Excess Adsorption Research Articles

Controlled Crystal Plane Orientations in the ZnO Transport Layer Enable High-Responsivity, Low-Dark-Current Infrared Photodetectors.

Colloidal quantum dots (CQD) have emerged as attractive materials for infrared (IR) photodetector (PD) applications because of their tunable bandgaps and facile processing. Presently, zinc oxide is the electron-transport layer (ETL) of choice in CQD PDs; however, ZnO relies on continuous ultraviolet (UV) illumination to remove adsorbed oxygen and maintain high external quantum efficiency (EQE), speed, and photocurrent. Here, it is shown that ZnO is dominated by electropositive crystal planes which favor excessive oxygen adsorption, and that this leads to a high density of trap states, an undesired shift in band alignment, and consequent poor performance. Over prolonged operation without UV exposure, oxygen accumulates at the electropositive planes, trapping holes and degrading performance. This problem is addressed by developing an electroneutral plane composition at the ZnO surface, aided by atomic layer deposition (ALD) as the means of materials processing. It is found that ALD ZnO has 10× lower binding energy for oxygen than does conventionally deposited ZnO. IR CQD PDs made with this ETL do not require UV activation to maintain low dark current and high EQE.

Evaluation of Gas Adsorption in Nanoporous Shale by Simplified Local Density Model Integrated with Pore Structure and Pore Size Distribution.

Simplified local density (SLD) model has been widely used to describe the gas adsorption behaviors in porous media. However, the slit pore geometry and constant pore width associated with the SLD model may fail to represent the heterogeneous pore network structure in shale. In this study, a new method to integrate the SLD model with the slit and cylindrical pore structures as well as the pore size distribution (PSD) is proposed and validated by the grand canonical Monte Carlo (GCMC) simulations and the experimentally measured adsorption of methane on shale with complex pore network. Comparison results show that reasonably good agreement is achieved between the SLD model and GCMC simulations for both the gas adsorption isotherms and discrete-density profiles in multiwalled carbon nanoslit and nanotube. The corresponding average absolute percentage deviations (% AADs) are below 0.3 and 9.3 for gas adsorption isotherm and discrete-density profile, respectively. In addition, the SLD model coupled with the PSD of slit and cylindrical pores ranging from micro- to macropores properly characterizes the measured excess adsorption of methane on Wolfcamp shale core sample with % AADs between 1.7 and 3.6. It is found that when the pore volume is fixed, the gas adsorption isotherm and gas density profile are heavily dependent on the pore geometry and pore size. Furthermore, integrating the PSD into the SLD model can guarantee the valid identification of the adsorbed- and free-gas regions in flow channels with different sizes based on the gas density profiles. The findings of this study shed light on the effects of pore structure on gas adsorption in nanopores and enable us to precisely evaluate and predict the gas adsorption behaviors in slit and cylindrical pores over a wide range of pore sizes.

Short-Chain Fatty Acids Production from Anaerobic Fermentation of Sewage Sludge: The Effect of Higher Levels Polyaluminium Chloride.

With the annual increase in the sludge production in China’s sewage treatment plants, the problem of sewage sludge treatment and disposal is becoming more and more serious. Anaerobic fermentation can convert complex organic matter in sewage sludge into short-chain fatty acid, hydrogen, methane and other resources and is an effective method for sewage sludge treatment and disposal. At the same time, sewage sludge often contains flocculants, which will inevitably affect the effect of anaerobic fermentation. As a high-performance flocculant, polyaluminum chloride (PAC) is widely used in wastewater treatment and sewage sludge dewatering processes. Previous studies indicated that lower levels of PAC inhibit the effect of the anaerobic fermentation process of sewage sludge; on the other hand, it is necessary to understand the effects of higher levels of PAC in anaerobically fermented sewage sludge. The results showed that higher levels (0.2–1 g Al/g total solids (TS)) of PAC could promote acid production from anaerobically fermented sewage sludge. Moreover, mechanism studies suggest that higher levels (0.2–1 g Al/g total solids (TS)) of PAC caused excessive adsorption of the charge on the surface of the sewage sludge colloid and reversed the charge. The sewage sludge colloid was stabilized again, which increases the concentration of soluble proteins, polysaccharides, and soluble extracellular polymers (S-EPS) in the fermentation broth, thereby improving the anaerobically fermented sewage sludge efficiency. The results provided from this study may act as technical reference and guidance for the engineering application of sewage sludge anaerobic fermentation.

Carbon dioxide adsorption to 40 MPa on extracted shale from Sichuan Basin, southwestern China

CO2-enhanced shale gas recovery is a promising technology for promoting shale gas production and ideally for CO2 geological sequestration through sorption. Despite this, research studies to date have solely been performed at pressures and temperatures substantially lower than those that actually occur in shale formations. The thrust of this work is to measure and model the carbon dioxide adsorption behavior for the full spectrum of in situ pressure range up to 40 MPa with an intention to provide the baseline values of carbon sequestration planning for the Longmaxi shale formation, Sichuan China. In this study, CO2 adsorption isotherms were measured up to 40 MPa for one sample for five different temperatures (40, 60, 80, 100, and 120 °C) by using the gravimetric method. In the experimental program, we uniquely treated the shale with supercritical CO2 to extract the extractable components to eliminate the high-pressure CO2 extraction effect on adsorption. This pre-extraction was found to significantly reduce the specific surface area of the shale. All excess adsorption trends increased rapidly to maxima followed by the decline to a plateau. The negative excess (Gibbs) adsorptions were observed for two samples at 60 °C and at 40 and 60 °C. At 60 °C, maxima were observed near the critical pressure of CO2 (7.38 MPa) for all samples, which is attributed to the rapid increase of CO2 density near the critical pressure. Adsorption data were fit using several models and the Dubinin-Radushkevich model modified with k times the gas density (MDR + k model) was found to most closely describe the experimental results above 30 MPa. The model-fitted carbon-dioxide maximum absolute adsorption capacities (n0) were 0.150–0.272 mmol/g at 60 °C. Further, n0 decreased with increasing temperature. Thermodynamic data such as heats of adsorption were calculated and used to evaluate CO2 adsorption properties under various conditions. The data also showed that the total organic carbon content of the shale was the primary factor determining CO2 adsorption. The results of this work provide useful knowledge regarding the adsorption characteristics of actual shale formations and are expected to assist in future gas extraction and sequestration projects.

H2, N2, CO2, and CH4 Unary Adsorption Isotherm Measurements at Low and High Pressures on Zeolitic Imidazolate Framework ZIF-8

Excess adsorption of CO2, CH4, N2, and H2 on ZIF-8 was measured gravimetrically in the pressure range ranging from vacuum to 30 MPa at 298.15, 313.15, 333.15, 353.15, and 394.15 K using a magnetic suspension balance. The textural properties of the adsorbent material─i.e., skeletal density, surface area, pore volume, and pore-size distribution─were estimated by helium gravimetry and N2 (77 K) physisorption. The adsorption isotherms were fitted with the Sips isotherm model and the virial equation, and the values of isosteric heat of adsorption and Henry constants for the gases were determined using the latter.

Regulating the Electronic Configuration of Supported Iron Nanoparticles for Electrochemical Catalytic Nitrogen Fixation

AbstractElectrocatalytic nitrogen reduction reaction (eNRR) is a sustainable alternative to the traditional Haber–Bosch process due to its eco‐friendly nature and capability of utilizing renewable energy. However, its low Faradic efficiency (FE), caused by the excessive adsorption and reduction of protons, has been regarded as the main challenge, which leads to low ammonia yield as well. Herein, a carbon‐supported iron electrocatalyst is reported, which is fabricated by low‐temperature (300 °C) potassium vapor reduction of FeF3‐intercalated graphite fluoride, for efficient electrochemical nitrogen reduction. The strategy enables the unique formation of exposed Fe nanoparticles uniformly anchored on graphene and in situ doped with fluorine heteroatoms. These specific features can alter the electronic configuration of the Fe nanoparticles, leading to strong surface polarization that boosts nitrogen absorption capability for eNRR, resulting in high FE (41.6%) and ammonia yield rate (53.3 μg h‐1 mg‐1) simultaneously. First‐principle calculation attributes this enhanced eNRR capability to more empty orbitals carried by the Fe atoms through the electron transfer with F dopant and substrate. As a versatile strategy for synthesizing various ultrafine and highly dispersed metal nanoparticles on the carbon support, this work might shed light on rational designing essential electrocatalysts with effective electronic structure manipulation.

Adsorption of Polymer-Tethered Particles on Solid Surfaces.

We explore the behavior of polymer-tethered particles on solid surfaces using coarse-grained molecular dynamics simulations. Segment–segment, segment–core, and core–core interactions are assumed to be purely repulsive, while the segment–substrate interactions are attractive. We analyze changes in the internal structure of single hairy particles on the surfaces with the increasing strength of the segment–substrate interactions. For this purpose, we calculate the density profiles along the x, y, z axes and the mass dipole moments. The adsorbed hairy particles are found to be symmetrical in a plane parallel to the substrate but strongly asymmetric in the vertical direction. On stronger adsorbents, the particle canopies become flattened and the cores lie closer to the wall. We consider the adsorption of hairy nanoparticles dispersed in systems of different initial particle densities. We show how the strength of segment–substrate interactions affects the structure of the adsorbed phase, the particle–wall potential of the average force, the excess adsorption isotherms, and the real adsorption isotherms.

Methane adsorption capacity measurement in shale matrix nanopores at high pressure by low-field NMR and molecular simulation

Shale gas is an important unconventional gas resource because of its rich storage ability. The quantitative measurement of adsorption capacity is essential to shale gas exploration. However, traditional measurements, such as gravimetric and volumetric method, are influenced by excess adsorption effect and need to be corrected at high pressures. In this work, methane adsorption curves without excess adsorption effect were obtained through two ways: a low-field nuclear magnetic resonance (NMR) experimental measurement and the adsorption curves modification using density correction method by molecular simulation. Shale powder samples from the Longmaxi Formation, China, are used as representative sample in this work. In NMR experiments, the gas in packed beds, free spaces and nanopores is identified based on the multi-peaks in the NMR transverse relaxation spectrum, which guarantees the inexistence of excess adsorption effect. In simulations, considering the complex composition of the shale matrix and complicated pore shapes, the average density of methane in organic and inorganic nanopores with various size and shape was obtained using Grand Canonical Monte Carlo (GCMC) simulation, and the excess adsorption curve measured by gravimetric and volumetric method is corrected based on such density. Through comparing the NMR measured adsorption curve and corrected excess adsorption curve, it indicates that the adsorption curve measured via NMR was in good agreement with the modified adsorption curves by density correction, which validates the NMR experiment for measuring adsorption capacity of nanoporous media with complex structure, which is suitable for shale gas and hydrogen storage, as well as other adsorption processes.

Absolute adsorption and adsorbed volume modeling for supercritical methane adsorption on shale

Adsorbed methane significantly affects shale gas reservoir estimates and shale gas transport in shale formations. Hence, a practical model for accurately representing methane adsorption behavior at high-pressure and high-temperature in shale is imperative. In this study, a reliable mathematical framework that estimates the absolute adsorption directly from low-pressure excess adsorption data is applied to describe the excess methane adsorption data in literature. This method provides detailed information on the volume and density of adsorbed methane. The obtained results indicate that the extensively used supercritical Dubinin-Radushkevich model with constant adsorbed phase density underestimates absolute adsorption at high pressure. The adsorbed methane volume increases both the pressure and expands with the temperature. The adsorbed methane density reduces above 10 MPa, and approaches a steady value at high pressure. This study provides a novel method for estimating adsorbed shale gas, which is expected improve the prediction of shale gas in place and gas production.

Low salinity surfactant alternating gas/CO2 flooding for enhanced oil recovery in sandstone reservoirs

Surfactant alternating gas/CO2 (SAG) flooding is a promising enhanced oil recovery (EOR) technology, which has the potential to improve oil production beyond primary and secondary water flooding methods. However, the performance of SAG flooding is restricted due to instability under high salinity reservoir conditions and excessive surfactant adsorption. One convenient and relatively low-cost option to overcome the limitations and improve the performance of SAG flooding is the use of low salinity water (LSW). In this study, an innovative and effective approach in the form of a low salinity surfactant (LSS) system was developed to suitably enhance the efficacy of immiscible SAG flooding in sandstone reservoir cores. The impact of LSS solutions on various mechanisms responsible for EOR including surface and interfacial tension (IFT), wettability alteration, CO2-foam stability, and surfactant adsorption were investigated. The initial IFT measurements revealed that oil-water IFT could be lowered using low salinity formation water (FW), however a more effective reduction was possible only when surfactants were introduced in such a system to form LSS solutions. Similarly, reductions in the contact angle (from initial 122° to 45°) were achieved with LSS solutions which demonstrated favorable wettability alteration of the reservoir rock from oil-wet to water-wet conditions. Foam stability experiments revealed that the half-life of CO2-foams generated with LSS solutions was appreciably higher, thus indicating the positive impact of low salinity water on foam stability. Additionally, anionic LSS solutions displayed reduced surfactant adsorption behavior onto sandstone cores, whereas for cationic LSS solutions the adsorption values were comparatively higher and exhibited a reverse adsorption trend with decreasing salinity. Finally, core flooding experiments illustrated that significantly higher residual oil could be mobilized and recovered through the tertiary immiscible low salinity surfactant alternating gas/CO2 (LSSAG) flooding. Nearly 23% original oil in place (OOIP) was produced by employing anionic LSS solution as the chemical slug during the LSSAG flooding. However, under similar experimental conditions, LSSAG flooding with cationic LSS solution recovered only about 16 %OOIP despite its comparatively better wettability alteration and IFT performance. In summary, using anionic LSS solutions constitute an effective means to suitably improve the performance of immiscible SAG flooding in sandstone reservoir cores.

Molecular Simulation of Adsorption in Deep Marine Shale Gas Reservoirs

Deep marine shale gas reservoirs are extremely rich in the Sichuan basin in China. However, due to the in situ conditions with high temperature and high pressure (HTHP), in particular reservoir pressure being usually much higher than the test pressure, it is difficult to accurately clarify the adsorption behavior, as seepage theory plays an important role in shale gas reserves evaluation. Therefore, three kinds of sorbent, including illite, quartz and kerogen, and two simulation methods, containing the grand canonical ensemble Monte Carlo method and molecular dynamics method, are synthetically used to determine the methane adsorption behavior under HTHP. The results show that both absolute adsorption and excess adsorption decrease with the increase of temperature. When the pressure increases, the absolute adsorption increases quickly and then slowly, and the excess adsorption first increases and then decreases. The superposition of wall potential energy is strongest in a circular hole, second in a square hole, and weakest in a narrow slit. The effect of pore size increases with the decrease of the pore diameter. Under HTHP, multi-layer adsorption can occur in shale, but the timing and number of layers are related to the sorbent type.

Low-Field NMR Relaxation Analysis of High-Pressure Ethane Adsorption in Mesoporous Silicas.

Understanding the behaviour of short-chain hydrocarbons confined to porous solids informs the targeted extraction of natural resources from geological features, and underpins rational developments in separation, storage and catalytic conversion processes. Herein, we report the application of low-field (12.7 MHz) 1 H nuclear magnetic resonance (NMR) relaxation measurements to characterise ethane dynamics within mesoporous silica materials exhibiting mean pore diameters between 6 and 50 nm. Our measurements provide NMR-based adsorption isotherms within the range 25-50 bar and at ambient temperature, incorporating the ethane condensation point (40.7 bar at our experimental temperature of 23.6 °C). The quantitative nature of the acquired data is validated via a direct comparison of NMR-derived excess adsorption capacities with ex situ gravimetric ethane adsorption measurements, which are demonstrated to agree to within 0.2 mmol g-1 of the observed ethane capacity. NMR relaxation time distributions are further demonstrated as a means to decouple interparticle and mesopore dominated adsorption phenomena, with unexpectedly rapid relaxation rates associated with interparticle ethane gas confirmed via a direct comparison with NMR self-diffusion analysis.

Experimental characterization and molecular modeling of kerogen in Silurian deep gas shale from southern Sichuan Basin, China

A representative molecular model of kerogen is the prerequisite to the study on molecular interaction of fluid molecules with organic nanopores of shale. The molecular kerogen model in Silurian deep gas shale from southern China remains to be developed. In this work, the chemical structure of the targeted deep shale kerogen is characterized by organic geochemical measurements. The derived structural parameters are utilized to build the molecular structure of the kerogen unit. The kerogen unit shows a good representation of realistic kerogen structure in shale reservoir in terms of carbon skeleton, heteroatomic compositions and groups. The kerogen matrix and a extended kerogen slit model are constructed based on the kerogen unit, which match well with the experimental results in matrix density and kerogen porosity, respectively. The kerogen matrix is overall disordered with gentle stacking of polyaromatic fragments, due to the bendable aliphatic linkages and large-size aromatic units. The kerogen nanopores are not saturated with methane at deep shale reservoir conditions. At high pressure, the absolute adsorption tends to reach a maximum, while the excess adsorption shows a decreasing trend. The effect of pressure on the dissolved gas density is not pronounced. The generated kerogen model can serve as a starting point for further theoretical investigations on fluid storage and transport in organic nanopores of deep shale reservoir at microscopic scale.

Effect of thermal treatment on the physical properties of GG100 clone Eucalyptus wood

Thermal treatment can modify undesirable characteristics of some woods, dimensional instability, and excessive water adsorption. The present research work aimed to assess the effect of thermal treatment on the physical properties of clone GG100 Eucalyptus wood. Wood samples were obtained from 9 year-old trees. Samples were subjected to three types of thermal treatment (T1, T2, and T3). In T1, the wood was kept in a laboratory kiln at 100 °C for 180 min. In T2, hydrothermal treatment was performed in an autoclave at 120 °C for 120 min. In T3, the combined autoclave and laboratory kiln treatments were employed. The properties evaluated were apparent density (ρa); mass loss (ML); longitudinal (βl), radial (βr), tangential (βt), and volumetric shrinkage (βv); anisotropic factor; and equilibrium moisture content. The treatments caused a decrease of ρa and increase of ML. The Equilibrium Moisture Content (EMC) was lowest for T3, and had a negative correlation with ML, βt, and ∆v. The Pearson correlation analysis indicated the results of the thermal treatments were similar, but T1 presented the lowest variation of the physical properties compared to the other treatments, giving it the best predictability for practical uses.

Surface coverage control for dramatic enhancement of thermal CO oxidation by precise potential tuning of metal supported catalysts

Chemical heterogeneous catalysis maximizes performance by controlling the interactions between the catalyst and the substrates. Steady-state catalytic rates depend on the heat of adsorption and the resultant coverage of adsorbates, which in turn reflects the electronic structure of the heterogeneous catalyst surfaces. This study aims to free the surface from high coverage of a kind of substance by externally controlling the electrochemical potential of the catalysts for improved thermal-catalytic rates. We employed aqueous CO oxidation at 295 K as a model reaction, where strong binding of chemisorbed CO (CO*) to the metal surfaces and its high coverage led to inhibition of O2 accessing the surface site. Based on the establishment of coverage–potential–performance correlation, our potential-controlling experiments used an electrochemical configuration to identify the appropriate potentials of Pt/C catalysts that can drastically enhance the CO2 formation rate through the thermal reaction pathway. An anodic potential was applied to suppress the high coverage of chemisorbed CO; consequently, the catalytic testing recorded a 5-fold increase in thermal CO2 formation compared to the open-circuit counterpart with a faradaic efficiency (FE) of over 400%. In situ infrared spectroscopy corroborates the potential–coverage correlation, where the suppression of high CO* coverage due to pinning the catalyst potential triggered the enhancement of thermal-catalytic contribution to CO2 formation. Our extended study employing other metal catalysts also exhibited FEs exceeding unity. This work establishes a universal methodology of electrochemical tools for thermal catalysis to precisely tune the electrochemical potential of solids and achieve green and innovative reactions.

GCMC simulation of supercritical N<sub>2</sub> adsorption in single-walled carbon nanotubes

The development of supercritical fluid technology is becoming more and more mature. The research on the adsorption behaviors of supercritical fluid in nanoporous materials has theoretical significance and application value for the development and application of supercritical fluid technology. In this paper, the grand canonical Monte Carlo (GCMC) method is used to simulate the adsorption behaviors of N<sub>2</sub> in single-walled carbon nanotubes under supercritical condition and subcritical condition, and the isosteric heat of adsorption and integral molar enthalpy change in different adsorption systems are discussed. The results show that the adsorption isotherms of N<sub>2</sub> in SWCNT do not strictly follow the layered adsorption mechanism under supercritical condition, as a result of the increase of molecular thermal motion, the degree of free mobility becomes higher, and it is easier for nitrogen molecule to intersperse and jump between different molecular layers. The nitrogen adsorption isotherm has a peak, which decreases gradually with the increase of temperature, while the critical pressure at peak increases with the temperature increasing. Around the critical point temperature (126 K), a small change in pressure can cause large fluctuations in the bulk gas phase density, resulting in a sharp drop in the adsorption isotherm after peaking. What is different from the subcritical condition is that the adsorption peak of local density distribution curve of the fluid under supercritical condition cannot represent the increase of excess adsorption capacity, and the influence of gas phase density on the adsorption process cannot be ignored. By studying the adsorption integral molar enthalpy under the supercritical condition, it is found that the excess integral molar enthalpy decreases with the pore size increasing; the adsorption integral molar enthalpy decreases with the augment of pore size at lower pressure, but due to a fact that the proportion of gas phase fluid in large-pore SWCNTs increases at higher pressure, on the contrary, it increases with the pore size at higher pressure increasing.

ВЛИЯНИЕ СОСТАВА РАСТВОРИТЕЛЯ НА КИНЕТИКУ ГИДРОГЕНИЗАЦИИ 4-НИТРО-2'-ГИДРОКСИ-5'-МЕТИЛАЗОБЕНЗОЛА НА СКЕЛЕТНОМ НИКЕЛЕ В ВОДНЫХ РАСТВОРАХ 2-ПРОПАНОЛА

The article is devoted to the analysis of the kinetics of hydrogenation of 4-nitro-2'-hydroxy-5'-methylazobenzene on skeletal nickel in aqueous solutions of 2-propanol without additives and with additions of acetic acid and hydroxide. Elucidation of the effect of the solvent composition on the kinetics of transformations of compounds containing several reactive groups is a theoretical and practically significant problem. According to the data obtained, during the hydrogenation of 4-nitro-2'-hydroxy-5'-methylazobenzene on skeletal nickel, the introduction of an acid or base into an aqueous solution of 2-propanol of azeotropic composition leads to a change in the ratio of directions in the parallel-sequential scheme of transformations of the starting compound. With the introduction of acetic acid, the contribution of the direction due to the transformation of the azo group noticeably increases, while the introduction of sodium hydroxide completely suppresses this process and the addition of hydrogen in the first phase of the reaction is carried out exclusively at the nitro group in the starting 4-nitro-2'-hydroxy -5'-methylazobenzene. The change in the contributions of the directions associated with the transformation of the azo or nitro group in 4-nitro-2′-hydroxy-5′-methylazobenzene cannot be caused by a change in the excess adsorption values of the hydrogenated compound. When the adsorption values of 4-nitro-2'-hydroxy-5'-methylazobenzene change within 30%, the rate constants of hydrogenation of the starting compound under the influence of the solvent change more than 8 times. One of the reasons for such a change in the observed rate constants for the hydrogenation of 4-nitro-2'-hydroxy-5'-methylazobenzene may be a change in the ratio of forms of hydrogen adsorbed on the catalyst surface under the influence of a solvent.

Calculation and analysis of excess adsorption and surface tension of aqueous surfactant solutions under pool boiling conditions

In order to realize the theoretical calculation of surface tension of aqueous surfactant solution under pool boiling conditions, the relationships between surfactant adsorption and bubble behaviors were analyzed. The models of surfactant excess adsorption at liquid-vapor interface and surface tension of aqueous surfactant solution were developed. The parameters in developed models were determined in detail by experiments with ionic surfactant of sodium dodecyl sulfate (SDS) and non ionic surfactant of Triton X-114. Based on the established models, the local surfactant excess adsorption and surface tensions under pool boiling conditions were calculated and analyzed. The results show that bubble behaviors and surfactant adsorption generally take place simultaneously. In low heat flux range, the heat flux has little influence on the excess adsorption and surface tension, while in high heat flux range, the excess adsorption decreases and the surface tension increases significantly with the increasing heat flux. The bubble growth is so fast in high heat flux range that the surfactant adsorption at the liquid-vapor interface has no enough time to reach equilibrium, which leads to the decrease of excess adsorption and the increase of surface tension with the increasing heat flux.

Structural and thermodynamic properties of inhomogeneous fluids in rectangular corrugated nano-pores

Based on the free-energy average method, an area-weighted effective potential is derived for rectangular corrugated nano-pore. With the obtained potential, classical density functional theory is employed to investigate the structural and thermodynamic properties of confined Lennard–Jones fluid in rectangular corrugated slit pores. Firstly, influence of pore geometry on the adsorptive potential is calculated and analyzed. Further, thermodynamic properties including excess adsorption, solvation force, surface free energy and thermodynamic response functions are systematically investigated. It is found that pore geometry can largely modulate the structure of the confined fluids, which in turn influences other thermodynamic properties. In addition, the results show that different geometric elements have different influences on the confined fluids. The work provides an effective route to investigate the effect of roughness on confined fluids. It is expected to shed light on further understanding about interfacial phenomena near rough walls, and then provide useful clues for the design and characterization of novel materials.

Molecular dynamics study of a covalent organic framework as highly-efficient and biocompatible carriers for doxorubicin delivery: the role of nanopores

The development of highly-efficient loading, targeted delivery and controlled-release of drug carrier systems is of great significance in tumor treatment. Although various kinds of nano-carriers have been widely studied as potential anticancer delivery materials, the major concern of cytotoxicity is still an important issue before real medical applications. This is due to the strong interactions between nano-structure carriers and biomacromolecules. Herein, a covalent organic framework (COF), triazine triphenyl imine (TTI), is proposed as a promising candidate for efficient delivery and release of the anti-cancer drug, doxorubicin (DOX), by using molecular dynamics simulations. Our results demonstrated that despite there being huge pores in TTI, enough contact sites can be provided to attract the drug by π–π interactions between the anthracene rings of DOX and the framework of TTI. The loading capacity of DOX on the TTI monolayer even reach 743% because the nanopores exclude some invalid adsorption sites that exist in other 2D nano-carriers. Interestingly, the DOX molecules can not only spontaneously adsorb on the surface of the TTI monolayer in natural conditions, but also effectively release from the TTI carrier under acidic pH level. For the TTI multilayers, similar loading capacity had also been achieved due to the pore walls also playing a key role in adsorbing the DOX molecules. Moreover, by simulating a model protein interacting with TTI, mild biocompatibility of TTI monolayer and multilayer could also be achieved due to the periodic nanopores limiting the excessive adsorption with the protein that could maintain the native structure. Our results highlight the essential roles of the patterned nano-porous structure in the TTI sheets for both efficient DOX loading and release, with high biocompatibility, and provides valuable insight into COF-based nano-carriers in potential drug delivery applications.