X-ray photoelectron spectroscopy (XPS)

Working principle & Instrumentation 

XPS instrumentation 

XPS (photoelectron spectroscopy) is a surface-sensitive technique used to analyze the elemental composition, chemical state, and electronic state of elements on the surface of a material.

In Xps photoelectrons emitted from material as function of their binding energy in the sample, allowing for the identification of elements and their chemical states. It is highly sensitive to the top few nanometers of a material, making it valuable for surface analysis. XPS provide more athentic data than EDX.

XPS instrument typically consists of an X-ray source,usually Mg kα hv=1253.6ev line width = 0.7ev Al kα hv=1486.6ev line width=0.85ev, an hemisphere electronenergy analyzer outer negative and inner positve lining to intact electron in center, and a detector. X-rays are used to excite electrons from the sample, and the emitted photoelectrons are analyzed based on their kinetic energy (KE). XPS involves irradiating a material's surface with X-rays, which causes the emission of photoelectrons from the inner electron shells of atoms. The kinetic energy and number of emitted electrons are measured through detecter or analyser to determine the binding energy (BE) and abundance of each element providing information about the material's elemental composition electronic structure density and chemical states. Xps measures mostly top 10nm and provide surface information. Total energy of the system is hv=KV+BE+Φ si is work function, Xps can be used in line profiling of the elemental composition across the surface or 

in depth profiling when pair with ion beam itching. 

Sample Preparation Samples should be clean free of contamination. Conductive samples are preferred to avoid charging effects. Additionally, samples may need to be rotated during analysis to ensure a representative surface is probed.

Results Interpretation XPS spectra show peaks corresponding to different elements, the position of these peaks provides information about the chemical state of the elements. The intensity of the peaks is proportional to the elemental concentration. Different peaks are making in single graph shows oxidation state known as deconvolution, when one peak get difused new one is start making this 

type of peaks called satellite peaks indicate the change in the oxidation state.

XPS spectrum 

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X-ray Diffraction (XRD)

Working principle & Instrumentation 

XRD instrumentation 

XRD (X-ray Diffraction) is versatile nondistructive technique used to analyze the crystallographic structure of materials by measuring the diffraction pattern of X-rays as they interact with a crystalline 

sample.

XRD provides information about crystal structure, lattice parameters, phase composition, and preferred orientation of crystallites in a sample. Many materials are made up of tiny crystallites the chemical composition and structural type of these crystals is called their phase materials can be single phase or multiphase mixture and may conatin crystalline and non cryastalline components. In an X-ray diffracto meter different crystalline phases gives different diffraction patterns. Phase identification can be perform by comparing X-ray diffraction patteren obtained from unknown samples to patterens inreference data base. In XRD atoms of the sample donot absorb X-ray at all they just reflect them .if we did not get any peak in the material its mean the material 

is amrophous other vice it will be crystalline.

The XRD instrument consists of an X-ray tube, a sample holder, a crystal monochromator or a diffracting crystal, and a detector. The instrument used to maintain the angle and rotate the sample is termed a goniometer. The X-ray beam interacts (constractive interference) with the sample and the diffracted X-rays are detected to generate a diffraction pattern. The wavelegth of X-ray used is of the same order of magnitude of the distance between the atom in crystalline lattice. This gives rise to a diffraction pattern that can be analysied by number of ways usually sherrer equation D=Kλ/βcosϴ is used for crystalline size determination D=crystallite size K=0.9 (scherrer constant) λ= 0.15406nm (wave length of X-ray source) β=FWHM(in radians) ϴ= peak position (in radians) Bragges law nλ=2dsineϴ d= nλ/2sineϴ d= interplaner spacing or d spacing (in Ǻ) is used for mesurement of interplaner spacing or d spacing.

Sample Preparation Samples should be finely powdered and homogenously dispersed to ensure representative results. Amorphous materials may not produce diffraction patterns, as XRD is most effective for crystalline samples.

Results Interpretation XRD results are typically presented as a diffraction pattern, where peaks correspond to specific crystallographic planes. The position and intensity of these peaks provide information about the crystal structure and phase composition of the materialPeak width is inversly proportion to crystal size.

XRD graph 

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Fourier Transform Infrared Spectroscopy (FTIR)

Working principle & Instrumentation 

 FTIR instrumentation 

FTIR (Fourier Transform Infrared Spectroscopy) is analytical technique for determining functional group and crystal orientations. Their nature may be of organic or inorganic. FTIR contain IR source to produce IR radiation Interferometer (Michelson interferometer) which contain beam splitter, stationary mirror and moving mirror. Which split the beam into two beams two possiblities are,one is destructive interference called OPD (optical path difference) height and valley (crest and trough) of IR not match in beam spliter when it rejoin and cancel the effect of each other.

ZPD (zero path difference ) height and valley (crest and trough) of IR beams match is known as constructive interferences which gives results when fall on sample.

Basic principle is that electrons between different elements absorbed IR radiations at different frequencies matching to it in the range in FTIR this interaction (measures absorbance or emittence) These signals are decoded by applying techniques Fourier transformation to produced spectra usually in the mid-IR region corresponds to wavenumbers 4000 to 400cm-1 .

Sample prepration Samples for FTIR analysis must be prepared in a form suitable for transmission or reflection of infrared light. This often involves creating thin films, in disc or KBr wafer method by using potassium bromide (KBr) 3:1 ratio (3% KBR : 1% sample) mix well with each other grinding, mashing then place it in pressing disc press through hydraulic press applying pressure of 8 to 10 mega pascal to attain very thin crackless pellet place it in analyzer chamber to analyze. In direct method Liquids can analyize directly droping few drops on analyzer The goal is to present a uniform and representative sample.

Results interpretation FTIR spectra display peaks at specific wavenumbers corresponding to molecular vibrations. Peaks indicate the presence of certain functional groups or bonds. The intensity and position of these peaks provide information about the concentration and type of chemical bonds in the sample. 

Upto 4000cm-1 to 1500cm-1 is Known as functional group region 1500cm-1 to 400cm-1 known as finger print region specific for each material, match the spectra with IR data base to identify the functional group and materials.

FTIR spectra

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Surface Area Analyzer (SSA)

Working principle & Instrumentation 

SAA instrumentation 

The SSA (Surface Area Analyzer) is used to measure the specific surface area of a material, providing information about its porosity and the extent of available surface for chemical interactions. 

SAA quantifies the surface area by adsorbing gas molecules onto the material's surface and measuring the amount adsorbed. The data is then used to calculate the specific surface area. SAA typically consists of a degas system to remove adsorbed gases from the material, a sample cell where adsorption occurs, and a detection system to measure the adsorbed gas quantity. Instruments may use various inert and some other adsorptive gases like nitrogen. Principle is the gas adsorption onto the sample's surface. The amount of gas adsorbed is directly related to the surface area. The BET (Brunauer, Emmett, Teller) theory is commonly employed, which assumes the formation of a monolayer (as Langmuir theory) or multilayer of gas molecules on the surface. By analyzing the gas adsorption isotherm, the surface area of the material can determined accurately.

It is essential for characterizing materials with porous structures, like catalysts, adsorbents, and powders. It provides valuable information for researchers and industries involved in areas such as catalysis,  material science, environmental science etc. Pore volume and pore area distributions in the mesopore and macropore ranges by the BJH (Barrett, Joyner, Halenda) method of gas adsorption and desorption using a variety of thickness equations including a user-defined, standard isotherm (graph of gas adsorpition vs relative pressure).

Sample Preparation Samples need to be prepared by degassing to remove any previously adsorbed gases or contaminants. This is crucial for accurate measurements. Samples are often finely powdered or have a high surface area, such as porous materials like zeolites or activated carbon.

Results interpretation The specific surface area is determined by analyzing the quantity of gas adsorbed at various pressures. A plot of adsorption isotherm (adsorbed gas versus pressure) is created. Specific surface area is calculated using models such as the BET (Brunauer, Emmett, and Teller) equation systematically and provide BET isotherm gas adsorption graph. The BET theory is commonly employed, which assumes the formation of a monolayer (as langmuir theory) and can be multilayer of gas molecules on the surface.

SAA graph

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Pore Size Distribution (PSD)

Working principle & Instrumentation 

PSD instrumentation 

 

Pore size distribution analysis is used to determine the range of pore sizes within a material. This information is crucial for understanding the material's properties, especially in fields like material science, catalysis, and filtration.

PSD provides data on the distribution of pore sizes, indicating the variety of pore dimensions within a material. This information is vital for assessing how easily fluids can move through the material and its suitability for specific applications.

Various techniques are used for PSD analysis, including gas adsorption methods (often with instruments like BET analyzers (works on the BET theory principle ),

The BET (Brunauer, Emmett, and Teller) theory is commonly employed, which assumes the formation of a monolayer (as Langmuir theory) or multilayer of gas molecules on the surface. 

Mercury intrusion porosimetry (pore structure diameter volume etc), and nuclear magnetic resonance (NMR) methods. Each technique offers different insights into pore size distribution.

The principle varies based on the technique employed. In gas adsorption methods like BET, the principle involves the adsorption of gas molecules onto the surface of the material. In mercury intrusion porosimetry, mercury is forced 

into the pores, and the intrusion pressure is related to pore size. NMR methods rely on the interactions between nuclear spins and the material's structure to infer pore size distribution. Each method exploits different physical principles to 

provide information about the material's porosity.

Sample Preparation Sample preparation depends on the technique used. For gas adsorption methods, the material is typically degassed to remove adsorbed gases. In mercury intrusion porosimetry, the sample is impregnated with mercury. NMR methods require specific sample handling for accurate results.

Results interpretation PSD results are often presented as a plot showing the 

percentage of pores within specified size ranges. The shape of the distribution curve provides insights into the homogeneity of the pore size within the material.

PSD graph 

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Point of Zero Charge (PZC)

Working principle & Instrumentation  

PZC instrumentation 

The Point of Zero Charge (PZC or pH

PZC) is a characteristic of a material's surface at which the material carries no net electrical charge. It is a critical parameter in understanding the surface charge behavior of materials, particularly in the context of colloidal systems and adsorption phenomena. It is that value of PH where surface attain neutrality.

The PZC is related to the protonation or deprotonation of functional groups on the material's surface. At the PZC, the concentrations of positively and negatively charged sites are equal, surface attain neutrality, Experimental methods involve determining the pH at which the material exhibits no net charge. This is often done by measuring the zeta potential or by titrating the material. with an acid or a base and monitoring the surface charge In salt addition method first Prepared 600ml 0.1M stalk solution of Sodium nitrate, take 40ml of this solution in fourteen different Erlenmeyer or conanical flasks one by one set the different pH value (1 to 14) of the solution with either adding acid or base drop vice through droper carefully Nitric acid (0.1 M) or Sodium hydroxide (0.1 M) by using a pH meter addjust different pH value from (1 to 14) has been set these are the initial pH (pHi) values then in each flask add desirable composite or material whose pzc want to be determin placed all these flask in orbital shaker and shake at speed of 150 rpm on the orbital shaker at room temperature for 24 hours or set the parameters of your own choice according to sample requirement. After equlibrium filter the contents, and record the pH of beaker containg the filtrate known as final pH (pHf) then find the change in pH by ΔpH=pHi _ pHf then draw the graph against ΔpH and pHi the line intersect or coside on the zero is its PZC.

Sample Preparation Sample preparation depends on the technique used in salt addition method Care fully salt solution prepared 0.1 M adjust their pH (1 to 14 by adding acidc or basic solution drope vice in it) Disperse the cleaned material in each of the prepared solutions. This could involve mixing the material with the solution and allowing it to equilibrate.

Results interpretation The pH below the PZC, the surface is positively charged, and above the PZC, it becomes negatively charged. PZC is crucial for predicting the adsorption behavior of ions and molecules onto a material's surfaces.

Figure PZC graph 

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Thermogravimetry Analysis (TGA)

Working principle & Instrumentation 

TGA instrumentation 

Thermal analysis are Techniques in which a physical property of a substance is measured as a function of temperature whilst the substance is subjected to a controlled temperature programme certain techniques lie in this here we discuse TGA and DTA in detail.

Thermogravimetry (TGA) is a technique in which the mass of a substance is measured as a function of temperature while the substance is subjected to a controlled temperature programme. The record is the thermogravimetric or TG curve or graph the mass should be plotted on the ordinate decreasing downwards and temperature (T) or time (t) on the abscissa increasing from left to right.

A thermobalance is used for weighing a sample continuously while it is being heated (in a given enivornement, air, N2, CO2, He, Ar, etc ) or cooled. The heating rate is the rate of temperature increase, which is customarily quoted in degrees per minute (on the Celsius or Kelvin scales). The heating or cooling rate is said to be constant when the temperature/time curve is linear. 

The initial temperature, Ti, is thattemperature (on the Celsius or Kelvin scale) at which the cumulative-mass change reaches a magnitude that the thermobalance can detect. The final temperature, Tf, is that temperature (on the Celsius or Kelvin scale) at which the cumulative mass change reaches a maximum. The reaction interval is the temperature difference between Tf and Ti as defined above. TG measures changes in sample mass, indicating processes such as decomposition, oxidation, or phase transitions. DTA can perform with it for physical property of substance is measured as a function of temperature at controlled temperature programme.

Sample Preparation Samples are usually finely ground and placed in a sample holder. It's crucial to have a representative sample and to account for factors like sample size and packing density, as they influence the thermal behavior.

Results interpretation In TG, weight loss or gain is observed as a function of temperature, providing information about processes like decomposition or oxidation. Plateau A plateau is that part of the TG curve where the mass is essentially constant. And decline line in grapgh shows decrease in mass as function of temperature.

TGA graph 

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