Adsorption Of Volatile Organic Compounds Research Articles

Enhanced photocatalytic performance of Mn-doped CeO2 nanoribbons for VOCs degradation: Investigating charge rearrangement and local electric field effects

In this study, we investigate Mn-doped CeO2 nanoribbons as photocatalysts to address the issue of performance enhancement in volatile organic compounds (VOCs) removal. Our primary focus centers on elucidating the interplay between charge rearrangement and local electric field (LEF) effects to uncover how these key factors collectively contribute to the improved photocatalytic performance. The successful doping of Mn atoms into the CeO2 lattice resulted in a strong dopant/matrix interaction effect. In situ XPS and density functional theory (DFT) calculations confirmed significant local charge rearrangement due to the dopant-induced local electric field, promoting charge carrier separation. The Mn dopant facilitated the generation of superoxide and hydroxide radicals. DFT simulations showed that Mn doping promoted VOCs adsorption on CeO2, favoring the subsequent oxidation process. The Mn-doped CeO2 nanoribbons achieved enhanced photodegradation performance of HCHO and CH3COCH3 compared to CeO2. This work aims to provide guidance and insights for the development of advanced photocatalysts.

Thermal desorption from zeolite layer for VOC detection

Volatile organic compounds (VOCs) are being considered for a wide range of applications, since they provide information on specific processes (e.g., metabolic processes in humans and plants). To date, environmental VOCs detection can be accomplished with low selectivity using both portable photoionization techniques or using gold standard laboratory techniques (e.g., gas and liquid chromatography, mass spectrometry), getting higher performances and limitations in terms of portability, availability of equipment and of consumption of time. Hereafter, a modified photoionization technique based on a thin zeolite layer for the selective adsorption of VOCs was investigated, exploiting the processes of thermal adsorption and desorption. Zeolite through the inherent nanoporous structure possesses specific electrical characteristics, strongly influenced by the adsorption of the molecules within the framework. Experimental analysis of its electrical and adsorption/desorption properties of propionic and succinic acids was performed. Results demonstrated how the use of a thin nanoporous layer allows to increase the selectivity of commercial photoionization detector during VOC detection, evidencing the potentiality of this technique for the development of low-cost and high-performance sensors in various applications.

Influence of Volatile Organic Compound Adsorption on the Characteristics of Organic Field-Effect Transistors and Rules for Gas-Sensing Measurements.

Owing to the advantages of organic field-effect transistors (OFETs) in the versatility of organic synthesis, multiparameter measurement, and signal amplification, sensors based on OFETs have received increasing attention for detecting volatile organic compounds (VOCs). However, false device operation and gas-sensing measurements often occur to vitiate the advantages of OFETs and even output error gas-sensing signals. In this work, by experimentally and theoretically studying the effects of VOC adsorption on the operational characteristics of the OFET, the proper operations of OFETs in gas-sensing measurements were clarified. The multiparameter measurements of OFETs showed that the source-drain current was the optimized parameter for achieving high responsivity, and other OFET parameters could be used for fingerprint analysis. By operating OFETs in the near-threshold region, the amplification effect was switched to enhance the responsivity by orders of magnitude to VOCs, while in the overthreshold region, the OFETs had a low signal-to-noise ratio. Besides, a counteraction effect and an uncertainty effect were discovered, leading to error gas-sensing signals. A theoretical study was carried out to reveal the dependency of the gas-sensing properties of OFETs on VOC adsorption. A series of rules were proposed for guiding the measurements of OFET sensors by taking full advantage of transistors in gas-sensing applications.

Synthesis of graphene oxide from biomass waste: Characterization and volatile organic compounds removal

This research study focuses on analyzing the effects of graphene oxide (GO) synthesized from subabul, pine, and copperpod biomass waste for the adsorption of volatile organic compounds (VOCs). Five different VOCs i.e., benzene, xylene, carbon tetrachloride, n-hexane, and toluene were utilized for the sorption experiment. A modified Hummers process was carried out for the successful GO production from biomass waste and the obtained GO was confirmed using SEM, Raman spectroscopy, FTIR, and XRD. The existence of 2D-mode and G-mode in Raman spectroscopy as well as O-H and C=O groups in the FTIR confirmed the GO synthesis. The sorption efficiency of SGO, PGO, and CGO for different VOCs was in the range 82–146, 74–144, and 126–166 mg g−1, respectively. The sorption of VOCs was also affected by feedstock type, contact time, and dose of GO. The sorption efficiency of GO increased with a long contact time and higher surface area. Furthermore, for statistical analysis, ANOVA was used. For the kinetics of VOCs sorption, the pseudo-second-order model was utilized, which well fitted with the findings of this research study. The excellent sorption performance of GO produced from biomass waste made it a potential adsorbent for the sorption of VOCs.

Composites derived from co-pyrolysis of residual biomass with aluminium slag as effective materials for volatile organic compounds removal

Co-pyrolysis is an important method to transform hazardous waste into new materials, and composites based on biochar and metal oxides could constitute new types of adsorbents for volatile organic compounds (VOCs). In this study, residual biomass (corn cob, rapeseed and walnut shell) was co-pyrolyzed at 650OC with aluminum slag (AlS), and different composites were synthesized. Biocomposites have been used as adsorbents for the removal of VOCs (such as acetone and toluene). The results showed that the biocomposite obtained from corn cob and AlS has a higher adsorption capacity for acetone, while the composite obtained from walnut shell and AlS showed a higher adsorption capacity for toluene. All prepared composites showed a higher adsorption rate than the corresponding pure biochars. After eighth cycles of adsorption/desorption, the results obtained showed the sample AlS650-Na/BCCC presented a good adsorption performance for acetone ( 318 mg/ g) in the first three cycles, and then the adsorption capacity decreased slowly, with the increase in the number of adsorption cycles. However,the adsorption capacity of 254.41 mg/g was still high after the eighth cycles.A similar behavior was presented by the AlS325-Na/BCWS composite for toluene adsorption.Therefore,AlS/BC composites could be used as a potential adsorbents in VOCs removal.

Specific Recognition and Adsorption of Volatile Organic Compounds by Using MIL-125-Based Porous Fluorescence Probe Material.

The severity of the volatile organic compounds (VOCs) issue calls for effective detection and management of VOC materials. Metal-organic frameworks (MOFs) are organic-inorganic hybrid crystals with promising prospects in luminescent sensing for VOC detection and identification. However, MOFs have limitations, including weak response signals and poor sensitivity towards VOCs, limiting their application to specific types of VOC gases. To address the issue of limited recognition and single luminosity for specific VOCs, we have introduced fluorescent guest molecules into MOFs as reference emission centers to enhance sensitivity. This composite material combines the gas adsorption ability of MOFs to effectively adsorb VOCs. We utilized (MIL-125/NH2-MIL-125) as the parent material for adsorbing fluorescent molecules and selected suitable solid fluorescent probes (FGFL-B1) through fluorescence enhancement using thioflavin T and MIL-125. FGFL-B1 exhibited a heightened fluorescence response to various VOCs through charge transfer between fluorescent guest molecules and ligands. The fluorescence enhancement effect of FGFL-B1 on tetrahydrofuran (THF) was particularly pronounced, accompanied by a color change from yellow to yellowish green in the presence of CCl4. FGFL-B1 demonstrated excellent adsorption properties for THF and CCl4, with saturated adsorption capacities of 655.4 mg g-1 and 811.2 mg g-1, respectively. Furthermore, FGFL-B1 displayed strong luminescence stability and reusability, making it an excellent sensing candidate. This study addresses the limitations of MOFs in VOC detection, opening avenues for industrial and environmental applications.

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.

Removal of binary and ternary synergistic mixtures of ozone and VOCs by activated carbon filter: Mathematical modelling

Evaluating the activated carbon filter's performance in removing gaseous pollutants is essential to determining the filter maintenance schedule for indoor environments. This paper describes the development of a mathematical model to predict an activated carbon filter's performance for removing mixtures of ozone and volatile organic compounds (toluene and limonene) at their low-level concentrations in typical indoor environments. Mass transfer equations were employed to estimate the filter's dynamic behaviour by including the reaction rates of ozone with carbon surfaces and the reactive volatile organic compound, as well as the adsorption isotherm for a single volatile organic compound or binary mixtures of volatile organic compounds. The reaction rate constant for the ozone-limonene reaction was calculated by fitting the model to the experiment results of their binary mixture at 9 ppm of limonene and 0.1 ppm of ozone. Additionally, the ozone-exposed filters at 0.1 ppm were used to perform adsorption tests to determine the parameters of the Dubinin-Radushkevich isotherm using experimental results at 9, 30, 50, 70, and 90 ppm of volatile organic compounds. The Dubinin-Radushkevich isotherm was extended using the volume exclusion theory to consider the effect of by-products on the removal modelling of the binary mixture of ozone and limonene and the ternary mixture of ozone, limonene, and toluene.The model was able to show the reduced accessibility of the surface of activated carbon for reaction with ozone because of the adsorption of volatile organic compounds and generated by-products (keto-limonene and carvone). The initial influence is of minor magnitude; however, as the surface load intensifies, its significance can progressively amplify over time. Pre-exposing the filter to ozone prior to conducting adsorption tests was able to capture the average change in the adsorption properties of the filter. These considerations in the modelling result in a remarkable predictive capability in determining the breakthrough behaviour of the filter in removing the binary or ternary mixture of ozone and volatile organic compounds at various concentrations. The insignificant effect of the homogeneous reaction between ozone and limonene for the investigated experimental setup was confirmed by comparing the predictions made by the proposed model with those made by another model that considers the homogeneous reaction. Finally, the sensitivity analysis revealed that the model is more sensitive to adsorption isotherm parameters compared to the reaction kinetic parameter between ozone and limonene.

Low-content Pt loading on a post-treatment-free zeolite for efficient catalytic combustion of toluene

One of the main techniques for removing volatile organic compounds (VOCs) from the environment is catalytic combustion technology. Noble metal-loaded Zeolite catalysts have a promising future in the field of VOCs catalysis. In this study, NaA, NaX, NaY and ZSM-5 were produced by a simple hydrothermal method, and Pt particles were loaded onto the zeolite. Among the four zeolite-supported Pt catalysts with similar loading loads, Pt/NaA has the best catalytic oxidation performance of toluene, and the total conversion of toluene can be achieved at 160 °C. At the same time, it has good repeatability, and stability. A series of characterizations indicate the synthesis of pure phase NaA zeolites and the presence of a number of acid sites, active oxygen and Pt0 species. The presence of these active substances promoted the adsorption and final oxidation of VOCs by the catalyst, which enabled Pt/NaA to exhibit the most excellent catalytic oxidation performance for toluene. In situ DRIFTS showed that surface reactive oxygen species in Pt/NaA acted as an important role in the catalytic oxidation of toluene. The preparation of high efficiency zeolite catalysts by simple synthesis method has broad future in the field of VOCs treatment.

Superior pore size for enhancing the competitive adsorption of VOCs under high humid conditions: An experiment and molecular simulation study

Water vapor greatly decreases the adsorption capacity of activated carbons (AC) for low-concentration volatile organic compounds (VOCs) under high humid conditions. However, the design and synthesis of AC with high adsorption selectivity for VOCs/water vapor still remains a challenge. In this paper, a hydrophobic hierarchical porous AC was synthesized by using g-C3N4 as the pore-forming agent and the roles of pore sizes on the competitive adsorption were studied by experiments and simulation calculations. The results showed that pore size of 0.59–1.50 nm had a stronger correlation with toluene dynamic adsorption capacity. The largest adsorption capacity of single toluene and water vapor occurred in the 1.0 nm and 0.7 nm slit pore, respectively. During the toluene adsorption at 70 RH%, the superior pore size was 0.7–1.30 nm, and the maximum value appeared in the 1.0 nm pore without pore condensation of water clusters. Furthermore, a quantitative relationship that the superior pore size of VOCs at 70 RH% was 0.86–1.52 S (S is the longest distance of VOCs molecule) was summarized. In addition, a lower surface oxidation degree would broaden superior pore size range. This study provides a theoretical preference for designing AC for target VOCs removal from high humid conditions.

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.