In search for a straight-forward and economical drying technique for aerogel materials, removing the main obstacle for the wide-spread application of aerogel materials — their tremendous costs — researchers from the University of Newcastle have been inspired by the way dragonflies and damselflies dry their lightweight and porous wings under ambient conditions.
In the course of their research the scientist stumbled upon the fact, that dragonflies dry their highly porous wings — which make up only 2 % of their entire bodyweight despite their large size — in a matter of a handful of hours (sometimes even as little as one hour) during their final metamorphosis into the adult. They hypothesized that this rapid but at the same time gentle drying process of the aerogel-like wings at ambient conditions can be attributed to the involvement of just one simple chemical compound — bicarbonate.

Schematic of novel APD drying technique deploying sodium bicarbonate and TMCS

The formation of sodium chloride (NaCl) and CO₂ from sodium bicarbonate, which takes place upon the addition of trimethylchlorosilane (TMCS), was found to be a straight forward technique to produce CO₂ inside an aqueous porous medium, with the formed gas preventing pore collapse in the course of successive ambient pressure drying (APD), mimicking this process (supposedly) occurring in nature. As schematically shown in the figure on the right, this means that CO₂ formed in situ works as a stabilizer
Schematic of novel APD drying technique deploying sodium bicarbonate and TMCS. of the gel pores, acting against the capillary pressure arising when the solvent is removed from the gel network via APD.

The suggested drying technique was tested using silica gels synthesized from tetraethoxysilane, which were placed into a sodium bicarbonate solution for 24 h after aging. Before drying the gels at ambient pressure (60 °C), small quantities of TMCS were poured upon them to initiate the CO₂-forming reaction and hence prevent pore collapse. To further enhance the aerogel properties by removing the by-product NaCl from the gel pores an additional washing step was added to the procedure either after or during the drying step.

The resulting aerogels were found to exhibit similar properties as samples prepared via supercritical CO₂ drying, exhibiting bulk densities as low as 0.06 g/cm³, porosities exceeding 98 % and specific surface areas of up to 700 m²/g, highlighting the great suitability of this drying technique for the manufacturing of silica aerogels. Further testing showed that the same process can also be applied to dawsonite (NaAlCO₃(OH)₂) aerogels synthesized with aluminum sec-butoxide and therefore is not limited to silica aerogels.

a) and b) SEM images of damselfly wing, c) Silica aerogel produced via novel bio-inspired APD technique, d) SEM image of silica aerogel structure.

Certainly, the most outstanding characteristics of the suggested aerogel synthesis route are its simplicity, cost-efficiency, scalability and wide applicability, making it a strong alternative to conventional drying techniques. Especially its ultra low material cost, estimated at $4 per kilogram of aerogel, and the absence of any specialized or hazardous processing conditions (such as elevated temperatures or pressures and toxic materials) could propel the presented approach to market maturity and hence make aerogel materials accessible for commercial sectors, such as the building or clothing industry.

More details: Han et al. “Bioinspired Synthesis of Monolithic and Layered Aerogels” Advances Materials. https://doi.org/10.1002/adma.201706294

Read more at:
http://www.millenniumpost.in/world/dragonfly-wings-inspire-new-generation-of-aerogels-296492 https://phys.org/news/2018-04-world-oldest-insect-aerogels.html

Quantum dot-sensitized solar cells (QDSCs) are the third generation of solar cells, using quantum dots as the absorbing photovoltaic material, which allow for larger theoretical efficiencies than conventional silica based cells. 
In addition to the major problems of this cell type — insufficient light absorption and electron hole recombination on the QD-electrolyte interface — which have been addressed in recent years yielding efficiencies up to 11 %, one great obstacle standing in the way of their large scale implementation is electrolyte loss due to evaporation. To avoid this undesired leakage of electrolyte entailing inferior cell performance, solid electrolyte carrier membranes have been introduced. Generally, synthetic polymer membranes have been deployed for this purpose. However, in light of environmental aspects, requiring a shift towards bio-compatible and renewable components, bio-based membranes are a logical replacement for their synthetic counterparts.

With the aim of devising biocompatible QDSC carrier membranes, scientists from the Aalto University in Finland have tested bio-based aerogel materials in QDSC cells, consisting of a CdS-sensitized photo-anode, a Pt counter electrode and a polysulfide redox electrolyte (see figure below).

Schematic of deployed QDSC architecture equipped with bio-based aerogel electrolyte carrier membrane.

To investigate the effect of different biopolymers, aerogels consisting of bacterial cellulose (BC), cellulose nanofibers (CNF), chitin nanofibers (ChNF) and TEMPO-oxidized CNF (TOCNF) were synthesized via gelation, solvent exchange and freeze-drying. Apart from their different fibrillar structures, the polymers exhibited a variety of different functional groups and surface charges, facilitating an investigation of the impact of these properties on cell performance.

Subsequent to gel drying, the aerogel samples were soaked with the polysulfide electrolyte, yielding free standing, flexible and stable structures in all four cases, allowing for easy sample handling and cell assembly.

Photocurrent-voltage (J-V) curves obtained under irradiation with one sun for reference QDSC and QDSCs equipped with bio-based polymer aerogel membranes.

The resulting membrane equipped QDSCs were then tested under irradiation of one sun (=1000 W/m2) to compare their performance to that of a reference cell filled with the untapped liquid electrolyte. All samples exhibited a similar photocurrent-voltage behavior, which can be seen in the figure on the right. Furthermore, the obtained values for the internal charge transfer resistance were comparable for all five cell type, suggesting that the membranes did not interfere with the internal charge transfer. Lastly, it was determined that neither membrane type had any detrimental effects on the polysulfide redox reaction, despite the difference surface charges of the deployed polymers.
In light of these findings, the authors concluded that cellulose and chitin based aerogels are suitable materials for organic electrolyte carrier membranes in QDSCs, since the performance of all aerogel-equipped samples was on par with that of the membrane-free reference cell. Out of the four different precursor materials, the researchers see the greatest promise in BC aerogels, due to its cost-efficient production technique via microbial fermentation and the resulting high purity of the biopolymer, guaranteeing a cheap and straight-forward production of BC aerogel membranes.

Certainly, the presented study can only be considered as an initial foray into the field of bio-based aerogel electrolyte carrier membranes. Future work will have to investigate the performance of such materials in more elaborate QDSC architectures to assess their potential for large scale implementation. Still, this pioneering work encourages endeavors aiming at the application of aerogel materials in photovoltaics. In case further work on this topic will underpin these findings, aerogels surely have the potential to become integral building blocks of next generation solar cells.

More details: Borghei et al. “Biobased aerogels with different surface charge as electrolyte carrier membranes in quantum dot-sensitized solar cell” Cellulose, 2018. https://doi.org/10.1007/s10570-018-1807-2

The Association of Advanced Porous Materials (Advapor) is to offer a € 3000 award to the “best” PhD completed in the field of Advanced Porous Materials. Defense must occur before June 2019.
The decision will be made by the steering team of the Advapor association and “best” will be judged on both technical merit and potential impact within our growing industry.
The award is designed to support the winning candidate in the presentation & publication of their work.

The award will be announced at the 2018 Aerogel Seminar in Hamburg.

Any candidate wishing to apply for this award must submit a concise summary of their work to info@advapor.org by the 31st July 2018.

Summary should include:

• Thesis Title
• Research establishment name & supervisor/s
• Detailed Abstract (2 pages maximum)
• Duration of the work
• List of associated publications
• Supervisor letter of support
• Contact details of applicant

The Aerogel Seminar will take place at the Technical University Hamburg 24-16 /9 /2018. 
Join now at our Website www.Advapor.org & help determine the future of Advanced Porous Materials.

PhD award Advapor pdf-Download

The Aerogel Seminar 2018 date is fast approaching. To get a gist of what’s in store, click the video from a previous aerogel conference organized in Hamburg (2014)

Read more at:
https://www.basf.com/de/products-and-industries/plastics-rubber/corpus/ideas-and-solutions/discussions-centered-on-the-material-of-the-future.html

Cotton is widely considered as a promising precursor material for aerogels due to its biodegradability, abundance, and non-toxicity. Furthermore, it is a low cost and renewable resource, making it an auspicious material for the addressing of environmental problems. Therefore, numerous studies have reported the utilization of cotton aerogels as superabsorbents for various different applications (e.g. cleaning up of oil spills or water purification).
Based on recent developments, allowing for the production of modified hydrophobic cotton aerogels, researchers from the South China University of Technology Guangzhou have come up with a new ingenious field of application — the trapping of methane bubbles, released by underground sea sediments, from water.

This application is of a special interest as methane is a very potent greenhouse gas, being responsible for approximately one fifth of the atmospheric greenhouse effect. Since aquatic system such as lakes, rivers or oceans are considered to be major sources of methane, releasing trapped gases to the atmosphere via bubbles, the capturing and safe storage of methane bubbles originating from marine environments could mitigate the negative impacts of climate change substantially.

In order to explore this idea, the research team from the South China University of Technology synthesized cotton aerogels (CAs) of varying cotton concentrations via freeze-drying. To ensure the hydrophobicity of the aerogels, the CAs were thereafter silanized with methyltrimethoxysilane, using a thermal chemical vapor deposition method. This resulted in stable monolithic cotton aerogels, which showed promising methane absorption characteristics under both static and dynamic conditions.
By submerging the different hydrophobic cotton aerogels (HCAs) in artificial seawater and exposing them to gaseous methane, it was found that the static absorption capacity increased with decreasing cotton concentration (i.e. larger porosity) and increasing submergence depth. Furthermore, the assessment of the dynamic absorptivity of the samples via compression/recovery cycles revealed that the process exhibits an outstanding repeatability, as the samples retained their absorption capacity to large extents.
With the aim of investigating a continuous strategy to safely transport methane above sea level, a pipe connecting the HCAs to the water surface was attached to the aerogel monoliths. This approach, which is schematically shown in the figure below, led to a steady and controlled transport of methane to the surface, as the bubbles trapped within the aerogel travelled through the pipe due to the existing pressure difference, resulting in an immediate recovery of the aerogel absorption capacity.

Schematic of continuous methane bubble trapping via a HCAs connected to a pipe.

 
Certainly, the reduction of methane emissions from lakes and oceans could have a substantial positive impact on the world-wide greenhouse gas emissions. Therefore, the novel findings motivate a further investigation of the climate change mitigation potential of the deployment of (aerogel-based) methane bubble absorbents in aquatic systems.
The hydrophobic aerogels investigated in this study are not only captivating because of their excellent methane absorptivity, but also exhibit outstanding properties in terms of bio-compatibility and non-toxicity, paving the way for large scale deployment even in fragile eco-systems.
If further positive results in this field can be achieved, the trapping of methane from seawater could even become an economical process, with the captured methane being sold to compensate for the required investment and operational costs.

More details: Nan Li  et al. “A Low-cost, Sustainable and Environmentally Sound Cellulose Absorbent with High Efficiency for Collecting Methane Bubbles from Seawater” ACS Sustainable Chem. Eng. https://pubsdc3.acs.org/doi/pdf/10.1021/acssuschemeng.8b00146

Despite their intriguing characteristics (e.g. ultralow density, high porosity & electrical conductivity), the application of carbon aerogels is generally limited by their poor mechanical strength and brittleness. Researchers from the Zhejiang University (China) were now able to manufacture highly flexible, binary carbon aerogels (bCAs) consisting of graphene and multi-walled carbon nanotubes (MWNTs), which can resist compressive and tensile stresses. These novel bCAs were successfully used as strain sensors to detect complex three dimensional movements.

The novel aerogels were fabricated by creating an aqueous solution equipped of graphene oxide and MWNTs which was then given shape by additive 3D-printing. Thereafter, the structures were freeze-dried before being chemically or thermally reduced.

Owing to their hierarchical assembly, which is schematically shown in the figure below, the novel bCAs exhibit an extraordinary stretching stability over a wide range of conditions (e.g. temperatures from 93-773 K). Furthermore, they exhibit a noteworthy fatigue resistance, being able to retain their structural shape to great extents for at least 100 cycles at 200 % tensile strain.

Schematic of hierarchical assembly of bCAs, stretching from centimeter to nanometer range. Fourth order: Graphene and MWNT molecular blocks; Third order: graphene laminates; Second Order: Polygon cell; First Order: Macroscopic truss structure

Another key characteristic of the bCAs is their change in resistance in tension (gentle increase) and compression (steep increase). Exploiting this feature, the researchers equipped the joints of a snake-like robot with bCAs to be able to sense the robot’s movements and configurations. As shown in the figure below, a sensor array consisting of three bCAs was sufficient to map the continuously changing configurations and hence accurately identify the robot’s movements.

Illustration of working principle of a three bCAs sensor array to identify the movements of a snake-like robot

 
The authors identify other potential applications of the bCAs in wearable electronic devices, lightweight mechanical devices and fields of application requiring robustness and reliability in the most extreme conditions (e.g. aerospace engineering). Furthermore, the researchers are confident that their assembly method can be deployed for the fabrication of other highly stretchable aerogel materials.

More details: Fan Guo et al. “Highly stretchable carbon aerogels.” Nature Communications. https://www.nature.com/articles/s41467-018-03268-y
Read more: https://phys.org/news/2018-03-rubbery-carbon-aerogels-greatly-applications.html

The German chemical company BASF Polyurethanes GmbH has won the German Design Award for its Excellent Product Design in the category Building and Elements. The jury selected the aerogel insulation material SLENTITE® due to its unique combination of properties, facilitating space-saving insulation concepts which open up entirely new creative possibilities to architects and designers.

Award-winning SLENTITE® aerogel material for ultra thin building insulation

The novel aerogel material, consisting of 90 % air, allows for the reduction of insulation thicknesses by 50 %, when compared to standard insulation materials. Besides its outstanding thermal insulation properties, it is the first solid, breathable aerogel panel produced from polyurethane. Furthermore, it is easily machined without excessive dust generation, allowing for tailored shapes & sizes and direct application on walls or facades.

Consequently, the SLENTITE^® thermal insulation panels eclipse any commercial insulation material while fulfilling all demands placed on modern building materials.
Its honoring by the German Design Award jury could spark the interest of potential customers and competitors, stimulating the aerogel insulation material market.

Read more:
http://www.german-design-award.com/en/the-winners/gallery/detail/17074-slentite.html
https://www.basf.com/en/company/news-and-media/news-releases/2018/02/p-18-120.html
https://www.bi-medien.de/artikel-24501-bm-extrem-schlanke-daemmplatte-von-basf.bi

Recently, we have reported on the potential of aerogel sorbents for CO₂ capture and storage (CCS). Despite their favorable properties, the deployed amine functionalized aerogels (AMAs) were found to require optimization to allow for their successful economical implementation. Increasing the activity and capacity of solid sorbents while decreasing their cost, is therefore an issue which is currently under investigation. Researchers from the US and Sri Lanka now report to have found an efficient, cheap and environmentally benign solid CO₂ sorbent: KOH-activated carbon chitin aerogels.

The novel sorbent material was synthesized from commercial chitin powder from shrimp shells, which was dispersed in a sodium-urea-water solution. Repeated freezing/thawing cycles of this solution resulted in the formation of a stable hydrogel, which subsequently was freeze-dried to obtain a chitin aerogel. Thereafter, carbonization of the aerogel was achieved by heating the sample to 800 °C under nitrogen atmosphere. In the last step, the aerogel was again heated to 850 °C (under N₂ atmosphere) in the presence of potassium hydroxide (KOH) to obtain the activated carbon aerogel. Consequently, the inexpensive manufacturing technique, which does not require any costly or toxic chemicals, and the abundance of the precursor materials facilitate the cheap production of chitin-based CO₂ sorbents.

The final activated carbon aerogels were found to exhibit large specific surface areas (> 500 m²/g), more than 35 times larger than that of their parent chitin aerogels. Additionally, the micro pore volume, which is an important parameter for CO₂ capture, increased by the factor of 95 between the chitin aerogel and the carbonized and KOH-activated sample. These two factors explain why the obtained CO₂ sorptivity value of 0.48 mmol/g (1 atm, 0 °C), obtained for the chitin aerogel, could be vastly increased to 5.02 mmol/g by further processing (i.e. carbonization and activation). As shown in the figure below, similar increase in sample sorptivity was also measured at room temperature (0.28 mmol/g and 3.44 mmol/g, respectively). This means that the morphological changes taking place inside the aerogel structure during carbonization and activation have a significant impact on the final sorbent properties.

CO2 adsorption isotherms at 1 atm and 0 °C (a) and 1 atm and 25 °C (b) for chitin aerogels (1), carbonized chitin aerogels (2) and KOH-activated chitin aerogels

The authors conclude that they have found an environmentally benign and very inexpensive way of manufacturing highly active chitin-based sorbents for CO₂ capture. Additionally, the sorbents are synthesized from a biopolymer, making the final material biodegradable and non-toxic.

More details: Dassanayake, R.S., Gunathilake, C., Abidi, N. et al.; Activated carbon derived from chitin aerogels: preparation and CO2 adsorption, Cellulose (2018). https://doi.org/10.1007/s10570-018-1660-3

Fragility and brittleness have always been flaws of delicate three-dimensional aerogel structures. Especially when exposed to harsh conditions (e.g. in aerospace applications), their frailty has limited the broad application of aerogels in such fields. A Chinese team of researchers from the Beijing Jiaotong University has now attended to this matter. By equipping a ZrO₂–SiO₂ aerogel with Polycrystalline ZrO₂ fibers (ZrO_2f), aerogels possessing high thermal and mechanical resilience have been devised. Astonishingly, these monolithic aerogels do not only excel in terms of stability, but also show low bulk densities and thermal conductivities.

The idea of adding a fibrous agent to the aerogel matrix is that, when dispersed evenly throughout the matrix, the fibers act as an additional mechanical backbone. This means that the fibers hinder fracturing and irreversible deformation through fiber-bridging and crack-deflection (see Figure below) when the monolithic structure is being strained. Furthermore, due to the even dispersion of the fibers in the aerogel matrix, the contribution of heat conduction through the fibers is minimized and hence the overall heat conductivity increases only marginally upon addition of the fibrous ZrO₂.

a) Image of ZrO2f/ZrO2-SiO2 aerogel monolith; b)–d) SEM images of fractures of the aerogel composite.

In summary, these effects lead to highly insulating aerogels possessing compressive strengths 3-10 times higher than previously reported. Therefore, applications in very demanding environments are facilitated, which might prove to be significant in aerospace engineering and other fields in which stable and highly insulating materials are essential.

More details: Xianbo Hou, Rubing Zhang and Daining Fang; An ultralight silica-modified ZrO₂–SiO₂ aerogel composite with ultra-low thermal conductivity and enhanced mechanical strength, Scripta Materialia Volume 143, 15 January 2018, Pages 113-116. http://doi.org/10.1016/j.scriptamat.2017.09.028

Researchers from the Kyoto University (Japan) successfully synthesized transparent, machinable, scalable, super-compressible, highly elastic and super-insulating polyvinylpolymethylsiloxane aerogels and xerogels. Remarkably, the study reports that these outstanding features were present not only in aerogels produced using supercritical drying, but in those produced using ambient pressure drying, too.

The sample preparation was achieved by mixing vinylmethyldimethoxysilane (VMDMS) or vinylmethyldiethoxysilane (VMDES) with 1-5 % of di-tert-butyl peroxide (DTBP), to initiate the radical polymerization at 120 °C, yielding a transparent viscous liquid mainly containing polyvinylmethyldimethoxysilane (PVMDMS) or polyvinylmethyldiethoxysilane (PVMDES). Thereafter, BzOH, H₂O and tetramethylammonium hydroxide (TMAOH) were added to the liquid and the mixture was heated to 80 °C for one hour to obtain transparent and flexible gels. Prior to solvent exchange with isopropanol (IPA), the gels were aged between four or five days at 80-100 °C. Removal of the liquid was subsequently accomplished in three different ways (see Figure below): (1) supercritical drying with CO₂; (2) solvent exchange into n-hexane followed by drying at ambient pressure; (3) direct drying from IPA at ambient pressure.

Comparison of different drying methods to obtain PVMDMS or PCMDES aerogels and xerogels.

It was established that key to the intriguing properties of the dried aerogels and xerogels are their homogeneous porous nanostructure, composed of flexible hydrocarbon chains chemically cross-linked with polymethylsiloxanes. Notably, this type of nanostructure structure exhibited low densities (0.16-0.22 g/cm³) and heat conductivities (15.0-15.4 mW/m K), as well as high specific surface areas (900-1000 m²/g), good transparency (>80 % light transmittance), and extraordinary flexibility (see attached video). Additionally, the flexible network structures allowed for a recovery of the evaporation-induced gel shrinkage through a “spring-back” effect (see Figure below), making the supercritical drying step dispensable.

Progression of gel volume during ambient pressure drying. “spring-back” effect yields xerogels of nearly the same volume as the parent gel.

In summary, these findings imply that an ultra-low cost pathway to manufacture aerogels by ambient pressure drying while still preserving extraordinary properties required for applications as superinsulators has been established. This means that one of the main obstacles for the broad application of aerogels — their high manufacturing costs — has been overcome, which might pave the way for their large scale deployment.

More details: Zu et al.; Transparent, Superflexible Doubly Cross-Linked Polyvinylpolymethylsiloxane Aerogel Superinsulators via Ambient Pressure Drying , ACS Nano, January 8, 2018. https://doi.org/10.1021/acsnano.7b07117

Video of aerogel bending test: Click Here