Uniform Nanopores Research Articles

Li+/Mg2+ separation by membrane separation: The role of the compensatory effect

Lithium extraction from salt-lake brines by membrane separation has become a trend to satisfy the global increasing market demand of lithium. Although some progresses have been achieved in membrane fabrication, traditional theories like steric hindrance and Donnan effect struggle to comprehensively explain why Li+/Mg2+ separation factor and Li + permeation could be simultaneously improved, which is also one of the key challenge for this technology. By using uniform nanopores in covalent organic frameworks as the model system, we herein demonstrate that the compensatory effect of pore-wall groups on ionic hydration plays a significant role in Li+/Mg2+ separation: compensation to Li+ second hydration shells is beneficial to Li+ permeation while that to first shells is counterproductive; meanwhile less compensation to Mg2+ hydration is more advantageous to rejecting Mg2+. Via non-equilibrium molecular dynamics simulations, moderately-electropositive nanopores are discovered to be capable of simultaneously enhancing separation factor and Li+ permeation. Balanced ratio of hydrophilic and positively-charged groups on pore walls ensures the nanopores possess suitable compensatory effects that can accelerate Li + permeation while rejecting Mg2+. In contrast, hydrophobic, hydrophilic and strongly-electropositive nanopores are not competent due to their excessively weak or strong compensatory effects. The findings and understandings can be also applicable to other kinds of nanoporous materials and help to inspire other ion-separation applications.

3D Artificial Solid-Electrolyte Interphase for Lithium Metal Anodes Enabled by Insulator-Metal-Insulator Layered Heterostructures.

Despite considerable efforts to prevent lithium (Li) dendrite growth, stable cycling of Li metal anodes with various structures remains extremely difficult due to the direct contact of the liquid electrolyte with Li. Rational design of solid-electrolyte interphase (SEI) for 3D electrodes is a promising but still challenging strategy for preventing Li dendrite growth and avoiding lithium-electrolyte side reactions in Li-metal batteries. Here, a 3D architecture is constructed with g-C3 N4 /graphene/g-C3 N4 insulator-metal-insulator sandwiched nanosheets to guide uniform Li plating/stripping in the van der Waals gap between the graphene and the g-C3 N4 , and the function of which can be regarded as a 3D artificial SEI. Li deposition on the surface of g-C3 N4 is suppressed due to its insulating nature. However, its uniform lithiophilic sites and nanopore channels enable homogeneous lithium plating between the graphene and the g-C3 N4 , prohibiting the direct contact of the electrolyte with the Li metal. The use of the g-C3 N4 -layer-modified 3D anode enables long-term Li deposition with a high Coulombic efficiency and stable cycling of full cells under high cathode loading, limited Li excess, and lean electrolyte conditions. The concept of a 3D artificial SEI will shed light on developing safe and stable Li-metal anodes.

High-efficient hydrogen purification through two-dimensional CrI3 membrane via a first-principles calculation

Porous two-dimensional materials are potential candidates for the realization of gas separation, which are crucial for developing clean energy sources. Here, we found that CrI3 monolayer which has uniform nanopores around 2.9 Å in intrinsic structures can simultaneously fulfill the requirements of both high permeability and high selectivity. Our results show that the diffusion energy barriers of H2 and impurity gases (N2, CO, CO2, H2O and CH4) passing through the nanopores of CrI3 monolayer are 0.27 eV, 1.49 eV, 1.31 eV, 1.54 eV, 0.87 eV and 3.88 eV, respectively, which indicates that these impurity gases hardly pass through the CrI3 monolayer and H2 can be effectively separated from the gases mixture. Also, at the temperature of 300 K, the permeability of H2 (1 × 10−5 mol·m−2·s−1·pa−1) is significantly larger than the minimum acceptable permeability for industry (6.7 × 10−9 mol·m−2·s−1·pa−1). Thus, the CrI3 monolayer is a promised candidate of the hydrogen purification for the future applications.

A separator based on natural illite/smectite clay for highly stable lithium-sulfur batteries

In spite of high theoretical specific capacity and specific energy of lithium-sulfur (Li-S) batteries, the poor cycle stability caused by polysulfides shuttle severely hinders their real-world applications. Here, a natural clay mineral (illite/smectite, ISC) and carbon black (C) coated Celgard@2400 (ISC/C@Celgard) separator is reported. The separator shows super-electrolyte-philicity and good mechanical stability. The low-cost and eco-friendly ISC with abundant –OH groups can quickly trap a lot of polysulfides by Li–O and Li–S bonding with polysulfides. The ISC/C layer with uniform nanopores can also inhibit polysulfides shuttle by physical shield. Moreover, good electrical conductivity of the ISC/C layer can reactivate the adsorbed polysulfides and thus enhance S utilization. So, the separator endows the Li-S battery with very high initial reversible capacity (1322 mA h g−1) at 0.1 C and excellent cycle stability with low capacity decay rate (0.054% per cycle) during 500 cycles at 1.0 C. Furthermore, a very high areal capacity (5.9 mAh cm−2) is achieved for the battery composed of the separator and the self-supporting high S loading (8.9 mg cm−2) CNT/S cathode at 0.32 mA cm−2. This study opens the possibility of developing advanced separators using natural clay minerals for highly stable Li-S batteries.

Formation of a self-organized nanoporous structure with open-top morphology on 304L austenitic stainless steel

A novel and simple method is reported for producing a self-organized nanoporous structure on austenitic stainless steel (SUS-304L) with open-top morphology. Uniform nanopores with a quasi-hexagonal arrangement were obtained on a very large scale with no crack formation by using single-step anodization. Electropolishing of SUS-304L in ethylene glycol monobutyl ether and perchloric acid electrolyte prior to anodization was the key factor to obtain self-organized and regularly ordered nanopores. Under optimized electropolishing conditions, a honeycomb-like patterned morphology of shallow nanopores was developed on the surface of SUS-304L. Anodization of the patterned morphology in ethylene glycol-based electrolyte generated self-organized and ordered nanopores. Morphology, structure and chemical analyses of the samples were carried-out using FESEM, EDAX, XRD, XPS and ToF-SIMS. FESEM images revealed the formation of hexagonal and ordered nanopores with uniform diameter. EDAX analysis confirmed that the nanoporous oxide layer is composed of iron, chromium, nickel and oxygen. A blue energy shift in the XPS spectra was observed after annealing, which is attributed to the absence of F-species. ToF-SIMS depth profile analysis confirmed the high content of chromium oxide on the surface of the nanoporous oxide layer. The hexagonal nanoporous ordered morphology is useful in anti-corrosion and decoration applications.

Polyamide nanofiltration membrane with highly uniform sub-nanometre pores for sub-1\u2009\xc5 precision separation

Separating molecules or ions with sub-Angstrom scale precision is important but technically challenging. Achieving such a precise separation using membranes requires Angstrom scale pores with a high level of pore size uniformity. Herein, we demonstrate that precise solute-solute separation can be achieved using polyamide membranes formed via surfactant-assembly regulated interfacial polymerization (SARIP). The dynamic, self-assembled network of surfactants facilitates faster and more homogeneous diffusion of amine monomers across the water/hexane interface during interfacial polymerization, thereby forming a polyamide active layer with more uniform sub-nanometre pores compared to those formed via conventional interfacial polymerization. The polyamide membrane formed by SARIP exhibits highly size-dependent sieving of solutes, yielding a step-wise transition from low rejection to near-perfect rejection over a solute size range smaller than half Angstrom. SARIP represents an approach for the scalable fabrication of ultra-selective membranes with uniform nanopores for precise separation of ions and small solutes.

Breath figure-derived porous semiconducting films for organic electronics.

Porous semiconductor film morphologies facilitate fluid diffusion and mass transport into the charge-carrying layers of diverse electronic devices. Here, we report the nature-inspired fabrication of several porous organic semiconductor-insulator blend films [semiconductor: P3HT (p-type polymer), C8BTBT (p-type small-molecule), and N2200 (n-type polymer); insulator: PS] by a breath figure patterning method and their broad and general applicability in organic thin-film transistors (OTFTs), gas sensors, organic electrochemical transistors (OECTs), and chemically doped conducting films. Detailed morphological analysis of these films demonstrates formation of textured layers with uniform nanopores reaching the bottom substrate with an unchanged solid-state packing structure. Device data gathered with both porous and dense control semiconductor films demonstrate that the former films are efficient TFT semiconductors but with added advantage of enhanced sensitivity to gases (e.g., 48.2%/ppm for NO2 using P3HT/PS), faster switching speeds (4.7 s for P3HT/PS OECTs), and more efficient molecular doping (conductivity, 0.13 S/m for N2200/PS).

Fabrication and synthesis of uniform TiO2 nanoporous and nanotubular structures on dual-phase Ti–6Al–4V alloy using electron-beam irradiation

Developing homogeneous TiO2 nanoporous arrays (NPAs) and nanotubular arrays (NTAs) on biphasic Ti alloys is challenging. The present study used large-pulse electron-beam (LPEB) irradiation prior to anodizing, and ascertained its effectiveness for developing homogeneous TiO2 NPAs and NTAs on a dual (α + β)-phase Ti–6Al–4V alloy for the first time. The morphological features, structural characteristics, and corrosion resistance of the TiO2 NTAs formed on the LPEB-irradiated Ti–6Al–4V alloy were compared to those obtained on the untreated alloy. The irradiation transformed the dual (α + β)-phase structure into a single α′-martensite phase with a uniform distribution of alloying elements, and enabled the formation of a smooth surface finish with reduced surface roughness. The modified surface facilitated the formation of homogenous NPAs and NTAs. Annealing in air at 500 °C for 2 h transformed the amorphous as-prepared TiO2 NTAs into a mixture of anatase and rutile phases. Despite the appearance of cracks and an increase in intertubular spacing, the NTAs did not collapse. The NTAs formed on the untreated and LPEB-irradiated Ti–6Al–4V alloy provided better corrosion protection than their nonanodized counterparts.

Preparation and Characterization of Nanoporous Alumina as Ceramic Membrane Materials

To meet growing electricity demand and greenhouse gas emission limitation in the future, it is urgency to improve existing power plant more efficientand less CO2 emission. Oxygen combustion instead of air combustion is quite good to raise up the fossil fuels efficiency. And separation oxygen from the air by ionic conductance at high temperatures is promising in large fuel power plants. Ionic separation processes by ceramic dense membrane need a good support porous membranes with good mechanical and permeable property. Present research reports the porous alumina with nanoporous structure was prepared by vacuum filtration and rapid sintering as a kind of porous support layer in the oxygen ceramic separation membrane. The microstructure of nanoporous alumina was analysed, the mechanical properties and gas permeability were tested and compared with some conventional pore-former method made porous ceramics. The uniform nanopores alumina ceramics with both high strength and high permeability achieved by a vacuum filtrate and rapid sintering method is a candidate as the porous support application in fuel cell and gas separation field.

Immunotherapeutic silk inverse opal particles for post-surgical tumor treatment

Recurrence of malignant tumor after surgical resection is the main reason of cancer treatment failure. Here, a novel kind of silk inverse opal particles (SIOPs) for post-surgical tumor treatment is presented, and it is derived from colloid crystal bead templates by negatively replicating. Because of their abundant uniform nanopores, interconnected nanochannels and excellent biocompatibility, SIOPs could not only carry great amount of anti-tumor drugs for tumor therapy, but also could provide support for cell adhesion, proliferation and differentiation as the 3D spherical scaffolds which is beneficial to the tissue repair at resection sites. It is demonstrated that the antibody drugs could maintain their high biological activity without any influences during the preparation of SIOPs and these particles were able to enhance the therapeutic efficacy and promote tissue regeneration after surgical resection with their multifunctional features. These prominent properties indicate the great potentials of SIOPs as a promising strategy for efficient postoperative cancer therapy.

Large‐Area Aminated‐Graphdiyne Thin Films for Direct Methanol Fuel Cells

A two-dimensional (2D) carbon nanofilm with uniform artificial nanopores is an ideal material to ultimately suppress the fuel permeation in the proton exchange membrane fuel cells. Graphdiyne has great mechanical strength, high dimensional stability, and controllable nanopores, and has good prospects to play this crucial role. It is found that graphdiyne nanofilm with amino groups and natural nanopores can be easily prepared with high integrity. The aminated graphdiyne has good compatibility with the Nafion matrix owing to the acid-base interaction between them. The excellent comprehensive properties of graphdiyne in selectivity, dimensional stability, and integrity effectively improve the power performance and stability of fuel cells at wide temperature. Our results can be developed into a universal method that can easily realize the selective separation of ions and small molecules, and open a new way for the emerging applications in green energy.

Hierarchically porous structured carbon derived from peanut shell as an enhanced high rate anode for lithium ion batteries

Abstract In recent years, biomass-derived carbon in the energy storage system has attracted tremendous attention due to low cost, scalable, meso/microporous nature. Here we describe the synthesis of peanut shell activated carbon (PSAC) by scalable and low power microwave method using KOH as an activation agent. The structural, surface area, porosity, and morphological properties of PSAC are characterized by different techniques such as XRD, Raman, XPS, N2 adsorption/desorption, FESEM and HRTEM analysis. FESEM and HRTEM confirm the highly distributed interconnected hierarchically porous structure with uniform nanopores over the surface and the achieved high surface area of PSAC is 525.685 m2 g−1. Furthermore, the PSAC is explored as an anode electrode material for Li-ion batteries (LIBs). The obtained reversible capacity is 680 mAh g−1 at 0.05 C rate after 100 cycles. The achieved rate capability, high reversible capacity and stability of the PSAC electrode mainly depend on its excellent conductivity, high surface area, rich porosity, more edges defects sites and hierarchically porous structured morphology.

Rice Husk‐Based 3D Porous Silicon/Carbon Nanocomposites as Anode for Lithium‐Ion Batteries

Silicon/carbon (Si/C) nanocomposites with 3D porous structure are prepared by a high‐temperature hydrothermal treatment and subsequent magnesiothermic reduction using rice husks (RHs) and NaCl as Si/C sources and potential porogens. In this strategy, interconnected and uniform nanopores are introduced into RHs under the assistance of NaCl and high pressure while the organic components are carbonized, and the intermediate products (porous SiO2/C nanocomposites) are formed. The porous structure is maintained well during the high‐temperature hydrothermal treatment. After the magnesiothermic reduction of the porous SiO2/C nanocomposites, a 3D porous Si/C nanocomposite is formed, which provides rapid transferring channels for the lithium ions and accommodates volumetric changes during electrochemical cycling, leading to an improved electrochemical performance.

In vitro and in vivo hemocompatibility assessment of ultrathin sulfobetaine polymer coatings for silicon-based implants.

Highly uniform silicon nanopore membranes were developed for applications in implantable bioartificial organs. A robust, readily scalable, non-fouling surface coating is required to enhance silicon nanopore membrane hemocompatibility. However, the coating must be ultrathin to keep the nanopores from occluding. Recently, zwitterionic brush polymers have demonstrated significantly lower fouling under biological conditions. In this study, we explore ultrathin zwitterionic poly(sulfobetaine methacrylate) (pSBMA) surface coating at sub-5 nm thickness. Membrane hydraulic permeability was measured before and after surface modification of silicon nanopore membranes, and pores were found to be patent and in agreement with coating thickness measurements. Coating stability was analyzed under biological shear as well as under blood flow in vitro and in vivo. Following exposure to shear over 24 h, coatings were characterized via X-ray photoelectron spectroscopy, goniometry, and ellipsometry, and found to survive biological shear. In vitro blood experiments with fresh human blood as well as in vivo 7-day and 26-day implants in a porcine model demonstrate minimal platelet adhesion and activation with pSBMA surface modification compared to unmodified silicon exposed to fresh human blood in vitro. These results demonstrate that ultrathin pSBMA surface modification is a viable choice for application in blood contacting implants with critical nanoscale features.

Lignin-Derived Nitrogen-Doped Porous Carbon as a High-Rate Anode Material for Sodium Ion Batteries

Nitrogen-doped carbon anode materials have been prepared by a hard-template (SiO2 nanoparticles) method, in which alkali lignin-derived azo polymer (AL-azo-NO2) was used as a low-cost carbon precursor. The as-prepared N-doped carbon materials show a honeycomb-like morphology with uniform nanopores. These materials are able to reversibly insert Na+ ions and show promising cycling performance. In particular, the porous carbon material with larger surface area and pore volume delivers a higher initial capacity of 205 mAh g−1 in the voltage range of 0.01–2 V at 50 mA g−1, compared to the material with lower surface area and pore volume (only 155 mAh g−1). The former also exhibits much better rate capability than the latter. Even at a high current density of 1 A g−1, it shows a high specific capacity of 101 mAh g−1 after 1100 cycles, which retains 92% of its initial capacity. Electrochemical impedance spectroscopy (EIS) results prove that the enhanced electrochemical performance is attributed to the improved Na+-ions kinetics in this material. This work presents an alternative approach for the synthesis of high-rate carbonaceous anode materials for sodium ion batteries from low cost and sustainable feedstock.

Two‐Step Activated Carbon Cloth with Oxygen‐Rich Functional Groups as a High‐Performance Additive‐Free Air Electrode for Flexible Zinc–Air Batteries

AbstractA flexible air electrode (FAE) with both high oxygen electrocatalytic activity and excellent flexibility is the key to the performance of various flexible devices, such as Zn–air batteries. A facile two‐step method, mild acid oxidation followed by air calcination that directly activates commercial carbon cloth (CC) to generate uniform nanoporous and super hydrophilic surface structures with optimized oxygen‐rich functional groups and an enhanced surface area, is presented here. Impressively, this two‐step activated CC (CC‐AC) exhibits superior oxygen electrocatalytic activity and durability, outperforming the oxygen‐doped carbon materials reported to date. Especially, CC‐AC delivers an oxygen evolution reaction (OER) overpotential of 360 mV at 10 mA cm−2 in 1 m KOH, which is among the best performances of metal‐free OER electrocatalysts. The practical application of CC‐AC is presented via its use as an FAE in a flexible rechargeable Zn–air battery. The bendable battery achieves a high open circuit voltage of 1.37 V, a remarkable peak power density of 52.3 mW cm−3 at 77.5 mA cm−3, good cycling performance with a small charge–discharge voltage gap of 0.98 V and high flexibility. This study provides a new approach to the design and construction of high‐performance self‐supported metal‐free electrodes.

Size Fractionation of Fluorescent Graphene Quantum Dots Using a Cross-Flow Membrane Filtration System.

Graphene quantum dots (GQDs) have received great attention as optical agents because of their low toxicity, stable photoluminescence (PL) in moderate pH solutions, and size-dependent optical properties. Although many synthetic routes have been proposed for producing GQD solutions, the broad size distribution in GQD solutions limits its use as an efficient optical agent. Here, we present a straightforward method for size fractionation of GQDs dispersed in water using a cross-flow filtration system and a track-etched membrane with cylindrical uniform nanopores. The GQD aqueous suspension, which primarily contained blue-emitting GQDs (B-GQDs) and green-emitting GQDs (G-GQDs), was introduced to the membrane in tangential flow and was fractionated with a constant permeate flow of about 800 L m−2 h−1 bar−1. After filtration, we observed a clear blue PL spectrum from the permeate side, which can be attributed to selective permeation of relatively small B-GQDs. The process provided a separation factor (B-GQDs/G-GQDs) of 0.74. In the cross-flow filtration system, size-dependent permeation through cylindrical nanochannels was confirmed by simulation. Our results demonstrate a feasible method facilitating size fractionation of two-dimensional nanostructures using a cross-flow membrane filtration system. Since membrane filtration is simple, cost-effective, and scalable, our approach can be applied to prepare a large amount of size-controlled GQDs required for high performance opto-electronics and bio-imaging applications.

Porous anodic oxide film with self-healing ability for corrosion protection of aluminum

Nanopores in aluminum oxide film served as vessels for corrosion inhibitor to add self-healing ability. Aluminum oxide films were immersed into a solution containing corrosion inhibitor to fill the nanopores. To monitor polarization resistance, the aluminum oxide film was coated with polymer, which was then scratched with a knife-edge. Uniform and large nanopores demonstrated a higher level of polarization resistance. The corrosion inhibitor was released in two steps: a large release due to dissolution was followed by a more sustained release due to corrosion inhibitor desorption.

Constructing Universal Ionic Sieves via Alignment of Two-Dimensional Covalent Organic Frameworks (COFs).

The shuttle effect of electrode materials always leads to capacity loss and poor cycle life of batteries. Two-dimensional (2D) covalent organic frameworks (COFs) with uniform and controllable nanopores provide a promising strategy for fabricating ionic sieves to inhibit the shuttle effect. However, the insoluble nature of COFs made it difficult to fabricate compact and ordered membranes of COFs. Herein, we report a novel method for facilely anisotropic ordering of 2D COFs via depositing COFs onto graphene. The resulted double-layer membranes acting as ionic sieves impressively inhibit the shuttle effect and exhibit versatility to both organic sodium-ion batteries and Li-S batteries, leading to high cyclability.

Constructing Universal Ionic Sieves via Alignment of Two‐Dimensional Covalent Organic Frameworks (COFs)

AbstractThe shuttle effect of electrode materials always leads to capacity loss and poor cycle life of batteries. Two‐dimensional (2D) covalent organic frameworks (COFs) with uniform and controllable nanopores provide a promising strategy for fabricating ionic sieves to inhibit the shuttle effect. However, the insoluble nature of COFs made it difficult to fabricate compact and ordered membranes of COFs. Herein, we report a novel method for facilely anisotropic ordering of 2D COFs via depositing COFs onto graphene. The resulted double‐layer membranes acting as ionic sieves impressively inhibit the shuttle effect and exhibit versatility to both organic sodium‐ion batteries and Li‐S batteries, leading to high cyclability.