O2 Physisorption in Coal Pore: Effects of Pore Size, Pressure, Temperature and Function Group

In this paper, the physical adsorption characteristics of oxygen in coal pores were systematically investigated by the Grand Canonical Monte Carlo and the COMPASS force field. Firstly, coal pore structures of different sizes were constructed by graphite slit models and different groups. Secondly, the physisorption behavior of oxygen in graphite slit models of different sizes was simulated. Finally, the physisorption behavior of oxygen in graphite slit models at different pressures and temperatures was analyzed. The results showed that the physisorption density and excess physical adsorption of oxygen were divided into the rapidly decreasing stage (0.4-0.7 nm), the slowly decreasing stage (0.7-1.4 nm), and the stable stage (1.4 nm-5 nm) with the increase of coal pores, and the excess oxygen physisorption amount was more sensitive to the change of pressure. The O2 isosteric heat of physisorption decreased with increasing pore size of coal. Oxygen is more strongly adsorbed by hydroxyl and ether bonds than by methyl, carboxyl and carbonyl groups. Through this study, the mechanism of oxygen physical adsorption in coal pores and the characteristics influenced by temperature and pressure can be better understood.

Hygroscopic Properties of Sweet Cherry Powder: Thermodynamic Properties and Microstructural Changes

Understanding sorption isotherms is crucial in food science for optimizing the drying processes, enhancing the shelf-life of food, and maintaining food quality during storage. This study investigated the isotherms of sweet cherry powder (SCP) using the static gravimetric method. The experimental water sorption curves of lyophilized sweet cherry powder were determined at 30°C, 40°C, and 50°C. The curves were then fitted to six isotherm models: Modified GAB, Halsey, Smith, Oswin, Caurie, and Kühn models. To define the energy associated with the sorption process, the isosteric sorption heat, differential entropy, and spreading pressure were derived from the isotherms. Among the six models, the Smith model is the most reliable in predicting the sorption of the cherry powder with a determination coefficient (R2) of 0.9978 and a mean relative error (MRE) ≤1.61. The values of the net isosteric heat and differential entropy for the cherry increased exponentially as the moisture content decreased. The net isosteric heat values varied from 10.63 to 90.97 kJ mol−1, while the differential entropy values varied from 27.94 to 273.39 J. mol−1K−1. Overall, the enthalpy-entropy compensation theory showed that enthalpy-controlled mechanisms could be used to regulate water adsorption in cherry powders.

Experimental Determination and Modeling of the Moisture-Sorption Isotherms and Isosteric Heat of Tobacco Leaves

During a forced convection sun drying and storage operation, the equilibrium water content of a product to be dried is critical. These figures are frequently derived using isothermal sorption curves. The calculation of isotherms is a necessary step in determining the distribution and intensity of water connections in products. for that this paper concentrates on the experimental determination of the adsorption-desorption isotherms for various temperatures (40, 50, and 60℃) of the Nicotiana Tabacum L plants. From which we had established the relationship between the water activity and the water content in the product. However, the aforementioned determination was carried out by the static gravimetric method. Eight saturated salt solutions have been utilized in applications such as (KOH, KCl, MgCl2, MgNO3, K2CO3, BaCl2, K2SO4, and NaCl). Hygroscopic equilibrium was completed after 13 days for temperature 40℃, 11 days for 50℃, and 9 days for 60℃. The overall experimental sorption curves are summarized by six models (HENDERSON, modified HALSEY, OSWIN, GAB, modified BET, and PELEG). The sorption isotherms built using the Clausius–Clapeyron equation were used to determine the net isosteric temperatures of desorption and adsorption of Nicotiana Tabacum L. The results for the adsorption-desorption isotherms found are type III according to IUAPC. Following the smoothing of the experimental results by different used models, it was found that the models of GAB and Peleg allow having the lowest mean relative errors and correlation coefficient.

Comparative study between adsorbents based on magnetic nanoferrite. Application to the removal of methyl orange from wastewater

Magnetic ferrite (Mg-doped bismuth ferrite) and its clay-based composite (Mg-doped bismuth ferrite-bentonite) were prepared by self-combustion method utilizing glycine as fuel and served for the removal of methyl orange (MO) from aqueous solutions. The ferrite-based adsorbents were characterized by the measurement of specific surface area (BET), scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD). The different experimental parameters that affect the performance of this reaction such as: temperature, contact time, initial dye concentration and mass of adsorbent were investigated. The point of zero charge pH (pHPZC) was determined for the two adsorbents. Langmuir and Freundlich adsorption models were employed to provide a description of the equilibrium isotherms. Adsorption tests showed that the equilibrium time is a function of the initial concentration of dye. The adsorption kinetic study indicated that the equilibrium adsorption is established after 300 minutes for Mg-doped bismuth ferrite, while it is established after 180 minutes for Mg-doped bismuth ferrite-bentonite composite. Furthermore, this suggests that the adsorption of MO on both adsorbents can be perfectly described by pseudo-second order kinetics. The maximum adsorption capacity determined by the mathematical model of Langmuir is equal to 181.8 mg.g-1 for Mg-doped bismuth ferrite and to 188.7 mg.g-1 for its composite, at 298 K. Adsorption isotherms shows that the Freundlich model perfectly represents adsorption of methyl orange to the prepared Mg-doped bismuth ferrite. The ferrite/bentonite composite has 2-50 nm-sized pores and is indeed a mesoporous material. The small pores observed on the surface of the adsorbents are in line with type IV isotherm, with possible capillary condensation of the adsorbate. Moreover, Langmuir model seems to be the most suitable model for the absorption of methyl orange on the Mg-doped bismuth ferrite-bentonite composite. The thermodynamic parameters related to the sorbent/adsorbate system indicate that adsorption is spontaneous and exothermic. The determination of isosteric heat of adsorption suggested that it is indeed a physisorption characterized by weak intermolecular forces between MO and the surface.

A Multifunctional 3D Supermolecular Co Coordination Polymer With Potential for CO2 Adsorption, Antibacterial Activity, and Selective Sensing of Fe3+/Cr3+ Ions and TNP

A 3D supermolecular structure [Co3(L)2 (2,2′-bipy)2](DMF)3(H2O)3 1) (H3L = 4,4′,4″-nitrilotribenzoic acid) has been constructed based on H3L, and 2,2′-bipy ligands under solvothermal conditions. Compound 1 can be described as a (3, 6)-connected kgd topology with a Schläfli symbol (43)2(46.66.83) formed by [Co3(CO2)6] secondary building units. The adsorption properties of the activated sample 1a has been studied; the result shows that 1a has a high adsorption ability: the CO2 uptakes were 74 cm3·g−1 at 273 K, 50 cm3·g−1 at 298 K, the isosteric heat of adsorption (Qst) is 25.5 kJ mol−1 at zero loading, and the N2 adsorption at 77 K, 1 bar is 307 cm3 g−1. Magnetic measurements showed the existence of an antiferromagnetic exchange interaction in compound 1, besides compound 1 exhibits effective luminescent performance for Fe3+/Cr3+ and TNP.