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

Shielding the Hägg carbide by a graphene layer for ultrahigh carbon efficiency during syngas conversion

Fischer-Tropsch synthesis represents a key endeavor aimed at converting nonpetroleum carbon resources into clean fuels and valuable chemicals. However, the current state-of-the-art industrial FTS employing Fe-based catalysts is still challenged by the low carbon efficiency (<50%), mainly attributed to the prominent formation of CO2 and CH4 resulting from the nonregulated side water gas shift reaction. Herein, we describe a shielding strategy involving the encapsulation of the active Hägg carbide (χ-Fe5C2) by a graphene layer, exhibiting excellent resilience under reaction conditions and exposure to air, thereby eliminating the need for reduction or activation before the Fischer-Tropsch synthesis reaction. The graphene layer helps to stabilize the Hägg carbide active phase, and more importantly, greatly suppresses the side water gas shift reaction. Theoretical calculations suggest that graphene shielding inhibits the water gas shift reaction by reducing the absorption strength of OHx species. Remarkably, the optimum χ-Fe5C2@Graphene catalyst demonstrates a minimized CO2 and CH4 formation of only 4.6% and 5.9%, resulting in a high carbon efficiency (ca. 90%) for value-added products. These results are expected to inspire unique designs of Fe-based nanocomposite for highly efficient FTS with regulated carbon transfer pathways.

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.

Understanding the Adsorption Kinetics of Acetone in Humid Activated Carbons: Perspectives from Adsorption-Breakthrough Experiments and Molecular Simulations

The presence of water vapor influences the adsorption equilibrium and kinetics of volatile organic compounds (VOCs) in porous materials. By combination of breakthrough experiments and molecular simulations, the competitive adsorption mechanisms of water vapor and acetone on activated carbon with different textures and surface chemical properties at different humidity levels were investigated. Adsorption capacity decreases with increasing relative humidity owing to the formation of preferential adsorption sites between water and the activated carbon surface, while the adsorption rate initially increases and then decreases with increasing relative humidity. Experimental and simulation results revealed that the existence of a small amount of water changed the pore size distributions of activated carbon, thereby promoting the diffusion of acetone molecules. As the relative humidity increased, a portion of the acetone dissolved in water, resulting in a reduction in the adsorption rate. The response of different functional groups to relative humidity was further clarified by molecular simulation. Activated carbons with a high electrostatic interaction with acetone were less affected by humidity and thus exhibit greater potential as adsorbents.

Adsorption kinetics, isotherms, and selectivity of trihalomethanes and haloacetonitriles by granular activated carbon

The performance capability of granular activated carbon (GAC) adsorption in terms of disinfection by-product (DBPs) removal was investigated with synthetic water containing 1) trihalomethanes (THMs), 2) haloacetronitriles (HANs), and 3) Mix-THMs & HANs. The initial 20 min of adsorption resulted in the maximum adsorption rate, with the total THMs, total HANs, and total Mix-THMs & HANs being 4.972, 2.071, and 6.460 µg/gGAC-min, respectively. GAC dosage affects the adsorption selectivity of THMs and HANs. Under a low GAC dosage, the selectivity of GAC adsorbs more bromo-THMs than chloro-THMs. The adsorption selectivity of THMs on GAC following bromoform > dibromochloromethane > bromodichloromethane > chloroform was investigated. As the GAC concentration increased, the selectivity of THM adsorption by GAC became comparable. Chloro-HAN, in contrast to THMs, has a higher adsorption selectivity than bromo-HAN. Trichloroacetonitrile was removed by GAC more rapidly than the other HAN species when the GAC dose was increased. The toxin of bromoform was primarily eliminated through GAC adsorption, caused by a greater removal rate than that of the other THMs. As an implemented measure, GAC is introduced to reduce THMs and HANs and the toxic contents associated with THMs and HANs.

Comparison of perfluoroalkyl substance adsorption performance by inorganic and organic silicon modified activated carbon

Owing to the persistence and increasingly stringent regulations of perfluoroalkyl substances (PFAS), it is necessary to improve their adsorption capacities using activated carbon (AC). However, their adsorption capacities are suppressed by dissolved organic matter (DOM). In this study, two ACs modified with organic silicon (C-OS) and inorganic silicon (C-IS) were synthesized and used for the adsorption of PFAS in raw water (RW). The results showed that the PFAS adsorption capacity of C-IS was much less influenced by DOM than that of the original AC (C-virgin). In RW, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) adsorption capacities on C-IS were 15.08 and 3.65 times higher than those on C-virgin, respectively. DOM had less influence on the PFOA and PFOS adsorption kinetics of C-IS than C-OS and C-virgin. Under multi-PFAS condition, C-IS also exhibited slower desorption of short-chain PFAS and breakthrough in batch and column tests, respectively. Characterization of the ACs before and after adsorption and independent gradient modelling indicated that hydrogen bond interactions between the O-Si of C-IS and the -COOH or -CSO3H groups of PFAS contributed to PFAS adsorption. Density functional theory calculations demonstrated that the adsorption energy of C-IS was much lower than that of C-OS and C-virgin. The arrangement of PFAS molecules on C-OS was chaotic owing to the hydrophobic siloxane chain, whereas the arrangement of PFAS on C-IS was orderly in multi-layer or semi-micelle status and more favorable to PFAS adsorption. This study provides a new strategy for avoiding adverse effects of DOM on PFAS adsorption.

Extrusion Printing of Surface-Functionalized Metal-Organic Framework Inks for a High-Performance Wearable Volatile Organic Compound Sensor

Wearable sensors hold immense potential for real-time and non-destructive sensing of volatile organic compounds (VOCs), requiring both efficient sensing performance and robust mechanical properties. However, conventional colorimetric sensor arrays, acting as artificial olfactory systems for highly selective VOC profiling, often fail to meet these requirements simultaneously. Here, a high-performance wearable sensor array for VOC visual detection is proposed by extrusion printing of hybrid inks containing surface-functionalized sensing materials. Surface-modified hydrophobic polydimethylsiloxane (PDMS) improves the humidity resistance and VOC sensitivity of PDMS-coated dye/metal-organic frameworks (MOFs) composites. It also enhances their dispersion within liquid PDMS matrix, thereby promoting the hybrid liquid as high-quality extrusion-printing inks. The inks enable direct and precise printing on diverse substrates, forming a uniform and high particle-loading (70 wt%) film. The printed film on a flexible PDMS substrate demonstrates satisfactory flexibility and stretchability while retaining excellent sensing performance from dye/MOFs@PDMS particles. Further, the printed sensor array exhibits enhanced sensitivity to sub-ppm VOC levels, remarkable resistance to high relative humidity (RH) of 90%, and the differentiation ability for eight distinct VOCs. Finally, the wearable sensor proves practical by in situ monitoring of wheat scab-related VOC biomarkers. This study presents a versatile strategy for designing effective wearable gas sensors with widespread applications.

Single-Component Adsorption Equilibria of CO2, CH4, Water, and Acetone on Tapered Porous Carbon Molecular Sieves

Engineered carbon molecular sieves (CMSs) with tapered pores, high surface area, and high total pore volume were investigated for their CO2, CH4, water, and acetone adsorption properties at 288.15, 298.15, 308.15 K, and pressures of <1 bar. The results were compared with BPL carbon. The samples exhibited higher adsorption capacity for CO2 compared to BPL carbon, with Carboxen 1005 being the highest due to the presence of ultramicropores (pores smaller than 0.8 nm). Similar observations were made for CH4 except at 288.15 K. Although the CMSs exhibited higher hydrophobicity than BPL carbon, the latter had the highest acetone uptake for all investigated temperatures due to its higher oxygen content, which facilitates stronger interactions with polar VOC molecules. Heats of adsorption were calculated using the Clausius-Clapeyron equation after fitting the isotherms with the dual-site Langmuir-Freundlich model, and results largely corroborated the order of adsorption capacities of CO2, CH4, and water on the carbon materials.

Effect of different defects on the competitive adsorption of formaldehyde and water on the surface of carbon materials: Density functional theory study

The adsorption of formaldehyde by carbon materials is extremely limited and is also greatly influenced by the competitive adsorption of water. Therefore, it is of great significance to investigate the effect of different defects on the competitive adsorption of formaldehyde and water on the surface of carbon materials, and consequently the targeted modification of carbon materials to promote the adsorption of formaldehyde in air. In this study, multi-scale simulations were conducted to explore the problem of competitive adsorption of water and formaldehyde on the surface of carbon materials by quantum chemistry and molecular dynamics. IGMH, QTAIM, energy decomposition, electron transfer, and so on were used to conduct a comprehensive analysis of the problem of competitive adsorption of water and formaldehyde on the surface of carbon materials. The reasons for the formation of competitive adsorption between water and formaldehyde were firstly clarified, and then the adsorption interactions of different oxygen-containing functional groups on formaldehyde and water were investigated separately, which were found that the competitive adsorption of water and formaldehyde molecules by different types of oxygen-containing functional groups caused different results. And the introduction of intrinsic defects can promote the adsorption of formaldehyde in the presence of water competition for adsorption, which can well compensate the inhibitory effect of water on the adsorption of formaldehyde with strong polar functional groups. Finally, the results obtained from simulations were used to guide the modification experiments, and the experimental results were in accord with the simulation results. This study provides a new idea for the preparation of materials for efficient formaldehyde adsorption under certain humidity.

Ambient-mediated wetting on smooth surfaces

A consensus was built in the first half of the 20th century, which was further debated more than 3 decades ago, that the wettability and condensation mechanisms on smooth solid surfaces are modified by the adsorption of organic contaminants present in the environment. Recently, disagreement has formed about this topic once again, as many researchers have overlooked contamination due to its difficulty to eliminate. For example, the intrinsic wettability of rare earth oxides has been reported to be hydrophobic and non-wetting to water. These materials were subsequently shown to display dropwise condensation with steam. Nonetheless, follow on research has demonstrated that the intrinsic wettability of rare earth oxides is hydrophilic and wetting to water, and that a transition to hydrophobicity occurs in a matter of hours-to-days as a consequence of the adsorption of volatile organic compounds from the ambient environment. The adsorption mechanisms, kinetics, and selectivity, of these volatile organic compounds are empirically known to be functions of the substrate material and structure. However, these mechanisms, which govern the surface wettability, remain poorly understood. In this contribution, we introduce current research demonstrating the different intrinsic wettability of metals, rare earth oxides, and other smooth materials, showing that they are intrinsically hydrophilic. Then we provide details on research focusing on the transition from wetting (hydrophilicity) to non-wetting (hydrophobicity) on somooth surfaces due to adsorption of volatile organic compounds. A state-of-the-art figure of merit mapping the wettability of different smooth solid surfaces to ambient exposure as a function of the surface carbon content has also been developed. In addition, we analyse recent works that address these wetting transitions so to shed light on how such processes affect droplet pinning and lateral adhesion. We then conclude with objective perspectives about research on wetting to non-wetting transitions on smooth solid surfaces in an attempt to raise awareness regarding this surface contamination phenomenon within the engineering, interfacial science, and physical chemistry domains.

Self-Assembled Core-Shell Structure MgO@TiO2 as a K2CO3 Support with Superior Performance for Direct Air Capture CO2

Traditional carbon capture and storage technologies for large point sources can at best slow the rate of increase in atmospheric CO2 concentrations. In contrast, direct capture of CO2 from ambient air, or "direct air capture" (DAC), offers the potential to become a truly carbon-negative technology. Composite solid adsorbents fabricated by impregnating a porous matrix with K2CO3 are promising adsorbents for the adsorption capture of CO2 from ambient air. Nevertheless, the adsorbent can be rapidly deactivated during continuous adsorption/desorption cycles. In this study, MgO-supported, TiO2-stabilized MgO@TiO2 core-shell structures were prepared as supports using a novel self-assembled (SA) method and then impregnated with 50 wt % K2CO3 (K2CO3/MgO@TiO2, denoted as SA-KM@T). The adsorbent exhibits a high CO2 capture capacity of ∼126.6 mg CO2/g sorbent in direct air adsorption and maintained a performance of 20 adsorption/desorption cycles at 300 °C mid-temperature, which was much better than that of K2CO3/MgO. Analysis proved that the core-shell structure of the support effectively inhibited the reaction between the active component (K2CO3) and the main support (MgO) by the addition of TiO2, resulting in higher reactivity, thermal stability, and antiagglomeration properties. This work provides an alternative strategy for DAC applications using adsorbents.

Management of typical VOCs in air with adsorbents: status and challenges

The serious harm of volatile organic compounds (VOCs) to the ecological environment and human health has attracted widespread attention worldwide. With economic growth and accelerated industrialization, the anthropogenic emissions of VOCs have continued to increase. The most crucial aspect is to choose the appropriate adsorbent, which is very important for the VOCs removal. The search for environmentally friendly VOCs treatment technologies is urgent. The adsorption method is one of the most promising VOCs emission reduction technologies with the advantages of high cost-effectiveness, simple operation, and low energy consumption. One of the most critical aspects is the selection of the appropriate adsorbent, which is very important for the removal of VOCs. This work provides an overview of the sources and hazards of VOCs, focusing on recent research advances in VOCs adsorption materials and the key factors controlling the VOCs adsorption process. A summary of the key challenges and opportunities for each adsorbent is also provided. The adsorption capacity for VOCs is enhanced by an abundant specific surface area; the most efficient adsorption process is achieved when the pore size is slightly larger than the molecular diameter of VOCs; the increase in the number of chemical functional groups contributes to the increase in adsorption capacity. In addition, methods of activation and surface modification to improve the adsorption capacity for VOCs are discussed to guide the design of more advanced adsorbents.

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.

Revealing the Pore Size-Dependent Sorption Mechanism of Toluene and Cetane in Porous Carbon by Nuclear Magnetic Resonance

The adsorption of contaminants by porous carbon has been extensively studied by conventional isotherm and kinetic methods. However, the co-adsorption behavior and sorption sites of multiple contaminants in different-sized pores remain unclear. Herein, the nuclear magnetic resonance (NMR) approach is performed to investigate the adsorption mechanism of toluene and cetane in the confined space of carbon at the molecular level. The ring current effect induces the variation in the NMR chemical shifts of in-pore adsorbed toluene and cetane, realizing the identification of pore-dependent adsorption sites for contaminant removal. Cetane has a slower adsorption kinetic but a higher binding energy than toluene, which could squeeze toluene from micropores to larger pores with increasing adsorption quantity. This leads to a stronger competitive adsorption effect in small micropores than in mesopores. Accordingly, hierarchical porous carbons are determined to be the most effective adsorbents for the adsorption of coexisting contaminants. This study not only provides an effective NMR method to reveal the adsorption mechanism in the confined space of porous carbon at the molecular level but also offers new insights into the pore size-dependent adsorption of activated carbon for petroleum contaminant treatment.

Optimized Sieving Effect for Ethanol/Water Separation by Ultramicroporous MOFs

High-purity ethanol is a promising renewable energy resource, however separating ethanol from trace amount of water is extremely challenging. Herein, two ultramicroporous MOFs (UTSA-280 and Co-squarate) were used as adsorbents. A prominent water adsorption and a negligible ethanol adsorption identify perfect sieving effect on both MOFs. Co-squarate exhibits a surprising water adsorption capacity at low pressure that surpassing the reported MOFs. Single crystal X-ray diffraction and theoretical calculations reveal that such prominent performance of Co-squarate derives from the optimized sieving effect through pore structure adjustment. Co-squarate with larger rhombohedral channel is suitable for zigzag water location, resulting in reinforced guest-guest and guest-framework interactions. Ultrapure ethanol (99.9 %) can be obtained directly by ethanol/water mixed vapor breaking through the columns packed with Co-squarate, contributing to a potential for fuel-grade ethanol purification.

Competitive adsorption characteristics of gasoline evaporated VOCs in microporous activated carbon by molecular simulation

The activated carbon in the vehicle's carbon canister needs to adsorb a variety of VOCs (Volatile Organic Compounds) emitted by gasoline evaporation, while the difference in gas adsorption capacity can lead to adsorption competition phenomena. In this study, three typical VOCs (toluene, cyclohexane, and ethanol) were selected to study the adsorption competition characteristics between multi-component gases at different pressures by molecular simulation method. In addition, the effect of temperature on adsorption competition was also investigated. The results show that the selectivity of activated carbon to toluene is negatively correlated with the adsorption pressure, but the opposite is true for ethanol, and the change of cyclohexane is not significant. The competitive order of the three VOCs is toluene > cyclohexane > ethanol at low pressure, which becomes ethanol > toluene > cyclohexane at high pressure. With increasing pressure, the interaction energy decreases from 12.87 kcal/mol to 11.87 kcal/mol, where the electrostatic interaction energy increases from 1.97 kcal/mol to 2.54 kcal/mol. In microporous activated carbon, the competition is mainly manifested in that ethanol preempts the low-energy adsorption sites of toluene in the pore size of 10 Å to 18 Å, while gas molecules near the surface of activated carbon or in smaller pore sizes are stably adsorbed without competition. Despite the fact that high temperature decreases the total adsorption capacity, activated carbon selectivity for toluene increases instead, while the competitiveness of polar ethanol decreases significantly.

Engineering microbial cells with metal chelating hydroxylated unnatural amino acids for removable of synthetic pollutants from water

Lead (Pb²⁺) is a well-known heavy metal and toxic synthetic industrial pollutant in the ecosystem and causes severe threats to living organisms. It is paramount to develop a sustainable microbial engineering approach to remove synthetic pollutants from the environment. Genetic code engineering is emerging as an important microbial engineering tool in biosciences to biosynthesis congener protein production beyond the canonical set of natural molecules and expand the chemistries of living cells. Here, we prepare cells expressing unnatural amino acid encoded congener proteins for effectively removable toxic synthetic industrial pollutants (Pb²⁺) with high binding efficiency. Native and the developed congener proteins expressing cells adapted the Langmuir and Sips adsorption model that recommends uniform adsorption with Pb²⁺ ions. This could be due to a more significant number of functional groups on the protein surface. Fluorescence spectroscopic, field emission scanning electron microscope, X-ray photoelectron spectroscopic analysis, and protein-metal molecular stimulation coordination allowed us to explore the role of hydroxylation on Pb²⁺ adsorption. The bioreactor filled with immobilized protein-containing active granules showed >90% of lead removal in the contaminated water samples. The desorption of bound Pb2+ from GFP and its variants were studied by varying the pH to reuse the proteins for subsequent usage. We observed that about 70% of the GFP and its variants could be recycled and >75% of fluorescence efficiency could be recovered. Among all the variants, GFPHPDP exhibits high affinity and maintains the reusability efficiency in 7 consecutive cycles. These results suggest that genetic code engineering of cells encoding unnatural amino acids could be a next-generation microbial engineering tool for manipulating and developing the microbial strain's selective and effective removal of synthetic pollutants from the environment.

Triple-Phase Interface Engineered Hierarchical Porous Electrode for CO2 Electroreduction to Formate

The aqueous electrochemical CO2 reduction to valuable products is seen as one of the most promising candidates to achieve carbon neutrality yet still suffers from poor selectivity and lower current density. Highly efficient CO2 reduction significantly relies on well-constructed electrode to realize efficient and stable triple-phase contact of CO2 , electrolyte, and active sites. Herein, a triple-phase interface engineering approach featuring the combination of hierarchical porous morphology design and surface modification is presented. A hierarchical porous electrode is constructed by depositing bismuth nanosheet array on copper foam followed by trimethoxy (1H,1H,2H,2H-heptadecafluorodecyl) silane modification on the nanosheet surface. This electrode not only achieves highly selective and efficient CO2 reduction performance with formate selectivity above 90% over wide potentials and a partial current density over -90 mA cm-2 in H-cell but also maintains a superior stability during the long-term operation. It is demonstrated that this remarkable performance is attributed to the construction of efficient and stable triple-phase interface. Theoretical calculations also show that the modified surface optimizes the activation path by lowering thermodynamic barriers of the key intermediates *OCHO for the formation of formate during electrochemical CO2 reduction.

Efficient adsorption of dyes from aqueous solution using a novel functionalized magnetic biochar: Synthesis, kinetics, isotherms, adsorption mechanism, and reusability

In this study, a novel adsorbent, dodecylbenzene sulfonic acid (DBSA) functionalized magnetic biochar (DBSA-Fe₃O₄@BC), was synthesized and used to efficiently remove dyes from aqueous solution. The results indicated that DBSA-Fe₃O₄@BC exhibited an excellent adsorption capacity for Rhodamine B (RhB), and the maximum adsorption capacity for RhB at 298 K was 367.67 mg/g, which was approximately 2.3-1.2 folds than that of BC, dodecylsulfonic acid functionalized biochar (DSA@BC), DBSA@BC, Fe₃O₄@BC, and DSA-Fe₃O₄@BC. The possible adsorption mechanisms for RhB adsorption by DBSA-Fe₃O₄@BC included pore filling, electrostatic attraction, H bond, and surface complexation. Importantly, structural control presented that the simultaneous introduction of alkyl and phenyl groups significantly enhanced RhB adsorption by DBSA-Fe₃O₄@BC through hydrophobic and π-π interaction. Combined ethanol (EtOH) desorption and H₂O₂ oxidation regeneration, DBSA-Fe₃O₄@BC remained high-performance for RhB adsorption after six cycles (97.44%), indicating its outstanding reusability. In summary, DBSA-Fe₃O₄@BC exhibited a prospective application for dyeing wastewater treatment.

New insights into physicochemical properties of different particulate size-fractions and dissolved organic matter derived from biochars and their sorption capacity for phenanthrene

To improve the knowledge of the heterogeneity and sorption behavior of biochars on hydrophobic organic contaminants (HOCs), pristine biochars (PBCs, 400 and 700 °C) were fractionated into four particulate fractions (S_fBCs) and dissolved organic matter derived from biochars (DBC), then the sorption capacities of them towards phenanthrene were examined. Results showed that the OC-normalized sorption distribution coefficients (K_oc) of PBCs were generally at intermediate levels among that of S_fBCs and DBCs. The logK_oc values of S_fBCs increased as particle sizes decreased. By virtue of the higher micropore volume, specific surface area, aromaticity and hydrophobicity, the lowest S_fBCs (0.45-10 µm, BC_0.45-10) exhibited remarkably higher logK_oc. Besides, although S_fBCs from 700 °C generally showed larger logK_oc than counterparts from 400 °C, almost no difference was observed for logK_oc values of BC_0.45-10 fractions from 400 and 700 °C. We thus speculated that particle size might have stronger effect on their sorption capacity than pyrolysis temperature. Although DBCs exhibited dramatically lower logK_oc values than nano-scale S_fBCs, they were interestingly comparable to large-sized S_fBCs. Our findings thus suggested the importance of small particulate biochar species and DBCs on HOCs transport should be both highlighted since these fractions were highly dynamic in the environment.

Research on Adsorption and Desorption Performance of Gas-Phase Naphthalene on Hydrophobic Modified FDU-15

Naphthalene (NAP) is a typical gaseous polycyclic aromatic hydrocarbons (PAHs) pollutant that displays toxicological effects on biosystems. Ordered mesoporous carbon has relatively adequate adsorption capacity; however, the attached hydrophilic functional groups were proven to affect the adsorption performance in the presence of moisture. In this paper, trimethylchlorosilane (TMCS) is used to carry out the hydrophobic modification of ordered mesoporous carbon FDU-15, and the adsorption and desorption properties of FDU-15 were studied. Furthermore, the adsorption isotherms of naphthalene on FDU-15 and modified FDU-15 were fitted by L-F equation, and the kinetic parameters of desorption of naphthalene on modified FDU-15 were analyzed based on the method of temperature programming desorption (TPD). The results showed that the micropore volume and specific surface area of FDU-15 were significantly increased after hydrophobically modified by TMCS, and the polar functional groups of the hydrophobically modified FDU-15 were significantly reduced. Furthermore, the adsorption of naphthalene by FDU-15 before and after modification conformed to the L-F equation (R2 > 99%), and the adsorption of naphthalene by modified FDU-5 at low concentration was significantly improved due to the increase of micropores. Based on desorption kinetic performance study of modified FDU-15, it can be seen that the adsorption kinetic characteristics of naphthalene on the modified FDU-15 conform to the mechanical function of the JMA equation. When the mass ratio of TMCs to FDU-15 is 1:10 in the modification process, the pore structure and surface hydrophobicity of the modified FDU-15 reach an excellent balance. At this time, the adsorbent had the optimum desorption performance under experimental conditions, and the desorption activation energy was decreased from 60.98 kJ/mol of FDU-15 to 50.28 kJ/mol.