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Diagnostic Methods
Published in Ranjeet Kumar Sahu, Somashekhar S. Hiremath, Corona Discharge Micromachining for the Synthesis of Nanoparticles, 2019
Ranjeet Kumar Sahu, Somashekhar S. Hiremath
UV-vis spectroscopy is a technique used for identifying qualitatively the presence of colloidal metallic nanoparticles, which shows characteristic absorption spectra. In particular, it is used for measuring the surface plasmon resonance spectra of nanoparticles. In UV-vis spectroscopy, the absorption of light or electromagnetic waves passing through a sample is measured at different wavelengths in the near ultraviolet and visible portions of the spectrum. When sample molecules are exposed to light and having an energy that matches a possible electronic transition within the molecule, some of the light energy will be absorbed as the electron is promoted to a higher energy orbital. The spectrometer records the wavelengths at which absorption occurs, together with the degree of absorption at each wavelength. The resulting spectrum is presented as a plot of absorbance versus wavelength. Absorbance usually ranges from 0 (no absorption) to 2 (99% absorption), and is precisely defined in context with spectrometer operation.
Air quality experiments
Published in Abhishek Tiwary, Ian Williams, Air Pollution, 2018
In terms of analytical determination, compounds of Group I metals and of the heavier Group II metals give a visible colour to a methane/air flame when aspirated into it. With other metallic elements, the energy required to excite atoms present in a flame is too high and any atoms produced by the flame remain in their ground state. If light is shone through the flame, however, these atoms may absorb the light and be raised to higher electronic states. The result is an atomic line absorption spectrum. This process is used for analysis in the atomic absorption spectrometry. To achieve the required sensitivity and selectivity for an element, the light to be absorbed is produced in a discharge lamp containing the element as a cathode. This light is then passed through a long acetylene/oxygen flame into which the analyte is aspirated. Acetylene/oxygen is used since at this temperature most compounds are atomised. The light is then detected by a spectrophotometer which can measure the absorbance at a particular wavelength. It is usually found that over a certain range of concentration the absorbance is approximately proportional to concentration.
Semiconductors as Gas Sensors
Published in Sunipa Roy, Chandan Kumar Sarkar, MEMS and Nanotechnology for Gas Sensors, 2017
Sunipa Roy, Chandan Kumar Sarkar
The Beer–Lambert law states that the absorbance of a solution is directly proportional to the solution’s concentration. Thus, UV/VIS spectroscopy can be used to determine the concentration of a solution. A UV/VIS spectrophotometre may be used as a detector. The presence of an analyte gives a response which can be assumed to be proportional to the concentration. The height of the peak for a particular concentration is known as the response factor. The method is most often used in a quantitative way to determine concentrations of an absorbing species in solution, using the Beer–Lambert law: A=−log10(I/I0)=ε.c.L
Aspects of photobioreactor and algadisk in CO2 sequestration and biomass production
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
S. Sivasangari, T. Vel Rajan, J. Nandhini
A standard chart was generated (Absorbance vs Concentration) by measuring the absorbance values of four samples whose dry mass concentration was already known (Mohamed Abubakar et al. 2016). The absorbance of the samples were measured at the peak wavelength by identifying the wavelength at which maximum absorbance was obtained. The concentration of microalgal samples was determined using Eq. (2) by filtering it through membrane filters using vacuum suction whose initial weight was already known. Filters were then dried in hot air oven at 105-110°C for 24 h then cooled to room temperature to get final weight. Later, the absorbance of samples collected from the reactors was determined at peak wavelength to obtain the concentration of biomass from the standard chart thus generated.
Experimental study and kinetic model analysis on photothermal catalysis of formaldehyde by manganese and cerium based catalytic materials
Published in Journal of the Air & Waste Management Association, 2023
Zhiqiang Wang, Wei Xiao, Fangzhu Zhang, Shimin Zhang, Wufeng Jin
A (absorbance) is an important parameter to measure the ability of a solution or solid to absorb light. Its formula is A = lg(1/T), 1 represents the incident light intensity, and T represents the projected light intensity. In the formula, only T cannot be greater than 1, and it has nothing to do with A. When the absorbance exceeds 1, it means that more than 90% of the light intensity is absorbed by the sample. Overall, the absorbance of 1 is a critical value. It can be seen from Figure 3 that the MnOx-CeO2 catalyst has a very high absorbance in the wavelength range of 200–1000 nm. In the wavelength range of 1000–1500 nm, the absorbance showed a decreasing trend, but even at 1500 nm, the absorbance was still greater than 0.5. At 1800 nm, there is a serious fluctuation in the data, which is due to switch the light source for the near-infrared light during the test. In addition, the MnOx-CeO2 catalyst exhibits good light absorption characteristics in the wavelength range of 200–2500 nm (the radiation wavelength received on the ground is mainly concentrated in the range of 0.295–2.5 μm), and the average absorbance is about 0.8. Therefore, the catalyst has an ideal light absorption capacity, and the catalyst surface can reach a higher catalytic temperature under the action of solar radiation when purifying formaldehyde, thereby stimulating the catalytic activity, and maintaining a high formaldehyde catalytic efficiency.
Fourier-transform infrared analysis and interpretation for bituminous binders
Published in Road Materials and Pavement Design, 2023
Laurent Porot, Virginie Mouillet, Alexandros Margaritis, Hamzeh Haghshenas, Michael Elwardany, Panos Apostolidis
Conversion does not modify the peak wavelength number. In literature, spectra are usually plotted in both modes. According to Beer’s law, absorbance is proportional to the concentration as in Equation (2) where A(x) is the absorbance for a wavelength number x, I0 and I are the intensities of the incident light and transmitted light, respectively, ϵi(x) is the molar attenuation coefficient or absorptivity of the attenuating species, l is the optical path length, and ci is the concentration of the molecule inside the solution. Then, to identify unknown groups or to make a comparison between spectra, absorbance or transmittance modes may be used. As the absorbance is proportional to the concentration, it can be used easier for quantitative analyses.