Summer Project Anup

A STUDY PROJECT ON NANOTECHNOLOGY FOR SUSTAINABLE FUTURE DURING MAY-JUNE 2009 AT IISc BANGALORE

Submitted By ANUP MAHESH SAVALE KVPY Reg. No. 1071213 2nd yr Integrated M.S., IISER, Pune.

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CERTIFICATE This is to certify that Mr. Anup Mahesh Savale has successfully completed the summer project on the topic “Nanotechnology for sustainable future”, under my guidance during May-June 2009.

Dr. P Balachandra Principal Research Scientist

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ACKNOWLEDGEMNE NT It is my honour to express my gratitude and sincere thanks to Dr. P. Balachandra, Principal Research Scientist, Department of Management Studies, Indian Institute of Science, Bangalore for giving me an opportunity to pursue my summer project under his valuable guidance. I further want to extend my gratitude to the Chairman, Department of Management Studies, Indian Institute of Science for granting me the library and the computer facilities in the department which greatly helped me in grasping some valuable knowledge under my belt. Last but not the least; I want to thank my parents for their immense love, faith and moral support at each and every instant of my life.

Anup Mahesh Savale 3

CONTENTS Introduction Nanotechnology- A bird’s eye view

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1 An insight into the global problems

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2 Nanotechnology: A key to energy crisis

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2.1 Advancements in fossil fuels

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2.2 Advancements in Li batteries

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2.3 Applications in Renewable energy utilization

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2.3.1

Electricity generation with solar energy

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2.3.2

Hydrogen production with solar energy

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2.3.3

Solid state hydrogen storage

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2.3.4

Utilization of hydrogen with fuel cells

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Nanotechnology: A step towards better environment 3.1 Water purification

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3.1.1

Ceramic membranes

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3.1.2

Nanocatalysts

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3.1.3

Iron remediation

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4 Barriers to the nanotechnology advancements 4.1 Nano-hazards 4.2 Nano-regulation

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5 Conclusion

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References Bibliography Internet sources 4

INTRODUCTION In the present world, everyone one of us wants to improve our own living standards in the society and simultaneously wants to have a greener habitat. We crave to earn more money but still wish to have a hygienic environment. Basically, what we desire is nothing but sustainability. As such, sustainability can be defined as “Improving the quality of human life while living within the carrying capacity of supporting eco-systems”. Crudely speaking, when all the three societal, environmental and economical factors are considered for development, we are directing to sustainable development. Efforts have been made to handle all the three factors effectively by science and technological research, efficient management skills and also by some law amendments i.e. introducing some new rules and regulations along with relaxing others. None of these have completely succeeded in giving hopes of a sustainable tomorrow. But advancements in the field of ‘nanotechnology’ have given all of us the hope of a better tomorrow. Nanotechnology is continuously being portrayed as a force that will help to materialize ultimate solutions to today’s economical and technological problems. To put into words the power of nanotechnology the following citation is the best. ‘Never before has any civilization had the unique opportunity to enhance human performance on the scale that we will face in the future. The convergence of nanotechnology, biotechnology, information technology, and cognitive science (NBIC) is creating a set of powerful tools that have the potential to significantly enhance human performance as well as transform society, science, economics, and human evolution.’[1]

NANOTECHNOLOGY- A BIRD’S EYE VIEW 5

The naive and direct answer to the frequently posed question “what exactly is Nanotechnology?” is to say that it is a technology concerning processes which are relevant to physics, chemistry and biology taking place at a length scale of one divided by 100 million of a metre. Maybe a little bit more enlightening although equally naive is to say that nanotechnology is the art of producing little devices and machines, somewhat at the molecular scale [2]. However the scientific definition which I admit may be slightly involved for a nonspecialized person is to say that nanotechnology is a technology applied in the grey area between classical mechanics and quantum mechanics. Classical mechanics is the mechanics governing the motion of all the objects we can see with our naked eye. This is a mechanics which obeys deterministic laws and which we can control to a very far extent. For example, falling of an apple; if we know the height from which the apple fell, we can find the time after which it will reach the ground and also the speed at that very time. By contrast, quantum mechanics which is the mechanics controlling the motion of things like the electron, the proton, the neutron and the like is completely probabilistic [I]. We know nothing about the motion of the electron except that there is a probability that the electron may be here or there. Even crazier than this, if we know the exact location of an electron, it is impossible to know its speed, and if we know the exact speed of the electron it is impossible to know its exact location. This is well stated as the ‘Heisenberg uncertainty principle’. The question then which poses itself is ‘when does a classical object like an apple or so changes its nature to a quantum object like an electron?’ Somewhere between these two scales these changes happen, but this does not happen suddenly. There is a grey area between these two scales which is neither classical nor quantum. Theoretical physicists call it the mesoscopic system [3]. This is what is called by nonphysicists the nanoworld. A nanosystem is therefore something which is sufficiently small that we could not see with our naked eye and not 6

even with an ordinary microscope [3]. However it is sufficiently larger than an electron so that we can control it in principle if we have a very fine tool to manipulate the system. Approaching nanotechnology from another point of view, namely that of industrial production, we can say that the majority of our industrial products are so far bulk industry or bulk production. To produce a wooden chair, we take a large trunk of a tree and cut it down to smaller sizes and fit these pieces together until we produce a chair. However nature operates in a very different way. To produce the trunk of a tree, nature grows a tree. It starts with a very small seed. This seed has all the information needed to grow a tree. In nanotechnology, we are trying partially to imitate nature and to build things starting with atoms. So we have moved now from the traditional bulk industry which is wasteful and accompanied by a great deal of pollution to the atomic scale industry which we call nanotechnology [II]. Nanotechnology has immense potential. In fact, nanotechnology discoveries are currently causing a domino effect of innovation across nearly every science and engineering field. As more and more technologists learn the fundamentals of nanotechnology, and more unusual nanoscale properties are understood, more powerful uses are being imagined. Perhaps the most globally exciting nano application is in the area of energy. Humanity’s future prosperity and energy availability, as well as the quality of the global environment, is the most important area that will be affected by nano applications.

1. AN INSIGHT INTO THE GLOBAL PROBLEMS

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Prior to the deep investigation of the technological road of ‘nano’ to the much desired sustainable environment, I would like to first state the problems which humanity faces today, which have to be sought out at any cost to reach to the pleasing future.

TABLE-1*

Ranking 1 2 3 4 5 6 7 8 9 10

Problem Energy Clean Water Food Environment Population Disease War/Terrorism Poverty Education Land

(*Source: Williams, 2006)

Table 1 shows the top ten problems in front of humanity today. As we can see energy tops the list. To justify energy crisis as the biggest problem, I would just ask this question “What would happen if quantities of inexpensive, environmentally friendly, and widely available energy were in abundant supply?” As to everyone’s agreement the answer is that it would solve a lot of society’s material problems. Solving the problem of energy, deals with the problems of war, poverty and land issues to an extent. Another big problem is the availability of clean water. There’s a lot of water on this planet (over 70 percent of the Earth’s surface, in fact), but it’s salty and not always accessible. Solving this problem and energy crisis solves the problem of food as there’s a lot of arable land (land fit for cultivation) in the world, but we don’t have water to irrigate crops and energy to provide 8

clean water everywhere. Simultaneously, solving the above problems can take care of the population explosion and certainly can fulfil needs of all the people. Another important hurdle in our path is pollution and other environmental problems. Noticeably, a lot of our environmental problems result from the kind of energy we use, now mostly fossil fuels, like oil, natural gas, and coal, but also wood and animal waste for heating or cooking. These fuels produce a lot of CO2, soot, and other atmospheric contaminants that pollute the air and are a major cause of global warming [III]. Thus, to get the pleasure of a sustainable environment, we have to overcome the hurdles of energy crisis and environmental problems. Since, nanomaterials have several intriguing properties that may be exploited for technological applications; hopes of many are tied with them.

2. NANOTECHNOLOGY: A KEY TO ENERGY CRISIS 2.1 Advancements in Fossil Fuels 9

Today about 80% of global energy use is ingrained in chemical energy stored in fossil fuel reserves. With the increase in global requirements of fossil fuels and our failure in keeping in pace with the energy needs of the world; has made it necessary to maximize the profits from the available resources. Hence, improvement in the performance of both gas and diesel engines is needed. To enable the production of more super ultra-low emission vehicles, higher quality fuels are needed. This requires advances in catalyst technology to: • Improve catalyst reactivity, selectivity, and yield. • Optimize and reduce active species loading levels. • Improve catalyst durability and stability under exposure to the operating environment. • Reduce reliance on precious-metal-based and corrosive catalysts. • Produce lower cost, less energy-intensive and more environmentally friendly catalysts. ( *source: www.nano.gov) In essence, catalytic processes are nanoscale because reactions take place on the surface. An interesting property of some particular nanomaterials is their unusually high chemical reactivity. This has led to the widespread use of metal and metal oxide nanoparticles as commercial catalysts in the chemical and petrochemical industries. Metal nanoparticles are also currently employed within catalytic converters in automobiles as three-way catalysts. Three-way catalysts catalyze the following three reactions: • Oxidation of unburned hydrocarbons • Oxidation of CO • Reduction of nitrogen oxides Envirox, Cerium oxide containing nanoparticle is studied a lot and it has been recognised for some time that cerium oxide could give a cleaner burning fuel. It increases fuel efficiency only by 5% or so. Currently research is going on to search for other nanoparticles that can be used as catalysts. But the main problem faced is that until 10

nanoparticles could be manufactured, the catalyst simply settles down to the bottom of the gas tank. Nanoparticles are small enough to stay in solution.

2.2 Advancements in Li Batteries Ultra-capacitors and various batteries are getting benefitted from moving to the nanoscale. Breakthroughs in the performance of thermoelectrics have already occurred as a result of advancements at the nanoscale. Lithium ion batteries have now become ubiquitous due to their high voltage (3.6V), high energy density and long life cycle (>1000 cycles) relative to other battery types, such as Ni-Cd, Ag-Zn, Ni-hydride and lead acid batteries. Applications are widespread in portable consumer electronics, including notebook computers, cellular telephones, MP3 players and camcorders. Like other batteries, Li ion batteries are composed of a cathode and anode separated by an electrolyte. Significant research efforts have been undertaken to find new materials for cathode, anode and electrolyte to improve the life cycle and increase the energy density of the Li ion battery. Many of these efforts have involved the development of nanomaterials, in large part due to their higher internal surface area [4]. Nanomaterials that have been proposed as an anode material in Li ion batteries are mainly metal nanoparticles, carbon nanotubes and nano-composites that combine these two materials. High Li capacity has been obtained for numerous elements, including Ag, Sn, Al, Si, Sb, Bi and Pb, as an alternative to graphite [5]. Some of the widely studied lithium storage materials are Sn nanoparticles and Si nanoparticles, both of which have high storage capacity arising from the stoichiometry Li22Sn5 and Li22Si5 respectively. 2.3 Applications in Renewable Energy Utilization Due to excessive increase in the energy demands and the lack of potential of current energy sources to fulfil it, has brought a pressing 11

need for alternative energy sources that are both renewable and environmentally benign. Among a limited number of options, solar energy represents an important renewable energy resource that can be directly converted into electricity using photovoltaic (PV) devices. Solar radiation is also a renewable energy for splitting water to produce hydrogen, which is regarded as the cleanest transportation fuel. The oxidation of hydrogen through the use of fuel cells generates electricity, where water constitutes the only emission. Fuel cells represent an effective and practical approach to convert hydrogen produced from solar and other sources into electricity. While solar energy is virtually inexhaustible, it is limited in the amount of the energy that can be converted and stored for practical utilization at a given time. In order for solar energy to be the major contributor to the generation of electricity and clean transportation fuel (hydrogen), the efficiencies of PV and solar water-splitting devices need to be improved. Likewise, high performance fuel cells as well as high capacity hydrogen-storage materials have to be realized, in order for hydrogen to become the primary fuel for transportation systems. Technological breakthroughs and revolutionary developments are needed in order to achieve effective conversion, storage, and utilization of renewable energy resources. Nanotechnology, particularly the developments of nanoscale materials and structures, including the methods to create them, offers a new paradigm for realizing the goals of renewable energy research.

2.3.1 ELECTRICITY GENERATION WITH SOLAR ENERGY Harvesting energy from sunlight using PV technology has been considered an essential pathway to energy sustainability. Typically, a photo-voltage is generated when light-induced excess charge carriers in a semiconductor are separated in space, so the process is determined by the fundamental properties of light absorption and carrier transport of the semiconductor material. A PV device, or solar 12

cell, converts absorbed photons directly into electrical charges that are used to energize an external circuit. Large scale manufacturing of these devices would enable a significant fraction of future energy needs to be supplied by solar energy. Current production of PV devices is dominated by a p-n junction type, single crystalline and polycrystalline silicon modules termed as ‘first-generation’ technology and occupy 90% of the current market. While the ‘second generation’ technologies based on CdS, CdTe and other types of multiple semiconductor layers are still under development, nanostructured ‘third generation’ PV technologies have gained much attention due to their potential of achieving competitive cost/ efficiency ratios [6]. One class of nano-structured PV devices that may have significant benefits at a low cost alternative to conventional p-n junction type modules is the dye- sensitized solar cells (DSSC), also known as Gratzel cell. Central to DSSC is a nano-structured network of a wide band gap semiconductor, usually TiO2 (titanium dioxide), which is covered with a monolayer of organic dye molecules. Deposited on a transparent conductive oxide layer and in contact with a redox electrolyte or an organic hole-conductor, the TiO2, nanomaterial offers a large surface area for the adsorption of lightharvesting molecules. While pure TiO2, absorbs light only in the UV region, when modified with dye molecules it can absorb light in the visible wavelengths. In addition, synthesis and modification of various types of TiO2 nanomaterials have attracted significant attention recently due to the improvement of material processing techniques. For instance, ordered mesoporous TiO2 nanocrystalline film improves the solar conversion efficiency by about 50% compared to that of traditional films of same thickness made from randomly oriented nanocrystals [7]. Other than nanocrystals, TiO2 nanotubebased DSSCs are found to display higher efficiency, possibly due to increase of electron density in nanotube electrodes.

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Various elements have been used as dopants to modify the physical properties of TiO2 nanostructures and extend optical absorption into the visible region. For example, it was found that TiO2 nanocrystals can take up to 8% of nitrogen atoms into the lattice, compared to 2% in thin films and micro-scale TiO2 powders [8]. Such doped nanomaterials absorb well into the visible spectrum of light as compared to the pure TiO2 material that only absorbs in the UV region. Additionally, the photo-current due to visible light at moderate bias is increased to about 200 times or so compared to the case when pure TiO2 electrodes are used [9]. Different from DSSCs, semiconductor quantum dots (QDs) based solar cells represent another category of nano-structured PV devices. Significant progress is being made in forming 3-D arrays of QDs. Hybrid solar cells consisting of QDs and organic semiconductors polymers have also been reported, for example, with CdSe QDs embedded in a hole-conducting polymer (MEH-PPV) [10].Although the conversion efficiency of hybrid QD solar cells is relatively low, improvements are being made over time to time.

2.3.2 HYDROGEN PRODUCTION WITH SOLAR ENERGY Besides direct generation of electricity using PV devices, another path of utilizing solar energy, especially for energy supply to the transportation systems, is the production of hydrogen by splitting water. Solar-driven water splitting through the use of photoelectrochemical (PEC) cells has many attractive features over other hydrogen production approaches; both the energy source and the reactive medium (water) are renewable and readily available, and the resultant fuel product (hydrogen) as well as the emissions (water) from the utilization of the fuel is environmentally benign. TiO2 nanomaterials represent the most important semiconductor catalysts for splitting water and producing hydrogen. When TiO2 14

absorbs light with energy larger than its band gap, electrons and holes are generated in the conduction and valence bands, respectively. The photo-generated electrons and holes induce redox reactions- water molecules are reduced by the electrons to form H2 and oxidized by the holes to form O2, leading to overall water splitting. The width of the band gap and the potentials of the conduction and valence bands are critical to the efficiency of solar water splitting. The bottom level of the conduction band has to be more negative than the reduction potential of H+/H2 (0 V vs. normal hydrogen electrode), while the top level of the valence band has to be more positive than the oxidation potential of O2/H2O (1.23V). The photo-catalytic characteristics of TiO2 are strongly affected by the surface properties, such as surface states, surface chemical groups, surface area, and active reaction sites, as well as charge separation mobility, and lifetime of photo-generated carriers [11]. Well-dispersed metal nanoparticles can act as miniphotocathode trapping electrons, while addition of carbonate salts to Pt-loaded TiO2 suspensions yields efficient water splitting. A bare nTiO2 nanocrystalline film electrode is actually unstable during watersplitting reactions under illumination, but its stability could be significantly improved when covered with Mn2O3. The overvoltage for the evolution of oxygen is of the order 0.6eV for n-TiO2 electrodes loaded with RuO2. The morphology of TiO2 nanomaterials affects their photo-catalytic activities. Highly ordered TiO2 nanotube arrays are actually found out to be able to efficiently decompose water under UV irradiation [12].The nanotube wall thickness is actually considered to be a key factor influencing the magnitude of the photoanodic response and the overall efficiency of the water-splitting reaction. In order to improve the efficiency of solar water splitting by semiconductor nanostructures, it is also necessary to shift the wavelength of light absorption away from UV (2% of sunlight) to the visible range of the solar spectrum. A variety of dopants have 15

been employed to modify the optical properties of TiO2 nanomaterial for solar hydrogen production. Water splitting is induced with visible light in colloidal solutions of Cr-doped TiO2 nanoparticles deposited with ultrafine Pt or RuO2. Br and Cl co-doped nanocrystalline TiO2 with the absorption edge shift to a lower energy region displays higher efficiency for water splitting than pure TiO2. Composite nanostructured semiconductors have also been developed for visible-light water-splitting. A self-driven system for a water-splitting reaction under illumination was achieved with the combination of single crystal p –SiC and nanocrystalline n-TiO2 photo-electrodes [13]. A nanocomposite polycrystalline Si/ doped TiO2 solar water-splitting structure was proposed for high efficiency and low cost by combining the advantages of Si and doped TiO2. An n-Si electrode with surface alkylation and metal nanoparticle coating offers an efficient and stable PV characteristic, and TiO2 doped with other elements, such as nitrogen and sulphur, could induce water photo-oxidation (oxygen photo evolution) by visible light illumination. A high solar-to-chemical conversion efficiency of more than 10% was predicted for such a system [14].

2.3.3 SOLID-STATE HYDROGEN STORAGE Among the various alternative energy strategies is the building of an energy infrastructure that uses hydrogen as the primary energy carrier. The energy produced by the Sun can be converted, stored, and distributed in the form of hydrogen. A major challenge to realizing hydrogen economy is the development of high capacity and safe hydrogen-storage materials. In general, hydrogen may be stored in the form of pressurized gas, liquefied hydrogen, or can be chemically or physically bonded to a suitable solid-state material. Of the three hydrogen-storage approaches, solid-state storage has the highest volumetric density of hydrogen. While gaseous and liquid state storage requires extremely high pressure or low temperature, solid 16

state hydrogen-storage materials could store hydrogen at near-ambient temperatures and pressures. Particularly for transportation applications, storing pressurized or liquefied hydrogen requires a large footprint container that is not only a safety concern but also easily takes up a significant fraction of space in the vehicle. Therefore, solid-state storage is potentially the most convenient and the safest method for storing and distributing hydrogen for transportation systems. The use of nanostructured solid-state materials serves multiple functions; they improve the kinetics by increasing the diffusivity, reducing the reaction distance, and increasing the reaction surface area. The fundamental mechanisms for solid-state hydrogen storage in nanomaterials include chemisorption and physisorption [11]. Chemisorption starts with dissociation of hydrogen molecules and chemical bonding of the hydrogen atoms by integration in the lattice of a solid material, e.g. metal hydrides. This process inherently involves large enthalpy changes and normally requires high operation temperature and a catalyst for fast hydrogen uptake and release. In contrast, physisorption mainly involves the adsorption of hydrogen molecules on the surface of nanomaterials through weak intermolecular forces- the van der Waals interaction. As a consequence, the force is less material specific compared to the case of chemisorption. Since the Van der Waals forces between the hydrogen molecule and the surface is in the lower kJ mol-1 range, it is necessary to apply low temperatures to achieve a sufficient amount of adsorbed hydrogen. Nevertheless, release of physiosorbed hydrogen can be fast because of the weak molecular forces. The ideal material for hydrogen storage would achieve a compromise between having the hydrogen too weakly bonded to the storage material, resulting in a low storage capacity at room temperature and too strong a bonding, thus requiring high temperatures to release the hydrogen. Solid-state nanomaterials currently being investigated for hydrogen storage include carbon 17

nanomaterials, metal-organic frameworks, and nanocrystalline metal and complex hydrides, among others. Physisorption of hydrogen molecules in nanostructured materials has been explored extensively; examples include various forms of carbon, clathrates, and metal-organic frameworks. Significant storage capacity was initially reported for hydrogen storage using carbon nanotubes [15]. Later investigations suggested that desorption of hydrogen appear to originate from Ti alloy particles introduced during the ultrasonic treatment rather than from the CNTs. For hydrogen chemisorption, the most studied materials are metal hydrides and related complex hydrides. Small hydrogen atoms can readily enter the interstitials of many metals and alloys to form hydrides. Since a high weight fraction of hydrogen in the solid-state hydrogen-storage materials are required for practical transportation system applications, research to enhance the hydrogen capacity in metal hydrides has been focussed on those based on light weight elements such as magnesium. A complete class of nanostructured all-inorganic materials, the nanoporous metal inorganic (oxide) networks, for solid-state hydrogen storage has been developed. The nanoporous metalinorganic materials have a linked 3-D network of M: SiO2 and similar nanostructures that include a monolayer or nanoparticles of metal/alloys (denoted M), implemented into a nanoporous oxide network. Current research is focussed on the particular nanoparticles of M which provides maximum storage capacity for solid-state hydrogen.

2.3.4 UTILIZATION OF HYDROGEN WITH FUEL CELLS One effective way to use chemical energy stored in hydrogen is to directly convert it into electricity through the use of a fuel cell. Fuel cells harness the chemical energy of hydrogen to generate electricity 18

without combustion and pollution. The development of fuel cells as a clean, environmentally friendly energy source is widely anticipated. The use of hydrogen as a fuel is particularly attractive, since the main product produced would be water, with effectively zero emissions. Even the economical use of other hydrocarbon fuels beyond petrol, diesel and CNG may have global benefits, as this may reduce the demands for hydrocarbon fuels. Fuel cells operate by converting chemical potential energy directly into a current or voltage by coupling an electrochemical oxidation reaction with an electrochemical reduction reaction. There are numerous number of fuel-cells formed till date. Some of them are: proton exchange membrane, direct methanol, molten carbonate, phosphoric acid and solid oxide fuel cells. High-temperature fuel cells such as molten carbonate, solid oxide and phosphoric acid fuel cells have recently been employed for several applications, particularly those where waste heat can be employed to reach and maintain the operating temperature. For e.g. waste heat is widely generated throughout industrial chemical plants, sometimes making fuel cells an economical energy source. At the operating temperature of these fuel cells, the anode and cathode reactions are typically fairly facile, making the use of electrocatalysts, which are often in the form of nanoparticles, unnecessary. In addition, nanomaterials may subject to grain growth, sintering, dissolution and other unwanted chemical reactions at high temperature. On the other hand, nanomaterials are much more compatible with low temperature fuel cells, which are needed for many transportation and consumer applications where intermittent operation is typical and power requirements are relatively modest. The most common low temperature fuel cells are the polymer electrolyte membrane fuel cell (PEMFC) and the direct methanol fuel cell (DMFC), where the following reactions occur: Anode (PEMFC):

H2  2H+ + 2e19

Anode (DMFC):

CH3OH + H2O  CO2 + 6H+ + 6e-

Cathode (PEMFC and DMFC): O2 + 4H+ + 4e-  2H2O When considering the use of nanomaterials in fuel cells, many observers would first consider the use of nanoparticle catalysts in both anode and cathode. Hydrogen reduction takes place at the anode of a PEMFC. This process is most facile due to its simple reaction mechanism and Pt nanoparticles are widely used as electrocatalysts for this reaction. The main problem is that Pt catalysts can be easily poisoned by trace CO in the H2 fuel, and so far the best performance has been attained by PtRu bimetallic nanoparticle catalysts, preferably with a 1:1 ratio of Pt: Ru, that facilitate CO desorption. Ternary and quaternary catalysts have also been widely investigated in laboratories [IV]. The methanol reduction at anode of DMFC and O2 reduction at cathode of both DMFC and PEMFC, involve more complex mechanisms and multi-step electron transfer, making electrocatalysts more difficult. O2 Reduction is most facile on Pt nanoparticle catalysts, and the use of Pt alloys with transition metals such as Co, Cr, Ti and Zr has been thoroughly investigated. Similarly, methanol oxidation has been widely studied on Pt nanoparticle catalysts alloyed with a wide variety of different transition metals, including Ru, Os and Sn. Given that the expensive Pt catalyst contributes significantly to the overall fuel cell cost, non-Pt catalyst materials are also under intensive investigation for both PMFCs and DMFCs [16]. However, Pt and its alloys in nanoparticle form remain the best catalysts for the reactions in low-temperature fuel cells. [IV] In addition to this, carbon nanotubes and carbon nanofibres have been widely investigated for possible application into the catalyst supports for the operating PEMFCs and DMFCs [17]. The main improvement that is envisioned is increased utilization for the Pt catalyst supported on carbon nanotubes. Currently, for long term usage and better commercialization of both PEMFCs and DMFCs,

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catalyst agglomeration, catalyst dissolution and carbon corrosion are the primary barriers from which the researchers want to get rid of.

3. NANOTECHNOLOGY: A STEP TOWARDS BETTER ENVIRONMENT Environment is one of the pillars of sustainability. We all have to take care of it. It is our responsibility to keep it clean and healthy. Sometimes it seems that the ills of the environment are too big to handle. Some people give up in the face of these looming giant problems. However, nanotechnologists believe that this difficult task can be accomplished with the help of nanotechnology. The design and manipulation of atomic and molecular scale materials offers great possibilities for environmental cleanup. Unique properties of new nanoscale materials can produce advances in cleaner energy production, energy efficiency, water treatment, and environmental remediation. Researchers are trying to determine how different kinds of environmental contaminants bind to or could be transported with nanomaterials through groundwater systems or how cell interactions/toxicity might occur. 3.1 Water Purification As the population of the world is increasing at a rapid pace we require greater volumes of potable water for both drinking and agriculture purpose. Thus, the needs for better purification methods have become particularly important. The use of nanomaterials may offer big improvements to existing water purification techniques and materials and may well bring about new ones. Furthermore, nanomaterials have the potential supplying water treatment and purification in remote areas where electricity is not available. Engineered nanomaterials are a new class of materials, relatively unknown to most environmental engineers and water treatment workers. However, this is changing. With more and more research on 21

safe, improved, low-cost, and efficient ways to treat water, general water treatment methods will begin to change, too. 3.1.1 CERAMIC MEMBRANES Membranes and filters of all sizes are used to separate various compounds and chemicals. Depending on their properties, they have greater or lesser success. In ultrafiltration, pressure pushes against one side of an ultrafiltration membrane, forcing water and low molecular weight compounds through its pores. Larger molecules and suspended solids move across the membrane, getting more concentrated as they are blocked because of their larger size. Centre for Biological and Environmental Nanotechnology (CBEN) researchers at Rice University have developed a reactive membrane from iron oxide ceramic membranes (ferroxanes). Due to iron’s unique chemistry, these reactive membranes provide a platform for removing contaminants and organic waste from water and cleaning them up. Ferroxane materials have even been found to decompose the contaminant benzoic acid [III]. When using aluminium oxide ceramic membranes (alumoxanes) as the ceramic nanomembrane material, membrane thickness, pore size scattering, permeability, and surface chemistry can be altered by changing the first layering of alumoxane particles. Membrane thermal properties can be changed to create a range of pore sizes. Nanostructured ceramic membranes treat and purify water both actively and passively. Ceramic membranes could be placed inline within conventional treatment systems for final cleaning of polluted water and air. 3.1.2 NANO CATALYSTS Although nanofiltration membranes are important in water purification, nanoparticles either in solution or attached to membranes can help ensure that pollutants chemically degrade and don’t just 22

travel somewhere else. Nano-catalysts are currently being studied for their environmental applications. Catalytic treatments can lower polluted water treatment costs by making it possible for purification methods to be specifically designed to treat chemicals at a particular site. Dr. Daniel R. Strongin, chemistry professor at Temple University in Philadelphia, has used protein structures to design and assemble metal oxide nanoparticles that could be used in environmental remediation. By using nanoparticles made from biological components as nanocatalysts, Strongin and others have been looking at how nanoparticles may be used in environmental remediation (cleaning up polluted areas). Reactions that would make polluting metals clump or separate out of solution so they aren’t transported downstream or soak into groundwater are also studied [III].

3.1.3 IRON REMEDIATION Wei-Xian Zhang of Pennsylvania’s Lehigh University has shown the potential of iron nanoscale powder that is able to clean up soil and groundwater previously contaminated by industrial pollutants. Iron, one of the most abundant metals on Earth, thus might prove to be the cleaning agent of various contaminated industrial sites, underground storage tank leakages, landfills, and abandoned mines. The answer seems to come from the fact that iron oxidizes easily and forms rust. However, when metallic iron oxidizes around contaminants such as trichloroethylene, carbon tetrachloride, dioxins, or PCBs, these organic molecules are broken down into simple, far less toxic carbon compounds. Similarly, with toxic heavy metals such as lead, nickel, mercury, or even uranium, oxidizing iron reduces them to an insoluble form that is locked within the soil, rather than being mobile, so they could become part of the food chain and their impacts could be more widespread. Since iron has no known toxic 23

effect and is plentiful in rocks, soil, water, and nearly everything on the planet, several companies now use a ground iron powder to clean up their industrial wastes before releasing them into the environment. This is great for new wastes, but wastes that have already soaked into the soil and water must be taken care of as well. Here we use the nanoscale iron particles which are 10 to 1000 times more reactive than commonly used iron powders. Smaller size also gives nano-iron a much larger surface area, allowing it to be mixed into slurry and pumped straight into the centre of a contaminated site, like a giant injection. Upon arrival, the particles flow along with the groundwater, decontaminating the environment as they go [IV]. Iron particles are not changed by soil acidity, temperature, or nutrient levels. Their size (1–100 nm in diameter and 10–1000 times smaller than most bacteria) allows them to move between soil particles. Laboratory and field tests have shown that nanoscale iron particles treatment drops contaminant levels around the injection well within a day or two and nearly eliminates them within a few weeks, bringing the treated area back into compliance with federal groundwater quality standards [V]. Results have also indicated that the nanoscale iron stays active in the soil for six to eight weeks before the nanoscale particles become dispersed completely in the groundwater and become less concentrated than naturally occurring iron. This method is also a lot cheaper than digging up contaminated soil and treating it a little at a time, as has been done in the past at highly polluted sites.

4. BARRIERS TO ADVANCEMENTS

THE

NANOTECHNOLOGY

“Technology cuts both ways” is a phrase commonly associated to almost every technology. Nanotechnology is not an exception to this. Signs of nanotechnology’s continuing maturation abound. Most experts focus on the continuing surge in nanotechnology research and development (R&D). Perhaps most surprising is the fact that 24

nanotechnology commercialization is moving forward at a lightning speed. Thousands of tons of nanomaterials are already being produced each year. The nanomaterials now being manufactured, marketed and purchased are inevitably finding their way into the natural environment. Entry can occur accidentally or intentionally over the course of a nanomaterials lifecycle, during manufacturing, transportation, use, recycle, or disposal. The current wave of nanoproducts includes an inordinate number of sunscreens, cosmetics, and other personal care products, as the personal care industry is the leading sector in the manufacturing and marketing of nano-products. These products enter the environment via the household waste streams and other nanomaterials, such as those used in electronics, fuel cells, and tires, will be worn off or leak out over a period of use or after product disposal. Still other nanomaterials will reach the environment through landfills or other methods of disposal (e.g. residual sunscreens or cosmetics in containers). Finally, some nanomaterials may be introduced deliberately into the natural environment for environmental remediation purposes. For example, I have earlier indicated that iron nanoparticles could be used to clean up contaminated soil by neutralizing contaminants (e.g. DDT and dioxin). As many industries involved in nanotechnology expand, and increase in number and variety of nano-enhanced products available; both industrial and domestic nano-waste will also logically increase in quantity [VI]. 4.1 Nano-Hazards Humans and animals have been encountering naturally occurring nanomaterials for millions of years. Nature produces some nanoparticles, like salt nanocrystals found in ocean air or carbon nanoparticles emitted from fire. Thus, one could feel that there is no danger as such in the nanoscale. However, it is only recently that scientists have developed the techniques for synthesizing and characterizing many new materials with at least one dimension on the nanoscale. The concern is that nanomaterials now in development are 25

different than anything that exists in nature. The materials engineered or manufactured to the nanoscale can exhibit different fundamental physical, biological and chemical properties from bulk materials of the same substance. Just as the size and physics properties of engineered nanoparticles can give them exciting properties, those same new properties- tiny size, high surface area/volume ratio; high reactivity- can also create unique and unpredictable human health and environmental risks. Swiss insurance giant Swiss Re noted that: ‘Never have before the risk and opportunities of new technology been as closely linked as they are in nanotechnology. It is precisely those characteristic which make nanoparticles so valuable that give rise to concern regarding hazards to human beings and environment alike.’[VI] These new properties create numerous human health risks. For starters, due to their size, nanoparticles have unprecedented mobility: they are more easily taken up by the human body and can cross biological membranes, cells, tissues and organs more efficiently than larger particles. Once in the blood stream, nanomaterials can circulate throughout the body and can be taken up by the organs and tissues, including the brain, kidney, liver, heart, bone marrow, spleen and nervous system. When inhaled, they reach all regions of the respiratory tract, and can move out of it via different pathways and mechanisms. When in contact with the skin, there is an evidence of penetration of the dermis and subsequent translocation via the lymph nodes .When ingested, systematic uptake can occur [V]. Second, the change in the physicochemical and structural properties of engineered nanoparticles can also be responsible for a number of material interactions that can lead to toxicological effects. Once inside the cells, they can interfere with the cell signalling, cause structural damage and cause harmful damage to DNA. There is a dependant relationship between size and surface area and nanoparticle toxicity; as particles are engineered smaller on the nanoscale, they are 26

more likely to be toxic [V]. Many relatively inert and stable chemicals (e.g. carbon) pose toxic risk in their nanoscale form.

4.2 Nano-Regulation Due to over publicity and hype of the term ‘nano’, everyone is having an eye on the advancements in nanotechnology. Nanotechnology though being touted as the future solution for almost all our technological requirements, has to be assessed carefully and with regard to safety, health and environmental issues so that we do not repeat the mistakes made in the past with regards to asbestos and CFCs. [18] However, there is no universal assessment of nanotechnology’s risks or of its hazards and opportunities. Nano-products, materials, applications and devices are governed today within the existing framework of statutes, laws, regulations and policies. The main question is whether current regulatory controls are adequate to meet the many concerns posed by the ability of nanotechnology to create products whose structures, devices and systems have novel properties and structures because of their size. This question still remains unanswered [VI]. Yet, the most pressing issue may be not in the creation of new, but in the enforcement of old, regulations on the industries that create and process these new materials. Advocating for regulation of nanotechnological innovation with yet uncertain and inconclusive demonstrated risks, without clearly understanding how the regulatory system are designed to work, dilutes the very purpose for which they were intended while simultaneously impairing the progress of transformative, disruptive, emerging, converging or enabling technologies [VI]. How can one regulate something that cannot be seen, and that is not even here yet? Even more, why impose such an unnecessary restraint on its advance and choke the very opportunities 27

nanotechnology may present? Ultimately, will promulgating regulation diminish that alleged risks, produce different risks, deprive the end users of expected benefits, or simply silence the political reaction of the nano-twisting activists? To reduce uncertainties and ensure a sustainable introduction of nanotechnology, efforts must be made to establish a common discussion platform that facilitates an open dialogue on risk analysis, risk management, and acceptable options for risk transfer.

5. CONCLUSION There is no doubt that nanotechnology-enabled environmental remediation and renewable energy technologies are starting to scale up dramatically. As they become mature and cost effective in the decades to come, we will have a greener environment and then eventually renewable energy could replace the traditional, environmentally unfriendly, fossil fuels; thus providing us a sustainable environment to live in. However, these developments are only at the beginning stage and the insecurity that is connected with the production of these new materials currently outweigh their possible advantages. The optimal commercial use of nanotechnology is crucially dependent on crossdisciplinary dialogue, which should address the full scope of the two sides of the risk: potential hazards and inherent opportunities. As unexpected losses can destroy economic investments, far-sighted thinking is necessary. I personally, think that the principal prerequisite for successful risk assessment in a technology as multifaceted as nanotechnology is finding a harmony among the industry representatives, policy makers, and research institutes concerned. It is one that must extend across national borders, regulatory discrepancies, and different perceptions of risks and benefits. 28

Summing up, Nanotechnology is a field where neither the probability nor the extent of potential benefits and losses can be calculated precisely. To analyse these benefits and to measure those against their possible losses along with providing a crystal clear picture before everyone still seems to be a huge challenge in front of us.

REFERENCES: PAPERS: Canton J. Designing the future: NBIC technologies and human performance enhancement. In Roco M.C and Montemagno C.D. The co-evolution of human potential and converging technologies New York: Annals of the New York Academy of Sciences; 2004.pp. 186-198. 2. Drexler KE. Engines of creation. Fourth Estate, London, 1990. 3. Ando.T et al.1998. Mesoscopic physics and electronics Heidelberg: Springer 4. Liu H.K, Wang G.X, Guo.Z, Wang.J, Konstantinov.K.2006 .J.Nanosci. Nanotechnol., 6, 1-15 5. Besenhard J.O, Yang.J, Winter.M, J. Power Sources 1997, 68, 87-90. 6. Shaheen SE, Ginley DS, Jabbour GE. 2005. Organic based photovoltaics: toward low-cost power generation. MRS Bulletin 30:10. 7. Zukalova M, Liska P, Gratzel M. 2005. Organized mesoporous TiO2 films exhibiting greatly enhanced performance in DSSC. Nano Letters 5:1789. 8. Chen et al. 2005b. Formation of oxynitride as the photocatalytic enhancing site in N-doped titania nanocatalysts: comparison to a commercial nanopowder. Advanced Functional Material. 15:41. 1.

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Lindgren et al. 2003. Photoelectrochemical and optical properties of nitrogen doped TiO2 films prepared by reactive DC magnetron sputtering. Journal of Physical Chemistry 107:5709. 10.Greenham et al. 1996. Charge separation and transport in conjugated polymer/semiconductor-nanocrystal composites studied by photoluminescence quenching and photoconductivity. Physical Review 54:17628. 11.Mao S.S, Chen X .2007. Selected nanotechnologies for renewable energy applications. Int. J. Energy Res. 31:619. 12.Mor et al. 2005. Enhanced photocleavage of water using titania nanotube arrays. Nano Letters 5:191. 13.Akikusa J, Khan SUM. 2002. Photoelectrolysis of water to hydrogen in p-SiC/Pt and p-SiC/n-TiO2. Int. J. Hydrogen Energy 27:863. 14.Takabayeshi et al. 2004. A nano-modified Si/TiO2 composite electrode for efficient solar water splitting. J. Photochem. Photobiol. 166:107. 15.Dillon et al. 1997. Storage of hydrogen in SWNTs. Nature 386:377. 16.Wang .B 2005. J.Power Sources.152, 1-15. 17.Lee. K, J. Zhang .J, Wang .H, Wilkinson D.P .2006. J. Appl. Electrochem 36:507. 18.Hansen H.F, Maynard .A, Baun.A, Tickner.J.A. 2008. Nature Nanotechnology 3:444. 9.

BOOKS: Ball P. (1994) Designing the molecular world, New Jersey: Princeton. II. Foster LE. (2006) Nanotechnology, New York: Prentice Hall. III. Williams L. (2007). Nanotechnology Demystified, Tata McGraw-Hill. I.

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HF (2008). Nanotechnology: Environmental aspects Vol.2, John Wiley and sons. V. Kumar C. (2006). Nanomaterials-Toxicity, Health and Environmental Issues, John Wiley and sons. VI.Cameron NMS, Mitchell M.E., (2007) Nanoscale: Issues and perspectives for the Nano Century, John Wiley and sons.

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Wikipedia: www.wikipedia.org National Nanotechnology Initiative: http://www.nano.gov Nano Science and Technology Institute: http://www.nsti.org EnvironmentalChemistry.com site on periodic table: http://environmentalchemistry.com/yogi/periodic/Pb.html National Institute of Standards and Technology: http://www.nist.gov Environmental Protection Agency Nanotechnology page: http://es.epa.gov/ncer/nano National Centre for Environmental Research: http://es.epa.gov/ncer/publications/nano/index.html Department of Energy, “Energy Efficiency and Renewable Energy”: http://www.eere.energy.gov Richard E. Smalley Institute for Nanoscale Science and Technology at Rice University: http://www.cnst.rice.edu Small Times news: http://www.smalltimes.com

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