UiO-66 Framework Research Articles

Development of high refractive index UiO-66 framework derivatives via ligand halogenation.

UiO-66 is a Zr-based metal-organic framework (MOF) with exceptional chemical and thermal stability. The modular design of a MOF allows the tuning of its electronic and optical properties to obtain tailored materials for optical applications. Making use of the halogenation of the 1,4-benzenedicarboxylate (bdc) linker, the well-known monohalogenated UiO-66 derivatives were examined. In addition, a novel diiodo bdc based UiO-66 analogue is introduced. The novel UiO-66-I2 MOF is fully characterized experimentally. By applying density functional theory (DFT), fully relaxed periodic structures of the halogenated UiO-66 derivatives are generated. Subsequently, the HSE06 hybrid DFT functional is used to calculate the electronic structures and optical properties. The obtained band gap energies are validated with UV-Vis measurements to assure a precise description of the optical properties. Finally, the calculated refractive index dispersion curves are evaluated underlining the capabilities to tailor the optical properties of MOFs by linker functionalization.

Magnetic Nanocomposites of Coated Ferrites/MOF as Pesticide Adsorbents.

Magnetic metal-organic frameworks (MMOFs) are gaining increased attention as emerging adsorbents/water remediation agents. Herein, a facile development of novel MMOFs comprised of coated ferrite nanoparticles (MNPs) and UiO-66 metal-organic framework is reported. In specific, coated Co- and Zn-doped ferrite magnetic nanoparticles were synthesized as building block while the metal-organic framework was grown in the presence of MNPs via a semi-self-assembly approach. The utilization of coated MNPs facilitated the conjugation and stands as a novel strategy for fabricating MMOFs with increased stability and an explicit structure. MMOFs were isolated with 13-25 nm crystallites sizes, 244-332 m2/g specific surface area (SSA) and 22-42 emu/g saturation magnetization values. Establishing the UiO-66 framework via the reported semi-self-assembly resulted in roughly 70% reduction in both magnetic properties and SSA, compared with the initial MNPs building blocks and UiO-66 framework, respectively. Nonetheless, the remaining 30% of the magnetization and SSA was adequate for successful and sufficient adsorption of two different pesticides, 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T), while the recovery with a commercial magnet and reuse were also found to be effective. Adsorption and kinetic studies for all three MMOFs and both pesticides were performed, and data were fitted to Langmuir-Freundlich isotherm models.

Construction of the π-complexation desulfurization adsorbent containing Cu+ at defective sites of UiO-66

Adsorption desulfurization is a very effective method to remove thiophenic compounds from fuels. The metal–organic frameworks (MOFs) have emerged as a new type of desulfurization adsorbents because of their porous nature and large specific surface area. In this study, Cu2+ was covalently introduced into the UiO-66 framework at the defective sites by the solvothermal method. Further, the π-complexation adsorbent UiO-66-Cu(I) containing Cu+ for adsorption desulfurization was synthesized by the methanol vapor-induced reduction. The adsorption performance was tested for the removal of thiophene from the model fuels with different sulfur concentrations. In comparison with the pristine UiO-66, the adsorbent UiO-66-Cu(I) has a higher adsorption capacity for thiophene, reaching 14.8 mg S/g. The competitive adsorption results indicated that UiO-66-Cu(I) has good selectivity for thiophene in the presence of aromatic compounds. From the recycling experiments, this adsorption still has the 86 % of the initial capacity after four cycles, indicating that the adsorbent has a good recycling performance.

Optimization of MOF Synthesis

Synthesis optimization of the metal organic framework (MOF) UiO-66 has been carried out using 2-aminoterephthalic acid functional group, a zirconium salt and a modulator grafted into the UiO-66 framework. Reaction parameters such as the effects of temperature, reaction time, the nature of the zirconium salt and the ligand, the molar ratio between the zirconium salt and the ligand, the quantity of the modulator, the solvent and the effect of added water have been investigated. The synthesized MOFs have demonstrated excellent chemical and thermal stability, which ensured them to be used as carriers for drug delivery.

Controlling the Adsorption and Release of Ocular Drugs in Metal-Organic Frameworks: Effect of Polar Functional Groups.

A series of UiO-66 materials with different functional groups (-H, -NH2, and -NO2) have been evaluated for the adsorption and release of a common ocular drug such as brimonidine tartrate. UiO-66 samples were synthesized under solvothermal conditions and activated by solvent exchange with ethanol. Experimental results suggest that the incorporation of surface functionalities gives rise to the development of structural defects (missing linker defects) but without altering the basic topology of the UiO-66 framework. These defects improve the adsorption performance of the parent metal-organic framework (MOF), while the bulkier functionalities infer slower release kinetics, with the associated benefits for prolonged delivery of brimonidine. Among the evaluated MOFs, defective UiO-66-NO2 can be proposed as the most promising candidate due to the combination of a larger brimonidine volumetric uptake (680 mg/cm3), a prolonged delivery (period of up to 25 days), a small particle size, and a larger instability. Contrariwise, at high concentrations UiO-66-NO2 has higher toxicity toward human retinal pigment epithelium cells (ARPE-19) compared to the pure and NH2-functionalized UiO-66.

UiO-66(Zr/Ti) for catalytic PET polycondensation

PET (poly(ethylene terephthalate)) is one of the most important type of thermoplastic polyesters and widely used in various fields. Titanium-based catalysts are environmentally friendly and have higher catalytic activity than antimony-based catalysts when used in industry. However, titanium-based catalysts are prone to hydrolysis and result in discolored products. UiO-66 (Zr/Ti) with different Ti4+ contents were successfully synthesized via one-step method. The material was characterized by XRD, SEM, FT-IR, XPS, BET and TG techniques. The results demonstrates that Ti4+ was integrated into the UiO-66 framework. NH3-in situ DRIFTS, pyridine-IR, and NH3-TPD were used to explore the acidic properties of the samples, which proved that stable Lewis acidic sites are present in the samples even at 300 °C. The catalytic performance of UiO-66 (Zr/Ti) containing different Ti4+ was explored under different conditions. At the same time, the scale-up experiment was carried out in a 5 L reactor, and the PET chips obtained had a lower b value. The catalytic reaction mechanism of UiO-66(Zr/Ti) was demonstrated by DFT calculations and the catalytic performance was close to Sb-based catalysts.

Aerobic activation of alcohols on Zn-promoted atomically-dispersed Ru sites encapsulated within UiO-66 framework for imine synthesis

Direct oxidative coupling of alcohols and amines is an environmental-benign and atomic-economy approach for imine synthesis. We disclosed that UiO-66 framework successfully confined Ru to single-atom scale with assistance of oxophilic Zn2+ promoter. This RuZn@UiO-66 catalyst showed a highest TOF of 78 h-1 among all Ru catalysts in literature and attained > 99% yield to benzylideneaniline in the model reaction in an O2 atmosphere at a low temperature without alkaline additives. In addition, this catalyst demonstrated satisfying gram-scale imine synthesis, wide substrate scope and stable reusability. Kinetic investigations and in situ characterizations allowed getting insights to active sites, amphoteric carrier and reaction mechanism. Dynamic interactions between Ru and Zn based on their ratios induced electron-deficient Ru0 active sites promoted by oxophilic Zn2+ species. Hence, primary alcohols can be efficiently converted to the corresponding aldehydes using molecular O2, i.e., the rate-determining step. Besides, Zr4+-O2- pairs on UiO-66 provided adequate acidic-basic sites for the tandem catalysis.

Size- and ion-selective adsorption of organic dyes from aqueous solutions using functionalized UiO-66 frameworks

In the current context of environmental degradation, the development of novel size- and ion-selective adsorption materials for efficient wastewater treatment is a pressing concern. In this study, the selective adsorption properties of the metal–organic frameworks UiO-66, sulfo-functionalized UiO-66, and amino-functionalized UiO-66 are investigated using the organic dyes methylene blue, rhodamine B, methyl orange, and acid red 52 as model pollutants. Owing to the different molecular size of the dyes, UiO-66 showed a high adsorption capacity for methylene blue and methyl orange, whereas large rhodamine B and acid red 52 were not easy to be adsorbed in the micropores of the UiO-66 framework. In addition, the sulfo- and amino-functionalization of the UiO-66 framework enhanced the adsorption capacity for methylene blue and methyl orange, respectively. The ion-selective adsorption properties of the UiO-66 framework were demonstrated using mixed solutions of methylene blue and methyl orange. Although both compounds were moderately adsorbed into UiO-66, methylene blue and methyl orange were selectively adsorbed using sulfo-functionalized UiO-66 and amino-functionalized UiO-66, respectively. This combined size-selectivity and ion-selectivity renders functionalized UiO-66 a promising adsorbent for the removal of organic pollutants from aqueous solutions.

Creating Cu(I)-decorated defective UiO-66(Zr) framework with high CO adsorption capacity and selectivity

• Defective UiO-66 was rapidly fabricated by continuous-flow microwave synthesis. • The surface area and pore width of UiO-66 (Zr) were improved by defects. • The most defective 25Cu(I)@UiO-66 had the highest CO uptake capacity of 2.44 mmol/g. • Defective Cu(I)@UiO exhibited improved CO selectivity. • Cu(I)@UiO-66(Zr) showed good renewability and oxygen-resistant ability. Developing a highly effective material for CO storage and separation is a challenge. In this study, we first used microwave-assisted continuous-flow synthesis to create defective UiO-66(Zr) frameworks with improved surface area and pore structures, which is highly efficient for large-scale production. The defect concentration of UiO-66(Zr) was rapidly and effectively controlled within a short reaction time of 10 min. Different amounts of Cu 2+ were loaded onto defective UiO-66 samples, followed by reducing Cu 2+ to Cu + to obtain Cu(I)@UiO-66 adsorbents (Cu(I)@UiO). X-ray diffraction (XRD), N 2 -adsorption, FT-IR, SEM, TEM, thermogravimetric analysis (TGA), and XPS analyses were used to characterize the physicochemical properties of the prepared adsorbent materials. Gas adsorption experiments revealed that Cu(I)-decorated defective UiO-66 exhibited high CO adsorption capacity due to the π complexation between Cu + and CO. The CO adsorbing amount and CO selectivity onto the Cu(I)@UiO-66 samples were improved by adjusting the defect concentration and Cu(I) load on the UiO-66 host. The breakthrough experiment confirms that this defective Cu(I)@UiO adsorbent can efficiently separate CO/N 2 mixture under dynamic mixture flow conditions. Furthermore, after several cyclic adsorption–desorption experiments, the defective Cu(I)@UiO-66 is highly regenerable and has a good oxygen-resistant ability. The study describes a simple and scalable method for producing π-complexation adsorbent for CO adsorption.

Enhanced CO2 adsorption performance on amino-defective UiO-66 with 4-amino benzoic acid as the defective linker

UiO-66(Zr), one of the Zr-based metal–organic frameworks (MOFs), is a potential adsorbent for gas separation owing to its large surface area, easily tunable pore structure, and high chemical/thermal stability. Nevertheless, its CO2 adsorption amount is somewhat modest in comparison to that of various MOFs. In this study, 4-aminobenzoic acid (PABA) as amino-defective linker was mixed to terephthalic acid at various compositions in a one-step synthesis of UiO-66(Zr) framework. This new restructuring strategy produced defective UiO-66(Zr) with enhanced porosity owing to the missing-linker defects, simultaneously formed –NH2 groups in the framework, leading to the improvement of the CO2 capture capacity. At 298 K and 100 kPa, the defective UiO-66 modified with 10% PABA exhibited the highest CO2 uptake capacity of ~ 2.47 mmol g−1 and ideal adsorbed solution theory (IAST)-based CO2/N2 selectivity of ~ 46, which surpass many other CO2 benchmark adsorbents. This opens a new perspective for developing defective UiO-66(Zr) adsorbent contained amine functional groups, which can improve CO2 separation performance.

Facile synthesis of magnetic framework composite MgFe2O4@UiO-66(Zr) and its applications in the adsorption-photocatalytic degradation of tetracycline.

Recently, metal-organic framework (MOF)-based hybrid composites have attracted significant attention in photocatalytic applications. In this work, MgFe2O4@UiO-66(Zr) (MFeO@UiO) composites with varying compositions were successfully synthesized via facile in situ assemblies. Depositing the UiO-66(Zr) framework onto ferrite nanoparticles yielded a composite structure having a lower bandgap energy (2.28-2.60 eV) than that of the parent UiO-66(Zr) (~3.8 eV). Moreover, the MFeO@UiO composite exhibited magnetic separation property and improved porosity. The removal experiment for tetracycline (TC) in aqueous media revealed that the MFeO@UiO composite exhibited a high total TC removal efficiency of ca. ~94% within 45-min preadsorption and 120-min visible-light illumination, which is higher than that of pristine ferrite and UiO-66(Zr). The enhanced photodegradation efficiency of MFeO@UiO is attributed to efficient interfacial charge transfer at the heterojunction and the synergistic effect between the semiconductors. Radical scavenging experiments revealed that photogenerated holes (h+) and hydroxyl radicals (·OH) were the major reactive species involved in TC photodegradation. Moreover, the prepared MFeO@UiO nanocomposite showed good recyclability and renewability, making it a potential material for wastewater treatments.

Ultra-deep removal of Pb by functionality tuned UiO-66 framework: A combined experimental, theoretical and HSAB approach

A specific functionality in the adsorbent materials plays a significant role for the selective capture of heavy metals based on Pearson's Hard-Soft-Acid-Base (HSAB) concept. Herein, we introduced single and double amino- and thiol-functionalities into the UiO-66 framework, which acted as hard and soft base sites for heavy metal adsorption, respectively. The synthesized adsorbents (labelled as NH2-UiO-66, (NH2)2-UiO-66, SH-UiO-66 and (SH)2-UiO-66) were applied for the selective removal of lead (Pb) ions from contaminated water. The removal efficiency of Pb was about 64, 85, 75 and 99% (pH = 6, T = 30 °C, sample dosage = 10 mg, Pb concentration = 100 mg L−1), respectively, based on available number of interacting sites in the respective adsorbent. To elaborate HSAB concept, the interacting sites of these functional groups towards Pb were explored by identifying their possible types of interactions in terms of soft acid-base affinity, coordinate and covalent bonding, chelation, π-π interactions and synergetic effect of bonding. Density functional theory (DFT) simulation was used to confirm these interactions and to help the better understanding of adsorption mechanism. Model fitting and characterization of Pb-sorbed adsorbents were also performed to reveal kinetics, order of adsorptive reaction, thermodynamics and adsorption mechanism. Moreover, the optimization of adsorptive removal was performed by controlled parameters including time, initial concentration, pH and temperature. The reusability and selectivity of these adsorbents along with recovery of Pb(II) were also assessed. This study presents the conceptual framework for the design of functional adsorbents in the removal of heavy metals using the HSAB principle as an intended guideline.

Aerobic epoxidation of styrene over Zr-based metal-organic framework encapsulated transition metal substituted phosphomolybdic acid

• Hybrid composites TM-HPA@UiO-66 (TM = Fe, Co, Ni, or Cu) and HPA@UiO-66 were solvothermal synthesized. • Heteropoly acid compounds are uniformly dispersed in the cage of metal organic framework. • Co-HPA@UiO-66 exhibits high catalytic activity, selectivity and stability for styrene epoxidation. • Aerobic epoxidation of styrene over Co-HPA@UiO-66 involves an acylperoxy radical route. • The UiO-66 framework provides an ideal environment for stabilizing the heteropoly acid compounds. Catalytic epoxidation of styrene with molecular oxygen is regarded as an eco-friendly alternative to producing industrially important chemical of styrene oxide (STO). Recent efforts have been focused on developing highly active and stable heterogeneous catalysts with high STO selectivity for the aerobic epoxidation of styrene. Herein, a series of transition metal monosubstituted heteropolyacid compounds (TM-HPAs), such as Fe, Co, Ni or Cu-monosubstituted HPA, were encapsulated in UiO-66 frameworks (denoted as TM-HPA@UiO-66) by direct solvothermal method, and their catalytic properties were investigated for the aerobic epoxidation of styrene with aldehydes as co-reductants. Among them, Co-HPA@UiO-66 showed relatively high catalytic activity, stability and epoxidation selectivity at very mild conditions (313 K, ambient pressure), that can achieve 82 % selectivity to STO under a styrene conversion of 96 % with air as oxidant and pivalaldehyde (PIA) as co-reductant. In addition, the hybrid composite catalyst can also efficiently catalyze the aerobic epoxidation of a variety of styrene derivatives. The monosubstituted Co atoms in Co-HPA@UiO-66 are the main active sites for the aerobic epoxidation of styrene with O 2 /PIA, which can efficiently converting styrene to the corresponding epoxide through the activation of the in-situ generated acylperoxy radical intermediate.

Boosting molecular recognition of acetylene in UiO-66 framework through pore environment functionalization

The potential of metal–organic frameworks (MOFs) for application in gas separation processes has been widely recognized. Nonetheless, due to their structural instability and high cost, few MOFs have been utilized in the industry. Among them, UiO-66 is one of the most promising materials which displays good structural stability and its preparation is considered economical. Notably, it also provides a valuable platform for the construction of other robust MOFs for various applications. Herein, trifluoromethyl ligands were introduced into the UiO-66 framework to optimize pore environment also to improve its C2H2 recognition ability. Single component adsorption and the corresponding IAST calculation confirmed that compared to UiO-66, UiO-66-(CF3)2 exhibited 2 ~ 3 times higher selectivity for C2H2/C2H4 and C2H2/CO2 separation. Enhanced selectivity resulted in a significantly improved C2H4 separation productivity (56 compared to 36 cm3/cm3) and a reduction in the co-adsorption time. Importantly, the modified UiO-66 framework could be prepared using a simple method and inherited a highly stable structure and good cycling performance of the original material.

Encapsulating Keggin‐H 3 PW 12 O 40 into UIO‐66(Zr) for manufacturing the biodiesel

In the presence of acetic acid as modulated agent, Keggin-H3PW12O40 (K-PW12) has been encapsulated into UIO-66(Zr) by the solvothermal method. The as-synthesized K-PW12@UIO-66(Zr) composite has further been characterized by PXRD, TG, FTIR, ICP-AES, N2 isothermal adsorption, SEM and TEM. The results exhibit that Keggin-H3PW12O40 is entrapped into the interior cage of UIO-66(Zr) framework which is enlarged by losing terephthalic acid linker in the presence of acetic acid. K-PW12@UIO-66(Zr) composite can efficiently catalyse the esterification of methanol and oleic acid into biodiesel.

Modeling of Diffusion of Acetone in UiO-66

Highly porous zirconium-based metal–organic frameworks (MOFs) have been widely studied as materials for sorption and destruction of chemical warfare agents (CWAs). It is important to understand the diffusion of CWAs, their reaction products, and environmental molecules through MOFs to utilize these materials for protection against CWA threats. As a first step toward this goal, we study adsorption and diffusion of acetone in pristine UiO-66. We have chosen to study UiO-66 because it has been demonstrated to be effective for destruction of CWAs and simulants; we use acetone because it is a prototypical polar organic molecule small enough to be expected to diffuse fairly rapidly through nondefective UiO-66. We specifically examine the impact of framework flexibility and hydrogen bonding between acetone and the OH groups on the nodes of the framework on the diffusivity of acetone. We find that inclusion of flexibility is essential for meaningful predictions of diffusion of acetone. We have identified the dynamics of the three linkers making up the triangular window between adjacent pores as the critical factor in controlling diffusion of acetone. We demonstrate from experiments and first-principles calculations that acetone readily hydrogen bonds to UiO-66 framework OH groups. We have modified the classical potential for UiO-66 to accurately model the framework–acetone hydrogen bonds, which are not accounted for in many MOF potentials. We find that hydrogen bonding decreases the diffusivity by about 1 order of magnitude at low loading and about a factor of 3 at high loading. Thus, proper accounting of hydrogen bonding and framework flexibility are both critical for obtaining physically realistic values of diffusivities for acetone and similar-sized polar molecules in UiO-66.

Adsorption and diffusion of H2 and CO on UiO-66: A Monte Carlo simulation study

Metal-organic frameworks (MOFs) are a new class of nanoporous materials that have attracted much attention for the adsorption of small molecules, due to the large size of the cavities. In this study, we investigate the adsorption and diffusion of hydrogen (H2) and carbon monoxide (CO) guest molecules to the UiO-66 framework, as one of the most widely used MOFs, by using Monte Carlo simulation method. The results prove that an increment in the temperature decreases the amount of the adsorbed H2 and CO on the UiO-66 framework. While an enhancement of the pressure increases the amount of the adsorbed H2 and CO on the UiO-66 framework. Besides, the adsorption of H2 and CO on UiO-66 is the type I isotherm. The calculated isosteric heat for CO/UiO-66 is slightly higher than that of H2/UiO-66. The means of square displacement (MSD) value is less for CO molecule; hence, the movement of the guest molecule within the host cavity slows down and the guest molecule travels a shorter distance over a period of time. The guest molecule with higher molecular mass possesses less mobility, and therefore, it will have less permeability.

Solvothermal synthesis of Co-substituted phosphomolybdate acid encapsulated in the UiO-66 framework for catalytic application in olefin epoxidation

Hybrid composites of phosphomolybdic acid@UiO-66 (PMo12@UiO-66) and Co-substituted phosphomolybdic acid@UiO-66 (PMo11Co@UiO-66) were synthesized using the direct solvothermal method. A variety of characterization results demonstrated that phosphomolybdic acid (PMo12) or Co-substituted phosphomolybdate acid (PMo11Co) clusters are uniformly dispersed in the cages of Zr-based metal-organic UiO-66 frameworks. The catalytic properties of these hybrid composites were investigated by applying the epoxidation of olefins with tert-butyl hydroperoxide as the oxidant. Compared to PMo12@UiO-66, PMo11Co@UiO-66 showed a much higher catalytic activity and was simply recovered by filtration and reused for at least ten runs without significant loss of catalytic activity. Particularly, PMo11Co@UiO-66 can efficiently convert cyclic olefins like limonenes to epoxides, and its selectivity to 1,2-limonene oxide reached 91% in the presence of a radical inhibitor such as hydroquinone. The excellent catalytic activity and stability of the hybrid composite PMo11Co@UiO-66 are mainly attributed to the uniform distribution of highly active PMo11Co units within the smaller cages of UiO-66, to the suitable surface polarity of the hybrid composite for facilitating the access of reagents and solvent, and to the strong interface-interactions between the polyoxometalate and the UiO-66 framework.

Synergistic dual-Li+ sites for CO2 separation in metal-organic framework composites

Although Li incorporation into adsorbent has been considered as an efficient method to enhance the selectivity for CO2 capture, the reported results are not desired. Herein, we proposed a dual-Li+ sites synergistic strategy to boost CO2 affinity and selectivity. The synergistic dual-Li+ sites in MOF are constructed by incorporating polyacrylic acid (PAA) with rich flexible carboxyl sites into stable UiO-66 framework, followed by neutralization with LiOH solution. Interestingly, 0.1 M Li+@PAA@UiO-66 composites exhibit steep absorption isotherm at low pressure range, which has never been observed in any other Li doped adsorbent, suggesting ultrahigh CO2 affinity. Meanwhile, 0.1 M Li+@PAA@UiO-66 composites show very high selectivity for CO2 over N2 or CH4 (6341 and 1904 at 298 K, respectively) at zero coverage, surpassing all the reported Li doped adsorbents. The DFT calculations reveal that synergistic dual-Li+ sites show much stronger interactions with CO2 than that of traditional single Li+ site. This work not only proposes a strategy of constructing synergistic dual-Li+ sites in MOF to boost CO2 adsorption and separation, but also provides a promising CO2 adsorbent with high efficiency, high water stability and recyclability, low cost and commercially available raw materials, as well as simple and feasible preparation process.

Modulation of driving forces fo UiO-66 analog adsorbents by decoration with amino functional groups: Superior adsorption of hazardous dyes

Metal–organic frameworks (MOFs) are promising adsorbents that can be improved for practical applications by functionalization. Herein, we report UiO-66-NH2, an amino-modified MOF with a superior toxic dye adsorption performance. Uncoordinated –NH2 groups were successfully introduced into the UiO-66 framework to modulate the adsorption driving forces between toxic organic dyes and the UiO-66-NH2 adsorbent by varying the molar ratios of the organic linkers 2-aminoterephthalic acid and terephthalic acid (H2BDC-NH2:H2BDC). The adsorption uptakes of the UiO-66-NH2 adsorbent with a H2BDC-NH2:H2BDC of 1:9 were 538.2 mg g−1 for methyl orange and 224.2 mg g−1 for methylene blue, which were respectively 207.2% and 815.1% higher than those of undecorated UiO-66. The adsorption behavior of the modified UiO-66-NH2 adsorbent is controlled by the synergistic interplay between π–π interactions, electrostatic attraction/repulsion, and hydrogen bonding, as well as the pore volume of the adsorbent.