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Comprehensive Array of Ample Analytical Strategies for Characterization of Nanomaterials
Published in Vineet Kumar, Praveen Guleria, Nandita Dasgupta, Shivendu Ranjan, Functionalized Nanomaterials I, 2020
Nitesh Dhiman, Amrita Singh, Aditya K. Kar, Mahaveer P. Purohit, Satyakam Patnaik
Surface area and porosity are the two unique features that impact the quality and utility of nanomaterials. Gas sorption analysis (both adsorption and desorption) is commonly used to determine the surface area and porosity of porous NPs. This physical adsorption of gas molecules on solid surface can be explained by using the BET theory (Gelb and Gubbins, 1998; Naderi, 2015). In a gas sorption experiment, several cycles of controlled doses of an inert gas, such as nitrogen, krypton, or argon are introduced to adsorb, and later, withdrawn and desorbed forming a monolayer or multilayers of gas molecules adsorbed on the NPs surface. The sample material is placed in a vacuum chamber at a constant and very low temperature (liquid nitrogen (77.4 K)), and subjected to a wide range of pressures, to generate sorption isotherms. The amounts of gas molecules adsorbed or desorbed are determined by the pressure variations due to the adsorption or desorption of the gas molecules by the material. By knowing the area occupied by one adsorbate molecule, and using an adsorption model, the total surface area of the material can be determined. Chemisorption analyses can provide much of the information needed to evaluate catalyst materials in the design and production phases, as well as after a period of use. Unlike physisorption, chemisorption, however, is highly selective and occurs only between certain adsorptive and adsorbent species, and only if the chemically active surface is cleaned of previously adsorbed molecules. For example, a CuO NPs prepared for potent antibacterial applications has a mean surface area of 15.69 m2/g determined by BET (Ren et al., 2009). (Jörg et al., 2012) synthesized spherical ordered mesoporous carbon NPs for applying as cathode material in Li–S batteries. These NPs have high inner porosity of 2.32 cm3 g−1 and a surface area of 2445 m2g−1 for reversible capacity and better cycling efficiency.
Properties of Spray-freeze-dried Products and their Characterization
Published in S. Padma Ishwarya, Spray-Freeze-Drying of Foods and Bioproducts, 2022
The BET concept of SSA calculation is based on the adsorption, i.e., adhesion of the atoms or molecules of an unreactive gas onto the solid particles under study. It is based on the assumptions that the gas molecules would physically adsorb on a solid in layers, infinitely and that the layers are non-interactive such that the BET theory is applicable to each layer (Raja & Barron, 2021). A typical set-up of the BET instrument is shown in Figure 10.16. Before the gas adsorption analysis of spray-freeze-dried powders, a known quantity of the sample solid material (≤ 0.5 g) is placed in a glass cell and degassed for 24 hours or a minimum of 16 hours under helium at a sufficiently high temperature to remove unwanted vapors and gases from its surface. This step is critical as incomplete degassing of the sample can lead to underestimation of the reported SSA value. The selected degassing temperature must be the highest possible one that promotes water vapor removal within a shorter time, but without damaging the sample's structure. Nevertheless, for SFD powders, it has been observed that the degassing step is not adequate for the complete removal of adsorbed moisture. This is because of the low glass transition temperature of SFD powders, due to which higher degassing temperatures cannot be applied without damaging the solid sample. Hence, an additional preliminary step of drying the powders for 24 h under vacuum is practiced (Brunaugh et al., 2019). Then, the sample is shifted to the analysis port and cooled by a cryogenic liquid to enhance its interaction with the gas. Subsequently, a known amount of gas (adsorbate) is released into the sample cell with the aid of a calibrated piston. Nitrogen is the commonly used adsorbate owing to its high purity and strong interaction with most solids. Prior to the injection of nitrogen gas and also after each measurement, a gas such as helium that does not adsorb onto the sample is injected for a blank run and to calibrate the dead volume in the sample cell (Raja & Barron, 2021).
Determination of activated carbon fiber adsorption capacity for several common organic vapors: applications for respiratory protection
Published in Journal of the Air & Waste Management Association, 2021
Margaret Summers, Jonghwa Oh, Claudiu T. Lungu
To obtain surface area measurements and micropore characterization, ACF media underwent nitrogen adsorption at 77 K using a Micromeritics ASAP 2020 Physisorption Analyzer (Micromeritics Corp, Norcross, GA). Total specific surface area and average pore diameter of ACFs were determined by the Brunauer-Emmett-Teller (BET) method. BET theory describes the adsorption of gas particles onto a solid surface based on the assumption of multilayer adsorption. The BET method is often used by convention to estimate the surface area of microporous carbons (Webb and Orr 1997).
Elevated CO-free hydrogen productivity through ethanol steam reforming using cubic Co-Nanoparticles based MgO catalyst
Published in Environmental Technology, 2022
Radwa A. El-Salamony, Asmaa S. Morshedy, Ahmed M.A. El Naggar
Nitrogen adsorption/desorption isotherm was measured at −196 °C on a (NOVA 3200 apparatus, Quantachrome Corporation, Boynton Beach, Florida, USA). The sample wAS degassed at 200 °C overnight in a nitrogen atmosphere before adsorption to ensure a dry and clean surface. The BET surface area (SBET) was calculated using the Brunauere-Emmette-Teller (BET) theory. The Barrett, Joyner, and Halenda (BJH) method used for estimating pore size distribution (PSD) and pore volume.
Adsorption of sodium dodecyl benzene sulfonate onto carbonate rock: Kinetics, equilibrium and mechanistic study
Published in Journal of Dispersion Science and Technology, 2018
Nassim Hemmati, Amir Tabzar, Mohammad Hossein Ghazanfari
BET isotherm: The BET theory aims to explain the physical adsorption of gas molecules onto a solid surface and serves as the basis for an important analysis technique for the measurement of the specific surface area of a material. In 1938, Stephen Brunauer, Paul Hugh Emmett, and Edward Teller published an article about the BET theory for the first time[46]; “BET” consists of the first initials of their family names.