With the arising of global climate change and resource shortage, in recent years, increased attention has been paid to environmentally friendly materials. Trees are sustainable and renewable materials, which give us shelter and oxygen and remove carbon dioxide from the atmosphere. Trees are a primary resource that human society depends upon every day, for example, homes, heating, furniture, and aircraft. Wood from trees gives us paper, cardboard, and medical supplies, thus impacting our homes, school, work, and play. All of the above-mentioned applications have been well developed over the past thousands of years. However, trees and wood have much more to offer us as advanced materials, impacting emerging high-tech fields, such as bioengineering, flexible electronics, and clean energy. Wood naturally has a hierarchical structure, composed of well-oriented microfibers and tracheids for water, ion, and oxygen transportation during metabolism. At higher magnification, the walls of fiber cells have an interes...

https://www.fpl.fs.fed.us/documnts/pdf2016/fpl_2016_zhu001.pdf

Wood-Derived Materials for Green Electronics, Biological Devices, and Energy Applications.

As a newly developed material, carbon gels have been receiving considerable attention due to their multifunctional properties. Herein, we present a facile, green, and template-free route toward sponge-like carbonaceous hydrogels and aerogels by using crude biomass, watermelon as the carbon source. The obtained three-dimensional (3D) flexible carbonaceous gels are made of both carbonaceous nanofibers and nanospheres. The porous carbonaceous gels (CGs) are highly chemically active and show excellent mechanical flexibility which enable them to be a good scaffold for the synthesis of 3D composite materials. We synthesized the carbonaceous gel-based composite materials by incorporating Fe3O4 nanoparticles into the networks of the carbonaceous gels. The Fe3O4/CGs composites further transform into magnetite carbon aerogels (MCAs) by calcination. The MCAs keep the porous structure of the original CGs, which allows the sustained and stable transport of both electrolyte ions and electrons to the electrode surface, ...

Biomass-Derived Sponge-like Carbonaceous Hydrogels and Aerogels for Supercapacitors

Biopolymer aerogels were among the first aerogels produced, but only in the last decade has research on biopolymer and biopolymer-composite aerogels become popular, motivated by sustainability arguments, their unique and tunable properties, and ease of functionalization. Biopolymer aerogels and open-cell foams have great potential for classical aerogel applications such as thermal insulation, as well as emerging applications in filtration, oil-water separation, CO2 capture, catalysis, and medicine. The biopolymer aerogel field today is driven forward by empirical materials discovery at the laboratory scale, but requires a firmer theoretical basis and pilot studies to close the gap to market. This Review includes a database with over 3800 biopolymer aerogel properties, evaluates the state of the biopolymer aerogel field, and critically discusses the scientific, technological, and commercial barriers to the commercialization of these exciting materials.

Biopolymer Aerogels and Foams: Chemistry, Properties, and Applications.

Developing a synthetic methodology for the fabrication of hierarchically porous metal-organic monoliths that feature high surface area, low density and tunable porosity is imperative for mass transfer applications, including bulky molecule capture, heterogeneous catalysis and drug delivery. Here we report a versatile and facile synthetic route towards ultralight micro/mesoporous metal-organic aerogels based on the two-step gelation of metal-organic framework nanoparticles. Heating represents a key factor in the control of gelation versus crystallization of Al(III)-multicarboxylate systems. The porosity of the resulting metal-organic aerogels can be readily tuned, leading to the formation of well-ordered intraparticle micropores and aerogel-specific interparticle mesopores, thereby integrating the merits of both crystalline metal-organic frameworks and light aerogels. The hierarchical micro/mesoporosity of the Al-metal-organic aerogels is thoroughly evaluated by N₂ sorption. The good accessibility of the micro/mesopores is verified by vapour/dye uptake, and their potential for utilization as effective fibre-coating absorbents is tested in solid-phase microextraction analyses.

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A synthetic route to ultralight hierarchically micro/mesoporous Al(III)-carboxylate metal-organic aerogels.

Hollow nano-objects have raised interest in applications such as sensing, encapsulation, and drug-release. Here we report on a new class of porous materials, namely inorganic nanotube aerogels that, unlike other aerogels, have a framework consisting of inorganic hollow nanotubes. First we show a preparation method for titanium dioxide, zinc oxide, and aluminum oxide nanotube aerogels based on atomic layer deposition (ALD) on biological nanofibrillar aerogel templates, that is, nanofibrillated cellulose (NFC), also called microfibrillated cellulose (MFC) or nanocellulose. The aerogel templates are prepared from nanocellulose hydrogels either by freeze-drying in liquid nitrogen or liquid propane or by supercritical drying, and they consist of a highly porous percolating network of cellulose nanofibrils. They can be prepared as films on substrates or as freestanding objects. We show that, in contrast to freeze-drying, supercritical drying produces nanocellulose aerogels without major interfibrillar aggregation even in thick films. Uniform oxide layers are readily deposited by ALD onto the fibrils leading to organic-inorganic core-shell nanofibers. We further demonstrate that calcination at 450 °C removes the organic core leading to purely inorganic self-supporting aerogels consisting of hollow nanotubular networks. They can also be dispersed by grinding, for example, in ethanol to create a slurry of inorganic hollow nanotubes, which in turn can be deposited to form a porous film. Finally we demonstrate the use of a titanium dioxide nanotube network as a resistive humidity sensor with a fast response.

Inorganic Hollow Nanotube Aerogels by Atomic Layer Deposition onto Native Nanocellulose Templates

Cellulose–silica aerogels

Functionalisation and chemical characterisation of cellulose-derived carbon aerogels

Evaluation of lightweight and flexible insulating aerogel blankets based on Resorcinol-Formaldehyde-Silica for space applications

Lightweight superinsulating Resorcinol-Formaldehyde-APTES benzoxazine aerogel blankets for space applications

Novel various aerogel-like materials were prepared from the biomass, cellulose and cellulose derivatives, either from their solutions or via physical or chemical gelation and drying in CO2 under supercritical conditions. Two classes of materials will be discussed: based on pure cellulose and on cellulose acetate. Pure cellulose highly porous material, Aerocellulose, was made from cellulose dissolved in green solvents, aqueous NaOH or ionic liquids. An overview of the main preparation steps is given, from cellulose dissolution and solution-state properties, to regeneration kinetics, solvent exchange and drying. The porosity of Aerocellulose is higher than 90% with pore sizes from a few tens of nanometers to a few tens of micrometers. The density ranges from 0.06 to 0.3 g/cm3. Aerogels based on cellulose acetate were synthesised by crosslinking cellulose acetate dissolved in acetone with a non-toxic isocyanate as a cross-linker, using different catalysts (dibutyltin dilaurate, a triethylamine and pyridine). Mesoporous nanostructured network was obtained after drying; pore sizes vary from 10 to 30 nm and density from 0.25 to 0.85 cm3/g. Two applications of these new materials are discussed: as thermal insulators and carbons in proton exchange membrane fuel cell.

Claudia Hildenbrand

Papers

Cellulose–silica aerogels

Functionalisation and chemical characterisation of cellulose-derived carbon aerogels

Evaluation of lightweight and flexible insulating aerogel blankets based on Resorcinol-Formaldehyde-Silica for space applications

Lightweight superinsulating Resorcinol-Formaldehyde-APTES benzoxazine aerogel blankets for space applications

Preparation, properties and applications of novel cellulose and cellulose acetate aerogels