Nitride Aerogels Research Articles

A topologically substituted boron nitride hybrid aerogel for highly selective CO2 uptake

A topologically mediated synthesis of porous boron nitride aerogel has been experimentally and theoretically investigated for carbon dioxide (CO2) uptake. Replacement of the carbon atoms in a precursor aerogel of graphene oxide and carbon nanotubes was achieved using an elemental substitution reaction, to obtain a boron and nitrogen framework. The newly prepared BN aerogel possessed a specific surface area of 716.56 m2/g and exhibited an unprecedented twentyfold increase in CO2 uptake over N2, adsorbing 100 cc/g at 273 K and 80 cc/g in ambient conditions, as verified by adsorption isotherms via the multipoint Brunauer-Emmett-Teller (BET) method. Density functional theory calculations were performed to give hints on the mechanism of such high selectivity of CO2 over N2 adsorption in BN aerogel, which may be due to the interaction between the intrinsic polar nature of B–N bonds and the high quadrupole moment of CO2 over N2.

Oxygen-doped carbon nitride aerogel: A self-supported photocatalyst for solar-to-chemical energy conversion

Herein, self-supported oxygen-doped carbon nitride aerogel (OCNA) was successfully fabricated through a facile self-assembly method combined with hydrothermal process, without adopting any harmful solvents or cross-linking agents. The fabrication mechanism of OCNA was discussed. OCNA exhibited much faster charge separation efficiency, longer carriers’ lifetime than bulk carbon nitride (BCN). More importantly, oxygen-doping led to a more negative conduction band (CB) position and narrower band gap (Eg). Hence, the spectral response range of OCNA was extended dramatically and the hydrogen evolution rate (HER) of OCNA (λ > 510 nm) was about 26 times as high as that of BCN prepared herein. OCNA exhibited a remarkable apparent quantum yield (AQY) of 20.42% at 380 nm, 7.43% at 420 nm and 1.71% at 500 nm, superior to most of the reported C3N4-based materials. This work paves a facile colloid chemistry strategy to assemble self-supported 3D CNA that could be widely adopted in the sustainability field.

Low-power catalytic gas sensing using highly stable silicon carbide microheaters

A robust silicon carbide (SiC) microheater is used for stable low-power catalytic gas sensing at high operating temperatures, where previously developed low-power polycrystalline silicon (polysilicon) microheaters are unstable. The silicon carbide microheater has low power consumption (20 mW to reach 500 °C) and exhibits an order of magnitude lower resistance drift than the polysilicon microheater after continuously heating at 500 °C for 100 h and during temperature increases up to 650 °C. With the deposition of platinum nanoparticle-loaded boron nitride aerogel, the SiC microheater-based catalytic gas sensor detects propane with excellent long-term stability while exhibiting fast response and recovery time (~1 s). The sensitivity is not affected by humidity, nor during 10% duty cycling, which yields a power consumption of only 2 mW with frequent data collection (every 2 s). With a simple change of heater material from silicon to SiC, the microheater and resulting catalytic gas sensor element show significant performance improvement.

Assembly of ultrasmall Cu3N nanoparticles into three-dimensional porous monolithic aerogels.

We present for the first time the synthesis of transition metal nitride aerogels, specifically Cu3N aerogels by destabilizing colloidal Cu3N nanoparticles into gels using controlled heat treatment. The resulting aerogels consist of interconnected three-dimensional networks with ultrasmall-sized nanoparticle bridges of a surface area of 381 m(2) g(-1) and only 5% relative density.

Gas Sensors: Platinum Nanoparticle Loading of Boron Nitride Aerogel and Its Use as a Novel Material for Low‐Power Catalytic Gas Sensing (Adv. Funct. Mater. 3/2016)

Gas Sensors: Platinum Nanoparticle Loading of Boron Nitride Aerogel and Its Use as a Novel Material for Low‐Power Catalytic Gas Sensing (Adv. Funct. Mater. 3/2016)

Platinum Nanoparticle Loading of Boron Nitride Aerogel and Its Use as a Novel Material for Low‐Power Catalytic Gas Sensing

A high‐surface‐area, highly crystalline boron nitride aerogel synthesized with nonhazardous reactants has been loaded with crystalline platinum nanoparticles to form a novel nanomaterial that exhibits many advantages for use in a catalytic gas sensing application. The platinum nanoparticle‐loaded boron nitride aerogel integrated onto a microheater platform allows for calorimetric propane detection. The boron nitride aerogel exhibits thermal stability up to 900 °C and supports disperse platinum nanoparticles, with no sintering observed after 24 h of high‐temperature testing. The high thermal conductivity and low density of the boron nitride aerogel result in an order of magnitude faster response and recovery times (<2 s) than reported on alumina support and allow for 10% duty cycling of the microheater with no loss in sensitivity. The resulting 1.5 mW sensor power consumption is two orders of magnitude less than commercially available catalytic gas sensors and unlocks the potential for wireless, battery‐powered catalytic gas sensing.

Ultralight boron nitride aerogels via template-assisted chemical vapor deposition.

Boron nitride (BN) aerogels are porous materials with a continuous three-dimensional network structure. They are attracting increasing attention for a wide range of applications. Here, we report the template-assisted synthesis of BN aerogels by catalyst-free, low-pressure chemical vapor deposition on graphene-carbon nanotube composite aerogels using borazine as the B and N sources with a relatively low temperature of 900 °C. The three-dimensional structure of the BN aerogels was achieved through the structural design of carbon aerogel templates. The BN aerogels have an ultrahigh specific surface area, ultralow density, excellent oil absorbing ability, and high temperature oxidation resistance. The specific surface area of BN aerogels can reach up to 1051 m2 g−1, 2-3 times larger than the reported BN aerogels. The mass density can be as low as 0.6 mg cm−3, much lower than that of air. The BN aerogels exhibit high hydrophobic properties and can absorb up to 160 times their weight in oil. This is much higher than porous BN nanosheets reported previously. The BN aerogels can be restored for reuse after oil absorption simply by burning them in air. This is because of their high temperature oxidation resistance and suggests broad utility as water treatment tools.

Nanoscale structure and superhydrophobicity of sp(2)-bonded boron nitride aerogels.

Aerogels have much potential in both research and industrial applications due to their high surface area, low density, and fine pore size distribution. Here we report a thorough structural study of three-dimensional aerogels composed of highly crystalline sp(2)-bonded boron nitride (BN) layers synthesized by a carbothermic reduction process. The structure, crystallinity and bonding of the as-prepared BN aerogels are elucidated by X-ray diffraction, (11)B nuclear magnetic resonance, transmission electron microscopy, and resonant soft X-ray scattering. The macroscopic roughness of the aerogel's surface causes it to be superhydrophobic with a contact angle of ∼155° and exhibit high oil uptake capacity (up to 1500 wt%). The oil can be removed from the BN aerogel by oxidizing in air without damaging the crystalline porous structure of the aerogel or diminishing its oil absorption capacity.

Synthesis of Highly Crystalline sp2-Bonded Boron Nitride Aerogels

sp(2)-Bonded boron nitride aerogels are synthesized from graphene aerogels via carbothermal reduction of boron oxide and simultaneous nitridation. The color and chemical composition of the original gel change dramatically, while structural features down to the nanometer scale are maintained, suggesting a direct conversion of the carbon lattice to boron nitride. Scanning and transmission electron microscopies reveal a foliated architecture of wrinkled sheets, a unique morphology among low-density, porous BN materials. The converted gels display a high degree of chemical purity (>95%) and crystalline order and exhibit unique cross-linking structures.

Formation and Pore Structure of Boron Nitride Aerogels

Gels containing a poly(borazinyl amine) and tetrahydrofuran were processed by CO2 supercritical drying techniques followed by pyrolysis. The resulting BN ceramic aerogels are highly porous, and the microstructure, porosity, and surface area characteristics have been examined. The aerogels show excellent thermal stability exhibiting surface areas in excess of 350 m2/g and porosities greater than 0.8 even when heated in argon at 1500°C for 8 h. By removing solvent via evaporation before supercritical drying, the mean pore radius can be varied between 3.6 and 10 nm.

Boron Nitride and Composite Aerogels from Borazine Based Polymers

ABSTRACTPoly(borazinylamines) have been processed in THF and toluene solvents and aerogel forms produced by supercritical drying methods. The polymer aerogels have been pyrolyzed and porous amorphous and crystalline BN monoliths have been produced. These have been characterized and effects of processing factors on surface area and pore structure are described.