Adsorption Of Volatile Organic Compounds Research Articles

Bimetallic Fe-Mn loaded H-ZSM-5 zeolites for excellent VOCs catalytic oxidation at low-temperatures: Synergistic effects and catalytic mechanisms

The development of catalysts with high adsorption and low-temperature catalytic characteristics for the decomposition of volatile organic compounds (VOCs) is of great importance for air purification. Herein, H-ZSM-5 (proton form Zeolite Socony Mobil-5) zeolite -supported Fe-Mn elements were synthesized via a two-step procedure (hydrothermal and precipitation methods). These zeolite-supported bimetal Fe-Mn catalysts exhibited a mesoporous structure, uniform distribution of Fe-Mn elements, excellent catalytic-oxidation capacity for toluene at low-temperatures, and high stability. Due to interactive synergies between the bimetallic Fe and Mn, the Fe2-Mn1/H-ZSM-5 (ratio of Fe and Mn was 2:1 with a total amount of 15 % to H-ZSM-5) exhibited 100 % toluene-conversion at 200 °C and T90 = 195 °C (temperature of toluene-conversion at 90 %) with GHSV = 20,000 mL/(g∙h). Its distinguishing catalytic-oxidation abilities at low temperatures were due to abundant oxygen-vacancies, adequate acidic-sites and various active oxygen-species, which improved the adsorption of toluene and expedited its degradation. The Fe2-Mn1/H-ZSM-5 catalyst also demonstrated a good resistance to humidity and renewable catalytic properties over five cyclic tests. The in-situ DRIFTS and LC-MS results revealed that toluene was decomposed to benzyl-alcohol, benzaldehyde, benzoate-acid, formates or/and acetate step by step, and finally CO2 and H2O. The mechanism of toluene oxidation over Fe2-Mn1/H-ZSM-5 catalysts was proposed and elucidated via the Mars–van-Krevelen (MVK) model. This study comprehensively explored the adsorption and decomposition kinetics of VOCs over bimetal decorated H-ZSM-5, which was useful toward the design of highly efficient catalysts for the removal of VOCs.

Development of ultra-high surface area polyaniline-based activated carbon for the removal of volatile organic compounds from industrial effluents

Removing volatile organic compounds (VOCs) from aqueous solutions is critical for reducing VOC emissions in the environment. Activated carbons are widely used for removal of VOCs from water. However, they show less application feasibility and low removal due to less surface area. Here, a cost-effective and high surface area activated carbonized polyaniline (ACP) was synthesized to sustainable removal of VOCs from water. The ACP microstructure, surface properties, and pore structure were investigated using Brunauer–Emmett–Teller (BET) theory, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The specific surface area of ACP6:1 (2988.13 m2/g) was greater than that of commercial activated carbon (PAC) (1094.49 m2/g), indicating that it has excellent VOC adsorption capacity. The effects of pH, initial VOC concentration, time, temperature, and ionic strength were studied. According to kinetic and thermodynamic studies on VOCs adsorption, it is an exothermic and spontaneous process involving rate-limiting kinetics. Adsorption isotherms follow the Freundlich isotherm model, suggesting that the adsorbent surface is heterogeneous with multilayer adsorption and maximum ACP adsorption capacities of 1913.9, 2453.3, 1635.8, and 3327.0 mg/g at 293 K for benzene, toluene, ethylbenzene, and perchloroethylene, respectively, representing a 3- to 5-fold improvement over PAC. ACP is a promising adsorbent with a high adsorption efficiency for VOC removal.

Competitive adsorption of VOCs (benzene, xylene and ethylbenzene) with Fe3O4@SiO2-NH@BENZOPHENONE magnetic nanoadsorbents

Volatile organic compounds (VOCs), which are toxic, mutagenic and carcinogenic, are considered a critical factor for air pollution and cause serious harm to the eco-environment and human health. In this study, Fe3O4, Fe3O4@SiO2-NH2, Fe3O4@SiO2-NH@BENZOFENONE were synthesized as new magnetic nanoadsorbents (MNAs) and used for the first time in the removal of gas-phase benzene, xylene and ethylbenzene. The synthesised MNAs were characterized by SEM-EDS, TEM, FTIR, XRD, VSM, TGA and BET analyses. The characterization results showed that the MNAs have mesoporous structure, type IV physioresorption and type H3 hysteresis loop character. In order to clarify the comparative and competitive adsorption behaviour, the adsorption capacity of Fe3O4@SiO2-NH@BENZOFENONE MNA was found to be in the order of xylene > ethylbenzene > benzene in both single, binary and ternary component systems. The adsorption kinetics of benzene, xylene and ethylbenzene with Fe3O4@SiO2-NH@BENZOFENONE MNA were found to be governed by multistep mechanisms. Fe3O4@SiO2-NH@BENZOFENONE MNA showed reuse efficiencies of 83.07%, 84.35% and 82.99% after 5 cycles for benzene, xylene and ethylbenzene respectively. In the framework of the results, Fe3O4@SiO2-NH@BENZOPHENONE MNA, which has a high potential in terms of both adsorption capacity and reuse efficiency, is proposed as a promising adsorbent for the efficient removal of benzene, xylene and ethylbenzene.

Study on Thermal Risk of Coal-Based Activated Carbon after Adsorbing Acetone, Cyclohexane, and Butyl Acetate.

Combustion and explosion accidents of the mixture may occur after the adsorption of volatile organic compounds (VOCs) by coal-based activated carbon (CBAC). It is of great significance to explore the oxidation and combustion performance of CBAC before and after adsorbing VOCs in order to prevent the reoccurrence of fire and explosion. Based on the CBAC sample commonly used in industrial production, three types of CBAC samples after adsorbing VOCs, i.e., acetone, cyclohexane, and butyl acetate, were prepared. The oxidation and combustion characteristics of the samples before and after adsorbing VOCs are measured and analyzed by thermal analyzer and cone calorimeter. Thermal analysis results indicate that during the oxidation process, the VOCs in the adsorbed samples will burn in the early stage, generating amounts of heat which may accelerate the oxidation and combustion of CBAC. According to the combustion performance experiments by cone calorimeter, it is also found that the combustion rate of CBAC after adsorbing VOCs is significantly enhanced. The time to ignition is shortened, the heat release rate becomes larger, and the time to reach the peak of heat release rate is significantly moved forward. In addition, the CO yield of the adsorbed sample is significantly improved. In general, VOC adsorption in CBAC can promote oxidation reactions and may result in an enhanced combustibility of CBAC.

Drastically boosting acetone capture by O/N co-doped Enteromorpha porous carbon: Key role of optimizing pore structure and improving surface polarity

Porous carbon exhibits great potential for removing volatile organic compounds (VOCs) due to its high specific surface and rich porous structure. However, the nonpolar surface of porous carbon leads to its unsatisfactory adsorption of polar VOCs. Here, the Enteromorpha-based O/N co-doped porous carbon (EONC) material was prepared using a two-step pyrolytic activation, including pre-carbonization with urea to improve the surface polarity, followed by KOH activation to optimize the pore structure. The EONC has a high specific surface (3026 m2/g), chemical compositions (9.8% N and 15.5% O), and ID/IG ratio (0.963). The results reveal that the adsorption capacity of EONC for acetone could reach up to 461.7 mg/g at appropriate reaction conditions. The adsorption mechanism of EONC for acetone is mainly attributed to the polar interaction forces of acetone by abundant O/N functional groups on the surface and the ultrahigh specific surface area derived from the rich two-dimensional pore structures. Combined with correlation analysis and theoretical calculations, we found that compared to other O/N functional groups, the carbonyl (–CO) and pyrrolic-N are more beneficial for the capture of acetone. Therefore, EONC, with excellent pore structure and appropriate surface polarity, is a promising material for removing polar VOCs in practical applications.

Analysis of CNT-based SAW sensor for the detection of volatile organic compounds

This paper presents a multi-layer one-port surface acoustic wave (SAW) sensing device and its response based on the adsorption of different volatile organic compounds (VOCs). The finite element method was used to model and simulate a multi-layered SAW device. A piezoelectric substrate 128ᵒ YX-cut Lithium Niobate (LiNbO3), polyisobutylene (PIB) polymer, and carbon nanotube (CNT) multilayer SAW resonating sensor was modeled and used for generating Rayleigh waves. Electromechanical coupling coefficient (K2), admittance (Y11), S-parameter (S11), and metallization ratio (MR) were computed for the proposed heterostructured device. The sensing properties of proposed SAW sensor was investigated for several organic compounds such as trichloroethylene (C2HCl3), trichloromethane (CHCl₃), acetone (C3H6O), acetonitrile (C2H3N), cyclohexane (C6H12), dichloromethane (CH2Cl2) and diethyl ether (C4H10O). Eigenfrequency analysis of the SAW sensor was evaluated from 100 ppm to 500 ppm gas concentration at room temperature. The observed results were compared with the existing research and found to be more effective in terms of sensitivity.

Enhancements on volatile organic compounds (VOCs) adsorption and desorption performance of ZSM-5 by fabricating hierarchical MCM-41.

ZSM-5 zeolite has been considered a promising adsorbent for capturing VOCs. However, its hydrophilicity and narrow micropore structure limit their practical application especially under humid atmospheres. In this study, the pure silica mesoporous molecular sieve MCM-41 was assembled on ZSM-5 zeolite with different SiO2/Al2O3 ratios (SARs) via a surfactant-mediated recrystallization method. Then, its adsorption-desorption behaviors were investigated using n-hexane, toluene, and ethyl acetate as VOC model molecules. The results showed that the hydrophobicity of ZSM-5/MCM-41 composites and their VOC diffusion behaviors were significantly improved. Furthermore, the SARs of the ZSM-5 precursors had a remarkable influence on the adsorption performance of ZSM-5/MCM-41 composites. ZSM-5/MCM-41(130) was the optimum option, and its dynamic adsorption capacity for ethyl acetate (111.30 mg·g-1) was higher than that of the corresponding ZSM-5 zeolites even under statured humidity. Meanwhile, the ratios of dynamic adsorption capacities at humid and dry atmospheres (qs,wet/qs,dry) of ZSM-5/MCM-41(130) for n-hexane, toluene, and ethyl acetate were 84.89%, 61.46%, and 73.81% respectively. The results will provide guidelines for the preparation of hydrophobic adsorbents.

Activated carbon preparation based on the direct molten-salt electro-reduction of CO2 and its performance for VOCs adsorption

The conversion of CO2 into activated carbon (AC) for the adsorption of volatile organic compounds (VOCs) is a green strategy to treat waste by waste. In this study, CO2 was converted into a series of mesopore-enriched AC (MS-AC500, MS-AC550, and MS-AC600) by molten salt (MS) electrochemical method under different temperatures, and the prepared adsorbents were employed for the rapid adsorption of VOCs. The results showed that MS-AC500, MS-AC550, and MS-AC600 had a rich internal pore structure with specific surface area and pore volume of 816.70, 1062.05, 1255.50 m2/g and 0.58, 0.73, 0.84 cm3/g, respectively. The pore structures and surface chemistry of the adsorbents were positively correlated with the adsorption capacity, the adsorption amounts of MS-AC500, MS-AC550, and MS-AC600 were 244.89, 306.38, 414.39 mg/g for toluene and 279.29, 366.19, 460.10 mg/g for chlorobenzene, respectively. The superior adsorption capacity for chlorobenzene is mainly because chlorobenzene is a polar molecule and the C-O bonds inside the adsorbents have an attractive effect on the unpaired electrons inside the polar molecule. Simulation of the adsorption process of the adsorbents confirmed that the adsorption of both toluene and chlorobenzene was a physical adsorption process. Moreover, the adsorption-desorption cycle of chlorobenzene was more stable than that of toluene, and the durability of the adsorbent was above 95% after 5 cycles. This study can remove VOCs while reducing CO2 greenhouse gas, providing a feasible green route to treat waste by waste.

Effect of adsorbate geometry and hydrogen bonding on the enhanced adsorption of VOCs by an interfacial Fe3O4–rGO heterostructure

Volatile organic compounds (VOCs) produced from a wide range of industrial and household chemicals are toxic to human health. Hence, effective VOC removal strategies such as adsorption are essential. Developing a carbon-based adsorbent for the selective adsorption of VOCs without affecting its inherent adsorption capacity is challenging. In this study, we prepared three Fe3O4-doped reduced graphene oxide (Fe-rGO) materials via a liquid-phase reduction technique under acidic, neutral, and basic coagulation conditions. The Fe-rGO adsorbents exhibited a hydrolysis-induced GO network with a wrinkled layer morphology. Acidic conditions yielded an rGO surface with a large number of O-functional groups (epoxy and carboxylic groups), which act as anchoring sites for the growth of Fe3O4 nanoparticles. The synergistic effect of Fe3O4 domains and O active sites led to the effective and selective adsorption of amphiphilic VOCs including C4-C7 alkanes, ketones, and aromatic compounds (10.8–63.2 mg g−1). Experimental analyses and density functional theory calculations revealed three crucial factors that determine the improved amphiphilic VOC adsorption of the Fe-rGO materials: geometry of the adsorbate, hydrogen bonding at the rGO surface, and Fe3O4 nanoparticles controlling the charge density. Our facile and effective rGO surface manipulation strategy involving the fabrication of a metal oxide–carbon heterostructure provides a selective adsorption platform for amphiphilic VOCs.

Volatile Organic Compounds Adsorption Capacities of Zeolite/Activated Carbon Composites Formed by Electrostatic Self-Assembly.

Activated carbon (AC) is a broad-spectrum adsorbent but is flammable and has low adsorption capacities for polar and/or high-boiling volatile organic compounds (VOCs), while zeolites exhibit high thermal stability but poor adsorption of macromolecular and nonpolar VOCs. In this study, zeolite/AC composites were synthesized with the aim of obtaining broad-spectrum, efficient, and safe adsorbents for VOCs. Dimethyldiallylammonium chloride (DDA)-modified AC was used as a carrier for an in situ hydrothermal reaction enabling assembly with zeolites due to electrostatic attraction. Interface models were constructed for their phases, which revealed the binding force and simulated the binding process. The adsorption and flame resistance of the composites were evaluated. The results showed that DDA effectively modified AC to give it a long-lasting positive charge in solutions. High-silicon and pure-silicon zeolites exhibited low negative charges or were even neutral; it was difficult to combine with the modified AC via electrostatic attractions. Instead, LTA zeolites with high aluminum contents and negative charges were used, and the seed-induction method was used. Ethanol and ultrasonic dispersion were used to prevent agglomeration of the seeds and modified AC powder, so they were self-assembled electrostatically. Moreover, the crystallization time was extended and composites with high zeolite loadings were successfully prepared. According to the model calculation, the binding energy between the zeolite and AC before and after the DDA modification were 324.97 and 1076.46 kcal mol-1, respectively, and the distance between them was shortened by 2.7 Å after DDA treatment. As a result, AC and zeolite combined more closely and exhibited a stronger binding energy. The adsorption capacity for highly polar dichloromethane was improved by zeolite loading on the AC, and the bed penetration time was doubled. However, impregnation with inorganic sodium enhanced the reactivities of the organic components in the composite, and the ignition point was slightly reduced. Furthermore, the electrostatic self-assembly method can expand to prepare the LTA zeolite/columnar AC composite from shaped AC, greatly improving its application prospects.

Designing novel perlite-Fe3O4@SiO2@8-HQ-5-SA as a promising magnetic nanoadsorbent for competitive adsorption of multicomponent VOCs

Volatile organic compounds (VOCs), which emerge as multicomponent pollutants through many industrial processes, pose a serious threat to human health and the eco-environment due to their volatility, toxicity and dispersion. Hence, the study of competitive adsorption of multicomponent VOCs is of practical and scientific importance. Herein, the perlite-supported Fe3O4@SiO2@8-hydroxyquinoline-5-sulfonic acid (perlite-Fe3O4@SiO2@8-HQ-5-SA) was designed as a novel magnetic nanoadsorbent by a simple strategy and employed for the competitive adsorption of multicomponent toluene, ethylbenzene and xylene in the vapor-phase targeted as VOCs. The successfully prepared perlite-Fe3O4@SiO2@8-HQ-5-SA was characterized by means of SEM, EDX, FT-IR, VSM and BET analyses. Adsorption capacities of 558 mg/g, 680 mg/g and 716 mg/g were achieved for single component toluene, ethylbenzene and xylene, respectively. It was concluded that the adsorption capacities for both binary and ternary components were significantly decreased compared to single component adsorption. The competitive adsorption capacity order of the binary and ternary component VOCs was xylene > ethylbenzene > toluene due to their competitive dominance. The rate-limiting kinetic analysis indicated that the adsorption rates were determined by both the film diffusion and intraparticle diffusion. The analysis of the error metrics demonstrated that the three-parameter isotherm models better described the adsorption data compared to the two-parameter models. In particular, the Toth model provided the closest fit to the experimental equilibrium data. The thermodynamic analysis indicated the spontaneous nature and probability (ΔG° <0), exothermic (ΔH° <0), physical (ΔH° <20 kJ/mol) and a declination in the degree of randomness (ΔS° <0) of the adsorption processes. The reuse efficiency of perlite-Fe3O4@SiO2@8-HQ-5-SA for toluene, ethylbenzene and xylene decreased to only by 88.91%, 88.07% and 87.16% after five recycles. The perlite-Fe3O4@SiO2@8-HQ-5-SA has a significant adsorptive potential compared to other adsorbents reported in the literature, thus it could be recommended as a promising nanoadsorbent for VOCs in industrial processes.

A wet impregnation approach to synthesize MIL-101(Cr) with open metal sites and their application in the adsorption of volatile organic compounds

The simple wet impregnation method reported a series of MIL-101(Cr) materials doped with copper acetate paddle wheel species. Powder X-ray diffraction and SEM studies showed the MOF frameworks remained intact during wet impregnation, and SEM- EDX, XPS, and N2 adsorption analyses confirmed the successful copper acetate loading. Volatile organic compounds adsorption capabilities of these materials were further examined, and it found that copper acetate doped MIL-101 (Cr) possesses up to 61% improvement in toluene uptake as compared to pristine MIL-101 (Cr) at a low partial pressure of P/P0 = 0.10 under 298.1 K. This performance improvement is attributed to the unsaturated open metal sites introduced by molecular copper acetate with a paddle wheel structure. This study provides not only a new series of promising VOC removal MOFs with unsaturated Cu(II) open metal sites but also a simple, widely applicable method for introducing Cu(II) open metal sites into MOFs by using molecular copper species with predefined paddle wheel structure.

Competitive adsorption characteristics of VOCs and water vapor by activated carbon prepared from Fe/N-doped pistachio shell.

Various materials have been developed to capture volatile organic compounds (VOCs) to mitigate air pollution. However, sorbent materials with excellent resistance to water are rare. Here, several Fe/N-doped activated carbons (ACs) have been prepared to capture VOCs in humid environments. The ACs were analyzed by various characterization techniques, such as BET, SEM, XPS, XRD, FTIR, and Raman. The results showed that Fe/N doping resulted in the specific surface area of the ACs increasing by 500 to 1000 m2g-1, the average pore size increasing to approximately 2nm, improved mesoporous structure, higher graphitization, lower hydrophilicity, and polarity. The VOCs adsorption performance of the ACs was evaluated by static and dynamic adsorption experiments. The uptake of toluene and ethyl acetate by ACs was enhanced to 224mgg-1 and 135mgg-1, respectively. And ACs were able to maintain 70 to 80% VOCs adsorption capacity for VOCs at 80% relative humidity. Furthermore, the microscopic mechanisms were investigated by the grand canonical Monte Carlo method (GCMC). The highly graphitized structure and the N functional groups favored the VOC adsorption process and discouraged the adsorption of water vapor. This work affirmed the dominance of Fe/N-doped carbon, which will contribute to the evolution of water-resistant VOCs adsorbent materials.

Hierarchical porous carbon with tunable apertures and nitrogen/oxygen heteroatoms for efficient adsorption and separation of VOCs

Porous carbon materials are good adsorbent candidates for removing volatile organic compounds (VOCs) due to their reliability and cost-effectiveness. Especially, the pore size distribution (PSD) of porous carbon materials plays a critical role in VOCs adsorption and separation. In this study, we present benzimidazole-derived porous carbons (BICs) with controllable pore size and oxygen/nitrogen heteroatoms. The pore size is controlled by adjusting the reaction degree of inorganic salt (K2CO3) and nitrogen-containing groups in the system. The tunable pore size distribution makes BICs highly efficient for the adsorption and separation of VOCs. BIC-3-900 exhibits a dominant pore size distribution of 3.0–4.0 nm and an exceptionally high total pore volume of 2.42 cm3/g, leading to ultra-high adsorption capacities for benzene and methanol (22.19 and 52.65 mmol/g, respectively) at 293 K. In addition, BIC-1-700 dominated by the micropore size is more favorable for adsorbing low-concentration small molecule VOCs (with a dynamic adsorption capacity of 4.21 mmol/g for methanol at 3800 ppm). In terms of the adsorptive separation performance, BIC-1-900 has an efficient benzene/methanol selectivity (∼30.13) due to its PSD (1.2–2.0 nm) which was more favorable for capturing low-concentration benzene. Moreover, both experimental and simulation (GCMC and DFT) results demonstrate that the abundant N/O heteroatoms doping in BIC-1-700 results in charge heterogeneity and stronger electrostatic affinity for polar VOCs molecules. Herein, our findings suggest that BICs with controllable pore size and oxygen/nitrogen heteroatoms have significant potential in practical VOCs capture and separation.

Hierarchical diffusion pathways into VOC adsorption films by direct ink writing and ammonium carbonate treatment

In-situ thermally restorable adsorption films exhibited brilliant performance for indoor volatile organic compounds (VOCs) purification with negligible wind resistance and considerable lifetime. However, the morphology of adsorption films should be restructured for better adsorption kinetics. This study structured adsorption films with submillimeter-sized channels by direct ink writing (DIW). Submicron-micron-sized porous structure was further fabricated through ammonia carbonate treatment. Pore size distribution characterization proved 33% of extra mesopores were created in the hierarchical porous adsorption film. Dynamic adsorption behaviours for formaldehyde and toluene illustrated that the hierarchical porous adsorption film exhibited an over 80% initial one-pass efficiency for both formaldehyde and toluene, improved by 20% over the plane adsorption film. The purification rate was also significantly improved by 83% and 67% for formaldehyde (from 0.059 mg g-1h−1 to 0.106 mg g-1h−1) and toluene (from 0.143 mg g-1h−1 to 0.239 mg g-1h−1), respectively. This study proposed a method for conveniently preparing multi-scale porous structured adsorption components under mild conditions. The hierarchical diffusion pathways induced by DIW and ammonium carbonate treatment will enhance the adsorption kinetics and the purification performance of the adsorption film, overcoming the weak purification performance and short material lifetime of the existing indoor VOCs adsorption components. This research can be further applied to gas separation, as well as gas sensing, as DIW can achieve sub-millimeter scale resolution, providing a versatile approach for heat and mass transfer enhancement in chemical and environmental fields.

Effect of functional groups on VOCs adsorption by activated carbon: DFT study

Volatile organic compounds (VOCs) have attracted increasing attention in the field of environmental control due to their harmful effects on human health and the environment. Activated carbon is promising as an adsorbent for VOCs. The physisorption of six VOCs (methane (CH4), dichloromethane (CH2Cl2), ethylene (C2H4), formaldehyde (HCHO), ethanol (C2H5OH), and toluene (C7H8)) by four activated carbon models (without functional group (NF), with hydroxyl (HD), pyridine (PD), and pyrrole (PR) group, respectively) was studied in combination with their electrostatic potential (ESP). The results show that ESP plays a decisive role in the adsorption of CH4, CH2Cl2, C2H4, HCHO, and C2H5OH, as their adsorption is mainly carried out by H-bonds. The functional group affects the adsorption process by changing the ESP distribution on the activated carbon surface. The orders of the absolute ESP values on the plane and edge of activated carbon are PR>HD>NF>PD and HD>PR>PD>NF, respectively, so that the order of the interaction strength and the physisorption energy are almost the same. Meanwhile, dispersion can enhance adsorption and change the order. For example, the order of CH2Cl2 adsorption at the activated carbon edge is PD>HD>PR>NF. C7H8 is difficult to be adsorbed at the activated carbon edge, but it can be adsorbed on the plane by a π-π stacking interaction whose strength is controlled by the relative molecular mass of activated carbon. This study will guide the design of activated carbon for efficient adsorption of VOCs.

Effect of microstructure in mesoporous adsorbents on the adsorption of low concentrations of VOCs: An experimental and simulation study

This study evaluated the adsorption of five volatile organic compounds (VOCs) on Opoka, precipitated silica, and palygorskite, to elucidate the effect of their pore size on VOCs adsorption. The adsorption capacity of these adsorbents is not only highly correlated with their surface area and pore volume, but also notably improved by the presence of micropores. The variation in adsorption capacity for different VOCs was primarily influenced by their boiling point and polarity. Palygorskite, which had the smallest total pore volume (0.357 cm3/g) but the largest micropore volume (0.043 cm3/g) among the three adsorbents, exhibited the highest adsorption capacity for all tested VOCs. Additionally, the study constructed slit pore models of palygorskite with micropores (0.5 and 1.5 nm) and mesopores (3.0 and 6.0 nm), calculated and discussed the heat of adsorption, concentration distribution, and interaction energy of VOCs adsorbed on different pore models. The results revealed that the adsorption heat, concentration distribution, total interaction energy, and van der Waals energy decrease with increasing pore size. The concentration of VOCs in 0.5 nm pore was nearly three times that in 6.0 nm pore. This work can also provide guidance for further research on using adsorbents with mixed microporous and mesoporous structures to control VOCs.

Biomimetic Metal-Organic Framework-Based Photonic Crystal Sensor for Highly Sensitive Visual Detection and Effective Discrimination of Benzene Vapor.

Due to the large specific surface area and continuous pores in structures, metal-organic frameworks (MOFs) show great advantages in the adsorption of volatile organic compounds (VOCs). Photonic crystal (PC) sensors derived from MOFs are promising for the visual detection of VOC gases. However, they still have problems of low sensitivity and poor color saturation and tunability. Here, inspired by vapor-sensitive scales of Tmesisternus isabellae beetle and scattering light absorption of polydopamine, a porous one-dimensional PC sensor is constructed by combining ZIF-8 with TiO2@PDA nanoparticles. The PC sensor shows significant color changes under different concentrations of benzene vapor and reaches a detection limit of 0.8 g/m3. It has a response time of less than 1 s and maintains stable optical performance after 100 times of reuse. Moreover, ZIF-67 and ZIF-7 are both incorporated into the PCs for comparison; it reveals that ZIF-8 shows superior benzene detecting property. Additionally, the synergistic adsorption of VOCs in inner and outer holes of the ZIF-8 layer is demonstrated by real-time mass monitoring with quartz crystal microbalance with dissipation. This study provides a valuable reference for the fabrication of high-quality MOF-based PC sensors and sensing mechanism study between microscopic molecular adsorption and macroscopic performance.

Biomass Derived, Hierarchically Porous, Activated Starbons® as Adsorbents for Volatile Organic Compounds.

The use of potassium hydroxide activated Starbons® derived from starch and alginic acid as adsorbents for 29 volatile organic compounds (VOCs) was investigated. In every case, the alginic acid derived Starbon® (A800K2) was found to be the optimal adsorbent, significantly outperforming both commercial activated carbon and starch derived, activated Starbon® (S800K2). The saturated adsorption capacity of A800K2 depends on both the size of the VOC and the functional groups it contains. The highest saturated adsorption capacities were obtained with small VOCs. For VOC's of similar size, the presence of polarizable electrons in lone pairs or π-bonds within non-polar VOCs was beneficial. Analysis of porosimetry data suggests that the VOC's are being adsorbed within the pore structure of A800K2 rather than just on its surface. The adsorption was completely reversible by thermal treatment of the saturated Starbon® under vacuum.

Adsorption of volatile organic compounds on activated carbon with included iron phosphate

Adsorption of volatile organic compounds on activated carbon with included iron phosphate