Molecular Dynamics Simulation on the Adsorption Behavior of Toluene and Ethyl Acetate and Pore Structure Effects in Activated Carbon Synergistically Regulated by Pyridinic/Pyrrolic Nitrogen

Molecular Dynamics Simulation on the Adsorption Behavior of Toluene and Ethyl Acetate and Pore Structure Effects in Activated Carbon Synergistically Regulated by Pyridinic/Pyrrolic Nitrogen | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Molecular Dynamics Simulation on the Adsorption Behavior of Toluene and Ethyl Acetate and Pore Structure Effects in Activated Carbon Synergistically Regulated by Pyridinic/Pyrrolic Nitrogen Yansong Wu, Jiancheng Zhang, Dong Li, Hanbing Qi, Zhihua Wang, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8791300/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract To address the challenge of competitive adsorption and separation arising from the coexistence of nonpolar hydrocarbons (TL-toluene) and polar solvents (EAC-ethyl acetate) in oilfield associated gas and produced-water treatment, this study employs grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations to systematically investigate the adsorption mechanisms and pore-confinement effects of pyridinic-N and pyrrolic-N doped activated carbons toward toluene and ethyl acetate. The results demonstrate that nitrogen doping induces electronic cloud redistribution and constructs polar adsorption sites, thereby enhancing π–π interactions with toluene and electrostatic attraction with ethyl acetate, respectively. As a consequence, the capacity retention of the polar component is significantly improved under competitive adsorption conditions.In-depth analysis based on slit-pore models reveals a distinctive pore-size effect. At a critical micropore width of 1.0 nm, an anomalous “selectivity reversal” is observed, wherein the adsorption amount of the polar component surpasses that of the nonpolar component. Mechanistic investigations confirm that this phenomenon originates from a “competition-induced structural reconstruction” process: toluene preferentially occupies the pore walls, forcing ethyl acetate molecules to retreat toward the pore center, where they self-assemble into a high-density sandwich-like cluster with a “Wall–Toluene–EAC–Toluene–Wall” configuration. Energy analyses indicate that the penetrative long-range electrostatic field generated by the N-doped surface acts synergistically with physical squeezing effects imposed by spatial confinement, effectively stabilizing the polar molecular clusters at the pore center.The proposed “sub-nanometer physical squeezing–chemical field stabilization” mechanism provides a theoretical foundation for the rational design of adsorption materials targeting complex multicomponent VOC systems. Oilfield VOCs mitigation molecular dynamics simulation nitrogen-doped activated carbon selective adsorption competition-induced reconstruction Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction During petroleum and natural gas exploitation as well as downstream petrochemical processing, large quantities of associated gas and industrial wastewater containing volatile organic compounds (VOCs) are inevitably released[ 1 – 2 ]. Unlike the low-concentration VOCs typically found in ambient air, emissions from oilfield sources are characterized by complex compositions and large concentration fluctuations. In such systems, nonpolar petroleum hydrocarbons (eg, toluene, TL) often coexist with polar organic solvents used in production processes (eg, ethyl acetate, EAC)[ 3 ]. This complex “polar/nonpolar” mixture poses significant challenges for end-of-pipe treatment. On the one hand, increasingly stringent environmental emission standards must be met; on the other hand, efficient separation and resource recovery of components with different polarities is of considerable economic value [ 4 ].Adsorption technology, owing to its deep purification capability and solvent recovery potential, has been widely applied in oilfield VOCs mitigation. Among various adsorbents, activated carbon (AC) remains the most commonly used material because of its low cost and well-developed pore structure[ 5 ]. However, conventional activated carbon exhibits pronounced hydrophobicity and nonpolar surface characteristics, which lead to severe “selectivity failure” when treating complex oilfield VOC mixtures[ 6 – 7 ]. In multicomponent competitive adsorption systems, nonpolar hydrocarbons such as toluene—with stronger adsorption potentials—tend to dominate the adsorption sites and displace polar molecules like ethyl acetate through competitive exclusion. This results in a markedly shortened breakthrough time for polar components in adsorption beds, severely limiting purification efficiency and recovery purity[ 8 – 9 ]. Therefore, developing novel carbon-based adsorbents that can maintain high adsorption capacity while exhibiting specific selectivity under strong competitive conditions is crucial for addressing the challenges of complex oilfield VOC treatment.To tailor the surface chemical properties of carbon materials, heteroatom doping (eg, nitrogen, oxygen, and sulfur) has been demonstrated as an effective strategy to enhance surface polarity and modulate electronic structures[ 10 ]. In particular, incorporating nitrogen atoms (pyridinic-N and pyrrolic-N) into the carbon framework can induce charge redistribution and generate high-energy polar sites, thereby strengthening electrostatic attraction or hydrogen-bond interactions with polar molecules such as ethyl acetate. Simultaneously, conjugation effects enable regulation of the π-electron system, preserving π–π interactions with the aromatic rings of toluene[ 11 ]. Although experimental studies have suggested that nitrogen doping can improve the adsorption performance toward mixed VOCs, current understanding is largely based on macroscopic observations and lacks atomistic insight into host–guest interactions within confined pores. Especially under strong competition between large hydrocarbon molecules and small polar solvents in sub-nanometer slit pores, the spatial arrangement of adsorbates and the synergistic roles of surface chemical sites and physical confinement in governing separation selectivity remain poorly understood.In this context, the present study focuses on representative oilfield VOC components (toluene/ethyl acetate) and employs grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations to construct pyridinic-N and pyrrolic-N modified activated carbon models. The objective is to elucidate, at the molecular level, the regulatory mechanisms of nitrogen doping on competitive adsorption behavior, with particular emphasis on the influence of pore size on adsorption selectivity and the identification of a unique “competition-induced structural reconstruction” mechanism under confined conditions. The findings of this work are expected to provide a theoretical basis for the rational design of high-performance adsorbents for efficient separation and resource recovery under complex oilfield operating conditions. 2. Model Construction and Simulation Details 2.1 Model Construction In this study, all models required for molecular simulations were constructed using Materials Studio 2020 software. To ensure simulation accuracy, the COMPASSII force field[ 12 ] and forcefield-assigned charges were employed throughout the process.First, toluene (TL) and ethyl acetate (EAC) were selected as representative non-polar and polar VOCs, respectively. Their initial configurations were constructed using the Visualizer module, as shown in Figs. 1 (a) and 1(b). Subsequently, geometry optimization was performed using the Forcite module under convergence criteria consisting of an energy tolerance of 1.0×10 − 4 kcal/mol, a force tolerance of 0.005 kcal/mol/Å, and a displacement tolerance of 5.0×10 − 5 Å.Regarding adsorbent modeling, a pure activated carbon (Pure-AC) skeleton was constructed based on edge-hydrogen-saturated graphene microcrystalline fragments (Fig. 1 (c)). The nitrogen-doped modified model (N-AC) was then created by introducing pyridinic nitrogen (Pyridinic-N) and pyrrolic nitrogen (Pyrrolic-N) (Fig. 1 (d)). All fragments subsequently underwent structural relaxation to eliminate lattice distortion.Based on the aforementioned optimized fragments, a Virtual Porous Carbon (VPC) model with three-dimensional periodic boundary conditions[ 13 ] was constructed using the Monte Carlo packing algorithm within the Amorphous Cell module (Fig. 1 (g)). The target density was controlled within the range of 0.55 g/cm³[ 14 ], and the model was subjected to high-temperature annealing to achieve a thermodynamically stable disordered pore structure.As shown in Fig. 1 (e), the geometrically optimized nitrogen-doped graphene sheets exhibited sp2 network rearrangement and local lattice distortion induced by the introduction of heteroatoms; these were selected as the fundamental building blocks to simulate the surface chemical heterogeneity of the modified activated carbon. Based on this, the BuildLayers tool was utilized to construct a series of slit pore models covering the range from limiting micropores to mesopores (Fig. 1 (h)). By precisely regulating the distance (H) between parallel sheets, this study aims to deeply investigate the synergistic adsorption mechanism involving the pore size confinement effect and surface polar sites, as well as to determine the optimal and limiting pore sizes for the adsorbates. 2.2. Simulation Details 2.2.1. Virtual Porous Carbon Model The adsorption performance of the constructed Pure-AC and N-AC virtual porous models was systematically investigated using the Grand Canonical Monte Carlo (GCMC) method within the Sorption module[ 15 ]. The COMPASSII force field and forcefield-assigned charges were employed throughout the simulations to accurately describe the adsorbent-adsorbate and adsorbate-adsorbate interactions based on the Metropolis sampling algorithm.At 298 K, single-component adsorption isotherms for toluene and ethyl acetate were first calculated over a pressure range covering the Henry's region up to 100 kPa, in order to quantitatively evaluate the enhancement effect of nitrogen doping on adsorption capacity. Subsequently, to simulate actual operating conditions and elucidate the competitive adsorption mechanism, binary competitive adsorption simulations were conducted with a gas phase molar ratio set to 1:1( \(\:{\text{y}}_{\text{tol}}\text{：}{\text{y}}_{\text{ea}}\text{=1:1}\) ), based on which the adsorption selectivity of the materials was analyzed.Following this, based on the adsorption loadings obtained from the Sorption module, the models were reconstructed using the Forcite module. The task was set to 'Dynamics', and the NVT ensemble was selected for molecular dynamics simulations[ 16 ]. The temperature was maintained at 298 K with a time step of 1 fs, comprising 10,000 total steps for a total simulation time of 10 ps. Upon completion of these calculations, Monte Carlo simulations of the adsorption behavior were performed.Furthermore, to provide an in-depth atomic-scale analysis of the specific host-guest interactions, the Radial Distribution Functions (RDFs) of the adsorbate molecules relative to the active sites were calculated. For all simulations,1×10 6 steps were allocated for system equilibration, followed by 2×10 6 steps for production statistics, ensuring thermodynamic equilibrium and statistical convergence of the adsorption data. 2.2.2. Slit Pore Model To deeply analyze the confinement effect at the atomic scale and precisely pinpoint the optimal geometric configuration for VOC capture, this study constructed a series of N-doped graphene slit pore models with gradient interlayer spacings based on the Sorption module. The regulatory mechanism of pore size on adsorption behavior was systematically investigated using the Grand Canonical Monte Carlo (GCMC) algorithm under the COMPASS II force field.First, a quantitative "pore size–adsorption density" structure-activity relationship was established by calculating the single-component adsorption isotherms of toluene and ethyl acetate. Furthermore, the limiting cutoff pore size and optimal matching pore size for the adsorbates were precisely identified utilizing the principle of host-guest potential energy field superposition.On this basis, to explore the interplay between steric hindrance and surface chemical affinity under strong competitive environments, equimolar binary competitive adsorption simulations were further implemented. The analysis of local density distributions intuitively revealed the dominant adsorption sites within the slit channels, as well as the layered stacking and structural reconstruction behaviors of the molecules. All simulations were conducted at 298 K, strictly executing 1×10 6 \times equilibration steps and 2 ×10 6 \times production statistics steps to ensure the accuracy and convergence of phase space sampling in these complex confined systems. 3. Results and Discussion The equilibrium adsorption configuration diagrams and adsorption capacity data, derived from the adsorption isotherm calculations, visually reveal the mechanism by which nitrogen doping influences the microscopic adsorption behavior of activated carbon.A comparison of the single-component adsorption systems indicates that toluene and ethyl acetate molecules within the pores of Pure-AC are relatively dispersed and limited in number. They are primarily located near the pore walls, suggesting weak surface affinity. In contrast, the adsorbate density in the N-AC model is significantly increased, with molecules tending to accumulate around the nitrogen-containing functional groups; this observation is highly consistent with the trend of improved adsorption capacity.In the binary competitive adsorption system, Pure-AC exhibits marked competitive inhibition and repulsion effects, resulting in a substantial decline in adsorption capacity. Conversely, N-AC retains a high binary loading with a uniform distribution and shows no significant adsorption collapse, thereby confirming the stability of nitrogen doping under complex operating conditions.Combined with microscopic structural analysis, this superior adsorption performance is primarily attributed to the regulation of the local electronic structure and surface polarity of the carbon skeleton by the introduced pyridinic and pyrrolic nitrogen. On one hand, the nitrogen-containing functional groups enhance the charge heterogeneity of the pore wall surface, reinforcing the strong electrostatic anchoring interaction with the polar ester groups of ethyl acetate. On the other hand, the redistribution of the π cloud induced by nitrogen doping promotes π − π interactions between the carbon skeleton and the aromatic rings of toluene.This mechanism of "synergistic polarity enhancement and π − π interactions" compellingly demonstrates that introducing nitrogen-containing functional groups is an effective strategy for improving the adsorption capacity and competitive adsorption stability of activated carbon for multi-component VOCs. Table 1 Adsorption capacities of toluene and ethyl acetate on different activated carbons adsorbed amount of TL(per cell) adsorbed amount of EAC(per cell) Pure-AC 100 single-component adsorption 106 69 33 binary competitive adsorption N-AC 102 single-component adsorption 107 71 35 binary competitive adsorption 3.1. Influence of Virtual Porous Carbon Models on the Adsorption of Toluene and Ethyl Acetate 3.1.1. Adsorption Isotherms and Competitive Mechanism Analysis As shown in Fig. 3 (a–b), the adsorption isotherms of Pure-AC and N-AC under single-component conditions exhibit typical Type I characteristics[ 17 ], indicating that micropore filling is the dominant adsorption mechanism. Compared with Pure-AC, N-AC shows a higher adsorption affinity in the low-pressure region, which is particularly pronounced for ethyl acetate, suggesting that nitrogen doping effectively enhances the interactions between the adsorbent and polar VOC molecules. However, in the high-pressure saturation region, the adsorption capacities of the two adsorbents gradually converge, implying that under near-saturation conditions, the total adsorption uptake is primarily constrained by the available micropore volume, while the influence of surface chemistry becomes less significant[ 18 ].In contrast, under binary competitive adsorption conditions (Fig. 3 (c–d)), the adsorption behavior exhibits pronounced divergence. Toluene maintains a higher adsorption capacity across the entire pressure range, demonstrating a clear competitive advantage, whereas the adsorption of ethyl acetate is significantly suppressed. The tabulated data further quantitatively confirm this phenomenon: at a total pressure of 100 kPa, the capacity retention rates of toluene on Pure-AC and N-AC are 68.41% and 69.61%, respectively, while those of ethyl acetate are only 30.86% and 32.33%. Compared with single-component adsorption, toluene retains approximately 70% of its adsorption capacity in the binary system, indicating its strong competitive dominance; in contrast, the adsorption capacity of ethyl acetate decreases drastically, reflecting severe suppression under limited adsorption sites.These asymmetric competitive behaviors indicate that competitive adsorption is not governed solely by pore structure but is strongly dependent on molecular-level interactions between the adsorbates and the adsorbent[ 19 ]. Aromatic toluene molecules can form stable host–guest interactions with the carbonaceous framework through strong π–π interactions, thereby preferentially occupying high-energy adsorption sites and exerting competitive exclusion on ethyl acetate. Nevertheless, nitrogen doping partially mitigates the competitive disadvantage of the polar component. Compared with Pure-AC, N-AC increases the competitive adsorption capacity of ethyl acetate from 33 to 35 per cell, corresponding to an increase in the capacity retention rate to 32.33%, indicating that nitrogen-containing high-energy polar adsorption sites can enhance the selective adsorption of polar molecules via electrostatic induction and dipole–dipole interactions.Overall, while micropore filling determines the maximum adsorption capacity of the materials, molecular-scale interactions dominate adsorption selectivity and competitive behavior in multicomponent VOC systems. The capacity retention rate can serve as an effective quantitative indicator for evaluating competitive adsorption strength[ 20 ]. Nitrogen doping does not alter the dominant competitive position of toluene but effectively enhances the adsorption stability of ethyl acetate under strong competitive conditions[ 21 ], thereby improving the overall removal performance of activated carbon toward complex VOC mixtures. Table 2 Comparison of saturated adsorption capacities (100 kPa) under single-component and binary competitive conditions and the calculated capacity retention rates.( Note : \(\:\text{Capacity}\text{}\text{Retention}\text{}\text{Rate}\text{=}\frac{{\text{q}}_{\text{binary}}}{{\text{q}}_{\text{single}}}\text{×}\) 100%) adsorbent type adsorbate components q single per cell) \(\:{\text{q}}_{\text{binary}}\) per cell capacity retention(%) competitive condition Pure-AC TL 100.87 69 68.41% dominant component EAC 106.94 33 30.86% suppressed component N-AC TL 102 71 69.61% dominant component EAC 107 35 32.33% suppressed component 3.1.2 Microscopic mechanism analysis of host–guest interactions As shown in Fig. 4 (a), in the Pure-AC system, the Radial Distribution Function (RDF) curve (green line) between the carbon skeleton and the carbonyl oxygen atom of ethyl acetate presents a gradual monotonic upward trend, with no obvious characteristic peaks observed. This phenomenon indicates a lack of specific interactions between the unmodified carbon surface and polar ethyl acetate molecules, suggesting that their adsorption behavior is primarily governed by weak van der Waals forces.In contrast, the N-O RDF curve (red line) in the N-AC system exhibits a characteristic peak at r ≈ 2.0 Å and forms a broad shoulder peak with an intensity of approximately 1.55 in the range of 3.5 − 5.0 Å[ 22 ]. The short-range peak (2.0 Å) confirms the existence of direct strong electrostatic interactions or hydrogen bonding tendencies between some ethyl acetate molecules and surface N sites; meanwhile, the broader peak at a longer distance (3.5 − 5.0 Å) reveals the long-range electrostatic field effect generated by N-doping. This long-range force establishes an enlarged "capture radius," capable of binding ethyl acetate molecules around active sites via penetrating electrostatic attraction, even when the adsorbate cannot directly contact the surface sites (eg, when separated by toluene during competitive adsorption). This microscopic evidence is physically highly self-consistent with the "sandwich" confined structure observed in slit pores discussed later. The peak intensity of the N-AC system is significantly higher than that of Pure-AC (g(r) > 1.5 vs g(r) ≈ 1.2), confirming that nitrogen-containing functional groups construct high-affinity adsorption active domains on the carbon skeleton, effectively enriching ethyl acetate molecules through electrostatic induction. This microscopic mechanism aligns well with the experimental results showing a significant increase in adsorption capacity in the low-pressure region of the macroscopic adsorption isotherms.To further investigate the enhancement mechanism of N-doping on the adsorption of non-polar molecules, Fig. 4 (b) compares the RDF curves of the toluene benzene ring center relative to skeletal N atoms (red line) and ordinary C atoms (green line). The results show that both curves exhibit characteristic peaks at 3.8 − 4.0 Å[ 23 – 24 ], confirming that π − π stacking is the primary driving force for toluene adsorption[ 25 – 26 ]. Crucially, the RDF peak intensity of N-TL (g(r) ≈ 2.6) is significantly higher than that of C-TL (g(r) ≈ 2.2). This significant difference strongly proves that the introduction of heteroatom N induces electron cloud rearrangement in the carbon skeleton, constructing local adsorption sites with stronger electron affinity. This significantly enhances the π − π interactions between the adsorbent and the toluene aromatic rings[ 27 ], revealing the microscopic physical origin of the improved toluene adsorption capacity on N-AC.Furthermore, to elucidate the competitive inhibition mechanism of toluene against ethyl acetate in the binary system, Fig. 4 (c) compares the RDF curves of ethyl acetate (target atom pair: N-O) under single-component and binary environments. As shown, after the introduction of toluene, the peak intensity of the N-O RDF exhibits a distinct attenuation. This indicates that toluene molecules, by virtue of their strong π − π interactions and larger molecular kinetic diameter, dominate within the pores, generating significant steric hindrance effects and competitively occupying the adsorption space of ethyl acetate. However, crucially, although the peak intensity decreased, the RDF characteristic peak in the binary system did not completely disappear and still maintained a considerable intensity (g(r)max ≈ 1.75). This microscopic evidence compellingly indicates that the polar sites introduced by N-doping construct a specific "adsorption refuge." Even in a strong competitive environment dominated by toluene, these high-energy sites can still firmly anchor some ethyl acetate molecules via strong electrostatic attraction, preventing them from being completely displaced by non-polar toluene. 3.2. Influence of Slit Pore Structure on Adsorption Behavior 3.2.1. Regulatory Effect of Slit Pore Structure on Competitive Adsorption Figure 5 systematically illustrates the regulatory patterns of slit pore width (H) on the competitive adsorption behavior of toluene (TL) and ethyl acetate (EAC). In single-component systems (blue lines in Fig. 5 a and 5 b), both adsorbates exhibit characteristic capacity oscillation behaviors due to matching packing effects. However, upon the introduction of the competing component (red lines), the adsorption performances of the two diverge significantly: toluene suffers severe competitive displacement across the entire pore size range, resulting in a sharp decay in adsorption capacity, whereas ethyl acetate exhibits unique dual-zone adsorption characteristics.First, in the mesopore transition region of 16–18 Å, ethyl acetate demonstrates remarkable anti-competition resilience and capacity retention. Although non-polar toluene still dominates at these pore sizes, the long-range electrostatic field induced by N-doped sites effectively stabilizes the multilayer adsorption structure, preventing the adsorption collapse of polar molecules due to spatial competition.To quantify this separation efficiency, the calculated adsorption selectivity coefficients (S EAC/TL) (Fig. 5 c) reveal a critical phenomenon of "selectivity inversion." Although toluene maintains a thermodynamic advantage (S 15Å) by virtue of stronger non-specific dispersion forces (π − π interactions), the selectivity coefficient rises sharply and breaches the baseline to reach a maximum value when the pore width contracts to the critical micropore window of H ≈ 10 Å[ 28 – 29 ].This fundamental inversion is attributed to the synergistic effect of sub-nanometer physical confinement and surface chemical modification: at this dimension, bulky toluene molecules face severe steric hindrance effects and packing frustration, whereas smaller EAC molecules benefit from the electrostatic anchoring of N-doped sites, thereby achieving an effective reversal against the non-polar competitor and realizing selective capture. 3.2.2. Competition-Induced Microstructural Reconstruction and Energetic Origins To elucidate the physical origins of the high selectivity at the molecular level, we conducted an in-depth analysis of the adsorption mechanism by combining local density distributions (Figs. 6 a, 6 b) with interaction energy decomposition (Fig. 6 c).As shown in Fig. 6 b, in the wide pore (H = 20 Å), upon introducing the competing component, the density distribution of EAC (red filled region) undergoes an overall attenuation in intensity while maintaining a configuration similar to that of the single-component system (black dashed line). This reveals a typical competitive loss mechanism characterized by "random displacement."However, when the pore width contracts to the optimal selectivity window (H = 10 Å, Fig. 6 a), the system undergoes a dramatic "competition-induced structural reconstruction." In stark contrast to the "double-layer" distribution near the pore walls observed in the single-component system, EAC molecules in the binary system are forced to retreat from the walls, instead forming a highly localized "squeezed monolayer" (red peak) in the pore center.This anomalous squeezing effect stems from the stronger wall-fluid interactions that prompt toluene molecules to preferentially occupy sites on the graphene surface, thereby "blockading" EAC molecules in the pore center. Crucially, the extremely high density of this central layer (with a peak significantly higher than that of the single-component system) indicates that under the synergistic compression of intermolecular interactions and the confinement potential, EAC molecules form closely packed high-density clusters, thereby maximizing the compensation for capacity loss.Further energy component analysis (Fig. 6 c) reveals the thermodynamic essence governing this reconstruction behavior. As the pore size decreases, the total interaction energy of EAC molecules (∣Etotal∣) reaches a maximum (approximately 220 kJ/mol) at H = 10 − 12 Å, confirming that this dimension provides the deepest thermodynamic potential well. Although van der Waals interactions (blue bars) dominate the total energy, the electrostatic interaction contribution (red bars) exhibits a significant specific enhancement in the narrow micropore of H = 10 Å. Within this strongly confined space, the squeezed EAC molecular clusters can achieve effective coupling with N-doped sites via long-range electrostatic interactions[ 30 ]. This additional electrostatic stabilization acts as a critical "chemical anchor," effectively compensating for the entropy loss caused by steric hindrance effects, thereby establishing an energetic advantage for EAC in the fierce competition with non-polar toluene. 3.2.3. Competition-Induced Reconstruction and Spatial Self-Organization Mechanisms Based on the microscopic density and energy analyses mentioned above, Fig. 7 proposes a mechanistic model for the competition-induced structural reconstruction within the optimal 10 Å micropore.In the non-competitive single-component system (Fig. 7 a), driven by the electrostatic attraction of N-doped sites, EAC molecules are directly anchored to the carbon pore wall surface, forming a stable "bilayer" configuration to maximize fluid-wall interactions.However, upon introducing toluene (Fig. 7 b), the adsorption landscape undergoes a fundamental reversal: leveraging the advantage of strong π − π stacking, toluene molecules preferentially occupy and blockade the wall sites, forming a dense hydrophobic lining (shown in purple). Crucially, this preferential occupation does not lead to the complete exclusion of EAC; instead, it triggers a significant "squeezing effect"—EAC molecules are forced to retreat into the sub-nanometer confined space between two layers of toluene. Under the synergistic compression of confinement potential and intermolecular repulsion, they self-organize into an extremely high-density "monolayer" cluster at the pore center [ 30 ].This unique "sandwich-like" TL-EAC-TL configuration not only constitutes the structural basis for the macroscopic selectivity inversion but also reveals a key design principle: in N-doped micropores, the loss of wall sites can be effectively energetically compensated by the high-density spatial rearrangement of adsorbates within the confined space, thereby achieving efficient capture of low-concentration polar VOCs. 4. Conclusion This study addresses the long-standing challenge of separating polar/nonpolar components in the treatment of complex oilfield VOC mixtures. By integrating grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations, we elucidate—at the atomistic level—the competitive adsorption mechanisms and pore-size effects of nitrogen-doped activated carbon toward a representative hydrocarbon component (TL) and a solvent component (EAC). The results show that nitrogen doping not only enhances surface affinity through the combined contributions of π–π stacking and electrostatic interactions, but also creates an anti-displacement “electrostatic shelter” for the polar component that is disadvantaged under competitive conditions. Notably, at a critical pore width of 1.0 nm, the system exhibits an anomalous “selectivity reversal,” enabling preferential capture of polar ethyl acetate. This behavior is attributed to a unique “competition-induced reconstruction” mechanism: toluene preferentially occupies the pore walls, driving ethyl acetate toward the pore center, where it self-assembles into a high-density sandwich-like cluster with a “Wall–TL–EAC–TL–Wall” configuration, which is effectively stabilized by the long-range electrostatic field generated by the N-doped surface. The synergistic mechanism revealed here—combining “sub-nanometer physical squeezing” with “chemical-field stabilization”—provides theoretical guidance for designing advanced adsorbents for efficient separation and resource-oriented recovery of solvent-containing off-gases in oilfield applications. Declarations Author Contribution Haiqian Zhao: Conceptualization, Methodology, Molecular simulation, Data analysis, Writing – original draft, Writing – review & editing.Yansong Wu: Model construction, Simulation setup, Data curation.Jiancheng Zhang: Validation, Formal analysis.Dong Li: Visualization, Figure preparation.Hanbing Qi: Software, Technical support.Zhihua Wang: Investigation, Resources.Xue Chen: Supervision, Funding acquisition.All authors have read and approved the final manuscript. References Feng, Z., Xu, Y., Kobayashi, K., Dai, L., Zhang, T., Agathokleous, E., Yue, X.: Ozone pollution threatens the production of major staple crops in East Asia. Nat. Food. 3 , 47–56 (2022) Li, K., Jacob, D.J., Liao, H., Qiu, Y., Shen, L., Zhai, S., Kuk, S.K.: Ozone pollution in the North China Plain spreading into the late-winter haze season. Proceedings of the National Academy of Sciences, 118(10), e2015797118. (2021) Zhang, Q., Mo, S., Li, J., Sun, Y., Zhang, M., Chen, P., Ye, D.: In situ DRIFT spectroscopy insights into the reaction mechanism of CO and toluene co-oxidation over Pt-based catalysts. Catal. Sci. Technol. 9 (17), 4538–4551 (2019) Guo, X., Li, X., Gan, G., Wang, L., Fan, S., Wang, P., Liu, S.: Functionalized activated carbon for competing adsorption of volatile organic compounds and water. ACS Appl. Mater. Interfaces. 13 (47), 56510–56518 (2021) Huang, X., Tang, M., Li, H., Wang, L., Lu, S.: Adsorption of multicomponent VOCs on various biomass-derived hierarchical porous carbon: a study on adsorption mechanism and competitive effect. Chemosphere. 313 , 137513 (2023) Chen, Z., He, R.: Competitive adsorption characteristics of gasoline evaporated VOCs in microporous activated carbon by molecular simulation. J. Mol. Graph. Model. 121 , 108444 (2023) Su, C., Guo, Y., Chen, H., Zou, J., Zeng, Z., Li, L.: VOCs adsorption of resin-based activated carbon and bamboo char: Porous characterization and nitrogen-doped effect. Colloids Surf., A. 601 , 124983 (2020) Guo, Y., Su, C., Chen, H., Wang, J., Liu, B., Zeng, Z., Li, L.: Hierarchical porous carbon with tunable apertures and nitrogen/oxygen heteroatoms for efficient adsorption and separation of VOCs. Chem. Eng. J. 471 , 144558 (2023) Wang, C., Hu, Z., Wang, Z., Zhao, H., He, M., Li, D., Zhou, W.: Synergistic modulation of in-plane N-doping and intrinsic vacancy defects in activated carbon for enhanced formaldehyde adsorption. Environ. Res., 123492. (2025) Chen, Y., Qu, Z., Sun, F., Li, X., Wang, J., Li, J., Zhao, G.: Revealing the role of hierarchical pore in alleviating competitive adsorption between different-sized VOCs: A mechanistic study using coal-based activated carbon with tunable porous hierarchy. Sep. Purif. Technol. 359 , 130609 (2025) Li, J., Yin, Y., Cheng, T., Chen, H., Yang, L., Wu, H.: Superior pore size for enhancing the competitive adsorption of VOCs under high humid conditions: an experiment and molecular simulation study. J. Environ. Chem. Eng. 11 (5), 111091 (2023) Sun, H., Jin, Z., Yang, C., Akkermans, R.L., Robertson, S.H., Spenley, N.A., Todd, S.M.: COMPASS II: extended coverage for polymer and drug-like molecule databases. J. Mol. Model. 22 (2), 47 (2016) An, Y., Fu, Q., Zhang, D., Wang, Y., Tang, Z.: Performance evaluation of activated carbon with different pore sizes and functional groups for VOC adsorption by molecular simulation. Chemosphere. 227 , 9–16 (2019) Wang, M., Sheng, Y.: Molecular simulation to analyze the influence of ultrafine particles on activated carbon adsorbing low concentration toluene. Build. Environ. 213 , 108875 (2022) Dong, X., Xu, W., Liu, R., Chen, Z., Lu, N., Guo, W.: Insights into adsorption and diffusion behavior of shale oil in slit nanopores: A molecular dynamics simulation study. J. Mol. Liq. 359 , 119322 (2022) Zhang, J., Shao, J., Zhang, X., Jiang, H., Zhang, S., Zhang, S., Chen, H.: Molecular simulation of different VOCs adsorption on nitrogen-doped biochar. Fuel. 372 , 132127 (2024) Mao, H., Tang, J., Chen, J., Wan, J., Hou, K., Peng, Y., Reimer, J.A.: Designing hierarchical nanoporous membranes for highly efficient gas adsorption and storage. Sci. Adv. 6 (41), eabb0694 (2020) Yang, Y., Sun, C., Lin, B., Huang, Q.: Surface modified and activated waste bone char for rapid and efficient VOCs adsorption. Chemosphere. 256 , 127054 (2020) Liu, L., Ahmadi, Y., Kim, K.H., Kukkar, D., Szulejko, J.E.: The relative dominance of surface oxygen content over pore properties in controlling adsorption and retrograde behavior of gaseous toluene over microporous carbon. Sci. Total Environ. 906 , 167308 (2024) Lillo-Ródenas, M.A., Cazorla-Amorós, D., Linares-Solano, A.: Behaviour of activated carbons with different pore size distributions and surface oxygen groups for benzene and toluene adsorption at low concentrations. Carbon. 43 (8), 1758–1767 (2005) Lashaki, M.J., Kamravaei, S., Hashisho, Z., Phillips, J.H., Crompton, D., Anderson, J.E., Nichols, M.: Adsorption and desorption of a mixture of volatile organic Compounds: Impact of activated carbon porosity. Sep. Purif. Technol. 314 , 123530 (2023) Meng, X., Yang, L., Jiang, W., Yao, L.: Adsorption of acetone and toluene by N-functionalized porous carbon derived from ZIF-8. J. Ind. Eng. Chem. 111 , 137–146 (2022) Zaman, M.W.U., Phule, A.D., Elkaee, S., Kim, S.Y., Yang, J.H.: Excellent adsorption and catalytic oxidation of toluene facilitated by metal-free nitrogen-doped mesoporous biochar. Sep. Purif. Technol. 353 , 128378 (2025) Liao, J., Yin, K., Chen, X., Huang, B.: Defect-rich N doped porous carbon derived from Camellia shells for chlorobenzene adsorption. New J. Chem. 48 (22), 10273–10283 (2024) Li, S., Song, K., Zhao, D., Rugarabamu, J.R., Diao, R., Gu, Y.: Molecular simulation of benzene adsorption on different activated carbon under different temperatures. Microporous Mesoporous Mater. 302 , 110220 (2020) Yao, F., Wang, X., Zhao, G., Peng, W., Zhu, W., Wang, Y., Ye, D.: Nitrogen-Doped Porous Biochar via Azotobacter chroococcum-Based Nitrogen Fixation for Improved Volatile Organic Compound Adsorption. ACS ES&T Eng. 5 (2), 402–413 (2024) Wen, X., Su, Z., Cheng, J., Song, S., Guan, W., Cheng, P., Zhao, X.: Dual-functional oxygen-modified pitch-based spherical activated carbon enhanced VOCs capture: Experiment-simulation integration. J. Environ. Chem. Eng., 119100. (2025) Zhang, W., Li, G., Yin, H., Zhao, K., Zhao, H., An, T.: Adsorption and desorption mechanism of aromatic VOCs onto porous carbon adsorbents for emission control and resource recovery: recent progress and challenges. Environ. Science: Nano. 9 (1), 81–104 (2022) Zhou, K., Ma, W., Zeng, Z., Ma, X., Xu, X., Guo, Y., Li, L.: Experimental and DFT study on the adsorption of VOCs on activated carbon/metal oxides composites. Chem. Eng. J. 372 , 1122–1133 (2019) Zhao, G., Wang, Y., Xie, L., Wang, S., Ji, Y., Sun, X., Ye, D.: Development of nitrogen-rich hierarchical porous carbon for high selective adsorption of methanol in multi-VOCs waste gas recovery processes. Sep. Purif. Technol. 353 , 128478 (2025) Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8791300","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":588685576,"identity":"66b6414e-197e-4f0c-ba7b-4bf80b736f7c","order_by":0,"name":"Yansong Wu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Yansong","middleName":"","lastName":"Wu","suffix":""},{"id":588685577,"identity":"27a9eba5-7cd4-4480-bf83-f76637b9b6e5","order_by":1,"name":"Jiancheng Zhang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Jiancheng","middleName":"","lastName":"Zhang","suffix":""},{"id":588685578,"identity":"1c833d14-277a-46a8-9d95-04ea586900d5","order_by":2,"name":"Dong Li","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Dong","middleName":"","lastName":"Li","suffix":""},{"id":588685583,"identity":"17289dfe-0485-4048-a924-319e34df27f7","order_by":3,"name":"Hanbing Qi","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Hanbing","middleName":"","lastName":"Qi","suffix":""},{"id":588685584,"identity":"602a00c6-cc85-40bc-8995-f329e3745378","order_by":4,"name":"Zhihua Wang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Zhihua","middleName":"","lastName":"Wang","suffix":""},{"id":588685585,"identity":"5424d6ff-b005-434b-a1e4-2dfff99d9884","order_by":5,"name":"Xue Chen","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Xue","middleName":"","lastName":"Chen","suffix":""},{"id":588685586,"identity":"beb1c473-cb39-4a84-a199-116467458c6d","order_by":6,"name":"Haiqian Zhao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2klEQVRIie3RIQvCQBTA8TcGlw5WT4T5CYSDgTAY+lVuCGcZFovxxqr2hX0Lwfx0sKRYFwyzLA1kzaJo1LSzCd4/vx/vHQdgMv1gDuDs1j4Cd3JKUI/0Yqx6KZEelIXQIzzfVX1K9iFgxDUvK3LBKUVhqUNbNjB2h6pDWKtCCMbOc9teb/wMpt4IO4jNDgI5rxcEjts+BQy3XYQMrq0SIg9XENV65DU0BcQ8TCEieoQBSitW0uOs8PyMa7xlgijtuwpc7iSXslmO3U7yuZLqfs0b+VaYTCbTX/QEzbFKG8x4ueQAAAAASUVORK5CYII=","orcid":"","institution":"","correspondingAuthor":true,"prefix":"","firstName":"Haiqian","middleName":"","lastName":"Zhao","suffix":""}],"badges":[],"createdAt":"2026-02-05 02:23:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8791300/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8791300/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102510610,"identity":"1f2b64e5-ed89-473d-aacb-c5eeccf97520","added_by":"auto","created_at":"2026-02-12 12:26:43","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":481175,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Toluene model; (b) Ethyl acetate model; (c) Carbon fragment for virtual porous carbon; (d) Carbon sheet for slit pore model; (e) Modified carbon fragment for virtual porous carbon; (f) Modified carbon sheet for slit pore model; (g) Virtual porous carbon model; (h) Slit pore model.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8791300/v1/361945b879dcd33b0b3abff2.png"},{"id":102510595,"identity":"aba6d964-f1a7-47c1-8d3f-1100e1d5eacf","added_by":"auto","created_at":"2026-02-12 12:26:33","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":567826,"visible":true,"origin":"","legend":"\u003cp\u003eAdsorption of toluene/ethyl acetate on Pure-AC (a, b); Binary competitive adsorption on Pure-AC (c); Adsorption of toluene/ethyl acetate on N-AC (d, e); Binary competitive adsorption on N-AC (f). (Red adsorbates represent toluene molecules, and green adsorbates represent ethyl acetate molecules).\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8791300/v1/1d379fa05646c2fac6209d10.png"},{"id":102510611,"identity":"15f21a38-d508-494b-8b12-ce0c3765f358","added_by":"auto","created_at":"2026-02-12 12:26:44","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":90201,"visible":true,"origin":"","legend":"\u003cp\u003eSingle-component adsorption isotherms of toluene (a); Single-component adsorption isotherms of ethyl acetate (b); Binary adsorption isotherms of toluene (c); Binary adsorption isotherms of ethyl acetate (d).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8791300/v1/1d171edafc41d01afd239ca1.png"},{"id":102510613,"identity":"7a3ccf98-b686-493a-9f8c-5e0988f4584c","added_by":"auto","created_at":"2026-02-12 12:26:45","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":67028,"visible":true,"origin":"","legend":"\u003cp\u003e(a) RDFs between the carbon skeleton of Pure-AC and the carbonyl oxygen of ethyl acetate (C-O, green line), and between the nitrogen in N-AC and the carbonyl oxygen of ethyl acetate (N-O, red line); (b) RDFs of the toluene benzene ring center relative to skeletal N atoms (red line) and skeletal C atoms (green line); (c) Comparison of RDF curves for ethyl acetate relative to N-AC active sites in single-component (EAC, red line) and binary (EAC-TL, green line) systems.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8791300/v1/d3486c433ab08e84e39dba80.png"},{"id":102510557,"identity":"e53d45ff-a738-4d45-b81e-7a9789140fbb","added_by":"auto","created_at":"2026-02-12 12:26:26","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":80316,"visible":true,"origin":"","legend":"\u003cp\u003eInfluence of slit pore width (H) on the adsorption performance of single-component and binary systems at 298 K.Adsorption capacities of (a) toluene (TL) and (b) ethyl acetate (EAC). Blue lines represent single-component adsorption isotherms; red lines represent binary mixture adsorption isotherms. (c) Variation of adsorption selectivity of ethyl acetate over toluene (S EAC/TL) with pore width. The horizontal dashed line indicates the non-selective baseline (S=1).\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8791300/v1/0a76bf25f63f39392dc018c9.png"},{"id":102510591,"identity":"5f872bc7-6404-4686-bb28-4457c833b585","added_by":"auto","created_at":"2026-02-12 12:26:32","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":109573,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructural and energetic analysis of the competitive adsorption mechanism. Local density distributions of ethyl acetate (EAC) in (a) narrow pores (H=10 Å) and (b) wide pores (H=20 Å). Black dashed lines represent single-component systems; red solid lines and filled regions represent binary mixture systems. Arrows indicate the phenomena of \"squeezed center\" and \"competitive loss.\" (c) Variation of the average interaction energy of EAC with pore width in the binary system and its energy contributions (Blue: van der Waals interactions; Red: Electrostatic interactions). The asterisk (*) marks the critical pore size where optimal energy matching occurs.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8791300/v1/779bea9a31c9ef6c2f47ecf5.png"},{"id":102510594,"identity":"821034c2-79cb-46e1-9b35-916f5a8788b1","added_by":"auto","created_at":"2026-02-12 12:26:32","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":371633,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the competition-induced structural reconstruction mechanism in a 10 Å slit pore. (a) In the single-component system, ethyl acetate (EAC) molecules (red/white ball-and-stick) are directly adsorbed onto the N-doped carbon pore walls via electrostatic interactions, forming a stable \"wall-anchored bilayer\" structure. (b) In the binary mixture system, toluene molecules (purple sticks) preferentially occupy the wall sites by virtue of strong π−π stacking interactions, constructing a \"sandwich-like\" structure. This preferential occupation generates a significant \"squeezing effect,\" forcing EAC molecules to aggregate toward the pore center to form a high-density monolayer cluster, thereby maintaining a high adsorption capacity.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8791300/v1/ca95afe9db0bc3acabb189c7.png"},{"id":105125637,"identity":"d3c0b309-91d3-476e-84be-bb2d31c3d562","added_by":"auto","created_at":"2026-03-21 21:09:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2629925,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8791300/v1/a5d0dca4-76fc-490e-b4c7-f8b5c3efb26d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Molecular Dynamics Simulation on the Adsorption Behavior of Toluene and Ethyl Acetate and Pore Structure Effects in Activated Carbon Synergistically Regulated by Pyridinic/Pyrrolic Nitrogen","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eDuring petroleum and natural gas exploitation as well as downstream petrochemical processing, large quantities of associated gas and industrial wastewater containing volatile organic compounds (VOCs) are inevitably released[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Unlike the low-concentration VOCs typically found in ambient air, emissions from oilfield sources are characterized by complex compositions and large concentration fluctuations. In such systems, nonpolar petroleum hydrocarbons (eg, toluene, TL) often coexist with polar organic solvents used in production processes (eg, ethyl acetate, EAC)[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. This complex \u0026ldquo;polar/nonpolar\u0026rdquo; mixture poses significant challenges for end-of-pipe treatment. On the one hand, increasingly stringent environmental emission standards must be met; on the other hand, efficient separation and resource recovery of components with different polarities is of considerable economic value [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].Adsorption technology, owing to its deep purification capability and solvent recovery potential, has been widely applied in oilfield VOCs mitigation. Among various adsorbents, activated carbon (AC) remains the most commonly used material because of its low cost and well-developed pore structure[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. However, conventional activated carbon exhibits pronounced hydrophobicity and nonpolar surface characteristics, which lead to severe \u0026ldquo;selectivity failure\u0026rdquo; when treating complex oilfield VOC mixtures[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In multicomponent competitive adsorption systems, nonpolar hydrocarbons such as toluene\u0026mdash;with stronger adsorption potentials\u0026mdash;tend to dominate the adsorption sites and displace polar molecules like ethyl acetate through competitive exclusion. This results in a markedly shortened breakthrough time for polar components in adsorption beds, severely limiting purification efficiency and recovery purity[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Therefore, developing novel carbon-based adsorbents that can maintain high adsorption capacity while exhibiting specific selectivity under strong competitive conditions is crucial for addressing the challenges of complex oilfield VOC treatment.To tailor the surface chemical properties of carbon materials, heteroatom doping (eg, nitrogen, oxygen, and sulfur) has been demonstrated as an effective strategy to enhance surface polarity and modulate electronic structures[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. In particular, incorporating nitrogen atoms (pyridinic-N and pyrrolic-N) into the carbon framework can induce charge redistribution and generate high-energy polar sites, thereby strengthening electrostatic attraction or hydrogen-bond interactions with polar molecules such as ethyl acetate. Simultaneously, conjugation effects enable regulation of the π-electron system, preserving π\u0026ndash;π interactions with the aromatic rings of toluene[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Although experimental studies have suggested that nitrogen doping can improve the adsorption performance toward mixed VOCs, current understanding is largely based on macroscopic observations and lacks atomistic insight into host\u0026ndash;guest interactions within confined pores. Especially under strong competition between large hydrocarbon molecules and small polar solvents in sub-nanometer slit pores, the spatial arrangement of adsorbates and the synergistic roles of surface chemical sites and physical confinement in governing separation selectivity remain poorly understood.In this context, the present study focuses on representative oilfield VOC components (toluene/ethyl acetate) and employs grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations to construct pyridinic-N and pyrrolic-N modified activated carbon models. The objective is to elucidate, at the molecular level, the regulatory mechanisms of nitrogen doping on competitive adsorption behavior, with particular emphasis on the influence of pore size on adsorption selectivity and the identification of a unique \u0026ldquo;competition-induced structural reconstruction\u0026rdquo; mechanism under confined conditions. The findings of this work are expected to provide a theoretical basis for the rational design of high-performance adsorbents for efficient separation and resource recovery under complex oilfield operating conditions.\u003c/p\u003e"},{"header":"2. Model Construction and Simulation Details","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Model Construction\u003c/h2\u003e \u003cp\u003eIn this study, all models required for molecular simulations were constructed using Materials Studio 2020 software. To ensure simulation accuracy, the COMPASSII force field[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] and forcefield-assigned charges were employed throughout the process.First, toluene (TL) and ethyl acetate (EAC) were selected as representative non-polar and polar VOCs, respectively. Their initial configurations were constructed using the Visualizer module, as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a) and 1(b). Subsequently, geometry optimization was performed using the Forcite module under convergence criteria consisting of an energy tolerance of 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e kcal/mol, a force tolerance of 0.005 kcal/mol/\u0026Aring;, and a displacement tolerance of 5.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e \u0026Aring;.Regarding adsorbent modeling, a pure activated carbon (Pure-AC) skeleton was constructed based on edge-hydrogen-saturated graphene microcrystalline fragments (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c)). The nitrogen-doped modified model (N-AC) was then created by introducing pyridinic nitrogen (Pyridinic-N) and pyrrolic nitrogen (Pyrrolic-N) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(d)). All fragments subsequently underwent structural relaxation to eliminate lattice distortion.Based on the aforementioned optimized fragments, a Virtual Porous Carbon (VPC) model with three-dimensional periodic boundary conditions[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] was constructed using the Monte Carlo packing algorithm within the Amorphous Cell module (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(g)). The target density was controlled within the range of 0.55 g/cm\u0026sup3;[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], and the model was subjected to high-temperature annealing to achieve a thermodynamically stable disordered pore structure.As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(e), the geometrically optimized nitrogen-doped graphene sheets exhibited sp2 network rearrangement and local lattice distortion induced by the introduction of heteroatoms; these were selected as the fundamental building blocks to simulate the surface chemical heterogeneity of the modified activated carbon. Based on this, the BuildLayers tool was utilized to construct a series of slit pore models covering the range from limiting micropores to mesopores (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(h)). By precisely regulating the distance (H) between parallel sheets, this study aims to deeply investigate the synergistic adsorption mechanism involving the pore size confinement effect and surface polar sites, as well as to determine the optimal and limiting pore sizes for the adsorbates.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Simulation Details\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1. Virtual Porous Carbon Model\u003c/h2\u003e \u003cp\u003eThe adsorption performance of the constructed Pure-AC and N-AC virtual porous models was systematically investigated using the Grand Canonical Monte Carlo (GCMC) method within the Sorption module[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The COMPASSII force field and forcefield-assigned charges were employed throughout the simulations to accurately describe the adsorbent-adsorbate and adsorbate-adsorbate interactions based on the Metropolis sampling algorithm.At 298 K, single-component adsorption isotherms for toluene and ethyl acetate were first calculated over a pressure range covering the Henry's region up to 100 kPa, in order to quantitatively evaluate the enhancement effect of nitrogen doping on adsorption capacity. Subsequently, to simulate actual operating conditions and elucidate the competitive adsorption mechanism, binary competitive adsorption simulations were conducted with a gas phase molar ratio set to 1:1(\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{y}}_{\\text{tol}}\\text{：}{\\text{y}}_{\\text{ea}}\\text{=1:1}\\)\u003c/span\u003e\u003c/span\u003e), based on which the adsorption selectivity of the materials was analyzed.Following this, based on the adsorption loadings obtained from the Sorption module, the models were reconstructed using the Forcite module. The task was set to 'Dynamics', and the NVT ensemble was selected for molecular dynamics simulations[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. The temperature was maintained at 298 K with a time step of 1 fs, comprising 10,000 total steps for a total simulation time of 10 ps. Upon completion of these calculations, Monte Carlo simulations of the adsorption behavior were performed.Furthermore, to provide an in-depth atomic-scale analysis of the specific host-guest interactions, the Radial Distribution Functions (RDFs) of the adsorbate molecules relative to the active sites were calculated. For all simulations,1\u0026times;10\u003csup\u003e6\u003c/sup\u003e steps were allocated for system equilibration, followed by 2\u0026times;10\u003csup\u003e6\u003c/sup\u003e steps for production statistics, ensuring thermodynamic equilibrium and statistical convergence of the adsorption data.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2. Slit Pore Model\u003c/h2\u003e \u003cp\u003eTo deeply analyze the confinement effect at the atomic scale and precisely pinpoint the optimal geometric configuration for VOC capture, this study constructed a series of N-doped graphene slit pore models with gradient interlayer spacings based on the Sorption module. The regulatory mechanism of pore size on adsorption behavior was systematically investigated using the Grand Canonical Monte Carlo (GCMC) algorithm under the COMPASS II force field.First, a quantitative \"pore size\u0026ndash;adsorption density\" structure-activity relationship was established by calculating the single-component adsorption isotherms of toluene and ethyl acetate. Furthermore, the limiting cutoff pore size and optimal matching pore size for the adsorbates were precisely identified utilizing the principle of host-guest potential energy field superposition.On this basis, to explore the interplay between steric hindrance and surface chemical affinity under strong competitive environments, equimolar binary competitive adsorption simulations were further implemented. The analysis of local density distributions intuitively revealed the dominant adsorption sites within the slit channels, as well as the layered stacking and structural reconstruction behaviors of the molecules. All simulations were conducted at 298 K, strictly executing 1\u0026times;10\u003csup\u003e6\u003c/sup\u003e\\times equilibration steps and 2 \u0026times;10\u003csup\u003e6\u003c/sup\u003e \\times production statistics steps to ensure the accuracy and convergence of phase space sampling in these complex confined systems.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003eThe equilibrium adsorption configuration diagrams and adsorption capacity data, derived from the adsorption isotherm calculations, visually reveal the mechanism by which nitrogen doping influences the microscopic adsorption behavior of activated carbon.A comparison of the single-component adsorption systems indicates that toluene and ethyl acetate molecules within the pores of Pure-AC are relatively dispersed and limited in number. They are primarily located near the pore walls, suggesting weak surface affinity. In contrast, the adsorbate density in the N-AC model is significantly increased, with molecules tending to accumulate around the nitrogen-containing functional groups; this observation is highly consistent with the trend of improved adsorption capacity.In the binary competitive adsorption system, Pure-AC exhibits marked competitive inhibition and repulsion effects, resulting in a substantial decline in adsorption capacity. Conversely, N-AC retains a high binary loading with a uniform distribution and shows no significant adsorption collapse, thereby confirming the stability of nitrogen doping under complex operating conditions.Combined with microscopic structural analysis, this superior adsorption performance is primarily attributed to the regulation of the local electronic structure and surface polarity of the carbon skeleton by the introduced pyridinic and pyrrolic nitrogen. On one hand, the nitrogen-containing functional groups enhance the charge heterogeneity of the pore wall surface, reinforcing the strong electrostatic anchoring interaction with the polar ester groups of ethyl acetate. On the other hand, the redistribution of the π cloud induced by nitrogen doping promotes π\u0026thinsp;\u0026minus;\u0026thinsp;π interactions between the carbon skeleton and the aromatic rings of toluene.This mechanism of \"synergistic polarity enhancement and π\u0026thinsp;\u0026minus;\u0026thinsp;π interactions\" compellingly demonstrates that introducing nitrogen-containing functional groups is an effective strategy for improving the adsorption capacity and competitive adsorption stability of activated carbon for multi-component VOCs.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAdsorption capacities of toluene and ethyl acetate on different activated carbons\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eadsorbed amount of TL(per cell)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eadsorbed amount of EAC(per cell)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003ePure-AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003esingle-component adsorption\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e106\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ebinary competitive adsorption\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eN-AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e102\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003esingle-component adsorption\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e107\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ebinary competitive adsorption\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Influence of Virtual Porous Carbon Models on the Adsorption of Toluene and Ethyl Acetate\u003c/h2\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1. Adsorption Isotherms and Competitive Mechanism Analysis\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a\u0026ndash;b), the adsorption isotherms of Pure-AC and N-AC under single-component conditions exhibit typical Type I characteristics[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], indicating that micropore filling is the dominant adsorption mechanism. Compared with Pure-AC, N-AC shows a higher adsorption affinity in the low-pressure region, which is particularly pronounced for ethyl acetate, suggesting that nitrogen doping effectively enhances the interactions between the adsorbent and polar VOC molecules. However, in the high-pressure saturation region, the adsorption capacities of the two adsorbents gradually converge, implying that under near-saturation conditions, the total adsorption uptake is primarily constrained by the available micropore volume, while the influence of surface chemistry becomes less significant[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].In contrast, under binary competitive adsorption conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c\u0026ndash;d)), the adsorption behavior exhibits pronounced divergence. Toluene maintains a higher adsorption capacity across the entire pressure range, demonstrating a clear competitive advantage, whereas the adsorption of ethyl acetate is significantly suppressed. The tabulated data further quantitatively confirm this phenomenon: at a total pressure of 100 kPa, the capacity retention rates of toluene on Pure-AC and N-AC are 68.41% and 69.61%, respectively, while those of ethyl acetate are only 30.86% and 32.33%. Compared with single-component adsorption, toluene retains approximately 70% of its adsorption capacity in the binary system, indicating its strong competitive dominance; in contrast, the adsorption capacity of ethyl acetate decreases drastically, reflecting severe suppression under limited adsorption sites.These asymmetric competitive behaviors indicate that competitive adsorption is not governed solely by pore structure but is strongly dependent on molecular-level interactions between the adsorbates and the adsorbent[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Aromatic toluene molecules can form stable host\u0026ndash;guest interactions with the carbonaceous framework through strong π\u0026ndash;π interactions, thereby preferentially occupying high-energy adsorption sites and exerting competitive exclusion on ethyl acetate. Nevertheless, nitrogen doping partially mitigates the competitive disadvantage of the polar component. Compared with Pure-AC, N-AC increases the competitive adsorption capacity of ethyl acetate from 33 to 35 per cell, corresponding to an increase in the capacity retention rate to 32.33%, indicating that nitrogen-containing high-energy polar adsorption sites can enhance the selective adsorption of polar molecules via electrostatic induction and dipole\u0026ndash;dipole interactions.Overall, while micropore filling determines the maximum adsorption capacity of the materials, molecular-scale interactions dominate adsorption selectivity and competitive behavior in multicomponent VOC systems. The capacity retention rate can serve as an effective quantitative indicator for evaluating competitive adsorption strength[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Nitrogen doping does not alter the dominant competitive position of toluene but effectively enhances the adsorption stability of ethyl acetate under strong competitive conditions[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], thereby improving the overall removal performance of activated carbon toward complex VOC mixtures.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of saturated adsorption capacities (100 kPa) under single-component and binary competitive conditions and the calculated capacity retention rates.(\u003cem\u003eNote\u003c/em\u003e:\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{Capacity}\\text{}\\text{Retention}\\text{}\\text{Rate}\\text{=}\\frac{{\\text{q}}_{\\text{binary}}}{{\\text{q}}_{\\text{single}}}\\text{\u0026times;}\\)\u003c/span\u003e\u003c/span\u003e100%)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eadsorbent type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eadsorbate components\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eq\u003csub\u003esingle\u003c/sub\u003e per cell)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{q}}_{\\text{binary}}\\)\u003c/span\u003e\u003c/span\u003e per cell\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ecapacity retention(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ecompetitive condition\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePure-AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e68.41%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003edominant component\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEAC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e106.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30.86%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003esuppressed component\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eN-AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e102\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e69.61%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003edominant component\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEAC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e107\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e32.33%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003esuppressed component\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e\u003cstrong\u003e3.1.2 Microscopic mechanism analysis of host\u0026ndash;guest interactions\u003c/strong\u003e\u003c/p\u003e\u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a), in the Pure-AC system, the Radial Distribution Function (RDF) curve (green line) between the carbon skeleton and the carbonyl oxygen atom of ethyl acetate presents a gradual monotonic upward trend, with no obvious characteristic peaks observed. This phenomenon indicates a lack of specific interactions between the unmodified carbon surface and polar ethyl acetate molecules, suggesting that their adsorption behavior is primarily governed by weak van der Waals forces.In contrast, the N-O RDF curve (red line) in the N-AC system exhibits a characteristic peak at r\u0026thinsp;\u0026asymp;\u0026thinsp;2.0 \u0026Aring; and forms a broad shoulder peak with an intensity of approximately 1.55 in the range of 3.5\u0026thinsp;\u0026minus;\u0026thinsp;5.0 \u0026Aring;[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The short-range peak (2.0 \u0026Aring;) confirms the existence of direct strong electrostatic interactions or hydrogen bonding tendencies between some ethyl acetate molecules and surface N sites; meanwhile, the broader peak at a longer distance (3.5\u0026thinsp;\u0026minus;\u0026thinsp;5.0 \u0026Aring;) reveals the long-range electrostatic field effect generated by N-doping. This long-range force establishes an enlarged \"capture radius,\" capable of binding ethyl acetate molecules around active sites via penetrating electrostatic attraction, even when the adsorbate cannot directly contact the surface sites (eg, when separated by toluene during competitive adsorption). This microscopic evidence is physically highly self-consistent with the \"sandwich\" confined structure observed in slit pores discussed later. The peak intensity of the N-AC system is significantly higher than that of Pure-AC (g(r)\u0026thinsp;\u0026gt;\u0026thinsp;1.5 vs g(r)\u0026thinsp;\u0026asymp;\u0026thinsp;1.2), confirming that nitrogen-containing functional groups construct high-affinity adsorption active domains on the carbon skeleton, effectively enriching ethyl acetate molecules through electrostatic induction. This microscopic mechanism aligns well with the experimental results showing a significant increase in adsorption capacity in the low-pressure region of the macroscopic adsorption isotherms.To further investigate the enhancement mechanism of N-doping on the adsorption of non-polar molecules, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b) compares the RDF curves of the toluene benzene ring center relative to skeletal N atoms (red line) and ordinary C atoms (green line). The results show that both curves exhibit characteristic peaks at 3.8\u0026thinsp;\u0026minus;\u0026thinsp;4.0 \u0026Aring;[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], confirming that π\u0026thinsp;\u0026minus;\u0026thinsp;π stacking is the primary driving force for toluene adsorption[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Crucially, the RDF peak intensity of N-TL (g(r)\u0026thinsp;\u0026asymp;\u0026thinsp;2.6) is significantly higher than that of C-TL (g(r)\u0026thinsp;\u0026asymp;\u0026thinsp;2.2). This significant difference strongly proves that the introduction of heteroatom N induces electron cloud rearrangement in the carbon skeleton, constructing local adsorption sites with stronger electron affinity. This significantly enhances the π\u0026thinsp;\u0026minus;\u0026thinsp;π interactions between the adsorbent and the toluene aromatic rings[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], revealing the microscopic physical origin of the improved toluene adsorption capacity on N-AC.Furthermore, to elucidate the competitive inhibition mechanism of toluene against ethyl acetate in the binary system, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c) compares the RDF curves of ethyl acetate (target atom pair: N-O) under single-component and binary environments. As shown, after the introduction of toluene, the peak intensity of the N-O RDF exhibits a distinct attenuation. This indicates that toluene molecules, by virtue of their strong π\u0026thinsp;\u0026minus;\u0026thinsp;π interactions and larger molecular kinetic diameter, dominate within the pores, generating significant steric hindrance effects and competitively occupying the adsorption space of ethyl acetate. However, crucially, although the peak intensity decreased, the RDF characteristic peak in the binary system did not completely disappear and still maintained a considerable intensity (g(r)max\u0026thinsp;\u0026asymp;\u0026thinsp;1.75). This microscopic evidence compellingly indicates that the polar sites introduced by N-doping construct a specific \"adsorption refuge.\" Even in a strong competitive environment dominated by toluene, these high-energy sites can still firmly anchor some ethyl acetate molecules via strong electrostatic attraction, preventing them from being completely displaced by non-polar toluene.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Influence of Slit Pore Structure on Adsorption Behavior\u003c/h2\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1. Regulatory Effect of Slit Pore Structure on Competitive Adsorption\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e systematically illustrates the regulatory patterns of slit pore width (H) on the competitive adsorption behavior of toluene (TL) and ethyl acetate (EAC). In single-component systems (blue lines in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb), both adsorbates exhibit characteristic capacity oscillation behaviors due to matching packing effects. However, upon the introduction of the competing component (red lines), the adsorption performances of the two diverge significantly: toluene suffers severe competitive displacement across the entire pore size range, resulting in a sharp decay in adsorption capacity, whereas ethyl acetate exhibits unique dual-zone adsorption characteristics.First, in the mesopore transition region of 16\u0026ndash;18 \u0026Aring;, ethyl acetate demonstrates remarkable anti-competition resilience and capacity retention. Although non-polar toluene still dominates at these pore sizes, the long-range electrostatic field induced by N-doped sites effectively stabilizes the multilayer adsorption structure, preventing the adsorption collapse of polar molecules due to spatial competition.To quantify this separation efficiency, the calculated adsorption selectivity coefficients (S EAC/TL) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec) reveal a critical phenomenon of \"selectivity inversion.\" Although toluene maintains a thermodynamic advantage (S\u0026thinsp;\u0026lt;\u0026thinsp;1.0) in the wide-pore region (H\u0026thinsp;\u0026gt;\u0026thinsp;15\u0026Aring;) by virtue of stronger non-specific dispersion forces (π\u0026thinsp;\u0026minus;\u0026thinsp;π interactions), the selectivity coefficient rises sharply and breaches the baseline to reach a maximum value when the pore width contracts to the critical micropore window of H\u0026thinsp;\u0026asymp;\u0026thinsp;10 \u0026Aring;[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].This fundamental inversion is attributed to the synergistic effect of sub-nanometer physical confinement and surface chemical modification: at this dimension, bulky toluene molecules face severe steric hindrance effects and packing frustration, whereas smaller EAC molecules benefit from the electrostatic anchoring of N-doped sites, thereby achieving an effective reversal against the non-polar competitor and realizing selective capture.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2. Competition-Induced Microstructural Reconstruction and Energetic Origins\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo elucidate the physical origins of the high selectivity at the molecular level, we conducted an in-depth analysis of the adsorption mechanism by combining local density distributions (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb) with interaction energy decomposition (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec).As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb, in the wide pore (H\u0026thinsp;=\u0026thinsp;20 \u0026Aring;), upon introducing the competing component, the density distribution of EAC (red filled region) undergoes an overall attenuation in intensity while maintaining a configuration similar to that of the single-component system (black dashed line). This reveals a typical competitive loss mechanism characterized by \"random displacement.\"However, when the pore width contracts to the optimal selectivity window (H\u0026thinsp;=\u0026thinsp;10 \u0026Aring;, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea), the system undergoes a dramatic \"competition-induced structural reconstruction.\" In stark contrast to the \"double-layer\" distribution near the pore walls observed in the single-component system, EAC molecules in the binary system are forced to retreat from the walls, instead forming a highly localized \"squeezed monolayer\" (red peak) in the pore center.This anomalous squeezing effect stems from the stronger wall-fluid interactions that prompt toluene molecules to preferentially occupy sites on the graphene surface, thereby \"blockading\" EAC molecules in the pore center. Crucially, the extremely high density of this central layer (with a peak significantly higher than that of the single-component system) indicates that under the synergistic compression of intermolecular interactions and the confinement potential, EAC molecules form closely packed high-density clusters, thereby maximizing the compensation for capacity loss.Further energy component analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec) reveals the thermodynamic essence governing this reconstruction behavior. As the pore size decreases, the total interaction energy of EAC molecules (∣Etotal∣) reaches a maximum (approximately 220 kJ/mol) at H\u0026thinsp;=\u0026thinsp;10\u0026thinsp;\u0026minus;\u0026thinsp;12 \u0026Aring;, confirming that this dimension provides the deepest thermodynamic potential well. Although van der Waals interactions (blue bars) dominate the total energy, the electrostatic interaction contribution (red bars) exhibits a significant specific enhancement in the narrow micropore of H\u0026thinsp;=\u0026thinsp;10 \u0026Aring;. Within this strongly confined space, the squeezed EAC molecular clusters can achieve effective coupling with N-doped sites via long-range electrostatic interactions[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. This additional electrostatic stabilization acts as a critical \"chemical anchor,\" effectively compensating for the entropy loss caused by steric hindrance effects, thereby establishing an energetic advantage for EAC in the fierce competition with non-polar toluene.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.2.3. Competition-Induced Reconstruction and Spatial Self-Organization Mechanisms\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on the microscopic density and energy analyses mentioned above, Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e proposes a mechanistic model for the competition-induced structural reconstruction within the optimal 10 \u0026Aring; micropore.In the non-competitive single-component system (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea), driven by the electrostatic attraction of N-doped sites, EAC molecules are directly anchored to the carbon pore wall surface, forming a stable \"bilayer\" configuration to maximize fluid-wall interactions.However, upon introducing toluene (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb), the adsorption landscape undergoes a fundamental reversal: leveraging the advantage of strong π\u0026thinsp;\u0026minus;\u0026thinsp;π stacking, toluene molecules preferentially occupy and blockade the wall sites, forming a dense hydrophobic lining (shown in purple). Crucially, this preferential occupation does not lead to the complete exclusion of EAC; instead, it triggers a significant \"squeezing effect\"\u0026mdash;EAC molecules are forced to retreat into the sub-nanometer confined space between two layers of toluene. Under the synergistic compression of confinement potential and intermolecular repulsion, they self-organize into an extremely high-density \"monolayer\" cluster at the pore center [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].This unique \"sandwich-like\" TL-EAC-TL configuration not only constitutes the structural basis for the macroscopic selectivity inversion but also reveals a key design principle: in N-doped micropores, the loss of wall sites can be effectively energetically compensated by the high-density spatial rearrangement of adsorbates within the confined space, thereby achieving efficient capture of low-concentration polar VOCs.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThis study addresses the long-standing challenge of separating polar/nonpolar components in the treatment of complex oilfield VOC mixtures. By integrating grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations, we elucidate\u0026mdash;at the atomistic level\u0026mdash;the competitive adsorption mechanisms and pore-size effects of nitrogen-doped activated carbon toward a representative hydrocarbon component (TL) and a solvent component (EAC). The results show that nitrogen doping not only enhances surface affinity through the combined contributions of π\u0026ndash;π stacking and electrostatic interactions, but also creates an anti-displacement \u0026ldquo;electrostatic shelter\u0026rdquo; for the polar component that is disadvantaged under competitive conditions. Notably, at a critical pore width of 1.0 nm, the system exhibits an anomalous \u0026ldquo;selectivity reversal,\u0026rdquo; enabling preferential capture of polar ethyl acetate. This behavior is attributed to a unique \u0026ldquo;competition-induced reconstruction\u0026rdquo; mechanism: toluene preferentially occupies the pore walls, driving ethyl acetate toward the pore center, where it self-assembles into a high-density sandwich-like cluster with a \u0026ldquo;Wall\u0026ndash;TL\u0026ndash;EAC\u0026ndash;TL\u0026ndash;Wall\u0026rdquo; configuration, which is effectively stabilized by the long-range electrostatic field generated by the N-doped surface. The synergistic mechanism revealed here\u0026mdash;combining \u0026ldquo;sub-nanometer physical squeezing\u0026rdquo; with \u0026ldquo;chemical-field stabilization\u0026rdquo;\u0026mdash;provides theoretical guidance for designing advanced adsorbents for efficient separation and resource-oriented recovery of solvent-containing off-gases in oilfield applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eHaiqian Zhao: Conceptualization, Methodology, Molecular simulation, Data analysis, Writing \u0026ndash; original draft, Writing \u0026ndash; review \u0026amp; editing.Yansong Wu: Model construction, Simulation setup, Data curation.Jiancheng Zhang: Validation, Formal analysis.Dong Li: Visualization, Figure preparation.Hanbing Qi: Software, Technical support.Zhihua Wang: Investigation, Resources.Xue Chen: Supervision, Funding acquisition.All authors have read and approved the final manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eFeng, Z., Xu, Y., Kobayashi, K., Dai, L., Zhang, T., Agathokleous, E., Yue, X.: Ozone pollution threatens the production of major staple crops in East Asia. Nat. Food. \u003cb\u003e3\u003c/b\u003e, 47\u0026ndash;56 (2022)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, K., Jacob, D.J., Liao, H., Qiu, Y., Shen, L., Zhai, S., Kuk, S.K.: Ozone pollution in the North China Plain spreading into the late-winter haze season. Proceedings of the National Academy of Sciences, 118(10), e2015797118. (2021)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, Q., Mo, S., Li, J., Sun, Y., Zhang, M., Chen, P., Ye, D.: In situ DRIFT spectroscopy insights into the reaction mechanism of CO and toluene co-oxidation over Pt-based catalysts. Catal. Sci. Technol. \u003cb\u003e9\u003c/b\u003e(17), 4538\u0026ndash;4551 (2019)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuo, X., Li, X., Gan, G., Wang, L., Fan, S., Wang, P., Liu, S.: Functionalized activated carbon for competing adsorption of volatile organic compounds and water. ACS Appl. Mater. Interfaces. \u003cb\u003e13\u003c/b\u003e(47), 56510\u0026ndash;56518 (2021)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHuang, X., Tang, M., Li, H., Wang, L., Lu, S.: Adsorption of multicomponent VOCs on various biomass-derived hierarchical porous carbon: a study on adsorption mechanism and competitive effect. Chemosphere. \u003cb\u003e313\u003c/b\u003e, 137513 (2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen, Z., He, R.: Competitive adsorption characteristics of gasoline evaporated VOCs in microporous activated carbon by molecular simulation. J. Mol. Graph. Model. \u003cb\u003e121\u003c/b\u003e, 108444 (2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSu, C., Guo, Y., Chen, H., Zou, J., Zeng, Z., Li, L.: VOCs adsorption of resin-based activated carbon and bamboo char: Porous characterization and nitrogen-doped effect. Colloids Surf., A. \u003cb\u003e601\u003c/b\u003e, 124983 (2020)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuo, Y., Su, C., Chen, H., Wang, J., Liu, B., Zeng, Z., Li, L.: Hierarchical porous carbon with tunable apertures and nitrogen/oxygen heteroatoms for efficient adsorption and separation of VOCs. Chem. Eng. J. \u003cb\u003e471\u003c/b\u003e, 144558 (2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, C., Hu, Z., Wang, Z., Zhao, H., He, M., Li, D., Zhou, W.: Synergistic modulation of in-plane N-doping and intrinsic vacancy defects in activated carbon for enhanced formaldehyde adsorption. Environ. Res., 123492. (2025)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen, Y., Qu, Z., Sun, F., Li, X., Wang, J., Li, J., Zhao, G.: Revealing the role of hierarchical pore in alleviating competitive adsorption between different-sized VOCs: A mechanistic study using coal-based activated carbon with tunable porous hierarchy. Sep. Purif. Technol. \u003cb\u003e359\u003c/b\u003e, 130609 (2025)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, J., Yin, Y., Cheng, T., Chen, H., Yang, L., Wu, H.: Superior pore size for enhancing the competitive adsorption of VOCs under high humid conditions: an experiment and molecular simulation study. J. Environ. Chem. Eng. \u003cb\u003e11\u003c/b\u003e(5), 111091 (2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSun, H., Jin, Z., Yang, C., Akkermans, R.L., Robertson, S.H., Spenley, N.A., Todd, S.M.: COMPASS II: extended coverage for polymer and drug-like molecule databases. J. Mol. Model. \u003cb\u003e22\u003c/b\u003e(2), 47 (2016)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAn, Y., Fu, Q., Zhang, D., Wang, Y., Tang, Z.: Performance evaluation of activated carbon with different pore sizes and functional groups for VOC adsorption by molecular simulation. Chemosphere. \u003cb\u003e227\u003c/b\u003e, 9\u0026ndash;16 (2019)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, M., Sheng, Y.: Molecular simulation to analyze the influence of ultrafine particles on activated carbon adsorbing low concentration toluene. Build. Environ. \u003cb\u003e213\u003c/b\u003e, 108875 (2022)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDong, X., Xu, W., Liu, R., Chen, Z., Lu, N., Guo, W.: Insights into adsorption and diffusion behavior of shale oil in slit nanopores: A molecular dynamics simulation study. J. Mol. Liq. \u003cb\u003e359\u003c/b\u003e, 119322 (2022)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, J., Shao, J., Zhang, X., Jiang, H., Zhang, S., Zhang, S., Chen, H.: Molecular simulation of different VOCs adsorption on nitrogen-doped biochar. Fuel. \u003cb\u003e372\u003c/b\u003e, 132127 (2024)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMao, H., Tang, J., Chen, J., Wan, J., Hou, K., Peng, Y., Reimer, J.A.: Designing hierarchical nanoporous membranes for highly efficient gas adsorption and storage. Sci. Adv. \u003cb\u003e6\u003c/b\u003e(41), eabb0694 (2020)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang, Y., Sun, C., Lin, B., Huang, Q.: Surface modified and activated waste bone char for rapid and efficient VOCs adsorption. Chemosphere. \u003cb\u003e256\u003c/b\u003e, 127054 (2020)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, L., Ahmadi, Y., Kim, K.H., Kukkar, D., Szulejko, J.E.: The relative dominance of surface oxygen content over pore properties in controlling adsorption and retrograde behavior of gaseous toluene over microporous carbon. Sci. Total Environ. \u003cb\u003e906\u003c/b\u003e, 167308 (2024)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLillo-R\u0026oacute;denas, M.A., Cazorla-Amor\u0026oacute;s, D., Linares-Solano, A.: Behaviour of activated carbons with different pore size distributions and surface oxygen groups for benzene and toluene adsorption at low concentrations. Carbon. \u003cb\u003e43\u003c/b\u003e(8), 1758\u0026ndash;1767 (2005)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLashaki, M.J., Kamravaei, S., Hashisho, Z., Phillips, J.H., Crompton, D., Anderson, J.E., Nichols, M.: Adsorption and desorption of a mixture of volatile organic Compounds: Impact of activated carbon porosity. Sep. Purif. Technol. \u003cb\u003e314\u003c/b\u003e, 123530 (2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMeng, X., Yang, L., Jiang, W., Yao, L.: Adsorption of acetone and toluene by N-functionalized porous carbon derived from ZIF-8. J. Ind. Eng. Chem. \u003cb\u003e111\u003c/b\u003e, 137\u0026ndash;146 (2022)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZaman, M.W.U., Phule, A.D., Elkaee, S., Kim, S.Y., Yang, J.H.: Excellent adsorption and catalytic oxidation of toluene facilitated by metal-free nitrogen-doped mesoporous biochar. Sep. Purif. Technol. \u003cb\u003e353\u003c/b\u003e, 128378 (2025)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiao, J., Yin, K., Chen, X., Huang, B.: Defect-rich N doped porous carbon derived from Camellia shells for chlorobenzene adsorption. New J. Chem. \u003cb\u003e48\u003c/b\u003e(22), 10273\u0026ndash;10283 (2024)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, S., Song, K., Zhao, D., Rugarabamu, J.R., Diao, R., Gu, Y.: Molecular simulation of benzene adsorption on different activated carbon under different temperatures. Microporous Mesoporous Mater. \u003cb\u003e302\u003c/b\u003e, 110220 (2020)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYao, F., Wang, X., Zhao, G., Peng, W., Zhu, W., Wang, Y., Ye, D.: Nitrogen-Doped Porous Biochar via Azotobacter chroococcum-Based Nitrogen Fixation for Improved Volatile Organic Compound Adsorption. ACS ES\u0026amp;T Eng. \u003cb\u003e5\u003c/b\u003e(2), 402\u0026ndash;413 (2024)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWen, X., Su, Z., Cheng, J., Song, S., Guan, W., Cheng, P., Zhao, X.: Dual-functional oxygen-modified pitch-based spherical activated carbon enhanced VOCs capture: Experiment-simulation integration. J. Environ. Chem. Eng., 119100. (2025)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, W., Li, G., Yin, H., Zhao, K., Zhao, H., An, T.: Adsorption and desorption mechanism of aromatic VOCs onto porous carbon adsorbents for emission control and resource recovery: recent progress and challenges. Environ. Science: Nano. \u003cb\u003e9\u003c/b\u003e(1), 81\u0026ndash;104 (2022)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou, K., Ma, W., Zeng, Z., Ma, X., Xu, X., Guo, Y., Li, L.: Experimental and DFT study on the adsorption of VOCs on activated carbon/metal oxides composites. Chem. Eng. J. \u003cb\u003e372\u003c/b\u003e, 1122\u0026ndash;1133 (2019)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhao, G., Wang, Y., Xie, L., Wang, S., Ji, Y., Sun, X., Ye, D.: Development of nitrogen-rich hierarchical porous carbon for high selective adsorption of methanol in multi-VOCs waste gas recovery processes. Sep. Purif. Technol. \u003cb\u003e353\u003c/b\u003e, 128478 (2025)\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Oilfield VOCs mitigation, molecular dynamics simulation, nitrogen-doped activated carbon, selective adsorption, competition-induced reconstruction","lastPublishedDoi":"10.21203/rs.3.rs-8791300/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8791300/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTo address the challenge of competitive adsorption and separation arising from the coexistence of nonpolar hydrocarbons (TL-toluene) and polar solvents (EAC-ethyl acetate) in oilfield associated gas and produced-water treatment, this study employs grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations to systematically investigate the adsorption mechanisms and pore-confinement effects of pyridinic-N and pyrrolic-N doped activated carbons toward toluene and ethyl acetate. The results demonstrate that nitrogen doping induces electronic cloud redistribution and constructs polar adsorption sites, thereby enhancing π\u0026ndash;π interactions with toluene and electrostatic attraction with ethyl acetate, respectively. As a consequence, the capacity retention of the polar component is significantly improved under competitive adsorption conditions.In-depth analysis based on slit-pore models reveals a distinctive pore-size effect. At a critical micropore width of 1.0 nm, an anomalous \u0026ldquo;selectivity reversal\u0026rdquo; is observed, wherein the adsorption amount of the polar component surpasses that of the nonpolar component. Mechanistic investigations confirm that this phenomenon originates from a \u0026ldquo;competition-induced structural reconstruction\u0026rdquo; process: toluene preferentially occupies the pore walls, forcing ethyl acetate molecules to retreat toward the pore center, where they self-assemble into a high-density sandwich-like cluster with a \u0026ldquo;Wall\u0026ndash;Toluene\u0026ndash;EAC\u0026ndash;Toluene\u0026ndash;Wall\u0026rdquo; configuration. Energy analyses indicate that the penetrative long-range electrostatic field generated by the N-doped surface acts synergistically with physical squeezing effects imposed by spatial confinement, effectively stabilizing the polar molecular clusters at the pore center.The proposed \u0026ldquo;sub-nanometer physical squeezing\u0026ndash;chemical field stabilization\u0026rdquo; mechanism provides a theoretical foundation for the rational design of adsorption materials targeting complex multicomponent VOC systems.\u003c/p\u003e","manuscriptTitle":"Molecular Dynamics Simulation on the Adsorption Behavior of Toluene and Ethyl Acetate and Pore Structure Effects in Activated Carbon Synergistically Regulated by Pyridinic/Pyrrolic Nitrogen","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-12 12:25:09","doi":"10.21203/rs.3.rs-8791300/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"23ba32b4-035f-4fe8-a7b2-76acbfa5e991","owner":[],"postedDate":"February 12th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-21T21:08:45+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-12 12:25:09","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8791300","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8791300","identity":"rs-8791300","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}