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Item type:Publication, Access status: with files , Review and perspectives on the sustainability of organic aerogels(American Chemical Society (ACS), 2025-04-25); ; ; ; Aerogels are exceptionally lightweight materials characterized by their high open porosity and remarkable specific surface area, currently used across a wide array of industrial sectors from construction to energy storage and have great potential for expanding their applicability and unlocking new market opportunities. Driven by global economic growth and an intensifying environmental crisis, there is a growing demand for engineering innovations that prioritize sustainability. Aerogels are well-positioned to support these sustainability efforts. Their unique properties make them ideal for energy-saving solutions, environmental remediation, and more efficient use of resources. As the demand for eco-conscious technologies rises, aerogels are poised to contribute significantly to the development of greener, more efficient products and processes across multiple industries. The sustainability of aerogel technology is crucial for the mid-to-long-term future, yet its current status has been scarcely reviewed in the literature. This Perspective explores and critically reviews significant advances on organic and hybrid aerogels in the current socioeconomic scenario, with selected case studies endorsing their contribution to the UN Sustainable Development Goals. It also identifies research gaps while proposing innovative strategies to enhance the sustainability of aerogel production through the application of circular economy principles. Key strategies discussed involve the fabrication of aerogels using eco-friendly sources, such as biopolymers derived from biorefinery processes or from waste materials. Additionally, this Perspective examines the development of methods for the reuse, recycling, and end-of-life management of aerogels, along with the implementation of more efficient processing routes. Ultimately, this work highlights the need for comprehensive assessments of aerogel sustainability through life cycle assessment (LCA) and evaluations of safety and toxicity. By addressing these critical aspects, the potential of aerogels to contribute to a more sustainable future appears highly favorable from both commercial and research perspectives, paving the way for a circular aerogel economy and providing a lasting impact to the society in which we live.Publicationtype: Review Article61 9 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Whey protein isolate-based aerogels with improved hydration properties for food packaging applications(American Chemical Society (ACS), 2024-01-03); ; ; ; Ioannou, DimosthenisIn the present work, tannin-modified whey protein isolate (WPI/tannin) aerogels were synthesized, and their hydration properties were evaluated. The materials were prepared by introducing two different tannins (one hydrolyzable and one condensed) in the protein matrix via thermal-induced gelation of neutral or alkaline aqueous solutions (pH 7, 9, or 11) at 80 °C. WPI and WPI/tannin aerogels are nanostructured porous materials with high BET surface areas (216-353 m2 g-1). Subsequently, WPI and WPI/tannin aerogels were hydrophobized via silanization (with bis(trimethylsilyl)amine) in the gas phase (HWPI and HWPI/tannin aerogels). As a result of silanization, BET surface areas were reduced to 87-242 m2 g-1. The hydration properties of all aerogels were studied by measuring the water uptake and water contact angles. Pristine WPI aerogels absorbed high amounts of water (up to 4794% w/w in 24 h), swelled, and eventually disintegrated. WPI/tannin aerogels prepared with the condensed tannin absorbed more water (219-559% w/w) than those prepared with the hydrolyzable tannin (81-88% w/w). In any case, the water uptake was significantly lower compared with that of pristine WPI aerogels. After silanization, all aerogels absorbed much smaller amounts of water (39-84% w/w). The reduced water uptake was in agreement with the water contact angles, which were in the ranges 35-55° for WPI aerogels, 40-60° for WPI/tannin aerogels, 80-86° for HWPI aerogels, and 100-116° for HWPI/tannin aerogels. These results clearly indicate that both the introduction of tannin in the protein matrix and the silanization of the solid network are necessary to obtain water-stable WPI-based aerogels. There is an immense need for replacing the existing plastic-based food packaging with biobased and biodegradable materials. In this context, our results address the major disadvantage of most biobased materials (i.e., poor stability in aqueous environments) and render these new aerogels good candidates for food packaging applications.Publicationtype: Journal Article23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Metal-doped carbons from polyurea-crosslinked alginate aerogel beads(Royal Society of Chemistry (RSC), 2021-03-24); ; ; ; Metal-doped polyurea-crosslinked alginate aerogel beads (X-M-alginate; M: Ca, Co, Ni, Cu) were prepared via the reaction of an aromatic triisocyanate (Desmodur RE) with the -OH groups on the surface of pre-formed M-alginate wet gels, and with adsorbed gelation water. The X-M-alginate aerogels consisted of 49-63% polyurea and contained 2-7% metal ions; they were fibrous macro/meso/microporous materials with porosities up to 94% v/v, and BET surface areas 245-486 m2 g-1, comparable to those of native M-alginate aerogels (258-542 m2 g-1). The pyrolysis of X-M-alginate aerogels (M: Co, Ni, Cu) at 800 °C yielded carbon aerogels (X-M-C; 33-37% yield) doped with the corresponding metal (as well as with Cu2O in the case of X-Cu-C), with crystallite sizes of around 22 nm. The X-M-C aerogels retained the general fibrous morphology of their precursor (X-M-alginate) aerogels, and while X-Co-C and X-Ni-C appeared similar, the fibrous morphology of X-Cu-C was distinctly different, indicating an effect of the metal on the nanostructure of the corresponding carbon. The porosities of all X-M-C aerogels were in the range of 88-92% v/v, including macro-, meso- and micropores. Their BET surface areas were in the range of 426-541 m2 g-1, of which 208-319 m2 g-1 was allocated to micropores. In addition to the metals, XPS, Raman and FTIR analyses showed the presence of oxygen and nitrogen functionalities. Carbon in the X-M-C aerogels showed signs of stacking of graphene oxide sheets (14-15 nm), but also a low degree of graphitization and a large number of defects. This work provides a direct, inexpensive method for the preparation of fibrous metal-, oxygen- and nitrogen-doped carbon aerogels with potential for catalytic and electrochemical applications.Publicationtype: Journal ArticleScopus© Citations 16 151 243 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Mechanically Strong Polyurea/Polyurethane-Cross-Linked Alginate AerogelsTwo types of preformed alginate wet gels, one with a low (30-35%) and the other with a high (65-75%) content of glucuronic acid, were reacted with an aliphatic triisocyanate that was priorly allowed to diffuse in the pores. This reaction formed urethane groups on the surface of the alginate framework and also formed a polyurea (PUA) network connecting these urethane groups via respective reactions of the triisocyanate with alginate surface -OH groups or with gelation water remaining adsorbed on the inner surfaces of the wet gels. These processes formed a conformal nanothin film of PUA around the alginate network. After drying the wet gels with the supercritical fluid CO2, we obtained PUA/polyurethane-cross-linked alginate (X-alginate) aerogels. Although X-alginate aerogels are essentially copolymers, unlike all copolymers mentioned in previous literature reports, the relative topology of the alginate and the cross-linker is defined at the nanoscopic scale rather than at the molecular level. For the systematic study of X-alginate aerogels as a function of synthetic conditions, the experimental protocol was designed according to the central circumscribed rotatory design model using the alginate and the triisocyanate concentration as independent variables. Empirical models were derived for all relevant material properties by fitting experimental data to the two independent variables. The chemical identity of all samples was confirmed with attenuated total reflectance-Fourier transform infrared spectroscopy and solid-state 13C and 15N cross-polarization magic angle spinning NMR spectroscopy. The percentage of PUA uptake in X-alginate aerogels (58-98%) was calculated from skeletal density data. Scanning electron microscopy showed that all samples were nanofibrous, indicating that PUA coated conformally the skeletal network of both alginates, and the micromorphology remained the same as in the native (non-cross-linked) samples. X-alginate aerogels are mechanically strong materials, in contrast to their native counterparts, which are extremely weak mechanically. Compared to various organic aerogels from the literature, X-alginate aerogels can be as stiff as many other polymeric aerogels with 2 or 3 times higher densities. In addition, X-alginate aerogels are good candidates for sound insulation applications, as the speed of sound in most samples was estimated to be significantly lower than the speed of sound in dry air.Publicationtype: Journal Article59 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Polyurea-crosslinked biopolymer aerogel beads(Royal Society of Chemistry (RSC), 2020); ; ; ; Polyurea-crosslinked calcium alginate (X-Ca-alginate) and chitosan (X-chitosan) aerogel beads have been prepared via reaction of an aliphatic triisocyanate (Desmodur N3300) with the –OH groups of calcium alginate or the –NH2 groups of chitosan preformed wet gels, forming surface urethane or urea groups, respectively, and the subsequent formation of a polyurea conformal coating of the network via reaction of the triisocyanate with adsorbed water retained on the inner surfaces of the wet gels. That conformal coating is evident by SEM, which showed that all aerogels, native and crosslinked, were fibrous and their micromorphology did not change after crosslinking. The chemical identity of the new materials was confirmed with ATR-FTIR spectroscopy and solid-state 13C and 15N CPMAS NMR spectroscopy. The percent uptake of polyurea in X-Ca-alginate aerogels (43–66%) and X-chitosan aerogels (31–51%) was calculated from skeletal density data. This work expands the methodology for polymer-crosslinked alginate aerogels from monoliths to beads, and from alginates to chitosan, establishing its generality for all biopolymer aerogels. Possible applications of these materials include environmental remediation and conversion to carbon aerogels.Publicationtype: Journal ArticleScopus© Citations 26 177 204 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Strategies toward catalytic biopolymers: Incorporation of tungsten in alginate aerogelsWe report the synthesis of W-doped biopolymer aerogels with potential applications to catalysis. The biopolymers were based on alginate, a cost-efficient natural material, and were prepared in environmentally friendly water/ethanol solutions. Gelation of alginate was induced by crosslinking with Ca2+. The resulting wet-gels were impregnated with an ethanolic solution of the ditungsten complex [W2(μ-OEt)2(OEt)2(EtOH)2Cl4] ({W = W}8+) and were dried with supercritical fluid (SCF) CO2 to yield W-doped alginate aerogels containing 10% w/w tungsten. Dry materials were characterized with FTIR, SEM/EDS, TGA, N2 porosimetry and He pycnometry. The bulk densities were low (<0.1 g cm−3), porosities were high (96% v/v), as well as the BET surface areas (380 m2/g). Pyrolysis of those aerogels at 800 °C under Ar yielded carbon along with a mixture of calcium tungstates, i.e., CaWO4 and Ca3WO6 (weight ratio: 70:30), while pyrolysis under O2 yielded the same tungstates, but with a different weight ratio (10:90). This can be a new process for Ca3WO6, which, due to its ordered double perovskite structure, is ideal for doping with metal ions, at relatively low temperature (800 °C versus >1000 °C in the literature).Publicationtype: Journal Article155