Adsorption of multicomponent VOCs on various biomass-derived hierarchical porous carbon: A study on adsorption mechanism and competitive effect

Hierarchical porous carbon nanofibrous membranes with elaborated chemical surfaces for efficient adsorptive removal of volatile organic compounds from air

Volatile organic compounds (VOCs) in the air pose great health risks to humans and the environment. Adsorptive separation technology has proven effective in mitigating VOC pollution, with the adsorbent being the critical component. Therefore, the development of highly efficient adsorbent materials is crucial. Carbon nanofibers, known for their physical-chemical stability and rapid adsorption kinetics, are promising candidates for removing VOCs from the air. However, the relatively simple porous structures and inert surface chemical properties of traditional carbon nanofibers present challenges in further enhancing their application performance further. Herein, a hierarchical porous carbon nanofibrous membrane was prepared using electrospinning technology and a one-step carbonization & activation method. Phenolic resin and polyacrylonitrile were used as co-precursors, with silica nanoparticles serving as the dopant. The resulting membrane exhibited a specific surface area of up to 1560.83 m2/g and surfaces rich in functional O-/N- groups. With a synergistic effect of developed micro- and meso-pores and active chemical surfaces, the carbon nanofibrous membrane demonstrated excellent adsorption separation performance for various VOCs, with comparable adsorption capacities and fast kinetics. Moreover, the membrane displayed remarkable reusability and dynamic adsorption performance for different VOCs, indicating its potential for practical applications.

Agri-food waste biosorbents for volatile organic compounds removal from air and industrial gases - A review

Approximately 1.3 billion metric tons of agricultural and food waste is produced annually, highlighting the need for appropriate processing and management strategies. This paper provides an exhaustive overview of the utilization of agri-food waste as a biosorbents for the elimination of volatile organic compounds (VOCs) from gaseous streams. The review paper underscores the critical role of waste management in the context of a circular economy, wherein waste is not viewed as a final product, but rather as a valuable resource for innovative processes. This perspective is consistent with the principles of resource efficiency and sustainability. Various types of waste have been described as effective biosorbents, and methods for biosorbents preparation have been discussed, including thermal treatment, surface activation, and doping with nitrogen, phosphorus, and sulfur atoms. This review further investigates the applications of these biosorbents in adsorbing VOCs from gaseous streams and elucidates the primary mechanisms governing the adsorption process. Additionally, this study sheds light on methods of biosorbents regeneration, which is a key aspect of practical applications. The paper concludes with a critical commentary and discussion of future perspectives in this field, emphasizing the need for more research and innovation in waste management to fully realize the potential of a circular economy. This review serves as a valuable resource for researchers and practitioners interested in the potential use of agri-food waste biosorbents for VOCs removal, marking a significant first step toward considering these aspects together.

Anti-competitive adsorption of gaseous benzene on hydrophilic microporous carbon in humid conditions

The adsorption capture of ambient volatile organic compounds (VOCs) is of practical importance for air quality management. Herein, unique anti-competitive adsorption behavior of benzene on a hydrophilic activated carbon (Procarb-900 (P900)) is evidenced in the presence of competing components (e.g., formaldehyde (FA) and/or moisture). Contrary to general expectations, the adsorption capacity of 10 Pa benzene (QB) onto P900 (30 mg) at the 99 % breakthrough level improves from 144.8 to 187 mg g-1 as the relative humidity (RH) increases from 0 to 25 %. Such pattern is maintained at 183.9 mg g-1 even at the relatively high RH of 50 %. Furthermore, QB exhibits a remarkable increase of 56.1 % (to 226.0 mg g-1) in the binary phase (100 ppm benzene plus 50 ppm FA) relative to its single phase (144.8 mg g-1). The kinetic studies confirm the occurrence of anti-competitive adsorption of benzene under humid conditions with the unusual decrease in rate constants at the elevated RHs (i.e., 25 and 50 %). The thermodynamic studies suggest the exothermic nature of benzene adsorption onto P900. The hydrophilicity of P900's outer surface promotes the preferential adsorption of polar FA and water vapor over non-polar benzene, which deforms the activated carbon texture and lowers the pore size distribution (PSD). The narrow PSD enhances benzene uptake in the complex systems due to the confinement effect. Overall, this study offers insights into the unique anti-competitive adsorption of non-polar VOCs (e.g., benzene) on hydrophilic microporous adsorbents in the presence of potential interferences such as polar water vapor and FA. These findings offer a guideline for the practical implementation of adsorption techniques for gaseous VOCs in humid conditions.

Simultaneously enhancing toluene adsorption and regeneration process by hierarchical pore in activated coke: a combined experimental and adsorption kinetic modeling study

Activated coke is a type of commonly used adsorbent for benzene series VOCs such as toluene, but traditional microporous activated coke usually faces the challenge of poor regeneration performance. Herein, based on self-made activated cokes with typical pore configuration, we found that adsorption and regeneration of toluene can be simultaneously enhanced by constructing hierarchical pore in activated coke. Correlations of pore configuration with toluene adsorption capacity and regeneration efficiency reveal that micropore contributes for strong toluene adsorption; meso-macropore provides mass transfer channel for toluene desorption and regeneration process. Hierarchical porous activated coke prepared from Zhundong subbituminous coal not only achieves the highest toluene adsorption capacity of 340.92 mg·g-1, but also can retain more than 90% of initial adsorption capacity after five adsorption-regeneration cycles. By contrast, micropore-dominant activated cokes can only retain 70% of initial adsorption capacity. Adsorption kinetic modelling on adsorption breakthrough curves shows that hierarchical porous activated coke prepared from Zhundong subbituminous coal exhibits high adsorption and diffusion rate constants of 14.39 and 33.45 min-1, respectively, much higher than those of micropore-dominant activated cokes. Due to the accelerated surface adsorption and diffusion processes induced by meso-macropore, toluene adsorption and regeneration behavior can be simultaneously improved. Results from this work validated the role of pore hierarchy in toluene adsorption-regeneration process, providing guidance for designing high-performance activated coke with synergistically improved toluene adsorption capacity and regeneration performance.

Synthesis and characterization of fluorescent poly(α-cyclodextrin)/carbon quantum dots composite for efficient removal and detection of toluene and xylene from aqueous media

This study reports the synthesis and characterization of a supramolecular composite comprised of carbon dots (CDots) embedded within net-poly[(α-cyclodextrin)-ν-(citric acid)] (α-CD/CA/CDots) for the removal and detection of toluene and xylene from aqueous media. The remarkable stability of CDots within the composite enables the preservation of photoluminescence properties for prolonged storage and extended UV-light irradiation. As demonstrated, following the adsorption of both organic compounds, the composite detected them in the aqueous medium due to a fluorescence quenching mechanism. Spectroscopic analyses reveal that the accessible Stern-Volmer quenching constants for toluene and xylene are KSVa = 15.4 M-1 and KSVa = 10.3 M-1, respectively. As a result, the α-CD/CA/CDots composite were sensitive to the tested volatile organic compounds (LODtoluene = 3.7 mg/L and LODxylene = 4.9 mg/L). Optimal conditions for toluene and xylene adsorption were found, allowing to achieve noticeable adsorption capabilities (qe(toluene) = 68.9 and qe(xylene) = 48.2 mg/g) and removal efficiencies exceeding 70%. Different characterization techniques confirmed the successful synthesis of the composite and elucidated the interaction mechanisms between the adsorbent and the tested compounds. In summary, the multifunctionality demonstrated by the α-CD/CA/CDots composite ranks it as an efficient and promising adsorbent and detection probe for this class of water contaminants.

PCDD/F adsorption enhancement over nitrogen-doped biochar: A DFT-D study

Polychlorinated dibenzo-p-dioxin/furans (PCDD/F) have a great threat to the environment and human health, resulting in controlling PCDD/F emissions to regulation far important for emission source. Considering 2,3,4,7,8-pentachlorodibenzo-p-furan (PeCDF) identified as the most contributor to international toxic equivalent, 2,3,4,7,8-PeCDF can be considered as the target molecule for the adsorption of PCDD/F emission from industries. With the aim to in-depth elucidate how different types of nitrogen (N) species enhance 2,3,4,7,8-PeCDF on the biochar and guide the specific carbon materials design for industries, systematic computational investigations by density functional theory calculations were conducted. The results indicate pristine biochar intrinsically interacts with 2,3,4,7,8-PeCDF by π-π electron donor and acceptor (EDA) interaction, six-membered carbon rings of PeCDF parallel to the biochar surface as the strongest adsorption configuration. Moreover, by comparison of adsorption energy (-150.16 kJ mol-1) and interaction distance (3.593 Å) of pristine biochar, environment friendly N doping can enhance the adsorption of 2,3,4,7,8-PeCDF on biochar. Compared with graphitic N doping and pyridinic N doping, pyrrolic N doping biochar presents the strongest interaction toward 2,3,4,7,8-PeCDF molecule due to the highest adsorption energy (-155.56 kJ mol-1) and shortest interaction distance (3.532 Å). Specially, the enhancing adsorption of PeCDF over N doped biochar attributes to the enhancing π-π electron EDA interaction and electrostatic interaction. In addition, the effect of N doping species on PeCDF adsorbed on the biochar is more than that of N doping content. Specially, the adsorption capacity of N doping biochar for PCDD/F can be improved by adding pyrrolic N group most efficiently. Furthermore, pyrrolic N and pyridinic N doping result in the entropy increase, and electrons transform from pyrrolic N and pyridinic N doped biochar to 2,3,4,7,8-PeCDF molecule. A complete understanding of the research would supply crucial information for applying N-doped biochar to effectively remove PCDD/F for industries.

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.

The resin-supported iron-copper bimetallic composite as highly active heterogeneous Fenton-like catalysts for degradation of gaseous toluene

In this study, a resin-supported iron-copper bimetallic heterogeneous Fenton catalyst with excellent removal performance, superior economy and outstanding recoverability was synthesized by an impregnation method and used to remove gaseous toluene. Experiments disclosed that 3-FeCu@LXQ-10 possessed extremely high catalytic capacity. At a temperature of 30 °C, an initial toluene concentration of 200 mg/m3 and H2O2 atomization amount of 3 mmol/h, the toluene removal efficiency of 3-FeCu@LXQ-10 was 97.50%. Experimental tests had revealed that the bimetallic supported catalysts exhibited higher catalytic activity than single metal-supported catalysts, owing to an interaction effect between iron and copper metal ions. Furthermore, electron paramagnetic resonance (EPR) and radical quenching tests were carried out, and the results indicated •OH radicals performed a key role in the Fenton-like process. In addition, the iron-copper bimetallic catalysts exhibited good reusability and stability characteristics during six degradation cycles. This study shows promising potential in using FeCu@LXQ-10 as a heterogeneous catalyst for removing toluene.

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.

New Porous Carbon Material Derived from Carbon Microspheres Assembled in Hollow Carbon Spheres and Its Application to Toluene Adsorption

In this paper, a new porous carbon material adsorbent was prepared using carbon microspheres assembled in hollow carbon spheres (HCS) with a hydrothermal method. Transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and Raman spectroscopy were used to characterize the adsorbents. It was found that the diameter of carbon microspheres derived from 0.1 mol/L glucose was about 130 nm, which could be inserted inside HCS (pore size was 370-450 nm). The increase in glucose concentration would promote the diameter of carbon microspheres (CSs), and coarse CSs could not be loaded in the mesopores or macropores of HCS. Thus, the C_0.1@HCS adsorbent had the highest Brunauer-Emmett-Teller surface area (1945 m²/g) and total pore volume (1.627 cm³/g). At the same time, C_0.1@HCS posed a suitable ratio of micropores and mesopores, which could provide adsorption sites and volatile organic compound diffusion channels. Moreover, oxygen-containing functional groups -OH and C═O in CSs were also introduced into HCS, and the adsorption capacity and regenerability performance of the adsorbents were improved. The dynamic adsorption capacity of C_0.1@HCS for toluene reached 813 mg/g, and the Bangham model was more suitable for describing the toluene adsorption process. The adsorption capacity was stably kept above 770 mg/g after eight adsorption-desorption cycles.

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.