Adsorption Temperature Research Articles

Preparation and adsorption properties of magnetic chitosan/sludge biochar composites for removal of Cu2+ ions

The magnetic chitosan/sludge biochar composite adsorbent was prepared using chitosan, Fe3O4, and sludge biochar as raw materials. The composite adsorbent was able to achieve rapid solid–liquid separation under an applied magnetic field. The morphology and microstructure of the composite adsorbent were characterized by FTIR, XRD, SEM, VSM, and BET analysis. The adsorption performance of the composite adsorbent on Cu2+ was investigated through static adsorption experiments, and the effects of adsorbent dosage, initial concentration of Cu2+, initial pH of the solution, and adsorption temperature on the adsorption efficiency of Cu2+ were discussed. The results showed that chitosan and Fe3O4 were successfully loaded on sludge biochar. When the initial concentration of Cu2+ was 30 mg/L, the dosage of the magnetic chitosan/sludge biochar composite material was 0.05 g, the adsorption time was 180 min, pH was 5, and the temperature was room temperature, the maximum removal rate of Cu2+ reached 99.77%, and the maximum adsorption capacity was 55.16 mg/g. The adsorption kinetics and adsorption isotherm data fitted well with the pseudo-second-order kinetic model and Langmuir adsorption isotherm model, indicating that the adsorption process was chemisorption with monolayer coverage.

Effect of natural organic residues on the adsorption capacity of layered silicate alumina clay

ABSTRACT Layered silicate clay can be modified with organic residues to enhance its adsorption properties and make it suitable for the removal of industrial hazardous substances in various industries. The modification process involves treating the clay with specific organic residues that can interact with and capture the targeted hazardous compounds effectively. Novel nano-composite adsorbing system was developed by inserting the products of powdered certain marine plant within the layers of layered silicate alumina clay (LS) through impregnation technique in order to form layered silicate alumina organic residue (LSOR). The SEM images showed clear agglomerations within the newly formed composite. Moreover, according to data obtained from Scherer equation extracted from XRD data all compounds under investigation were within the nanoscale. The newly prepared LSOR nano-composite showed a significant high adsorption capacity than the main reactants involved in the adsorbent formation process (LS and OR). The effects of various experimental factors were followed up using batch system, and kinetics and isotherms of CR dye adsorption were calculated accordingly. Adsorbent dosage, working temperature, and pH value all have a significant impact on CR removal percentage. Regarding the optimum conditions, the best temperature for CR adsorption onto LSOR is 40°C at a neutral pH medium. Adsorption isotherm study shows that the adsorption process could be followed up using Langmuir adsorption isotherm for OR while it follows Freundlich isotherm for LS adsorbent and can be followed up successfully by Temkin isotherm model in case of LSOR. Finally, field tests revealed that the LSOR nano-catalyst removed mixed dyes from industrial wastewater with a 93% performance. This outcome further solidifies the potential of LSOR nano-adsorbents as an eco-friendly solution for the treatment and reuse of industrial wastewater. It highlights the significant contribution of these new nano-adsorbents in promoting sustainable practices and addressing the challenges associated with industrial wastewater management.

Optimized hydrogen purification for fuel cell quality from quinary coke oven gas via layered pressure swing adsorption under non-isothermal conditions

Coke oven gas from steel industries offers a valuable hydrogen rich fuel but is accompanied by impurities, such as CH4 and CO2, that contribute to the environmental footprint. The process of extracting H2 from coke oven gas not only provides clean energy from the alternative source, but also prevents the release of these impurities. Motivated by the promising H2 source alternative, a 2-bed, 6-step pressure swing adsorption system operating under non-isothermal conditions was used to purify H2 from coke oven gas. A validated multi-component adsorption model was developed via Aspen Adsorption to simulate and optimize the process. The validated model revealed strong correlations between the factors (adsorption pressure, adsorption temperature, adsorption time, and H2 concentration) and responses (purity and recovery of H2). The findings indicated that increasing the H2 feed concentration resulted in an improvement in H2 purity but a decline in recovery. Conversely, an extended duration of adsorption exhibited an adverse influence on both the purity and recovery of H2. Furthermore, the study indicates that higher adsorption pressure and temperature were correlated with lower H2 purity but improved recovery performance. To optimize the pressure swing adsorption process, the desirability function was applied within the response surface methodology model, enabling the determination of optimal conditions for the purification process. The optimized H2 purity and recovery were found to be 99.995% and 62.758%, respectively, at H2 feed concentration of 49%, adsorption time of 160 s, pressure of 6 atm, and adsorption temperature of 293 K.

Synthesis of Carboxymethylcellulose–Acrylamide–Montmorillonite Composite Hydrogels for Wastewater Purification

The three-dimensional network and ample pore structure of novel hydrogel materials enable outstanding adsorption performance for pollutants such as methylene blue (MB) and Cr6+ ions in wastewater. In order to develop an environmentally friendly hydrogel with high adsorption performance and low cost, a type of carboxymethyl cellulose (CMC) composite hydrogel was synthesised with montmorillonite (MMT) via chain radical polymerization, which gives it great potential for application in the field of wastewater purification. A series of hydrogel samples were characterised through SEM, FTIR and nitrogen porosimetry analysis, indicating the successful intercalation of MMT nanosheets into the hydrogel crosslinking network. The mass ratio of CMC to MMT, the amounts of adsorbent, the initial concentration of wastes, pH, and the adsorption temperature were investigated and optimised for hydrogel adsorption performance. When the initial concentration of MB is 60 mg/L, pH is 7, the dosage of MB is 0.5 g/L, and the adsorption temperature is 30 °C, the hydrogel sample the highest adsorption capability for MB removal, with an adsorption amount of 112.9 mg/g. When the initial concentration of Cr6+ is 10 mg/L with a pH of 7, the highest adsorption capacity of the hydrogel for Cr6+ removal is 1.35 mg/g. The fitting results of the isothermal models, the kinetic models, internal particle diffusion models and the thermodynamics of the experimental data of the adsorbate adsorption process show that the adsorption of MB by hydrogel is a spontaneous segmented process of multi-layer physical and chemical adsorption. Additionally, the adsorption of Cr6+ ions by hydrogel is a spontaneous segmented process of multi-layer physical adsorption.

Sorptive removal of cadmium using the attapulgite modified by the combination of calcination and iron.

Sorptive removal of cadmium (Cd) from the aqueous solutions using the easily available natural materials is an attractive method. However, the adsorption efficiencies of these materials, such as clays, are typically low. Besides, they are generally in relatively low stability and renewability, which restrict their application. Thus, modification of these materials to enhance their performance on Cd removal has gained growing attentions. Herein, the integration of calcination and ferric chloride (FeCl3) was used to modify a typical clay, i.e., attapulgite, to increase the adsorption sites, and thus to develop a robust adsorbent for Cd. Under the optimum conditions for attapulgite modification (i.e., the mass ratio of FeCl3 to attapulgite was 1:2, calcination temperature was 350 °C, and calcination time was 1.5 h) and Cd adsorption (i.e., initial pH of 6.0, adsorption temperature of 25 °C, and adsorbent dosage of 1.0 g/L), the maximum adsorption capacity of the modified attapulgite toward Cd was 149.9 mg/g. Mechanisms of surface complexation and electrostatic attraction were involved in the efficient removal of Cd. The adsorption of Cd increased with pH due to the increased electrostatic attraction. Metal cations inhibited the Cd adsorption through competing with the adsorption sites. The changes of Gibbs-free energy during the adsorption of Cd were lower than zero and decreased with temperature, suggesting the process was spontaneous and endothermic. The removal efficiency of Cd after 5 times of recycle maintained at 82% of that of the raw modified attapulgite demonstrated the stability of the adsorbent. These results suggested that the modified attapulgite is robust for Cd removal and is promising for land application.

Preparation of modified zeolite/chitosan composites and study on the adsorption performance of Pb2+

AbstractAs one of the most common pollutants in wastewater, heavy metals seriously threaten human health and survival, and among the current removal methods, the adsorption method has attracted the most attention because of its simple and safe operation. Zeolite is a substance with a unique spatial structure, cheap cost, and environmental friendliness. Zeolite is a substance with a unique spatial structure, cheap cost, and environmental friendliness. Due to its size and high surface area‐to‐volume ratio, zeolite exhibits excellent adsorption and ion exchange properties and is a promising adsorbent. In this paper, the modified zeolite chitosan composite film was prepared by solution method by dissolving chitosan in acetic acid solution as the solvent, and the effects of zeolite content, modifier type, initial pH, pore‐making agent, adsorption time, adsorption temperature, initial concentration, and feeding amount were studied. The optimal conditions for Pb2+ adsorption were 40% modified zeolite content, 293 K in 100 mg/L solution, a feeding amount of 1 g/L, pH = 5.5, and a removal rate of 96.6% in 24 h. The isotherm is consistent with the Langmuir adsorption model, which is manifested as single‐molecule chemical adsorption, and the highest saturated adsorption capacity is 139.6 mg/g. After five cycles, it still has a greater than 90% initial adsorption effect.Highlights Chitosan‐modified zeolite composite membranes are inexpensive. After adsorption, the sorbent is easy to recover.

In-depth descriptive investigation of composite sorbent based self-assembled magnetic halloysite nanotube-graphene oxide: Actual use case study for rutin

In this study, a three-dimensional nanocomposite with magnetic features made of magnetic iron oxide nanoparticles (Fe3O4), graphene oxide (GO) and halloysite nanotube (Hal) was prepared and introduced for rutin separation from real sample based on magnetic solid phase extraction (MSPE) process. Hal was modified with chitosan (Hal-COS) and showed positive charge, which can combine with GO by electrostatic force self-assembly to fabricate Hal-GO. Based on this, in-situ growth of magnetic sphere on the surface of Hal-GO demonstrated high specific surface area, chemical and thermal stability, water solubility, and capacity of easy separation in aqueous solution. Several characterizations including FT-IR, HRTEM, TGA and XRD evidenced the successful synthesis of the nanocomposite. The results showed that the optimum adsorption pH was 6 and the optimum adsorption temperature was 25 °C. In addition, further experiments showed that the adsorption process conformed to the Langmuir adsorption model and pseudo-second-order kinetic model, which indicated that the maximum equilibrium adsorption capacity was 107.8 mg g−1 and the maximum equilibrium adsorption time was 120 min. With the optimized conditions, the methodological validation experiments showed that the linear range of MSPE based on Fe3O4@(Hal-GO) combined with HPLC was 10–100 μg mL−1, the correlation coefficient of the fitting equation was 0.9991, the LOD and LOQ reached 0.87 μg mL−1 and 2.9 μg mL−1 respectively. It was confirmed that prepared Fe3O4@(Hal-GO) supported efficient enrichment of rutin when the results were compared to those of other studies.

Plasma-assisted synthesis of nano-sulfur adsorbent for efficient removal of mercury from flue gas

Adsorbents injection technology is one of the most promising strategies to control mercury emission from flue gas. However, existing literature has shown leaching risk of mercury and halogen from commercial halogen impregnated adsorbents. Therefore, we proposed a novel and convenient fabrication method for nano-sulfur adsorbent assisted with nonthermal plasma technology in order to address these issues. The morphology, number concentration and size distribution of as-obtained nano-sulfur particles was determined by High Resolution Transmission Electron Microscopy (HRTEM) and Scanning Mobility Particle Sizer (SMPS). The mercury adsorption experiments showed nano-sulfur adsorbent (removal efficiency: 88.2 %) was more effective than micron-sized elemental sulfur (less than 10 %). Furthermore, the chemical composition of elemental sulfur allotropes (S6, S7 and S8) was determined using High-performance Liquid Chromatography-Mass Spectrometry (HPLC-MS). It was found that nano-sulfur particles contained higher proportions of S6 (1.53 %) and S7 (1.29 %) allotropes, which are the active materials in elemental sulfur. To investigate the effects of adsorption temperature and simulated flue gas on the performance of nano-sulfur adsorbent, the optimal adsorption temperature of 110 °C was determined, indicating its suitability for coal-fired power plants equipped with a low-temperature electrostatic precipitator system. Additionally, it was observed that simulated flue gas had slight inhibitory effects on the adsorbent performance, with a reduction of approximately 5 % in Hg0 removal efficiency. In summary, this research proposed a novel method for synthesizing nano-sulfur adsorbent and revealed the differences in sulfur allotropes' reactions with mercury, thereby deepening our understanding of the mercury-sulfur reaction mechanism.

Experimental investigation and thermodynamic modeling of adsorption equilibria of MSC30 with R32 for supercritical adsorption cooling systems

In the present study, the adsorption isotherms of difluoromethane (R32) on the activated carbon (MSC 30) throughout a temperature range of 25 °C to 150 °C and pressures up to 3000 kPa are measured for possible application in adsorption cooling systems. The Dubinin-Astakhov model was used to fit the experimental data. A thermodynamic model is proposed in this study to investigate the adsorption potential under supercritical conditions. The model is validated using the isotherm data from the experiments and literatures for different working pairs. The validation results exhibited a good agreement between the proposed model and the experimental data, signifying the precision and dependability of the model. The corresponding adsorption isosteric heat model was derived and verified, taking into account both the inclusion and exclusion of the adsorbed volume correction. Furthermore, the developed models were utilized in the equilibrium analysis of an adsorption heat pump to evaluate the performance of the system in terms of the theoretical coefficient of performance (COP) and specific cooling energy (SCE). The analysis covered the driving heat source temperature ranging from 30 °C to 150 °C, with different evaporation temperatures and adsorption temperatures. The results showed that the maximum COP value of 0.47 for the adsorption heat pump system employing the MSC30+R32 pair was achieved at a desorption temperature of 115 °C, at which the SCE was 315.5 kJ·kg−1. The results can potentially improve the accuracy of predicting adsorption behavior and contribute to the development of more efficient and effective adsorption systems.

Efficient adsorption of CO2 by amino-functionalized short pore SBA-15: Influence of pore length on adsorption capacity and amino efficiency

Amino-functionalized SBA-15 (AS) with different pore lengths (short pore: 300 nm, SAS and long pore: several tens μm, LAS) were synthesized and applied for CO2 adsorption. The adsorption capacity and amino efficiency affected by pore length, temperature and amino-functionalization were systematically investigated. It was found that CO2 adsorption behavior strongly depended on the pore length, amino-functionalization and adsorption temperature. With decreasing pore length, the adsorption capacity and amino efficiency increased. The amino efficiency increased and the adsorption capacity decreased with increasing temperature. The obtained SAS with short pore exhibited the highest adsorption capacity (1.58, 1.26 and 0.96 mmol CO2/g) and amino efficiency (0.07, 0.19 and 0.27 mol CO2/mol N) under 273, 298 and 323 K at 1 bar, respectively, owing to the high utilization of internal pores. Furthermore, the obtained adsorbents showed good temperature adaptability and reusability. The results demonstrated the potential of the obtained adsorbents for CO2 adsorption.

Defective UiO-66 metal–organic gels for optimizing gaseous toluene capture

Developing high-performance sorbents for volatile organic compounds (VOCs) is urgently required for environmental cleaning and personnel protection. Zirconium-based metal–organic frameworks (Zr-MOFs) have been deemed attractive candidates for gaseous toluene capture due to their superior stability and high adsorption capacity. However, the practical application of powdered Zr-MOFs is hindered by inherent limitations. Here, we report a series of defective UiO-66 metal–organic gels (G66-X) with variable missing linker deficiency by altering the modulator concentration. The defect concentration of the adsorbents has a significant impact on the porosity and gaseous toluene adsorption capacity. Dynamic breakthrough results reveal that G66-9 demonstrates optimal breakthrough time of 336 min/g and uptake amount of 334 mg/g, outperforming those of many other typical toluene adsorbents. The breakthrough times and the uptake capacities dramatically decrease with the increase of adsorption temperature. An outstanding regeneration performance of adsorbents can almost maintain even after five adsorption–desorption cycles.

Adsorption performance and mechanism of Li+ from brines using lithium/aluminum layered double hydroxides-SiO2 bauxite composite adsorbents

A combined method of solid-phase alkali activation and surface precipitation was used to prepare the lithium/aluminum layered double hydroxides-SiO2 loaded bauxite (LDH-Si-BX) and applied to adsorb Li+ in brines. In the study, various characterization techniques such as SEM, XRD, BET, Zeta potential, and x-ray photoelectron spectroscopy (XPS) were applied to characterize and analyze the adsorbents. The adsorption-desorption performance of LDH-Si-BX for Li+ in brines was systematically investigated, including adsorption temperature, adsorption time, Li+ concentration, and regeneration properties. The results indicated that the adsorption kinetics were better fitted by the pseudo-second-order model, whereas the Langmuir model could match the adsorption isotherm data and the maximum Li+ capacity of 1.70 mg/g at 298K. In addition, in the presence of coexisting ions (Na+, K+, Ca2+, and Mg2+), LDH-Si-BX showed good selective adsorption of Li+, and the pH studies demonstrated that the adsorbents had better Li+ adsorption capacity in neutral environments. In the adsorption process of real brines, LDH-Si-BX had a relatively stable adsorption capacity, and after 10 cycles of adsorption and regeneration, the adsorption capacity decreased by 16.8%. It could be seen that the LDH-Si-BX adsorbents prepared in this report have the potential for Li+ adsorption in brines.

Carrageenan-grafted-poly(acrylamide) magnetic nanocomposite modified with graphene oxide for ciprofloxacin removal from polluted water

The κ-carrageenan-grafted-poly(acrylamide)/Fe3O4-GO (κ-car-g-PAAm@Fe3O4-GO) adsorbent was attained in three stages, utilizing grafted poly(acrylamide) (PAAm) onto κ-carrageenan (κ-car) in Fe3O4 and graphene oxide (GO) presence. Various characteristic analyses were carried out to peruse the chemical properties, morphological features, thermal stability, magnetic behavior, and porosity of the prepared nanoadsorbent. According to the results obtained from the analyses, the prepared nanoadsorbent showed superparamagnetic behavior. It rendered a semicrystalline structure by Fe3O4 presence in the amorphous matrix of the κ-car-g-PAAm. The SEM images exhibit well dispersion of the Fe3O4 magnetic nanoparticles (MNPs) and lamellar GO sheets throughout the hydrogel context. Besides, along with the GO incorporation into the structure, the BET surface area (2.361 m2/g), pore volume (0.008 cm3/g), and pore size (137.49 nm) of the κ-car-g-PAAm@Fe3O4-GO nanoadsorbent were higher than κ-car-g-PAAm@Fe3O4. The maximum adsorption capacity (Qmax) at an ambient temperature for CPFX adsorption was 1146.467 mg/g. These adsorption experiments’ data were described by the Freundlich isotherm, and the pseudo-second-order explains the adsorption kinetics well. The retrievability of the prepared nanoadsorbent was studied and indicated that it could be isolated effectively and reused in three consecutive cycles without remarkable adsorption efficiency loss.

Surface oxidation modification of nitrogen doping biochar for enhancing CO2 adsorption

The purpose of this paper is to demonstrate a surface oxidation modification strategy of nitrogen doping biochar for enhancing CO2 adsorption. The porous structure and surface group distribution of nitrogen doping biochars before and after modification (remarked as TF and OTFs) were characterized. Then the thermodynamic and kinetic characteristics of CO2 adsorption such as adsorption capacity, selectivity and activation energy were systematically investigated. The results indicated that the modified biochars OTFs exhibited high adsorption capacity of CO2 between 5 and 8 mmol·g-1 at 100 kPa and 273 K. The oxidation modification affected CO2 adsorption behaviors by the ways of adjusting surface pore size and surface group distributions. The former decreased the mass transfer diffusion resistance of CO2 from gas phase to biochar surface by transforming some micropores to the mesopores. And the later improved the adsorption selectivity of CO2 to the other gases such as N2 based on the interaction difference enhancement by those oxygen-containing (OFGs) and nitrogen-containing functional groups (NFGs). When the molar ratios of CO2/N2 in gas mixture were 1:1 and 15:85, the modified biochar OTF-10 exhibited the better selectivity, and the maximum selectivities of CO2 to N2 at 273 K were 44.7 and 69.4, respectively. Furthermore, the behavior of CO2 adsorption on the biochars well conformed to the quasi-first-order dynamical model, accompanied by the higher adsorption rate of CO2 and activation energy. The obtained activation energies for TF and OTF-10 were 12.98 and 16.62 kJ·mol-1, respectively. The higher activation energy for OTF-10 meant that the adsorption temperature had a stronger effect on adsorption rate of CO2.

Adsorption mechanisms and regeneration heat analysis of a solid amine sorbent during CO2 capture in wet flue gas

H2O is an important fraction in industrial flue gas, and its impact on CO2 adsorption and energy consumption during CO2 capture in wet flue gas are important concerns by both industry and academia. This study investigated the adsorption mechanisms of CO2 and H2O and the corresponding regeneration heats of a commercial sorbent experimentally. By analyzing the adsorption isotherms of CO2 and H2O, it is found that the adsorption of CO2 and H2O on the sorbent is mainly chemisorption and multilayer physisorption respectively, which are also reflected by the measured adsorption heats. To evaluate the regeneration heat more accurately, a modified model was proposed, which considered the sensible heat required to heat the adsorbed H2O from adsorption to desorption temperature. By analyzing the influencing factors of regeneration heat based on the modified model, the heat due to the desorption of the co-adsorbed H2O in wet flue gas contributes the most. Further, energy-saving strategies e.g. increasing the adsorption temperature, reducing the H2O content of flue gases and using steam as the stripping gas during desorption are provided. In addition, increasing the CO2 working capacity and reducing the sorbent's affinity to H2O are two main improvement directions of the current solid amine sorbents.

CO2 Physisorption over an Industrial Molecular Sieve Zeolite: An Experimental and Theoretical Approach.

The present work studies the adsorption of CO2 using a zeolitic industrial molecular sieve (IMS) with a high surface area. The effect of the CO2 feed concentration and the adsorption temperature in conjunction with multiple adsorption-desorption cycles was experimentally investigated. To assess the validity of the experimental results, theoretical calculations based on well-established equations were employed and the values of equilibrium, kinetic, and thermodynamic parameters are presented. Three additional column kinetic models were applied to the data obtained experimentally, in order to predict the breakthrough curves and thus facilitate process design. Results showed a negative correlation between temperature and adsorption capacity, indicating that physical adsorption takes place. Theoretical calculations revealed that the Langmuir isotherm, the Bangham kinetic model (i.e., pore diffusion is the rate-determining step), and the Thomas and Yoon-Nelson models were suitable to describe the CO2 adsorption process by the IMS. The IMS adsorbent material maintained its high CO2 adsorption capacity (>200 mg g-1) after multiple adsorption-desorption cycles, showing excellent regenerability and requiring only a mild desorption treatment (200 °C for 15 min) for regeneration.

Adsorption mechanism of CO2/CH4/N2 by the synergistic effect of N/S-doped and functional groups in coal at different temperatures and pressures

Doping-modified coal samples can effectively enhance the adsorption of CO2. In order to investigate the micro-mechanism of the adsorption of different gases by the synergistic effect of N/S atomic doping and functional groups in coal, the microporous constructed by N/S doping with different functional groups in coal at different temperatures and pressures were investigated based on a series of grand canonical Monte Carlo (GCMC) computational simulations. The adsorption amount, heat of adsorption, diffusion coefficient, interaction energy and relative density distribution of CO2/CH4/N2 by the model. It was found that coal samples with more N-doped carboxyl groups could adsorb CO2 better, and coal samples with more N-doped aliphatic functional groups should be selected for adsorption of CH4 and N2, and the N-COOH system had the most stable adsorption state of CO2, and the amount of N-modified coal samples adsorbed CO2 was higher than that of CH4 and N2 at the adsorption temperature of 293.15 K.The diffusion coefficients of the gas molecules showed an increasing trend with the adsorption temperature, and the relative density distributions of CO2/CH4/N2 in the N-doped micropore model were larger than those in the S-doped system. These noteworthy findings provide a valuable theoretical foundation for the advancement of novel adsorbent materials.

Synthesis of porous and activated carbon from lemon peel waste for CO2 adsorption

The concentration of CO2 in the atmosphere has been increasing and is soon to reach a threatening level for life on the planet. Porous carbons made from biobased materials including from waste resources can be applied to selectively adsorb CO2 from large industrial sites and then lower atmospheric CO2 emissions. In this work, we synthesized highly porous carbons from lemon-peel wastes using two-step activation process involving hydrothermal carbonization followed by chemical activation with KOH, and KOH + alum at 800 °C. The sample activated with KOH + alum has the highest BET surface area (2143 m2/g) and total pore volume of 1.3 cc/g. Although the KOH activated sample has a lower surface area (1113 m2/g), it has better CO2 adsorption capacity ranging up to 4.5 mmol/g because of its well-developed pore structures and a high proportion (90 %) of micropore distributions. The isosteric heat of adsorption lower than 40 kJ/mol indicated that adsorption is mainly driven by physisorption. Better CO2/N2 selectivity suggested a high affinity of the activated carbons towards CO2. Particularly, the sample activated with KOH had selectivity in the range of 20 at the highest adsorption temperature (40 °C), making it a potentially viable option for direct CO2 adsorption applications from large industrial sources.

Gaussian process regression for prediction of hydrogen adsorption temperature–pressure dependence curves in metal–organic frameworks

A Gaussian Process Regression (GPR) model was proposed for high-throughput prediction of H2 adsorption isotherms of MOFs at varied temperatures based on classical density functional theory (cDFT) calculations. First, hydrogen adsorption isotherms of 17,644 selected orthorhombic MOFs from 324,426 hypothetical structures at different teperatures were calculated using the cDFT method, while 3- parameter or 4-parameter Langmuir equations were employed to fit those isotherm data and obtain the optimized isotherm parameters of each MOF. Second, the 3-parameter and 4-parameter targeted GPR models were established and trained using seven geometrical features of each MOF as inputs. It was found that our trained GPR models can accurately predict the hydrogen adsorption capacities of MOFs within the range of continuous temperature and pressure variations. Finally, the transferability of our GPR model was further discussed by three different strategies including hydrogen adsorption isotherm validations of unseen MOFs, the experimental MOFs, and the seen MOFs at the extended temperatures, respectively. It was shown that our GPR model exhibits high-performance in predicting hydrogen adsorption isotherms of unseen 306,782 hypothetical MOFs or those of seen hypothetical MOFs at the extended temperatures (258 K and 358 K). The GPR-predicted hydrogen adsorption isotherms of the randomly selected 4 different MOFs from 17,644 orthorhombic MOFs are also good agreement with those calculated by the cDFT method. However, there is still much room for improvement in the prediction accuracy for experimental MOFs such as ZIF-8 and IRMOF-1. The GPR model developed in this work, based on cDFT calculations, will help to advance the design and screening of MOFs for hydrogen separation processes of industrial importance.

Research on the main control factors of gas desorption in middle and low rank coals based on orthogonal testing

To study the factors influencing gas desorption by middle rank and low rank coal, gas adsorption and desorption experiments of middle rank and low rank coal samples were designed with the orthogonal test method by considering the particle sizes, adsorption equilibrium pressures, temperatures and water contents of the coal samples, and the main factors affecting gas desorption from the middle rank and low rank coal samples were investigated. The results showed that there were obvious differences in the desorption capacity of the middle rank and low rank coals in the designed experimental scheme, and the maximum cumulative amounts of gas desorbed were 6.11 ml/g for Xinjiang low rank coal and 6.50 ml/g for Hebi middle rank coal. The relative sensitivities to the factors affecting gas desorption by Xinjiang low rank coal decreased in the order adsorption equilibrium pressure > particle size > water content > temperature, which the effect of adsorption equilibrium pressure on gas desorption from Xinjiang low rank coal was the most obvious and main controlling factor for gas desorption from Xinjiang low rank coal. The relative sensitivities to the factors affecting gas desorption by Hebi middle rank coal decreased in the order particle size > adsorption equilibrium pressure > temperature > water content, which the effect of particle sizes on gas desorption from Hebi middle rank coal was the most obvious and main controlling factor for gas desorption from Hebi middle rank coal. The cumulative amounts of gas desorbed from Xinjiang low rank coal first increased and then decreased with increasing coal grain sizes, and the cumulative amounts of gas desorbed from the Hebi middle rank coal gradually decreased with increasing coal grain size. The cumulative amounts of gas desorbed from both Xinjiang low rank coal and Hebi middle rank coal gradually increased with increasing adsorption equilibrium pressure.