Mass transfer in VOC adsorption on zeolite: experimental and theoretical breakthrough curves

Tuning the Hierarchical Pore Structure and the Metal Site in a Metal-Organic Framework Derivative to Unravel the Mechanism for the Adsorption of Different Volatile Organic Compounds

Volatile organic compounds (VOCs) are one of the main classes of air pollutants, and it is important to develop efficient adsorbents to remove them from the atmosphere. To do this most efficiently, we need to understand the mechanism of VOC adsorption. In this work, we described how the metal organic framework (MOF), ZIF-8, was used as a precursor to generate MOF derivatives (Zn-GC) through temperature-controlled calcination, which had adjustable metal sites and hierarchical pore structure. It was used as a model adsorbent to study the adsorption and desorption characteristics of different VOCs. Zn-GC-850 with developed pores exhibited higher adsorption performance for the benzene series, whereas Zn-GC-650 with more metal sites had a better adsorption capacity for oxygen-containing VOCs. By tuning the molecular structure of the VOCs, we revealed the adsorption mechanism of different VOCs at the molecular level. The more developed hierarchical pore structure obtained at the higher temperature facilitates the diffusion of the benzene series, and the noncovalent interaction between their methyl group(s) and the carbonized MOF derivatives improves the adsorption affinity; while the higher exposure of Zn sites obtained at lower temperature favors the adsorption of oxygen-containing VOCs by Zn-O bonds. The mass transfers of VOCs and the role of the adsorbent were simulated by multiple theoretical models. This study strengthens the basis for the design and optimization of the adsorbent and catalyst for VOCs treatment.

Management of typical VOCs in air with adsorbents: status and challenges

The serious harm of volatile organic compounds (VOCs) to the ecological environment and human health has attracted widespread attention worldwide. With economic growth and accelerated industrialization, the anthropogenic emissions of VOCs have continued to increase. The most crucial aspect is to choose the appropriate adsorbent, which is very important for the VOCs removal. The search for environmentally friendly VOCs treatment technologies is urgent. The adsorption method is one of the most promising VOCs emission reduction technologies with the advantages of high cost-effectiveness, simple operation, and low energy consumption. One of the most critical aspects is the selection of the appropriate adsorbent, which is very important for the removal of VOCs. This work provides an overview of the sources and hazards of VOCs, focusing on recent research advances in VOCs adsorption materials and the key factors controlling the VOCs adsorption process. A summary of the key challenges and opportunities for each adsorbent is also provided. The adsorption capacity for VOCs is enhanced by an abundant specific surface area; the most efficient adsorption process is achieved when the pore size is slightly larger than the molecular diameter of VOCs; the increase in the number of chemical functional groups contributes to the increase in adsorption capacity. In addition, methods of activation and surface modification to improve the adsorption capacity for VOCs are discussed to guide the design of more advanced adsorbents.

Facile synthesis of mesoporous ZSM-5 aided by sonication and its application for VOCs capture

Application of ultrasound power to the mother liquor is popular pretreatment for zeolite synthesis which offers a simple way of accelerating crystallization process and finetuning the properties of nanocrystalline zeolites. In this work, sonication-aided synthesis of mesoporous ZSM-5 at low temperature and ambient pressure was systematically studied, in an attempt to reach efficient and benign synthesis of zeolites with hierarchical pore structure, which has wide applications as catalysts and sorbents. The effects of sonication duration, power density, sonication temperature and seeding on the crystallization of ZSM-5 were investigated. The obtained samples were characterized by XRD, SEM, BET and VOCs capture. High quality mesoporous ZSM-5 can be obtained by a facile 5 d synthesis at 363 K, much faster than conventional hydrothermal synthesis. The reduced synthesis time was mainly attributed to the enhanced crystallization kinetics caused by the fragmentation of seeds and nuclei, while sonication radiation had little impact on the nucleation process. Compared with control sample, mesoporous ZSM-5 prepared by sonochemical method had higher surface area and mesoporosity which demonstrated improved adsorption performance for the capture of isopropanol.

Removal of gaseous benzene by a fixed-bed system packed with a highly porous metal-organic framework (MOF-199) coated glass beads

The utility of nanomaterial adsorbents is often limited by their physical features, especially fine particle size. For example, a large bed-pressure drop is accompnied inevitably, if fine-particle sorbents are used in a packed bed system. To learn more about the effect of adsorbent morphology on uptake performance, we examined the adsorption efficiency of metal-organic framework 199 (MOF-199) in the pristine (fine powder) form and after its binding on to glass beads as an inert support. Most importantly, we investigated the effect of such coatings on adsorption of gaseous benzene (0.1-10 Pa) in a dry N₂ stream, particularly as a function of the amount of MOF-199 loaded on glass beads (MOF-199@GB) (i.e., 0,% 1%, 3%, 10%, and 20%, w/w) at near-ambient conditions (298 K and 1 atm). A 1% MOF-199 load gave optimal performance against a 0.1 Pa benzene vapor stream in 1 atm of N₂, with a two-to five-fold improvement (e.g., in terms of 10% breakthrough volume [BTV] (46 L atm [g.MOF-199)^-1], partition coefficient at 100% BTV (3 mol [kg.MOF-199]^-1 Pa^-1), and adsorption capacity at 100% BTV (20 mg [g.MOF-199]^-1 (areal capacity: 8.8 × 10^-7 mol m^-2) compared with those of 3%, 10%, and 20% loading. The relative performance of benzene adsorption was closely associated with the content of MOF-199@GB (e.g., 1% > 3% > 10% > 20%) and the surface availability (m² [g.MOF-199]^-1) such as 291 > 221 > 198 > 181, respectively. This study offers new insights into the strategies needed to expand the utility of finely powdered MOFs in various environmental applications.

Highly selective gas sensing enabled by filters

Portable and inexpensive gas sensors are essential for the next generation of non-invasive medical diagnostics, smart air quality monitoring & control, human search & rescue and food quality assessment to name a few of their immediate applications. Therein, analyte selectivity in complex gas mixtures like breath or indoor air remains the major challenge. Filters are an effective and versatile, though often unrecognized, route to overcome selectivity issues by exploiting additional properties of target analytes (e.g., molecular size and surface affinity) besides reactivity with the sensing material. This review provides a tutorial for the material engineering of sorption, size-selective and catalytic filters. Of specific interest are high surface area sorbents (e.g., activated carbon, silica gels and porous polymers) with tunable properties, microporous materials (e.g., zeolites and metal-organic frameworks) and heterogeneous catalysts, respectively. Emphasis is placed on material design for targeted gas separation, portable device integration and performance. Finally, research frontiers and opportunities for low-cost gas sensing systems in emerging applications are highlighted.

Dynamic adsorption/desorption of p-xylene on nanomorphic MFI zeolites: Effect of zeolite crystal thickness and mesopore architecture

Zeolites have attracted great interest as an adsorbent for the removal of volatile organic compounds. However, they suffer from low adsorption capacities due to severe diffusion limitations. Here, the effects of zeolite thickness and mesopore architecture on dynamic adsorption of p-xylene have been examined with a number of MFI-type zeolites with different crystal thicknesses and mesopore openings (i.e. open mesopore, constricted mesopore), which were prepared via hydrothermal synthesis with various organic structure-directing agents and post-synthetic desilication. The results showed that the breakthrough time of MFI zeolite could be improved by more than 2.3 times by reducing the crystal thickness of zeolite to a single-unit-cell dimension (∼2 nm). The time improvement can be attributed to the short diffusion path length that results in easy access of p-xylene to intracrystalline micropores and a large external crystal surface area. In the case of mesopore openings, the presence of constricted mesopores caused the mass transfer of p-xylene into zeolite adsorbents to slow down while open mesopores did not. Furthermore, mesopore opening is an important factor for the desorption behavior of p-xylene. Adsorbed p-xylene by mesoporous zeolites could be desorbed at lower temperatures only when facile diffusion to the exterior through mesoporous channels was possible.

Dual-function surface hydrogen bonds enable robust O2 activation for deep photocatalytic toluene oxidation

Extensive hydrogen-bonds between the hydroxyl-rich BiOCl surface and phosphoric acid significantly facilitate oxygen vacancy formation, O₂ activation, and deep toluene oxidation.

Synthesis and Adsorption Performance of a Hierarchical Micro-Mesoporous Carbon for Toluene Removal under Ambient Conditions

Ordered mesoporous carbons (OMCs) were synthesized in this study through a soft template method and then activated by employing different mass ratios of KOH/OMCs to obtain KOH-activated ordered mesoporous carbons (KOMCs) with hierarchical pore structures. To verify the adsorption capacity, the KOMCs have been subjected to toluene emission-reduction experiments. The KOMCs were characterized by TEM, XRD, N2 adsorption-desorption isotherms, and Raman spectroscopy. The pore structure of OMCs was found to be effectively optimized by the activation with KOH, with the BET-area and total pore volume values reaching as high as 2661 m2 g-1 and 2.14 cm3 g-1 respectively. Then, the dynamic adsorption capacity of toluene on KOMCs was investigated via breakthrough curves, which can be well described by the Yoon and Nelson (Y-N) model. The dynamic adsorption capacities of toluene exhibit the following order: OMC < KOMC-1 < KOMC-5 < KOMC-3. The sample activated by KOH/OMC with a mass ratio of 3:1 (KOMC-3) demonstrated the highest toluene adsorption capacity of 355.67 mg g-1, three times higher in comparison with the untreated carbon (104.61 mg g-1). The modified hierarchical porous carbons also exhibited good recyclability. The KOMCs with rich pore structure, high toluene adsorption capacity, and superior reusability thus display a huge potential for volatile organic compound (VOC) elimination.

Aldehydes gas ozonation monitoring: Interest of SIFT/MS versus GC/FID

Two analytical techniques - online Gas Chromatography coupled with Flame Ionization Detector (often used method for VOCs monitoring) versus Selected Ion Flow Tube coupled with Mass Spectrometry (a more recent technique based on direct mass spectrometry) - were compared in association to an ozone-based gas treatment. Selecting aldehydes as the representative VOCs, their concentrations were monitored during ozonation experiments by both techniques in parallel. Contradictory results were obtained in the presence of ozone. Aldehydes were up to 90% removed due to a reaction with ozone according to GC/FID analysis, whereas with SIFT/MS, aldehydes concentration remained at the same level during the experiments regardless of the ozone presence. In addition, it was demonstrated that the apparent aldehydes removal was affected by GC injector temperature, varying from 90% (when it was at 250 °C) to 60% (at 100 °C). Meanwhile, even when the ozonation reactor was heated to 100 °C, no aldehydes conversion was evidenced by SIFT/MS, suggesting that the GC injector temperature was not the only interference-causing parameter. The ozone-aldehyde reaction is probably catalyzed by some material of GC injector and/or column. An ozone-GC interference was therefore confirmed, making unsuitable the use of GC/FID with silicone stationary phase to monitor aldehydes in presence of high concentrations of ozone (at least 50 ppmv). On the other hand, SIFT/MS was validated as a reliable technique, which can be employed in order to measure VOCs concentrations in ozonation processes.

Metal organic frameworks as potent treatment media for odorants and volatiles in air

The presence of odorants/volatiles in the air exerted various types of negative impacts on the surrounding environment. Their concentrations in indoor/outdoor air, if exceeding the threshold level, may not only affect human health but also deteriorate living standards. To maintain and enhance the quality of life, a better tool for the removal of these molecules is in great demand. Metal-organic frameworks (MOFs) and their associated materials offer an excellent platform for the treatment of odorants/volatiles in air (and water) systems. The diversity of ligands and metal ions in their frame imparts large loading capacities and excellent selectivity for a variety of targetable VOCs and/or odorants. This review discusses the use of MOFs and their composites to treat odorants/volatile molecules in gaseous media, with extensive discussion of their adsorptive uptakes, along with methods for their synthesis and regeneration. Moreover, the progression of odorant/volatile removal by MOFs is considered, with a special note on future directions in this emerging research field.

Effect of competing ions and causticization on the ammonia adsorption by a novel poly ligand exchanger (PLE) ammonia adsorption reagent

In this paper, a poly ligand exchanger, Cu(II)-loaded chelating resin named ammonia adsorption reagent (AMAR), bearing the functional group of weak iminodiacetate acid, was prepared to efficiently remove ammonia from solutions. Batch adsorption equilibrium experiments were conducted under a range of conditions. The effects of pH on the removal of ammonia by AMAR were investigated at 25 °C. The copper loaded on the resin forms a complex with NH₃ in solution under alkaline condition. The effect of alkaline dosage (AD) on the ammonia adsorption was investigated. The maximum breakthrough bed volumes were obtained when the AD was set as 0.75 mmol OH^-/mL. The higher AD did not guarantee the better ammonia removal efficiency due to the forming of Cu(OH)₂ precipitate between OH^- in solutions and Cu(II) on the resin. The effect of competing ions on the adsorption breakthrough curve of virgin AMAR and causticized AMAR was also investigated. The results demonstrated that the existence of competing ions had a negative impact on the adsorption capacity for both virgin AMAR and causticized AMAR. After causticization, the AMAR was more resistant to the competing ions comparing with virgin AMAR. The bivalent Ca²⁺ affects the ammonia adsorption more than does the monovalent Na⁺.

Predicting the lifetime of organic vapor cartridges exposed to volatile organic compound mixtures using a partial differential equations model

In this study, equilibria, breakthrough curves, and breakthrough times were predicted for three binary mixtures of four volatile organic compounds (VOCs) using a model based on partial differential equations of dynamic adsorption coupling a mass balance, a simple Linear Driving Force (LDF) hypothesis to describe the kinetics, and the well-known Extended-Langmuir (EL) equilibrium model. The model aims to predict with a limited complexity, the BTCs of respirator cartridges exposed to binary vapor mixtures from equilibria and kinetics data obtained from single component. In the model, multicomponent mass transfer was simplified to use only single dynamic adsorption data. The EL expression used in this study predicted equilibria with relatively good accuracy for acetone/ethanol and ethanol/cyclohexane mixtures, but the prediction of cyclohexane uptake when mixed with heptane is less satisfactory. The BTCs given by the model were compared to experimental BTCs to determine the accuracy of the model and the impact of the approximation on mass transfer coefficients. From BTCs, breakthrough times at 10% of the exposure concentration t10% were determined. All t10% were predicted within 20% of the experimental values, and 63% of the breakthrough times were predicted within a 10% error. This study demonstrated that a simple mass balance combined with kinetic approximations is sufficient to predict lifetime for respirator cartridges exposed to VOC mixtures. It also showed that a commonly adopted approach to describe multicomponent adsorption based on volatility of VOC rather than adsorption equilibrium greatly overestimated the breakthrough times.

Application of high silica zeolite ZSM-5 in a hybrid treatment process based on sequential adsorption and ozonation for VOCs elimination

In this study, a hydrophobic synthetic zeolite, namely ZSM-5 is chosen as an adsorbent/catalyst for toluene removal. Experimental results showed that toluene adsorption onto ZSM-5 was favourable, following a Langmuir adsorption isotherm model. ZSM-5 zeolite was regenerated using gaseous ozone at low temperature. Adsorbed toluene was oxidised, releasing mainly CO2 and H2O. Traces of oxidation by-products such as acetic acid and acetaldehyde were formed and remained adsorbed after the oxidativate regeneration with ozone. After four successive cycles of adsorption/ozonation, the adsorption efficiency was not affected (92%-99%). These results showed that volatile organic compound (VOC) removal by adsorption onto ZSM-5 zeolite followed by ozone regeneration could be used as a promising hybrid process for the control of VOC emissions in terms of efficiency.

Prediction of the breakthrough curves of VOC isothermal adsorption on hypercrosslinked polymeric adsorbents in a fixed bed

The new method established in this paper has good accuracy for predicting the adsorption capacity and breakthrough curve without requiring experiments.

Competitive adsorption of VOCs from binary aqueous mixtures on zeolite ZSM-5

Adsorption equilibria of methyl tert-butyl ether (MTBE)/toluene (TOL), and 1,2-dichloroethane (DCE)/MTBE binary mixtures in aqueous solution on ZSM-5 were measured over a wide range of concentrations.

Performance of mesoporous silicas (MCM-41 and SBA-15) and carbon (CMK-3) in the removal of gas-phase naphthalene: adsorption capacity, rate and regenerability

The adsorption isotherms of gas-phase naphthalene on mesosilicas MCM-41 and SBA-15, and mesocarbon CMK-3 were determined by column tests at 125 °C, with feed concentrations ranging from 7.63 × 10⁻⁵ to 4.64 × 10⁻² mol m⁻³ (1.88 to 1140 ppm).

Fixed-bed adsorption of toluene on high silica zeolites: experiments and mathematical modelling using LDF approximation and a multisite model

The adsorption of toluene (TOL) as a target volatile organic compound has been studied experimentally and modelled on various hydrophobic zeolites: Faujasite (FAU), ZSM-5 (Z) and Mordenite (MOR). The influence of the nature of the compensating cation (H+ or Na+) has also been investigated for ZSM-5 zeolite, which is known to possess three kinds of adsorption sites (sinusoidal channels, straight channels and intersections). Type I isotherms observed on FAU, Na-Z and MOR fitted well with the Langmuir model. A deviation from a type I isotherm was observed for H-Z, because of the structure of this zeolite. The Successive Langmuir Model was more successful to fit the 'bump' of the experimental curve than the Double Langmuir. Classical shapes were found for MOR, FAU and Na-Z breakthrough curves that were fitted with good accuracy using the Linear Driving Force (LDF) approximation. In the case of H-Z, a change of profile was observed during the dynamic adsorption and the differences seen between the Na-Z and H-Z behaviours were explained by the strong interactions between Na+ and adsorbed TOL at the intersection sites. The Na+ cations prevented reorientation of TOL molecules at the intersection and thereby avoided the filling of the sinusoidal channel segments. Thus, a specific model was developed for fitting the breakthrough curve of H-Z. The model developed took into account these two types of adsorption sites with the overall uptake for each site being given by an LDF approximation.

Oxidative regeneration of toluene-saturated natural zeolite by gaseous ozone: the influence of zeolite chemical surface characteristics

In this study, the effect of zeolite chemical surface characteristics on the oxidative regeneration of toluene saturated-zeolite samples is investigated. A Chilean natural zeolite (53% clinoptilolite, 40% mordenite and 7% quartz) was chemically modified by acid treatment with hydrochloric acid and by ion-exchange with ammonium sulphate. Thermal pre-treatments at 623 and 823K were applied and six zeolite samples with different chemical surface characteristics were generated. Chemical modification of natural zeolite followed by thermal out-gassing allows distinguishing the role of acidic surface sites on the regeneration of exhausted zeolites. An increase in Brønsted acid sites on zeolite surface is observed as a result of ammonium-exchange treatment followed by thermal treatment at 623K, thus increasing the adsorption capacity toward toluene. High ozone consumption could be associated to a high content of Lewis acid sites, since these could decompose ozone into atomic active oxygen species. Then, surface oxidation reactions could take part among adsorbed toluene at Brønsted acid sites and surface atomic oxygen species, reducing the amount of adsorbed toluene after the regenerative oxidation with ozone. Experimental results show that the presence of adsorbed oxidation by-products has a negative impact on the recovery of zeolite adsorption capacity.

Experimental device for dioxin vapour generation: a steady and adjustable source of gaseous 2,3-DCDD

PCDD/Fs are Persistent Organic Pollutants (POPs), generated by incomplete combustion of carbonaceous and chlorinated compounds. Because of their toxicity, they have to be monitored at emission, from stationary sources like waste incinerator. In the framework of the development of an on-line analyser, the laboratory prototype requires a gaseous dioxin source. We detail the principles of a dynamic generator based on the sublimation of solid sample and on the diffusion method. Such a device has to supply a polluted flow at steady and adjustable concentration of dioxin. The dioxin generation rate is determined by the weight loss of the solid sample. It is constant during time for temperatures ranging between 75 and 100°C and for generation flow rates greater than or equal to 50 mL min(-1). Variation of generation rate with temperature is predictable. With the increasing of temperature, emitted concentration increases while the increase of the inlet pressure decreases the concentration. Helium carrier gas leads to a higher generation rate than with N2 in agreement with mass and molecular volume ratio. Thus, the outlet concentration and flow rate can be settled independently in the range of 3-100 ppm and 50-200 mL min(-1).

Functionalized hollow siliceous spheres for VOCs removal with high efficiency and stability

Functionalized hollow siliceous spheres (HSSs) have been prepared by surface modification with trimethylchlorosilane (TMCS) for the removal of volatile organic compounds (VOCs). The resultant HSSs-TMCS possesses a uniform and well-dispersed hollow spherical structure, high surface area, large total pore volume, high VOCs adsorption capacity, and small water vapor adsorption capacity. The adsorption and desorption performance of HSSs-TMCS under static (n-hexane and 93# gasoline) and dynamic (n-hexane) conditions was investigated. Compared with commercial silica gel (SG) and activated carbon (AC), HSSs-TMCS show higher capacity of adsorbing n-hexane and 93# gasoline with good stability and low water vapor adsorption capacity under static adsorption conditions, higher dynamic adsorption capacity and stable breakthrough time under dynamic adsorption conditions. The high efficiency and stability of functionalized HSSs are associated with their unique hollow morphology and structure parameters. The designed HSSs-TMCS with high VOCs removal capacity and recyclability are promising candidates for the treatment of air pollution.

Evaluation of the potential of volatile organic compound (di-methyl benzene) removal using adsorption on natural minerals compared to commercial oxides

This study is dedicated to the investigation of the potential of volatile organic compounds (VOC) adsorption over low cost natural minerals (bentonite and diatomite). The performances of these solids, in terms of adsorption/desorption properties, were compared to commercial adsorbents, such as silica, alumina and titanium dioxide. The solids were first characterized by different physico-chemical methods and di-methyl benzene (dMB) was selected as model VOC pollutant for the investigation of adsorptive characteristics. The experiments were carried out with a fixed bed reactor under dynamic conditions using Fourier Transform InfraRed spectrometer to measure the evolution of dMB concentrations in the gaseous stream at the outlet of the reactor. The measured breakthrough curves yields to adsorbed amounts at saturation that has been used to obtain adsorption isotherms. The latters were used for determination of the heat involved in the adsorption process and estimation of its values using the isosteric method. Furthermore, the performances of the studied materials were compared considering the adsorption efficiency/cost ratio.

Adsorption equilibrium and kinetics for SO2, NO, CO2 on zeolites FAU and LTA

In order to develop a single-step process for removing SO(2), NO, CO(2) in flue gas simultaneously by co-adsorption method. Pure component adsorption equilibrium and kinetics of SO(2), NO, and CO(2) on zeolite NaY, NaX, CaA were obtained respectively. Equilibrium data were analyzed by equilibrium model and Henry's law constant. The results suggest that Adsorption affinity follows the trend SO(2)>CO(2)>NO for the same adsorbent. Zeolite with stronger polar surface is a more promising adsorbent candidate. Kinetics behavior was investigated using the breakthrough curve method. The overall mass transfer coefficient and diffusivity factor were determined by a linear driving force model. The results are indicative of micropore diffusion controlling mechanism. NaY zeolite has the minimum resistance of mass transfer duo to the wide pore distribution and large pore amount. CaA zeolite exhibits the highest spatial hindered effect. Finally, co-adsorption effect of SO(2), NO, and CO(2) were investigated by multi-components breakthrough method. SO(2) and NO may form new adsorbed species, however, CO(2) presents a fast breakthrough. Chemical adsorption causes SO(2) transforms to SO(4)(2-), however, element N and C are not detected in adsorbed zeolites.

Probing the adsorption characteristic of metal-organic framework MIL-101 for volatile organic compounds by quartz crystal microbalance

As volatile organic compounds (VOCs) are a major group of air pollutants, development of materials for efficient adsorption and removal of VOCs is of great significance in both environmental and analytical sciences. Here we report metal-organic frameworks (MOFs) MIL-101 for the effective adsorption of VOCs at atmospheric pressure. A simple device was designed for quartz crystal microbalance (QCM), and six VOCs with various functional groups and polarities, i.e., n-hexane, toluene, methanol, butanone, dichloromethane, and n-butylamine, were chosen as targets to probe the adsorption properties of MIL-101. The developed device allows measurement of the adsorption isotherms and monitoring of the dynamic process for the adsorption of VOCs on MOFs, and also provides a useful tool for characterization of MOFs. The adsorption isotherms of the VOCs on MIL-101 followed the Dubinin-Astakhov equation with the characteristic energy from 5.70 (methanol) to 9.13 kJ mol(-1) (n-butylamine), Astakhov exponent from 0.50 (n-butylamine) to 3.03 (n-hexane), and the limiting adsorption capacity from 0.08 (n-hexane) to 12.8 (n-butylamine) mmol g(-1). MIL-101 exhibited the strongest affinity to n-butylamine, but the weakest affinity to n-hexane. The determined Astakhov exponents and the isosteric heats of adsorption revealed the energetic heterogeneity of MIL-101. MIL-101 showed the most energetically homogeneous for n-hexane, but the most energetically heterogeneous for n-butylamine. The dynamic process of adsorption monitored by the QCM system demonstrated the distribution of the sorption sites within MIL-101. The metal sites within the MIL-101 were vital in adsorption process. MIL-101 gave much higher affinity and bigger adsorption capacity to VOCs than activated carbon, offering great potential for real applications in the adsorption and removal of VOCs.