Adsorption-desorption Dynamics Research Articles

Non-Markovian Diffusion and Adsorption-Desorption Dynamics: Analytical and Numerical Results.

The interplay of diffusion with phenomena like stochastic adsorption-desorption, absorption, and reaction-diffusion is essential for life and manifests in diverse natural contexts. Many factors must be considered, including geometry, dimensionality, and the interplay of diffusion across bulk and surfaces. To address this complexity, we investigate the diffusion process in heterogeneous media, focusing on non-Markovian diffusion. This process is limited by a surface interaction with the bulk, described by a specific boundary condition relevant to systems such as living cells and biomaterials. The surface can adsorb and desorb particles, and the adsorbed particles may undergo lateral diffusion before returning to the bulk. Different behaviors of the system are identified through analytical and numerical approaches.

Optimizing unconventional gas extraction: The role of fracture roughness

In unconventional reservoir engineering, such as coalbed methane and shale gas extraction, fracture behavior is pivotal in gas accumulation, migration, and extraction, acting as a primary channel for gas flow. Current research inadequately addresses the quantitative impact of fracture roughness on gas extraction. In this study, we introduce a novel interdisciplinary model that quantitatively characterizes shale fracture roughness and correlates it with shale permeability. This model comprehensively considers factors affecting shale extraction, including fracture roughness, in situ stress, reservoir deformation, and adsorption-desorption dynamics. It provides a thorough analysis of how fracture roughness influences gas seepage, extraction efficiency, and reservoir stability under various physical conditions. Our validated findings reveal that fracture roughness significantly affects shale permeability, stress responses, and displacement. As the fracture roughness coefficient χ increases from 0.2 to 1.0, the maximum reduction in gas pressure within the hydraulically fractured region is 4.7%, while the maximum increase in reservoir stress is 2.8%. In shale reservoirs near extraction well, particularly in hydraulically fractured zones, the maximum decrease in shale gas pressure is 11.1%, and the maximum increase in stress is 3.2%, which offer a groundbreaking approach for optimizing extraction rates and ensuring project safety in the industry.

Linear enhancement of mechanical compliance by zeolite filling in a compact loudspeaker

A zeolite filling in the rear cavity of a compact loudspeaker enhances the sound pressure amplitude of the loudspeaker system with a frequency range up to ∼500 Hz, but its intrinsic mechanisms remain elusive. We theoretically consider the gas adsorption–desorption behavior on zeolite that can be dynamically perturbed by sound pressure from the diaphragm of the loudspeaker. By merging equivalent circuit theory with gas thermodynamic theory, a linear relationship between mechanical compliance and zeolite volume in the rear cavity is quantitatively modeled. Confirmed by electroacoustic impedance experiments, the linear relationship with a slope of 1.92 mF cm−3 reveals the intrinsic ability of porous material to enhance mechanical compliance by adsorption of gas onto the zeolite in the rear cavity. This study correlates the kinetic behavior of air molecules on zeolite and acoustic behavior; it offers a novel insight to improve the performance of a compact loudspeaker by simple filling with porous material and introduces a comprehensive method for evaluating gas adsorption–desorption dynamics in porous media.

Unraveling the role of polysaccharide-goethite associations on glyphosate’ adsorption–desorption dynamics and binding mechanisms

HypothesisGlyphosate retention at environmental interfaces is strongly governed by adsorption and desorption processes. In particular, glyphosate can react with organo-mineral associations (OMAs) in soils, sediments, and aquatic environments. We hypothesize mineral-adsorbed biomacromolecules modulate the extent and rate of glyphosate adsorption and desorption where electrostatic and noncovalent interactions with organo-mineral surfaces are favored. ExperimentsHere we use in-situ attenuated total reflectance Fourier-transform infrared, X-ray photoelectron spectroscopy, and batch experiments to characterize glyphosate’ adsorption and desorption mechanisms and kinetics at an organo-mineral interface. Model polysaccharide-goethite OMAs are prepared with a range of organic (polysaccharide, PS) surface loadings. Sequential adsorption–desorption studies are conducted by introducing glyphosate and background electrolyte solutions, respectively, to PS-goethite OMAs. FindingsWe find the extent of glyphosate adsorption at PS-goethite interfaces was reduced compared to that at the goethite interface. However, increased polysaccharide surface loading resulted in lower relative glyphosate desorption. At the same time, increased PS surface loading yielded slower glyphosate adsorption and desorption kinetics compared to corresponding processes at the goethite interface. We highlight that adsorbed PS promotes the formation of weak noncovalent interactions between glyphosate and PS-goethite OMAs, including the evolution of hydrogen bonds between (i) the amino group of glyphosate and PS and (ii) the phosphonate group of glyphosate and goethite. It is also observed that glyphosate’ phosphonate group preferentially forms inner-sphere monodentate complexes with goethite in PS-goethite whereas bidentate configurations are favored on goethite.

Adsorption of Phenols from Aqueous Solution with A pH-Sensitive Surfactant-Modified Bentonite

The presence of organic pollutants in wastewater remains a prominent environmental concern due to the related ecological and health hazards. In response, this study employs an adsorptive methodology to address the removal of phenol and catechol, utilizing an organo-bentonite material modified with a pH-responsive switchable surfactant, dodecyldimethylamine oxide (C12DAO). The synthesized organo-bentonite (C12DAO-Bt) manifests commendable thermostability resulting from thermogravimetric analyses. The adsorption capacities of C12DAO-Bt concerning phenol and catechol intensify with the augmentation of the C12DAO/bentonite mass ratio. The utmost adsorption capacities of 150C12DAO-Bt, deduced through a pseudo-second-order kinetic model, stand at 5.72 mg·g−1 for phenol and 5.55 mg·g−1 for catechol, respectively. Subject to modification by a pH-responsive surfactant, conditions leaning towards weakly acidic and neutral conditions (pH = 6~7) are conducive to the adsorption of phenolic compounds. Conversely, alkaline conditions (pH = 8~9) facilitate the dissociation of adsorbates from adsorbents. The augmentation of cationic strength within the examined scope incites the adsorption procedure while impeding the desorption efficacy. In the case of cationic species with comparable ionic strengths, Na+ exhibited a superior effect on the adsorption–desorption dynamics of phenol, while Ca2+ exerts a more pronounced effect on those of catechol. Moreover, even following five consecutive acid–base regulation cycles, C12DAO-Bt retains a relatively high adsorption capacity and desorption efficacy, which underscores its exceptional regenerative capacity for removing phenolic compounds from wastewater.

Spontaneous and scanning-assisted desorption-adsorption dynamics in porous supramolecular networks at the solution-solid interface.

Self-assembled molecular networks (SAMNs) are formed by the spontaneous assembly of molecules on surfaces. On conductive atomically flat surfaces, and also at the liquid-solid interface, scanning tunneling microscopy (STM) can follow their growth dynamics. Desorption and adsorption dynamics are difficult to probe through the liquid-solid interface. Porous molecular networks are of particular interest because they may act as platforms for sensing and host-guest chemistry. Very little is known though about their stability, particularly in a liquid environment. To this end, we have investigated the desorption/adsorption dynamics of supramolecular porous monolayers of alkoxylated dehydrobenzo[12]annulene (DBA) derivatives at the interface between highly oriented pyrolytic graphite, the substrate, and 1-phenyloctane, the liquid. To trace the dynamics, structurally analogous chiral DBA derivatives were used as marker molecules, which co-assemble with the achiral ones forming the supramolecular network. This approach reveals the time scales of the adsorption/desorption dynamics, the significance of temperature, and the important role of the STM tip in inducing dynamics.

Modeling Interfacial Interaction between Gas Molecules and Semiconductor Metal Oxides: A New View Angle on Gas Sensing.

With the development of internet of things and artificial intelligence electronics, metal oxide semiconductor (MOS)-based sensing materials have attracted increasing attention from both fundamental research and practical applications. MOS materials possess intrinsic physicochemical properties, tunable compositions, and electronic structure, and are particularly suitable for integration and miniaturization in developing chemiresistive gas sensors. During sensing processes, the dynamic gas-solid interface interactions play crucial roles in improving sensors' performance, and most studies emphasize the gas-MOS chemical reactions. Herein, from a new view angle focusing more on physical gas-solid interactions during gas sensing, basic theory overview and latest progress for the dynamic process of gas molecules including adsorption, desorption, and diffusion, are systematically summarized and elucidated. The unique electronic sensing mechanisms are also discussed from various aspects including molecular interaction models, gas diffusion mechanism, and interfacial reaction behaviors, where structure-activity relationship and diffusion behavior are overviewed in detail. Especially, the surface adsorption-desorption dynamics are discussed and evaluated, and their potential effects on sensing performance are elucidated from the gas-solid interfacial regulation perspective. Finally, the prospect for further research directions in improving gas dynamic processes in MOS gas sensors is discussed, aiming to supplement the approaches for the development of high-performance MOS gas sensors.

Carbon monoxide-sensing of SnS nanoflakes induced by the electron-trapped polaron upon the substituted-lithium

Two-dimensional (2D) SnS with wrinkled lattice and strong oxidation resistance exhibits malleable talents and great potential for gas-sensing applications. But it suffers the inherent disadvantage of low sensitivity towards weakly polarized gases like CO. Herein, inspired by the unique atomic real polarization and orbital penetration of lithium, a distinct polarized configuration of 2D Li-substituted SnS is proposed for achieving a moderate CO adsorption-desorption dynamics at room temperature. The 2D nanoflakes of Li-SnS, synthesized via one-step solvothermal method, reveal highly sensitive and selective performances towards trace CO as low as 2 ppm at RT. Conducting with first-principles calculations, the substitutional doping of Li in SnS crystal is unveiled as the knob to modulate the electronic state of SnS. The enhanced electron-deficiency states and the local vibration modes of Li atoms, urge the coupling of electrons and longitudinal-optical phonons to form a polaron on each Li site. These polarons serve as efficient electron traps, and synergize with anharmonic local vibrations of Li atoms to form energy state fluctuation, promoting CO adsorption-desorption dynamics and carrier transport for the SnS system. This work provides novel perspectives for understanding the structure-electrical configurations of 2D materials and the microscopic mechanism of gas adsorption.

High-yield solar-driven atmospheric water harvesting of metal-organic-framework-derived nanoporous carbon with fast-diffusion water channels.

Solar-driven, sorption-based atmospheric water harvesting (AWH) offers a cost-effective solution to freshwater scarcity in arid areas. Creating AWH devices capable of performing multiple adsorption-desorption cycles per day is crucial for increasing water production rates matching human water requirements. However, achieving rapid-cycling AWH in passive harvesters has been challenging due to sorbents' slow water adsorption-desorption dynamics. Here we report an MOF-derived nanoporous carbon, a sorbent endowed with fast sorption kinetics and excellent photothermal properties, for high-yield AWH. The optimized structure (40% adsorption sites and ~1.0 nm pore size) has superior sorption kinetics due to the minimized diffusion resistance. Moreover, the carbonaceous sorbent exhibits fast desorption kinetics enabled by efficient solar-thermal heating and high thermal conductivity. A rapid-cycling water harvester based on nanoporous carbon derived from metal-organic frameworks can produce 0.18 L kgcarbon-1 h-1 of water at 30% relative humidity under one-sun illumination. The proposed design strategy is helpful to develop high-yield, solar-driven AWH for advanced freshwater-generation systems.

Modeling galvanostatic charge\u2013discharge of nanoporous supercapacitors

Molecular modeling has been considered indispensable in studying the energy storage of supercapacitors at the atomistic level. The constant potential method (CPM) allows the electric potential to be kept uniform in the electrode, which is essential for a realistic description of the charge repartition and dynamics process in supercapacitors. However, previous CPM studies have been limited to the potentiostatic mode. Although widely adopted in experiments, the galvanostatic mode has rarely been investigated in CPM simulations because of a lack of effective methods. Here we develop a modeling approach to simulating the galvanostatic charge–discharge process of supercapacitors under constant potential. We show that, for nanoporous electrodes, this modeling approach can capture experimentally consistent dynamics in supercapacitors. It can also delineate, at the molecular scale, the hysteresis in ion adsorption–desorption dynamics during charging and discharging. This approach thus enables the further accurate modeling of the physics and electrochemistry in supercapacitor dynamics.

Adsorption-desorption dynamics of synthetic and naturally weathered microfibers with toxic heavy metals and their ecological risk in an estuarine ecosystem

Microfibers (MFs) in aquatic and marine ecosystems adsorb toxic heavy metals and then transfer the heavy metals enriched MFs to living organisms. In this research paper, the adsorption-desorption dynamics of heavy metals onto MFs was studied by using theoretical models and experimental investigations. The adsorption of metals onto MFs was well correlated for the Freundlich model and the adsorption kinetics follows pseudo-second order rate equation. The adsorption capacity of naturally weathered MFs was 30.8 mg g−1 which is about 35% higher than the synthetic fiber of similar range of size of MFs. The leaching of heavy metals from MFs was found that 90–95% of adsorbed metals were leached within 24 h. The leaching of Ti(II) and Al(III) were slower than the other metal ions. The salinity has shown decrease in adsorption capacity of MFs for heavy metals. Based on the Nemerov pollution index (PN), the naturally weathered MFs enriched with heavy metals in sediments became heavily polluted with PN values between 2.98 and 3.49. The risk index value of 396 represents that the bottom dwellers and other marine organisms in the Narmada estuary high risk from MFs and MFs enriched with metals. This study indicates that MFs play dominant role in fate and distribution of heavy metals in the estuarine ecosystems.

Adsorption-desorption and leaching behavior of diuron on selected Kenyan agricultural soils

In this work, the adsorption-desorption dynamics of diuron in three typical Kenyan agricultural soils, Nzoia (NZ), Thika (TH) and Machakos (MK) was investigated. The equilibrium adsorption data, tested against three classical nonlinear adsorption isotherms, was best described by the Freundlich model. The Freundlich adsorption constant, (KF), increased in the order MK > TH > NZ soil. Additionally, the negative Gibb's free energy values indicate the adsorption processes were thermodynamically spontaneous and physical. Multiple linear regression analysis indicated that the adsorption-desorption behavior was controlled by the clay and phosphorus contents of the soil. Phosphorus negatively affected the adsorption of diuron and promoted desorption. The groundwater ubiquity score (GUS) indicated that diuron movement rating in MK soil was ‘moderate’ while the movement in TH and NZ soils was ‘high’.

Role of the Morphology of Sulfonic Resin Catalysts in the Etherification of Ethanol with iso-Butylene: A Review

The influence of the morphology of the sulfonic resins on their catalytic properties for the etherification of ethanol with isobutylene has been analyzed. It is shown that the influence of the morphology is complex, and can be manifested through various factors: the accessibility and energetics of acid sites, the adsorption–desorption dynamics of reagents, and the mass transfer conditions. It has been established that the effect of morphology on the acidity of sulfonic resin is manifested in the difference of the energetics of external and internal acid sites. Regardless of morphology, the stoichiometry of ethanol sorption on sulfonic resins corresponds to 1 molecule per 1 acid site. The volcano-shape temperature dependence of the activity of sulfonic resins for ethanol etherification is due to the thermodynamics of the reaction (high-temperature branch) and the mass transfer characteristics of the catalyst (low-temperature branch). Due to various conditions of the mass transfer, the morphology determines the optimal process temperature and, consequently, the activity of the catalyst.

A review of metal-organic frameworks (MOFs) as energy-efficient desiccants for adsorption driven heat-transformation applications

Energy-efficient alternative cooling technologies are necessary to reduce the sharp rise in building energy requirements. The currently employed vapor compression air-conditioners are non-environmentally friendly and exhibit low efficiency due to the concurrent handling of sensible and latent cooling loads. Adsorption chillers and desiccant dehumidifiers are promising alternatives that can trim the overall carbon footprint. Their cooling energy efficiency is dependent on the adsorption characteristics of the employed desiccants. Conventional desiccants suffer from low equilibrium capacity, slow adsorption-desorption dynamics, the needs for high regeneration temperatures, and the lack of hydrothermal and cyclic stabilities. With excellent hydrophilicity, exceptional structural integrity, and specific host-guest interactions, metal-organic frameworks (MOFs) are deemed to be the next generation of advanced materials with tailorable structures for specific applications. In this review article, we focus on the recent developments in MOFs and their potential employment in several state-of-the-art applications such as heat transformation, energy storage, and water harvesting. The advantages of MOFs over conventional pure and composite desiccant materials are discussed, and the key factors necessary for synthesizing stable MOFs are reviewed comprehensively. The experimental and computational characterization techniques employed to investigate the properties of MOFs are studied. Lastly, factors that are essential to screen MOFs for specific applications are analyzed, and key research gaps and technological advancements pertaining to material development and engineering demands are also highlighted. In sum, this review article offers an extensive update on the latest trends in water-sorbing MOFs and is intended to serve as a one-stop archive for its potential applicability.

Control of the NO–NH3 SCR Behavior of Cu-ZSM-5 by Variation of the Electronic State of Copper

The effect of NH4OH/Cu2+ in a copper-acetate solution on the properties of ion-exchanged Cu-ZSM-5 catalysts in the selective catalytic reduction of NO by NH3 (NO–NH3 SCR) has been studied. The temperature programmed desorption of ammonia (NH3-TPR) on Cu-ZSM-5 and the ammonia adsorption–desorption dynamics at 75–300 °C were studied to identify and quantify the nature of acid sites and ammonia desorption heat of Cu-ZSM-5. The Cu-ZSM-5 catalysts containing Cu-structures with extra-lattice oxygen were active in the low-temperature SCR, whereas those with isolated Cu2+ ions were active in the high-temperature SCR. It was shown that Cu-structures with extra-lattice oxygen were generated during the ion exchange of H-ZSM-5 with a water-ammonia solution of copper-acetate where the NH4OH/Cu2+ ratio was in the range of 6–15. Isolated Cu2+ ions were produced in the ion-exchange mode with the ammonia-free solution.

Governing Influence of Thermodynamic and Chemical Equilibria on the Interfacial Properties in Complex Fluids.

We propose a comprehensive analysis and a quasi-analytical mathematical formalism to predict the surface tension and contact angles of complex surfactant-infused nanocolloids. The model rests on the foundations of the interaction potentials for the interfacial adsorption-desorption dynamics in complex multicomponent colloids. Surfactant-infused nanoparticle-laden interface problems are difficult to deal with because of the many-body interactions and interfaces involved at the meso-nanoscales. The model is based on the governing role of thermodynamic and chemical equilibrium parameters in modulating the interfacial energies. The influence of parameters such as the presence of surfactants, nanoparticles, and surfactant-capped nanoparticles on interfacial dynamics is revealed by the analysis. Solely based on the knowledge of interfacial properties of independent surfactant solutions and nanocolloids, the same can be deduced for complex surfactant-based nanocolloids through the proposed approach. The model accurately predicts the equilibrium surface tension and contact angle of complex nanocolloids available in the existing literature and present experimental findings.

Enhancing Analytical Separations Using Super-Resolution Microscopy

Super-resolution microscopy is becoming an invaluable tool to investigate structure and dynamics driving protein interactions at interfaces. In this review, we highlight the applications of super-resolution microscopy for quantifying the physics and chemistry that occur between target proteins and stationary-phase supports during chromatographic separations. Our discussion concentrates on the newfound ability of super-resolved single-protein spectroscopy to inform theoretical parameters via quantification of adsorption-desorption dynamics, protein unfolding, and nanoconfined transport.

Remobilization Dynamics of Caffeine, Ciprofloxacin, and Propranolol following Evaporation-Induced Immobilization in Porous Media.

Changing weather conditions can cause cycles of wetting and drying in the unsaturated zone. When porewater evaporates, any nonvolatile solutes present in the pores will be driven to adsorb and ultimately precipitate on solid surfaces. When media are subsequently resaturated through rainfall infiltration, the remobilization of solutes likely depends on both the hydraulics of resaturation and the dynamics of dissolution processes. The focus of this work was to study the dynamics of remobilization of three different emerging contaminants (caffeine, ciprofloxacin, and propranolol) and two model compounds (fluorescein and sulforhodamine B) from porous media following evaporation of porewater. Remobilization column experiments were conducted to study this phenomenon and were evaluated using a finite difference model developed to simulate the adsorption-desorption dynamics during resaturation and elution. Results indicate that dissolution dynamics become increasingly important with increasing adsorption affinity for solid surfaces. Trends in observed elution behavior are not well-predicted from chemical properties, such as solubility. One of the most significant observations of the work is the presence of spikes in elution concentrations well above initial porewater concentration, resulting from the hydraulics of the resaturation process. The effect is most significant in highly mobile compounds that exhibit low adsorption affinity for solid surfaces.

Interfacial mechanisms for stability of surfactant-laden films.

Thin liquid films are central to everyday life. They are ubiquitous in modern technology (pharmaceuticals, coatings), consumer products (foams, emulsions) and also serve vital biological functions (tear film of the eye, pulmonary surfactants in the lung). A common feature in all these examples is the presence of surface-active molecules at the air-liquid interface. Though they form only molecular-thin layers, these surfactants produce complex surface stresses on the free surface, which have important consequences for the dynamics and stability of the underlying thin liquid film. Here we conduct simple thinning experiments to explore the fundamental mechanisms that allow the surfactant molecules to slow the gravity-driven drainage of the underlying film. We present a simple model that works for both soluble and insoluble surfactant systems in the limit of negligible adsorption-desorption dynamics. We show that surfactants with finite surface rheology influence bulk flow through viscoelastic interfacial stresses, while surfactants with inviscid surfaces achieve stability through opposing surface-tension induced Marangoni flows.

Adsorptive Removal of Carbamazepine and Diatrizoate in Iron Oxide Nanoparticles Amended Sand Column Mimicing Managed Aquifer Recharge

The sorption–desorption of recalcitrant pharmaceuticals in sand/soil columns can be used to infer performance of managed aquifer recharge. Removal of carbamazepine (CBZ) and diatrizoate (DTZ) from synthetic wastewater, containing 100 µg·L−1 of each pharmaceuticals, was studied in recirculating sand columns amended with uncoated or methacrylic acid (MAA) coated magnetite nanoparticles. Removal of CBZ and DTZ in MAA-magnetite column (68.34% and 61.91%, respectively) was much higher than that with uncoated magnetite (53.47% and 50.26%, respectively). Rapid decrease of dissolved organic carbon concentrations across nanoparticle amended columns (between 42.28% and 50.08% on Day 1), followed by slow recuperation suggests adsorption–desorption dynamics and competition of dissolved organic matter for sorption sites. Core-level binding energy and charge analysis for Fe(2s) and O(1s) in X-ray photoelectron spectroscopy suggests involvement of physisorption process on the NP surfaces.