Chatelier's Principle Research Articles

Rate expression model from thermodynamics application and optimal kinetic parameters determination for urea synthesis and production process

Urea, an essential organic fertilizer, enhances soil fertility by providing 0.466 nitrogen for maximum crop yield. In this study, urea is synthesized from NH3 and CO2 in an equilibrium reaction process adhering to Le Chatelier's principle, maintained under process conditions: flow rate of 63.5 kg/s, temperature of 184 °C, and pressure of 160 kg/cm2. A new rate expression model, formulated in terms of extent of reaction and mole fraction, was developed based on mass action relations and thermodynamic models. Two industrial reactors were considered: a plug flow reactor (PFR) at Notore and a continuous stirred tank reactor (CSTR) at Indorama plants. Transient reactor models, based on material and energy balance conservation principles, were numerically resolved using MATLAB version 2020 with specified input conditions. A non-linear regression statistical optimization model was employed to refine kinetic parameter values, ensuring optimal and high-quality urea yield. Model validations were conducted using literature data, revealing higher urea yields of 0.726 and 0.7032 for the CSTR and PFR, respectively. Deviations (0.134, 0.10 to 1.135 and 0.635, 0.326 to 0.850) and root mean square errors (RMSE) (0.043, 0.033 to 0.193 and 0.137, 0.087 to 0.162) were observed when validated against plant and literature values for the CSTR and PFR respectively. The refined kinetic parameters (activation energies, Arrhenius constants, and rate constants) exhibited negligible deviations (0.0004–0.0466 and 0.0004 to 0.0491) and RMSE (0.0228, 0.0055, and 0.0256 and 0.0241, 0.0096, and 0.0269) when validated against plant data, significantly enhancing urea yield in CSTR and PFR reactors respectively.

Analysis of Leakage and Diffusion Characteristics and Hazard Range Determination of Buried Hydrogen-Blended Natural Gas Pipeline Based on CFD.

Injecting hydrogen into natural gas pipelines is an economical and efficient method of hydrogen transportation. However, the addition of hydrogen leads to significant hydrogen corrosion and embrittlement in the pipelines, especially in harsh and concealed underground conditions, where leak accidents are frequent and difficult to detect. This Article uses Le Chatelier's Principle to determine the hazardous range of hydrogen-blended natural gas (HBNG) by employing numerical simulation, it examines the gas leakage and diffusion characteristics before and after hydrogen injection as well as under different hydrogen blending ratio (HBR). Additionally, considering the density of the mixed gas, a prediction model for the diffusion hazard range of hydrogen-mixed natural gas is established based on multivariate regression theory. The results show that after a leakage occurs in HBNG the diffusion range in soil is wider compared to methane, with higher corresponding pressure and velocity values. Moreover, as the HBR increases, the farthest danger range (FDR) of the HBNG also increases. When the leakage of the buried HBNG pipeline occurs for 1 min, the difference in FDR between HBR 25% and HBR 5% is 0.005 m. After 30 min, this difference increases to 0.019 m, indicating that with longer leakage duration, the potential explosion risk resulting from increased HBR becomes greater. Factors such as pipeline pressure increase, larger leak hole size, and decreased burial depth all contribute to an increase in FDR, with pipeline pressure change having the greatest impact and burial depth change having the smallest impact. The maximum error of the predicted model for the diffusion hazard range of hydrogen-mixed natural gas is 9.385%, and the average error is 2.376%, demonstrating the accuracy of the prediction results. This study provides guidance for monitoring underground hydrogen-blended natural gas pipeline leaks, offers a basis for determining the repair range of pipelines, and ensures the safe transportation of hydrogen-mixed natural gas pipelines.

Fostering scientific reasoning competencies: investigating impacts of cross- and within-content area experimentation using the competency triad

ABSTRACT Educational standards and science education research suggest that experiments can be used to foster scientific reasoning competencies. So far, little is known about whether to sequence experiments from one or multiple content areas for this purpose. Therefore, we compared two sequences in an experimental study to investigate the influence of content areas of experiments on competencies’ development: Based on the same underlying structure, the first, homogeneous sequence includes four kinetics experiments. The second, heterogeneous sequence involves experiments from kinetics, thermodynamics, and redox chemistry. A total of 97 students participating in undergraduate chemistry lab courses were randomly assigned to one of the sequences. The changes in competencies within the sequences were compared based on the ‘competency triad’ differentiating between underlying knowledge (dispositions), the use of this knowledge (processes), and the quality of the resulting investigations (products). The results show that both sequences are comparably suitable to foster scientific reasoning competencies. However, in the post-experiments, we found a tendency of increased inadequate or irrelevant content-related reasoning by bringing in and conflating concepts from previous experiments such as activation energy or the chemical equilibrium (in particular Le Chatelier's principle). We discuss these findings concerning the consequences of sequencing experiments for fostering scientific reasoning.

Pressure-Induced Enhancement in Chemical Looping Reforming of CH4: A Thermodynamic Analysis with Fe-Based Oxygen Carriers.

Chemical looping reforming of methane (CLRM) with Fe-based oxygen carriers is widely acknowledged as an environmentally friendly and cost-effective approach for syngas production, however, sintering-caused deactivate of oxygen carriers at elevated temperatures of above 900 °C is a longstanding issue restricting the development of CLRM. Here, in order to reduce the reaction temperature without compromising the chemical-looping CH4 conversion efficiency, we proposed a novel operation scheme of CLRM by manipulating the reaction pressure to shift the equilibrium of CH4 partial oxidation towards the forward direction based on the Le Chatelier's principle. The results from thermodynamic simulations showed that, at a fixed reaction temperature, the reduction in pressure led to the increase in CH4 conversion, H2 and CO selectivity, as well as carbon deposition rate of all investigated oxygen carriers. The pressure-negative CLRM with Fe3O4, Fe2O3 and MgFe2O4 could reduce the reaction temperature to below 700 °C on the premise of a satisfactory CLRM performance. In a comprehensive consideration of the CLRM performance, energy consumption, and CH4 requirement, NiFe2O4 was the Fe-based OCs best available for pressure-negative CLRM, especially for an excellent syngas yield of 23.08 mmol/gOC. This study offered a new strategy to address sintering-caused deactivation of materials in chemical looping from the reaction thermodynamics point of view.

A review of methane-driven two-step thermochemical cycle hydrogen production

Solar thermochemical cycling is a promising approach to utilizing solar energy to produce H2 and CO, which can be further synthesized into liquid fuels via Fischer-Tropsch reactions, making storage and transportation easier. Despite the potential high theoretical efficiency, factors such as the high temperature and low oxygen partial pressure required for the reduction restrict the large-scale application of this technology. In the near-to-medium term, in order to accelerate the popularization and application of this technology, according to Le Chatelier's principle, the assisted reduction of methane can greatly reduce the demand for high-temperature materials and ultra-low oxygen partial pressure. However, the addition of methane will also bring additional challenges, such as carbon emissions and carbon deposition. Reducing the influence of factors such as material sintering and irreversible loss on system efficiency in the experiment will be essential for the development of this technology. This paper focuses on the methane-driven two-step thermochemical cycle hydrogen production process, summarizes its reaction mechanism, thermodynamic analysis, kinetic analysis, oxygen carrier material doping, and experimental research in detail, and comprehensively analyzes the effect of material properties and irreversible loss on the system. According to thermodynamic and kinetic analysis, rational selection and doping of metal oxygen carrier materials can effectively reduce the reaction temperature, improve gas production rates, and enhance structural stability. Analyzing and trying to reduce various irreversible losses of the system, such as reradiation energy loss, conduction energy loss, etc., and taking appropriate heat recovery measures will help to improve the system efficiency of the actual cycle. This paper would be valuable for the development of this technology and for achieving the goal of carbon neutrality.

Single-zinc vacancy unlocks high-rate H2O2 electrosynthesis from mixed dioxygen beyond Le Chatelier principle.

Le Chatelier's principle is a basic rule in textbook defining the correlations of reaction activities and specific system parameters (like concentrations), serving as the guideline for regulating chemical/catalytic systems. Here we report a model system breaking this constraint in O2 electroreduction in mixed dioxygen. We unravel the central role of creating single-zinc vacancies in a crystal structure that leads to enzyme-like binding of the catalyst with enhanced selectivity to O2, shifting the reaction pathway from Langmuir-Hinshelwood to an upgraded triple-phase Eley-Rideal mechanism. The model system shows minute activity alteration of H2O2 yields (25.89~24.99 mol gcat-1 h-1) and Faradaic efficiencies (92.5%~89.3%) in the O2 levels of 100%~21% at the current density of 50~300 mA cm-2, which apparently violate macroscopic Le Chatelier's reaction kinetics. A standalone prototype device is built for high-rate H2O2 production from atmospheric air, achieving the highest Faradaic efficiencies of 87.8% at 320 mA cm-2, overtaking the state-of-the-art catalysts and approaching the theoretical limit for direct air electrolysis (~345.8 mA cm-2). Further techno-economics analyses display the use of atmospheric air feedstock affording 21.7% better economics as comparison to high-purity O2, achieving the lowest H2O2 capital cost of 0.3 $ Kg-1. Given the recent surge of demonstrations on tailoring chemical/catalytic systems based on the Le Chatelier's principle, the present finding would have general implications, allowing for leveraging systems "beyond" this classical rule.

Why Does Monoamine Oxidase (MAO) Catalyze the Oxidation of Some Tetrahydropyridines?

Results pertaining to the mechanism of the oxidation of the tertiary amine 1-methyl-4-(1-methyl-1-H-pyrrol-2-yl)-1,2,3,6-tetrahydropyridine (MMTP, a close analog of the Parkinsonism inducing compound MPTP) by 3-methyllumiflavin (3MLF), a chemical model for the FAD cofactor of monoamine oxidase, are reported. MMTP and related compounds are among the few tertiary amines that are monoamine oxidase B (MAO-B) substrates. The MMTP/3MLF reaction is catalytic in the presence of O2 and the results under anaerobic conditions strongly suggest the involvement of radical intermediates, consistent with a single electron transfer mechanism. These observations support a new hypothesis to explain the MAO-catalyzed oxidations of amines. In general, electron transfer is thermodynamically unfavorable, and as a result, most 1° and 2° amines react via one of the currently accepted polar pathways. Steric constraints prevent 3° amines from reacting via a polar pathway. Those select 3° amines that are MAO substrates possess certain structural features (e. g., a C-H bond that is α- both to nitrogen and a C=C) that dramatically lower the pKa of the corresponding radical cation. Consequently, the thermodynamically unfavorable electron transfer equilibrium is driven towards products by an extremely favorable deprotonation step in the context of Le Chatelier's principle.

Developing high-power Li||S batteries via transition metal/carbon nanocomposite electrocatalyst engineering.

The activity of electrocatalysts for the sulfur reduction reaction (SRR) can be represented using volcano plots, which describe specific thermodynamic trends. However, a kinetic trend that describes the SRR at high current rates is not yet available, limiting our understanding of kinetics variations and hindering the development of high-power Li||S batteries. Here, using Le Chatelier's principle as a guideline, we establish an SRR kinetic trend that correlates polysulfide concentrations with kinetic currents. Synchrotron X-ray adsorption spectroscopy measurements and molecular orbital computations reveal the role of orbital occupancy in transition metal-based catalysts in determining polysulfide concentrations and thus SRR kinetic predictions. Using the kinetic trend, we design a nanocomposite electrocatalyst that comprises a carbon material and CoZn clusters. When the electrocatalyst is used in a sulfur-based positive electrode (5 mg cm-2 of S loading), the corresponding Li||S coin cell (with an electrolyte:S mass ratio of 4.8) can be cycled for 1,000 cycles at 8 C (that is, 13.4 A gS-1, based on the mass of sulfur) and 25 °C. This cell demonstrates a discharge capacity retention of about 75% (final discharge capacity of 500 mAh gS-1) corresponding to an initial specific power of 26,120 W kgS-1 and specific energy of 1,306 Wh kgS-1.

The Le Chatelier's principle enables closed loop regenerating ternary cathode materials for spent lithium-ion batteries

The surging number of spent lithium-ion batteries (LIBs) has created great challenges to the ecological environment and lithium resources, and how to achieve high-value recycling of spent LIBs is an effective route to address the current challenges. In this paper, based on Le Chatelier's principle, we propose a strategy for efficient and green closed-loop recycling and utilization of spent NCM523 without alkali solution using Le Chatelier's principle. Citric acid as leaching agent, and oxalic acid with larger pKa as precipitant is susceptible to release H+ in the carboxylic acid group and combine with citrate ion after adding to the leaching solution. The compound decomposition reaction occurs in the system to obtain oxalic acid precursor and citric acid simultaneously, realising the closed-loop utilisation of leaching solution recycling. The regeneration of LiNi0.5Mn0.3Co0.2O2 (NCM523) was successfully achieved by combining the salt solution precipitation and roasting processes, resulting in a leaching rate of more than 99 % for Li, Ni, Co and Mn. The restored NCM523 exhibits uniform particle size distribution and intact laminar structure, as well as good cycling stability and rate performance as cathode materials for LIBs. The strategy is more atom economy efficiency and enviro-friendly than traditional pyrometallurgical and hydrometallurgical recycling technologies, which enables green and efficient closed-loop recycling of spent LIBs. This work provides an efficient and economic solution for the recovery and regeneration of spent lithium-ion battery cathode materials.

Inhibition of Vanadium Cathodes Dissolution in Aqueous Zn-Ion Batteries.

Aqueous zinc-ion batteries (AZIBs) have experienced a rapid surge in popularity, as evident from the extensive research with over 30 000 articles published in the past 5 years. Previous studies on AZIBs have showcased impressive long-cycle stability at high current densities, achieving thousands or tens of thousands of cycles. However, the practical stability of AZIBs at low current densities (<1C) is restricted to merely 50-100 cycles due to intensified cathode dissolution. This genuine limitation poses a considerable challenge to their transition from the laboratory to the industry. In this study, leveraging density functional theory (DFT) calculations, an artificial interphase that achieves both hydrophobicity and restriction of the outward penetration of dissolved vanadium cations, thereby shifting the reaction equilibrium and suppressing the vanadium dissolution following Le Chatelier's principle, is described. The approach has resulted in one of the best cycling stabilities to date, with no noticeable capacity fading after more than 200 cycles (≈720h) at 200mA g-1 (0.47C). These findings represent a significant advance in the design of ultrastable cathodes for aqueous batteries and accelerate the industrialization of aqueous zinc-ion batteries.

Surfaces of Atmospheric Droplet Models Probed with Synchrotron XPS on a Liquid Microjet.

ConspectusThe atmosphere is a key part of the earth system comprising myriad chemical species in all basic forms of matter. Ubiquitous nano- and microscopic aerosol particles and cloud droplets suspended in the air play crucial roles in earth's climate and the formation of air pollution. Surfaces are a prominent part of aerosols and droplets, due to the high surface area to bulk volume ratios, but very little is known about their specific properties. Many atmospheric compounds are surface-active, leading to enhanced surface concentrations in aqueous solutions. Their distribution between the surface and bulk may determine heterogeneous chemistry and many other properties of aerosol and cloud droplets, but has not been directly observed.We used X-ray photoelectron spectroscopy (XPS) to obtain direct molecular-level information on the surface composition and structure of aqueous solutions of surface-active organics as model systems for atmospheric aerosol and cloud droplets. XPS is a vacuum-based technique enabled for volatile aqueous organic samples by the application of a high-speed liquid microjet. In combination with brilliant synchrotron X-rays, the chemical specificity of XPS allows distinction between elements in different chemical states and positions within molecular structures. We used core-level C 1s and N 1s signals to identify the alkyl and hydrophilic groups of atmospheric carboxylic acids, alkyl-amines, and their conjugate acids and bases. From this, we infer changes in the orientation of surface-adsorbed species and quantify their relative abundances in the surface. XPS-derived surface enrichments of the organics follow trends expected from their surface activities and we observed a preferential orientation at the surface with the hydrophobic alkyl chains pointing increasingly outward from the solution at higher concentrations. This provides a first direct experimental observation of well-established concepts of surface adsorption and confirms the soundness of the method.We mapped relative abundances of conjugate acid-base pairs in the aqueous solution surfaces from the respective intensities of distinctive XPS signals. For each pair, the protonation equilibrium was significantly shifted toward the neutral form in the surface, compared to the bulk solution, across the full pH range. This represents an apparent shift of the pKa in the surface, which may be toward either higher or lower pH, depending on whether the acid or base form of the pair is the neutral species. The surface shifts are broadly consistent with the relative differences in surface enrichment of the individual acid and base conjugates in binary aqueous solutions, with additional contributions from nonideal interactions in the surface. In aqueous mixtures of surface-active carboxylate anions with ammonium salts at near-neutral pH, we found that the conjugate carboxylic acids were further strongly enhanced. This occurs as the coadsorption of weakly basic carboxylate anions and weakly acidic ammonium cations forms ion-pair surface layers with strongly enhanced local abundances, increasing the probability of net proton transfer according to Le Chatelier's principle. The effect is stronger when the evaporation of ammonia from the surface further contributes to irreversibly perturb the protonation equilibrium, leaving a surplus of carboxylic acid. These surface-specific effects may profoundly influence atmospheric chemistry mediated by aqueous aerosols and cloud droplets but are currently not taken into account in atmospheric models.

Equilibrium/Le Chatelier's Principle

Equilibrium/Le Chatelier's Principle

Room-Temperature Solvent Evaporation Induced Crystallization: A General Strategy for Growth of Halide Perovskite Single Crystals by Applying the Le Chatelier's Principle.

The growth of high-quality halide perovskite single crystals is imperative to study their intrinsic physical properties and to realize high-performance optoelectronic devices. Here, a room-temperature solvent evaporation-induced crystallization (RTSEIC) method is reported based on Le Chatelier's principle, which provides a general strategy to grow halide perovskite single crystals including 3D, 2D, 1D, and 0D, and either hybrid or all-inorganic halide perovskites. Taking 2D n-BA2 PbBr4 (n-BA = butylammonium) as an example, the room-temperature crystallization kinetics is demonstrated. The centimeter-sized n-BA2 PbBr4 single crystals exhibit an extremely small full width at half maximum (FWHM) of 0.024° in (0 0 2) plane rocking curve and a small trap density of 2.74× 1010 cm-3 . The superior crystalline quality endows the n-BA2 PbBr4 single crystal ultraviolet photodetectors with recorded performance among reported n-BA2 PbBr4 ultraviolet photodetectors, demonstrating a detectivity reaching 1.8× 1013 Jones, a fast response time of 55 µs and a high on-off ratio of 104 . The low-cost, simple, general, and efficient RTSEIC method is anticipated to promote the blossoming of halide perovskites single crystals.

Self-Association of the Anion of 7-Oxodeoxycholic Acid (Bile Salt): How Secondary Micelles Are Formed.

Bile acid anions are steroidal biosurfactants that form primary micelles due to the hydrophobic effect. At higher concentrations of some bile acid anions, secondary micelles are formed; hydrogen bonds connect primary micelles. Monoketo derivatives of cholic acid, which have reduced membrane toxicity, are important for biopharmaceutical examinations. The main goal is to explain why the processes of formation of primary and secondary micelles are separated from each other, i.e., why secondary micelles do not form parallel to primary micelles. The association of the anion of 7-oxodeoxycholic acid (a monoketo derivative of cholic acid) is observed through the dependence of the spin-lattice relaxation time on total surfactant concentration T1 = f(CT). On the function T1 = f(CT), two sharp jumps of the spin-lattice relaxation time are obtained, i.e., two critical micellar concentrations (CMC). The aggregation number of the micelle at 50 mM total concentration of 7-oxodeoxycholic acid anions in the aqueous solution is 4.2 ± 0.3, while at the total concentration of 100 mM the aggregation number is 9.0 ± 0.9. The aggregation number of the micelle changes abruptly in the concentration interval of 80-90 mM (the aggregation number determined using fluorescence measurements). By applying Le Chatelier's principle, the new mechanism of formation of secondary micelles is given, and the decoupling of the process of formation of primary and secondary micelles at lower concentrations of monomers (around the first critical micellar concentration) and the coupling of the same processes at higher equilibrium concentrations of monomers (around the second critical micellar concentration) is explained. Stereochemically and thermodynamically, a direct mutual association of primary micelles is less likely, but monomeric units are more likely to be attached to primary micelles, i.e., 7-oxodeoxycholic acid anions.

Quantifying the Contribution of Hot Electrons in Photothermal Catalysis: A Case Study of Ammonia Synthesis over Carbon-supported Ru Catalyst.

Photothermal catalysis is one of the most promising green catalytic technologies, while distinguishing the effects of hot electrons and local heating remains challenging. Herein, we reported that the actual reaction temperature of photothermal ammonia synthesis over carbon-supported Ru catalyst can be measured based on Le Chatelier's principle, enabling the hot-electron contribution to be quantified. By excluding local heating effects, we established that the activation energy via photothermal catalysis was much lower than that of thermocatalysis (54.9 vs. 126.0 kJ mol-1), stemming from hot-electron injection lowering the energy barriers for both N2 dissociation and intermediates hydrogenation. Furthermore, hot-electron injection acted to suppress carbon support methanation, giving the catalyst outstanding operational stability over 1000 h. This work provides new insights into the hot-electron effects in ammonia synthesis, guiding the design of high-performance photothermal catalysts.

A Novel Carbon Dioxide Desorption Phenomena using Potassium Acetate Aqueous Solution

A novel CO2 absorbent, 50–75 wt.% aqueous potassium acetate solution (AcK(aq)), which showed a CO2 absorption capacity of ~ 0.2 mol CO2/mol, and could almost immediately completely desorb CO2 on addition of 40 wt.% H2O at 30 ℃ was investigated. This novel phenomenon seemed contrary to the Le Chatelier's principle because H2O is reactant in this system. After characteristics of products by FTIR and XRD diffraction pattern, the novel desorption behavior was attributed to the acid-base reaction between KH(CH3COO)2 and KHCO3 precipitates within the absorbent sludge. As H2O was added, both compounds re-dissolved and CO2 was released. A similar observation was made when the absorbent sludge was heated to temperatures above 60 ℃, owing to an increase in solubility with temperature. The mechanism of CO2 captured and released by AcK(aq) was proposed in this study. This novel energy-saving CO2 absorption and desorption behavior reveals that AcK(aq) has a high potential for application in the commercial production process.

Stability of layer-by-layer nanofiltration membranes in highly saline streams

Layer-by-layer (LBL) assembly is an essential method for the preparation of nanofiltration (NF) membranes, offering tunable charge and pore size, high water permeability, and good anti-fouling properties, making them highly suitable for resource recovery, seawater desalination, and other fields. Despite their advantages, LBL NF membranes suffer from salinity instability, limiting their use in highly saline streams. This perspective review provides a summary of the fundamental physical and chemical principles of LBL assembly related to the salinity stability of LBL NF membranes. We critically analyze the driving force of LBL assembly, the binding strength of polyelectrolyte (PE) pairs, and the overcompensation of LBL membranes. We also discuss the factors affecting overcompensation level with respect to two different time scales. Furthermore, we examine the relationship between overcompensation level and salinity stability of LBL membranes, considering physical (osmotic pressure) and chemical (Le Chatelier's principle) aspects. Our analysis demonstrates that the salinity stability of LBL NF membranes in highly saline solutions can be improved by selecting PEs with stronger binding strength, increasing the overcompensation level, and chemical crosslinking. These methods not only enhance the salinity stability of LBL NF membranes but also offer greater potential for their future application in highly saline streams.

Experimental and computational studies of the effects of high hydrostatic pressure on biomolecular interactions.

Understanding the thermodynamic mechanisms of adaptation of biomacromolecules to high hydrostatic pressure can help shed light on how piezophilic organisms can survive at pressures reaching over 1,000 atmospheres at the bottom of the oceans (Ando N, et al. Annu. Rev. Biophys. 2021:50:343). Here I will summarize our recent experimental and computational work on various aspects of the effects of high hydrostatic pressure on biomacromolecules. Particular emphasis will be made on the volume changes, ΔV, that accompany conformational transitions in biomacromolecules such as proteins, protein-ssDNA complexes, and dsDNA duplexes. The importance of ΔV comes from the fact that it defines the pressure dependence of stability ΔV = (dΔG/dP)T. Thus, the response of the system to changes in pressure is driven by Le Chatelier's principle: if volume changes upon unfolding are positive, increase in hydrostatic pressure will lead to an increase in stability, whereas if the changes are negative, the stability will decrease with the increase in hydrostatic pressure. The results will be discussed in terms of relative contributions of volumes changes associated with voids and hydration to the net volume changed that accompany conformational transitions in biomacromolecules.

Investigation on small molecule-aptamer dissociation equilibria based on antisense displacement probe

Food safety is a major issue to public health and have attracted global attention. Fast, sensitive, and reliable detection methods for food hazardous substances is highly desirable. Aptamers which can bind to the target molecules with high affinity and specificity represent an attractive tool for the recognition of food hazardous substances, which play an important role in the development and application of new food safety detection technology. But current assays for characterizing small molecule-aptamer binding are limited by either the mass sensitivity or the size differentiation ability. Herein, we proposed a comprehensive method for assessing the dissociation equilibria of small molecule-aptamer, which is immobilized-free under ambient conditions. The design employs the Le Chatelier's principle and could be used to effectively measure small molecule-aptamer interactions. ATP binding aptamer and anti-aflatoxin B1 aptamer were used as the model system to determine their affinity, in which their dissociation equilibria measurements are in excellent close to their previous work. Due to the simplicity and sensitivity of this new method, we believe that it could be recommended as an effective tool for characterizing small molecule-aptamer interactions and promote the further application of small molecular aptamer in food safety.

A general method for rapid synthesis of refractory carbides by low-pressure carbothermal shock reduction

Refractory carbides are attractive candidates for support materials in heterogeneous catalysis because of their high thermal, chemical, and mechanical stability. However, the industrial applications of refractory carbides, especially silicon carbide (SiC), are greatly hampered by their low surface area and harsh synthetic conditions, typically have a very limited surface area (<200 m2 g-1), and are prepared in a high-temperature environment (>1,400 °C) that lasts for several or even tens of hours. Based on Le Chatelier's principle, we theoretically proposed and experimentally verified that a low-pressure carbothermal reduction (CR) strategy was capable of synthesizing high-surface area SiC (569.9 m2 g-1) at a lower temperature and a faster rate (∼1,300 °C, 50 Pa, 30 s). Such high-surface area SiC possesses excellent thermal stability and antioxidant capacity since it maintained stability under a water-saturated airflow at 650 °C for 100 h. Furthermore, we demonstrated the feasibility of our strategy for scale-up production of high-surface area SiC (460.6 m2 g-1), with a yield larger than 12 g in one experiment, by virtue of an industrial viable vacuum sintering furnace. Importantly, our strategy is also applicable to the rapid synthesis of refractory metal carbides (NbC, Mo2C, TaC, WC) and even their emerging high-entropy carbides (VNbMoTaWC5, TiVNbTaWC5). Therefore, our low-pressure CR method provides an alternative strategy, not merely limited to temperature and time items, to regulate the synthesis and facilitate the upcoming industrial applications of carbide-based advanced functional materials.