Mass Transfer Channels Research Articles

Engineering of metal Co/Ni-CoO nanoparticles embedded in N-doped unclosed hollow carbon nanoboxes as a highly efficient bifunctional electrocatalyst for overall water splitting

Hollow materials are attracting considerable attention in water electrolysis due to their clear internal space and large surface areas. However, the completely enclosed hollow nanostructures are affected by the large mass-transfer resistance and incompletely exposure of the inner space. Here, an unclosed hollow electrocatalyst consisting of metal Co-loaded Ni-doped CoO multiphase nanoparticles inserted in N-doped hollow carbon shells (Co/Ni-CoO@NC) is designed and constructed by a room-temperature stirring corrosion method and subsequent pyrolysis. The as-prepared Co/Ni-CoO@NC displays outstanding electrocatalytic activities for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolytes. And the optimized products show an ultra-small overpotential of only 61 mV at 10 mA cm−2 current density for HER. For OER, the overpotential is 215 mV at the same current density. The excellent catalytic properties of Co/Ni-CoO@NC are mainly due to the high electrical conductivity of nitrogen-doped carbon materials (NC), the great specific surface area of the hollow NC nanoboxes, the exposed internal space and accessible active sites, and the abundant mass transfer channels of the hollow architectures. Moreover, the obtained catalysts exhibit excellent durability and stability in HER and OER applications. This research develops a feasible way to construct bifunctional unclosed hollow electrocatalysts for decomposing water.

Dormancy and double-activation strategy for construction of high-performance mixed-matrix membranes.

Mixed-matrix membranes (MMMs) have the potential for energy-efficient gas separation by matching the superior mass transfer and anti-plasticization properties of the fillers with processability and scaling up features of the polymers. However, construction of high-performance MMMs has been prohibited due to low filler-loading and the existence of interfacial defects. Here, high MOF-loaded, i.e., 55 wt %, MMMs are developed by a 'dormancy and double-activation' (DDA) strategy. High MOF precursor concentration suppresses crystallization in the membrane casting solution, realizing molecular level mixing of all components. Then, the polymeric matrix was formed with uniform encapsulation of MOF nutrients. Subsequently, double-activation was employed to induce MOF crystallization: the alkali promotes MOFs nucleation to harvest small porous nanocrystals while excessive ligands activate the metal ions to enhance the MOFs conversion. As such, quasi-semi-continuous mass transfer channels can be formed in the MMMs by the connected MOFs nanocrystals to boost the gas permeability. The optimized MMM shows significantly ameliorated CO2 permeability, i.e., 2841 Barrer, five-fold enhancement compared with pristine polymer membrane, with a good CO2 /N2 selectivity of 36. Besides, the nanosized MOFs intensify their interaction with polymer chains, endowing the MMMs with good anti-plasticization behaviour and stability, which advances practical application of MMMs in carbon capture.

Dormancy and double‐activation strategy for construction of high‐performance mixed‐matrix membranes

AbstractMixed‐matrix membranes (MMMs) have the potential for energy‐efficient gas separation by matching the superior mass transfer and anti‐plasticization properties of the fillers with processability and scaling up features of the polymers. However, construction of high‐performance MMMs has been prohibited due to low filler‐loading and the existence of interfacial defects. Here, high MOF‐loaded, i.e., 55 wt %, MMMs are developed by a ‘dormancy and double‐activation’ (DDA) strategy. High MOF precursor concentration suppresses crystallization in the membrane casting solution, realizing molecular level mixing of all components. Then, the polymeric matrix was formed with uniform encapsulation of MOF nutrients. Subsequently, double‐activation was employed to induce MOF crystallization: the alkali promotes MOFs nucleation to harvest small porous nanocrystals while excessive ligands activate the metal ions to enhance the MOFs conversion. As such, quasi‐semi‐continuous mass transfer channels can be formed in the MMMs by the connected MOFs nanocrystals to boost the gas permeability. The optimized MMM shows significantly ameliorated CO2 permeability, i.e., 2841 Barrer, five‐fold enhancement compared with pristine polymer membrane, with a good CO2/N2 selectivity of 36. Besides, the nanosized MOFs intensify their interaction with polymer chains, endowing the MMMs with good anti‐plasticization behaviour and stability, which advances practical application of MMMs in carbon capture.

Transformation from Knudsen diffusion to facilitated diffusion for CO2 in confined mass transfer channels of polyimide mixed matrix membranes

Incorporation of porous materials in a polymeric membrane is an effective strategy for improving the gas permeability of the resulting mixed matrix membranes (MMMs). However, effective improvement of selectivity of membrane toward CO2 separation is still a significant challenge due to the insufficient CO2 capture performance of porous materials. In this study, polyimide (PI)-based MMMs with enhanced CO2 capture performance were prepared for CO2 separation. First, an ionic liquid (IL) with a high affinity for CO2 was immobilized in the inner pore structures of two types of mesoporous silica (SiO2) molecules to form IL@SiO2 composites. These composites were used as nanofillers to construct the MMMs. The stable immobilization of IL inside the pores of the mesoporous SiO2 indicated that the IL@SiO2 and MMMs both exhibited higher adsorption selectivity for CO2. The gas solubility coefficient of the MMMs was positively proportional to their maximum gas adsorption capacity, which was determined by the gas adsorption capacity of the PI polymer and nanofillers. More interestingly, the diffusion coefficients of different gases in the MMMs were closely related to the confined mass transfer channels introduced by the nanofillers. The diffusion of CO2 in the confined mass transfer channels of MMMs was facilitated and N2 diffusion was slightly inhibited, which increased the diffusion selectivity of the resulting MMMs for CO2. Combined with Maxwell–Wagner–Sillar model calculations for gas permeation, it was confirmed that IL immobilization transformed the diffusion mode of CO2 in the confined mass transfer channels of the MMMs from Knudsen diffusion to facilitated diffusion. However, the immobilization of excessive ILs in the mesopores blocked the mass transfer channels of the MMMs, resulting in lower gas permeability and decreased CO2 separation selectivity.

Quaternized hollow TiO2-enhanced the dye adsorption capacity and photogenerated carrier separation for efficient reactive dye removal

Currently, titanium dioxide (TiO2) has been demonstrated as a significant photocatalyst for the efficient removal of reactive dyes in dyeing effluents. However, due to the easy recombination of photogenerated carriers and electrostatic repulsion with reactive dye, single TiO2 cannot achieve satisfactory removal efficiency to reactive dye which is commonly used in cellulose fibers dyeing. Therefore, we prepared hollow titanium dioxide (H-TiO2) by alkaline treatment etching method and introduced quaternary ammonium groups on the surface of H-TiO2 photocatalyst (QAS-H-TiO2) by nucleophilic addition reaction. Improving the adsorption capabilities of C. I. reactive red 2 (RR2) and simultaneously separating the photogenerated carriers via the nitrogen cation of the quaternary ammonium groups facilitated the enhancement of its RR2 removal. The experimental results indicated that the utilization of QAS-H-TiO2 substantially bolstered the removal efficiency of RR2. The impact of molecular structure of quaternary ammonium salts on the adsorption ability of RR2, and the mechanism of regulation for photogenerated carriers, were investigated. It was found that the grafting of the quaternary ammonium group enabled mass and electron transfer channels, resulting in faster adsorption of dyes and separation of photogenerated carriers. This study presents a novel approach for preparing efficient QAS-H-TiO2 for high-performance organic dye removal.

Encapsulation of lipase in zeolitic imidazolate framework-8 induced by polyethyleneimine to form a honeycomb structure with enhanced activity

Embedding an enzyme in the metal-organic frameworks (MOFs) gives good protection to the fragile enzyme. However, this may also restrain the enzyme activity because of the decreased substrate accessibility. Encapsulation of lipase AK from Pseudomonas fluorescens for preparing the enzyme-MOF composite (AK@ZIF-8-PEI) was performed through a new strategy based on polyethyleneimine and enzyme induced in-situ growth of zeolitic imidazolate framework-8 (ZIF-8). Characterizations indicate that AK@ZIF-8-PEI has a honeycomb structure and the hierarchical porosity formed during the preparation, which provides adequate mass transfer channels for catalytic applications. Activity evaluation shows that specific activity of AK@ZIF-8-PEI is 8-fold than the commercial lipase powder. AK@ZIF-8-PEI is demonstrated as an efficient catalyst in kinetic resolution of α-naphthol enantiomers through enantioselective transesterification. Within 12 h, the conversion and substrate enantiomeric excess (ees) reaches 49.8 % and 96.4 %, achieving an improved resolution than previous researches.

Trifunctional catalyst of FeCo,N-doped mixed-dimensional carbon for the high-performance zinc-air flow battery

Exploring efficient and highly stable non-precious metal trifunctional catalysts is imperative for the practical application of zinc-air flow batteries (ZAFBs) and overall water splitting (OWS). Herein, the FeCo and nitrogen-rich codoped one-dimensional carbon nanotubes cross-interpenetrated with birdhouse-like carbon nanosheets in mixed-dimensional carbon structure (FeCo,N-MDC) is constructed by a facile and universal method. Benefiting from the merits of hyper-dispersed FeCo-N/Ox and FeCo alloy active sites, high density of pyridine and graphitic nitrogen, ultra-high conducting carbon nanotubes, large surface area, and massive mass transfer channels can synergistically promote multifunctional catalysis. The resulting FeCo,N-MDC exhibits superior trifunctional activities with onset potential and half-wave potential of 0.994 V and 0.861 V for oxygen reduction reaction in 0.1 M KOH, oxygen evolution reaction and hydrogen evolution reaction overpotentials of 0.341 V and 0.272 V at 10 mA·cm−2 in 1 M KOH, respectively, and have long electrochemical stability. Moreover, the FeCo,N-MDC-based ZAFB has an open-circuit voltage of 1.517 V, a specific capacity of 808 mAh·g−1, the remarkable running stability for 300 h, which surpassed that of commercial Pt/C + RuO2 hybrid-driven device. Additionally, the hydrophilic FeCo,N-MDC, as both the anode and cathode electrodes, also display a hydrolysis reaction voltage of 1.603 V to deliver a current density of 10 mA·cm−2 and outstanding durability. What is more, the continuously mass-produced FeCo,N-MDC, and the alternative CoFe, N-MDC catalysts exhibit excellent performance in the same water-solvent environment. This effort presents a facile strategy for rationally designing economical and efficient mixed-dimensional catalysts for zinc-air flow batteries and more energy devices.

Hydrolytic hydrogen production behavior in NaCl solution of Mg and Mg-GO composite synthesized by mechanochemical reaction

With the help of the mechanochemical reaction (MCR) strategy, the composition optimization, structure regulation and surface modification of metallic Mg are realized by introducing GO in the high energy mechanical ball milling process to enhance the hydrogen production performance in NaCl solution. The synthetic process of Mg and Mg-GO composite by MCR is systematically optimized and the microstructure evolution as well as the hydrolytic hydrogen production behavior are investigated. Phase composition optimization and microstructure regulation can be effectively implemented during the MCR process. The response rate of the repeated hydrogen-filling MCR sample is faster than that of the single hydrogen-filling MCR sample. The hydrogen production rates at 298 K of 4, 8, 12, 16 and 20 h MCR Mg with repeated H2-filling can reach to 922, 934, 890, 917 and 1131 mL/g/min, respectively. The internal microstructure refinement, surface modification, moderate activity, appropriate particle size, surface defects and reasonable mass transfer channels of MCR 8 h Mg-GO composite are the reasons for the fast rates and high yields of hydrolytic hydrogen production. 365.3, 864.4 and 933.8 mL/g H2 can be produced by 8 h MCR Mg-GO composite within 1, 3 and 10 min, respectively. The hydrogen production rate of 8 h MCR Mg-GO composite is as high as ∼600 mL/g/min. Mechanochemical reaction strategy with catalyst is a useful method to improve the hydrolysis hydrogen production performance of metallic Mg when well matched with the added catalyst.

Carbon dots-based fluorescent molecularly imprinted photonic crystal hydrogel strip: Portable and efficient strategy for selective detection of tetracycline in foods of animal origin

Rapid, portable, and sensitive detection of tetracycline (TC) is crucial for the environment and human health. In this study, we developed carbon dots (CDs)-based fluorescent molecularly imprinted photonic crystal hydrogel (FMIPH) strips for TC detection in animal-derived foods. CDs emit fluorescent signals, and molecularly imprinted polymers provide specific recognition sites for TC. Inverse opal photonic crystals afford stable 3D macroporous mass transfer channels that considerably reduce binding time between TC and the strips. The portable FMIPH strip exhibited a linear fluorescence response to TC in the concentration range of 0.1–50 μg mL−1, with a detection limit of 0.067 μg mL−1. Good recoveries of TC (93.86–112.59%) were observed in TC-spiked commercially available pork, eggs, and milk. A combination of FMIPH strips with a portable fluorescent reading device could achieve sensitive, on-site, and real-time detection of TC in animal-derived foods.

Self‐Assembled Nanofibrous Hydrogels with Tunable Porous Network for Highly Efficient Solar Desalination in Strong Brine

AbstractHydrogel‐based solar evaporators (HSEs) emerged as energy‐efficient designs for water purification due to the reduced vaporization enthalpy in the hydrated polymeric network. However, it remains challenging for HSEs to achieve stable performance in desalination, partly due to the tradeoff between desired evaporation dynamics and salt tolerance. Here, composite hydrogels with tunable self‐assembled nanofiber networks are exploited for the engineering of solar evaporators with both high evaporation performance and resistance to salt accumulation. The nanofibrous hydrogel solar evaporators (NHSEs) present an intrinsic open network with high porosity, above 90%, enabling continuous water channels for efficient mass transfer. Theoretical modeling captures the complex nexus between microstructures and evaporation performance by coupling water transfer, thermal conduction, and vaporization enthalpy during evaporation. The mechanistic understanding and engineering tuning of the composites lead to an optimum configuration of NHSEs, which demonstrate a stable evaporation rate of 2.85 kg m−2 h−1 during continuous desalination in 20% brine. The outstanding performance of NHSEs and the underlying design principles may facilitate further development of practical desalination systems.

Macroporous Hydrogels Prepared By Ice Templating: Developments And Challenges†

Comprehensive SummaryMacroporous hydrogels are water‐swollen polymer networks with porous structures beyond the mesh size. They provide high specific surface areas and hieratical mass transfer channels which are desired for emerging applications including cell culturing, bio‐separation, and drug delivery. A variety of approaches have been developed to fabricate macroporous hydrogels, including gas foaming, porogen templating, phase separation, 3D printing, etc. Alternatively, ice templating utilizes the crystallization of water as the porogenation mechanism which doesn't need the leaching of porogens. The porous structures can be easily manipulated by controlling the morphology of ice (size, orientation, etc.) upon freezing. In addition, mechanical properties of obtained porous hydrogels are commonly better than those of other macroporous hydrogels since the pore walls are made up of concentrated polymers through the freezing step. These three characteristics, that is, the green process, the highly tunable morphology, and the enhanced mechanical strength make the ice templating a superior porogenation method. This review expects to give an overview on macroporous hydrogels prepared by the ice templating, namely, cryogels. Recent progresses on emerging cryo‐porogenation methods are introduced. Fundamental understanding concerning the behavior of the polymer chains during the formation of ice is proposed. Future opportunities on the application of cryogels are prospected.

Tailoring the interlayer channel structure of graphene oxide membrane with conjugated cationic dyes for butanol dehydration

For the design of high-performance GO membrane, the structure of intercalation material is a key consideration due to its decisive impacts on nanosheet assembly and mass transfer channel structure. Herein, conjugated cationic dyes were incorporated into GO interlayer channels. The large π-conjugated structure and delocalized positive charge can form π-π and electrostatic interactions with the non-oxidized region and negatively-charged group on GO nanosheet, respectively. Through interlayer cross-linking, the nanosheet orientation and interlayer bonding can be improved, conferring the membrane with higher anti-swelling capacity, more ordered channel structure, and controllably tailored interlayer d-spacing. The electron cloud density and planar structure of cationic dye molecules are evidenced to be critical in influencing membrane structure and separation performance. After incorporating conjugated cationic dyes, the separation factor for water/butanol separation can reach 5.3 times of that of pristine GO membrane, while the permeate flux also increases by 20%. This work provides a category of promising intercalation materials for GO membranes with good potential application in butanol dehydration.

Controlled One-Step Synthesis of MOF-on-MOF Cocatalysts for Two-Channel Electrocatalytic Conversion of CO2 to Formic Acid.

The synthesis of efficient and highly selective catalysts and rational reactor design play decisive roles in the industrial application of the electrocatalytic carbon dioxide reduction reaction (CO2 RR). In this study, a dual-metal-organic framework (MOF) copper-based catalytic electrode is designed and prepared in one step by in situ synthesis on a foamed copper substrate. The MOF-on-MOF structure can effectively inhibit the generation of H2 and CO, and further enhance the selectivity of HCOOH. Furthermore, by using cheap and durable poly(tetrafluoroethylene) (PTFE) instead of an expensive and fragile GDE, the optimized reactor design improves the stability and durability of the gas channel and the replaceability of the electrode. The structure-optimized reactor has a maximum Faradaic efficiency of 89.2% in neutral medium, and an average current density of 26.1mAcm-2 in the flow cell, which has comparable performance to a GDE and can continue to operate stably. The use of PTFE improves the service life of the gas mass transfer channel, and the independent catalytic electrode can provide good catalytic efficiency. These results provide new insights into the reaction mechanism of structurally recombined double MOFs and PTFE-optimized CO2 RR reactor designs, providing technical support for the practical industrial application of the CO2 RR.

Cryogels from Pt/γ-Fe2O3 and Pd/γ-Fe2O3 NPs as Promising Electrocatalysts for Ethanol Oxidation Reaction

Cryogels from noble metal NPs have proven to be highly efficient catalysts due to their high specific surface area which increases the mass transfer channels and catalytic active sites. By using metal oxides as co-catalysts, the costs of the material can be significantly reduced, while the catalytic activity can remain the same or even improve due to synergetic effects. In this work, we synthesize different cryogel thin films supported on modified ITO substrates from Pt, Pd nanoparticles (NPs), and mixtures of these noble metals with γ-Fe2O3 NPs in a very low concentration (1 wt% of the noble metal). Structural and elemental analysis of the samples are performed, along with the measurement and analysis of their catalytic activity. The electrocatalytic activity of the cryogels towards ethanol oxidation reaction (EOR) in alkaline media was evaluated by means of cyclic voltammetry. By mixing γ-Fe2O3 NPs with Pt or Pd NPs in the cryogel structure, we observe increased tolerance against poisonous surface intermediates produced during the EOR. Moreover, we observe an increase in the catalytic activity towards EOR in the case of the 1 wt% Pd/γ-Fe2O3 cryogel, making them promising materials for the development of direct ethanol fuel cells.

Oxygen-doped graphite carbon nitride as a fiber coating material for headspace solid-phase microextraction of organic phosphate esters

Efficient enrichment of trace organic phosphate ester (OPEs) pollutants from complex matrixes is essential for chromatographic analysis. Herein, oxygen-doped graphite carbon nitride (denoted as O-g-C3N4) was fabricated though thermal polycondensation of urea using H2O2 as an oxygen source. The resulting O-g-C3N4 material was loose and had homogeneous pores structure, with a specific surface area of 73.74 m2/g. The O-g-C3N4 was served as fiber coating material to create solid phase microextraction (SPME) device, with silica sol as adhesive for OPEs determination. Owing to the well-developed porosity of O-g-C3N4, which provides effective mass transfer channels for OPEs, the whole SPME procedure could be accomplished within 25 min. The O-g-C3N4 fiber coating offers excellent mechanical strength and high stability and being workable after 180 sampling. The developed approach revealed a good linearity for OPEs in ultrapure water at the concentrations of 0.01–100 µg/L with the LODs between 0.001 µg/L and 0.003 µg/L. In addition, relative recoveries of 85.24% ∼99.73% were achieved in tap water and river water. These findings suggested that the oxygen-doped g-C3N4 material has potential for headspace SPME of trace OPEs in various matrixes.

Hexagon flower-shaped architectures constructed of Fe-composited lanthanum hydroxide nanosheets for superior phosphate removal: Synthesis and mechanism study

In response to phosphorus pollution, developing functional materials for phosphate adsorption is an ideal method to reach an ultralow phosphate concentration in effluent. Herein, a hexagon flower-shaped architecture constructed of Fe-composited lanthanum (La)-based hydroxide nanosheets was fabricated from LaFe cyano-bridged metal frameworks (CMs) via a self-templating strategy using NH3‧H2O as the conversion reagent. The ion exchange process using weak alkaline reagent enables the formation of secondary nanosheets on the architecture, thus leading to a high surface area and a large number of mesopores that provide abundant active sites and mass transfer channels for phosphate adsorption. A superior adsorption capacity of 127.5 mg P/g can be obtained on the La/Fe-based architecture, which also shows satisfactory applicability over a wide pH range. A ligand exchange between -OH and phosphate ions is verified as the main adsorption mechanism, which properly accounts for its excellent selectivity for phosphate adsorption when coexisting with other anions/cations and natural organic matters. Overall, the present study provides a new method for constructing porous La-based hydroxide materials for phosphorus control in water.

Constraining mass transfer and common-envelope physics with post-supernova companion monitoring

ABSTRACT We present an analytical model that describes the response of companion stars after being impacted by a supernova in a close binary system. This model captures key properties of the luminosity evolution obtained from 1D stellar evolution calculations fairly well: a high-luminosity plateau phase and a decaying tail phase. It can be used to constrain the pre-supernova binary properties from the observed photometry of the companion star several years after the explosion in a relatively simple manner. The derived binary parameters are useful in constraining the evolutionary scenario for the progenitors and the physics of binary interactions. We apply our model to some known stripped-envelope supernova companions (SN1993J, SN2001ig, SN2006jc, SN2011dh, and SN2013ge). Combined with other observational constraints such as the pre-supernova progenitor photometry, we find that SN1993J and SN2011dh likely had relatively massive companions on wide orbits, while SN2006jc may have had a relatively low-mass companion on a tight orbit. This trend suggests that Type IIb supernova progenitors evolved from stable mass transfer channels and Type Ibc progenitors may have formed from common-envelope channels. The constraints on orbital separation helps us probe the highly uncertain common-envelope physics for massive stars, especially with multiple epochs of companion observations. We also highlight possible limitations of our model due to the assumptions made in the underlying 1D models.

Ultrathin carbon-embedded nickel oxide layer encapsulating sponge-like nickel for alkaline hydrogen oxidation

For hydrogen oxidation reaction (HOR), the kinetics in alkaline media is much sluggish than that in acidic media, and its catalyst mainly relies on noble metal-based materials, so it is of great significance to develop non-noble metal-based efficient HOR catalysts. In this work, based on the strong coordination interaction between transition metal cation and ligand molecule with lone pair electrons, a novel type of nickel-based aerogel-like material (Ni@NiO/C-400) is elaborately constructed. The material is composed of a spongy three-dimensional skeleton and a coated ultrathin layer，while the former is formed by the interconnection of metallic nickel nanorods and the latter contains nickel oxide species and embedded graphitic carbon island. The Ni@NiO/C-400 present certain exchange current density, kinetic current density and mass activity, implying obvious HOR activity. Based on the physicochemical characterization results, the Ni/NiO interface layer is formed on the catalyst surface and is supposed to provide moderate binding energy for H∗ and OH∗ and proposed to be a crucial origin of activity. Due to the accessible adsorption of intermediate species, exposure of active sites and protection for metallic nickel from over-oxidation, along with the favorable electronic conductivity enabled by the embedded graphitic carbon, the unique uneven thin layer on the catalyst surface also plays an important role in catalyzing HOR. Additionally, the three-dimensionally porous nickel framework endows abundant channels for electron transport and mass transfer during alkaline HOR process. The material-architecting strategy proposed in this work paves a new avenue for the rational design of non-noble metal catalysts.

Defective Carbon Derived Using a Dissolution-Recrystallization Strategy for Oxygen Reduction Electrocatalysis.

Dopant-free defective carbon electrocatalysts have been considered as promising alternatives to traditional precious metal electrocatalysts recently. Compared with precious metal catalysts and transition-metal catalysts, since there are no metals doped, electrochemical devices assembled with dopant-free defective carbons are free from environmental pollution and subsequent recovery problems. In order to obtain abundant carbon defects with high-intrinsic catalytic activity, the synthesis of dopant-free defective carbons requires complex and harsh preparation conditions. Therefore, the construction of active defects with efficient utilization, especially through a simple process, is still a great challenge for the development of dopant-free defective carbon electrocatalysts. Herein, dissolution-recrystallization strategy was employed to design Zn-MOF-74 precursors for the synthesis of dopant-free defective carbons, realizing the synchronous manipulation of high ratio of carbon defects and highly exposed mass transfer channels. One-dimensional porous defective carbon nanorods (d-CNRs), which exhibited excellent oxygen reduction reaction (ORR), electrocatalytic activity, and molecular selectivity, were synthesized by directly carbonizing rodlike Zn-MOF-74 precursors. Attributed to the dissolution-recrystallization strategy, with the activation of in situ-formed ZnO, the synthesized d-CNRs exhibited unique pore-crack nested porous structures, which carried abundant defects as activity sites for ORR and showed a surprisingly high specific surface area of 2459 m2/g with a high ratio of mesopores. d-CNRs also showed promising applications in Zn-air batteries with a stable long-term discharge of no obvious voltage drop after 60 h. The dissolution-recrystallization strategy provided a simple controllable pathway for the efficient construction of dopant-free defective carbon electrocatalysts.

Constructing low-friction mass transfer channel in laminar graphene oxide membrane for efficient molecular separation with enhanced permeability

In recent years, graphene oxide (GO) has attracted increasing interest in fabricating next-generation separation membranes. The perm-selectivity of laminar GO membrane is generally determined by their interlayer nanochannel structure. Herein, we used a new molecule called 5, 5′-diamine-2, 2′-biphenol (BIPOL-NH2) as the intercalator of laminar GO-based membrane to construct low-friction interlayer mass transfer channels. The aromatic BIPOL-NH2 molecules act as hydrophobic side walls of the mass transfer channels between adjacent GO nanosheets, reducing the interaction between water molecules and channel structure, thereby enhancing water permeability of GO membranes. This was confirmed by the further molecular dynamics simulation. Compared with pristine GO membrane, the BIPOL-GO membrane showed a water permeability increase by a factor of about 3 (up to 72.4 L m-2h−1 bar−1), which was consistent with our simulation results. Also, it represented excellent dye/salt separation performance (the selectivity of NaCl/CR is more than 117.2) and good structural stability. Overall, our work provides a novel and efficient approach to modify GO-based membranes for enhanced permeability.