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Chemical Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
The cadmium arachidate (CdA), prepared by the Langmuir-Blodgett (LB) technique, was used as multilayered buffer material on the acoustic sensor to promote the adhesion of the SWCNTs as sensing overlayers on the sensors. The Langmuir-Blodgett technique is a method of depositing crystalline films, one molecular layer at a time, by dipping the substrate into water containing a polymer, that forms a single layer of molecular chains on the surface. This layer is then transferred from the water to the substrate. The dipping is repeated to create an ordered multilayer film that does not require electrical poling (application of a strong electric field across the film) to orient the molecules. An LB film is a set of monolayers, or layers of organic material, one molecule thick, deposited on a solid substrate. It can consist of a single layer or many, up to a depth of several visible-light wavelengths.
Literature review
Published in Tejaswini Eregowda, Anaerobic treatment and resource recovery from methanol rich waste gases and wastewaters, 2019
The capacity of the ion exchange resins to adsorb the VFA can be quantified by fitting the equilibrium experimental data to isotherm models like Langmuir, Freundlich and Brunauer–Emmett–Teller (BET). Important parameters representing the affinity between the adsorbate and adsorbent as well as maximum adsorption capacities can be calculated to gain insight into the adsorption isotherm for single and multi-component systems (Hamdaoui and Naffrechoux, 2007). The primary assumptions for the Langmuir adsorption isotherm model are: (1) adsorption is monolayer, (2) the adsorption sites are finite, localised, identical and equivalent and (3) no lateral interaction or steric hindrance occurs between the adsorbed molecules, nor between the adjacent sites (Foo and Hameed, 2010; Guerra et al., 2014).
Theoretical studies on adsorption of organic molecules on metal surface
Published in Tanmoy Chakraborty, Prabhat Ranjan, Anand Pandey, Computational Chemistry Methodology in Structural Biology and Materials Sciences, 2017
The adsorption of organic molecule on the metal surface is either physisorption or chemisorption and is always an exothermic process. In physisorption the attractive force between the substrate (metal) and the adsorbate (molecule) is due to van der Waals interactions and electrostatic interactions [22]. For physisorption, the interaction energy between the substrate and adsorbate is typically less than - 20 kJ/mol[23] and the distance between adsorbate and substrate is higher than the length of covalent or ionic bonds. Chemisorption was first proposed by the American chemist Irving Langmuir in 1916. The adsorbate is bound to the substrate by covalent or ionic bond, much like those that occur between the bonded atoms of a molecule [22]. This is a slow process compared to physisorption. In chemisorption, a bond of the molecule may be broken and new chemical bond is formed between the adsorbate and the substrate. In chemisorption the interaction energy between the substrate and adsorbate is large, i.e., values above - 40 kJ/mol[24]. In addition, the length of the substrate-adsorbate bond is comparable with the normal covalent or ionic bonds. Because the chemisorption involves the formation of chemical bond with the metal surface, only a single layer ofmolecule, or a monolayer, can chemisorb to the surface.
Vitex doniana seed activated carbon for methylene blue adsorption: equilibrium and kinetics
Published in International Journal of Phytoremediation, 2023
Asokogene Oluwadayo Francis, Otoikhian Shegun Kevin, Muhammad Abbas Ahmad Zaini
Where, qe (mg/g) is the equilibrium capacity, Ce (mg/L) is the equilibrium dye concentration in solution, KL (L/mg) is the Langmuir equilibrium constant, Qm (mg/g) is the maximum monolayer capacity, KF (mg/g)(L/mg)1/n and 1/n are the Freundlich constants for capacity and surface heterogeneity, respectively, and KS (L/mg) and ns are the Sips constants. Langmuir isotherm assumes a monolayer adsorption with no lateral or steric interference, while Freundlich isotherm often describes a multilayer adsorption at low concentration system (Fosso-Kankeu et al. 2014; Vhahangwele and Mugera 2015). Sips isotherm combines the features of Langmuir and Freundlich models in forecasting heterogeneous surface adsorption (Elmorsi 2011; Chen 2013). The parameters were solved by non-linear regression using Microsoft Excel Solver, and the isotherm parameters are summarized in Table 2.
Effect of thiourea-modified biochar on adsorption and fractionation of cadmium and lead in contaminated acidic soil
Published in International Journal of Phytoremediation, 2020
Leila Gholami, Ghasem Rahimi, Abolfazl Khademi Jolgeh Nezhad
Langmuir isotherm theory assumes that adsorption occurs on a homogenous adsorbent surface, monolayer adsorption occurs at specific sites within the adsorbent carrying an equal number of adsorbed molecules, and no interaction occurs between adsorbed molecules. The equation for the Langmuir isotherm is as follows: where Qmax (mg kg−1) is the maximum adsorption capacity of the adsorbent, and b (L mg−1) is the Langmuir constant related to the adsorption capacity and adsorption rate, which indicates the affinity between the adsorbent and adsorbate. A dimensionless constant separation factor (RL) was also employed to determine whether adsorption is favorable or unfavorable, as follows:
Experimental investigation on phosphate adsorption, mechanism and desorption properties of Mn-Zn-Ti oxide trimetal alloy nanocomposite
Published in Journal of Dispersion Science and Technology, 2018
Milind Kondalkar, Umesh Fegade, Sanjay Attarde, Sopan Ingle
Langmuir isotherms assumes all the adsorption sites to be equivalent with formation of monolayer of adsorbate on the surface of the adsorbent i,e once a particular site occupied by adsorbate molecule further adsorption at that site is not possible.[29] There is no interaction between adsorbate molecules on the adjacent site. According to isotherm curves, the Langmuir isotherms parameters calculated from isotherm curve (Figure S3.) and presented in the Table 3. The positive values of KL indicate favorable adsorption. By considering correlation coefficients (R2) of the isotherm (0.954–0.966) adsorption process can be well described by Langmuir isotherm. Maximum adsorption capacity (q max) as calculated from Langmuir isotherm plot was found to be 151 mg/g.