Phase Adsorption Research Articles

Understanding the origins of reversible and hysteretic pathways of adsorption phase transitions in metal-organic frameworks

Phase behavior of nanoconfined fluids adsorbed in metal–organic frameworks is of paramount importance for the design of advanced materials for energy and gas storage, separations, electrochemical devices, sensors, and drug delivery, as well as for the pore structure characterization. Phase transformations in adsorbed fluids often involve long-lasting metastable states and hysteresis that has been well-documented in gas adsorption–desorption and nonwetting fluid intrusion-extrusion experiments. However, theoretical prediction of the observed nanophase behavior remains a challenging problem. The mesoscopic canonical, or mesocanonical, ensemble (MCE) is devised to study the nanophase behavior under conditions of controlled fluctuations to stabilize metastable and labile states. Here, we implement and apply the MCE Monte Carlo (MCEMC) simulation scheme to predict the origins of reversible and hysteric adsorption phase transitions in a series of practical MOF materials, including IRMOF-1, ZIF-412, UiO-66, Cu-BTC, IRMOF-74-V, VII, and IX. The MCEMC method, called the gauge cell method, allows to produce Van der Waals type isotherms with distinctive swings around the phase transition regions. The constructed isotherms determine the positions of phase equilibrium and spinodals, as well as the nucleation barriers separating metastable states. We demonstrate the unique capabilities of the MCEMC method in quantitative predictions of experimental observations compared with the conventional grand canonical and canonical ensemble simulations. The MCEMC method is implemented in the open-source RASPA and LAMMPS software packages and recommended for studies of adsorption behavior and pore structure characterization of MOFs and other nanoporous materials.

Operating characteristics of an adsorption chiller with heat and mass recovery scheme for low-grade heat source

Waste heat recovery from data center is regarded as one of the most promising application of adsorption refrigeration in the future. To better understanding of the system, the operating characteristics, including temperature, pressure and heat exchange capacity, of the adsorption chiller for such low-grade heat source should be revealed. Unfortunately, they have not been detailedly reported yet. In this paper, lab experiments on a silica gel-water adsorption chiller prototype with heat and mass recovery scheme are implemented. The results show that this chiller can achieve 3.17 kW of average cooling power and 0.482 of coefficient of performance under the conditions of 60 °C hot water inlet temperature, 30 °C cooling water inlet temperature and 22 °C chilled water inlet temperature. The temperature and pressure characteristics reveal that adsorbent bed desorption phase results in the worsening of the deviation from ideal cycle when compared to its adsorption phase. Hence, the heat and mass transfer performance of bed in desorption phase is prioritized to be enhanced. The analysis on heat exchange capacity indicates that mass recovery operation is more beneficial to the adsorption reaction. The optimal heat recovery time is found to be 24 s while the heat recovery efficiency is 0.711.

New insight into CH4 adsorption mechanism in coal based on modeling analysis of different adsorption theories

Based on the principle of Gibbs excess adsorption measurement, high-pressure isothermal adsorption and desorption experiments of CH4 were performed on fractured coal samples, and CH4 adsorption phase density was obtained by the intercept method according to the experimental data. The Langmuir model, BET model, DA model, and their corrected model, the supercritical adsorption models were used for the fitting analysis of CH4 excess adsorption capacity. A hybrid model of different adsorption theories was developed based on CH4 adsorption phase density and theoretical adsorption capacity predicted by the intercept method. The transition in the occurrence pattern and control mechanism of CH4 in coal were investigated. The fitting of the Langmuir model, BET model, DA model, and their corrected models, the SBET model, the SDA model, and the SDA-L model to the CH4 excess adsorption capacity in coal shows that all multilayer adsorption theory model is not suitable for fitting the CH4 excess adsorption capacity in coal. The uncorrected Langmuir model and DA model are only suitable for fitting the CH4 excess adsorption capacity in coal in the low-pressure stage (pressure below 10 MPa). The corrected Langmuir model, the corrected DA model, the SDA model, and the SDA-L model can be used to fit the CH4 excess adsorption capacity in coal, but they show some bias in predicting the theoretical CH4 adsorption capacity and the CH4 adsorption phase density. The fitting of the three main adsorption theory models suggests that there may be simultaneous monolayer adsorption and microporous filling adsorption. The fitting results of the hybrid model based on monolayer adsorption and microporous filling adsorption theory depend on showing that with the increase of temperature, the occurrence of CH4 in coal gradually changes from mainly monolayer adsorption to mainly microporous filling adsorption, and the transformation of occurrence mode is related to temperature and the development of pores in coal.

Single-file diffusion and its influence on membrane gas separation: A case study on UTSA-280

Gas permeation in metal-organic framework-based (MOF-based) membranes is often elucidated through the solution-diffusion model, where the adsorption and diffusion of gases play equally vital roles. This study draws attention to a unique phenomenon known as single-file diffusion (SFD) occurring within MOF membranes that possess ultramicropores with dimensions comparable to the gas molecules themselves. When SFD takes place, the separation performance becomes solely reliant on the adsorption quantities on the feed side of the membrane. As a proof of concept, we fabricated a UTSA-280 membrane and subjected it to testing using gas mixtures of CO2/N2 and CO2/CH4. Two crucial observations substantiate the occurrence of single-file diffusion. Firstly, in the gas mixtures, the diffusion coefficients of N2 or CH4 were observed to align closely with that of CO2, despite the intrinsic diffusion coefficients of CO2, N2, and CH4, as determined from single-gas permeation experiments, exhibiting differences. Secondly, the CO2 mole fractions within the adsorption phase closely mirrored those in the gas phase on the permeate side. Given the high adsorption selectivity of UTSA-280 for CO2, the UTSA-280 membrane delivers outstanding permeation selectivity for CO2/N2 (611) and CO2/CH4 (80.7). Our experimental findings are supported by mesoscale kinetic Monte Carlo simulations, which confirmed the relation between the CO2 compositions in the adsorption phase on the feed side and in the gas phase on the permeate side. Furthermore, density functional theory calculations revealed high energy barriers associated with CO2 surpassing its counterparts, rendering such processes unfavorable, thereby reinforcing our experimental findings regarding single-file diffusion.

Avoiding pitfalls in molecular simulation of vapor sorption: Example of propane and isobutane in metal-organic frameworks for adsorption cooling applications.

This study introduces recommendations for conducting molecular simulations of vapor adsorption, with an emphasis on enhancing the accuracy, reproducibility, and comparability of results. The first aspect we address is consistency in the implementation of some details of typical molecular models, including tail corrections and cutoff distances, due to their significant influence on generated data. We highlight the importance of explicitly calculating the saturation pressures at relevant temperatures using methods such as Gibbs ensemble Monte Carlo simulations and illustrate some pitfalls in extrapolating saturation pressures using this method. For grand canonical Monte Carlo (GCMC) simulations, the input fugacity is usually calculated using an equation of state, which often requires the critical parameters of the fluid. We show the importance of using critical parameters derived from the simulation with the same model to ensure internal consistency between the simulated explicit adsorbate phase and the implicit bulk phase in GCMC. We show the advantages of presenting isotherms on a relative pressure scale to facilitate easier comparison among models and with experiment. Extending these guidelines to a practical case study, we evaluate the performance of various isoreticular metal-organic frameworks (MOFs) in adsorption cooling applications. This includes examining the advantages of using propane and isobutane as working fluids and identifying MOFs with a superior performance.

Ammonium ion removal from aqueous solutions in the presence of organic compounds, using biochar from banana leaves. Competitive isotherm models

BackgroundIndustrial, e.g. food industrial and domestic wastewaters contain huge amount of compounds causing eutrophication, and should be removed with high cost during wastewater treatment. However, these compounds could be utilized as fertilizers too. Biochar can remove a wide range of pollutants from water, such as ammonium, which can be found in relatively high concentration in dairy wastewaters. However, adsorption performance may be affected by the presence of other wastewater pollutants. Thus, this study aims to determine the efficiency of biochar as an adsorbent of ammonium in aqueous solutions in the presence of some selected organic compounds of typical dairy wastewaters such as bovine serum albumin (BSA), lactose, and acetic acid. Methods: The biochar was produced from banana leaves at 300 °C, modified with NaOH, and characterized by Scanning Electron Microscope – Energy Dispersive X-Ray Spectroscopy (SEM-EDX), Fourier-transform infrared spectra (FTIR) analysis, and specific surface area measurements. Batch experiments were carried out to investigate the ammonium adsorption capacity and the ion competitive adsorption mechanism. Significant Findings: Results show that the surface structure of the biochar derived from banana leaves is different from other biochars previously studied; although the specific surface area is not very considerable and despite having nitrogen within the elemental composition, the biochar studied is capable of adsorbing 2.60 mg NH4+/m2, the highest ammonium removal in 2 h occurs at pH 9 and 500 mg biochar dose. Langmuir model in the monolayer phase analysis fits better for all scenarios and the maximum NH4+ adsorption capacity was 0.97 mg/g without organic compounds. In the multilayer adsorption phase, the isotherm model that best fits the data obtained is the Harkins-Jura model without organic compounds. The presence of organic compounds in the aqueous solution significantly impacts the adsorption of ammonium by biochar since it improves the adsorption capacity (1.132 mg/g BSA, 0.975 mg/g lactose, and 1.874 mg/g acetic acid). The Aranovich-Donohue isotherm model fitted the data obtained during ion competitive adsorption experiments well.

Amino Acid Ionic Liquid Coated Magnetic Core Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub> Nanoparticles Coupled with UV Spectrophotometry for the Separation /Analysis Congo Red

Congo red has strong tinting strength, low price that it was used in meat dyeing. Amino acid ionic liquids (AAILs) containing amino acid cations or anions are synthesized from natural amino acids, which has the characteristics of low toxicity. Nowadays, Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>@AAIL composites has seemly not been reported for the separation/analysis of congo red. In this work, Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>@AAIL nanoparticles were used as magnetic solid phase adsorbents in combination with UV spectrophotometry for separation of congo red.

Magnetic carbonaceous adsorbents derived from nanocomposites of hypercrosslinked polystyrenes

Two groups of porous composite adsorbents with magnetic properties were obtained by pyrolysis of nanocomposites of hypercrosslinked polystyrenes with immobilized iron and cobalt oxides. The structure of the adsorbents is characterized by electron microscopy, X-ray phase analysis, Raman spectroscopy, adsorption of N2, CO2. The carbonaceous adsorbents (granules 0.1–0.3 mm) possess magnetic properties and have a developed porous structure (three ultramicropore fractions of 0.3–0.9 nm, a specific surface area of up to 600 m2 g−1). The crystalline phase of the magnetic adsorbents consists of iron, cementite, maghemite (41, 49, 9 wt%), or cobalt, graphite (9, 87 wt%). Iron/cementite nanoparticles 30–200 nm or cobalt nanoparticles 9–40 nm are distributed uniformly in the carbon matrix of the adsorbents. Carbon nanosized layered structures form the shells (2–7 nm). The magnetic adsorbents are capable of absorbing toxic organic compounds up to 0.64 cm3 g−1. The resulting adsorbents can be applied in magnetic separation adsorption technologies.

Comparative analysis of CO2 and N2 adsorption on zeolite 4A: Thermodynamics parameters and site energy distribution investigations

Adsorption equilibrium data for CO2 and N2 on zeolite 4A were volumetrically measured at temperatures ranging from 278 K to 328 K and gas pressures up to 4 MPa. The experimental data was correlated using the high-pressure Langmuir, Sips, and DA adsorption isotherm models. The high-pressure DA model was found to be the optimal model for describing the adsorption isotherms on basis of nonlinear regression analysis. Subsequently, the thermodynamic parameters, including isosteric heat of adsorption (Hst), adsorption phase specific heat capacity (cpa), adsorption phase entropy (sa), and enthalpy (ha), considering the actual adsorption state, were estimated. The results demonstrate that the adsorption of CO2 on zeolite 4A is greater than that of N2. The higher Hst and ha values and the lower sa values of CO2 compared to N2, suggest a stronger surface interaction of CO2 with zeolite 4A, resulting in a more ordered arrangement of CO2 molecules than N2. Site energy distribution theory analysis indicates that less energy is required for CO2 adsorption and greater site energy heterogeneity of CO2 than those of N2 on zeolite 4A. The obtained results evidence that the studied zeolite 4A could be a promising candidate adsorbent for greenhouse gas capture.

Density Analysis of Adsorption Phase in the Thermodynamic Study of Shale Gas Adsorption.

Understanding the adsorption mechanism and precisely predicting the thermodynamic adsorption properties of methane at high pressure are crucial while very challenging for shale gas development. In this study, we demonstrated that the Langmuir adsorption model combining with different empirical methods to determine the adsorption phase density makes the calculated isothermal adsorption heat violate Henry's law at low pressure. For instance, the isothermal adsorption heat calculated by the Langmuir-Freundlich model contradicts Henry's law when the absolute adsorption quantity is zero. Given the current challenge in accurately calculating the adsorption phase density, it is necessary to impose constraints on the parameters of the adsorption model by adhering to Henry's law to maintain thermodynamic consistency. We found that the adsorption phase volume of methane molecules lies between the micropore volume and the total pore volume when shale adsorption reaches saturation. The adsorption mechanism involves not only filling micropores but also monolayer adsorption in meso-macro pores. The high-energy adsorption sites for methane are primarily concentrated in organic matter, while within these methane adsorption areas in shale, the high-energy adsorption sites for water are mainly located in kaolinite within clay minerals. The zero-pressure heat of adsorption is a temperature-independent thermodynamic index, yet it is influenced by the water content. It can therefore be selected as a quantitative measure to evaluate the impact of methane adsorption on water.

Mechanistic Evidence for Hg Removal from Wastewater by Biologically Produced Sulfur.

A significant quantity of biologically produced sulfur (BPS) is generated as a by-product of chemical and biological desulfurization processes applied to landfill gas treatment. The beneficial upcycling of BPS has seen limited use in the environmental context. The effectiveness and underlying mechanism of BPS as an adsorbent for removing Hg2+ from both solution and wastewater were elucidated based on experiments encompassing surface characterization, adsorption isotherms, kinetics, and thermodynamics. The BPS exhibited remarkable efficacy in removing Hg2+ from solution, with the Langmuir model accurately describing the adsorption process and showing a maximum adsorption capacity of 244 mg g-1. Surface analysis through X-ray photoelectron spectroscopy and scanning electron microscopy revealed that Hg2+ complexed with sulfide on BPS surfaces, forming stable HgS. The adsorbed Hg was strongly retained in BPS, with less than 0.2% of the adsorbed Hg desorbed by strong acids. Adsorption kinetics followed the double-exponential first-order model, showing an initial rapid adsorption phase wherein 75% of the initial Hg2+ was removed within 5 min, followed by a slower adsorption rate. The thermodynamic parameters suggested that adsorption of Hg2+ by BPS was a spontaneous and endothermic process. Additionally, BPS effectively removed Hg2+ from wastewater, showing preference for Hg over other co-existing metals. These findings underscore the potential of BPS as an effective adsorbent for Hg2+ removal from wastewater.

Exploring nature's filters: Peat-mineral mix for low and high-strength oilfield produced water reclamation

Nature-based solutions are encouraged for treating oilfield produced water from oil and gas extraction, a crucial undertaking that aligns with the Canadian oil sands industry's ambitious goal of zero waste, and the globally recognized Sustainable Development Goals (SDGs) pertaining to water conservation and ecosystem preservation. This study explored the use of peat-mineral mix (PMM), a leftover of inevitable oil sands mining, for treating low and high-strength wastewaters during biofiltration, which contained large molecular weight (44.3 kDa), which include alcohols, aliphatics, aromatics, and ketones, and can impart high toxicity to both fauna and flora (MicroTox: 99 %). The breakthrough curve indicated an effective initial adsorption phase driven by advection within the column dynamics. For complete organics removal and mechanistic insights, the wastewater was re-circulated in a continuous mode for up to 42 days. Here, we found that chemical oxygen demand was reduced from ∼85,000 mg/L to ∼965 mg/L). Kinetics investigations along with physicochemical characterization of PMM and wastewater suggested that chemisorption and anaerobic digestion contributed to the overall removal of contaminants. Chemisorption, led by hydrogen bonding and hydrophobic interactions, was the dominant mechanism, with a limited contribution from physical adsorption (surface area: 2.85 m2/g). The microbial community within the PMM bed was rich/diverse (Shannon > 6.0; Chao1 > 600), with ∼ 50 % unclassified phylotypes representing ‘microbial dark matter’. High electric conductivity (332.1 μS cm−1) of PMM and the presence of Geobacter, syntrophs, and Methanosaeta suggest that direct interspecies electron transfer was likely occurring during anaerobic digestion. Both low and high-strength wastewaters showed effective removal of dissolved organics (e.g., naphthenic acids, acid extractable fraction, oil and grease content), nutrients, and potentially toxic metals. The successful use of PMM in treating oilfield produced water offers promising avenues for embracing nature-based remediation solutions at oil refining sites.

Re-cognition of adsorption phase density and adsorption phase volume: Insights from methane adsorption behavior

The determination of adsorption phase density significantly influences the assessment of gas occurrence state and gas content within in-situ reservoirs, particularly for the evaluation of gas content in deep coalbed reservoirs. Despite the extensive research on adsorption phase density, various calculation methods encounter limitations due to the inability to directly measure it. Simultaneously, the considerable disparity in results obtained from various adsorption phase density methods hampers the accurate determination of adsorbed gas and free gas content in deep coal seams. To address these challenges, this study systematically reviews calculation methods and highlights issues related to adsorption phase density. Considering practical experimental conditions, two new calculation methods are proposed: the adsorption potential adsorption phase density (APD) method and limit adsorption phase density (LAD) method. These methods enable the directional calculation of adsorption phase density based on the unknown or known absolute adsorption amount. The obtained results reveal that the adsorption phase density obtained through the APD method exhibits variations in temperature and pressure. For different coal rank samples, the range of actual adsorption phase density at different temperatures under high pressures is expected to fall between 0.30 g/cm3 and 0.40 g/cm3. The range can serve as a theoretical upper limit value for refining adsorption phased density models. The adsorption phase density acquired through the LAD method exhibits variations in temperature and pressure, whereas the adsorption phase volume remains unaffected by changes in temperature and pressure. The computed outcomes from the LAD method align with those derived from nuclear magnetic resonance (NMR), adsorption phase volume (APV), and molecular simulation methods, affirming the accuracy and applicability of the adsorption phase density determined via the LAD method. It is envisaged that these research findings will enhance the precise determination of adsorption phase density and assist in discerning the occurrence state of deep coalbed methane and, potentially, carbon dioxide sequestration.

Investigating the Impact of Na2WO4 Doping in La2O3-Catalyzed OCM Reaction: A Structure–Activity Study via In Situ XRD-MS

The La2O3 catalyst exhibits good performance in OCM reactions for its promising C2 selectivity and yield. Previous studies have affirmed that the formation of carbonates in La2O3 impedes the catalyst’s activity as a result of poisoning from CO2 exposure. In this study, a series of Na2WO4-impregnated La2O3 catalysts were synthesized to investigate the poisoning-resistant effect. The bulk phase and kinetics of the catalysts were analyzed in reactors employed with in situ XRD-MS and online MS, focusing on the CO2 adsorption on La2O3 and the phase transition process to La2O2CO3 in temperature zone correlated to OCM light-off. In situ XRD analysis revealed that, with Na2WO4 doped, CO2 exposure at elevated temperatures formed La2O2CO3 in tetragonal crystal phases, exhibiting distinctive differences from the hexagonal phase carbonates in undoped commercial La2O3. The ability to develop tetragonal or monoclinic La2O2CO3 was suggested as a descriptor to assess the sensitivity of La2O3 catalysts to CO2 adsorption, a tunable characteristic found in this study through varying Na2WO4 doping levels. Coupled XRD-MS analysis of CO2 adsorption uptake and phase change further confirmed a positive dependence between the resistivity of La2O3 catalyst to CO2 adsorption and its low-temperature C2 selectivity. The results extended the previous CO2 poisoning effect from multiple perspectives, offering a novel modification approach for enhancing the low-temperature performance of La2O3 catalysts in OCM.

Substitution and Orientation Effects on the Crystallinity and PFAS Adsorption of Olefin-Linked 2D COFs.

Solid phase adsorbents with high removal affinity for per- and polyfluoroalkyl substances (PFAS) in aqueous environments are sought. We report the synthesis and investigation of COF-I, a new covalent organic framework (COF) with a good affinity for PFAS adsorption. COF-I was synthesized by the condensation reaction between 2,4,6-trimethyl-1,3,5-triazine and 2,3-dimethoxyterephthaldehyde and fully characterized. In addition to the high crystallinity and surface area, COF-I showed high hydrolytic and thermal stability. Further, we converted its hydrophobic surface to a hydrophilic surface by converting the ortho-methoxy groups to hydroxyl derivatives and produced a new hydrophilic olefin-linked two-dimensional (2D) COF. We experimentally measured the crystallinity of both COFs by X-ray diffraction and used atomistic simulations coupled with cross-polarization/magic angle spinning solid-state nuclear magnetic resonance (CP/MAS ssNMR) to determine the relative amounts of AA-stacking and AB-stacking present. COF-I, with its hydrophobic surface and methoxy groups in the ortho positions, showed the best PFAS adsorption. COF-I reduced the concentration of perfluorooctanoic acid from 20 to 0.069 μg L-1 and to 0.052 μg L-1 for perfluorooctanesulfonic acid. These amounts are lower than the U.S. Environmental Protection Agency advisory level (0.070 μg L-1). High efficiency, fast kinetic adsorption, and reusability of COF-I are advantages of COF-I for PFAS removal from water.

The Influence of Wettability Effect and Adsorption Thickness on Nanoconfined Methane Phase Behavior: Vapor-Liquid Co-Existence Curves and Phase Diagrams

Research interest in the behavior of methane inside nanopores has been growing, driven by the substantial geological reserves of shale gas and coalbed methane. The phase diagram of methane in nanopores differs significantly from its bulk state, influencing its existing form and pertinent physical properties—such as density and viscosity—at specific pressures and temperatures. Currently, there is a lack of effort to understand the nanoconfinement effect on the methane phase diagram; this is a crucial issue that needs urgent attention before delving into other aspects of nanoconfined methane behavior. In this study, we establish a fully coupled model to predict the methane phase diagram across various scales. The model is based on vapor-liquid fugacity equilibrium, considering the shift in critical pressure and temperature induced by pore size shrinkage and adsorption-phase thickness. Notably, our proposed model incorporates the often-overlooked factor of capillary pressure, which is greatly amplified by nanoscale pore size and the presence of the adsorption phase. Additionally, we investigated the impact of surface wettability, correlated to capillary pressure and the shift in critical properties, on the methane phase diagram. Our results indicate that (a) as pore size decreases, the methane phase diagram becomes more vertical, suggesting a transition from a gaseous to a liquid state for some methane molecules, which is contrary to the conventional phase diagram; (b) enhancing surface wettability results in a more vertical phase diagram, with the minimum temperature corresponding to 0 MPa pressure on the phase diagram, increasing by as much as 87.3%; (c) the influence of capillary pressure on the phase diagram is more pronounced under strong wettability conditions compared to weak wettability, and the impact from the shift in critical properties can be neglected when the pore size exceeds 50 nm.

Activated rice husk biochar for azo dye removal: batch adsorption, kinetics and thermodynamic studies

<p>The study aimed to analyze the adsorption behaviour of an activated rice husk biochar adsorbent in batch mode to expunge azo dye concentrations depletion from liquid solvents. The biochar adsorbent was formulated using different chemical synthesis processes, and its surface region was assessed using Nitrogen retention. The existence of the particular azo dyes was verified through SEM and EDX examinations. Additionally, XRD analysis was conducted to examine the intensity and crystalline structure of the activated biochar adsorbent. A batch mode study was conducted to ascertain the ideal adsorption parameters, including pH, contact time, biochar dose, and azo dye concentration. The adsorption kinetic studies supported the notion of a favourable adsorption interaction occurring through the mutual influence of the adsorbed matter and the adsorbing substrate. Most isotherm studies were well-fitted with regression values of isotherm models, indicating an adsorption process with non-uniform monolayer formation. Thermodynamic investigations validated that the binding forces between the adsorptive and the adsorbing phase are endothermic, and a significant amount of spent adsorbent was successfully recovered using a strong hydrochloric acid desorption process.</p>

Adsorption Performance of Different Wetland Substrates for Ammonia Nitrogen: An Experimental Study

To investigate the adsorption performance of different substrates for ammonia nitrogen in wastewater, adsorption experiments are conducted on four substrates, namely, zeolite, quartz sand, volcanic rock, and biological ceramsite, and the experimental data are analyzed using adsorption isotherms and three kinetic models. The results show that with the increasing dosage of the substrates, the adsorption capacity gradually decreases, and the removal rate gradually increases. The removal rates all show a rapid increase in the early stage (the first 14 h) and gradually reach a stable state in the later stage (after more than 48 h). The higher the concentration of ammonia nitrogen in the NH4Cl solution, the greater the unit adsorption capacity of ammonia nitrogen by the substrate, the longer the adsorption time required to reach adsorption equilibrium, the lower the total removal rate of ammonia nitrogen, and the longer it takes for the concentration of ammonia nitrogen in the substrate and solution to reach equilibrium. The adsorption capacity of zeolite to ammonia nitrogen is much higher than that of quartz sand, biological ceramsite, and volcanic rock, so zeolite is suitable as the wetland substrate. The adsorption of ammonia nitrogen by the four substrates is principally multi-molecular layer adsorption, and the adsorption phase is heterogeneous.

Unravelling the kinetics, isotherms, thermodynamics, and mass transfer behaviours of Zeolite Socony Mobil - 5 in removing hydrogen sulphide resulting from a dark fermentative biohydrogen production process.

Research into the speciation of sulfur and hydrogen molecules produced through the complex process of thermophilic dark fermentation has been conducted. Detailed surface studies of solid-gas systems using real biogas (biohydrogen) streams have unveiled the mechanisms and specific interactions between these gases and the physicochemical properties of a zeolite as an adsorbent. These findings highlight the potential of zeolites to effectively capture and interact with these molecules. In this study, the hydrogen sulphide removal analysis was conducted using 0.8 g of the adsorbent and at various reaction temperatures (25-125 °C), a flow rate of 100 mL min-1, and an initial concentration of approximately 5000 ppm hydrogen sulphide. The reaction temperature has been observed to be an essential parameter of Zeolite Socony Mobil - 5 adsorption capacity. The optimum adsorption capacity attains a maximum value of 0.00890 mg g-1 at an optimal temperature of 25 °C. The formation of sulphur species resulting from the hydrogen sulphide adsorption on the zeolite determines the kinetics, thermodynamics, and mass transfer behaviours of Zeolite Socony Mobil - 5 in hydrogen sulphide removal and Zeolite Socony Mobil - 5 is found to improve the quality of biohydrogen produced in thermophilic environments. Biohydrogen (raw gas) yield was enhanced from 2.48 mol H2 mol-1 hexose consumed before adsorption to 2.59 mol H2 mol-1 hexose consumed after adsorption at a temperature of 25 °C. The Avrami kinetic model was fitted for hydrogen sulphide removal on Zeolite Socony Mobil - 5. The process is explained well and fitted using the Temkin isotherm model and the investigation into thermodynamics reveals that the adsorption behaviour is exothermic and non-spontaneous. Furthermore, the gas molecule's freedom of movement becomes random. The adsorption phase is restricted by intra-particle diffusion followed by film diffusion during the transfer of hydrogen sulphide into the pores of Zeolite Socony Mobil - 5 prior to adsorption on its active sites. The utilisation of Zeolite Socony Mobil - 5 for hydrogen sulphide removal offers the benefit of reducing environmental contamination and exhibiting significant applications in industrial operations.

Surface phase diagrams from nested sampling.

Studies in atomic-scale modeling of surface phase equilibria often focus on temperatures near zero Kelvin due to the challenges in calculating the free energy of surfaces at finite temperatures. The Bayesian-inference-based nested sampling (NS) algorithm allows for modeling phase equilibria at arbitrary temperatures by directly and efficiently calculating the partition function, whose relationship with free energy is well known. This work extends NS to calculate adsorbate phase diagrams, incorporating all relevant configurational contributions to the free energy. We apply NS to the adsorption of Lennard-Jones (LJ) gas particles on low-index and vicinal LJ solid surfaces and construct the canonical partition function from these recorded energies to calculate ensemble averages of thermodynamic properties, such as the constant-volume heat capacity and order parameters that characterize the structure of adsorbate phases. Key results include determining the nature of phase transitions of adsorbed LJ particles on flat and stepped LJ surfaces, which typically feature an enthalpy-driven condensation at higher temperatures and an entropy-driven reordering process at lower temperatures, and the effect of surface geometry on the presence of triple points in the phase diagrams. Overall, we demonstrate the ability and potential of NS for surface modeling.