IR spectroscopy

Infrared Spectroscopy is the analysis of infrared light interacting with a molecule. This can be analyzed in three ways by measuring absorption, emission and reflection. The main use of this technique is in organic and inorganic chemistry. It is used by chemists to determine functional groups in molecules. IR Spectroscopy measures the vibrations of atoms, and based on this it is possible to determine the functional groups.5 Generally, stronger bonds and light atoms will vibrate at a high stretching frequency (wavenumber).
Topic hierarchy

How an FTIR Spectrometer Operates
FTIR spectrometers (Fourier Transform Infrared Spectrometer) are widely used in organic synthesis, polymer science, petrochemical engineering, pharmaceutical industry and food analysis. In addition, since FTIR spectrometers can be hyphenated to chromatography, the mechanism of chemical reactions and the detection of unstable substances can be investigated with such instruments.
Identifying the Presence of Particular Groups
This page explains how to use an infra-red spectrum to identify the presence of a few simple bonds in organic compounds.

Infrared: Application
Infrared spectroscopy, an analytical technique that takes advantage of the vibrational transitions of a molecule, has been of great significance to scientific researchers in many fields such as protein characterization, nanoscale semiconductor analysis and space exploration.

Infrared: Interpretation
Infrared spectroscopy is the study of the interaction of infrared light with matter. The fundamental measurement obtained in infrared spectroscopy is an infrared spectrum, which is a plot of measured infrared intensity versus wavelength (or frequency) of light.

Infrared: Theory
Infrared (IR) spectroscopy is one of the most common and widely used spectroscopic techniques employed mainly by inorganic and organic chemists due to its usefulness in determining structures of compounds and identifying them. Chemical compounds have different chemical properties due to the presence of different functional groups.

Interpreting Infrared Spectra
 The wavelengths found in infrared radiation are a little longer than those found in visible light. IR spectroscopy is useful for finding out what kinds of bonds are present in a molecule, and knowing what kinds of bonds are present is a good start towards knowing what the structure could be.

Gibb's Phase Rule

The Phase Rule describes the possible number of degrees of freedom in a (closed) system at equilibrium, in terms of the number of separate phases and the number of chemical constituents in the system. It was deduced from thermodynamic principles by J. W. Gibbs in the 1870s.
The Degrees of Freedom [F] is the number of independent intensive variables (i.e. those that are independent of the quantity of material present) that need to be specified in value to fully determine the state of the system. Typical such variables might be temperature, pressure, or concentration.
A Phase is a component part of the system that is immiscible with the other parts (e.g. solid, liquid, or gas); a phase may of course contain several chemical constituents, which may or may not be shared with other phases. The number of phases is represented in the relation by P.
The Chemical Constituents are simply the distinct compounds (or elements) involved in the equations of the system. (If some of the system constituents remain in equilibrium with each other whatever the state of the system, they should be counted as a single constituent.) The number of these is represented as C.
The rule is:
F = C - P + 2.


Reference 
http://kj-gibbs.uio.no/phase_rule.html

Corrosion and Its Prevention

The loss of material(metals or alloys) or its useful properties by chemical interaction with its environment is known as corrosion. Corrosion is an electrochemical process. Corrosion leads to a tremendous loss. Corrosion is the reverse of metal extraction.

Examples:

 Rusting of iron. 
Blackening of silver articles in atmosphere.
 Fogging of nickel.

Causes of corrosion

Most metals exist in nature in combined forms that is in the form of ore. So extraction of metal from its ores is an unnatural process in which component of a stable system is being separated. Ore extraction Metal corrosion corrosion product Stable gain es mteta stable loss of es stable During the process of extraction a number of steps like concentration, Roasting ,and Smelting are involved and finally the ore is reduced into metal. therefore metals in their finally refined state are highly unstable and have a tendency to revert back in their original state that is to stable state by the process of corrosion(oxidation).

Rusting of iron is the most popular example of corrosion.

Usually the Surface of metal is covered with a thin layer of oxide. When this layer is broken, bare surface is exposed to the environment and this area act as an anode while the remaining area act as cathode. since the medium is exposed to the atmosphere, it contain dissolved oxygen.

Types of corrosion

 Uniform corrosion:

This is also called general corrosion. The surface effect produced by most direct chemical attacks (e.g., as by an acid) is a uniform etching of the metal.

Galvanic Corrosion :
Galvanic corrosion is an electrochemical action of two dissimilar metals in the presence of an electrolyte and an electron conductive path. It occurs when dissimilar metals are in contact.

 Crevice or contact corrosion:

Crevice or contact corrosion is the corrosion produced at the region of contact of metals with metals or metals with nonmetals. It may occur at washers, under barnacles, under applied protective films.

Corrosion in Concrete Concrete is a widely-used structural material that is frequently reinforced with carbon steel reinforcing rods, post-tensioning cable or pre-stressing wires. The steel is necessary to maintain the strength of the structure, but it is subject to corrosion.

 Erosion corrosion :
Erosion corrosion is the result of a combination of an aggressive chemical environment and high fluid-surface velocities.

 Dealloying Dealloying is a rare form of corrosion found in copper alloys, gray cast iron, and some other alloys. Dealloying occurs when the alloy loses the active component of the metal and retains the more corrosion resistant component in a porous "sponge" on the metal surface.

Factors affecting corrosion

1. Presence of impurities in metals Speed of corrosion increases with the presence of impurities in the metals because these impurities help in setting up the voltaic cells.

 2. Presence of electrolyte Electrolytes present in water also increases the rate of corrosion e.g. corrosion of iron in sea water takes place in large extent than in distilled water because sea water contains salts i.e.electrolytes.

Position of metals in electrochemical series

Highly reactive metals undergo corrosion faster than least reactive metals. Reactivity of metals can be found from the electrochemical series. e.g.Au Cu Pb Fe Zn Al Mg Na K Reactivity increases 4. Presence of carbon dioxide in water Presence of carbon dioxide in natural water also increases the rusting of iron because it acts as an electrolyte and increases the flow of electron from one place to another.

 Presence of protective coating

When the iron surface is coated with the metal, which is more reactive than the iron, then the rate of corrosion is retarded e.g. when iron is coated with zinc, iron is protected from rusting.

PREVENTION OF CORROSION

Corrosion is slow but continuously eating away the metal and consequence of rusting. Rusting can be avoided by not letting moist air come in contact with the metal surface .Following methods could gain fully be adopted to minimize rusting and corrosion

 Methods of preventing corrosion and rusting

Tarring

 Painting

Enameling

 Galvanizing

 Sheradising

 Tin plating

 electroplating

 Tarring: metal is dipped in hot coal tar so that a film of it is sticks to the surface which protect the surface from rusting and corrosion. Pipes or ends of poles to be embedded in the earth are usually given this protective treatment.

 Painting: Paints usually the lead paints are applied on the surface to be protected. Exposed metal surfaces as in case of roof and bridge structure are given this treatment which has to be repeated after regular interval of time.

Enameling: Enamels consist of high grade bases like zinc oxide or lead oxide ground in oil or varnish. they dry slowly leaving a hard tough and elastic film which is smooth and durable.Enamle painted surfaces are washable and are not affected by acids,alkali,gases or steam. Even tough they are more costly than ordinary paints yet because of their durability. They are equally good for use both on external and internal work.

Galvanizing: Depositing a fine film of zinc on the iron/steel surfaces is termed as galvanizing. The surfaces to be galvanizing is first cleared of all foreign matter by giving it an acid wash to be followed by a wash of clean water. the surface is then dried and dipped in molten zinc.The fine film of zinc that get deposited protect the surface from contact with atmosphere and consequence oxidation. Removal of the zinc film caused by scratches.

Sheradising: Surface to be treated is cleaned of all foreign deposits by washing it with acid solution and then with clean water. It is then dried and covered with zinc dust and enclosed in steel boxes to be heated in a furnace under controlled temperatures. Molten zinc spreads over the whole surface and on cooling forms a thin protective layer. Sherading gives better protection than galvanizing.

Tin plating: After cleaning the surface with acid wash followed by wash with clean water and drying, it is dipped in a bath of molten tin. A protective covering of tin layer if left on the surface.

Electroplating: By the process of electrolysis a thin film of nickel,cromium,copper or zinc is deposited on the surface to be protected. The surface to be protected is made the cathode and the metal to be deposited is made the anode.

 https://slideplayer.com/slide/5705698/

TiO2 photocatalysis: Design and applications

 Abstract:

 

TiO2 photocatalysis is widely used in a variety of applications in the environmental and energy fields, self-cleaning surfaces, air and water purification systems, sterilization, hydrogen evolution etc.,.

 The dimensionality associated with the structure of a TiO2 material can affect its properties and functions, including its photocatalytic performance, and also more specifically its surface area, adsorption, reflectance, adhesion, and carrier transportation properties. TiO2 photocatalysts can be classified into zero-, one-, two-, and three-dimensional structures.

Introduction:

                  Photocatalysis is focusing area in recent years. Photocatalysis currently used in a various products across a wide range of research areas, such as  environmental and energy fields. The photocatalytic properties of certain materials have been used to convert solar energy into chemical energy to oxidize or reduce materials to obtain useful materials including hydrogen and hydrocarbons, and to remove pollutants and bacteria.

TiO2 has been the most widely studied and used in many applications because of its strong oxidizing abilities for the decomposition of organic pollutants, superhydrophilicity (A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water), chemical stability, long durability, non toxicity, low cost, and transparency to visible light. The photocatalytic properties of TiO2 are derived from the formation of photogenerated charge carriers (hole and electron) which occurs upon the absorption of UV light corresponding to the band gap. The photogenerated holes in the valence band diffuse to the TiO2 surface andreact with adsorbed water molecules, forming hydroxyl radicals (•OH). The photogenerated holes and the hydroxyl radicals oxidize nearby organic molecules on the TiO2 surface. Meanwhile, electrons in the conduction band typically participate in reduction processes, which are typically react with molecular oxygen in the air to produce superoxide radical anions((a radical is an atom, molecule, or ion that has an unpaired valence electron.With some exceptions, these unpaired electrons make radicals highly chemically reactive).


 TiO2 surfaces become superhydrophilic with a contact angle of less than 5◦ under UV-light irradiation.The majority of the holes are subsequently consumed by reacting directly with adsorbed organic species or adsorbed water, producing •OH radicals .a small proportion of the holes is trapped at lattice oxygen sites and may react with TiO2 itself, which weakens the bonds between the lattice titanium and oxygen ions.The construction of TiO2 nano- or micro-structures with interesting morphologies and properties has recently attracted considerable attention. Many TiO2 nanostructural materials, such as spheres, nanorods, fibers, tubes, sheets, and interconnected architectures, have been fabricated. Nanostructured TiO2 materials are widely used not only in photocatalysis, but also in dye-sensitized solar cells, lithium-ion batteries.It is well known that there are many factors which can exert significant influence on photocatalytic performance, including the size, specific surface area etc..,. the development of performance improvements by adjusting these factors remains the focus of photocatalysis research. Structural dimensionality is also a factor which can affect the photocatalytic performance and also has a significant impact on the properties of TiO2 materials. For example, a sphere with zero dimensionality has a high specific surface area, resulting in a higher rate of photocatalytic decomposition of organic pollutants.



 Reference :
https://www.sciencedirect.com/science/article/pii/S1389556712000421

Photocatalysis and it's mechanism

The term can be generally used to describe a process where light is  used to activate a substance.The photocatalyst that modifies the rate of a chemical reaction without itself being involved in the chemical transformation. Thus, the main difference between a conventional thermal catalyst and photocatalyst is that  the former is activated by heat whereas the latter is activated by photons of appropriate energy. The principle of photocatalysis is based on the activation of a semiconductor particulate material by the action of radiation with an appropriate wavelength.  Photocatalysis is used for the elimination of several pollutants ( alkanes, alkenes, phenols, aromatics, pesticides) and complete mineralization of the organic compounds.

When a photocatalyst is irradiated with a light of suitable wavelength, an electron is excited to the conduction band (CB), leaving behind a positive hole in the valence band (VB). The electron in the CB can be utilized to reduce any substrate, whereas the hole in the VB can be used for oxidizing some compounds.

Reference: Photocatalysis principles and applications by Rakshit ametha

Page number 9-11

TiO2 photocatalysis is widely used in a variety of applications and products in the environmental and energy fields, including self-cleaning surfaces, air and water purification systems, sterilization, hydro- gen evolution, and photoelectrochemical conversion. The development of new materials, however, is strongly required to provide enhanced performances with respect to the photocatalytic properties and to find new uses for TiO2 photocatalysis. In this review, recent developments in the area of TiO2 photo- catalysis research, in terms of new materials from a structural design perspective, have been summarized. The dimensionality associated with the structure of a TiO2 material can affect its properties and func-
tions, including its photocatalytic performance, and also more specifically its surface area, adsorption, reflectance, adhesion, and carrier transportation properties.


https://www.sciencedirect.com/science/article/pii/S1389556712000421

Operators in quantum mechanics

The principal
mathematical difference between classical mechanics and quantum mechan-
ics is that whereas in the former physical observables are represented by
functions , in quantum mechanics they
are represented by mathematical operators.

 An operator is a symbol for an
instruction to carry out some action, an operation, on a function. In most of
the examples we shall meet, the action will be nothing more complicated than
multiplication or differentiation.

Linear operator:

Schrödinger equation

The Schrödinger equation, sometimes called the Schrödinger wave equation, is a partial differential equation. It uses the concept of energy conservation (Kinetic Energy + Potential Energy = Total Energy) to obtain information about the behavior of an electron bound to a nucleus. It does this by allowing an electron's wave function, Ψ, to be calculated.
Solving the Schrödinger equation gives us Ψ and Ψ2. With these we get the quantum numbers and the shapes and orientations of orbitals that characterize electrons in an atom or molecule.

The Schrödinger equation gives exact solutions only for nuclei with one electron: H, He+, Li2+, Be3+, B4+, C5+, etc. In mathematical language, we say that analytic solutions for Ψ are possible only for one-electron systems. One-electron systems are often described as hydrogenic - meaning "like hydrogen.For all other atoms, ions, and molecules, no analytic solutions for Ψ are possible;


There is a time-dependent Schrödinger equation and a time-independent Schrödinger equation.

The time-independent equation considers the electron's quantum state to be unchanging, hence it considers the electron as a standing wave. The time-independent equation allows electron densities (i.e. the sizes and shapes of atomic and molecular orbitals) to be found using Ψ2, the square of the wave function.

The p orbitals below are examples of Ψ2:px,py,pz.



https://www.chemicool.com/definition/schrodinger_equation.html

Electronic structure

Electrons are the “glue” that holds the nuclei together in the chemical bonds of
molecules and ions. It  is the nuclei’s positive charges that bind the electrons to
the nuclei. Electronic structure theory deals with the quantum states of the electrons, usually within the Born- Oppenheimer approximation .It also addresses the forces that the electrons’ presence creates on the nuclei; it is these forces that determine the geometries and energies of various stable structures of the molecule as well as transition states connecting these stable structures. Because there are ground and excited
electronic states, each of which has different electronic properties, there are different
stable-structure and transition-state geometries for each such electronic state. Electronic
structure theory deals with all of these states, their nuclear structures, and the
spectroscopies.

Reference
http://simons.hec.utah.edu/NewUndergradBook/Chapter6

Effect of Li Adsorption on the Electronic and Hydrogen Storage Properties of Acenes

Due to the presence of strong static correlation effects and noncovalent interactions, accurate prediction of the electronic and hydrogen storage properties of Li-adsorbed acenes with n linearly fused benzene rings (n = 3-8) has been very challenging for conventional electronic structure methods.To meet this challenge using developed thermally-assisted-occupation density functional theory (TAO-DFT) with dispersion corrections.