Brunauer–Emmett–Teller Model Research Articles

Methylmercury sorption to polyethylene terephthalate (PET) fibers and relevance to environmental exposure

Abstract Considerable amounts of polyethylene terephthalate (PET) microplastic fibers are released into the environment by the laundering of polyester clothing. Microplastic fibers can be ingested by organisms in the environment. Therefore, it has been suggested that microplastic fibers act as vectors for adsorbed contaminants, which are subsequently desorbed in the gut of the organism. We undertook sorption isotherm experiments at pH 6, 7, and 8 to quantify the sorption of methylmercury (MeHg) to PET fibers. Sorption isotherms were fit to Langmuir, Freundlich, and Brunauer–Emmett–Teller models. Sorption decreased with increasing pH, which can be explained by physisorption on the negatively charged PET surfaces and the greater presence of neutral or negatively charged MeHg species at higher pH. We used the parameters obtained by the model fits to predict the likely concentration of MeHg on PET microplastic fibers in aquatic ecosystems with environmentally realistic MeHg concentrations. We calculated MeHg concentrations on PET microplastic fibers to be four orders of magnitude lower than previously observed concentrations of MeHg in seston (suspended particles comprising algae and bacteria) at the base of the aquatic food web. The results indicate that the presence of PET microplastic fibers in the environment do not elevate the MeHg exposure to organisms that ingest fibers in the environment.

Determination of Moisture Sorption Isotherm using Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) Models, Germination Capacity and Index Vigor of Soybean during Storage

Understanding the interaction between the equilibrium moisture content of a product and the surrounding air is crucial for guaranteeing product quality and preserving its characteristics throughout storage. The study of this tendency may be conducted utilizing sorption isotherms. This research aimed to study the moisture sorption characteristics of soybeans during storage, identify the most suitable mathematical model for the experimental data, and examine the relationship between the germination capacity and vigor index of soybeans with their moisture content and water activity. Moisture sorption characteristics of soybean, Anjasmara variety, were investigated at temperatures of 30ᵒC, 40ᵒC, and 50ᵒC, and water activities of 0.08 to 0.80, and were modelled using two different mathematical models, Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB). Both two mathematical models, BET and GAB, were found to effectively describe the moisture sorption data based on regression analyses and goodness of fit. Each model was statistically evaluated by coefficient of determination and deviation standard. The moisture sorption behaviour of soybean seeds displayed a sigmoidal pattern. The GAB models have been suggested to estimate the moisture content at certain humidity levels at 30ᵒC, 40ᵒC, and 50ᵒC temperatures. The BET models were suitable for temperatures between 30ᵒC and 40oC. The vigor and germination indicated exhibited a progressive and optimal trend at a water activity level of 0.32, followed by a decline at all three temperatures.

Treatment of seeds by cold ambient air plasma: combining impedance measurements with water sorption modeling to understand the impact of seed hydration

In this article, we focus on the plasma seed interaction and more specifically-on the feedback exerted by the seeds on the plasma properties. Dormant Arabidopsis seeds with different water contents (WC), namely 3%DW, 10%DW and 30%DW were exposed to cold ambient air plasma (C2AP) generated in a dielectric barrier device (DBD). It is found that increasing WC enhances the capacitive current of the DBD, generates a greater number of low energy streamers (characterized by current peaks lower than 10 mA) that preferentially interplay with the seeds. Since the resistive and capacitive components of the seeds modify the C2AP electrical properties, impedance measurements (also called LCRmetry) have been carried out to measure their main dielectric parameters before/after plasma exposure (seeds resistance, capacitance, complex relative permittivity, tangent loss and conductivity). It appears that WC significantly changes dielectric losses at low frequencies (<1 kHz) due to polarization relaxation of the polar molecules (i.e. water). LCRmetry further reveals that C2AP does not substantially alter seeds dielectric parameters, i.e. it neither adds or removes significant amounts of new materials, meaning that the relative starch, protein and lipid contents remain essentially unaffected. However, it cannot be discounted that some bulk properties of the Arabidopsis seeds may be modified, especially regarding their porosity. This characteristic could facilitate penetration of plasma-generated reactive oxygen species into the internal seed tissues, leading to the grafting of oxygenated groups. To corroborate this theory, water sorption isotherms have been achieved on Arabidopsis seeds and fitted with four thermodynamic models, including the Brunauer–Emmett–Teller model and the Generalized D’Arcy and Watt model. It is demonstrated that C2AP primarily strengthens water-seed affinity by modifying molecular interactions rather than changing the seed’s moisture layer. This occurs despite a potential decrease in the number of adsorption sites, indicating a significant increase in overall seed hydrophilicity after plasma treatment.

Comportamento higroscópico de pós de bacuri

Abstract The objective of this work was to evaluate the hygroscopic behavior and physical properties of powders from bacuri pulp freeze-dried with different drying adjuvants. Three samples were prepared by adding the maltodextrin, gum Arabic, and albumin adjuvants, at a concentration of 20% (w/w), to the pulp. The powders were analyzed for moisture content, hygroscopicity, and particle morphology. The adsorption isotherms were obtained using the models of Brunauer-Emmett-Teller (BET), Guggehneim-Anderson-de Bôer (GAB), Henderson, and Oswin at the temperatures of 25 and 40ºC. Moisture contents ranged from 2.12 to 2.90%, and the lowest value was observed for the powder containing albumin. Hygroscopicity varied from 3.64 to 6.02%, with the lowest value for the powder containing maltodextrin. The powder particles showed non-spherical and irregular shapes, being more agglomerated in the powder with maltodextrin. For the isotherm, the best fit was obtained with the BET model and a type-III behavior was observed, which is typical of foods rich in soluble sugars. Therefore, the adjuvants contribute to the physicochemical properties of the powders, making them less hygroscopic and with irregular-shaped particles.

Synthesis and characterizations of molybdenum-doped titanium dioxide nanoparticles for photocatalytic removal of chromium (VI) from aqueous solutions

The photocatalytic removal of toxic heavy metals using titanium dioxide nanoparticles is an emerging technology for environmental remediation. Pure and Mo-doped TiO2 nanoparticles were synthesized using a modified sol-gel process, and then characterized by field emission scanning electron microscopy (FE-SEM) and particle size analysis (PSA) to determine their morphology and size, while X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) were used to determine their crystalline phase and composition. Brunauer–Emmett–Teller (BET) analysis was used to measure the surface area and porosity of the synthesized catalysts applying Langmuir and BET models. The catalyst was mainly composed of spherical anatase TiO2 particles, with a diameter in the range of 15–75 nm, and the maximum doping percentage of Mo was 3.3%. The Langmuir surface area of pure and Mo-doped TiO2was 91.63 and 128.73 m2/g, and the average pore volume was 0.029 and 0.032 cm3/g, respectively. The nanomaterials were used in the photocatalytic removal of Cr(VI) from aqueous solutions, and the adsorption isotherms indicated that the catalyst uptake (qe,max) amounts for Mo-doped TiO2 and pure TiO2 were 12.5 and 6.5 mg/L, respectively. Moreover, the equilibrium removal percentage was improved from 41% for pure TiO2 to 90% for Mo-doped TiO2, which confirms that photocatalytic activity is enhanced by doping TiO2 with molybdenum.

Low Subcritical CO2 Adsorption-Desorption Behavior of Intact Bituminous Coal Cores Extracted from a Shallow Coal Seam.

This study focuses on improving fundamental understanding of low, subcritical CO2 adsorption-desorption behavior of bituminous coals with the aim to evaluate the utility of shallow-depth coal seams for safe and effective CO2 storage. Comprehensive data and a detailed description of coal-CO2 interactions, e.g., adsorption, desorption, and hysteresis behavior of intact bituminous coals at CO2 pressures <0.5 MPa, are limited. Manometric sorption experiments were performed on coal cores (50 mm dia. and 30- or 60-mm length) obtained from a 30 m deep coal seam located at the Upper Silesian Basin in Poland. Experimental results revealed that the adsorption capacities were correlated to void volume and equilibrium time under low-pressure injection (0.5 MPa). The positive deviation, observed in the hysteresis of adsorption-desorption isotherm patterns, and the increased sample mass at the end of the tests suggested CO2 pore diffusion and condensation. This behavior is vital for assessing low-pressure CO2 injection and storage capabilities of shallow coal seams where confining pressure is much lower than that of the deeper seams. Overall, CO2 adsorption depicts a type II adsorption isotherm and a type H3 hysteresis pattern of the IUPAC classification. Experimental results fitted better to the Brunauer-Emmett-Teller model than the Langmuir isotherm model. CO2 adsorption behavior of intact cores was also evaluated by characteristic curves. It was found that Curve I favored physical forces, i.e., the presence of van der Waals/London dispersion forces to describe the coal-CO2 interactions. However, analysis of Curve II indicated that the changing pressure-volume behavior of CO2 in the adsorbed phase, under low equilibrium pressures, cannot be ignored.

Response surface methodology for modeling the adsorptive uptake of phenol from aqueous solution using adsorbent polyethylene terephthalate microplastics

Optimization modeling and the interpretation of the adsorptive uptake of phenol from aqueous solution using pristine (Pr), modified (Mod-) and aged (Ag-) polyethylene terephthalate microplastics (PET MPs) as adsorbents at optimum conditions have been investigated. The surface morphology and functional groups of the MPs were evaluated using SEM and FTIR-ATR systems, while the surface area of the MPs was estimated using the Brunauer-Emmett Teller (BET) model. Experimentally determined optimization and Response Surface Methodology (RSM) were used to simulate and interpret the adsorption of phenol onto PET MPs, to determine the effects of four adsorption factors (contact-time, initial concentration, pH, and temperature) on the response (removal efficiency) using central composite design (CCD). The results showed that optimum operating conditions for the PET MPs adsorption of phenol from aqueous solution corresponds to contact-time of 77 minutes, 50 mg/L initial concentration, pH of 6, and temperature of 298 K respectively. The maximum removal efficiency of phenol ions under this operating condition was found to be 93.72%, 92.78% and 95.80% for Pr-PET MPs, Mod-PET MPs and Ag-PETMPs respectively. To understand the nature of the PET MPs sorption process, Redlich−Peterson (R-P), Elovich and Dubinin-Radushkevich (D-R) isotherms were employed. The results proved that, D-R model best fitted the PET MPs sorption process at 0.7214 ≤ R2 ≤ 0.9043. Elovich model confirmed the performances of the PET MPs uptake of phenol ions occurred by physical and exothermic processes. Their adsorption capacities followed Pr-PET MPs (0.226 mg/g) > Ag-PET MPs (0.216 mg/g) > Mod-PET MPs (0.126 mg/g) respectively.

Utilization of Iron Oxide Nanoparticles (Hematite) as Adsorbent for Removal of Organic Pollutants in Refinery Wastewater

The increasing of global energy demand leads to the huge amount of wastewaterassociated with refinery processes. Refinery wastewater (RWW) contains significant levels ofcontaminants and are characterized by enormous amounts of refinery effluent. Since the wastes ofrefinery processing is a reason to ecological contaminations, treatment is a vital step for eliminationof these pollutants. This study was designed to determine effect of pH, process time and nano hematitedose in order to eliminate the organics pollutants from the refinery wastewater using adsorptionprocess and MINITAB software. The nano hematite was characterized by Fourier transform infraredspectroscopy and scanning electron microscopy (SEM). The effect of adsorption time, nano adsorbentdose, and pH on the elimination of organic pollutants in the RWW was also investigated. The removalefficiency of organic content was 85.1% at pH 6.5, within time of 150 min, and adsorbent dose was0.9 g. The isotherms data of the adsorption process were determined by the Langmuir, Freundlich,and Brunauer-Emmett-Teller (BET) models. The latter demonstrated the highest adsorption kinetics,which ended up with a constant rate and higher adsorption capacity. These results indicated thatthe use of nano hematite was highly efficient in the removal of RWW organic pollutants withhigh adsorption capacity as determined by BET model

Surface Area Estimation: Replacing the Brunauer-Emmett-Teller Model with the Statistical Thermodynamic Fluctuation Theory.

Surface area estimation using the Brunauer–Emmett–Teller (BET) analysis has been beset by difficulties. The BET model has been applied routinely to systems that break its basic assumptions. Even though unphysical results arising from force-fitting can be eliminated by the consistency criteria, such a practice, in turn, complicates the simplicity of the linearized BET plot. We have derived a general isotherm from the statistical thermodynamic fluctuation theory, leading to facile isotherm fitting because our isotherm is free of the BET assumptions. The reinterpretation of the monolayer capacity and the BET constant has led to a statistical thermodynamic generalization of the BET analysis. The key is Point M, which is defined as the activity at which the sorbate–sorbate excess number at the interface is at its minimum (i.e., the point of strongest sorbate–sorbate exclusion). The straightforwardness of identifying Point M and the ease of fitting by the statistical thermodynamic isotherm have been demonstrated using zeolite 13X and a Portland cement paste. The adsorption at Point M is an alternative for the BET monolayer capacity, making the BET model and its consistency criteria unnecessary. The excess number (i) replaces the BET constant as the measure of knee sharpness and monolayer coverage, (ii) links macroscopic (isotherms) to microscopic (simulation), and (iii) serves as a measure of sorbate–sorbate interaction as a signature of sorption cooperativity in porous materials. Thus, interpretive clarity and ease of analysis have been achieved by a statistical thermodynamic generalization of the BET analysis.

Continuum-Scale Gas Transport Modeling in Organic Nanoporous Media Based on Pore-Scale Density Distributions

SummaryWe present a continuum-scale mass transport model informed by pore-scale density distribution for gas diffusion through organic nanoporous media. A diffusion model and a sorption model are developed by considering multiple transport and storage mechanisms, including bulk diffusion and Knudsen diffusion for free phase, and surface diffusion and multilayer adsorption for sorbed phase. The continuum-scale diffusion equation is derived based on the free-phase concentration for the overall mass conservation of free and sorbed phases, carrying a newly defined effective diffusion coefficient and capacity factor to account for multilayer adsorption. Diffusion in free and sorbed phases is coupled with the sorption model, which provides pore-scale multilayer adsorption properties by utilizing a pore-scale simplified local density (SLD) method combined with the modified Peng-Robinson equation of state (PR-EOS) for confinement effect. The model was first implemented to analyze adsorption data from a krypton (Kr) adsorption experiment on graphite. Then, we applied the developed diffusion model to conduct the sensitivity analysis of the effects of pore size on gas transport for Kr-graphite and methane-coal systems. The model was finally used to study Kr diffusion profiles through a coal matrix obtained by using X-ray micro-computed tomography (microCT) imaging. The results show that the sorbed phase occupies most of the pore space in organic nanopores with less than 10 nm due to multilayer adsorption, and surface diffusion contributes significantly to the total mass flux. Therefore, neglecting the volume of sorbed phase and surface diffusion in organic nanoporous rocks may result in considerable errors in the prediction of hydrocarbon production. We also compared Brunauer-Emmett-Teller (BET) and Langmuir models by analyzing adsorption data for the wide pressure range up to the saturation pressure. The comparison between BET and Langmuir models shows that the Langmuir model can only match the adsorption isotherm at low pressure and yield lower effective surface diffusion coefficients. Therefore, implementing a Langmuir model may be erroneous for organic nanoporous media with strong adsorption capacity, particularly when pore pressure is high.

PRELIMINARY EVALUATION OF COLOR STABILITY OF DATE FRUIT TABLETS

This paper reports on preliminary qualitative evaluation of relationship between color change and water activity (aw) of date (Phoenix dactylifera L., var. Mech-Degla) fruit tablets (DFTs) as natural supplement, in view to optimize their storage conditions. Eight types of DFTs were obtained, according to: i) mean particle size (225 and 282 μm) of the used fruit powder, and ii) compression pressure (5, 10, 15 and 20 kN) applied during the tableting process. The experimental adsorption curves, determined at 25°C using static-gravimetric method, were fitted to GAB (Guggenheim–Anderson–de Boer) and BET (Brunauer–Emmett–Teller) models. Results showed that the DFT color is significantly sensitive to aw since beyond the aw threshold value of 0.44, the DFT color changes from light grey to dark brown, independently of the particle size of fruit powder and compression pressure. Concerning the isotherm modeling, the both models tested seem especially suitable (R≈0,96 0.3≤MRE≤5 and SE≈0.03) for describing the experimental data for DFT obtained under a compression pressure of 5 kN from date fruit powder with mean particle size of 225 μm. The DFT color stability is considerably influenced by the environmental humidity. Considering the importance of color for consumer acceptance, the study deserves to be deepened concerning the quantitative analysis of the color (CIELab system), packaging of the tablets, etc.

Water Uptake as a Crucial Factor on the Properties of Cryogels of Gelatine Cross-Linked by Dextran Dialdehyde.

We investigated the water sorption properties of macroporous cryogels of gelatine (Gel) and dextran dialdehyde (DDA) prepared via cryogelation at 260 K and following the freeze drying processes. Water vapour sorption isotherms for aerogels were studied at 293 K by two independent methods: static-gravimetric and dynamic vapour sorption (DVS) over a water activity range of 0.11–1.0. Experimental data were fitted by use of the Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–de Boer (GAB) models. The BET model (for a water activity range of 0.1 ≤ p/po ≤ 0.5) was used to calculate the sorption parameters of the studied cryogels (the monolayer capacity, surface area and energy of interaction). In comparison with BET, the GAB model can be applied for the whole range of water activities (0.1 ≤ p/po ≤ 0.95). This model gave an almost perfect correlation between the experimental and calculated sorption isotherms using nonlinear least squares fitting (NLSF). Confocal Laser Scanning Microscopy (CLSM) was used to confirm the structural differences between various DDA:Gel cryogel compositions. Thermogravimetric analysis and DSC data for aerogels DDA:Gel provided information regarding the bonded water loss, relative remaining water content of the material and the temperature of decomposition. Estimation of the amount of bound water in the cryogels after the freeze drying process as well as after the cycle of treatment of cryogels with high humidity and drying was performed using DSC. The results of the DSC determinations showed that cryogels with higher gelatin content had higher levels of bonded water.

Adsorption Characteristics of CH4 and CO2 in Shale at High Pressure and Temperature.

This work presents the adsorption behavior and appearance characteristics of CH4 and CO2 on the Longmaxi shale at high pressure and temperature. To investigate the variation of gas adsorption patterns under the constraint of pressure and temperature, the applicability of the theories of monolayer adsorption, multilayer adsorption, and micropore filling was discussed. The preferential selection coefficient of CO2 for CH4 under different conditions was characterized by the absolute adsorption capacity (Vabs) ratio of CO2 to CH4 (αCO2/CH4). Moreover, the implication of the CO2 injection to enhance gas recovery and the CO2 capture and storage (EGR–CCS) process was analyzed. The results exhibit that the excess adsorption curves of CH4 are smooth, and the experimental temperature has no noticeable effect on the shape of curves. At the same time, a “sharp peak” is recorded in the excess adsorption curves of CO2 at low temperatures (30 and 55 °C) near the critical pressure, which is quite distinct from the smooth curves at high temperatures (80 and 100 °C). Correspondingly, there are two “jump pressure” values in the density curves (30 and 55 °C) of the adsorption system and the density curves are divided into three stages. The Dubinin–Astakhov and Brunauer–Emmett–Teller (BET) models show an optimum degree of fit for CH4 and CO2 adsorption curves under all experimental temperature and pressure conditions. The Langmuir model fits the adsorption curves of 80 and 100 °C better, while the BET model is appropriate for 30 and 55 °C. The adsorption affinity of CO2 is higher than CH4, with the value of αCO2/CH4 in the range of 2.47–12.16. The value of αCO2/CH4 increases with a rise in pressure but is inhibited by high temperatures, while the inhibition is negligible when the experimental temperature exceeds 80 °C. The adsorption preferential of CO2 is stronger in the shallow reservoir (αCO2/CH4 > 10.5), and the application prospect of the EGR process is promising. In contrast, the adsorption preferential is slightly weakened in the deep reservoir (αCO2/CH4 < 4.5), which can be considered for CO2 capture, utilization, and storage. Results from this investigation provide novel insights on the adsorption characteristics of CH4 and CO2 on the shale matrix at high pressure and temperature. They are also expected to give certain enlightenment for the EGR–CCS process.

The Study of Sorption Characteristics of Dried Crab Stick Product Using Dynamic Vapor Sorption

The research delved into the sorption characteristics of dried crab stick products using dynamic vapor sorption (DVS). The obtained sorption isotherm data, including equilibrium moisture content (Me) and water activity (aw), were fitted with 6 different sorption isotherm models, such as Brunauer-Emmett-Teller (BET), Guggenheim-Anderson-Boer (GAB), Pickett-Modified BET, Adam and Shove, Blahovec-Yanniotis, and Peleg. The results showed that the Peleg model was the best-describing model with a coefficient of determination (R2), chi-square (χ2), root mean square error (RMSE), and standard error of estimate (SEE) ranging from 0.988 to 0.998, 0.719 to 4.349, 0.431 to 2.609 and 0.692 to 1.703, respectively. According to the classification of the shape of moisture sorption isotherm, the isotherm type III and II were found in this research for adsorption and desorption, respectively. The GAB and BET models were used to estimate monolayer moisture content (M0) of the sample and it was found that the M0 ranged from 3.65 to 5.36 % dry basis and 4.57 to 4.83 % dry basis for GAB and BET models, respectively. Blahovec-Yanniotis’s model was applied in this work to investigate the contribution of water and the result showed that the contribution of solution water played a major in the moisture changes of the sample during the adsorption and desorption process. Moreover, sorption isotherm data were modeled with 0 and 1st order reaction kinetics, and the results demonstrated that 0 order and 1st order models were the most appropriate model to describe moisture changes behavior of the sample at each relative humidity step for adsorption and desorption, respectively.&#x0D; HIGHLIGHTS&#x0D; &#x0D; The construction of sorption isotherms of dried crab stick product using dynamic vapor sorption&#x0D; GAB and BET models were used to estimate monolayer moisture content&#x0D; Peleg model was the most appropriate model to describe sorption behaviors of dried crab stick product&#x0D; Blahovec-Yanniotis provided the contribution of water information of dried crab stick during adsorption and desorption processes&#x0D; The application of reaction order kinetics could provide the information of moisture changing behaviors at each relative humidity step for adsorption and desorption processes&#x0D; &#x0D; GRAPHICAL ABSTRACT

Sorption: A Statistical Thermodynamic Fluctuation Theory.

Can the sorption mechanism be proven by fitting an isotherm model to an experiment? Such a question arises because (i) multiple isotherm models, with different assumptions on sorption mechanisms, often fit an experimental isotherm equally well, (ii) some isotherm models [such as Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–de Boer (GAB)] fit experimental isotherms that do not satisfy the underlying assumptions of the model, and (iii) some isotherms (such as Oswin and Peleg) are empirical equations that do not have a well-defined basis on sorption mechanisms. To overcome these difficulties, we propose a universal route of elucidating the sorption mechanism directly from an experimental isotherm, without an isotherm model, based on the statistical thermodynamic fluctuation theory. We have shown that how sorbate–sorbate interaction depends on activity is the key to understanding the sorption mechanism. Without assuming adsorption sites and planar layers, an isotherm can be derived, which contains the Langmuir, BET, and GAB models as its special cases. We have constructed a universal approach applicable to adsorption and absorption, solid and liquid sorbents, and vapor and liquid sorbates and demonstrated its efficacy using the humidity sorption isotherm of sucrose from both the solid and liquid sides.

Porous nanocomposites by cotton-derived carbon/NiO with high performance for lithium-ion storage

Biomass materials have attracted extensive attention in functional composites because of the unique microstructure, renewability and electrochemical performance. Herein, porous NiO/C composites were synthesized through a hydrothermal reaction and calcination using cellulose-rich natural cotton as carbon source. The BET specific surface area of NiO/C composites was calculated to be 314.4 m2 g−1 basing on the Brunauer–Emmett–Teller model. As the LIB anode, NiO/C composites presented a high specific capacity of 727 mA h g−1 over 150 cycles at 100 mA g−1. Increasing the current density to 2 A g−1, enabled the specific capacity of NiO/C the electrode to reach 476 mA h g−1. Obviously, the unique nanostructure and synergistic effect of NiO and carbonaceous matrix made NiO/C composites exhibit the excellent lithium storage performance. The NiO/C composites are interconnected with each other and form nanopores leading to the large specific surface area, enabling the enhancement of electrolyte diffusion and providing additional routes for ion diffusion. In addition, the hybridized carbon substrate can mitigate the volume expansion and external bending stress of NiO/C composites during the lithiation/delithiation process.

The Brunauer–Emmett–Teller model on alumino-silicate mesoporous materials. How far is it from the true surface area?

Determining the surface area of porous materials through the Brunauer–Emmett–Teller (BET) model is a common practice. The method is generally applied in commercial software packages, where the assumptions are sometimes accepted by the experimenter whilst they may sometimes require a deeper analysis. One element of debate is the molecular cross-sectional area of the adsorptive. There is not yet agreement about the correctness of the BET model using a certain value for cross-sectional area of N2; the conventionally-used parameter seems to overestimate the surface areas. In this work, a preliminary study of a modified method is presented, which introduces an ‘apparent’ cross-sectional area for N2, which is smaller to the typically-used value. This value was obtained after measuring a number of relevant mesoporous materials in N2 and Ar, using a model that considers an apparent value for the cross-sectional area. The model predicts outcomes very close to the Ar-based measurements in terms of low relative error. Then, we went one step further and looked into the geometrical surface areas, also referred to as true surface areas. By combining prior studies with our work, it was found that the surface area, using N2 and the conventionally-used cross section, can be ca. 50% higher than the geometrical surface area. Therefore, the significance of the BET surface area seems to be far from well understood, though it is widely applied. This approach also allowed to define an ‘effective’ cross section for N2, that relates it to the geometrical surface area. Its value agrees with prior considerations for an epitaxial orientation of the N2 molecule with a hydroxylated silica surface. As a final recommendation, critical thinking is needed about the default settings in standardised calculations, which may not represent a reliable measure of the true surface area.

Hyphenated study on drying kinetics and ascorbic acid degradation of guava (Psidium guajava L.) fruit

AbstractIn this study, insights into the effect of process parameters (temperature: 55, 60 and 65°C; thickness: 3, 5, and 8 mm; time: up to 5 hr) on drying (mechanical, solar) kinetics and sorption behavior of guava fruits (variety: local and hybrid) with a focus on the degradation of ascorbic acid (AA) were established for the first time to the best of existing knowledge. The experimental results showed the highest moisture diffusion coefficient and lower activation energy (Ea) of 0.000326 cm2/s and 9.62 kcal/g.mole, respectively for hybrid mature guava variety; whereas, the highest AA degradation rate (0.107 mg AA/hr) with lower Ea (4.3 kcal/g.mole) was obtained for local mature guava variety. Besides, a mixed‐mode solar dryer assisted with a fan seemed to be efficient for drying guava fruit in comparison to drying under direct sunlight. In terms of sorption behavior, both local and hybrid guava followed sigmoidal (type II) shape isotherm where the experimental data were well fitted with Brunauer–Emmett–Teller (BET) model.Practical applicationThe drying conditions to have dried guava (Psidium guajava L.) fruit with high ascorbic acid (AA) were investigated. The mathematical model was successfully applied to describe the drying kinetics and degradation of AA of guava fruit. Process parameters and methods influencing drying kinetics and AA degradation rate were detailed. BET model fits well to describe the sorption isotherms of dried guava fruit, in understanding its storage behavior. The information of this study would help in the drying process optimization of guava fruit, in order to make them available in the off‐seasons.

Applicability Analysis of Determination Models for Nanopores in Coal Using Low-Pressure CO₂ and N₂ Adsorption Methods.

The development characteristics of nanopores (with pore sizes <200 nm) in coal are a key factor affecting the accumulation and migration of coalbed methane (CBM). Thus, an appropriate determination method and calculation model are essential for accurate nanopore representation. Based on the experiments of low-pressure CO₂ adsorption (LP-CO₂GA) at 273 K and low-pressure N₂ adsorption (LP-N₂GA) at 77 K on four coals with different ranks, the abilities of different models (e.g., Langmuir, Dubinin-Radushkevich (D-R), Dubinin-Astakhov (D-A), Brunauer-Emmett-Teller (BET) and nonlocal density functional theory (NLDFT)) to accurately predict the pore parameters were analyzed. The results showed that (1) for LP-N₂GA, the Langmuir model is only suitable for gas adsorptions at low relative pressure conditions (P/P0 < 0.01), and its error value increased with the relative adsorption pressure. The fitting results of the D-R model showed good agreement with the D-A model under low relative pressure of LP-CO₂GA (P/P0 < 0.01), and the D-A model had more accurate fitting results. The BET model is more accurate than the other models (φ = -1.2733%) only in the interval of LP-N₂GA with 0.05 < P/P0 < 0.35. The data also showed that the NLDFT model can maintain a higher fitting accuracy for LPCO₂/N₂GA processes at relative adsorption pressures from 0.001-0.9996. (2) Using LP-CO₂GA with the Langmuir, D-R, D-A, and NLDFT models, the micropore specific surface area (SSA; 66.9570-248.6736 m²/g) and pore volume (0.0201- 0.0997 cm³/g) were obtained, while the values of meso-/macropore SSA (0.0007-2.3398 m²/g) and pore volume (0.0036-0.04 cm³/g) were calculated by LP-N₂GA with the BET and NLDFT models. The results showed that the fitting accuracy in descending order was the D-R, D-A, Langmuir and NLDFT models. (3) In combination with the applicable model range, LP-CO₂GA with the NLDFT model was recommended for micropore analysis of the coal pore sizes from 0.36-1.1 nm, while LP-N₂GA combined with the NLDFT model was recommended for nanopore analysis of pore sizes from 1.1-200 nm. (4) The characteristics of pore development in the Beiloutian coal were analyzed using LP-CO₂/N₂GA combined with the NLDFT model. It was found that a pore volume and SSA less than 1.0 nm accounted for 88.82% of the total pore volume and 98.05% of the total SSA, indicating that micropores in coal are the main space for CBM storage and are key physical factors for the occurrence and migration of coalbed methane. The conclusions of this article will provide a basis for the accurate calculation of nanopores in coal.

N-Layer BET adsorption isotherm modeling for multimeric Protein A ligand and its lifetime determination

Langmuir and other single-layer adsorption isotherms show the binding behavior of natural Protein A ligands immobilized on a column. However, no models have been shown in literature to explain the adsorption phenomena on the recombinant high binding capacity Protein A resins. This study has characterized the Protein A binding domain distribution across the ligand with multi-layer adsorption isotherms for a recombinant Protein A resin. The adsorption data was analyzed using the Langmuir, Freundlich, Brunauer–Emmett–Teller (BET) and various other mathematical equations. The best fit of experimental data was obtained with n-layer BET model wherein the isotherms of Protein A exhibited Type IV behavior according to BET classification. Furthermore, the binding capacity was studied throughout the shelf life using the multi-layer adsorption isotherm model. Antibody adsorption isotherms of Protein A resin were obtained at preset duration of caustic incubation. The experiments were carried out for two conditions of sanitization agent, namely, caustic and caustic with salt. Static and dynamic isotherm analysis showed that a new resin had a lower binding capacity and the initial sanitization improved the binding capacity, probably by making the binding domains more accessible. The binding capacity at equilibrium, dynamic breakthrough and batch were also evaluated and reported in this paper. The study modeled the multimeric Protein A ligand and established the requirement of optimization for cleaning regime. This study provides a fundamental understanding of the binding patterns in the recombinant Protein A ligands through a working mathematical equation and improves the current knowledge of Protein A resin lifetimes.