Lightweight Hexagonal Boron Nitride Foam for CO2 Absorption

Stabilization and strengthening effects of filamentous nanocellulose in the foam forming of quartz paper

Compared with traditional papermaking, foam forming is a new papermaking technology that uses foam instead of water to disperse fibres, which can effectively solve the problem of poor evenness of ceramic paper, but the instability of foam itself affects the application of foam forming technology. Herein, a highly stable foaming agent for foam forming technology was prepared via physical reaction of lauryl dimethyl amine oxide (OB-2) with filamentous nanocellulose (cellulose nanofiber (CNF-C) and bacterial cellulose (BC)). Then, the quartz paper was prepared by foam forming technology. Firstly, hydrogen bond interactions between hydroxyl groups of the filamentous nanocellulose and hydrophilic moieties on OB-2 enabled the formation of a 3D nanonetwork layer on the surface of the bubble, which extended the half-life of the bubble and effectively prevented the bubble from bursting or coalescing. Then, the foam was extruded and cracked, and the filamentous nanocellulose was retained on the quartz fibres to prepare filamentous nanocellulose/quartz fibre paper by foam forming technology. The quartz paper exhibited excellent evenness and mechanical properties. In conclusion, the research of foam forming technology is of great significance to the application and development of special paper.

Condensation-assembly synthesis of three-dimensionally porous boron nitride for effective oil removal

A template-free pyrolysis route has been developed using condensation-assembly precursors made of trimethoxyboroxane (TMB) and melamine (M) to cater the requirements of an industrial real-world environment. The precursors contain abundant B-N bonds and exhibit a high level of interconnectivity, resulting in 3D-PBN with enhanced mechanical properties and the ability to be easily customized in terms of shape. Moreover, 3D-PBN demonstrates rapid adsorption kinetics and excellent reusability, efficiently removing up to 270% of its own weight of fuel within 30 s and being readily regenerated through simple calcination. Even after undergoing 50 cycles, the mechanical properties remain at a remarkable 80%, while the adsorption performance exceed 95%. Furthermore, a comprehensive analysis of thermal behavior from precursor to 3D-PBN has been conducted, leading to the proposal of a molecular-scale evolution process comprising four major steps. This understanding enables us to control the phase reaction and regulate the composition of the products, which is crucial for determining the characteristics of the final product.

Hexagonal boron nitride exfoliation and dispersion

Research on hexagonal boron nitride (hBN) 2-dimensional nanostructures has gained traction due to their unique chemical, thermal, and electronic properties. However, to make use of these exceptional properties and fabricate macroscopic materials, hBN often needs to be exfoliated and dispersed in a solvent. In this review, we provide an overview of the many different methods that have been used for dispersing hBN. The approaches that will be covered in this review include solvents, covalent functionalization, acids and bases, surfactants and polymers, biomolecules, intercalating agents, and thermal expansion. The properties of the exfoliated sheets obtained and the dispersions are discussed, and an overview of the work in the field throughout the years is provided.

Amorphous/Nanocrystalline, Lightweight, Wave-Transparent Boron Nitride Nanobelt Aerogel for Thermal Insulation

At present, the new generation of aircraft is developing in the direction of high speed, long endurance, high mobility, and repeatability. Some studies have shown that the surface temperature of the radome can reach even 1800 °C as the flight speed of the aircraft increases. However, the antenna inside the radome cannot serve at this temperature. Consequently, a thermal insulation system with electromagnetic wave-transparent ability and high-temperature resistance is urgently needed to protect the antenna from working normally. An aerogel material is known as "solid smoke," with the lowest density currently. Because of its high porosity (>90%) and the characteristics of nanopore size, its application in the field of thermal insulation always draws the attention of researchers. In this work, a novel amorphous/nanocrystalline boron nitride (BN) nanobelt aerogel was synthesized successfully. The BN aerogel shows lightweight (18 mg/cm3), good thermal stability (1400 °C under an inert atmosphere and 750 °C under an air atmosphere), wideband wave-transparent performance (dielectric constant of 1.03 and dielectric loss of 0.016 at 4-18 GHz), and thermal insulation property (43 mW/(m·K) at room temperature and 73 mW/(m·K) at 600 °C). The BN aerogel is a suitable candidate as an electromagnetic wave-transparent thermal insulator and fire-resistant material. What is more, the structural stability of the BN aerogel is good (Young's modulus remains basically constant during the fatigue tests), and the energy loss coefficient (∼0.56) is high; it also has the potential to be a mechanical energy dissipative material. The study on the amorphous/nanocrystalline BN nanobelt aerogel provides a new idea for structure design and performance optimization of a high-temperature electromagnetic functional insulation material.

Single atom solutions for carbon dioxide capture

New solvents are considered to be one of the effective methods to facilitate the reaction rate and lower the reaction energy barrier. However, the common method to develop a new solvent has come to a dead end. Thus, a single atom in solvent to produce a single atom solution is designed to create the breakthrough. Eight kinds of single atom solutions are prepared as new absorbents. Experiments prove the single atom in the solutions and their charge-producing effects. A density functional theory model is developed to analyze the microscale characteristics. Meanwhile, it has been applied in carbon dioxide capture. The CO₂ desorption rate is intensified in the single atom solution system due to the controlled reaction energy barrier. The results show that single atom solutions produce a maximum voltage of 2.12 V and, thus, contribute to near zero energy consumption by effectively harvesting the substantial waste heat below 373 K.

Single Step Assembly of Janus Porous Biomaterial by Sub-Ambient Temperature Electrodeposition

Janus porous biomaterials are gaining increasing attention and there are considerable efforts to develop simple, rapid, and scalable methods capable of tuning micro- and macro-structures. Here, a single-step electro-fabrication method to create a Janus porous film by the electrodeposition of the amino-polysaccharide chitosan is reported. Specifically, a Janus structure emerges spontaneously when electrodeposition is performed at sub-ambient temperature (0-5 °C). Sub-ambient temperature electrodeposition experiments show that: a Janus microstructure emerges (potentially as the result of a subtle alteration of the intermolecular interactions responsible for self-assembly); important microstructural features (pore size, porosity, and thicknesses) can be tuned by conditions; and this method is readily scalable (vs serial printing) and can yield complex tubular structures with Janus faces. In vitro studies demonstrate anisotropic cell guidance, and in vivo studies using a rat calvarial defect model further confirm the beneficial features of such Janus porous film for guided bone regeneration. In summary, these results further demonstrate that electro-fabrication provides a simple and scalable platform technology for the controlled functional structures of soft matter for applications in regenerative medicine.

Turbostratic Boron-Carbon-Nitrogen and Boron Nitride by Flash Joule Heating

Turbostratic layers in 2D materials have an interlayer misalignment. The lack of alignment expands the intrinsic interlayer distances and weakens the optical and electronic interactions between adjacent layers. This introduces properties distinct from those structures with well-aligned lattices and strong coupling interactions. However, direct and rapid synthesis of turbostratic materials remains a challenge owing to their thermodynamically metastable properties. Here, a flash Joule heating (FJH) method to achieve bulk synthesis of boron-carbon-nitrogen ternary compounds with turbostratic structures by a kinetically controlled ultrafast cooling process that takes place within milliseconds (10³  to 10⁴ K s^-1 ) is reported. Theoretical calculations support the existence of turbostratic structures and provide estimates of the energy barriers with respect to conversion into the corresponding well-aligned counterparts. When using non-carbon conductive additives, a direct synthesis of boron nitride is possible. The turbostratic nature facilitates mechanical exfoliation and more stable dispersions. Accordingly, the addition of flash products to a poly(vinyl alcohol) nanocomposite film coating a copper surface greatly improves the copper's resistance to corrosion in 0.5 m sulfuric acid or 3.5 wt% saline solution. FJH allows the use of bulk materials as reactants and provides a rapid approach to large quantities of the hitherto hard-to-access turbostratic materials.

Fe-Catalyzed CO2 Adsorption over Hexagonal Boron Nitride with the Presence of H2O

The energy barrier of CO₂ chemically adsorbed on hexagonal boron nitride (h-BN) is relatively big. In order to cut down the energy barriers and facilitate fast adsorption of CO₂, it is necessary to apply catalysts as a promoter. In this study, single-atom iron is introduced as the catalyst to reduce the energy barriers of CO₂ adsorbed on pure/doped h-BN. Through density functional theory calculations, catalytic reaction mechanisms, stability of single-atom iron fixed on adsorbents, CO₂ adsorption characteristics, and features of thermodynamics/reaction dynamics during adsorption processes are fully investigated to explain the catalytic effects of single-atom iron on CO₂ chemisorption. According to calculations, when CO₂ and OH^- get into activated states (i.e., CO₂^•- and ^•OH) with the help of single-atom iron, their chemical activities will be promoted to a large degree, which makes the transition state (TS) energy barrier of HCO₃^- to decrease by 92.54%. In the meantime, it is proved that single-atom iron could be stably fixed on doped h-BN with the binding energy larger than 2 eV to achieve sustainable catalysis. With the presence of single-atom iron, TS energy barriers of CO₂ adsorbed on h-BN with the presence of H₂O decreased by 94.39, 78.87, and 30.63% over pure h-BN, 3C-doped h-BN, and 3N-doped h-BN, respectively. In the meantime, thermodynamic analyses indicate that TS energy barriers are mainly determined by element doping and temperatures are a little beneficial to the reduction of TS energy barriers. With the above aspects combined, the results of this study could supply crucial information for massively and quickly capturing CO₂ in real industries.

Catalytic Effect of Ti or Pt in a Hexagonal Boron Nitride Surface for Capturing CO2

We investigated the effect of doping a hexagonal boron nitride surface (hBN) with Ti or Pt on the adsorption of CO2. We performed first-principles molecular dynamics simulations (FPMD) at atmospheric pressure, and 300 K. Pristine hBN shows no interaction with the CO2 molecule. We allowed the Ti and Pt atoms to interact separately, with either a B-vacancy or an N-vacancy. Both Ti and Pt ended chemisorbed on the surface. The system hBN + Ti always chemisorbed the CO2 molecule. This chemisorption happens in two possible ways. One is without dissociation, and in the other, the molecule breaks in CO and O. However, in the case of the Pt atom as dopant, the resulting system repels the CO2 molecule.

Interfacial Engineering to Tailor the Properties of Multifunctional Ultralight Weight hBN-Polymer Composite Aerogels

A common feature of aerogels is that they are brittle and suffer from poor mechanical properties. The development of high-performance, lightweight, and mechanically robust polymer composite aerogels may find use in a broad range of applications such as packaging, transportation, construction, electronics, and aerospace. Most aerogels are made of ceramic materials, such as silica, alumina, and carbide. These aerogels are dense and brittle. Two-dimensional (2D) layered nanostructures such as graphene, graphene oxide and hexagonal boron nitride (hBN) have promising potential in emerging technologies including those involved in extreme environmental conditions because they can withstand high temperatures, harsh chemical environments, and corrosion. Here, we report the development of highly porous, ultralightweight, and flexible aerogel composites made by the infiltration of various polymers into 2D hBN aerogels. The 2D hBN aerogels in which pore size could be controlled were fabricated using a unique self-assembly approach involving polystyrene nanoparticles as templates for ammonia borane into desired structures. We have shown that the physical, mechanical, and thermal properties of hBN-polymer composite aerogels can be tuned by the infiltration of different additives. We also performed theoretical calculations to gain insight into the interfacial interactions between the hBN-polymer structure, as the interface is critical in determining key material properties.

Pt/MnO2 Nanoflowers Anchored to Boron Nitride Aerogels for Highly Efficient Enrichment and Catalytic Oxidation of Formaldehyde at Room Temperature

The catalytic room temperature oxidation of formaldehyde (HCHO) is widely considered as a viable method for the abatement of indoor toxic HCHO pollution. Herein, Pt/MnO₂ nanoflowers anchored to boron nitride aerogels (Pt/MnO₂ -BN) were fabricated for the catalytic room temperature oxidation of HCHO. The three-dimensional Pt/MnO₂ -BN aerogels demonstrated superior catalytic activity as a result of the improved diffusion of the reactant molecules within the porous structure. Furthermore, the porous aerogels displayed excellent HCHO adsorption capacities, which promote a rapid HCHO gas-phase concentration reduction and a subsequent complete oxidation of the adsorbed HCHO. The combined adsorption and oxidation properties of the Pt/MnO₂ -BN aerogels enhance the oxidative removal of HCHO. The optimized Pt/MnO₂ -BN demonstrated excellent catalytic activity toward HCHO (200 ppm) at room temperature, achieving a 96 % formaldehyde conversion after 50 min.

Impact of structure, doping and defect-engineering in 2D materials on CO2 capture and conversion

2D material based strategies for adsorption and conversion of CO2 to value-added products.

Conversionless efficient and broadband laser light diffusers for high brightness illumination applications

Laser diodes are efficient light sources. However, state-of-the-art laser diode-based lighting systems rely on light-converting inorganic phosphor materials, which strongly limit the efficiency and lifetime, as well as achievable light output due to energy losses, saturation, thermal degradation, and low irradiance levels. Here, we demonstrate a macroscopically expanded, three-dimensional diffuser composed of interconnected hollow hexagonal boron nitride microtubes with nanoscopic wall-thickness, acting as an artificial solid fog, capable of withstanding ~10 times the irradiance level of remote phosphors. In contrast to phosphors, no light conversion is required as the diffuser relies solely on strong broadband (full visible range) lossless multiple light scattering events, enabled by a highly porous (>99.99%) non-absorbing nanoarchitecture, resulting in efficiencies of ~98%. This can unleash the potential of lasers for high-brightness lighting applications, such as automotive headlights, projection technology or lighting for large spaces.

Metal-Free Modified Boron Nitride for Enhanced CO2 Capture

Porous boron nitride is a new class of solid adsorbent with applications in CO2 capture. In order to further enhance the adsorption capacities of materials, new strategies such as porosity tuning, element doping and surface modification have been taken into account. In this work, metal-free modification of porous boron nitride (BN) has been prepared by a structure directing agent via simple heat treatment under N2 flow. We have demonstrated that textural properties of BN play a pivotal role in CO2 adsorption behavior. Therefore, addition of a triblock copolymer surfactant (P123) has been adopted to improve the pore ordering and textural properties of porous BN and its influence on the morphological and structural properties of pristine BN has been characterized. The obtained BN-P123 exhibits a high surface area of 476 m2/g, a large pore volume of 0.83 cm3/g with an abundance of micropores. More importantly, after modification with P123 copolymer, the capacity of pure CO2 on porous BN has improved by about 34.5% compared to pristine BN (2.69 mmol/g for BN-P123 vs. 2.00 mmol/g for pristine BN under ambient condition). The unique characteristics of boron nitride opens up new routes for designing porous BN, which could be employed for optimizing CO2 adsorption.

Structurally Controlled Cellular Architectures for High-Performance Ultra-Lightweight Materials

The design and synthesis of cellular structured materials are of both scientific and technological importance since they can impart remarkably improved material properties such as low density, high mechanical strength, and adjustable surface functionality compared to their bulk counterparts. Although reducing the density of porous structures would generally result in reductions in mechanical properties, this challenge can be addressed by introducing a structural hierarchy and using mechanically reinforced constituent materials. Thus, precise control over several design factors in structuring, including the type of constituent, symmetry of architectures, and dimension of the unit cells, is extremely important for maximizing the targeted performance. The feasibility of lightweight materials for advanced applications is broadly explored due to recent advances in synthetic approaches for different types of cellular architectures. Here, an overview of the development of lightweight cellular materials according to the structural interconnectivity and randomness of the internal pores is provided. Starting from a fundamental study on how material density is associated with mechanical performance, the resulting structural and mechanical properties of cellular materials are investigated for potential applications such as energy/mass absorption and electrical and thermal management. Finally, current challenges and perspectives on high-performance ultra-lightweight materials potentially implementable by well-controlled cellular architectures are discussed.

Lightweight, Superelastic Yet Thermoconductive Boron Nitride Nanocomposite Aerogel for Thermal Energy Regulation

Conventional three-dimensional (3D) thermal conductors or heat sinks are normally bulky solids with high density, which is cumbersome and not portable to satisfy current demands for soft and flexible electronic devices. To address this issue, here, a lightweight, superelastic yet thermally conductive boron nitride (BN) nanocomposite aerogel is designed by a facile freeze-drying method. The attained aerogel constituting of tailored interconnected binary inorganic-organic network structure exhibits low bulk density (6.5 mg cm^-3) and outstanding mechanical performances for compression, clotting, and stretching. Meanwhile, the aerogel has promising thermal stability and high thermal conductivity over wide temperature ranges (30-300 °C), validating the application even in extremely hot environments. Moreover, the aerogel can serve as a lightweight and elastic heat conductor for the enhancement of thermal energy harvest. Interestingly, during alternate strain loading/unloading under heating, the superelasticity and the anisotropy of thermal conductive transduction make the aerogel enable the elastic thermal energy capture and dynamic regulation. Therefore, our findings provide a potential use for the thermally conductive aerogel in future green energy applications.

Dual Functionalities of Few-Layered Boron Nitrides in the Design and Implementation of Ca(OH)2 Nanomaterials toward an Efficient Wall Painting Fireproofing and Consolidation

Preserving ancient wall paintings from damage has become a challenge over the years. Nanosized calcium hydroxide (Ca(OH)₂) has been identified as a promising material to preserve wall paintings. However, the synthesis of nanosized Ca(OH)₂ is extremely difficult. Here, we demonstrate a breakthrough in wall painting protection enabled by boron nitride nanosheets (BNNSs) through strategic synthesis Ca(OH)₂-BNNS nanohybrids using an aqueous method. The BNNS have two significant functionalities in the design and implementation of the Ca(OH)₂ nanomaterials. First, the introduction of BNNS results in the successful synthesis of uniform and nanosized Ca(OH)₂ (∼80 nm) in the nanohybrids, which can be attributed to the supersaturation-induced "etching-stripping" mechanism. More interestingly and importantly, a unique gradient penetration structure is strategically formed when applying Ca(OH)₂-BNNS hybrids on the wall paintings, i.e., the BNNS-rich layer will be at the surface of wall painting, whereas Ca(OH)₂ nanomaterials prefer to penetrate deep in to the wall paintings. This gradient structure will allow the BNNS-rich layer to protect the wall paintings from fire, which is the first report to date among the protection materials for wall paintings; at the same time, nanosized Ca(OH)₂ shows superior wall painting consolidation strength compared to commercial Ca(OH)₂ material. These results endow new applications of the newly emerging two-dimensional nanomaterials for protecting cultural heritage.

Three-Dimensional Functionalized Boron Nitride Nanosheets/ZnO Superstructures for CO2 Capture

Without any extra directing agents or surfactants, three-dimensional (3D) hierarchically cubic and spherical morphologies of functionalized boron nitride nanosheets (FBNNSs)/ZnO superstructures have been controlled successfully via the evaporation-induced solvothermal synthesis. As-resulted spherical FBNNSs/ZnO superstructures not only exhibit a high capture capacity of CO₂ around 63.4 cm³/g (124.5 mg/g) from 0 to 1 bar at 273 K but also show a good reusability of 10 cycles with an average removal ability up to 58.9 cm³/g (115.7 mg/g). The excellent adsorption property can be further explained by the chemisorption, van der Waals interaction, and H bonds from the surface of ZnO and the in-plane and edged amino groups of FBNNS. Therefore, the preparation of 3D FBNNSs/ZnO superstructures provides a new and promising material for CO₂ adsorption with tunable morphologies.

Interconnecting Bone Nanoparticles by Ovalbumin Molecules to Build a Three-Dimensional Low-Density and Tough Material

Natural building blocks like proteins and hydroxyapatite (HA) are found in abundance. However, their effective utilization to fabricate environment-friendly, strong, stiff, and tough materials remains a challenge. This work reports on the synthesis of a layered material from entirely natural building blocks. A simple process to extract HA from bones, while keeping collagen intact, is presented. These HA nanocrystals have a high aspect ratio as a result of the extraction method that largely retains the pristine nature of the HA. To fabricate the materials, polymerized egg white is used to induce toughness to the crystals where it acts like a load transfer entity between the crystals. As shown by atomic force microscope modulus mapping, the result is a layered material with a modulus that ranges from 3 to 180 GPa. Furthermore, the material exhibits self-stiffening behavior. Hydrogen and ionic bonds are likely to regulate the chemical interactions at the egg white/HA interface and are likely to be responsible for the observed high toughness and stiffness, respectively. The use of the HA/egg white composite as printed scaffolds is also demonstrated together with their biocompatibility.

Highly Surface-Active Ca(OH)2 Monolayer as a CO2 Capture Material

Greenhouse gas emissions originating from fossil fuel combustion contribute significantly to global warming, and therefore the design of novel materials that efficiently capture CO₂ can play a crucial role in solving this challenge. Here, we show that reducing the dimensionality of bulk crystalline portlandite results in a stable monolayer material, named portlandene, that is highly effective at capturing CO₂. On the basis of theoretical analysis comprised of ab initio quantum mechanical calculations and force-field molecular dynamics simulations, we show that this single-layer phase is robust and maintains its stability even at high temperatures. The chemical activity of portlandene is seen to further increase upon defect engineering of its surface using vacancy sites. Defect-containing portlandene is capable of separating CO and CO₂ from a syngas (CO/CO₂/H₂) stream, yet is inert to water vapor. This selective behavior and the associated mechanisms have been elucidated by examining the electronic structure, local charge distribution, and bonding orbitals of portlandene. Additionally, unlike conventional CO₂ capturing technologies, the regeneration process of portlandene does not require high temperature heat treatment because it can release the captured CO₂ by application of a mild external electric field, making portlandene an ideal CO₂ capturing material for both pre- and postcombustion processes.