Mass Transfer Barrier Research Articles

Immobilization of Coupled Enzymes onto Metalated Hierarchical Organic Microspheres.

Hierarchical organic microspheres (HOMs) have emerged as an ideal carrier for immobilizing biomacromolecules. In this research, an in-depth investigation into the structural characteristics of a striated HOM, known as HOM-15, has revealed the assembly mechanism of microspheres through weakly stacked two-dimensional structural units that are composed of V-shaped small organic molecules. With the leverage of this understanding, HOM-15 was adopted as a stable and reusable platform for co-immobilizing of ene-reductases and glucose dehydrogenases via metal ion bridging onto the surface of HOMs. The research demonstrates that metal ion bridging can finely tune the surface properties of HOM-15, thereby facilitating the immobilization of enzymes that would otherwise be impeded by electrostatic repulsion. Comparing HOM-15 to other microspherical variants revealed its superior biocatalytic performance, attributed to the reduction of the mass transfer barrier facilitated by its lamellar-stacking morphology. This novel biocatalytic system underscores the potential applications of HOMs in broader biocatalytic processes.

Optimized strategies for efficient CO2 trapping using hydrate technology by pressure adjustment

The hydrate-based method enhances oceanic CO2 storage capacity and is deemed beneficial for controlling greenhouse gas emissions. However, the non-uniform CO2 hydrate crystal interface in the sub-seabed storage layer acts as a barrier, slowing down mass transfer kinetics. This work employed in-situ nuclear magnetic resonance (NMR) technology to compare three different pressure adjustment strategies and observe CO2 bubble dispersion after hydrate dissociation, secondary nucleation, and crystal growth mechanism, along with pore water changes. The presence of micro/nano CO2 bubbles with high internal pressure and high specific surface area in the dissociation liquid significantly accelerated secondary micro-structural phase transition rates. The optimal hydrate-based CO2 storage efficiency reached up to 81.7 %. Moreover, the secondary formation of CO2 hydrates distributed more uniformly within the large, medium, and small pores and led to a significantly increased residual water conversion rate (reaching up to 88 %) in medium pores. The post-secondary formation of high-density hydrates resulted in low fluid mobility (T1/T2 mostly distributed in the range of 0 ∼ 10) and exhibited a mixed wettability state between pore fluids. Utilizing the “memory effects” of CO2 hydrate effectively overcame late-stage mass transfer barriers of solid hydrates films. Our findings extend the understanding of CO2 hydrate formation kinetics under pressure adjustment strategies.

Rare-Earth Lanthanum-Evoked Amorphization and Optimization to Boost Ambient Nitrogen Fixation over Single-Atom Catalysts.

Single-atom catalysts (SACs) have been widely studied in a variety of electrocatalysis. However, its application in the electrocatalytic nitrogen reduction reaction (NRR) field still suffers from unsatisfactory performance, due to the sluggish mass transfer and significant kinetic barriers. Herein, a novel rare-earth-lanthanum-evoked optimization strategy is proposed to boost ambient NRR over SACs. The incorporation of La with a large atomic radius tends to break the atomic long-range order and trigger the amorphization of SACs, endowing a greater density of dangling bonds that could modify affinity for reactants and adsorbates. Moreover, with unique 5d16s2 valence-electron configurations, its presence could further enrich the electron density and enhance the intrinsic activity of single-metal center via the valence orbital coupling. As expected, the La-modified catalyst presents excellent activity toward the electrochemical NRR, delivering a maximum ammonia yield rate of 33.91 μg h-1 mg-1 and a remarkable Faradaic efficiency of 53.82%.

A Novel PETG Microchannel Reactor for Microwave-Powered Biodiesel Production

Biodiesel stands at the forefront as a replacement for fossil diesel in compression ignition engines, particularly in the transportation sector where diesel engines are the primary movers. However, biodiesel production is hampered by poor heat and mass transfer during the transesterification reaction, leading to long production times and high costs due to inefficient energy utilisation. This study targets heat and mass transfer issues during the production of biodiesel via a synergic approach that combines microwave-assisted heating and microfluidics via a polyethylene terephthalate glycol (PETG) microchannel reactor. The transesterification reaction of palm oil and methanol was investigated using a full factorial design of experiments (DOE) method. Biodiesel yield was quantified via gas chromatographic analysis, and the results were optimised using statistical analysis. Optical analysis of slug quantification within the microchannel revealed that small slugs, smaller than 1 mm, accelerated the transesterification reaction. The composite-optimised experimental results, aimed at minimising energy costs and environmental impacts while maximising fatty acid methyl ester (FAME) yield, indicate a reaction temperature of 50 °C, a catalyst loading of 1.0 wt.%, and a 3:1 methanol to oil molar ratio. Regression analysis revealed that the reaction temperature was statistically insignificant when utilising the PETG microchannel reactor. This key finding positively impacts biodiesel production as it relates to significantly reduced energy intensity, costs, and emissions. Overall, this research work paves a pathway toward an energy-efficient and sub-minute rapid transesterification reaction, highlighting the effectiveness of microwave heat delivery and effects of microfluidics via the PETG microchannel reactor in overcoming heat and mass transfer barriers in biodiesel production.

Synergistic effect of PDA and PVP on nanosized Pd doped graphite felt/Ni electrode for promoting the electrocatalytic degradation of 2,4- dichlorophenoxyacetic acid

Reducing the mass transfer barrier for the diffusion of water and pollutants to Pd sites is an important measure to achieve efficient degradation of chlorinated organic compounds. Herein, a simple electroless deposition method for preparing a superhydrophilic nanosized Pd-loaded graphite felt/Ni electrode with the aid of the dispersibility of polyvinylpyrrolidone (PVP) and adhesiveness of polydopamine (PDA) is proposed. The GF/Ni/PDA/Pd-PVP electrode exhibited high electrocatalytic activity toward 2,4-dichlorophenoxyacetic acid (2,4-D) under the optimized conditions, namely degradation and dechlorination efficiencies of 90.5% and 88.53%, respectively, corresponding to 39% higher than that on the GF/Ni/Pd electrode. Experimental results revealed that PDA and PVP doping enhanced the hydrophilicity of the electrode, promoted the dispersibility of Pd nanoparticles (NPs), and the formation of Pd (111) and Ni (111) crystal facets. Compared to the electron-deficient PVP, the appropriate electron-donating ability of PDA promoted the formation of a suitable ratio of electro-deficient and electron-rich Pd, thus enhancing the production of Hads* and C-Cl scission. Moreover, theoretical calculation indicated that the doping of PDA and PVP optimized the adsorption energies of 2,4-D, Hads*, and the main dechlorination product PA, which was obtained via 4-electron transfer via Hads*. Therefore, this study provides a simple and feasible way to fabricate an efficient cathode for 2,4-D dechlorination.

ReaxFF molecular dynamics simulations of methane clathrate combustion.

Understanding the ignition and dynamic processes for the combustion of hydrate is crucial for efficient energy utilization. Through reactive force field molecular dynamics simulations, we studied the high-temperature decomposition and combustion processes of methane hydrates in a pure oxygen environment. We found that at an ignition temperature of 2800K, hydrates decomposed from the interface to the interior, but the layer-by-layer manner was no longer strictly satisfied. At the beginning of combustion, water molecules reacted first to generate OH•, followed by methane oxidation. The combustion pathway of methane is CH4→CH3•→CH3O•→CH2O→HC•O→HCOO•→CO(CO2). During the combustion process, a liquid water layer was formed between melted methane and oxygen, which hindered the reaction's progress. When there is no heat resistance, oxygen will transform into radicals such as OH• and O•, which have faster diffusion rates, allowing oxygen to conveniently cross the mass transfer barrier of the liquid water layer and participate in the combustion process. Increasing the amount of OH• may cause a surge in the reaction. On the other hand, when significant heat resistance exists, OH• is difficult to react with low-temperature hydrate components, but it can transform into O• to trigger the oxidation of methane. The H• generated has a sufficient lifetime to contact high-temperature oxygen molecules, converting oxygen into radicals that easily cross the water layer to achieve mass transfer. Therefore, finding ways to convert oxygen into various radicals is the key to solving the incomplete combustion of hydrates. Finally, the reaction pathways and microscopic reaction mechanisms of each species are proposed.

Functional ladder-like heterojunctions of Mo2C layers inside carbon sheaths for efficient CO2 fixation

The development of two-dimensional heterogeneous catalysts with highly exposed active site areas for heterogeneous catalytic systems is highly promising for achieving the green transformation of small molecules. 2D transition metal carbides (TMCs) show great promise for catalysis and carbon capture but suffer from heavy aggregation and autooxidation. Mass transfer barrier is also a standard problem of lamellar TMCs caused by slight aggregation of layers. Here, we successfully developed a method to prepare “ladder-like” heterojunctions of Mo2C layers confined inside nitrogen-rich carbon sheaths (2D-Mo2C@NC) via an effective oxygen-diffusion etching strategy, acting as efficient catalysts for CO2 fixation. The enhanced electron enrichment of the as-integrated 2D-Mo2C subunits induced by the Schottky barrier could further keep the exposed Mo2C surface from possible autooxidation and aggregation confronted by conventional 2D TMCs. The experimental results and density functional theory (DFT) calculation further demonstrate that electron-rich Mo2C could boost the adsorption and activation of CO2 for universal carbonylation of various diamines, providing a turnover frequency value (TOF) of 10.2 h−1 to produce benzimidazolone, which is 5.2 times of that of the state-of-the-art catalyst in the literature under even critical conditions.

SiO2-TiO2 Nanoparticle Aqueous Foam for Volatile Organic Compounds' Suppression.

Volatile organic compounds (VOCs) are prevalent soil contaminants. During the ex situ soil remediation process, VOCs may overflow from the soil and cause gas to diffuse into the atmosphere. Moreover, some VOCs, such as trichloromethane, are categorized by the EPA as emerging contaminants, imparting toxicity to organs, and the endocrine and immune systems, and posing a huge threat to human health and the environment. To reduce VOCs' emissions from contaminated soil, aqueous foam suppression is a prospective method that provides a durable mass transfer barrier for VOCs, and it has been widely used in odor control. Based on an aqueous foam substrate, in order to enhance the foam's stability and efficiency of suppression, SiO2-TiO2-modified nanoparticles have been used as stabilizing agents to improve the mechanical strength of liquid film. The nanoparticles are endowed with the ability to photocatalyze after the introduction of titanium dioxide. From SEM imaging, IR, and a series of morphological characterization experiments, the dispersibility of the SiO2-TiO2-modified nanoparticles was significantly improved under the polar solvent, which, in turn, increased the foam duration. The foam dynamic analysis experiments showed that the foam liquid half-life was increased by 4.08 h, and the volume half-life was increased by 4.44 h after adding the novel synthesized nanoparticles to the bulk foam substrate. From the foam VOC suppression test, foam with modified nanoparticles was more efficient in terms of VOCs' suppression, in contrast with its nanoparticle-free counterparts, due to the longer retention time. Moreover, in a bench-scale experiment, the SiO2-TiO2 nanoparticles foam worked against dichloroethane, n-hexane, and toluene for almost 12 h, with a 90% suppression rate, under UV irradiation, which was 2~6 h longer than that of UV-free SiO2-TiO2 nanoparticles, the KH-570-modified nanosilica foam, and the nanoparticle-free bulk foam. XPS and XRD results indicate that in SiO2-TiO2 nanoparticles, the proportion of titanium valence was changed, providing more oxygen vacancies compared to raw titanium dioxides.

Cation exchange resins enhance anaerobic digestion of sewage sludge: Roles in sequential recovery of hydrogen and methane

The recovery of renewable bioenergy from anaerobic digestion (AD) of sludge is a promising method to alleviate the energy problem. Although methane can be effectively recovered through sludge pretreatment by cation exchange resin (CER), the simultaneous enhancement of hydrogen and methane generation from AD using CER has not been extensively investigated. Herein, the effect of CER on the sequential recovery of hydrogen and methane and the corresponding mechanisms were investigated. When CER is introduced, the maximum increases for the hydrogen and methane production are 104.7 % and 35.3 %, respectively, confirming the sequential enhancement effects of CER on the hydrogen and methane production. Analyses of the variations in the main biochemical components with and without the effect of CER demonstrate that CER promotes sludge organic solubilisation, hydrolysis, and acidification in both hydrogen- and methane-production stages. Moreover, investigations of variations in the solid–liquid interfacial thermodynamics and removal rates of main multivalent metals of sludge reveal that the ion exchange reactions between the CER and sludge in the hydrogen-production stage provide the direct driving force of effective contact between bacteria and organic particulates. Additionally, the residual effect of the CER during methane production reduces the energy barrier for mass transfer and provides a driving force for this transfer. Further analyses of the microbial community structure and metagenomics indicate that CER directly drives the enrichment of hydrogen-producing bacteria (+ 15.1 %) and key genes encoding enzymes in the hydrogen-production stage. Moreover, CER indirectly induces the enrichment of methane-producing anaerobes (e.g. Methanosaeta: + 16.7 %, Methanosarcina: + 316.5 %); enhances the bioconversion of different substrates into methyl-coenzyme M; and promotes the metabolism pathway of acetoclastic process and CO2 reduction in the methane-production stage. This study can provide valuable insights for simultaneously enhancing the production of hydrogen and methane from AD through sequential recovery.

1D-2D intercalated network CMC@g-C3N4/IL membrane with high permeability and selectivity for the CO2 capture

The structural advantages of the membrane material itself are critical to the membrane separation performance. Two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheets can achieve minimal mass-transfer barrier and high gas sieving performance due to their ultra-thin thickness, inherent surface porosity and abundance of amine groups. However, the 2D g-C3N4 nanosheets are prone to stacking during the self-assembly process, which reduces the membrane permeability. Based on this line, herein, we proposed a concept of construction of 1D-2D intercalated network supported ionic liquid membrane composed by one-dimensional (1D) carboxymethylcellulose (CMC) and g-C3N4 nanosheets to overcome the low permeability of 2D graphitic carbon nitride membrane in separating CO2/N2 and CO2/CH4. The as-prepared 1D-2D intercalated network supported ionic liquid gas separation membrane exhibits superior CO2 permeance of 953.96 GPU, CO2/N2 selectivity of 55.46 in separation of CO2/N2, and CO2 permeance of 854.00 GPU, CO2/CH4 selectivity of 50.62 in separation of CO2/CH4. In addition, the resulting CMC@g-C3N4/IL membrane has excellent durability. After 120 h of testing, it still has outstanding separation performance. In short, this concept in this study provides an effective modulation of molecular sieving of g-C3N4 membrane for high-efficiency CO2 capture by combination of the advantages of the 1D (CMC) and 2D (g-C3N4) materials.

Improving efficiency and reducing enzyme inactivation during lipase-mediated epoxidation of α-pinene in a double-phase reaction system.

Chemoenzymatic epoxidation of olefin mediated by lipase is a green and environmentally friendly alternative process. However, the mass transfer barrier and lipase deactivation caused by the traditional organic-water biphasic reaction system have always been the focus of researchers' attention. To overcome these issues, we investigated the effects of reaction temperature and two important substrates (H2O2 and acyl donor) on the epoxidation reaction and interfacial mass transfer. As a result, we determined the optimal reaction conditions: a temperature of 30°C, 30wt-% H2O2 as the oxygen source, and 1M lauric acid as the oxygen carrier. Additionally, by simulating the conditions of shaking flask reactions, we designed a batch reactor and added a metal mesh to effectively block the direct contact between high-concentration hydrogen peroxide and the enzyme. Under these optimal conditions, the epoxidation reaction was carried out for 5h, and the product yield reached a maximum of 93.2%. Furthermore, after seven repetitive experiments, the lipase still maintained a relative activity of 51.2%.

Confined water–encapsulated activated carbon for capturing short-chain perfluoroalkyl and polyfluoroalkyl substances from drinking water

The global ecological crisis of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in drinking water has gradually shifted from long-chain to short-chain PFASs; however, the widespread established PFAS adsorption technology cannot cope with the impact of such hydrophilic pollutants given the inherent defects of solid-liquid mass transfer. Herein, we describe a reagent-free and low-cost strategy to reduce the energy state of short-chain PFASs in hydrophobic nanopores by employing an in situ constructed confined water structure in activated carbon (AC). Through direct (driving force) and indirect (assisted slip) effects, the confined water introduced a dual-drive mode in the confined water-encapsulated activated carbon (CW-AC) and completely eliminated the mass transfer barrier (3.27 to 5.66 kcal/mol), which caused the CW-AC to exhibit the highest adsorption capacity for various short-chain PFASs (C-F number: 3-6) among parent AC and other adsorbents reported. Meanwhile, benefiting from the chain length- and functional group-dependent confined water-binding pattern, the affinity of the CW-AC surpassed the traditional hydrophobicity dominance and shifted toward hydrophilic short-chain PFASs that easily escaped treatment. Importantly, the ability of CW-AC functionality to directly transfer to existing adsorption devices was verified, which could treat 21,000 bed volumes of environment-related high-load (~350 ng/L short-chain PFAS each) real drinking water to below the World Health Organization's standard. Overall, our results provide a green and cost-effective in situ upgrade scheme for existing adsorption devices to address the short-chain PFAS crisis.

Simultaneous inhibition of natural gas hydrate formation and CO2/H2S corrosion for flow assurance inside the oil and gas pipelines

Compatibility problems are observed during the co-injection of corrosion and gas hydrate inhibitors inside oil and gas pipelines, which reduces their performance. In this study, the newly synthesized dual-purpose inhibitors (DPIs) were developed to overcome the compatibility challenge between the inhibitors. A detailed experimental and computational study was performed to investigate the inhibition activity of DPIs. The results of constant cooling experiments showed that the inhibitors significantly prevented natural gas hydrate formation. DPI2 with a propyl pendant group was the best sample by providing a subcooling temperature of 18.1 °C at 5000 ppm. DPI1 and DPI3 decreased gas consumption by 2.6 and 2.4 times, respectively, compared to pure water. In addition, molecular dynamics simulation revealed that the transportation of gas molecules to the growing hydrate cages was disrupted due to DPI2 adsorption on the surface of the hydrate, which partially covered it and acted as a mass transfer barrier. Furthermore, the interaction of the anion part of the inhibitor with the nearest neighbor water molecules lowered the water activity to form the hydrogen-bonding networks for the hydrate formation. According to corrosion measurements, DPIs suppressed the corrosion rate of mild steel in H2S–CO2 saturated oilfield-produced water, and a maximum inhibition efficiency of 96.3% was obtained by adding 1000 ppm of DPI2. Moreover, the estimated adsorption energy of DPI2 were relatively high and matched with experimental data, implying that the inhibitor has a high degree of adsorption on the metal for forming a protective layer on the mild steel surface. These findings signified that DPIs provide a potential hybrid inhibition of corrosion and gas hydrate formation for flow assurance applications and reduce the operation costs.

Synthesis of methyl esters from Hippophae rhamnoides via pilot scale hydrodynamic cavitation intensification reactor

The current research demonstrates the capability of hydrodynamic cavitation (HC) for the manufacture of ester sourcing Hippophae rhamnoides (HiRO) seed oil, which is non-edible in nature. According to the authors' best knowledge, the HC pilot developed assembly has not been put to use in any research pertaining to the manufacturing of biodiesel from HiRO triglycerides. The vast majority of the research indicates that optimising the system for the production of biodiesel based on a particular criterion, such as yield, can lead to only one portion of the research. In order to achieve maximum efficiency in the transesterification reaction, it is necessary to optimise not only the amount of output but also the cavitational parameters. The process of transesterification was initiated to overcome mass transfer resistance. In a pilot HC reactor, four novel geometries (orifices disk) cavities were explored. These cavities were helped along by a double diaphragm pump. It was shown that the mass transfer barrier between immiscible reactants can be decreased by increasing the interfacial area, and this effect was observed during the transesterification reaction, which is characterised by significant turbulence induced by cavitating bubbles. This was accomplished by increasing the surface area of the interface between the reactants. When compared to mechanical stirring, using an orifice plate with 21 holes that were 1 mm in diameter resulted in an eightfold increase in yield efficiency and a sixfold reduction in response reaction time at 2 bar inlet pressure. Utilising the hydrodynamic cavitation contributes to the procedure's reduced impact on the natural environment. In conclusion, the Hippophae rhamnoides oil methyl ester (HiROM) that was produced through the process of hydrodynamic cavitation was demonstrated to be both time and energy efficient. The characteristics of the methyl ester that was synthesised were in accordance with the requirements of both EN14214 and ASTM D6751.

Enhancing Electrocatalytic Hydrodechlorination through Interfacial Microenvironment Modulation.

Electrochemical reduction (ER) is a promising approach to safely remove pollutants. However, sluggish reaction kinetics and significant side reactions considerably limit the applicability of this green process. Herein, we uncovered the previously ignored role of interfacial hydrophilicity in determining the ER performance through electron microscopy observations, contact angle (CA) analysis, and electrochemical measurements. A Pd/C electrocatalyst forms dense nanopores on the electrode surface, rendering it highly hydrophobic and achieving a CA of up to 145°. This imposes a large mass-transfer barrier for the diffusion of water and pollutants into Pd sites. Moreover, the release of H2 is suppressed, which changes the solid-liquid (Pd-polluted water) interface into a solid-gas (H2)-liquid interface. This further slows down mass transfer and the decontamination process. This dilemma can be easily alleviated by adding hydrophilic polymers like polyethylene glycol to increase hydrophilicity and improve mass transfer. By this way, the activity and Faraday efficiency of Pd/C in the electrochemical hydrodehalogenation of 2,4-dichlorophenol could be increased by 4-5 times. Moreover, this interfacial microenvironment modulation strategy is parallel to other approaches, such as Pd structural engineering, and therefore these strategies can be combined to further increase the electrochemical decontamination performance of electrocatalysts.

Simultaneously improving the hydrophobic property and flame retardancy of aluminum hypophosphite using rare earth based coupling agent for epoxy composites

AbstractA novel hydrophobic rare earth‐based aluminum hypophosphite (AHP) was prepared using rare earth aluminate coupling agent (REA) in a ball mill with a one‐step mechanochemistry method, and used as flame retardant for epoxy resin. It has been found that RaAHP‐4 (AHP was modified by 4 wt% REA) exhibited excellent hydrophobic properties with the water contact angle of 94.58°. The effect of RaAHP‐2 (AHP was modified by 2 wt% REA) and RaAHP‐4 on the flame retardancy, thermal stability, and hydrophobic properties of EP/6RaAHP‐2 and EP/6RaAHP‐4 composites were investigated. It has been found RaAHP‐2 and RaAHP‐4 can significantly improve the flame retardant performance of EP/6RaAHP‐2 and EP/6RaAHP‐4 composites. And the peak heat release rate (PHRR) and total heat release (THR) values of EP/6RaAHP‐4 were reduced by 50.44% and 35.59% compared with pure EP, respectively. Moreover, the maximum peak value of CO production rate from EP/6RaAHP‐4 decreased by 62.64% compared with that from EP/6AHP. The excellent flame retardant effect of EP/6RaAHP‐4 composites was obtained because RaAHP‐4 changed the formation of the char residue layer during the combustion process. In comparison, the compactness, expansion degree, and carbonization quality of the char residue layer from the samples with RaAHP‐2 or RaAHP‐4 have been significantly improved, which acted as a valuable barrier for heat and mass transfer. The above results showed that the one‐step synthesis method had high potential application in the large‐scale production of hydrophobic AHP.

Film formation kinetics of Methane-propane hydrate on gas bubble in MEG and luvicap EG solutions

Hydrate plugging in deep sea oil & gas transportation is the final result of morphological evolution of hydrate growth. However, effect of hydrate morphological evolution in the presence of hydrate inhibitors with respect to flow assurance is rarely studied. In this work, methane-propane hydrate forming system by suspending gas bubbles in pressurized aqueous phase was studied to evaluate the hydrate film growth kinetics in the presence of thermal and kinetic inhibitors (MEG, LuviCap EG) at subcooling levels of 10–15 K. Along with morphological observations with optical microscope, the results suggested that: (1) KHI showed better inhibition performance on hydrate growth with hydrate film as a barrier for mass transfer; (2) 4000 ppm performed as a threshold concentration of hydrate film formation on bubble; (3) crater structures, as potential mass transfer channels, are the morphological characteristics of KHIs adsorbing to the hydrate film. In addition, the effects of environmental factors on the growth kinetics of hydrate on bubble showed that the subcooling determined the lateral growth rate of hydrate film, the inhibitor concentration determined whether a film was formed, and the craters structure on the hydrate film determined the mass transfer in the initial thickening stage of hydrate film growth. The research could shed new light on fine-tuning of the inhibitor concentration and level of subcooling to effectively inhibit the growth of hydrate in gas pipelines and assure the multiphase flow in deep sea oil & gas transportation.

Pebax and CMC@MXene-Based Mixed Matrix Membrane with High Mechanical Strength for the Highly Efficient Capture of CO2

Sustainable and energy-efficient molecular separation requires membranes with high permeability and selectivity. Among various membranes, the mixed matrix membranes (MMMs) prepared from two-dimensional MXene materials with well-defined nanochannels are expected to be used for the precise separation of molecules. However, the stacking of a large number of 2D MXene nanosheets creates gas mass transfer barriers, resulting in a significant reduction in gas permeability. To solve this issue, herein, a high-performance self-supporting Pebax/CMC@MXene MMM was prepared by a combination of 2D MXene nanosheets with branched carboxymethyl cellulose (CMC) for CO2 gas separation from natural gas and flue gas. Gas separation experimental results show that the as-prepared self-supporting Pebax/CMC@MXene MMMs can significantly improve gas permeance and selectivity. When the loading of MXene nanosheets in the CMC@MXene filler was fixed at 1.5 mg/mL, the CO2 permeance of Pebax/CMC@MXene MMMs was found to be 521 GPU, and the CO2/N2 selectivity was calculated to be 40.1. Meanwhile, the CO2 permeance was measured to be 444 GPU, and the CO2/CH4 selectivity was calculated to be 40.4. In addition, the resulted as-prepared self-supporting Pebax/CMC@MXene MMM possesses excellent thermal stability and long-term durability; after a 60 h test, its separation performance has no obvious change. The work provides a novel strategy to construct MMMs with less mass transfer barrier for highly efficient capture of CO2 from natural gas and flue gas.

A dimensionally stable lithium alloy based composite electrode for lithium metal batteries

Lithium (Li) metal is regarded as the most promising anode material for next-generation secondary batteries due to its high theoretical specific capacity and low potential. However, the huge volume change and uncontrollable dendrites growth lead to its structural instability during charge/discharge processes. Herein, a lithium alloy-based composite (Li-Sn-Bi) is fabricated for the first time, by fusing Li metal and low melting Sn-Bi eutectic alloy to address the structural change of Li electrodes. In this composite electrode, Li3Bi alloy exhibits a skeleton structure that can alleviate dimensional change of the electrode, meanwhile Li-Sn alloys (Li22Sn5 and Li5Sn2) are embedded in the Li3Bi skeleton that uniform Li plating owing to their low lithium mass-transfer barriers. Thus, the Li-Sn-Bi electrode can preserve its structural integrity during the redox process by combining the respective role of each alloy. Notably, the lifespan of the symmetric battery with Li-Sn-Bi electrode exceeds 4000 h under a fixed capacity of 3 mAh cm−2 and sustains 2000 cycles at a high current density of 30 mA cm−2. This work provides a facile method to fabricate dimensionally stable Li composite electrodes for high-energy–density secondary lithium batteries.

Investigation on pH/temperature-manipulated hydrothermally reduced graphene oxide aerogel impregnated with MgCl2 hydrates for low-temperature thermochemical heat storage

A novel reduced graphene oxide aerogel (rGOA)-MgCl2 composite sorbent is developed by impregnation for low-temperature thermochemical heat storage. Salt particles are dispersed on tunable rGOAs via pH values and hydrothermal temperatures. Parameters of salt particles including salt content, size, and crystallinity strongly depend on reduction degree of the rGOAs. High reduction degree of the rGOAs can improve salt content in composite sorbents and the highest salt content reaches up to 97.3 wt%. Moreover, lower reduction degree of the rGOAs is conducive to formation of salt particles with smaller size and lower crystallinity. Therefore, the composite sorbents with lower salt contents possess better sorption kinetics owing to weaker mass transfer barrier and the maximum water uptake is up to 1.16 g/g at 95% humidity under 25 °C. Dehydration temperature of the composite sorbents decreases to varying degrees compared with that of pure MgCl2⸱6H2O. Mass energy density (Qm) and volume energy density (Qv) of the composite sorbents increase with the rise of salt contents. The largest Qm of 2225.7 J/g is 216.5 J/g higher than that of MgCl2⸱6H2O and the largest Qv reaches up to 0.709 GJ/m3. Heat storage capacity of the composite sorbent after 5 dehydration-hydration cycles remains above 95% of the original. All the results indicate that the composite sorbent is a potential candidate for long-term heat storage.