Nanoporous Surface Research Articles

Confined phase behavior of ethane in nanoporous media: An experimental investigation probing the effects of pore size and temperature

Ethane is rapidly becoming an efficient and dependable clean energy source for fast-growing and developing countries. It is the second most abundant natural gas after methane. However, it poses a major problem for ozone pollution and plays a significant role in greenhouse warming once released into the atmosphere. Therefore, understanding the mechanisms that govern its behavior during storage in natural and artificial nanoporous materials is essential for numerous industrial and environmental applications. In this work, the confined phase behavior of ethane was investigated in ordered mesoporous silica material MCM-41 at varying nanoscale-pore sizes and temperatures. Adsorption and desorption isotherms were experimentally measured for a wide range of nanopore diameters (7, 10.2, 11.3, and 12.3 nm) and temperatures (varying from −65 to −20 °C) using an automated gravimetric nanocondensation apparatus. This system enabled direct quantification of the mass of ethane adsorbed onto the surfaces of nanopores. We examined the impact of the pore diameter and temperature on the adsorption, capillary condensation, and evaporation of ethane in nanoporous media. The capillary condensation and evaporation pressures were determined using the Lorentzian functions. The accuracy of the measurements was confirmed by comparing the experimental bulk condensation pressures with those reported by the National Institute of Standards and Technology (NIST).The results demonstrate that the capillary condensation pressures increased with ascending pore diameters and temperatures. They also indicate that the degree of suppression of the saturation pressure due to confinement is predominant at low temperatures. The percent reduction in the pressure of vapor-liquid phase change decreased with an increase in temperature. A similar trend was observed with respect to changes in the pore size. The results showed that the effect of confinement was weakened as the nanopores became wider. Furthermore, insights were developed about the effects of pore diameter and temperature on the occurrence of the supercritical-like behavior of ethane in nanopores. A good agreement was evident between our results and the examples available in the literature.To the best of our knowledge, we present the first experimental study that describes the confined phase behavior of ethane using a patented gravimetric apparatus. This work presents a systematic approach to understand the effects of confinement in nanoporous media. Furthermore, it can aid the development of new ethane storage applications, especially the characterization of natural and artificial porous materials for energy and environment-related solutions.

Effects of Calcium Carbonate Microcapsules and Nanohydroxyapatite on Properties of Thermosensitive Chitosan/Collagen Hydrogels

Thermosensitive chitosan/collagen hydrogels are osteoconductive and injectable materials. In this study, we aimed to improve these properties by adjusting the ratio of nanohydroxyapatite particles to calcium carbonate microcapsules in a β-glycerophosphate-crosslinked chitosan/collagen hydrogel. Two hydrogel systems with 2% and 5% nanohydroxyapatite particles were studied, each of which had varying microcapsule content (i.e., 0%, 1%, 2%, and 5%). Quercetin-incorporated calcium carbonate microcapsules were prepared. Calcium carbonate microcapsules and nanohydroxyapatite particles were then added to the hydrogel according to the composition of the studied system. The properties of the hydrogels, including cytotoxicity and biocompatibility, were investigated in mice. The calcium carbonate microcapsules were 2-6 µm in size, spherical, with rough and nanoporous surfaces, and thus exhibited a burst release of impregnated quercetin. The 5% nanohydroxyapatite system is a solid particulate gel that supports homogeneous distribution of microcapsules in the three-dimensional matrix of the hydrogels. Calcium carbonate microcapsules increased the mechanical and physical strength, viscoelasticity, and physical stability of the nanohydroxyapatite hydrogels while decreasing their porosity, swelling, and degradation rates. The calcium carbonate microcapsules-nanohydroxyapatite hydrogels were noncytotoxic and biocompatible. The properties of the hydrogel can be tailored by adjusting the ratio of calcium carbonate microcapsules to the nanohydroxyapatite particles. The 1% calcium carbonate microcapsules containing 5% nanohydroxyapatite particle-chitosan/collagen hydrogel exhibited mechanical and physical strength, permeability, and prolonged release profiles of quercetin, which were superior to those of the other studied systems and were optimal for promoting bone regeneration and delivering natural flavonoids.

Nanocomposite Electrode of Titanium Dioxide Nanoribbons and Multiwalled Carbon Nanotubes for Energy Storage.

TiO2 is one of the most investigated materials due to its abundance, lack of toxicity, high faradaic capacitance, and high chemical and physical stability; however, its potential use in energy storage devices is constrained by its high internal resistance and weak van der Waals interaction between the particles. Carbon nanotubes are especially well suited for solving these issues due to their strong mechanical strength, superior electrical conductivity, high electron mobilities, excellent chemical and thermal stability, and enormous specific nanoporous surface. The hydrothermal approach was followed by chemical vapor deposition to produce a network composite of titanium dioxide nanoribbons (TNRs) and multi-walled carbon nanotubes (MWCNTs). The nanocomposite was characterized using a variety of methods. One phase of TiO2-B nanoribbons has porous pits on its surface, and MWCNTs are grown in these pits to produce a network-like structure in the nanocomposite. With a two-electrode supercapacitor configuration, the TNR/CNT gave a gravimetric capacitance of 33.33 F g-1, which was enhanced to 68.18 F g-1 in a redox-active electrolyte containing hydroquinone (HQ). Additionally, the areal capacitance per footprint was increased from 80 mF cm-2 in H2SO4 to 163.63 mF cm-2 in H2SO4/HQ. The TNR/CNT supercapacitor has superior cyclic stability than the previously reported TiO2-based electrodes, with 97.5% capacitance retention after 5000 cycles. Based on these results, it looks like the TNR/CNT supercapacitor could provide portable electronic power supplies with new ways to work in the future.

Random Walks and Sticky Surfaces: Single-Molecule Measurements of Solute Diffusion in Ethanol/Water-Filled Anodic Alumina Nanopores

Nanoporous anodic aluminum oxide (AAO) membranes are now being explored for use in advanced chemical separations, including in the dehydration of biofuels such as ethanol. Optimization of membrane performance requires an in-depth understanding of how solvent mixtures and solutes behave under nanoconfinement. In this work, the diffusion of rhodamine B (RhB) dye through 10 and 20 nm AAO nanopores filled with a series of ethanol/water mixtures (0–33% water) is explored by fluorescence correlation spectroscopy (FCS). RhB was found to diffuse through the pores by two distinct mechanisms with mean diffusion coefficients, Df and Ds, reflecting fast and slow diffusive motions, respectively, with values that differ by nearly 2 orders of magnitude. Both Df and Ds increased with pore size and were significantly smaller than Db, the RhB diffusion coefficient in bulk liquid. Mean Df values follow a composition-dependent trend that closely mimics the viscosity dependence of Db. Additional slowing of fast RhB diffusion is attributed to both hydrodynamic drag and electrostatic interactions with the nanopore surface. The mean Ds values exhibit a different trend with increasing water content, revealing an increase in Ds and a decrease in the contributions of slow diffusion to the observed dynamics. The fluorescence time transient data used in the analysis show that the slow diffusion process is strongly hindered and likely involves frequent adsorption of RhB to the pore surfaces. These results provide new insights into the detailed molecular-level mechanisms of mass transport in nanoporous AAO membranes.

Nanostructured Gallium Nitride Membrane at Wafer Scale for Photo(Electro)catalytic Polluted Water Remediation.

Photo(electro)catalysis methods have drawn significant attention for efficient, energy-saving, and environmental-friendly organic contaminant degradation in wastewater. However, conventional oxide-based powder photocatalysts are limited to UV-light absorption and are unfavorable in the subsequent postseparation process. In this paper, a large-area crystalline-semiconductor nitride membrane with a distinct nanoporous surface is fabricated, which can be scaled up to a full wafer and easily retrieved after photodegradation. The unique nanoporous surface enhances broadband light absorption, provides abundant reactive sites, and promotes the dye-molecule reaction with adsorbed hydroxyl radicals on the surface. The superior electric contact between the nickel bottom layer and nitride membrane facilitates swift charge carrier transportation. In laboratory tests, the nanostructure membrane can degrade 93% of the dye in 6 h under illumination with a small applied bias (0.5V vs Ag/AgCl). Furthermore, a 2 inch diameter wafer-scale membrane is deployed in a rooftop test under natural sunlight. The membrane operates stably for seven cycles (over 50 h) with an outstanding dye degradation efficiency (>92%) and satisfied average total organic carbon removal rate (≈50%) in each cycle. This demonstration thus opens the pathway toward the production of nanostructured semiconductor layers for large-scale and practical wastewater treatment using natural sunlight.

In-situ synthesis of ZnO onto nanoporous gold microelectrode for the electrochemical sensing of arsenic(III) in near-neutral conditions

The exploration of advanced electrochemical sensors towards highly toxic arsenic(III) has attracted growing interest in recent times. Herein, a ZnO decorated nanoporous Au (NPG) microelectrode was fabricated via a facile electrochemical alloying/dealloying method followed by thermal treatment, and developed for the electrochemical sensing of toxic As(III). Inspired by the electrochemical deposition of Zn and the formation of Au-Zn nanostructure on the surface of the Au microelectrode during the alloying/dealloying process, the in-situ evolution of the formed Au-Zn nanostructure to ZnO nanoparticles wrapped on the nanoporous Au surface was achieved. The ZnO/NPG microelectrode exhibited excellent electrochemical performance towards As(III) detection in near-neutral conditions (0.1 M phosphate buffer solution (PBS), pH: 5.0). A high sensitivity of 1.366 μA·ppb−1·cm−2 with a low limit of detection of 0.30 ppb (S/N = 3) was achieved at concentrations ranging from 1.0 ppb to 260 ppb. Moreover, the prepared ZnO/NPG microelectrode was successfully applied in the analysis of As(III) in tap and lake water samples with satisfactory recovery rates. The ZnO/NPG microelectrode presented exciting prospects for the electrochemical analysis of As(III) in near-neutral conditions.

Efficient Adsorption of Methyl Orange on Nanoporous Carbon from Agricultural Wastes: Characterization, Kinetics, Thermodynamics, Regeneration and Adsorption Mechanism

Nanoporous carbon derived from Moringa oleifera seed waste was synthesized by an original process of flash pyrolysis followed by zinc chloride impregnation. The N2-adsorption–desorption results of the optimized sample revealed a BET surface area of 699.6 m2/g and a pore size of 2 nm. It was evaluated for the adsorption of a mono azo dye, methyl orange (MeO), from aqueous solution. Four isothermal models (Langmuir, Freundlich, Dubinin–Radushkevic and Temkin) were applied to fit the experimental data. The results revealed that Langmuir is the most appropriate isothermal adsorption model to describe the adsorption process (X2 = 1.16); with an adsorption capacity 367.83 mg/g at 298 K, the interaction of MeO dye with the nanoporous carbon surface is a localized monolayer adsorption. The adsorption kinetics was consistent with the pseudo-second-order model and found to correlate well with the experimental data (X2 = 9.06). The thermodynamic study revealed a spontaneous and endothermic adsorption process, and the substances are adsorbed in a random manner. The desorption of MeO dye from MOC-ZnCl2 by sodium hydroxide solution was achieved to a level of about 84%, and the nanoporous carbon was recycled and reused at the fifth cycle. This work demonstrates that MOC-ZnCl2 could be employed as an alternative to commercially available activated carbon in the removal of dyes from wastewater.

On the optimal cathode catalyst layer for polymer electrolyte fuel cells: Bimodal pore size distributions with functionalized microstructures

A high advancement has been achieved in the design of proton exchange membrane fuel cells (PEMFCs) since the development of thin-film catalyst layers (CLs). However, the progress has slowed down in the last decade due to the difficulty in reducing Pt loading, especially at the cathode side, while preserving high stack performance. This situation poses a barrier to the widespread commercialization of fuel cell vehicles, where high performance and durability are needed at a reduced cost. Exploring the technology limits is necessary to adopt successful strategies that can allow the development of improved PEMFCs for the automotive industry. In this work, a numerical model of an optimized cathode CL is presented, which combines a multiscale formulation of mass and charge transport at the nanoscale(∼10nm)and at the layer scale(∼1μm). The effect of exterior oxygen and ohmic transport resistances are incorporated through mixed boundary conditions. The optimized CL features a vertically aligned geometry of equally spaced ionomer pillars, which are covered by a thin nanoporous electron-conductive shell. The interior surface of cylindrical nanopores is catalyzed with a Pt skin (atomic thickness), so that triple phase points are provided by liquid water. The results show the need to develop thin CLs with bimodal pore size distributions and functionalized microstructures to maximize the utilization of water-filled nanopores in which oxygen transport is facilitated compared with ionomer thin films. Proton transport across the CL must be assisted by low-tortuosity ionomer regions, which provide highways for proton transport. Large secondary pores are beneficial to facilitate oxygen distribution and water removal. Ultimate targets set by the U.S. Department of Energy and other governments can be achieved by an optimization of the CL microstructure with a high electrochemical surface area, a reduction of the oxygen transport resistance from the channel to the CL, and an increase of the catalyst activity (or maintaining a similar activity with Pt alloys). Carbon-free supports (e.g., polymer or metal) are preferred to avoid corrosion and enlarge durability.

Inner Wall and Outer Surface Distinguished Solid-State Nanopores for Sensing.

Solid-state nanopores, inspired by biological nanopores, have the advantages of good mechanical properties, stability, and easy modification. They have attracted wide attention in the fields of sequencing, sensing, molecular sieving, nanofluidic devices, nanoelectrochemistry, and energy conversion. Because of the ion/molecule transport characteristic of the pore, the research on solid-state nanopores mainly focuses on the functional modification of its inner wall. In recent years, the outer surface of nanopores has also attracted the attention of researchers, and the functional elements on the outer surface have the functions of anti-interference and ionic signal enhancement. In this perspective, we review research progress of inner wall and outer surface distinguished solid-state nanopores, highlight their processing and advantages, summarize their functions and applications in sensing, and give insight into further research.

Mechanical characterization of nanoporous two-dimensional Ti3C2 MXene membranes

• The Molecular Dynamics with ReaxFF potential were used to investigate the mechanical properties of nanoporous two-dimensional Ti 3 C 2 MXene. • Young's model decreases with the increase of the area of the nanoporous. • The fracture pressure decrease with the increase of separation distance in the zigzag direction due to anisotropy in the structure of MXene. • The nanoporous Ti 3 C 2 MXene membrane can maintain its mechanical integrity in the reverse osmosis desalination process. We performed a molecular dynamics simulation to study the mechanical properties of nanoporous two-dimensional Ti 3 C 2 MXene membranes. The aim is to find out whether these membranes are strong enough to maintain their mechanical integrity in the reverse osmosis desalination process. We modeled the atomic interaction potential of the Ti 3 C 2 system using a reactive force field (ReaxFF) potential. The obtained results indicate that the ultimate strength of nanoporous MXene membranes decreases with an increase in the nanoporous surface and the separation distance in the armchair direction. However, it increases with the decrease of separation distance following the zigzag direction. The Young's modulus of Ti 3 C 2 with a grating nanoporous (112 rectangle pores) was found to be equal to 475.699 GPa and 421.008 GPa, and the calculated fracture pressures at 300K were equal to 30.09 GPa and 28.25 GPa for porous with 28.666 Å 2 and 38.639 Å 2 respectively. The simulation findings are in good agreement with experimental ones for a sample without pores.

Concentration and diffusion of the redox probe as key parameters for label-free impedimetric immunosensing

Nanoporous surfaces are promising for label-free electrochemical biosensing. We formed nanopores directly on the electrode surface by means of assembling a dense layer of nonconductive nanoparticles. In our model affinity biosensor, covalent attachment of albumin protein on top of 40 nm polystyrene nanoparticles represented a capture of an analyte, resulting in blockage of the nanopores. Different bulk concentrations of the ferro/ferricyanide redox pair were probed by Faradaic electrochemical impedance spectroscopy and fast chronoamperometry. The character of the redox probe permeation towards the electrode surface differed in dependence on its concentration. These data were compared with the theoretical behavior of the free diffusion according to the Cottrell equation. Both the bulk concentration of the redox probe and the timescale of the experiment affected the performance of the electrochemical detection, demonstrating the importance of controlling these parameters in immunosensing applications.

Low-cost inkjet-printed humidity sensor using nanoporous surface on coated paper

The present work describes the behaviour of nanoporous structure on two coated papers for determining their suitability for relative humidity measurement. We found that the paper with smaller pore size was better in terms of response and relative humidity range. The nanoporous inorganic thin film with high surface to volume ratio is better to detect the presence of water molecules in the environment. The hydrophilic nature of the surface coating is thus found more active compared to cellulosic paper for sensing water vapour. Prototype sensors made by us responded to the whole range of 15%− 92% RH by combining the resistance and capacitance variations of the interdigitated electrode. The resistance variations provided better response over the range of 15%− 55% RH whereas capacitance variation was better in 55%− 92% RH. The novelty of the present work is using nanocoated papers which are low cost and bio-degradable for field applications.

Interlocked interface of W–Y2O3/CuCrZr joint obtained by W–Y2O3 surface nanoporosification and Cu magnetron sputtering

The development of a method for bonding W–Y2O3 composites and CuCrZr heat sinks, which can meet the requirements of future magnetic confinement fusion devices, is a key problem that needs to be urgently solved. In this work, CuCrZr was vacuum-diffusion-bonded with W–Y2O3 modified using surface nanoporosification, Cu magnetron sputtering, and annealing. Columnar Cu grains grew perpendicular to the surface nanoporous structure with a preferential Cu [111] orientation during sputtering deposition. A Cu layer was formed on the W–Y2O3 nanoporous surface after Cu sputtering deposition and annealing, resulting in an interlocked and tightly bonded interface. The obtained W–Y2O3/CuCrZr joint exhibited a shear strength of 217 MPa, which was much higher than that of a joint without interface modification (147 MPa). The interface of the W–Y2O3/CuCrZr joint was composed of an interaction layer formed by nano-sized W particles and sputter-deposited Cu. Deposited Cu was embedded in the surface nanopores on W–Y2O3, forming a semi-coherent W/Cu interface, realizing mechanical metallurgical bonding between the W–Y2O3 alloy and Cu, and thus enhancing the interface bonding strength. Improving the strength of W–Y2O3/CuCrZr joints by constructing a well-integrated interface facilitates the development of plasma-facing components for future China Fusion Engineering Test Reactor (CFETR).

Microstructure and mechanical properties of NiTi nanoporous structures fabricated with dealloying process

Dealloying is an emerging material processing technology to fabricate nanoporous functional surface. Systematic characterization of microstructure and mechanical properties for dealloyed surface is a basis for tailoring dealloying parameters. This paper aims to investigate the effect of dealloying treatment on the evolution of microstructures and mechanical properties of NiTi alloy. Firstly, nanoporous layer is fabricated with electrochemical dealloying method to dissolve nickel element selectively from NiTi alloy. Secondly, the microstructures of dealloyed layer are characterized and analyzed with microscopic test methods. The release characteristics of nickel ions from the sample surface before and after dealloying treatment were evaluated using SBF immersion tests. Thirdly, the mechanical properties of NiTi nanoporous structure are evaluated with nanoindentation and micro scratch tests. The results show that both elastic modulus and nanohardness of the NiTi nanoporous layer are over 80% lower than those of the matrix material. The super-elastic property of NiTi alloy is weakened. Meanwhile, the scratching force at the same scratching depth is reduced by over 30% after dealloying process. Instead of severe plastic deformation, irregular brittle fracture occurs along the scratched groove and it demonstrates the plasticity degradation of dealloyed surface. Finally, the weakening mechanism of nanoporous structures fabricated with dealloying treatment is discussed.

Synthesis of nanoporous copper by dealloying CuZrAl and CuZrAlAg amorphous ribbons in acidic solution

In this paper, the evolution of nanoporosities in Cu48Zr47Al5 and Cu45-xZr45Al5Ag5+x using a 0.5 M HF aqueous solution and maintaining a constant holding time of 24 h has been studied. The NPC structure with pores ranging from 50 to 500 nm decorated with nanocubes of Cu2O has been manufactured by dealloying the amorphous Cu48Zr47Al5 alloy. The bimetallic structure NPC/Ag is formed with pores ranging from 10 to 500 nm in the Cu45Zr45Al5Ag5 sample, showing that Cu and Ag do not form a solid solution and the Ag particles precipitate on the surface of interconnected nanopores and form an NPC/Ag composite. A partial dealloying of less noble elements is obtained for the Cu40Zr45Al5Ag10 alloy, which does not form an interconnected network of pores, only some craters with dimensions between 50 nm and 3 µm were obtained. The resulting NPC/Cu2O and NPC/Ag shows an open pore structure and a large surface area. The nanoporous copper synthesized by the dealloying route is suitable for potential applications in catalysis, sensors, etc.

Biohybrid Membrane Formation by Directed Insertion of Aquaporin into a Solid-State Nanopore.

Biohybrid nanopores combine the durability of solid-state nanopores with the precise structure and function of biological nanopores. Particular care must be taken to control how biological nanopores adapt to their surroundings once they come into contact with the solid-state nanopores. Two major challenges are to precisely control this adaptability under dynamic conditions and provide predesigned functionalities that can be manipulated for engineering applications. In this work, we report on the computational design of a distinctive class of biohybrid active membrane layers, built from the directed-insertion of an aquaporin-incorporated lipid nanodisc into a model alkyl-functionalized silica pore. We show that in an aqueous environment when a pressure difference exists between the two sides of the solid-state nanopore, the preferential interactions between the hydrocarbon tail of the lipid molecules that surround the aquaporin protein and the alkyl group functionalizing the interior surface of the silica nanopore enable the insertion of the aquaporin-incorporated lipid shell into the nanopore by forcing out the water molecules. The same preferential interactions are responsible for the structural stability of the inserted aquaporin-incorporated lipid shell as well as the water sealing properties of the lipid–alkyl interface. We further show that the aquaporin protein stabilized in the alkyl-functionalized silica nanopore preserves its biological structure and function in both pure and saline water, and, remarkably, its water permeability is equal to the one measured in the biological environment. The designed biohybrid membrane could pave the way for the development of durable transformative devices for water filtration.

Investigation of α-Synuclein and Amyloid-β(42)-E22Δ Oligomers Using SiN Nanopore Functionalized with L-Dopa.

Solid-state nanopores are an emerging technology used as a high-throughput, label-free analytical method for the characterization of protein aggregation in an aqueous solution. In this work, we used Levodopamine to coat a silicon nitride nanopore surface that was fabricated through a dielectric breakdown in order to reduce the unspecific adsorption. The coating of inner nanopore wall by investigation of the translocation of heparin. The functionalized nanopore was used to investigate the aggregation of amyloid-β and α-synuclein, two biomarkers of degenerative diseases. In the first application, we demonstrate that the α-synuclein WT is more prone to form dimers than the variant A53T. In the second one, we show for the Aβ(42)-E22Δ (Osaka mutant) that the addition of Aβ(42)-WT monomers increases the polymorphism of oligomers, while the incubation with Aβ(42)-WT fibrils generates larger aggregates.

Nanopore-Based Detection of Trace Concentrations of Multivalent Ions When Impurity Ions Are Present.

The feasibility of detecting a trace concentration of multivalent ions based on the ionic current rectification (ICR) of a nanopore when impurity ions might present is assessed. Adopting a bullet-shaped nanopore surface modified with tannic acid as an example, the detection of trace concentrations of Cu2+ (target ion) when Fe3+ (impurity) is present with K+ as background ions under various conditions is simulated. In particular, the influence of the reaction order of the association of target ions and tannic acid on the nanopore performance is examined. We show that the lower the background concentration the better the detection performance. For the examined background concentrations of 1, 10, 100, and 1000 mM, the optimal detection ranges are [0.5, 1000 μM] and [1, 1000 nM] for Cu2+ and Fe3+, respectively. The detection limits, 0.5 μM for Cu2+ and 1 nM for Fe3+, are lower than those that can be obtained from conventional instruments, suggesting the potential of applying the present nanopore-based approach. In addition, we also consider the presence of multiple ions, which can occur, for example, in detecting Cu2+ (target ion) when Fe3+ (impurity) might present or vice versa with K+ as background ions. The competitive adsorption of these three kinds of ions can yield complicated ICR behaviors.

Fabrication of Polymer Membrane Enzyme Reactors with a Dual-Responsive Feature for Cascade Enzyme Reaction Regulation.

Enzymes are known to drive biological processes efficiently and uniquely. However, the integration of multienzymes and immobilization technology to improve the stability of enzymes and boost the catalytic efficiency in cascade reactions by controlling the biocatalysis process in complex conditions via an external stimulus is still facing a significant challenge. Herein, we demonstrate a concept for cascade enzyme reaction regulation by controlling the catalytic efficiency step by step based on a dual-stimuli-responsive porous polymer membrane enzyme reactor (DPMER). Poly(styrene-maleicanhydride-acrylic acid-4-[(4-methacryloyloxy)phenylazo] benzoic acid) was designed for the fabrication of the DPMER with glutaminase and alanine aminotransferase as the model modified enzymes. Under UV light irradiation and by regulating the solution pH, the cascade enzyme reaction was carried out step by step. The polymer membrane surface demonstrated a configuration change while improving the enzymolysis efficiency of the DPMER. The enzymatic kinetics of the DPMER was investigated by a chiral capillary electrophoresis technique, and the cascade enzyme reaction regulation capability was evaluated. Under pH of 4.9 and 365 nm UV irradiation, the poly(4-[(4-methacryloyloxy)phenylazo] benzoic acid) and poly(acrylic acid) moieties changed from a "stretched state" to a "curled state" to form surface nanopores, which embedded the enzymes into the surface nanopores while causing the spatial confinement effect and enhancing the enzymolysis efficiency of the DPMER by 9.9-fold in comparison with the free enzymes. This concept provided a potential platform for cascade enzyme reaction regulation and highlighted the perspective of stimuli-responsive polymers.

Influence of Temperature on the Adsorption and Diffusion of Heavy Oil in Quartz Nanopore: A Molecular Dynamics Study

The desorption of heavy oil is one of the important indicators affecting the development efficiency of the remaining oil in nanopores. However, the study of the adsorption and diffusion mechanisms of heavy oil molecules in nanopores remains scarce. In this work, the influences of temperature on the adsorption and diffusion properties of the heavy oil four-fractions in quartz nanopore have been investigated via molecular dynamics simulations. Our results show that the heavy oil molecules will form a denser multilayer adsorption oil layer on the nanopore surface, and high temperature can alter the adsorption behaviors of the heavy oil four-fractions. As the temperature increases, the saturate molecules are desorbed from the nanopore surfaces, but the aromatic, resin, and asphaltene molecules maintain a tendency to aggregate towards the nanopore surface. In particular, the agglomeration behaviors of most saturate, aromatic and asphaltene molecules in nanopore can be suppressed by the confined space compared with the heavy oil molecules in oil droplet. In addition, the influence of temperature on the movement of heavy oil molecules in nanopore decreases compared with the oil molecules in a heavy oil droplet due to the confined space and adsorption effect. Interestingly, there is a competition phenomenon between the adsorption and diffusion of aromatic, resin, and asphaltene molecules in the nanopore, resulting in different adsorption behaviors with the increase in temperature. The results obtained in this paper will provide molecular-level theoretical guidance for understanding the adsorption and desorption mechanisms of heavy oil in nanopores.