Theoretical Adsorption Isotherms Research Articles

An adsorption isotherm identification method based on CNN-LSTM neural network.

The morphology of adsorption isotherms embodies a wealth of information regarding various adsorption mechanisms, rendering the classification and identification methodologies predicated on the shape of adsorption isotherms indispensably crucial. While research on classification techniques has been extensively developed, traditional methods of adsorption isotherm identification grapple with inefficiencies and a high margin of error. Neural network-based methodologies for adsorption isotherm identification serve as a countermeasure to these shortcomings, as they facilitate swift online identification while delivering precise results. In this paper, we deploy a hybrid of convolutional neural networks (CNN) and long short-term memory (LSTM) networks for the identification of adsorption isotherms. Extensive theoretical adsorption isotherms are generated via adsorption equations, forming a comprehensive training database, thereby circumventing the need for time-consuming and costly repetitive experiments. The F1-score, receiver operating characteristic (ROC) curves, and area under the ROC curve (AUC) are introduced as criteria to evaluate the identification performance and generalization ability of the model during the testing phase. The results highlight the model's superlative performance in the task of adsorption isotherm identification, with accuracy rates of 100% in both the training and validation sets. The mean F1-score obtained from the testing set reached 0.8885, with both macro-average and micro-average AUC exceeding 0.95. PyCharm was employed as an experimental and testing platform, with Python 3.9 serving as the programming language. TensorFlow 2.11.0 and Keras 2.10.0 were harnessed for the training and testing of CNN-LSTM, while numpy 1.21.5 and scipy 1.81 were utilized for the creation of training and validation datasets.

A Review on the Adsorption Isotherms and Design Calculations for the Optimization of Adsorbent Mass and Contact Time.

Adsorption is a widely used chemical engineering unit operation for the separation and purification of fluid streams. Typical uses of adsorption include the removal of targeted pollutants like antibiotics, dyes, heavy metals, and other small to large molecules from aqueous solutions or wastewater. To date several adsorbents that vary in terms of their physicochemical properties and costs have been tested for their efficacy to remove these pollutants from wastewater. Irrespective of the type of adsorbent, nature of the pollutant, or experimental conditions, the overall cost of adsorption depends directly on the adsorption contact time and the cost of the adsorbent materials. Thus, it is essential to minimize the amount of adsorbent and the contact time required. We carefully reviewed the attempts made by several researchers to minimize these two parameters using theoretical adsorption kinetics and isotherms. We also clearly explained the theoretical methods and the calculation procedures involved during the optimization of the adsorbent mass and the contact time. To complement the theoretical calculation procedures, we also made a detailed review on the theoretical adsorption isotherms that are commonly used to model experimental equilibrium data that can be used to optimize the adsorbent mass.

Triethylenetetramine-impregnated ZIF-8 nanoparticles for CO2 adsorption

One way to enhance the CO2 adsorption capacity of adsorbents is the incorporation of amines into the structure of the adsorbent. In this study, the impact of impregnation of zeolitic imidazolate framework (ZIF-8) with triethylenetetramine (TETA) over CO2 adsorption was surveyed. ZIF-8 and two TETA-impregnated ZIF-8 samples containing 10 wt% and 15 wt% of TETA were prepared and carefully characterized by Fourier-transform infrared (FTIR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA), N2 adsorption-desorption, and Field emission scanning electron microscope (FESEM) techniques. The CO2 adsorption capacity of prepared adsorbents was examined at various temperatures and pressures using the static volumetric method. Outcomes indicated that at lower pressures than 2.5 bars, the CO2 adsorption capacity of TETA-impregnated ZIF-8 samples was slightly higher than ZIF-8, but by increasing the pressure the ZIF-8 sample showed a higher CO2 adsorption capacity in comparison with TETA-impregnated ZIF-8 samples. Also, CO2 adsorption isotherms of prepared adsorbents were investigated using the Monte Carlo method. Theoretical CO2 adsorption isotherms were similar to experimental ones. Additionally, the CO2 diffusion coefficient in prepared adsorbents was surveyed using molecular dynamics simulation. Results indicated that with the incorporation of TETA molecules in the ZIF-8 structure the diffusion coefficient of CO2 was decreased.

Improvement to the Fractal Adsorption Isotherms of Porous Surfaces

The theoretical and experimental Adsorption Isotherms (AI) are essential for the study of surface area and porous structure in solid materials. Also, the fractal dimension characterizes the roughness of a surface which means that a smooth surface has dimension two, whereas that of a highly rugged surface approaches to three. So, although there are several methods to evaluate fractal adsorption isotherms the Fripiat proposal can be considered as the generalization of the Brunauer-Emmett-Teller (BET) formulation for homogeneous surfaces because it contains, as particular case, the classical BET relationship for fractal dimension D=2. However, in the fitting of experimental Nitrogen adsorption data with the Fripiat approach is compulsory to use the BET classical formula for the calculation of the C constant and the monolayer volume. Thus, in order to overcome such constraint, in this work is presented an alternative treatment of fractal adsorption isotherms as applied to porous surfaces. The proposal is based on a relationship between the physical adsorption in homogeneous and inhomogeneous surfaces followed to the assumption that the emerging series are well correlated with polynomials. i.e. we propose an improved formulation to the fractal dimension which is solved by lineal regression avoiding the use of classical parameters. As expected, our proposition contains as particular cases the BET and Fripiat’s formulas. As an example of the usefulness of our proposal, we consider the experimental data of isothermal adsorption obtained with Al2O3 that were synthesized via sol-gel at various temperatures; the results are in good agreement with the fractal dimension evolution and with the microporous and mesoporous structure of the materials under consideration.

Silica- Iron Oxide Nanocomposite Enhanced with Porogen Agent Used for Arsenic Removal.

This study aims to remove arsenic from an aqueous medium by adsorption on a nanocomposite material obtained by the sol–gel method starting from matrices of silica, iron oxide and NaF (SiO2/Fe(acac)3/NaF). Initially, the study focused on the synthesis and characterization of the material by physico–chemical methods such as: X-ray diffraction, FT-IR spectroscopy, Raman spectroscopy, atomic force microscopy, and magnetization. Textural properties were obtained using nitrogen adsorption/desorption measurements. The zero load point, pHpZc, was also determined by the method of bringing the studied system into equilibrium. In addition, this study also provides a comprehensive discussion of the mechanism of arsenic adsorption by conducting kinetic, thermodynamic and equilibrium studies. Studies have been performed to determine the effects of adsorbent dose, pH and initial concentration of arsenic solution, material/arsenic contact time and temperature on adsorption capacity and material efficiency. Three theoretical adsorption isotherms were used, namely Langmuir, Freundlich and Sips, to describe the experimental results. The Sips isotherm was found to best describe the experimental data obtained, the maximum adsorption capacity being ~575 µg As(III)/g. The adsorption process was best described by pseudo-second order kinetics. Studies have been performed at different pH values to establish not only the optimal pH at which the adsorption capacity is maximum, but also which is the predominantly adsorbed species. The effect of pH and desorption studies have shown that ion exchange and the physiosorption mechanism are implicated in the adsorption process. From a thermodynamic point of view, parameters such as ΔG°, ΔH° and ΔS° were evaluated to establish the mechanism of the adsorption process. Desorption studies have been performed to determine the efficiency of the material and it has been shown that the material can be used successfully to treat a real-world example of deep water with a high arsenic content.

Investigating H2 Adsorption in Isostructural Metal-Organic Frameworks M-CUK-1 (M = Co and Mg) through Experimental and Theoretical Studies.

A combined experimental and theoretical study of H2 adsorption was carried out in Co-CUK-1 and Mg-CUK-1, two isostructural metal-organic frameworks (MOFs) that consist of M2+ ions (M = Co and Mg) coordinated to pyridine-2,4-dicarboxylate (pdc2-) and OH- ligands. These MOFs possess saturated metal centers in distorted octahedral environments and narrow pore sizes and display high chemical and thermal stability. Previous experimental studies revealed that Co-CUK-1 exhibits a H2 uptake of 183 cm3 g-1 at 77 K/1.0 atm [ Angew. Chem., Int. Ed. 2007, 46, 272-275, DOI: 10.1002/anie.200601627], while that for Mg-CUK-1 under the same conditions is 240 cm3 g-1 on the basis of the experimental measurements carried out herein. The theoretical H2 adsorption isotherms are in close agreement with the corresponding experimental measurements for simulations using electrostatic and polarizable potentials of the adsorbate. Through simulated annealing calculations, it was found that the primary binding site for H2 in both isostructural analogues is localized proximal to the center of the aromatic rings belonging to the pdc2- linkers. Inelastic neutron scattering (INS) spectroscopic studies of H2 adsorbed in both MOFs revealed a rotational tunnelling transition occurring at around 8 meV in the corresponding spectra; this peak represents H2 adsorbed at the primary binding site. Two-dimensional quantum rotation calculations for H2 localized at the primary and secondary binding sites in both MOFs yielded rotational energy levels that are in agreement with the transitions observed in the INS spectra. Even though both M-CUK-1 analogues possess different metal ions, they exhibit similar electrostatic environments, modeled structures at H2 saturation, and rotational potentials for H2 adsorbed at the most favorable adsorption site. Overall, this study demonstrates how important molecular-level details of the H2 adsorption mechanism inside MOF micropores can be derived from a combination of experimental measurements and theoretical calculations using two stable and isostructural MOFs with saturated metal centers and small pore windows as model systems.

Deep neural networks in chemical engineering classrooms to accurately model adsorption equilibrium data

The latest industrial revolution, Industry 4.0, is progressing exponentially and targets to integrate artificial intelligence and machine learning algorithms with existing technology to digitalise chemical processes across the industry, especially in the area of online monitoring, predictive analysis and modelling. Machine learning algorithms are being constantly implemented in both academic laboratories and industry to uncover the underlying correlations that exist in the high-dimensional and complex experimental and synthetic data that describes a chemical process. Indeed soon, proficiency in artificial intelligence methodology will become a required skill of a chemical engineer. It is therefore becoming essential to train chemical engineers with these methods to help them to adapt to this new era of digitised industries. Keeping these issues in mind, we introduced deep neural networks to the final-year chemical engineering students through a computer laboratory exercise. The exercise was delivered in fast-track mode: the students were asked to develop deep neural networks to model and predict the equilibrium adsorption of uptake of three different acids by activated carbon at four different temperatures. In this manuscript, we discuss in detail this laboratory exercise from delivery and design to the results obtained and the students’ feedback. In the classroom, the students compared the adsorption equilibrium data obtained using the established theoretical adsorption isotherms and empirical correlations with the neural networks developed in the classroom. The experience obtained from the classroom confirmed that this exercise gave the students the essential knowledge on the AI and awareness on the jargons in the world of machine language and obtained the required level of coding skills to develop a simple neural net with one layer or a sophisticated deep networks to model an important unit operation in chemical engineering and to accurately predict the experimental outcomes.

Synthesis and characterization of highly elastic superabsorbent natural rubber/polyacrylamide hydrogel

A hydrogel based on natural rubber (NR) was developed. NR was simultaneously incorporated within NR-graft-polyacrylamide (NR-g-PAM) hydrogel to form, via physical chain entanglement, a freely mobile secondary polymer network. A semi-interpenetrating polymer network (semi-IPN) was formed. The amount of NR in the hydrogel was varied from 0 wt% to 50 wt% to optimize both mechanical and physical properties. The water absorption capacity of a hydrogel with 30 wt% of NR (30NR) was 15,200%. The compressive modulus of 30NR was 106.5 kPa, 650% higher than that of a pure PAM hydrogel. The formation of the semi-IPN structure improved mechanical properties while maintaining the adsorption performances of the hydrogels. NR-g-PAM hydrogels at all NR contents adsorbed cationic and anionic azo dyes. 30NR removed 90% of methylene blue (MB) from aqueous solution in less than 24 h with a maximum adsorption capacity of 538.3 mg g−1. Fitting the experimental data from 30NR to theoretical adsorption isotherms and the results of thermodynamic study indicated a monolayer adsorption of MB on a homogeneous surface via physisorption and the adsorption process was endothermic. This hydrogel showed reusability for MB removal, with efficiency as high as 70% on the 10th cycle. The NR-g-PAM hydrogels were photodegradable upon exposure to heat, UV light, and moisture.

A sorbent based on polyvinyl formal and polyacrylic acid for the removal of heavy metals from water solutions

The characteristics of a hybrid pH-sensitive hydrogel sorbent based on polyvinyl formal and polyacrylic acid, synthesized by radical copolymerization, were investigated in the process of removing copper (II), zinc (II) and nickel (II) metal ions from water solutions. A high efficiency of the extraction (up to 96%) of metal cations (Cu(II)>Zn(II)Ni(II)) was reveled at their concentration of up to 250 mg L–1 in the pH range of 5.8 to 6.8. The experimental data were analyzed by using theoretical kinetic models and adsorption isotherms. The developed polymer sorbent was shown to be promising for removing heavy metals, even after its multiple regeneration.

Exact matrix treatment of the statistical mechanics of adsorption of large aromatic molecules on graphene.

Experimental studies of adsorption from solution of the large aromatic molecules 1,2-dihydroxybenzene (catechol) and phenyl hydroquinone on graphene nanoplatelets show that at low coverage adsorption is followed by a transition which occurs from adsorbed molecules in flat to more vertically oriented states. Catechol adsorption isotherms exhibit 2 plateaus while phenyl hydroquinone shows 3 plateaus indicating 2 and 3 active conformers respectively participating in the adsorption process. Modelling such adsorption isotherms presents a challenge. Here, an exact matrix treatment of the statistical mechanics of a one-dimensional model of adsorption of catechol and dihydroquinone on graphene nanoplatelets is presented. The theoretical adsorption isotherms successfully reproduce all the features of both the catechol and dihydroquinone experimental adsorption isotherms. As suggested by the experimentalists, our theoretical model demonstrates that adsorbed phenyl hydroquinone molecules adopt a flat orientation at low concentrations and an edge orientation at higher coverage before eventually adopting a vertical configuration. Both catechol and phenyl hydroquinone can be described by our interconvertible monomer-dimer-trimer model. The theoretical adsorption isotherms obtained show several plateaus reflecting the types of conformer on the graphene surface.

Using Phragmites australis(Iraqi plant) to remove the Lead (II) Ions form Aqueous solution.

Lead remediation was achieved using simple cost, effective and eco-friendly way from industrial wastewater. Phragmitesaustralis (P.a) (Iraqi plant), was used as anovel biomaterial to remove lead ions from synthesized waste water. Different parameters which affected on adsorption processes were investigated like adsorbent dose, pH, contact time, and adsorbent particle size, to reach the optimized conditions (maximum adsorption). The adsorption of Pb (?) on (P.a) involved fast and slow process as a mechanism steps according to obey two theoretical adsorption isotherms; Langmuir and Freundlich. The thermos dynamic adsorption parameters were evaluated also. The (?H) obtained positive value that meanes adsorption of lead ions was an endothermic processwhile (?G)values were negative which means that adsorption of lead ions was a spontaneous process and the decrease in (?G) with temperature increasing revealed that lead ions adsorption on (P.a) became favorable with temperature increasing

Using Phragmites australis(Iraqi plant) to remove the Lead (II) Ions form Aqueous solution.

Lead remediation was achieved using simple cost, effective and eco-friendly way from industrial wastewater. Phragmitesaustralis (P.a) (Iraqi plant), was used as anovel biomaterial to remove lead ions from synthesized waste water. Different parameters which affected on adsorption processes were investigated like adsorbent dose, pH, contact time, and adsorbent particle size, to reach the optimized conditions (maximum adsorption). The adsorption of Pb (?) on (P.a) involved fast and slow process as a mechanism steps according to obey two theoretical adsorption isotherms; Langmuir and Freundlich. The thermos dynamic adsorption parameters were evaluated also. The (?H) obtained positive value that meanes adsorption of lead ions was an endothermic processwhile (?G)values were negative which means that adsorption of lead ions was a spontaneous process and the decrease in (?G) with temperature increasing revealed that lead ions adsorption on (P.a) became favorable with temperature increasing

Thermodynamic features of dioxins’ adsorption

In this paper, the six more poisonous species among all congeners of dioxin group are taken into account, and the P-T diagram for each of them is developed. Starting from the knowledge of vapour tensions and thermodynamic parameters, the theoretical adsorption isotherms are calculated according to the Langmuir’s model. In particular, the Langmuir isotherm parameters (K and wmax) have been validated through the estimation of the adsorption heat (ΔHads), which varies in the range 20–24kJ/mol, in agreement with literature values. This result will allow to put the thermodynamical basis for a rational design of different process units devoted to dioxins removal.

Mechanism of capacitive charge of electrodes on the basis of activated carbon materials in ZnI2 solution

The electrochemical and thermodynamic features of the iodine electrosorption process on the surface of microporous activated carbon materials (ACM) (ST BET=1600–1900m2×g-1) in 25 % ZnI2 aqueous solution are investigated. The kinetic reversibility of the process, electrode polarization, fractional surface coverage by iodine atoms (θІ) are found. The thermodynamic analysis of the surface adsorption compound of ACM with iodine allows using the known Frumkin adsorption ratios to describe the iodine adsorption process. Comparison of theoretical adsorption isotherms (TAI) and the relationship between the specific pseudocapacity (Cp) and θІ (Сp–θІ) with practical galvanostatic discharge curves built from experimental data is made, and the parameter of the interatomic interaction (g) in the adsorption monolayer is determined. Correlation of the data of electrochemical impedance spectroscopy (EIS) with the data of galvanostatic cycles (GC) is found. Good agreement of the EIS experimental data with transmission electrical equivalent circuit for the porous electrode is obtained. The study provides insights into the process mechanism, the EEC of the interface between electrode and electrolyte, and efficiency of the material as a positive electrode in molecular energy storage (MES) systems. Sufficiently high efficiency of GC of electrodes based on ACM1 (ST BET=1600 m2×g-1), and ACM2 (ST BET=1900 m2×g-1) in the MES system is obtained. The specific discharge of ACM1 Cd=1200 C×g-1 (θІ=0.99) with the Coulomb efficiency η=95 % almost reaches its maximum theoretical value 1,216 C×g-1 (θІ=1). The similarity of the experimental desorption isotherm and Сp-θІ- relationship of ACM1 gives an indication of the process mechanism by the Frumkin model with g=–0,88. The maximum value of ACM1 Cp=F×8.8 m2 obtained according to the EIS is close to 9.4 F×m-2 obtained according to the GC. At the same time, 70 % of the total pseudocapacity of ACM1 has a low time constant τ=RC=82 c.

Using in-situ adsorption dilatometry for assessment of micropore size distribution in monolithic carbons

We demonstrate that in-situ adsorption dilatometry provides a new opportunity for structural characterization of microporous carbons. We present experimental results for CO2 adsorption at 293 K and in-situ deformation obtained by dilatometry on a synthetic monolithic carbon sample. The carbon deformation in the course of adsorption is non-monotonic: the strain isotherm shows the sample contraction at low adsorption followed by progressive expansion. To evaluate structural and mechanical properties of the sample from the experimental adsorption and strain isotherms, a kernel of theoretical adsorption isotherms is obtained with the grand canonical Monte Carlo simulation of CO2 adsorption in a series of carbon micropores ranging from 0.22 to 2.0 nm. The respective kernel of adsorption stress isotherms is constructed using the thermodynamic model of adsorption stress. The pore volume and surface area distributions were calculated independently from a) the experimental excess adsorption isotherm by deconvoluting the generalized adsorption equation and b) the experimental strain isotherm by using the kernel of adsorption stress isotherms. The proposed method of determining the pore size distribution from the strain isotherm validates the thermodynamic model of adsorption stress in micropores and provides additional information about the sample material with respect to mechanical properties of the microporous matrix.

Adsorption isotherms and kinetics of a mixture of Pentafluoroethane, 1,1,1,2-Tetrafluoroethane and Difluoromethane (HFC-407C) onto granular activated carbon

In this study, experimental and theoretical adsorption isotherms and kinetics of HFC-407C onto activated carbon have been investigated. AquaSorb 2000 granular activated carbon has been used as adsorbent. An experimental apparatus has been designed and built and experimental investigations have been carried out across assorted adsorption temperatures that are useful to the operation of adsorption chillers. Experimental data of the adsorption uptake have been fitted with Dubinin–Astakhov (D-A) and Tóth equations. Experimental data of the adsorption kinetics have been fitted with linear driving force (LDF) and Fickian diffusion (FD) models. Both models are found to be able to simulate accurately the adsorption kinetics of the proposed pair. Isosteric heat of adsorption has been estimated based on the Clausius–Clapeyron equation considering non-ideal gas consideration. Pressure–temperature–concentration (P-T-C) diagram of the pair has been also presented. The data extracted here are useful for designing adsorption cooling/heat pump systems.

Protein adsorption in microengraving immunoassays.

Microengraving is a novel immunoassay forcharacterizing multiple protein secretions from single cells. During the immunoassay, characteristic diffusion and kinetic time scales and determine the time for molecular diffusion of proteins secreted from the activated single lymphocytes and subsequent binding onto the glass slide surface respectively. Our results demonstrate that molecular diffusion plays important roles in the early stage of protein adsorption dynamics which shifts to a kinetic controlled mechanism in the later stage. Similar dynamic pathways are observed for protein adsorption with significantly fast rates and rapid shifts in transport mechanisms when is increased a hundred times from 0.313 to 31.3. Theoretical adsorption isotherms follow the trend of experimentally obtained data. Adsorption isotherms indicate that amount of proteins secreted from individual cells and subsequently captured on a clean glass slide surface increases monotonically with time. Our study directly validates that protein secretion rates can be quantified by the microengraving immunoassay. This will enable us to apply microengraving immunoassays to quantify secretion rates from 104–105 single cells in parallel, screen antigen-specific cells with the highest secretion rate for clonal expansion and quantitatively reveal cellular heterogeneity within a small cell sample.

Adsorption isotherms and kinetics of HFC410A onto activated carbons

Experimental and theoretical adsorption isotherms and kinetics data of HFC410A onto activated carbons are reported. Activated carbon powder of type Maxsorb III and activated carbon fiber of type A-20 have been used as adsorbents. An experimental apparatus has been designed and built and experimental investigation has been carried out at five adsorption temperatures in the range of 10–50 °C. Experimental data has been fitted with Tóth and Dubinin–Astakhov (D–A) adsorption isotherm models and linear driving force (LDF) adsorption kinetics model. A range of adsorption parameters such as isosteric heat of adsorption, adsorption uptake and temperature dependence and Henry's law coefficients are evaluated. A correlation between Henry's law coefficients and isosteric heat of adsorption at limiting uptake is analyzed.

Ammonium Ion Adsorption and Settleability Improvement Achieved in a Synthetic Zeolite-Amended Activated Sludge

Municipal wastewater treatment plants typically exhibit two classic problems: high ammonium concentration in water after conventional biological treatment and, in some cases, poor activated sludge sediment ability. Potential solutions to these problems were investigated by adding a synthetic zeolite obtained from coal fly ash to different steps of activated sludge treatment. The experimental results for ammonium removal fit well with the theoretical adsorption isotherms of the Freundlich model with a maximum adsorption capacity of 13.72 mg·g−1. Utilization of this kind of zeolite to improve activated sludge sediment ability is studied for the first time in this work. It is found that the addition of the zeolite (1 g·L−1) to an activated sludge with settling problems significantly enhances its sediment ability and compact ability. This is confirmed by the sludge volume index (SVI), which was reduced from 163 ml·g−1 to 70 ml·g−1, the V60 value, which was reduced from 894 ml·L−1 to 427 ml·L−1, and the zeta potential (ζ), which was reduced from −19.81 mV to −14.29 mV. The results indicate that the addition of this synthetic zeolite to activated sludge, as an additional waste management practice, has a positive impact on both ammonium removal and sludge settleability.

Modeling Adsorption Properties on the Basis of Microscopic, Molecular, and Structural Descriptors for Nonpolar Adsorbents

We propose a method for analytically predicting single-component adsorption isotherms from molecular, microscopic and structural descriptors of the adsorbate-adsorbent system and concepts of statistical thermodynamics. Expressions for Henry's constant and the heat of adsorption at zero coverage are derived. These functions depend on the pore size, pore shape, chemical composition, and density of the adsorbent material. They quantify the strength of the solid-fluid interaction, which governs the low-pressure part of the adsorption isotherm. For intermediate and high pressures, the fluid-fluid interactions must also be taken into account. Both solid-fluid and fluid-fluid interactions are combined within the framework of the Ruthven statistical model (RSM). The RSM thus constructs theoretical adsorption isotherms that are entirely based on microscopic molecular and structural descriptors. The theoretical results that we obtained are compared with experimental data for the adsorption of pure CO2 and CH4 on all-silica zeolites. The developed methodology allows for the estimation of the optimum properties of a nonpolar adsorbent for the adsorption of CO2 in cyclic adsorption processes.