Adsorption Of Volatile Organic Compounds Research Articles

Electrospun Polyurethane/β-Cyclodextrin Composite Membranes for Aerosol Filtration and Adsorption of Volatile Organic Compounds from the Air

Introduction: Electrospun nanomembranes have been used for effective air filtration due to their potential for active surface modification. This study aims to synthesize polyurethane (PU) nanofiber membrane incorporated with different amounts of β-cyclodextrin (β-CD) to capture volatile organic compounds (VOCs) along with aerosol filtration from the air.
 Material and Methods: First, PU was synthesized by MDI method. A 10 wt% PU solution in DMF/MEK (1:1 wt) was prepared. Various amounts of β-CD powder (0, 1, 2, 3, and 5 wt% of PU) were dispersed in the prepared PU solution. Electrospining process was carried out under determined parameters (20 kV applied voltage, tip-to-collector distance of 10 cm, solution feed, and rate of 1 ml/h). The chemical structure and morphology of the produced samples were assessed by FTIR and SEM, respectively. Finally, air filtration and toluene adsorption of different electrospun membranes were measured.
 Results: The highest filtration performance was observed for PU with 1 wt% β-CD nanofiber. Due to increased efficiency (83.13%) and low-pressure drop (∆P = 19 pa), this sample had a considerable quality parameter. The results demonstrated that the membrane loaded with β-CD was able to adsorb hazardous and carcinogenic VOCs. It was confirmed that adding β-CD into PU improves the adsorption capacity due to forming a π complex and having a different tendency against capturing a variety of VOCs.
 Conclusion: The study results revealed that the PU nanofiber incorporated with β-CD, along with the ease of regeneration, can make them attractive for air filtration and VOCs adsorption.

Three birds with one stone: Designing a novel binder-free monolithic zeolite pellet for wet VOC gas adsorption

Zeolites are promising materials for the adsorption of volatile organic compounds (VOCs), thanks to their unique pore structure, large specific surface area, and excellent stability. However, the synthesis of monolithic zeolites with a well-defined macroscopic shape, significant mechanical strength, and high VOCs adsorption capacity in humid conditions remains challenging. Here, the synthesis of binder-free monolithic zeolite pellets, possessing robust mechanical strength, high adsorption capacity, and excellent water tolerance, is reported through a citric acid sacrifice strategy. By in situ dealuminization, Y zeolite pellets have greatly improved the specific surface area and mesopore volume, leading to superior acetone and toluene adsorption performance. Moreover, the extracted aluminum species produced during the dealuminization act as a “bridge” to promote the zeolite particles into pelletization with a sufficiently high mechanical strength. Under 90% relative humidity, the acetone and toluene adsorption capacity of the synthesized zeolite pellets reach above 90% of the adsorption capacity under dry conditions, showing potential in practical industrial application. It is anticipated that this synthetic strategy will benefit the forming and development of monolithic zeolite.

Hazardous molecules and VOCs sensing properties of Ti functionalized benzene: An ab initio study

Adsorption of volatile organic compounds (VOCs) viz. HCHO, CH4, CHF3 and CH3OH and hazardous gas molecules (NH3, HCN and Cl2) on Titanium-benzene (BTi) complex is investigated by first principle calculations at MP2/6–311 + +G* * level of theory. Interaction between the molecules and BTi complex is analysed with the help of change in structural parameters, vibrational frequencies, density of state plot and NBO charge analysis. The change in HOMO-LUMO gap and electron density state confirms the adsorption of hazardous gas molecules/VOCs on BTi complex. VOCs as well as hazardous gas molecules are chemisorbed on the BTi complex with adsorption energy in the range of 0.5–3.4 eV. ADMP-MD simulations performed at 300 K and 500 K have shown that all the molecules remain adsorbed on BTi complex during the simulations at 300 K as well as 500 K. Ab initio calculations as well as ADMP-MD simulations show that BTi complex shows excellent VOCs and hazardous gas molecule adsorption properties not only at ambient conditions but also for a wide range of temperature and pressure. The BTi complex can be used to design the hazardous gas molecule and VOCs sensor for different temperature and pressure.

Graphene-Based Materials for the Removal of Volatile Organic Compounds

Abstract: Volatile organic compounds (VOCs) are a group of organic compounds such as aromatic, aliphatic and chlorinated hydrocarbons, etc. VOCs are emitted into the atmosphere during the production of adhesives, paints, printing materials, building materials, and their use. Although several removal approaches have been employed to remove VOCs, researchers have not stopped exploring new methods and materials for VOCs treatment. Graphene has recently attracted enormous attention for fundamental research and potential applications due to its large specific surface area, high mechanical strength and flexibility, and good chemical and thermal stability. Here we briefly describe the recent progress in graphene-based materials (GBMs) for applications in VOCs removal. GBMs have been exploited as novel materials in VOC adsorption, membrane separation, and photocatalysis. Although the issues need to be further studied, such as biocompatibility, toxicity, and production at low cost, GBMs are promising for VOC removal, which is the current trends and future perspectives of the field. This mini-review represents the potential of GBMs for VOC treatment.

Preparation and evaluation of fine-tuned micropore biochar by lignin impregnation for CO2 and VOCs adsorption

The pore structure of adsorbent plays a critical role during the CO2 and volatile organic compounds (VOCs) adsorption. To improve the adsorption performance, fine-tuned micropore biochar was prepared by impregnation using sodium lignosulfonate as precursor. And the impregnated biochar was characterized and used as adsorbent to adsorb CO2 and VOCs (benzene and acetone). The results showed that the specific surface area (SSA) and micropore volume (Vmicropore) of impregnated biochar increased 3.27 and 5.02 times, which enhanced the CO2 adsorption amount obviously (77.02–102.88 mg/g). The pore structure of biochar was critical to CO2 capture, and high SSA, large Vmicropore and narrow aperture were benefits for the adsorption. Both Avrami fractional model and Freundlich model fitted the adsorption better, indicating the CO2 adsorption on impregnated biochar was multilayer adsorption and determined by both physical and chemical mechanisms. The adsorption was overwhelming exothermic process, thus increasing the temperature from 0 ℃ to 65 ℃ would decrease the adsorption amount by 74.22%-79.40%. High reusability (93.98%-98.21%) after 10 times adsorption-desorption cycles acknowledged the biochar was promising CO2 adsorbents. In addition, the impregnated biochar exhibited excellent VOCs adsorption performance, with the adsorption amount being 31.35–61.14 mg/g and 44.67–80.99 mg/g for benzene and acetone, respectively. All the results showed lignin impregnated biochar is a promising adsorbent for CO2 capture and pollution adsorption.

A versatile route to fabricate Metal/UiO-66 (Metal = Pt, Pd, Ru) with high activity and stability for the catalytic oxidation of various volatile organic compounds

The supported noble metal catalysts have been demonstrated outstanding catalytic performance for the catalytic degradation of volatile organic compounds (VOCs), but their high cost, easy poisoning and sintering deactivation limit their further applications. Herein, we proposed a flexible and universal strategy to prepare the highly dispersed metal nanoparticles (Pt, Pd, Ru) supported on metal–organic frameworks (metal/MOFs) through the impregnation-reduction method for the catalytic oxidation of VOCs. Metal/MOFs integrate MOFs with large surface area and high porosity for supplying VOCs adsorption sites and highly dispersed metal species for offering catalytic active sites. For example, Pt/UiO-66 NPs exhibited nearly 100% conversion efficiency and CO2 yield for the catalytic oxidation of various VOCs including ethyl acetate (260 °C), n-hexane (260 °C) and toluene (180 °C). Particularly, there was no obvious difference in the morphology, size, distribution, crystallinity, and composition of the fresh and used Pt/UiO-66 NPs from the TEM images, XRD spectra and XPS analysis. Besides, a series of metal/MOFs (Pt, Pd, Ru) exhibited high reusability, good water resistance as well as excellent stability over 150 h on the on-stream reactions for the degradation of ethyl acetate. Furthermore, the catalytic oxidation mechanism and pathways were revealed by the study of active sites and reaction intermediates via X-ray photoelectron spectroscopy (XPS), in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and proton transfer reaction-time of flight mass spectrometer (PTR-TOF-MS). We anticipate that this work may shed light on developing noble metal catalysts supported on porous materials for novel applications in environmental catalysis.

Deactivation Mechanisms of Engineering Adsorbents for VOCs Adsorption and the Lifetime-Prolonging Strategy

Adsorption–desorption process has been considered as a promising way for both the removal and recovery of volatile organic compounds (VOCs) from waste gases. However, during the engineering applications of the adsorbents, they would be deactivated or deteriorated. Herein, the deactivation mechanisms of different engineering VOC adsorbents (activated carbons and silica gels) by different processes or parameters have been investigated. It is found that the deactivation of adsorbents is mainly attributed to the following reasons: accumulation of VOCs in the pores, breaking of the pore structures due to the frequent-changing of processing conditions, occupation of the pores by water or other impurities, and so forth. For the temperature swing adsorption (TSA) process, the performance of adsorbents would be deteriorated by (i) the accumulation of VOCs due to incomplete desorption or (ii) the collapse of the pore structure of adsorbents (e.g., activated carbons and microporous silica gel) due to frequent cooling and heating between adsorption and desorption, respectively, leading to the deactivation of adsorbents. This phenomenon could be weakened when the pores in the adsorbents increased (e.g., the mesoporous silica gel, SG B). For the vacuum swing adsorption (VSA) process, the pore structure of adsorbents was slightly influenced during the adsorption–desorption cycles. The decrease in the adsorption capacity of adsorbents was mainly ascribed to the accumulation of VOC chemicals in the pores. In addition, in the TSA or VSA process, when the water vapor was present, the adsorption performance of adsorbents will be significantly reduced due to the occupation of adsorption sites by the water, resulting in faster deactivation. Considering the processing cost and lifetime of adsorbents, the TSA and VSA are combined together herein. The results show that, compared with the single TSA and VSA, the combined VSA–TSA process could be applied to different VOCs and improve the desorption rate of the adsorbents greatly at lower energy consumption and longer lifetime.

Integration of a micropreconcentrator with solid-phase microextraction for analysis of trace volatile organic compounds by gas chromatography-mass spectrometry

The analysis of toxic volatile organic compounds (VOCs) in environmental air is important because toxic VOCs induce adverse effects on human health. Although gas chromatography- mass spectrometry (GC–MS) is the standard instrument for analysis of trace VOCs in air, this mode of analysis requires preconcentration and cryogenic processes. The preconcentration and subsequent thermal desorption of VOCs require special instruments and a long time of processing sample that significantly limit applications of GC–MS for monitoring indoor and outdoor VOC levels. Using a microfabricated preconcentrator for VOC analysis also has the challenge of a large sample volume for concentration. Using solid-phase microextraction (SPME) for VOC analysis by GC–MS often approaches the limit of detection of the GC–MS instrument for trace VOCs in air. This work reports a simple method to integrate microfabricated preconcentrators with commercial SPME fibers in a two-stage concentration processes to achieve rapid and reliable measurement of trace VOCs in air by GC–MS. We designed and fabricated a preconcentrator with micropillars in a microfluidic chamber to support sorbents and to increase the heat transfer rate to the sorbents for rapid thermal desorption. The effects of air flow rates through the preconcentrator on VOCs adsorption and thermal desorption were optimized for increasing analytical accuracy of VOCs measurements. The integration of a micropreconcentrator with SPME enabled measurements of sub-ppb levels of benzene, toluene, ethylbenzene, and xylene (BTEX), and trichloroethylene (TCE) in environmental air by GC–MS.

Delignified wood filter functionalized with metal-organic frameworks for high-efficiency air filtration

Particulate matter (PM) pullution has emerged as a global concern. Herein, delignified wood functionalized with metal–organic frameworks (MOFs) was investigated for efficient PM removal. In particular, the lignin removal was realized by a deep-eutectic-solvent assisted process. By integrating three different MOFs into the porous wood matrix, wood-based filters with hierarchical structure were fabricated. The MOF particles including ZIF-8, MOF-199 and UiO-66 were deposited on the filters through in situ growth approach, thereby leading to a uniform MOF dispersion and strong wood-MOF adhesion. The ZIF-8 functionalized wood filter exhibited the highest PM removal performance, with PM2.5 and PM10 removal efficiencies of 89.8% and 91.6%, respectively. The superior PM capture ability of ZIF-8@Wood is attributed to the suitable surface property and sophisticated channels/pores. The gas transport pathways and PM capture mechanisms within wood filter were discussed in detail. This cost-effective and environmentally friendly filtration device provides a novel material platform for PM removal, and it could be extended for hazardous gas capture and volatile organic compound adsorption.

Alumina beads decorated copper-based coordination polymer particle filter for commercial indoor air cleaner

This paper provided an insight into the dual functionalities of air filter for the removal of multiple volatile organic compounds (VOCs) and Escherichia coli (E. coli) pathogen pollutants. In this regard, a cost-effective and eco-friendly method was developed to grow copper coordination polymer particles (Cu-CPP) onto porous alumina (Al2O3) support, resulting in the formation of Cu-CPP /Al2O3 composite beads. The use of coordination polymer particles can allow more control of the physical and chemical properties of the adsorptive materials at a molecular level through rational selection of metal nodes and organic ligands. Notably, excellent toluene adsorption capacities (256.97 mg g−1) and breakthrough behaviors were observed in Cu-CPP/Al2O3 beads. For the first time, the Cu-CPP/Al2O3 beads air filter was successfully scaled up and installed on a commercial air cleaner with 1 m3 test chamber for various VOCs adsorption. The Cu-CPP/Al2O3 beads air filter exhibited removal efficiency for formaldehyde (99.5%), toluene (99.5%), acetic acid (100%) and ammonia (100%), which are superior to conventional activated carbon. The E. coli was chosen as a model for testing the inactivation performance. The Cu-CPP/Al2O3 beads showed an efficiency of 97.02%, which was substantially higher than that of activated carbon (43.78%) after 120 min of exposure. This research paves the way for the development of multifunctional air filters based on copper coordination polymer particles, which would be excellent for commercial indoor air cleaner applications.

Effects of regulator ratio and guest molecule diffusion on VOCs adsorption by defective UiO-67: Experimental and theoretical insights

• Optimum proportion of benzoic acid for synthesis of more defects UiO-67. • Defects, methyl and benzene ring enhance π-π interaction to promote VOCs adsorption. • Multiple experiments and DFT calculation analyze interaction between VOCs and MOFs. The harm that is caused by volatile organic compounds (VOCs) has attracted worldwide attention. In production, industrial processes such as fossil fuel combustion, plastics, and paints have caused complex and diverse VOCs emissions. Therefore, studying the phenomenon and influencing factors of typical VOCs adsorption is of practical significance for the treatment of multicomponent VOCs. In this work, defective UiO-67 was prepared by changing the amount of benzoic acid. Then, the adsorption performance was tested, and the adsorption kinetics were considered. The experimental results showed that the 67-ben-10 sample (for which the molar ratio of Zr 4+ to benzoic acid was 1:10) achieved the maximum toluene adsorption capacity (480 mg g −1 ), which was due to the presence of more adsorption sites, higher benzoate content, strong π-π stacking and excellent adsorption diffusion behavior. In addition, the adsorption properties of the 67-ben-10 benzene series (BTX: benzene, toluene, o-xylene, p-xylene and m-xylene) and acetone were further investigated. The results showed that the adsorption performance was related to the polarizability of the VOCs molecules, the method of pore entry and the molecular size. Finally, through desorption experiments, density functional theory (DFT) and kinetics, the binding energy was confirmed to play an important role in adsorption and diffusion.

On the adsorption of volatile organic compounds on hydroxyl-functionalized carbon nanotubes in aqueous solution

Volatile organic compounds (VOCs) are among the primary concerns due to their practical threatening on living environment and human health. This work aims at examining the physical adsorption behavior of four representative VOC species on hydroxyl-functionalized CNTs in terms of molecular dynamics simulations. Simulation results indicate that the adsorption affinities of these four VOC species follow the order of toluene > ether > acetone > methanol for both the unfunctionalized and hydroxyl-functionalized CNTs. This adsorption preference is endorsed by the binding energy calculations based on the umbrella sampling algorithm. The surface modifications due to the introduction of hydroxyl groups affect both the adsorption mechanism and equilibrium configuration. The hydrogen-bond network near the adsorption region is rebuilt for stabilizing the adsorption kinetics. Compared to the dominant van der Waals interaction, the electrostatic interaction between the charged hydroxyl groups and the VOC molecules are found to be much less significant. With the increase of hydroxyl concentration, the adsorption affinity decays for all four VOC species. This conclusion is confirmed by both the binding free energies and the number of successfully adsorbed VOC molecules. The fundamental mechanism is due to the reduction of the originally hydrophobic area of CNTs surface and the additional bonding competition from water molecules. This work presents a molecular insight on the interaction between VOC molecules and hydroxyl-functionalized CNTs in aqueous solution. It can also benefit the development and design of smart filtration devices of VOC molecules for their early removal in aqueous solutions.

Fruit ripeness sensors based on poly(lactic acid)/polyaniline solution blow‐spun fibrous membranes

AbstractReal‐time ripening monitoring stands as an attractive way to guarantee quality control and prediction of shelf life during transport and prolonged storage of fruits and vegetables. Herein, we investigate the use of poly(lactic acid)/polyaniline (PLA/PANI) solution blow‐spun nanofibrous membranes as gas sensors for fruit ripening monitoring. PLA/PANI with different blend ratios was prepared by dissolving PANI in dichloroethane (DCE) for further mixing with PLA and spinning onto interdigitated microelectrode (IME). The ripening process of four different fruits (apple, orange, banana, and cashew peduncle), climacteric, and non‐climacteric fruits, was assessed over 72 h by real‐time monitoring changes in volatile organic compounds (VOCs) released during fruit ripening. Since adsorption of VOCs onto sensor surface causes changes in electrical response, which is directly related to the fruit ripening process, PANI addition was essential to monitor the ripening. However, higher concentrations (2% PANI in PLA) impair sensor conductivity and sensitivity because of the agglomeration of conductive polymer particles, which directly influences the sensitivity and the average fiber diameter. One of the main findings, here, was the clear distinction between different patterns of monitoring curves according to the category of the analyzed fruit (climacteric or non‐climacteric).

Adsorption of volatile organic compounds on pristine and defected nanographene

Adsorption of volatile organic compounds (VOCs) which are a class of air pollutants affecting the environment and human health is considered as the favourable technology for enrichment, separation and utilization of VOCs. In the present work, the adsorption properties of air polluting carbocyclic and heterocyclic VOCs such as toluene, p-xylene and indole onto pristine/defected nanographene (with and without dopants) are investigated using density functional theory (DFT). Adsorption of indole is higher (−0.544 to −1.786 eV) in pristine/defected nanographene (with and without dopant) than p-xylene and toluene. The reactivity of defect on adsorption of VOCs is found high for indole with defected nanographene (DG) and toluene with DG-N indicating the influence of sheet type for adsorption rely on the type of the VOCs adsorbate. The charge transfer and type of interaction between the sheet and VOCs are interpreted using Hirshfeld charge analysis, QTAIM and RDG analysis. The influence of VOCs adsorption is high on the electronegativity and electrophilicity index of the pristine/defected nanographene whereas energy gap and hardness show less influence. The noticeable changes in the TDOS and energy gap on adsorption of VOCs with respect to the type of sheet infers that the doped defected sheet have high affinity than the pristine sheet moreover, the suitable sheet for adsorption of VOCs depends on the type of VOCs adsorbate.

Remarkable performance of N-doped carbonization modified MIL-101 for low-concentration benzene adsorption

As a common volatile organic compound (VOC) species emitted from industrial production, benzene poses a severe threat to human health. Due to its ultra-high specific surface area and developed mesoporous structure, MIL-101 based metal–organic framework (MOF) materials are widely used in VOCs adsorption. However, MIL-101 has a poor ability to adsorb non-polar benzene due to its polar ligands and metal nodes. Herein, we presented a simple strategy of carbonization and nitrogen doping to modify MIL-101. The effect of various surface physicochemical properties of modified MIL-101 on its adsorptive capacity was thoroughly evaluated. The interaction mechanism between activated sites of modified MIL-101 and benzene was also deeply explored using density functional theory (DFT) calculation. The results showed that modified MIL-101 featured graphite skeletons doped with different N-containing functional groups. The adsorptive capacity of MCN-800 increased by 100% compared with that of pristine MIL-101, owing to the largest mesoporous volume and the greatest number of the pyridinic-N moiety. Moreover, both experimental and theoretical results proved that N-containing functional groups had a strong interaction with benzene through π-π interaction and N-H hydrogen bond, and pyridinic-N displayed a stronger interaction than pyrrolic-N and graphite-N. This study provides a valuable synthesis strategy of functionalized MOF adsorbents for the removal of low-concentration benzene pollution.

Hydrophobic shell structured NH2-MIL(Ti)-125@mesoporous carbon composite via confined growth strategy for ultra-high selective adsorption of toluene under highly humid environment

• NH 2 -MIL(Ti)-125 was confined grown into via ‘ship-in-the-bottle’ synthesis approach by Ti-clusters anchored OMC. • Hydrophobic shell (OMC) enhanced surface non-polar and humidity resistance on MIL(Ti)@OMC Ti. • MIL(Ti)@OMC Ti achieved interconnected micro-/mesoporous networks and accelerated mass transfer. • MIL(Ti)@OMC Ti showed high moisture-resistance and adsorption affinity for toluene at ultra-low pressure. • the mechanism of selective toluene adsorption and recycling performance were deeply investigated. Competitive adsorption of volatile organic compounds (VOCs) under high humidity is a critical but challenging issue in the applications of metal–organic frameworks (MOFs). In this work, hydrophobic-shell structured NH 2 -MIL(Ti)-125@mesoporous carbon composite was designed to enhance selective adsorption towards VOCs under humid conditions via confined growth strategy. Ti-clusters were first anchored into pores of ordered mesoporous carbon (OMC), and then confined grown into NH 2 -MIL(Ti)-125 via ‘ship-in-the-bottle’ approach. Hydrophobic shell of OMC concurrently protected the adsorption sites on NH 2 -MIL(Ti)-125 from H 2 O occupation and enhanced affinity towards non-polar toluene. Moreover, the resulting composited supplied abundant diffusion channels for toluene thereby accelerated the mass transfer though mesopores (OMC) and micropores (MOFs). As expected, the hydrophobic-shell NH 2 -MIL(Ti)-125@OMC composite efficiently enhanced hydrophobic property and toluene adsorption affinity. It obtained a dramatical increase in toluene adsorption capacity (3.86 mmol/g at 0.001 P / P 0 ) about 7.4 times of NH 2 -MIL(Ti)-125, and a 29% decrease in water vapor adsorption capacity (0.30 g/g at 1 mbar), which much superior than many reported expensive adsorbents. In addition, the composite induced more confined micropores to mesopores interconnected structure in MIL(Ti)@OMC Ti , and hence facilitated toluene diffusion. The toluene rate constant of pseudo-second-order adsorption ( k a ) on the MIL(Ti)@OMC Ti was up to 0.12 g/(mmol∙min), which was 1.2–2.0 times higher than those of the MIL(Ti) species. Moreover, breakthrough curve indicated that MIL(Ti)@OMC Ti showed 1.5 times of toluene working capacity with faster diffusivity at 80% RH compared to pure NH 2 -MIL(Ti)-125, while the latter exhibited much lower value of Q w / Q e than that of the former. This work provides a novel composite strategy for hydrophobic MOFs construction, and deeper understanding for VOCs/H 2 O competitive adsorption on MOFs composites in large scale applications.

Modeling the effect of humidity and temperature on VOC removal efficiency in a multistage fluidized bed adsorber

The competitive adsorption of volatile organic compounds (VOCs) and water vapor onto beaded activated carbon (BAC) in a fluidized bed adsorber is developed in the form of a two-phase model using the Manes method. The Manes method uses as input single component adsorption isotherms described by the Langmuir model for adsorption of VOCs and the Qi-Hay-Rood (QHR) model for adsorption of water vapor. The effect of temperature is accounted for using the linear van’t Hoff relationship for Langmuir affinity coefficient. The effects of relative humidity (RH) and temperature in the simulations are validated using experimental data, with very good agreement observed (e.g. R2 = 0.98 comparing overall removal efficiencies). Humidity begins to have an effect on the adsorption of 1,2,4-trimethylbenzene (TMB) on BAC starting at 70% RH in the form of a reduction in overall removal efficiency due to fewer available adsorption sites. The overall removal efficiency decreases from 93.0% at 70% RH to 85.4% at 90% RH, and then plateaus with further increase in RH up to 100%. In dry air, temperature variation has a small effect on removal efficiency, showing a reduction in modeled overall removal efficiency from 93.0% to 90.2% when the adsorption temperature increases from 22 to 50 ˚C. On the other hand, at high RH values, temperature has a larger and positive effect on removal efficiency due to RH change. Increasing the temperature of a stream of humid air (RH = 95%) from 22 to 27 °C increases the TMB removal efficiency by 6.9% from 85.3% to 92.2%. Taking into account the effect of humidity and temperature, the model can be used to help optimize fluidized bed adsorber operations in industrial applications.

Facile synthesis of magnesium-based metal-organic framework with tailored nanostructure for effective volatile organic compounds adsorption.

A novel Mg(II) metal-organic framework (Mg-MOF) was synthesized based on the ligand of 2,2'-bipyridine-4,4'-dicarboxylic acid. Single-crystal X-ray structural analysis confirmed that three-dimensional-nanostructure Mg-MOFs formed a monoclinic system with a channel size of 15.733 Å × 23.736 Å. N2 adsorption isotherm, Fourier transform infrared spectroscopy, thermogravimetric analysis and high-resolution transmission electron microscopy were performed to characterize the thermal stability and purity of the Mg-MOFs. The adsorption studies on four typical volatile organic compounds (VOCs) emitted during wood drying showed that Mg-MOFs have noteworthy adsorption capacities, especially for benzene and β-pinene with adsorptions of 182.26 mg g−1 and 144.42 mg g−1, respectively. In addition, the adsorption of Mg-MOFs mainly occurred via natural adsorption, specifically, multi-layer physical adsorption, accompanied by chemical forces, which occurred in the pores where the VOCs molecules combined with active sites. As an adsorbent, Mg-MOFs exhibit versatile behaviour for toxic gas accumulation.

Nitrogen doping and porous tuning carbon derived from waste biomass boosting for toluene capture: Experimental study and density functional theory simulation

Porous carbon materials derived from waste biomass are promising adsorbents for volatile organic compounds. However, it is still difficult to achieve optimal control of the carbon pore structure. In this study, a nitrogen-doped porous carbon (NPC) material with ultra-high surface area (3235 m2/g) and ultra-large pore volume (2.00 cm3/g) was prepared. The adsorption capacity of toluene on NPC (691.1 mg/g, 1000 ppm, 303 K) was significantly higher than previous studies. In addition, the correlations between surface area and adsorption capacity, as well as relative content of nitrogen and adsorption capacity elucidated that the adsorption process was dominated by the filling of micropores. Density functional theory simulation and poisoning experiments proved that pyridine-N as the active center promoted the adsorption capacity through π-π interaction. This work provided new insights into the resource utilization of waste biomass and the exploration of high-efficiency purification technologies for volatile organic pollutants.

Toluene and water vapor adsorption characteristics and selectivity on hydrophobic resin-based activated carbon

The competitive adsorption between volatile organic compounds (VOCs) and water vapor seriously decreases the adsorption capacity of adsorbents. In this paper, a series of hydrophobic spherical resorcinol-formaldehyde resin-based activated carbons (CRFs) were prepared and characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmet-Teller (BET) techniques. The adsorption equilibrium and selectivity of toluene and water vapor on CRFs were investigated systematically. Compared to other adsorbents, HCRF800 treated by hydrogen reduction exhibited the highest toluene uptake (8.64 mmol/g at 293 K) and the strongest hydrophobicity, which was much superior to commercial activated carbon. The results of isosteric heats showed that toluene on HCRF800 was higher than that of water vapor, indicating a stronger interaction between the adsorbent and toluene than water vapor. The adsorption selectivity of toluene/water vapor on CRFs was estimated by the Difference of Isosteric Heats (DIH) equation, and the results suggested that HCR800 possessed the highest selectivity, and the value was in the range of 9.5–52.3. Furthermore, HCRF800 also displayed good toluene uptake at different humidities and faster intra-particle diffusion behavior due to its lower content of surface oxygen groups. Temperature-programmed desorption experiments and Density Functional Theory calculations further revealed that surface oxygen groups had a negative effect on the selectivity of toluene/water, and the negative effect followed the order as O-CO > C-O > CO. Moreover, HCRF800 possessed excellent reversibility. These results demonstrated that HCRF800 would be a superior adsorbent for VOCs recycling from a humid atmosphere.