower temperatures, over shorter time scales than for larger particles. Although this does not affect the density of the final product but there is a chance of agglomeration.

Hard nanoparticles
Clay nanoparticles, when incorporated into polymer matrices, increase reinforcement, leading to stronger plastics. These nanoparticles are hard, and impart their properties to the polymer (plastic). Nanoparticles have also been attached to textile fibers in order to create smart and functional clothing.

Semisolid or soft nanoparticles
Semi-solid and soft nanoparticles have been manufactured. Of these notable is the liposome. Various types of liposome nanoparticles are currently used clinically as delivery systems for anticancer drugs, antibiotics and antifungal drugs and vaccines.

Dimensionality
Nanoparticles are generally classified based on their dimensionality, morphology, composition, uniformity, and agglomeration.

1D nanomaterials
These are one dimensional in the nanometer scale are typically thin films or surface coatings, and include the circuitry of computer chips and the antireflection and hard coatings on eyeglasses. These have been used in electronics, chemistry, and engineering.

2D nanomaterials
Two-dimensional nanomaterials have two dimensions in the nanometer scale. These include 2D nanostructured films, with nanostructures firmly attached to a substrate, or nanopore filters used for small particle separation and filtration. Asbestos fibers are an example of 2D nanoparticles.

3D nanomaterials
Materials that are nanoscaled in all three dimensions are considered 3D nanomaterials. These include thin films deposited under conditions that generate atomic-scale porosity, colloids, and free nanoparticles with various morphologies

Nanoparticle Uniformity



When nanoparticles are synthesized, high level of purity and uniformity of structure is necessary for putting these particles to use in private, industrial and military sectors. There must be high purity ceramics, polymers, glass-ceramics and material composites in creation of these particles. Nanoparticles are generally classified based on their dimensionality, morphology, composition, uniformity, and agglomeration.

Synthesis of nanoparticles
During synthesis, the process of condensation leads to fine powders with irregular particle sizes and shapes in a typical powder. This may lead to non-uniformity of structure in the packaged nanoparticles. That may result in packing density variations in the powder compact. In addition, uncontrolled agglomeration of powders due to attractive van der Waals forces may also result in non-homogenous formation nanoclusters and nanoparticle packages.

There are variations in stresses that can result in non-uniform drying shrinkage and this is directly proportional to the rate at which the solvent can be removed. Porosity and its distribution thus determines the process to a large extent. Such stresses have been associated with a plastic-to-brittle transition in consolidated bodies and lead to propagation of cracks.

Homogenisity may further be compromised where there are fluctuations in packing density in the compact as it is prepared for the kiln and during the sintering process. Some pores and other structural defects associated with density variations have been shown to play a detrimental role in the sintering process.

Thus the aim should be to produce nanomaterials of uniform size, shape and most importantly the distribution of components and porosity. This will maximize the green density. The containment of a uniformly dispersed assembly of strongly interacting particles in suspension requires total control over interparticle forces.

Nanoparticles with colloids
Nanoparticles with colloids can provide this feature and produce increased uniformity. Monodisperse powders of colloidal silica, for example, may be stabilized sufficiently to ensure a high degree of order in the colloidal crystal or polycrystalline colloidal solid which results from aggregation.

Such defective polycrystalline colloidal structures would appear to be the basic elements of submicrometer colloidal materials science. These may form the first step in developing a more rigorous understanding of the mechanisms involved in production of more uniform nanoparticles that can be used in various fields.

Nanoparticles - What are Nanoparticles?


A nanoparticle is a small object that behaves as a whole unit in terms of its transport and properties.

Size of nanoparticles

In terms of diameter, fine particles cover a range between 100 and 2500 nanometers, while ultrafine particles are sized between 1 and 100 nanometers. Nanoparticles may or may not exhibit size-related properties that are seen in fine particles. Despite being the size of the ultrafine particles individual molecules are usually not referred to as nanoparticles.
Nanoclusters have at least one dimension between 1 and 10 nanometers and a narrow size distribution. Nano powders on the other hand are agglomerates of ultrafine particles, nanoparticles, or nanoclusters. Nano particle sized crystals are called nanocrystals.
Colorized transmission electron micrograph showing chains of cobalt nanoparticles. Image credit: G. Cheng, A.R. Hight Walker/NIST
Colorized transmission electron micrograph showing chains of cobalt nanoparticles.

Nanoparticle research and uses

Nanoparticle research is currently the most studied branch of science with the number of uses of nanoparticles in various fields. The particles have wide variety of potential applications in biomedical, optical and electronic fields.

History of nanoparticle research

The history of nanoparticle research is long and the use of these particles dates back to the 9th century in Mesopotamia when artisans used these to generate a glittering effect on the surface of pots.

This lustre or glitter over pottery from the Middle Ages and Renaissance is due to a metallic film that was applied to the transparent surface of a glazing. The lustre can still be visible if the film has resisted atmospheric oxidation and other weathering.

The lustre is within the film itself which contained silver and copper nanoparticles dispersed homogeneously in the glassy matrix of the ceramic glaze. Artisans created the nanoparticles by adding copper and silver salts and oxides together with vinegar, ochre and clay, on the surface of previously-glazed pottery. Then the pots were placed into a kiln and heated to about 600 °C in a reducing atmosphere. With the heat the glaze would soften, causing the copper and silver ions to migrate into the outer layers of the glaze.
Michael Faraday provided the first description, in scientific terms, of the optical properties of nanometer-scale metals in his 1857 paper.

Uses and advantages of nanoparticles in medicine

Some of the uses of nanoparticles in biology and medicine include:
  • Creating fluorescent biological labels for important biological markers and molecules in research and diagnosis of diseases
  • Drug delivery systems
  • Gene delivery systems in gene therapy
  • For biological detection of disease causing organisms and diagnosis
  • Detection of proteins
  • Isolation and purification of biological molecules and cells in research
  • Probing of DNA structure
  • Genetic and tissue engineering
  • Destruction of tumours with drugs or heat
  • In MRI studies
  • In pharmacokinetic studies.
  • Nanoparticles are being increasingly used in drug delivery systems.  The advantages of using nanoparticles as a drug delivery system include:

  • The size and surface characteristics of nanoparticles can be easily manipulated. This could be used for both passive and active drug targeting
  • Nanoparticles can be made to control and sustain release of the drug during the transportation as well as the location of the release. Since distribution and subsequent clearance of the drug from the body can be altered, an increase in drug therapeutic efficacy and reduction in side effects can be achieved.
  • Choosing an appropriate matrix also helps in increasing the efficacy and reducing side effects
  • Targeted drugs may be developed
  • Various routes of administration including oral, nasal, injection, intra-ocular (within the eyes) etc. can be used.

Nanoparticles


Nanoparticles are formed through the natural or human mediated disintegration of larger structures or by controlled assembly processes. The associated processes occur either in the gas phase, in a plasma, in a vacuum phase or in the liquid phase. Particles are classified according to size: in terms of diameter, fine particles cover a range between 100 and 2500 nanometers. Nanoclusters have at least one dimension between 1 and 10 nanometers and a narrow size distribution. Nanopowders ,nanoparticles, or nanoclusters. Nanocrystals are nanometer sized single crystals. Many scientist researches have been done in this field due to a wide variety of potential applications in biomedical, optical and electronic fields.

Inert-gas condensation is frequently used to make nanoparticles from metals with low melting points. The metal is vaporized in a vacuum chamber and then supercooled with an inert gas stream. The supercooled metal vapor condenses into nanometer-sized particles, which can be entrained in the inert gas stream and deposited on a substrate.

A thermal plasma provides the energy necessary to do evaporation of small micrometer size particles and its temperatures are in the order of 10000k. Nanoparticles are formed upon cooling while exiting the plasma region. Silica sand can be vaporized with an arc plasma at atmospheric pressure. The resulting mixture of plasma gas and silica vapour can be rapidly cooled by quenching with oxygen, thus ensuring the quality of the fumed silica produced. Energy coupling to the plasma is done through the electromagnetic field generated by the induction coil. The plasma gas does not come in contact with electrodes, thus eliminating possible sources of contamination and allowing the operation of such plasma torches with a wide range of gases including inert, reducing, oxidizing and other corrosive atmospheres.

Attrition and pyrolysis are two methods to generate nanoparticles. In attrition, macro or micro scale particles are ground in a ball mill, a planetary ball mill, or other size reducing mechanism. The resulting particles are air classified to recover nanoparticles. In pyrolysis, a vaporous precursor is forced through an orifice at high pressure and burned. The resulting solid is air classified to recover oxide particles from by-product gases.

Nanotechnology In Civil Engineering


1. INTRODUCTION
Nanotechnology is not a new science and it is not a new technology.“Nanotechnology is an enabling technology that allows us to develop materials with improved or totally new properties”It is rather an extension of the sciences and technologies already developed for many years ,to examine the nature of our world at an ever smaller scale.Nanotechnology is the use of very small particles of material. A nanometer is a billionth of a meter.The size of the particles, is very important because at the length scale of the nanometer, 10-9m, the properties of the material actually become affected.

2. Nanotechnology In Construction….
The construction business will inevitably be a beneficiary of this nanotechnology.In fact it already is in the fields of concrete, steel and glass,and many more. Concrete is stronger, more durable and more easily placed; steel is made tougher ; glass is self-cleaning.Paints are made more insulating and water repelling.

3. Introduction To Nano Materials Nano particle: 
It is defined as a particle with at least one dimension less than 200nm.It is quantum dots if they are small enough (typically sub 10nm) such that jumps in energy levels occur.Nano composite : It is produced by adding Nano particle to a bulk material in order to improve the bulk material’s properties.

4. Carbon Nano Tubes (CNT) 
They are cylindrical with nanometer diameter.They can be several millimeters in lengththey have 5 times the Young’s modulus and 8 times (theoretically 100 times) the strength of steel whilst being 1/6th the density.Thermal conduction is also very high along the tube axis

5. Titanium oxide
Titanium dioxide is a widely used white pigment.It can oxidize oxygen or organic materials, and so added to paints, cements, windows, tiles, or other products for sterilizing, deodorizing and anti-fouling propertiesWhen incorporated into outdoor building materials can substantially reduce concentrations of airborne pollutants. Additionally, as TiO2 is exposed to UV light, it becomes increasingly hydrophilic ,thus it can be used for anti-fogging coatings or selfcleaning windows.

6. NANOTECHNOLOGY IN CONCRETE
Concrete is a mixture of cement, sand(fine aggregate), coarse aggregate and water.As concrete is most usable material in construction industry it’s been require to improve its quality. The mechanical behavior of concrete materials depends on phenomena that occur on a micro and a nano scale.

7. Nanotechnology in Concrete Nanotechnology can: modify the molecular structure of concrete material to improve the material's properties as shown in the chart.Nano-concrete is defined as “A concrete made with Portland cement particles that are less than 500 Nano-meters as the cementing agent”.

8. Concrete is, after all, a macro-material strongly influenced by its nano-properties.NANO-SILICA: 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-silicate hydrate) 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.

9. If these Nano-cement particles can be processed with Nano tubes and reactive Nano-size silica particles, conductive, strong, tough and room temperature processed ceramics can be developed both for electronic applications and coatings. Average size of Portland cement particle is about 50 microns.In thinner final products and faster setting time, micro cement with a maximum particle size of about 5 microns is being used. Therefore is reduced to obtain nano-portland cement.Hydration tests indicated that the Nano-cement had a more rapid hydration rate than Portland cement. 

10. TiO2 In Concrete TiO2 is a white pigment and can be used as an excellent reflective coating.it is hydrophilic and therefore gives self cleaning properties to surfaces to which it is applied. The process by which this occurs is that rain water is attracted to the surface and forms sheets which collect the pollutants and dirt particles previously broken down and washes them off. The resulting concrete, already used in projects around the world, has a white color that retains its whiteness very effectively unlike the stained buildings of the material’s pioneering past.

11. CNTs In ConcreteThe addition of small amounts (1% wt) of CNT’s can improve the mechanical properties of samples consisting of the main Portland cement phase and water.Oxidized multi-walled Nano tubes (MWNT’s) show the best improvements both in compressive strength (+ 25 N/mm2) and flexural strength (+ 8 N/mm2) compared to the samples without the reinforcement.A number of investigations have been carried out for developing smart concrete using carbon fibers.

12. NANOTECHNOLOGY AND STEEL
Need For Nanotechnology In Steel..Fatigue is a significant issue that can lead to the structural failure of steel subject to cyclic loading, such as in bridges or towers. This can happen at stresses significantly lower than the yield stress of the material and lead to a significant shortening of useful life of the structure.Stress risers are responsible for initiating cracks from which fatigue failure results and research has shown that the addition of copper Nanoparticle reduces the surface unevenness of steel which then limits the number of stress risers and hence fatigue cracking.Advancements in this technology would lead to increased safety, less need for monitoring and more efficient materials use in construction prone to fatigue issues.

13. Temperature restrictionAbove 750 F, regular steel starts to lose its structural integrity, and at 1100 F, steel loses 50 percent of its strength.A new formula infuses steel with nanoscale copper particles, this formula could maintain structural integrity at temperatures up to 1000 F.the new steel allows ultra-high strength to be combined with good formability, corrosion resistance and a good surface finish.

14. High Strength Steel Cables Current research into the refinement of the cementite phase of steel to a Nano-size has produced stronger cables. A stronger cable material would reduce the costs and period of construction, especially in suspension bridges .Sustainability is also enhanced by the use of higher cable strength as this leads to a more efficient use of materials.High rise structures require high strength joints and this in turn leads to the need for high strength bolts.

15. High strength bolts The capacity of high strength bolts is realized generally through quenching and tempering and the microstructures of such products consist of tempered martensite.When the tensile strength of tempered martensite steel exceeds 1,200 MPa even a very small amount of hydrogen embrittles the grain boundaries and the steel material may fail during use.vanadium and molybdenum Nanoparticle has shown that they improve the delayed fracture problems associated with high strength bolts, improving the steel micro-structure.

16. Two products in international marketSandvik NanoflexMMFX2 steelproduced by Sandvik Materials Technology(Sweden)desirable qualities of a high Young’s Modulus and high strength resistant to corrosion due to the presence of very hard nanometer-sized particlesThe use of stainless steel reinforcement in concrete structures is limited as it is cost prohibitive.produced by MMFX Steel Corp (America)has the mechanical properties of conventional steelhas a modified nano-structure that makes it corrosion resistantit is an alternative to conventional stainless steel, but at a lower cost.

17. NANOTECHNOLOGY AND GLASS (SELF CLEANING)
Vital role of glass in buildings The current state of the art in cladding is an active system which tracks sun, wind and rain in order to control the building environment and contribute to sustainability Consequently, there is a lot of research being carried out on the application of nanotechnology to glassMost of glass in construction is, on the exterior surface of buildings and the control of light and heat entering through glazing is a major issue. Research into nanotechnological solutions to this centers around four different strategies to block light& heat coming through windows.

18. Self cleaning glass using TiO2Titanium dioxide (TiO2) is usedin Nanoparticle form to coat glazing since it has sterilizing and anti-fouling properties. The particles catalyze powerful reactions which breakdown organic pollutants, volatile organic compounds and bacterial membranes. TiO2 is hydrophilic and this attraction to water forms sheets out of rain drops which then wash off the dirt particles broken down in the previous process. Glass incorporating this self cleaning technology is available on the market today.

19. Self cleaning glass. Fire and heat protection 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 fumed silica (SiO2) Nanoparticle which turns into a rigid and opaque fire shield when heated.For heat protection thin film coatings are being developed which are spectrally sensitive surface applications for window glass and filter out unwanted infrared frequencies of light (which heat up a room) and reduce the heat gain in buildings, however, these are effectively a passive solution. As an active solution, thermo chromic technologies are being studied which react to temperature and provide insulation to give protection from heating whilst maintaining adequate lighting.

20. Other technologies…A third strategy, that produces a similar outcome by a different process, involves photo chromic technologies which react to changes in light intensity.Electro chromic coatings are being developed that react to changes in applied voltage by using tungsten oxidelayer; thereby becoming more opaque atthe touch of a button. All these applications are intended to reduce energy use in cooling buildings.

21. NANO TECHNOLOGY IN OTHER DISCIPLINES

Nanotechnology and wood : Wood is also composed of nanotubes or “nanofibrils”, lignocelluloses are twice as strong as steel. Nanofibrils would lead to a new paradigm in sustainable construction Functionality onto lignocelluloses surfaces at the nanoscale could open new opportunities for such things as self-sterilizing surfaces, internal self-repair, and electronic lignocelluloses devices. Currently, however, research in these areas appears limited.Researchers 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 Nanoparticle and hydrophobic polymers.

Nanotechnology and coatings Nanotechnology is being applied to paints and insulating properties, produced by the addition of nano-sized cells, pores and particles, giving very limited paths for thermal conduction (R values are double those for insulating foam), are currently available.This type of paint is used, for corrosion protection under insulation since it is hydrophobic and repels water from the metal pipe and can also protect metal from salt water attack.

Elimination of toxic gases The absorption of carbon monoxide is done by using cuprous salt and adsorption of hydrocarbons is done by using a complex nanomaterial. i.e., Carbon Monolithic Aero gels.Production of Aero gels is done by sol-gel process.Adsorption capacity measurements show that modified hydrophobic Carbon aero gels are excellent adsorbents for different toxic organic compounds from water.

Conclusion In conclusion, nanotechnology offers the possibility of great advances whereas conventional approaches, at best, offer only incremental improvements.“At this moment the main limitation is the high costs of nanotechnology. Also concerns with the environmental effects”The waves of change being propagated by progress at the nanoscale will therefore be felt far and wide and nowhere more so than in construction due its large economic and social presence.

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