Adsorption behavior of multicomponent volatile organic compounds on a citric acid residue waste-based activated carbon: Experiment and molecular simulation

Green synthesis of a superhydrophobic porous organic polymer for the removal of volatile organic compounds at high humidity

Superhydrophobic porous organic polymers are potential sorbents for volatile organic compounds (VOCs) pollution control by suppressing the competition of water molecules on their surfaces. However, the synthesis of superhydrophobic reagents usually requires large amounts of organic solvents and a long reaction time (≥ 24 h). Herein, a green mechanochemical method was developed to synthesize a superhydrophobic polymer (MSHMP-1) with the advantages of using a small amount of organic solvents (5 mL/g) and a short reaction time (2 h). Meanwhile, MSHMP-1 with a water contact angle (WCA) of 162° exhibited a dramatically rich pore structure as revealed by its specific surface area (SSA) of 1780 m2/g. The decrease in the adsorption of benzene on MSHMP-1 due to the competition of water molecules, even at relative humidity of 90 %, was nonsignificant (<10 %), indicating the great application potential of MSHMP-1 in hydrophobic adsorption. Moreover, the adsorption capacity of MSHMP-1 was maintained after at least five adsorption-desorption cycles. Therefore, MSHMP-1 can be a remarkable adsorbent for the removal of hazardous VOCs, especially at high humidity levels.

Introducing Molecular Sieve into Activated Carbon to Achieve High-Effective Adsorption for Ethylene Oxide

Presently, ethylene oxide (EtO) is posing a significant threat to both human health and the environment due to occasional or deliberate emissions. However, few works so far have focused on this issue. It is urgent to explore novel and effective technology to protect against the threat of EtO. Herein, a series of AC/ZSM-5 composites were prepared to improve the adsorption performance for EtO, evaluated by dynamic breakthrough experiments. Particularly, the AC/ZSM-20% composite demonstrated a more excellent adsorption capacity of 81.9 mg/g at 25 °C and 50% RH than that of pristine AC and ZSM-5 with 32.5 and 52.3 mg/g, respectively. Moreover, the adsorption capacity of the AC/ZSM-20% composite remained constant even after five adsorption-desorption cycles. The adsorption mechanism of EtO on the composite is further revealed by density functional theory (DFT) calculations.

Research on the kinetics and degradation pathways of gaseous acetic acid ester organics

ABSTRACTDesigned to meet the specific needs of the printing industry exhaust gas emissions, this paper proposes a method for the degradation of gaseous acetic acid ester organics that is environmentally friendly, safe, and simple to use: micro-nano cavitation technology. In the process of using micro-nano cavitation technology to degrade acetic acid ester organics, the products in the degradation process were analyzed by gas chromatography-mass (GC-MS) spectrometry, and the degradation pathways of acetic acid ester organics were identified. Under high temperatures and high pressure caused by cavitation collapse, the C-C bond and C-O bond on the main chain of organic matter are cleaved to form low molecular products. Low-molecular intermediate products are continuously produced as the reaction advances, and these intermediate products are further oxidized and decomposed into carbon dioxide and water. Besides, the factors that influence the degradation rate of acetic acid ester organics were investigated. Based on the experimental data, acetic acid esters can degrade with the greatest efficiency when their initial concentration is 200 ± 50 mg/m3 and their treatment time is 20∼30 min. Moreover, the experiment was optimized using the response surface method. The results suggested that for an initial concentration of 155.544 mg/m3 and a reaction time of 21.961 min, the best degradation rate was 0.251 min-1. Micro-nano cavitation technology is a novel and promising technology for the degradation of volatile organic compounds, with a wide range of practical applications.

Dynamic Model Validation and Simulation of Acetone-Toluene and Benzene-Toluene Systems for Industrial Volatile Organic Compound (VOC) Abatement

Environmental impact mitigation is one of the grand challenges for industries globally. Volatile organic compounds (VOCs) are solvents whose emissions are potentially toxic to human health and ecosystems yet indispensable for the manufacturing of life-saving medicine. Adsorption with activated carbon columns is an established countermeasure for end-of-pipe emission control, whose efficiency, however, is impeded by irregular bed saturation due to the complex nature of its inputs. This work presents the application of a validated nonisothermal adsorption model to examine multicomponent trace mixtures of acetone-toluene and benzene-toluene on activated carbon. Our results indicate preferential adsorption of toluene over both acetone and benzene for all concentrations examined, which is in agreement with experimental data. Moreover, moderate temperature variations and pressure drops are revealed. Finally, Glueckauf's hodograph theory is employed for maximum outlet concentration prediction and compared with simulation results and experimental data, thus providing valuable insights into nonisothermal VOC abatement, which paves the way for industrial operation optimization.

Adsorptive interaction between typical VOCs and various topological zeolites: Mixture effect and mechanism

Adsorption is one of the most feasible and effective methods to alleviate the volatile organic compounds (VOCs) pollution. However, the mixture effect and mechanism for competitive adsorption of VOCs on zeolites are barely addressed. In this study, toluene, acetone, and ethyl acetate as prevalent VOCs species were removed by four potential zeolites (13X, USY, Beta, ZSM-5) in both single- and multi-component systems. The structure-property relationship between adsorbate-adsorbent pairs was revealed by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer, X-ray fluorescence, N2 adsorption and density function theory calculation. The molecular polarity and volatility of VOCs species played key roles in adsorption and the dynamic uptakes were generally listed as follows: ethyl acetate > toluene > acetone. As for the above VOCs mixtures, 13X zeolite selectively adsorbed oxygenated VOCs rather than toluene. In contrast, USY exhibited a preference to trap toluene. Ethyl acetate could be readily enriched by ZSM-5 and Beta selectively. The possible explanations and implications are discussed based on the subtle change in electron density. The results obtained are vital for understanding the mixture effect of VOCs adsorption and may guide the selection of proper adsorbent for real applications.

Food waste anaerobic digestion plants: Underestimated air pollutants and control strategy

Food waste management is an important global issue, and anaerobic digestion (AD) is a sustainable technology for treating food waste and developing a circular economy. Odor and health problems in AD plants have drawn increasing public attention. Therefore, this study investigated the odor characteristics and health risks in different workshops of food waste AD plants. At each site, the treatment capacities for kitchen and restaurant waste were 200 and 200-250 tons per day, respectively. Among the detected odorants, ethanol was the dominant component in terms of concentrations, while methanethiol, propanethiol, H2S, and acetaldehyde were the major odor contributors in different workshops. The odor contribution of propanethiol had been previously overlooked in several workshops. The unloading, pretreatment, and bio-hydrolysis workshops were identified as major areas requiring odor control. Besides odor, carcinogenic and non-carcinogenic risks commonly existed in food waste AD plants. The carcinogenic risk of acetaldehyde had been underestimated previously, and it was identified as the dominant carcinogen. Furthermore, benzene was a potential carcinogen. Non-carcinogenic risks were mainly caused by acetaldehyde, H2S, and ethyl acetate. The health risks were not always consistent with odor nuisance. Based on the odor and health risk assessments, several air pollution control strategies for food waste AD plants were proposed, including food waste source control, in-situ pollution control, and ex-situ pollution control.

Improving the adsorption performance of non-polar benzene vapor by using lignin-based activated carbon

Both indoor and outdoor contamination continually contain benzene vapor. It has primary concerns about long-term health risks to the living environment. Benzene is a crucial airborne pollutant in the environment due to its apparent acute toxicity, high volatility, and poor degradability. It is especially urgent to restrain benzene emissions due to the persistent concentration increase and stringent processes. Benzene adsorption is a highly efficient mechanism with low cost, low energy consumption, and a simple process. In this study, biomass-derived porous carbon materials (TCACs) were synthesized by pyrolysis activation combined with H3PO4, HNO3, and HCl. TCAC44 has the best activation conclusion, showing that surface area and pore volume were 1107 m2/g and 0.58 cm3/g treated with H3PO4 and so was chosen for subsequent benzene adsorption/desorption tests. The adsorption capacities of benzene for TCAC44 were increased from 58 mg/g for 35 °C + 95% RH to 121 mg/g for 25 °C + 15% RH and presented a higher adsorption capacity of benzene than TCAC101 and TCAC133. Otherwise, well recyclability of TCAC44 was revealed as the benzene adsorption capacity reductions were 22.49% after five adsorption-desorption cycles. Furthermore, the present study established the property-application relationships to promote and encourage future research on the newly synthesized innovative TCAC44 for benzene removal.

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.

Adsorption Behavior of Multi-Component BTEX on the Synthesized Green Adsorbents Derived from Abelmoschus esculentus L. Waste Residue

Benzene, toluene, ethylbenzene, and xylene (BTEX) removal is one of the most common difficulties in air pollution control. They are emitted from several processes, prejudicial to the environment and humans. BTEX leads to various environmental risks, and there is a significant need for a creating process for the complete removal of BTEX from air streams. This study's objective is the multi-component adsorption of BTEX pollutants from an air stream, by synthesizing activated carbons (ACs) under several operations. A lignocellulosic waste biomass, Abelmoschus esculentus L. (AE), was utilized as the precursor for synthesizing activated carbons (AE-ACs), and their surface chemical characteristics were investigated. Optimization processes were examined, and the change in the surface area of AE-ACs was investigated as change of some variables results like activation agent, impregnation ratio, temperature, and activation time. The maximum surface area of 968 m2/g and total pore volume of 0.51 cm3/g were attained at 1:2 impregnation ratio, activation time of 110 min, and activation temperature of 800 °C, under N2 atmosphere. A mixture of BTEX pollutants was employed to consider the effect of humidity (0.5, 1, 1.5, and 2 wt%) and initial concentrations (from 5 to 300 mg/m3), using a contact time of 120 min at the temperature of 25 °C. Under the studied conditions, the multi-component and single-component BTEX adsorption capacities by HCl-activated carbon, AE-ACH, were specifically achieved to 6.86-51.36 mg/g and 22-93.62 mg/g, respectively. Overall, Abelmoschus esculentus L. was exploited for the synthesis of AE-ACH which was successfully utilized for efficient BTEX capture from a polluted air stream.

Effective Phytosanitary Treatment for Export of Oriental Melons (Cucumis melo var L.) Using Ethyl Formate and Modified Atmosphere Packaging to Control Trialeurodes vaporariorum (Hemiptera: Aleyrodidae)

Trialeurodes vaporariorum (Hemiptera: Aleyrodidae), commonly known as greenhouse whitefly, is one of the main insect pests of Oriental melon (Cucumis melo var L.) in South Korea. T. vaporariorum is of concern as a quarantine pest for the exportation of C. melo in Southeast Asian countries. Due to future restrictions on the use of methyl bromide (MB) during quarantine, ethyl formate (EF) represents a potential alternative. In this study, we evaluated EF for its efficacy (probit-9 values) in enabling the export of Oriental melons. The probit-9 value of EF for controlling T. vaporariorum was 3.02 g·h/m³ after 2 h of fumigation. We also assessed the phytotoxicity of EF on melons when using modified atmosphere packaging (MAP) under low-temperature conditions, which is required for export and trade, to extend shelf-life. In scaled-up trials, we found 8 g/m³ EF for 2 h at 5 °C to be suitable as a new phytosanitary treatment against greenhouse whitefly for exported Oriental melons when using MAP. No phytotoxic damage was found 28 d after fumigation at 5 °C in terms of five quality parameters (firmness, sugar content, mass loss, color change, and external damage).

Swellable Array Strategy Based on Designed Flexible Double Hypercross-linked Polymers for Synergistic Adsorption of Toluene and Formaldehyde

High-capacity adsorption and removal of complex volatile organic compounds (VOCs) from real-world environments is a tough challenge for researchers. Herein, a swellable array adsorption strategy was proposed to realize the synergistic adsorption of toluene and formaldehyde on the flexible double hypercross-linked polymers (FD-HCPs). FD-HCPs exhibited multiple adsorption sites awarded by a hydrophobic benzene ring/pyrrole ring and a hydrophilic hydroxyl structural unit. The array benzene ring, hydroxyl, and pyrrole N sites in FD-HCPs effectively captured toluene and formaldehyde molecules through π-π conjugation and electrostatic interaction and weakened their mutual competitive adsorption. Interestingly, the strong binding force of toluene molecules to the skeleton deformed the pore structure of FD-HCPs and generated new adsorption microenvironments for the other adsorbate. This behavior significantly improved the adsorption capacity of FD-HCPs for toluene and formaldehyde by 20% under multiple VOCs. Moreover, the pyrrole group in FD-HCPs greatly hindered H₂O molecule diffusion in the pore, thus efficiently weakening the competitive adsorption of H₂O toward VOCs. These fascinating properties enabled FD-HCPs to achieve synergistic adsorption for multicomponent VOC vapor under a highly humid environment and overcame single-species VOC adsorption properties on state-of-the-art porous adsorbents. This work provides the practical feasibility of synergistic adsorption to remove complex VOCs in real-world environments.

New insights into hierarchical pore size and level of concentration in efficient removal of toluene vapor by activated carbon

The hierarchical pore structure of nanoporous carbon and gaseous toluene concentration co-mediated adsorption mechanism was examined. The KOH-activated carbons with tailorable high surface area (1126-3148 m²/g), large pore volume (0.446-2.08 cm³/g) and broadening average pore width (0.873-2.68 nm) were prepared. Dynamic adsorption was used to determine breakthrough curves and adsorption isotherms of toluene by as-prepared KOH-activated carbons and commercial activated carbons. The experimental results showed that the breakthrough time is positively correlated with ultramicropore volume of all activated carbons. The equilibrium amounts adsorbed (q_e) for toluene at 100 ppmv were as high as 454 mg/g on KOH-activated carbons. The q_e for toluene at P/P₀ < 0.017 dominated by ultramicropore volume of all activated carbons were attributed to the enhanced superposition of adsorption force field between adjacent ultramicropore walls. A large adsorption affinity is imperative to achieve high amounts adsorbed for toluene at low concentration. The toluene was firstly filled in ultramicropores then gradually occupied in wide micropores at 0.017 <P/P₀ < 0.1 and the q_e were linearly correlated with micropore volume. The q_e of toluene at P/P₀ > 0.1 were linearly correlated with volume of micropore and small mesopore. The governing porosity in adsorbing toluene is varied with the intruding concentration. These results provided new insights into adsorption mechanism and development of novel materials.

Preparation and Performance of Carbon-Based Ce-Mn Catalysts for Efficient Degradation of Acetone at Low Temperatures

Based on the porous carbon material from citric acid residue, catalysts of different Ce-Mn ratios were prepared with incipient-wetness impregnation (IWI) to delve into their acetone-degrading performance and relevant mechanisms. When the Ce-Mn molar ratio is 0.8, the prepared catalyst Ce_0.8-Mn/AC shows abundant and uniformly dispersed Mn and Ce particles on the surface. The content of Mn and Ce on the Ce_0.8-Mn/AC surface reaches 5.64% and 0.75%, respectively. At the acetone concentration of 238 mg/m³ (100 ppm), the laws of acetone degradation in different catalysts at different catalyzing temperatures and with various oxygen concentrations were studied, and we found that the rate of acetone degradation by Ce_0.8-Mn/AC can exceed 90% at 250 °C. Cerium oxide and manganese oxide are synergistic in the catalytic degradation of acetone. Adding cerium to manganese-based catalysts can increase the oxygen migration rate in the catalysts and thus raise the reduction rate of lattice oxygen in manganese oxide. The results offer new ideas and approaches for the efficient and comprehensive utilization of bio-fermentation by-products, and for the development of cheap and high degradation performance catalysts for acetone.

Study on adsorption of low-concentration methyl mercaptan by starch-based activated carbon

The development of a low-concentration methyl mercaptan adsorbing material for an efficient decontamination has become a hot research topic. In this study, carbonization activation was employed with starch and urea as carbon and nitrogen sources, respectively, to prepare a type of starch-based activated carbon. Subsequently, the product was used to adsorb low-concentration methyl mercaptan. Based on sorption experiments and molecular simulations, the underlying mechanism of the adsorption effect of the adsorbent's pore structure and surface oxygen- and nitrogen-containing functional groups on methyl mercaptan molecules were discussed. The results indicated that when the methyl mercaptan equilibrium concentration was 0.197 mg/L, the adsorption capacity of SUAC-16-2 for methyl mercaptan was 78.16 mg/g. Its adsorption performance was better than that of its previously reported counterparts. The well-developed microporous structure of SUAC-16-2 promoted the adsorption of methyl mercaptan. In addition, methyl mercaptan molecules could be broken down to produce CH₃S^- and H⁺ by the effect of the surface functional groups. Adjacent carbon atoms containing nitrogen and oxygen functional groups could better adsorb CH₃S^- and H⁺, and further strengthen the methyl mercaptan adsorption performance of activated carbon. The study could help to develop new technology for treatment of low concentration of methyl mercaptan in the air.

Preparing hierarchical porous carbon with well-developed microporosity using alkali metal-catalyzed hydrothermal carbonization for VOCs adsorption

Biomass-derived porous carbonaceous materials are efficient adsorbents for VOCs, but their traditional preparation method, pyrolysis combined with activation, suffers from high energy consumption, equipment corrosion, and low pore-making efficiency, which hinders their large-scale practical application. A novel method of alkali metal-catalyzed hydrothermal carbonization coupling with chemical activation for the preparation of microporous carbon is presented. Porous carbon with well-developed microporosity deriving from corn husk were prepared through the hydrothermal carbonization using potassium persulfate (K₂S₂O₈) as a catalyst and programmed heating activation process. And the products were applied to removal of typical oxygen-containing VOCs, ethyl acetate. The addition of K₂S₂O₈ in hydrothermal carbonization accelerated the biomass hydrolysis, decomposed the biopolymer, and formed functional hydrochars. Potassium salts introduced into the hydrochars, which acted as an activator in this programmed heating activation process, formed a great deal of micropores. The specific surface area of micropores increased by 81%, and the specific surface area of micropores less than 1 nm increased by 180%. The introduction of K₂S₂O₈ in preparation improved the adsorption performance of CH-based porous carbons 16.46% and 60.00% respectively at different preparation temperatures (600 °C and 800 °C). Basing on these results, the improvement of micropores less than 1 nm is directly related to the adsorption performance. This indicates that pores (<1 nm) respond well to the adsorption of ethyl acetate.

Adsorptive removal of some Cl-VOC's as dangerous environmental pollutants using feather-like γ-Al2O3 derived from aluminium waste with life cycle analysis

Herein, we designed a cost-effective preparation method of nanocomposite γ-Al₂O₃ derived from Al-waste. The produced material has a feather-like morphology, and its adsorption of some chlorinated volatile organic compounds (Cl-VOC's) such as benzyl chloride, chloroform and carbon tetrachloride (C₇H₇Cl, CHCl₃ and CCl₄) was investigated due to their potential carcinogenic effect on humans. It showed a characteristic efficiency towards the adsorptive removal of these compounds over a long period, i.e., eight continuous weeks, at ambient temperature and atmospheric pressure. After 8-weeks, the adsorbed amounts of these compounds were determined as: 325.3 mg C₇H₇Cl, 247.6 mg CHCl₃ and 253.3 mg CCl₄ per g of γ-Al₂O_3, respectively. CCl₄ was also found to be dissociatively adsorbed on the surface of γ-Al₂O₃, whereas CHCl₃ and C₇H₇Cl were found to be associatively adsorbed. The prepared γ-Al₂O₃ has a relatively high surface area (i.e., 192.2 m². g^-1) and mesoporosity with different pore diameters in the range of 25-47 Å. Furthermore, environmental impacts of the nanocomposite γ-Al₂O₃ preparation were evaluated using life cycle assessment. For prepartion of adsorbent utilising 1 kg of scrap aluminium wire, it was observed that potential energy demand was 288 MJ, climate change potential was 19 kg CO₂ equivalent, acidification potential was 0.115 kg SO₂ equivalent and eutrophication potential was 0.018 kg PO₄^3- equivalent.

Highly efficient degradation of hydrogen sulfide, styrene, and m-xylene in a bio-trickling filter

Controlling the release of malodorous gas discharged from wastewater treatment plants (WWTPs) has become an urgent environmental problem in recent years. In this study, a bio-trickling filter (BTF) inoculated with microorganisms acclimated to activated sludge in a WWTP was used as the degradation equipment. A continuous degradation experiment with hydrogen sulfide, styrene, and m-xylene in the BTF lasted for 84 days (12 weeks). The degradation capacities of the BTF for hydrogen sulfide, styrene, and m-xylene were evaluated, and the synergy and inhibition among the substrates during biodegradation are discussed. The results indicated that the degradation efficiencies of the BTF were as high as 99.2% for hydrogen sulfide, 94.6% for styrene, and 100.0% for m-xylene. When the empty bed residence time was 30 s, the maximum elimination capacities (EC) achieved for hydrogen sulfide was 38 g m^-3 h^-1, for styrene was 200 g m^-3 h^-1, and for m-xylene was 75 g m^-3 h^-1. Furthermore, the microbial species and quantity of microorganisms in the middle and top of the BTF were much higher than those at the bottom of the BTF. A variety of microorganisms in the BTF can efficiently degrade the typical and highly toxic malodorous gases released from WWTPs. This study can help increase the understanding of the degradation of a mixture of sulfur-containing substances and aromatic hydrocarbons in BTF degradation and promote the development of technologies for the reduction of a complex mixture of malodorous gas emissions from organic wastewater treatment.

Functionalized Activated Carbon for Competing Adsorption of Volatile Organic Compounds and Water

The interfacial interaction of activated carbon with volatile organic compounds (VOCs) is seriously affected by water vapor. Therefore, it is vital to enhance the hydrophobic performance of activated carbon for expanding its application in industrial and environmental fields. Herein, a series of hydrophobic activated carbon was fabricated by tailored mixed siloxane and applied in dynamic competitive adsorption at 0, 50, and 90% humidity. Simultaneously, the diffusion molecular models and multicomponent adsorption experiments were used to study the adsorption and diffusion mechanisms. The hydrophobicity of activated carbon was significantly improved by loading of mixed siloxane, in which the equilibrium water absorption decreased from 21.9 to 7.2% and the contact angles increased by 70.10°. Meanwhile, dynamic competitive adsorption at different humidities indicated that the siloxane-functionalized activated carbons (SACs) showed much better competitive adsorption performances for VOCs than original activated carbon, which was further confirmed by the theoretical calculations of adsorption energy. In addition, a remarkable adsorption selectivity and reusability could be demonstrated to VOCs with different polarities on SACs. This study not only provides a new strategy for the hydrophobic modification of activated carbon materials but also offers theoretical guidance for the treatment of gas streams with significant water contents.

Defect engineering-induced porosity in graphene quantum dots embedded metal-organic frameworks for enhanced benzene and toluene adsorption

The emerging environmental issues necessitate the engineering of novel and well-designed nanoadsorbents for advanced separation and purification applications. Despite recent advances, the facile synthesis of hierarchical micro-mesoporous metal-organic frameworks (MOFs) with tuned structures has remained a challenge. Herein, we report a simple defect engineering approach to manipulate the framework, induce mesoporosity, and crease large pore volumes in MIL-101(Cr) by embedding graphene quantum dots (GQDs) during its self-assembly process. For instance, MIL-101@GQD-3 (V_meso: 0.68 and V_tot: 1.87 cm³/g) exhibited 300.0% and 53.3% more meso and total pore volume compared to those of the conventional MIL-101 (V_meso: 0.17 and V_tot: 1.22 cm³/g), respectively, resulting in 1.7 and 2.8 times greater benzene and toluene loading at 1 bar and 25 °C. In addition, we found that MIL-101@GQD-3 retained its superiority over a wide range of VOC concentrations and operating temperature (25-55 °C) with great cyclic capacity and energy-efficient regeneration. Considering the simplicity of the adopted technique to induce mesoporosity and tune the nanoporous structure of MOFs, the presented GQD incorporation technique is expected to provide a new pathway for the facile synthesis of advanced materials for environmental applications.

A revised definition of dynamic adsorption coefficient for characterizing activated carbon instead of retention bed

Activated carbon (AC) retention beds are widely used in nuclear facilities, removing radioactive contaminants from exhaust air. Dynamic adsorption coefficient (DAC) is the core parameter to quantify the performance. Its definition has not been unified and it is affected by the geometry of the retention bed, the presence, the flow rate, and the concentration of adsorbate. So, DAC is currently a parameter characterizing the adsorption performance of the retention bed instead of the AC. In this regard, the definition of DAC should be revised, stripping away the influence of other factors. In this study, a 1D model for the AC column, a 2D model for blank piping, and a mathematical model for retention factor is developed. All are validated with simulations and experiments based on the "pulse dynamic method". They are used to analyze the factors affecting DAC quantitatively in detail, including the direct effect of blank piping, the indirect effect of blank piping by affecting the pulse height into the column, and the effect of krypton concentration distribution in the column. Finally, an improved definition of DAC characterizing AC instead of retention bed is given. This definition can be used as a reference for scholars who formulate relevant standards.

Degradation of the mixture of ethyl formate, propionic aldehyde, and acetone by Aeromonas salmonicida: A novel microorganism screened from biomass generated in the citric acid fermentation industry

Microorganisms play important roles in the degradation of volatile organic compounds. Aeromonas salmonicida strain (AEP-3) generated from biomass in the citric acid fermentation industry was screened and subjected to denaturing gradient gel electrophoresis (DGGE) fingerprinting and 16S rDNA gene sequencing. The growth conditions of AEP-3 in Luria-Bertani broth were optimized at 25 °C and approximately pH 7. AEP-3 was used to degrade ethyl formate, propionic aldehyde, or acetone alone and their mixture. The concentrations of ethyl formate, propionic aldehyde, and acetone were below 7500, 600, and 800 mg L^-1, respectively, and their maximum degradation efficiencies were 100%, 92.41%, and 34.75%. AEP-3 first degraded acetone and propionic aldehyde in the mixture, followed by ethyl formate. The degradation pathways of these organic compounds in the mixture and their substrate interactions during degradation were explored. Propionic aldehyde was first converted into propionic acid in the metabolic process and was involved in the subsequent carboxylic acid cycle. By contrast, ethyl formate was first hydrolyzed into formic acid and ethanol. Then, formic acid participated in the cyclic metabolism of carboxylic acid, whereas, ethanol was hydrolyzed into acetaldehyde and acetic acid through alcohol and aldehyde dehydrogenase. Additionally, acetone directly interacted with nitrate in the medium under the action of hydrogen ions and produced carbon dioxide, water, and nitrogen. Overall, this study provides a new degrading bacterium biodegradability toward the exhaust gas of citric acid fermentation.

pH-Dependent adsorption of aromatic compounds on graphene oxide: An experimental, molecular dynamics simulation and density functional theory investigation

This work provides a comprehensive understanding for the pH-dependent adsorption of aromatic compounds (ACs) on graphene oxide (GO). Isothermal and kinetics experiments indicated both adsorption capacity and adsorption rate were suppressed at higher pH, and the mechanisms were revealed by molecular dynamics simulations and density functional theory calculations. More specifically, π-π, hydrogen bond, vdWs, and water-mediated steric hindrance interactions were examined to reveal how pH affected the adsorption capacity, and microscopic dynamic adsorption process was captured to reveal how pH affected the adsorption rate. Results showed the reduced adsorption capacity at higher pH was mediated by increased electrostatic repulsion, weakened π-π interaction, and increased water-mediated steric hindrance. The pH-dependent behaviour of GO was responsible for the effect of pH on adsorption rate. Self-aggregation of GO at lower pH helped to capture ACs and created more favourable adsorption sites. Upon the adsorption of ACs on GO, GO/water/AC/water/GO sandwich-like structure formed, which was also mediated by solution pH. Overall, pH affects the adsorption of ACs on GO by regulating driving forces, adsorption process, and the configuration property of GOAC complex.