Check out this post to explore about fuel cells.. the future...
A fuel cell is an electrochemical cell that converts chemical energy (energy stored in bonds) into electrical energy by electrochemical reaction. These cells require a continuous input of fuel and oxygen as an oxidizing agent in order to sustain the reactions that generate the electricity.
Hydrogen Fuel Cell:
One of the most successful fuel cells uses the reaction of hydrogen as a fuel with oxygen to generate electricity. It consists of an electrolytic solution such as 25% KOH and two inert porous electrodes. Hydrogen and oxygen gases are bubbled through the anode and cathode compartment respectively where the following reaction takes place.
At Anode: hydrogen molecules are oxidized with the liberation of electrons, which then combine with hydroxide ions to form water.
At Catode: The electrons are absorbed by oxygen to form hydroxide ions.
The standard emf of the cell is given by
1.23 V. Therefore 80% of chemical energy is converted into electrical energy.
This post discuss the pH determination by colorimetric method. Two videos are attached for easy understanding.
Determination of pH:
pH determination measures the acidity or alkalinity of a solution using pH paper, indicators, or a pH meter to find hydrogen ion concentration.
Methods:
Electrometric Method (pH Meter): This is the most accurate method, utilizing a glass electrode to detect electromotive force (EMF) generated by hydrogen ions, often utilizing two- or three-point calibration with buffer solutions.
Colorimetric Method (pH Paper/Indicators): A less precise method involving pH paper or universal indicators that change color, which is then compared against a standard chart.
Working Principle:
The pH is measured by noting the various colour changes in this method. A universal indicator (e.g., B.D.H. universal indicator) and various buffer solutions in the pH range 3 to 11 are prepared. A drop of universal indicator is added to each buffer solution and the colour change is noted. Then, few drops of universal indicator are added to the solution of unknown pH. The colour of this solution is compared with the suitable buffer solution and the pH may be determined. Comparators are employed for the matching of colour tints. Hellige comparator is generally used in water analysis.
Here is the information about various polymer processing techniques in brief. The link for the study material is also provided.
Polymer Processing
We know that polymeric materials are used in many forms such as, tubes, rods, films,
sheets, foams, coatings, adhesives, moulded and fabricated articles etc. A majority of articles
are either moulded or fabricated. Some others are made by casting liquid pre-polymers into a
moulded and allow them to cure or crass linking. As per application of the polymeric
materials, they are converted into required shape and size by applying different processes.
Thus, the polymer processing is a technique to convert polymer into a broad spectrum of
useful shapes and structures. In other words, it is an engineering especially used to convert
polymeric materials into useful end products.
Corrosion is one of the most common phenomena that we observe in our daily lives. You must have noticed that some objects made of iron are covered with an orange or reddish-brown coloured layer at some point in time. The formation of this layer is the result of a chemical process known as rusting, which is a form of corrosion.
Cossorion, in general, is a process through which refined metals are converted into more stable compounds such as metal oxides, metal sulfides, or metal hydroxides.
rusting of iron involves the formation of iron oxides via the action of atmospheric moisture and oxygen.
an electrochemical process since it usually involves redox reactions between the metal and certain atmospheric agents such as water, oxygen, sulphur dioxide, etc.
Examples
1. When copper metal is exposed to the environment, we observe copper turning bluish-green in colour
2. Silver reacts with sulphur and sulphur compounds in the air, giving silver sulphide (Ag2S), which is black in colour.
3. Corrosion of Iron (Rusting)
Rusting of iron refers to the formation of rust, a mixture of iron oxides, on the surface of iron objects or structures. This rust is formed from a redox reaction between oxygen and iron in an environment containing water.
When Iron is exposed to air, the oxygen atoms bond with iron atoms, resulting in the formation of iron oxides. This weakens the bonds between the iron atoms in the object/structure.
The reaction of the rusting of iron involves an increase in the oxidation state of iron, accompanied by a loss of electrons.
Oxygen is a very good oxidizing agent whereas iron is a reducing agent. Therefore, the iron atom readily gives up electrons when exposed to oxygen. The chemical reaction is given by:
Fe → Fe2+ + 2e–
The oxidation state of iron is further increased by the oxygen atom when water is present.
4Fe2+ + O2 → 4Fe3+ + 2O2-
Now, the following acid-base reactions occur between the iron cations and the water molecules to produce hydroxides of iron.
Fe2+ + 2H2O ⇌ Fe(OH)2 + 2H+
Fe3+ + 3H2O ⇌ Fe(OH)3 + 3H+
The resulting hydroxides of iron now undergo dehydration to yield the iron oxides that constitute rust.
How can Rusting be Prevented?
1. Galvanization is the process of applying a protective layer of zinc on a metal. This can be done by dipping the metal to be protected in hot, molten zinc or by the process of electroplating.
2. Cathodic Protection - This can be done by making the iron as a cathode by attaching a sacrificial anode to it. This anode must have an electrode potential that is more negative than that of iron.
Commonly used as sacrificial anodes are magnesium, zinc, and aluminium.
3. Coatings - Many types of coatings can be applied to the surface of the exposed metal in order to prevent corrosion. Common examples of coatings that prevent corrosion include paints, wax tapes, and varnish.
Clusters are collections of atoms lying between individual atoms/molecules and bulk materials. In some materials, certain collections of atoms are more preferred due to energy minimization and exhibiting stable structures and providing unique properties to the materials. These collections of atom providing stable structures to the materials are called as MAGIC NUMBER. For example, one of the combination of 55 atoms of gold provides stable structure and hence its magic number is 55
What is cluster in nanotechnology?
Clusters are small aggregates of atoms and molecules. Small means really tiny pieces of matter—they are composed of a few to thousands of units and have a diameter of nanometers. Nanoclusters have at least one dimension between 1 and 10 nm and a narrow size distribution. Nanoclusters are composed of up to 100 atoms, but bigger ones containing 1000 or more are called nanoparticles.
What are nanoclusters used for?
Nanoclusters have potential uses in chemical reactors, telecommunications, microelectronics, optical data storage, catalysts magnetic storage, spintronic devices, electroluminescent displays, sensors, biological markers, switches, transducers and many other fields. The florescence silver nanoclusters have been extensively used as biological markers for photodynamic therapy.
What are metal nanoclusters?
Metal nanoclusters (NCs) are composed of a small number of atoms, up to dozens. These nanoclusters can consist of a single element or multiple elements, usually smaller than 2 nm. Compared with their larger counterparts, this nanocluster exhibits attractive electronic, optical and chemical properties. These particles have quasi-continuous energy levels and display intense colors due to surface plasmon resonance. If their dimension is further reduced to the size approaching the Fermi wavelength of electrons, the band structure becomes discrete energy levels. The ultrasmall metal nanoparticles display molecule-like properties and no longer exhibit plasmonic behavior. Metal NCs, such as AuNCs, AgNCs, CuNCs, and PtNCs, exhibit a marked photoluminescence property due to quantum confinement. The most studied among these metal NCs are AuNCs, AgNCs, and CuNCs.
What are gold nanoclusters?
Nanocluster are collective groups composed of a specific number of atoms or molecules held together through a certain interaction mechanism. Gold nanoclusters attract increasing attention due to their potential applications in sensing, catalysis, optoelectronics, and biomedicine.
How are gold nanoclusters made?
In one example, green-emitting gold nanoclusters could be prepared by adding mercaptoundecanoic acid (MUA) into small AuNP solutions prepared by the reduction of HAuCl4 with tetrakis(hydroxymethyl)phosphonium chloride (THPC).
Size
Nanoclusters: Typically have at least one dimension between 1–10 nanometers (nm).
Quantum dots: Typically have a diameter of 2–10 nm.
Composition
Nanoclusters: Made up of up to 100 atoms, but larger ones can contain 1000 or more atoms.
Quantum dots: Made of a semiconducting material.
Properties
Nanoclusters: Have strong fluorescence emission, good photostability, and high conductivity.
Quantum dots: A type of semiconductor nanocrystal.
Nanocomposites
Composite materials are prepared from the combination of two or more different materials with distinct chemical or physical characteristics. The resultant composite exhibits properties which are superior to its constituent materials.
Nanocomposites are broad range of materials consisting of two or more components, with at least one component having dimensions in the nm range (i.e. between 1 and 100 nm)
Nanocomposites consist of two phases (i.e nanocrystalline phase + matrix phase)
Nanocomposite means nanosized particles (i.e metals, semiconductors, dielectric materials, etc) embedded in different matrix materials (ceramics, glass, polymers, etc).
Nanocomposites differ from traditional composites in the smaller size of the particles in the matrix materials.
Classification:
nanocomposites can also be classified into three categories based on the matrix material type:
Polymer-matrix Nanocomposites - These nanocomposites are made from polymer matrix materials such as thermoplastic, thermoset polymers, layered silicates, and polyester
Ceramic-matrix Nanocomposites - These nanocomposites are made from ceramic matrix materials such as Al2O3 or SiC.
Metal-matrix Nanocomposites - These nanocomposites are made from a ductile metal or alloy matrix with nanosized reinforcement material.
Prepration:
Synthetic methods are commonly employed to prepare nanocomposites, such as lamination, soft lithography, solution casting, and spin-coating. Homogenous nanoparticle dispersion is a primary challenge during preparation. Dispersion affects phase interfaces and the final nanocomposite properties.
Different materials, structures, and compositions allow for fine-tuning of nanocomposite properties, such as electrical, mechanical, thermal, acoustical, and magnetic properties. Nanocomposites have given rise to the field of multifunctional materials.
Application Areas
Application areas in the automotive industry include engine covers, intake manifolds, door handles, mirror housings, and timing belt covers in various vehicle types. Applications in other commercial areas include vacuum impellers and blades, mower hoods, mobile phone covers, and power tool housings.
Nanocomposites in Food Packaging
Nanoclays, which are added to,polypropylene or polylactic acid packaging films, prevent the diffusion of oxygen or flavorings and thus prolong the shelf life of foods. Nanosilver has an antimicrobial effect and can be used in plastics composites, for example to manufacture food packaging such as films or containers to protect food from spoilage.
This post deals with Quantum dots, a new class of materials
that is neither molecular nor bulk. They have the
same structure and atomic composition as bulk
materials, but their properties can be tuned using
a single parameter, the particle’s size.
What is a quantum dot?
Quantum dots are tiny crystals of semiconducting material. The crystals are so small – just a few nanometers wide (diameter of 2–10 nm) – that their physical size actually confines the electrons in the material to the point that it changes their behaviour. This means that quantumphenomena determine the properties of these tiny crystals – hence the name quantum dots.
Changing the size of the particle changes its properties in a predictable way. This effect can be used to tune the band gap of the semiconductor so that dots emit different colours of light when illuminated by a single-wavelength source – smaller dots (e.g., 2-3 nm) providing higher energy emissions will emit blue light, while larger ones (e.g., 5-6 nm) providing lower energy emissions emit at the red end of the visible spectrum. This property is sometimes referred to as “quantum confinement.
Like other semiconductors, quantum dots tend to be made of combinations of transition metal and metalloid elements. Cadmium selenide and cadmium telluride are among the most regularly used materials.
Quantum Dot Production
There are various methods of producing quantum dots. The most typical is via a colloidal synthesis, which is the process of heating a solution, causing the precursors to decompose to form monomers, which then produce nanocrystals.
Quantum dots produced using this method can consist of compounds including indium arsenide, lead sulfide, lead selenide, and cadmium sulfide. Colloidal synthesis is a popular method as quantum dots can be produced in batches large enough to be potentially used for commercial applications.
Plasma synthesis is another popular technique for the production of quantum dots. This process enables the control of the composition, surface, size, and shape of the quantum dot, and it also reduces the challenges associated with doping.
Not every nanoparticle is a quantum dot. Only some materials (such as semiconductors) will show quantum size effects in their electronic structure when they are made into nanoscale particles.
Working Principle of a Quantum Dot
Within a quantum dot, there are confined valence band holes, conduction band electrons, or excitons. These are the particles that carry the electricity, and because of this confinement, the quantum dot has a distinct energy level. The optical absorption and emission of CdSe quantum dots can be tuned across nearly the entire visible range of the optical spectrum. This is possible because the energy bandgap of CdSe quantum dots varies between 1.8 eV (its bulk value) to 3 eV (in the smallest quantum dots)
Applications:
One of their most widely known uses is in forming the basis QLED television screens recognized as the “Q” in QLED TVs. where dots of different sizes are excited by blue light and then emit pure red and green light to give the three-colour output of the pixels in a TV screen. But they also have uses in biotechnology, catalysis, sensors, solar cells and more. In particular, the Nobel committee highlighted the use of quantum dots in medical devices that are used to map biological tissue because the dots’ fluorescence is brighter and longer-lived than that of other fluorescent tags such as molecular fluorophores. This means they can help to guide surgeons when removing tumours, for example.
Here is the intro and some properties of nano materials..
INTRODUCTION
The word “nano” derives from the latin word “nanus” and Greek word “𝜈 ́𝛼νς,” Both indicating a person of very low height, i.e. a dwarf. Nanomaterials are conventionally defined as materials having at least a dimension between 1 and 100 nm.
Common types of nanomaterials include nanofilaments,
nanotubes, nanowires, nanocables, nanothin film, dendrimers, quantum dots, composite materials, and other materials besides nanopowder. Because of the unique nanoscale (1–100 nm)
size, nanomaterials are different from microscopic atoms molecules and macro-objects in
terms of their physical, chemical, electrical, and magnetic properties.
On the basis of reduction in size of materials in different dimensions, nanomaterials are classified
into three groups.
Surface effects
Nanomaterials possess a large fraction of surface atom per unit volume. This dramatic increase in the ratio of the surface atom to interior atom in nanomaterials is responsible for great change in physical and other properties of the materials. When the size of the object is reduced
to a nanometric range the proportion of surface atom increased leading to substantially more
reactive surface sites. Thus nanomaterials possess high surface area over volume ratio, which leads them to interact with the environment more effectively compared to bulk materials. The surface atoms have less coordination that lead them to lesser stability and highly reactive than the interior atoms. A further consequence of this lower stability of atoms or molecules at the surface is the lower melting point of surface layers.
Properties of nanomaterials:
High surface area and quantum effects at the nanoscale are responsible for different properties of nanomaterials compared to bulk materials. The quantum confinement effects describe electrons in terms of energy levels, valence bands, conduction bands, and electron energy band gaps. The confinement means restricting the motion of randomly moving electrons to specific energy levels (discreteness). When the particle size is reduced to nanoscale, the band gap is increased as compared with the bulk materials, and it leads to wider in the separation between
the energy levels. Hence, properties such as melting point, fluorescence,
electrical conductivity, magnetic permeability, and chemical reactivity change as a function of
the size of the particle.
Electrical properties :
The electrical conductivity of nanomaterials is generally lower than the bulk materials due to the increase of the band gap energy with a decrease in particle size of the nanomaterials. In bulk metals, the valence and conduction bands overlap, while in metal nanoparticles there is a gap between these bands. The gap observed in metal nanoparticles can be similar in size to that seen in semiconductors (< 2 eV) or even insulators (> 2 eV). This results in a metal becoming a semiconductor.
Optical properties:
The optical properties such as reflection, transmission, absorption, and light emission of
the nanomaterials are completely dependent on their electronic structure. At nanoscale level, nanoparticles are so small that electrons in them are not as much as free to move as in case of bulk material. Due to this quantum confinement of electrons, nanoparticles react differently with light compared to the bulk material. Optical properties such as emission and adsorption occur when electron transition occurs between the highest occupied molecular orbital, which is a valence band, and the lowest unoccupied molecular orbital, which is essentially the conduction band. This optical bandgap increases with the decrease in particle size. Tuning the nanosize of a semiconductor means tuning of bandgap leading to light of certain wavelength being emitted. Thus the same material emits different colours depending on its size.
Example:
It is well known that gold has the characteristic yellow, brilliant color, but when gold is produced in the nanosized dimension range, its color invariably changes to red. In other words, gold shows
a color depending on the size of the gold particles. This phenomenon has an impressive example in the so-called Lycurgus cup now preserved at the British Museum in London.
This cup was probably created in Rome during the fourth century and shows a different color changing the light from opaque green to bright red. This is the most famous example of the so-called dichroic glass. Actually, it presents some tiny amount of nanosized gold and silver that gives these unusual optical properties. This happens because at the nanoscale range, the electron cloud located on the surface of a gold nanoparticle has the possibility to resonate with different wavelengths of light depending on their frequency.
Magnetic properties:
Compared to bulk materials nanomaterials show a variety of unusual magnetic behavior
due to the surface or interface effects. The magnetic properties of a magnet are described by its magnetisation curve (called hysteresis
curve which is the variation of intensity of magnetisation with applied magnetic field). These
curves show the property like whether a magnet can be used as permanent magnet or a
electromagnet etc…. The size of the material can change the property of a magnet by changing the magnetisation curves. Thus nanostructuring of bulk magnetic materials leads to changes in the
curves which can produce soft or hard magnets with improved properties. Thus the nanomaterials may become superparamagnetic, even though their corresponding
bulk materials are not magnetic. For example, Fe3O4 nanoparticles showed
superparamagnetic-like behavior, even though bulk iron oxide (Fe3O4) is ferromagnetic. Exceptional surface energy and the flipped orientation of the spin electrons of the Fe3O4
nanoparticles are responsible for this phenomenon. Superparamagnetic nanoparticles
are not magnetic when located in a zero magnetic field, but they quickly become magnetized
after an external magnetic field is applied. When they are below the superparamagnetic diameter, the nanoparticles can revert quickly to a nonmagnetized state after an external magnet is removed
Mechanical properties
Mechanical properties of nanomaterials may reach the theoretical strength, which are one
or two orders of magnitude higher than that of single crystals in the bulk form. The
enhancement in mechanical strength is simply due to the reduced probability of defects.
Carbon nanotubes are 100 times stronger than steel but six times lighter.
