Nanoscale Porosity Research Articles

Interfacial engineered, hierarchically porous, and underwater superelastic nanofibrous aerogels with rime-mimetic structure for superior micropollutant extraction

Developing nanofibrous aerogels with high surface area, nanoscale porosity, and robust underwater stability has been considered as one of the most promising strategies for designing the next-generation of high-efficiency extraction media, yet still facing great challenges. Herein, we report a size rearrangement of porous organic polymers (POPs) into superelastic rime-mimetic structured aerogels based on bacterial cellulose nanofibers (BCNs)-assisted interfacial engineering strategy. This strategy facilitates micro-interlocking between POP and BCN, significantly enhancing the attaching strength of POP particles at the POP/BCN interface. Thus, the optimized aerogels (PNAs) exhibit excellent underwater elasticity and compression fatigue resistance (∼0% plastic deformation after 500 compression cycles), as well as high BET surface area (305.44 m2/g) and hierarchical porosity (containing micro/meso/macropores), mainly due to the ultrahigh loading of POP particles (83.33 wt%). Given the possession of the abovementioned features and the careful selection of elution solvents guided by Hansen solubility parameter theory, PNAs exhibit a superior micropollutant adsorption capability (∼250 mg/g) and elution efficiency (concentrate sample volume by 50 times). The successful preparation of such material could inspire the development of next-generation hierarchically porous nanofibrous aerogel-based extraction media for water treatment.

Customized Nanostructured Ceramics via Microphase Separation 3D Printing.

To date, the restricted capability to fabricate ceramics with independently tailored nano- and macroscopic features has hindered their implementation in a wide range of crucial technological areas, including aeronautics, defense, and microelectronics. In this study, a novel approach that combines self- and digital assembly to create polymer-derived ceramics with highly controlled structures spanning from the nano- to macroscale is introduced. Polymerization-induced microphase separation of a resin during digital light processing generates materials with nanoscale morphologies, with the distinct phases consisting of either a preceramic precursor or a sacrificial polymer. By precisely controlling the molecular weight of the sacrificial polymer, the domain size of the resulting material phases can be finely tuned. Pyrolysis of the printed objects yields ceramics with complex macroscale geometries and nanoscale porosity, which display excellent thermal and oxidation resistance, and morphology-dependent thermal conduction properties. This method offers a valuable technological platform for the simplified fabrication of nanostructured ceramics with complex shapes.

Coupling grid nanoindentation and surface chemical analysis to infer the mechanical properties of shale mineral phases

Shale is a low-permeability, multi-phase, and multi-scale composite material with intrinsic heterogeneity in micro-texture and mineralogical composition. In this paper, relationships between the microscale texture and constituent phases of shale were investigated using SEM (scanning electron microscopy)/BSE (backscatter electron imaging)-EDS (energy-dispersive x-ray spectroscopy) methods, together with grid nanoindentation experiments. The mechanical properties of the constituent phases of the carbonate-rich Longmaxi shale samples were extracted based on the spatial distribution of mineral phases and the indentation interaction volume. We analyze the effects of particle size on the interpreted mechanical properties and establish a characteristic length scale based on a probabilistic analysis. The identified characteristic length for extracting the mechanical properties of constituent mineral phases from the grid nanoindentation technique is about 5.8–11.7 μm, i.e., up to 10 times greater than that proposed in prior research. A multi-scale mechanical model was established with considerations of a self-consistent scheme for granular morphology to link the microscopic characteristics with the multi-scale mechanical properties of shales. The modeling results show that the stiffness and the strength of the homogenized nano-porous illite/quartz aggregates in Longmaxi shale can be assessed from the nano-scale mechanical properties of the mineral phases and the nano-scale porosity. This study paves the way to accessing the mechanical properties of the constituent phases of composite materials based on the properties of their building blocks and provides extensive insights into their complex mechanical behavior, representing a major step towards developing reliable multi-scale models for engineering applications.

Liquid-Metal Solvents for Designing Hierarchical Nanoporous Metals at Low Temperatures.

Metallic nanoarchitectures hold immense value as functional materials across diverse applications. However, major challenges lie in effectively engineering their hierarchical porosity while achieving scalable fabrication at low processing temperatures. Here we present a liquid-metal solvent-based method for the nanoarchitecting and transformation of solid metals. This was achieved by reacting liquid gallium with solid metals to form crystalline entities. Nanoporous features were then created by selectively removing the less noble and comparatively softer gallium from the intermetallic crystals. By controlling the crystal growth and dealloying conditions, we realized the effective tuning of the micro-/nanoscale porosities. Proof-of-concept examples were shown by applying liquid gallium to solid copper, silver, gold, palladium, and platinum, while the strategy can be extended to a wider range of metals. This metallic-solvent-based route enables low-temperature fabrication of metallic nanoarchitectures with tailored porosity. By demonstrating large-surface-area and scalable hierarchical nanoporous metals, our work addresses the pressing demand for these materials in various sectors.

Rapid printing of nanoporous 3D structures by overcoming the proximity effects in projection two-photon lithography

ABSTRACT Large and deterministic 3D structures with nanoscale features and porosities are valuable for various applications but are challenging to print due to the proximity effects that lead to the merging of adjacently printed features. Here, this challenge has been overcome by minimising the proximity effects in projection two-photon lithography (P-TPL), which is a high-throughput photopolymerization-based 3D printing technique. Through empirical studies and physics-based computational models, it is demonstrated that the proximity effects arise from distinct optical and chemical sources. Processing conditions that individually minimise these sources have been identified. These insights have been leveraged to generate an interspersing P-TPL technique capable of rapidly printing 3D structures with features smaller than 300 nm, pores finer than 700 nm, and at rates greater than 0.5 mm2/s per layer. As interspersing P-TPL is up to 50 times faster than conventional point-scanning TPL, it can enable the scalable printing of nanoporous 3D structures.

Investigation of the Influence of Nanoscale Porosity in the Interfacial Layers on the Mechanical Properties of Helium Plasma-Exposed Tungsten

Porous layers emergent from the bulk tungsten (W) interface subsequent to helium (He) plasma exposure, under conditions relevant to thermonuclear experiments, were found to significantly modulate the structural attributes of the W─as deduced through nanoscale indentation measurements. Plastic deformation of nanofibers constituting the fuzzy surface layer, along with an increased yield strength with layer depth, was quantified. A power-law relationship between the indentation modulus (Eind) and the porosity of the fuzzy W was indicated. The surface roughness of the bulk W increases with temperature prior to fuzz formation, determined by AFM. A decrease in the Eind of the bulk W underneath the fuzzy layer with increasing sample temperature when exposed to plasma, in agreement with molecular-dynamics computations, was observed.

Increased phase coherence length in a porous topological insulator

The surface area of ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ thin films was increased by introducing nanoscale porosity. Temperature dependent resistivity and magnetotransport measurements were conducted both on as-grown and porous samples (23 and 70 nm). The longitudinal resistivity of the porous samples became more metallic, indicating the increased surface area resulted in transport that was more surfacelike. Weak antilocalization was present in all samples, and remarkably the phase coherence length doubled in the porous samples. This increase is likely due to the large Fermi velocity of the Dirac surface states. Our results show that the introduction of nanoporosity does not destroy the topological surface states but rather enhances them, making these nanostructured materials promising for low energy electronics, spintronics and thermoelectrics.

Nanoscale Porosity in Microellipsoids Cloaks Interparticle Capillary Attraction at Fluid Interfaces.

Anisotropic particles pinned at fluid interfaces tend toward disordered multiparticle configurations due to large, orientationally dependent, capillary forces, which is a significant barrier to exploiting these particles to create functional self-assembled materials. Therefore, current interfacial assembly methods typically focus on isotropic spheres, which have minimal capillary attraction and no dependence on orientation in the plane of the interface. In order to create long-range ordered structures with complex configurations via interfacially trapped anisotropic particles, control over the interparticle interaction energy via external fields and/or particle engineering is necessary. Here, we synthesize colloidal ellipsoids with nanoscale porosity and show that their interparticle capillary attraction at a water-air interface is reduced by an order of magnitude compared to their smooth counterparts. This is accomplished by comparing the behavior of smooth, rough, and porous ellipsoids at a water-air interface. By monitoring the dynamics of two particles approaching one another, we show that the porous particles exhibit a much shorter-range capillary interaction potential, with scaling intriguingly different than theory describing the behavior of smooth ellipsoids. Further, interferometry measurements of the fluid deformation surrounding a single particle shows that the interface around porous ellipsoids does not possess the characteristic quadrupolar symmetry of smooth ellipsoids, and quantitatively confirms the decrease in capillary interaction energy. By engineering nanostructured surface features in this fashion, the interfacial capillary interactions between particles may be controlled, informing an approach for the self-assembly of complex two-dimensional microstructures composed of anisotropic particles.

Nanoscale Porosity of High Surface Area Gadolinium Oxide Nanofoam Obtained With Combustion Synthesis

AbstractNanoscale gadolinium oxide (Gd2O3) is a promising nanomaterial with unique physicochemical properties that finds various applications ranging from biomedicine to catalysis. The preparation of highly porous Gd2O3 nanofoam greatly increases its surface area thereby boosting its potential for functional use in applications such as water purification processes and in catalytic applications. By using the combustion synthesis method, a strong exothermic redox reaction between gadolinium nitrate hexahydrate and glycine causes the formation of crystalline nanoporous Gd2O3. In this study, the synthesis of Gd2O3 nanofoam is achieved with combustion synthesis at large scale (grams). Its nanoscale porosity is investigated by nitrogen physisorption and its nanoscale 3D structure by electron tomography, and the formation process is investigated as well by means of in situ heating inside the transmission electron microscope. The bulk nanofoam product is highly crystalline and porous with a surface area of 67 m2 g−1 as measured by physisorption, in good agreement with the electron tomographic 3D reconstructions showing an intricate interconnected pore network with pore sizes varying from 2 to 3 nm to tens of nanometers. In situ heating experiments point to many possibilities for tuning the porosity of the Gd2O3 nanofoam by varying the experimental synthesis conditions.

Using Powder Metallurgy and Oxide Reduction to Produce Eco‐Friendly Bulk Nanoporous Nickel

A low cost and scalable powder‐based method for producing nanoporous Ni is demonstrated, and the only processing by‐product is water vapor. This is achieved by creating a metal–matrix composite of Ni and NiO that is then reduced under dilute hydrogen to create pure Ni with nanocrystalline structure and nanoscale porosity. The technique is demonstrated in loose powder and in thin and bulk compacts with centimeter dimensions. These compacts can withstand extensive deformation without disintegrating, performing similarly to wrought Ni in specific strength. The unique processing strategy and resulting material can be readily extended to other metals and alloys.

Nonanal Gas Sensors Using Porous Glass as a Reaction Field for Ammonia-Catalyzed Aldol Condensation.

Transmittance in porous-glass gas sensors, which use aldol condensation of vanillin and nonanal as the detection mechanism for nonanal, decreases because of the production of carbonates by the sodium hydroxide catalyst. In this study, the reasons for the decrease in transmittance and the measures to overcome this issue were investigated. Alkali-resistant porous glass with nanoscale porosity and light transparency was employed as a reaction field in a nonanal gas sensor using ammonia-catalyzed aldol condensation. In this sensor, the gas detection mechanism involves measuring the changes in light absorption of vanillin arising from aldol condensation with nonanal. Furthermore, the problem of carbonate precipitation was solved with the use of ammonia as the catalyst, which effectively resolves the issue of reduced transmittance that occurs when a strong base, such as sodium hydroxide, is used as a catalyst. Additionally, the alkali-resistant glass exhibited solid acidity because of the incorporated SiO2 and ZrO2 additives, which supported approximately 50 times more ammonia on the glass surface for a longer duration than a conventional sensor. Moreover, the detection limit obtained from multiple measurements was approximately 0.66 ppm. In summary, the developed sensor exhibits a high sensitivity to minute changes in the absorbance spectrum because of the reduction in the baseline noise of the matrix transmittance.

Flexible high-capacity and long-cyclability hydrogel batteries enabled by polyvalent vanadium ion redox chemistry

Aqueous secondary batteries based on nonflammable electrolytes are attracting extensive attention due to high safety, fast reaction kinetics, and low cost. Herein, we report the development of flexible hydrogel batteries based on polyvalent vanadium ion redox chemistry. In this battery, symmetrical composite hydrogel electrodes used as both cathode and anode are prepared by in-situ fabrication of highly porous 3D poly(N-isopropylacrylamide) scaffold alongside conductive multi-walled carbon nanotube networks and swollen with redox-active vanadium ion electrolyte. The abundant nanoscale porosity and channels in the hydrogel matrix are conducive to the infiltration/diffusion of vanadium ions and H+ ions, thus enabling high areal loading mass (13 mgv cm−2) and large areal capacity (0.99 mAh cm−2). The active materials in the flexible electrodes exist in the form of composite hydrogel state, which is beneficial to facilitate ion transport and electrochemical kinetics, delivering an impressive power density of 11 mW cm−2 at 10 mA cm−2. Moreover, the flexible vanadium ion hydrogel batteries also exhibit excellent mechanical properties and long-term durability of 1000 cycles. These merits make them promising for the applications in wearable and smart electronics.

Facile Microembossing Process for Microchannel Fabrication for Nanocellulose-Paper-Based Microfluidics.

Nanofibrillated cellulose paper (nanopaper) has gained growing interest as one promising substrate material for paper-based microfluidics, thanks to its ultrasmooth surface, high optical transparency, uniform nanofiber matrix with nanoscale porosity, and tunable chemical properties. Recently, research on nanopaper-based microfluidics has quickly advanced; however, the current technique of patterning microchannels on nanopaper (i.e., 3D printing, spray coating, or manual cutting and sticking), that is fundamental for application development, still has some limitations, such as ease-of-contamination, and more importantly, only enabling millimeter-scale channels. This paper reports a facile process that leverages the simple operations of microembossing with the convenient plastic micro-molds, for the first time, patterning nanopaper microchannels downing to 200 μm, which is 4 times better than the existing methods and is time-saving (<45 mins). We also optimized the patterning parameters and provided one quick look-up table as the guideline for application developments. As proof-of-concept, we first demonstrated two fundamental microfluidic devices on nanopaper, the laminar-mixer and droplet generator, and two functional nanopaper-based analytical devices (NanoPADs) for glucose and Rhodamine B (RhB) sensing based on optical colorimetry and surface-enhanced Raman spectroscopy, respectively. The two NanoPADs showed outstanding performance with low limits of detection (2 mM for glucose and 19fM for RhB), which are 1.25× and 500× fold improvement compared to the previously reported values. This can be attributed to our newly developed highly accurate microchannel patterning process that enables high integration and fine-tunability of the NanoPADs along with the superior optical properties of nanopaper.

Clarifying the effects of nanoscale porosity of silicon on the bandgap and alignment: a combined molecular dynamics-density functional tight binding computational study.

Porous silicon (pSi) has been studied for its applications in solar cells, in particular in silicon-silicon tandem solar cells. It is commonly believed that porosity leads to an expansion of the bandgap due to nano-confinement. Direct confirmation of this proposition has been elusive, as experimental band edge quantification is subject to uncertainties and effects of impurities, while electronic structure calculations on relevant length scales are still outstanding. Passivation of pSi is another factor affecting the band structure. We present a combined force field-density functional tight binding study of the effects of porosity of silicon on its band structure. We thus perform electron structure-level calculations for the first time on length scales (several nm) that are relevant to real pSi, and consider multiple nanoscale geometries (pores, pillars, and craters) with key geometrical features and sizes of real porous Si. We consider the presence of a bulk-like base with a nanostructured top layer. We show that the bandgap expansion is not correlated with the pore size but with the size of the Si framework. Significant band expansion would require features of silicon (as opposed to pore sizes) to be as small as 1 nm, while the nanosizing of pores does not induce gap expansion. We observe a graded junction-like behavior of the band gap as a function of Si feature sizes as one moves from the bulk-like base to the nanoporous top layer.

Sandwiched aramid nanofiber/Al2O3-coated polyolefin separators for advanced lithium–sulfur batteries

Separators have a significant impact on the safety and performance of Lithium-sulfur (Li–S) batteries. However, the current microporous polyolefin separators often suffer from inferior thermostability and electrolyte wettability. Here, a sandwiched separator based on aramid nanofibers (ANFs) and Al2O3 nanoparticles was exploited on the base of a polyolefin separator through a facile coating process. The thin coating layer involves an entangled ANF network and Al2O3 NPs combine high strength, toughness, desirable nanoscale porosity, excellent thermostability, and wettability, which are conducive to improving the pristine polyolefin separators. Notably, the hybrid coating layer and sandwiched construction endow the separator with the capabilities of reducing the shuttle effect and improving the electrochemical performance. The Li–S battery equipped with the obtained Al2O3/ANFs@PP separator delivers an enhanced first-cycle discharge capacity of 1233 mAh g-1 and 99.83% Coulombic Efficiency after 200 cycles at 0.5C. The mechanically robust, heat-resistant, wettable, and nano-porous separator could shed fresh insights into the development of advanced separators for polysulfide shuttle-free and long-life Li–S batteries.

Rapid Color-Switching of MnO2 Hollow-Nanosphere Films in Dynamic Water Vapor for Reversible Optical Encryption.

Drop-casting manganese oxide (MnO2 ) hollow nanospheres synthesized via a simple surface-initiated redox route produces thin films exhibiting angle-independent structural colors. The colors can rapidly change in response to high-humidity dynamic water vapor (relative humidity > 90%) with excellent reversibility. When the film is triggered by dynamic water vapor with a relative humidity of ≈100%, the color changes with an optimal wavelength redshift of ≈60nm at ≈600ms while there is no shift under static water vapor. The unique selective response originates from the nanoscale porosity formed in the shells by randomly stacked MnO2 nanosheets, which enhances the capillary condensation of dynamic water vapor and promotes the change of their effective refractive index for rapid color switching. The repeated color-switching tests over 100 times confirm the durability and reversibility of the MnO2 film. The potential of these films for applications in anti-counterfeiting and information encryption is further demonstrated by reversible encoding and decoding initiated exclusively by exposure to human breath.

N-Rich, Polyphenolic Porous Organic Polymer and Its In Vitro Anticancer Activity on Colorectal Cancer

N-rich organic materials bearing polyphenolic moieties in their building networks and nanoscale porosities are very demanding in the context of designing efficient biomaterials or drug carriers for the cancer treatment. Here, we report the synthesis of a new triazine-based secondary-amine- and imine-linked polyphenolic porous organic polymer material TrzTFPPOP and explored its potential for in vitro anticancer activity on the human colorectal carcinoma (HCT 116) cell line. This functionalized (-OH, -NH-, -C=N-) organic material displayed an exceptionally high BET surface area of 2140 m2 g-1 along with hierarchical porosity (micropores and mesopores), and it induced apoptotic changes leading to high efficiency in colon cancer cell destruction via p53-regulated DNA damage pathway. The IC30, IC50, and IC70 values obtained from the MTT assay are 1.24, 3.25, and 5.25 μg/mL, respectively.

Efficient room-temperature phosphorescence of covalent organic frameworks through covalent halogen doping.

Organic room-temperature phosphorescence, a spin-forbidden radiative process, has emerged as an interesting but rare phenomenon with multiple potential applications in optoelectronic devices, biosensing and anticounterfeiting. Covalent organic frameworks (COFs) with accessible nanoscale porosity and precisely engineered topology can offer unique benefits in the design of phosphorescent materials, but these are presently unexplored. Here, we report an approach of covalent doping, whereby a COF is synthesized by copolymerization of halogenated and unsubstituted phenyldiboronic acids, allowing for random distribution of functionalized units at varying ratios, yielding highly phosphorescent COFs. Such controlled halogen doping enhances the intersystem crossing while minimizing triplet-triplet annihilation by diluting the phosphors. The rigidity of the COF suppresses vibrational relaxation and allows a high phosphorescence quantum yield (ΦPhos ≤ 29%) at room temperature. The permanent porosity of the COFs and the combination of the singlet and triplet emitting channels enable a highly efficient COF-based oxygen sensor, with an ultra-wide dynamic detection range (~103-10-5 torr of partial oxygen pressure).

On-Chip Monolithic Integrated Multimode Carbon Nanotube Sensor for a Gas Chromatography Detector.

Carbon nanotube (CNT)-based chemiresistors are promising gas detectors for gas chromatography (GC) due to their intrinsic nanoscale porosity and excellent electrical conductivity. However, fabrication reproducibility, long desorption time, limited sensitivity, and low dynamic range limit their usage in real applications. This paper reports a novel on-chip monolithic integrated multimode CNT sensor, where a micro-electro-mechanical system-based bulk acoustic wave (BAW) resonator is embedded underneath a CNT chemiresistor. The device fabrication repeatability was improved by on-site monitoring of CNT deposition using BAW. We found that the acoustic stimulation can accelerate the gas desorption rate from the CNT surface, which solves the slow desorption issue. Due to the different sensing mechanisms, the multimode CNT sensor provides complementary responses to targets with improved sensitivity and dynamic range compared to a single mode detector. A prototype of a chromatographic system using the multimode CNT sensor was prepared by dedicated design of the connection between the device and the separation column. Such a GC system is used for the quantitative identification of a gas mixture at different GC conditions, which proves the feasibility of the multimode CNT detector for chromatographic analysis. The as-developed CMOS compatible multimode CNT sensor offers high sensing performance, miniaturized size, and low power consumption, which are critical for developing portable GC.

Fueling the Simulation Machine: Considerations for High-Resolution 3D Microscopy to Support Computational Modeling in Battery Research

To meet the rapidly evolving energy needs of a growing population, energy storage and conversion devices such as batteries must rapidly evolve as well. Battery materials and other functional energy materials derive their properties not from their static state, but from how they interact with other materials in their service environment. Furthermore, the microstructure of these materials strongly dictates their performance and how they interact with other components (like electrolytes, binders, etc). In order to accelerate this development cycle, researchers are increasingly integrating computational modeling into their materials and device development efforts.Computational analysis is progressing to the point where simulations can incorporate real material microstructures, simulate statistically equivalent structures, and predict performance changes based on changes to these microstructures. At the same time experimental techniques have emerged that can deliver representative volumes of high-quality, high-resolution 3D microstructural images from real devices and materials. The interplay between advanced computational analysis and evolving characterization capabilities means we are rapidly approaching the realization of the “materials by design” paradigm where new materials are designed and tested digitally with input and validation provided by advanced materials characterization techniques. Within this paradigm, however, it is critical that the experimental techniques provide accurate, realistic, and representative input to the computational models. In the case of microstructural information, this means generating 3-dimensional images that accurately represents the materials in question.One key example of this is for materials, like battery materials and electrodes, which contain micro- and nano-scale porosity. Acquiring image data that can reproduce real material properties and feed accurate simulations is challenging and relies on satisfying several conditions. For example, the volume must be representative of the “bulk” material microstructure. The (2D) image resolution must capture the relevant scope of material features, and the 3D image must accurately represent the material in all 3 dimensions and at appropriate length scales. The focused-ion beam scanning electron microscope (FIB-SEM) is capable of imaging these micro- and nano-scale pore networks in 3D but care must be taken when considering these experiments, especially when the intent is to use the images to feed computational models.We present here a review of the factors researchers must consider when tackling these demanding tasks and highlight experimental recommendations for leveraging FIB-SEM tomography to produce the most relevant imaging data in this context. We use a lithium-ion battery cathode as a test case to demonstrate this approach, but the outcome and methods can be leveraged across the materials research space and beyond.