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An ever-increasing number of applications of oxide aerogels places a high demand on wettability-tuning techniques. This work explores the possibility to cheaply prepare GeO2 aerogels with controlled wettability by an ambient pressure drying (APD) method. GeO2 aerogels are prepared via two synthetic routes. Surface modification is carried out by soaking the gels in a silylating agent solution; type and concentration of the modifier are optimized to achieve a large surface area. The aerogels have been characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, nitrogen adsorption and contact angle measurements. The effect of surface modification on the phase composition and particle size of the aerogels is described. In summary, the work provides a new cheap production method for the preparation of both hydrophobic and hydrophilic GeO2 aerogels with contact angle varying from 30° to 141° and with surface area of 90–140 m2/g, which facilitates the expansion of their diverse applications. GeO2 aerogel synthesis by APD is reported for the first time. [ABSTRACT FROM AUTHOR]

Polypropylene-based aerogels with high surface area have been developed for the first time. By chemical crosslinking of polypropylene with oligomeric capped-end amino compounds, followed by dissolution, thermally induced phase separation, and the supercritical CO2 drying process or freeze-drying method, the aerogels exhibit high specific surface areas up to 200 m2/g. Moreover, the silica-cage multi-amino compound was utilized in a similar vein for forming hybrid polypropylene aerogels. According to the SEM, the developed polypropylene-based aerogels exhibit highly porous morphology with micro-nanoscale structural features that can be controlled by processing conditions. Our simple and inexpensive synthetic strategy results in a low-cost, chemically resistant, and highly porous material that can be tailored according to end-use applications. [ABSTRACT FROM AUTHOR]

Aerogel composites were synthesized on the basis of the sodium alginate-chitosan interpolymer complex with the inclusion of calcium carbonate microparticles and supercritical drying. It is shown that the textural characteristics of materials did not depend on the morphology of calcium carbonate particles: the specific surface area of aerogels was almost the same for all materials, 380–400 m2/g. The developed porous structure of composites along with the polyelectrolyte nature determined their high water absorption (up to 110 g/g). To impart antimicrobial properties, the materials were impregnated with atranorin isolated from the lichen Hypogymnia physodes, which has a pronounced inhibitory effect on the bacterium P. mirabilis, the main causative agent of wound infections. The minimum suppressive concentration of atranorine was 1 mg/mL. The release of the main amount of atranorine aerosol material included in the matrix occurred within 4 hours, 50%. [ABSTRACT FROM AUTHOR]

The inherent characteristics of cellulose-derived aerogels, such as their natural abundance and environmental friendliness, make them highly interesting. However, its significant shrinkage before and after the supercritical drying procedure and low mechanical strength limit its potential application. Here, we propose a strategy to prepare cellulose diacetate aerogels (CDAAs) with low drying shrinkage, exceptional thermal insulation, and superior mechanical strength. The low drying shrinkage (radial drying shrinkage of 1.4%) of CDAAs is attributed to their relative strong networking skeletons, which are greatly formed by tert-butanol solvent exchange in exerting the interaction of reducing the surface tension force. In this case, CDAAs are eventually endowed with the low bulk density of 0.069 g cm−3 as well. Additionally, as-prepared CDAAs possess an abundant three-dimensional networking structure whose pore size is concentrated in the diameter range of ~50 nm, and the result above is beneficial for improving the thermal insulation performance (thermal conductivity of 0.021 W m−1 K−1 at ambient environmental and pressure conditions). On the other hand, the optimal compressive stresses of CDAAs at 3% and 5% strain are 0.22 and 0.27 MPa respectively, indicating a mechanically well robustness. The above evidence demonstrates indeed the exceptional thermal insulation and superior compressive properties of CDAAs. This work may provide a new solution for developing a kind of high-performance cellulose-derived aerogel in the future. [ABSTRACT FROM AUTHOR]

Tragacanth, an anionic polysaccharide, is a natural material widely investigated for the synthesis of aerogels as drug delivery vehicles. Its biocompatibility, biodegradability, and affordability are all key features for its use in pharmaceutical applications. In this study, tragacanth and tragacanth alginate composite aerogels were prepared using the sol-gel technique followed by supercritical drying. Paracetamol was selected as a model drug for drug loading and release studies owing to its high solubility in ethanol and low solubility in supercritical carbon dioxide. The paracetamol loading into the aerogel pores was confirmed by infrared spectroscopy (IR) and x-ray diffraction (XRD) spectra of the resulting samples. Scanning electron microscopy (SEM) images showed that all aerogels were porous with a macroporous-mesoporous network. Due to the high porosity of the prepared aerogels, a loading of 99 wt% (mg drug/mg aerogel) for tragacanth and 114 wt% (mg drug/mg aerogel) for composite aerogels was achieved. Moreover, the release rate of the drug could be modified by manipulating the aerogel composition. Tragacanth aerogels had a faster release rate, while the addition of alginate prolonged the release rate of the model drug. Various empirical release models were investigated and the release rate was found to follow the Korsmeyer-Peppas (Power Law) model suggesting a diffusion-based release kinetics. Based on the results, the feasibility of utilizing tragacanth for the preparation of drug-loaded aerogels was shown. Highlights: Tragacanth is a suitable polysaccharide for the synthesis of aerogels. Macropores/mesopores of all synthesized aerogels are suitable for drug loading. The presence of alginate retards the release of the model drug up to 20% at each time point. The release kinetics of the synthesized aerogels follow the Korsmeyer-Peppas model. [ABSTRACT FROM AUTHOR]

An ever-increasing number of applications of oxide aerogels places a high demand on wettability-tuning techniques. This work explores the possibility to cheaply prepare GeO2 aerogels with controlled wettability by an ambient pressure drying (APD) method. GeO2 aerogels are prepared via two synthetic routes. Surface modification is carried out by soaking the gels in a silylating agent solution; type and concentration of the modifier are optimized to achieve a large surface area. The aerogels have been characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, nitrogen adsorption and contact angle measurements. The effect of surface modification on the phase composition and particle size of the aerogels is described. In summary, the work provides a new cheap production method for the preparation of both hydrophobic and hydrophilic GeO2 aerogels with contact angle varying from 30° to 141° and with surface area of 90–140 m2/g, which facilitates the expansion of their diverse applications. GeO2 aerogel synthesis by APD is reported for the first time.

Protein (eggwhite) and chitosan aerogel microparticles characterized by low density, developed morphology, high specific surface area, high porosity, large volume, and small pore diameter, have been obtained. Particle size distribution curves were obtained by laser diffraction, from which the number average and aerodynamic diameters were calculated. The aerodynamic diameter of all of the obtained biopolymer aerogels lies in the range required for targeted delivery of active pharmaceutical ingredients (APIs) to the olfactory region of the nasal cavity. Experimental studies were performed to introduce the "melatonin" API in the pores of biopolymer aerogels at the solvent replacement and supercritical adsorption steps. The mass fractions of APIs in the resulting biopolymer aerogel–API pharmaceutical composites were determined by high-performance liquid chromatography. An X-ray powder diffraction analysis showed that API was present in pharmaceutical compositions mainly in the amorphous state. The results of in vivo experimental studies showed that in the case of intranasal administration of both biopolymer aerogel–API composites, the maximum concentration of API in brain tissues is reached already after 30 min. This proves that the obtained biopolymer aerogels based on protein (eggwhite) and chitosan are promising for use as API carrier matrices in the development of nasal drug delivery systems. [ABSTRACT FROM AUTHOR]

This article presents the results of modeling the hydrodynamics and mass transfer of the supercritical drying process in apparatuses of various volumes. Calculations of hydrodynamics and mass transfer were carried out using the Ansys Fluent software package, exemplified with devices of laboratory and industrial volumes—2 and 70 L, respectively. The modeling aimed to predict the time of supercritical drying and the feasibility of scaling the process. Continuum mechanics principles were employed to model hydrodynamics and mass transfer, treating the multicomponent system as a viscous compressible fluid. The calculation took place in two areas: within a porous body and in the free volume of an apparatus of a certain scale. Additionally, a study was conducted on the hydrodynamics and mass transfer of the process in the presence of a divider, necessary to minimize the formation of stagnant zones in the apparatus. For optimization purposes, the divider calculation was performed separately from the apparatus. The data obtained were then used in subsequent calculations of the hydrodynamics and mass transfer of the process, employing a user-defined function (UDF) written in the C programming language. A preliminary study of the kinetics of supercritical drying in a 2-L apparatus was carried out to assess the possibility of using the proposed mathematical model for an industrial-level apparatus. The simulation demonstrated that the proposed model is capable of describing the process of supercritical drying in devices of various volumes. Furthermore, calculated curves of the kinetics of supercritical drying, profiles of the velocity distribution of supercritical carbon dioxide, and the distribution of the concentration of isopropyl alcohol at various points in time across the cross-section of the apparatus were obtained. [ABSTRACT FROM AUTHOR]

The paper explores a method for the direct synthesis of functional compounds within the bulk of inorganic aerogels, coupled with the supercritical drying of composite materials. The processes for obtaining these materials are delineated into three main stages. The initial stage involves the synthesis of functional compounds on the gel surfaces. The subsequent stage entails the displacement of the solvent from the free volume of the apparatus by flowing supercritical carbon dioxide through the autoclave. The final stage is the supercritical drying process, leading to the removal of solvent from the material pores. The work provides detailed parameters for conducting both synthesis and supercritical drying processes. Additionally, a technological scheme of an industrial installation with a volume of 70 liters, employed for conducting supercritical processes and situated in Niagara LLC, Shchelkovo, is presented and described. To model these processes, a mathematical model was developed using the CHEMCAD software package, facilitating the determination of material and heat balances for individual devices and the overall technological scheme. The paper also calculates the impact of the amount of isopropyl alcohol on carbon dioxide consumption. An analysis of energy costs for the synthesis of functional compounds within aerogel volumes is conducted based on the acquired data. The mathematical model enables the identification of an energy- and resource-efficient method for the technological design of synthesis and supercritical drying processes. Notably, a reduction in energy costs within the technological scheme is achieved through the utilization of heat after compression. [ABSTRACT FROM AUTHOR]

Aerogels containing rare earth elements are promising compounds for designing various functional materials, since they combine the properties of aerogels - high surface area and porosity, and the luminescent and catalytic properties of rare earth elements. A modified sol-gel method was developed to produce mixed rare earth oxide aerogels (Eu2O3/Gd2O3, Eu2O3/Yb2O3, and Gd2O3/Yb2O3) with high metal to metal molar ratio (1:1) and individual (Eu2O3, Gd2O3, and Yb2O3) aerogels. Rare earth nitrates, propylene oxide, and citric acid were used for the synthesis of monolithic halogen-free rare earth oxide aerogels. The aerogels obtained by supercritical drying in CO2 possess mesoporous structure and high surface area (180–350 m2/g). Uniform distribution of elements in binary oxides was confirmed by EDX. Calcination at 600–800 °С causes crystallization of the amorphous aerogels. XRD patterns of the binary oxides after calcination corresponded to single phase cubic ( I a 3 ¯ ) structure of rare earth M2O3 oxide, which indicated the formation of solid solutions. The Eu2O3/Gd2O3 and Eu2O3 aerogels demonstrate strong luminescence in visible region at near UV excitation, which was also observed after calcination of the aerogels at 800 °C. Highlights: Binary (Eu2O3/Gd2O3, Eu2O3/Yb2O3, and Gd2O3/Yb2O3) and individual (Eu2O3, Gd2O3, and Yb2O3) aerogels with high surface areas were synthesized by supercritical drying in CO2. Influence of propylene oxide and citric acid concentrations on sol-gel process in RE nitrate solutions was studied. After calcination at 600–800 °С the amorphous aerogels get crystalline structure, the binary oxides demonstrate single phase. The binary and individual oxides were characterized by XRD, IR, nitrogen absorption, SEM methods. The as-prepared and calcinated europium-containing aerogels demonstrate luminescence in visible region at near UV excitation. [ABSTRACT FROM AUTHOR]

A new para-aramid aerogel based on a polymer made by the reaction of terephthaloyl dichloride with 2-(4-aminophenyl)-1H-benzimidazol-5-amine (PABI) is introduced. The aerogel readily bound Pd (+2) ions and was used as a hydrogenation catalyst in some industrially actual reactions. The new material, which did not contain p-phenylenediamine moieties, was prepared in two form factors: bulk samples and spherical pellets of 700–900 μm in diameter. Aerogels were synthesized from 1% or 5% solutions of PABI in N,N-dimethylacetamide via gelation with acetone or isopropanol and had a density of 0.057 or 0.375 g/cm3 depending on the concentration of the starting PABI solution. The specific surface area of the obtained samples was 470 or 320 m2/g. Spherical pellets containing Pd were prepared from a solution of PdCl2 in PABI and were used as heterogeneous catalysts for the gas-phase hydrogenation of unsaturated organic compounds presenting the main types of industrially important substrates: olefins, acetylenes, aromatics, carbonyls, and nitriles. Catalytic hydrogenation of gaseous hexene-1, hexyne-3, cyclohexene, and acrylonitrile C=C bond proceeded with a 99% conversion at ambient pressure, but the catalyst failed to reduce acetone at 150 °C and benzene and ethyl acetate even at 200 °C. The only product of acrylonitrile hydrogenation was propionitrile. The prepared catalysts showed high selectivity, which is important for the chemistry of complex organic compounds. [ABSTRACT FROM AUTHOR]

In this study, aerogels based on graphene oxide decorated with iron oxide nanoparticles are obtained by drying in supercritical isopropanol. For the synthesized samples with the calculated initial iron contents of 9, 18 and 36 wt %, the morphology and structure of the graphene matrix and iron-containing nanoparticles are studied using the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. Comparative investigations are conducted to analyze the carbon and hydrogen composition within the synthesized aerogels structure, followed by an assessment of their magnetic properties at ambient temperature. Sorption experiments are carried out for the extraction of heavy and rare earth elements from multicomponent aqueous solutions of a complex composition. [ABSTRACT FROM AUTHOR]

Aerogels are three-dimensional nanostructures of non-fluid colloids connected to porous networks made of loosely packed bonded particles. They are often manufactured utilizing the sol-gel technique following a drying procedure like supercritical, freeze, or ambient pressure drying. It is the lightest solid material and has several unique qualities, including excellent insulation. Intrinsic brittleness and porous nature make their processing and handling complex, which restrict applicability in several real-world dynamic situations. An effective strategy to strengthen the silica aerogel structure is manufacturing composites with an incorporated fibrous material, which expands their uses considerably. This study covers the scientific synthesis, characterization, and applications of silica aerogel. It encourages silica aerogel composites/blankets that are strengthened by additives and fibrous material made from a wide variety of fibers and fabrics, as well as their manufacturing processes and properties. The effect of fibrous material (fiber and fabric) embedment on the final properties of composites has been extensively discussed, considering the amount of loading in the matrix and their unique characteristics, such as density, shrinkage, mechanical, thermal, and acoustic properties. Fiber-reinforced silica aerogel composites'/blankets applications are briefly discussed, indicating advancements in aerogel functions such as thermal sensors, acoustic insulators, and technical textiles such as protective clothing, medical textiles, and insulation blankets. [ABSTRACT FROM AUTHOR]

A simple and easily operated supercritical CO 2 dryer was designed and manufactured with the aim of producing high-surface-area mesoporous α-Fe 2 O 3 (hematite) and NiO aerogels. The gels were synthesized by a sol−gel method with the aid of propylene oxide (PO), as the gelation agent, and then dried and calcined at different conditions. The effects of drying and calcination conditions on the physicochemical properties of the final aerogels were investigated using X-ray diffraction (XRD), N 2 adsorption-desorption, Fourier-transformed infrared spectroscopy (FT-IR), and field emission scanning electron microscopy (FE-SEM) analyses. It was demonstrated that α-Fe 2 O 3 and NiO aerogels with high surface areas and mesoporosities could be successfully synthesized using the home-made supercritical CO 2 dryer. Supercritical drying of the gels resulted in α-Fe 2 O 3 (186 m2/g) and NiO (178 m2/g) aerogels with 186% and 34% higher surface areas, respectively, than xerogels obtained via simple drying at 80°C using a laboratory oven. In addition, the results showed that supercritical CO 2 drying could enhance preservation of the porous network of the oxide nanostructures at high calcination temperatures via suppression of sintering phenomenon. Calcination of α-Fe 2 O 3 and NiO aerogels at 600°C yielded 225% and 53% higher surface areas than the corresponding xerogel, confirming the significance of drying step in the sol − gel method. Asphaltene adsorption from a model oil with asphaltene concentration of 3000 ppm indicated that the aerogels possessed higher adsorption capacities for the bulky asphaltene molecules than xerogels calcined at the same temperature of 600°C, which was due to their enhanced textural properties. [ABSTRACT FROM AUTHOR]

Cheap sodium silicate was selected as silicon source, and hydrochloric acid was added to sodium silicate as a one-step catalyst to explore sol-gel and modified process parameters, and compare the effects of atmospheric drying, freeze drying and supercritical drying on the physical properties of SiO2 aerogel, and finally determine the best preparation process of SiO² aerogel. BET, SEM, FTIR, XRD, ZETA and other characterization methods were used to analyze the samples. The result showed that when the water glass and deionized water are stirred and hydrolyzed at a volume ratio of 1:4, under the condition of pH=4 sol gel, is the best preparation condition. Compared with the three drying methods, the SiO2 aerogel obtained by supercritical drying has the best physical properties, with a specific surface area of 754. 750 m²/g, an average pore size of 15. 457 nm, a total pore volume of 3.160 cm³/g, a bulk density of 0. 033 g/cm³, Zeta potential of-27.7 mV, thermal conductivity 0. 016 2 W/(m.K). [ABSTRACT FROM AUTHOR]

This article reports the synthesis of an aerogel involving reduced graphene oxide (rGO) and polyethylenimine (PEI), and describes its potential application as an effective sorbent to treat Hg(II) contaminated water. The rGO/PEI sorbent was synthetized using a supercritical CO2 method. N2 physisorption, electron microscopy, and elemental mapping were applied to visualize the meso/macroporous morphology formed by the supercritical drying. The advantages of the synthetized materials are highlighted with respect to the larger exposed GO surface for the PEI grafting of aerogels vs. cryogels, homogeneous distribution of the nitrogenated amino groups in the former and, finally, high Hg(II) sorption capacities. Sorption tests were performed starting from water solutions involving traces of Hg(II). Even though, the designed sorbent was able to eliminate almost all of the metal from the water phase, attaining in very short periods of time residual Hg(II) values as low as 3.5 µg L−1, which is close to the legal limits of drinking water of 1–2 µg L−1. rGO/PEI exhibited a remarkably high value for the maximum sorption capacity of Hg(II), in the order of 219 mg g−1. All of these factors indicate that the designed rGO/PEI aerogel can be considered as a promising candidate to treat Hg(II) contaminated wastewater. [ABSTRACT FROM AUTHOR]

Dyes abundance in wastewaters poses environmental threats, and a cost-effective strategy to remediate dyed water is adsorption: this process could be enhanced using nanostructured sorbents, that expose high surface areas. In this work, chitosan aerogel adsorbents were produced by supercritical CO 2 assisted drying, working at 200 bar, 35 °C, and CO 2 mass flow rate of 0.8 kg/h. FESEM images proved that the delicate biopolymeric network was intact thanks to near-zero surface tension at the interface between CO 2 and the liquid, and large supercritical fluid diffusivity. Methyl Orange (MO) and Crystal Violet (CV) were used as model anionic and cationic dyes, respectively. Changing dye initial concentration, chitosan aerogel showed different behavior at low and large driving forces, for both CV and MO. Adsorption experiments proved that MO could be not completely removed by aqueous solutions: whereas, CV removal was successful with removal efficiencies up to 89.0 ± 1.1 % from a 10 ppm solution, using 50 mg of aerogel. FT-IR analysis proved that chitosan active sites were more effectively involved with CV rather than MO. Kinetic analysis, carried out for both dyes, showed that the process follows a pseudo-second order kinetics, related to internal mass transfer resistances and diffusion phenomena. [Display omitted] • Chitosan aerogels were produced using supercritical CO 2 drying at 200 bar/35 °C. • 50 mg of 3 % w/w nanostructured chitosan aerogels were used for dye adsorption. • Crystal Violet removal was enhanced with respect to Methyl Orange. • The system dye-aerogel behaves differently at low and large driving forces. • Both dyes follow Freundlich isotherm and a pseudo-second order kinetics. [ABSTRACT FROM AUTHOR]

The production of novel materials and value-added chemicals from lignin has received considerable attention in recent years. Due to its abundant occurrence in nature, there is a growing interest in utilizing lignin as a feedstock for functional materials production, for example aerogels. Much like in the synthesis of phenol-based resins, the vacant ortho positions of the aromatic rings in lignin can crosslink with formaldehyde and form polymeric gels. After drying the hydrogels with supercritical CO2, highly porous aerogels are obtained. Current study focuses on the preparation and thorough parametrization of organosolv lignins from different types of lignocellulosic biomass (aspen, pine, and barley straw) as well as their utilization for the preparation of lignin-5-methylresorcinol-formaldehyde aerogels. The thorough structural characterization of the obtained aerogels was carried out by gas adsorption, IR spectroscopy, and scanning electron microscopy. The obtained lignin-based monolithic mesoporous aerogels had specific surface areas and total pore volumes in the upward ranges of 450 m2/g and 1.4 cm3/g, respectively. [ABSTRACT FROM AUTHOR]

Porous materials, cryogels and aerogels, were synthesized based on a sodium alginate–chitosan interpolymer complex via freeze-drying and supercritical drying. It was shown that the specific surface area of aerogels was approximately ten times higher than that of cryogels due to the developed mesoporous structure and amounted to 260 m2/g. The polyelectrolyte nature of the obtained materials, their dimensional stability, and their high water absorption (15 and 45 g/g for cryogel and aerogel, respectively) allowed us to use the obtained materials for sorption-application therapy. To impart antimicrobial properties, the materials were impregnated with usnic acid isolated from the lichen Usnea subfloridana, which has antibacterial activity against Escherichia coli bacteria and the microorganism species Staphylococcus aureus and Bacillus subtilis. It was shown that the minimum inhibitory concentration of usnic acid for these test cultures was 0.03 mg/mL. The resulting materials are capable of a slow release of usnic acid over 5 h, while its maximum release was 60% for aerogel and 30% for cryogel. The kinetics of usnic acid release of from both materials is adequately described by the Korsmeyer–Peppas equation. [ABSTRACT FROM AUTHOR]

A technique is described for the preparation of a universal composite nanomaterial for effective sorption purification of water from pollutants of different chemical nature. The proposed material is a nanocomposite based on reduced graphene oxide, which is modified with polyaniline as a functional organic component and also includes oxidized carbon nanotubes as a reinforcing agent. The use of polyaniline makes it possible to substantially increase the activity and sorption capacity of the developed graphene material. A number of nanocomposites are developed, the preparation technologies of which differ in the final stage, i.e., the drying of the preliminarily obtained hydrogel. Furthermore, the effect of the additional stage of final sample carbonization is studied. The surface morphology of the materials is examined by scanning electron microscopy. The specific surface area and the parameters of the porous space are determined by nitrogen adsorption. The specific surface area of the materials increases in accordance with the choice of drying technology for the initial hydrogel (drying oven, 80 m2/g → freeze drying, 180 m2/g → supercritical drying, 290 m2/g), increases additionally after the carbonization stage, and reaches a value of about 350 m2/g. The sorption capacities of nanocomposites with respect to organic dyes methylene blue (MB) and sunset yellow (SY) and with respect to heavy metals (for example, zinc ions) are determined. It is found that the sorption value ranges from 1380 to 1800 mg/g for MB, from 159 to 300 mg/g for SY, and from 31 to 230 mg/g for zinc. At the same time, the sample processed under supercritical conditions with subsequent carbonization exhibits the best characteristics. [ABSTRACT FROM AUTHOR]

Aerogel materials characterized by a developed mesoporous structure and a specific surface area of up to 260 m2/g are obtained based on an alginate–chitosan interpolyelectrolyte complex (IPEC) using supercritical fluids. The introduction of CaCO3 microparticles into the composition at the stage of formation of the IPEC allows increasing the textural characteristics of the samples by a factor of 1.5; thus, the specific surface area of the composite aerogels is 400 m2/g, the average pore size is 19.3 nm, and the total pore volume is 1.93 cm3/g. The new materials are superadsorbents; thus, 1 g of the aerogel retains up to 60 g of the liquid while maintaining its shape. The possibility of using the obtained composite aerogels to create wound coatings with the inclusion of an antiseptic drug substance (furacilin) is shown. It is found that the furacilin release profile from the aerogel matrix corresponds to the dynamics of controlled release for all the samples of the aerogels. It is shown that 88–95% of the furacilin is released from the aerogel matrix within 5 h, which is due to the developed surface of the carrier. [ABSTRACT FROM AUTHOR]

In present research, we synthesized cobalt-based silica nanocomposites (Co-SiO2) from cobalt nitrate [Co(NO3)2] and tetraethoxysilane (TEOS) precursors by using a simple sol-gel method followed by supercritical drying techniques. The physicochemical and textual properties of the as synthesized nano composites were thoroughly investigated. The results indicated that the Co-SiO2 aerogels demonstrated homogeneous dispersion cobalt nanoparticles within silica matrix with mesoporous morphology, large specific surface area (802 m2/g) and larger pore size (9 nm) with less volume shrinkage. The physicochemical properties of the cobalt based silica nanomaterial were characterized by XRD, SEM, N2 adsorptiondesorption and FTIR techniques. Cobalt-based silica nanocomposites can be produced using TEOS-based precursor and supercritical drying techniques. The prepared (Co-SiO2) nanocatalyst due to its magnetic nature with higher surface area (802 m²/g) can be utilized in many emerging fields such as catalysis, water desalination, water splitting, gas-sensing application and organic pollutant degradation [ABSTRACT FROM AUTHOR]

Utilizing the abundant biogas resources in an efficient and sustainable way helps to mitigate the energy and environmental problems. CH4 oxy-CO2 reforming reaction is a promising technic and an efficient catalyst for the reaction is in great demand. In this work, Ru was incorporated into monometallic Co/MgO-Al2O3 aerogel catalyst via supercritical drying process combined with sol–gel method and a series of Co-Ru bimetallic aerogel catalyst with different Ru contents was synthesized. Catalytic performance screening for the catalysts indicated that combination of Ru and Co significantly raised the activity of monometallic catalysts, e.g., the activity of Co15-Ru0.2 (Co content: 15 wt.%, Ru content: 0.2 wt.%) was 64.7% and 63.9% higher than those of the monometallic Co15 and Ru0.5 catalysts, respectively. The results also indicated that Co/Ru ratio had a great influence on the catalytic activity: Co15-Ru0.2 > Co15-Ru0.1 ≈ Co15-Ru0.5 > Co15-Ru0.05 > Ru0.5 > Co15. XRD, BET, H2-TPR, XPS, TEM, TG/DSC, and FESEM analyses were performed, disclosing that the reducibility and active metal particle size of the catalysts can be manipulated by the Co/Ru ratio due to the transportation of bulk Co2+ to the surface. The Co15-Ru0.2 catalyst had a mean active metal particle size below 10 nm and medium reducibility, resulting in a high activity and stable performance. Highlights: A Co-Ru/MgO-Al2O3 aerogel was prepared by sol-gel combined with supercritical deposition method. The addition of Ru destabilized the Co spinel and promoted the reduction of Co species. The synergy between Co-Ru promoted the catalytic performance which were better than the monometallic catalysts. Co15-Ru0.2 showed the highest CH4 reforming activity and resistance to inactive carbon. [ABSTRACT FROM AUTHOR]

Aerogels are a special class of porous material, which have excellent physicochemical properties such as low density, high porosity, high surface area and adjustable surface chemistry. Aerogels were first prepared several decades ago, but never truly commercialized due to their high cost. Technological advancements in the production and quality of different types of aerogel cut costs down and market factors increase demand. Therefore, the viability of this porous material on the several applications has been widely studied. Among the various high-performance applications, aerogel has attracted significant attention as a chemical sorbent and catalyst for CO2 capture and conversion as well as methane conversion to value-added products. Although aerogel performance for zero CO2 emission to the environment is promising, some drawbacks of aerogels such as complicated drying process, mechanically weak structure and processing cost should also be considered in material development. Ultimately this review article will cover an overview regarding the aerogels synthesis, processing and their recent applications in CO2 capture and conversion.

Abstract—Aerogel materials based on the interpolymer complex of alginate with chitosan using supercritical fluids technology were obtained. It was established that obtained aerogels have a developed mesoporous structure and a specific surface area of up to 243 m2/g. The average pore size equals 14.8 nm. The possibility of using the aerogels with the inclusion of antibiotic levomycetin as a basis for creating wound dressings was shown. It was estimated that slow release of the drug (70% during 5 h) from the aerogel matrix provides prolonged and safe supply of the drug to the surface of a wound. [ABSTRACT FROM AUTHOR]

• BSM aerogels were produced by ethanol-induced gelation and supercritical drying. • Paracetamol was loaded into the BSM aerogels using the gas antisolvent process. • RSM was used for the modeling and optimization of paracetamol loading into aerogel. • Effect of temperature, pressure and drug loading was investigated on drug loading. • Aerogels were characterized by SEM, FTIR, XRD and N 2 adsorption/desorption. In this work, paracetamol (PCM) loading into Balangu seed mucilage (BSM) aerogels was investigated using the combination of supercritical drying and gas antisolvent (GAS) precipitation method. Response surface methodology (RSM) was implemented for the modeling and optimization of drug loading into the aerogel matrix. The temperature (40–60 °C), pressure (8–24 MPa) and drug solution concentration (0.2–0.6 M) were considered as the range of operating variables. The prepared aerogels were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and N 2 adsorption-desorption analysis. The optimal operating conditions were determined to be the pressure of 8 MPa, the temperature of 40 °C and the drug solution concentration of 0.2 M in which the maximum drug loading (DL) of 33% was achieved. The RSM verified that R2 and modified R2 of the model were 98.53% and 97.25%, respectively. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Mass transfer model applied to supercritical drying of particles in packed beds. • Influence of the process parameters were studied. • Strategy for rational selection of process conditions is suggested. Abstract We apply here the previously developed mass transfer model (Part 1) for drying of aerogel monoliths to the supercritical drying of particles in a packed bed. We analyzed the influence of the operating conditions, flow rate, particle and autoclave size on the drying time and consumption of carbon dioxide. Although the model requires certain improvement to quantitatively predict the experimental drying kinetics, it captures all features of the supercritical drying: (i) transition of the limiting mass transfer step between diffusion in the gel and convection in the bulk fluid; (ii) role of CO 2 density as natural variable for analysis of the CO 2 consumption; (iii) influence of the autoclave dimensions on the drying process. We suggest a unified approach towards the analysis of drying process based on a dimensionless number. Practical recommendations on the rational selection of process parameters to achieve appropriate combinations of drying time and CO 2 consumption are formulated. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Alginate-based aerogels with a cylindrical shape were produced. • A custom-made extrusor specifically develop for this applications was used. • Nanostructured morphology of Ca- and Cu-Alg-hydrogels was preserved. • Alg-Ch-aerogels with microporosity of chitosan and nanofibers of alginate were obtained. Abstract Alginate-based aerogels with a cylindrical shape to be used for medical applications were produced by supercritical drying. First, alginate (Alg) solutions at different polymer concentrations (from 5% to 15% w/w) were extruded using a new custom-made device, in a coagulation bath of CaCl 2 at 5% w/w or CuSO 4 at 1.5% w/v, where hydrogels were generated; then, the corresponding aerogels were produced by supercritical drying at 200 bar and 45 °C for 4 h. Scanning electron microscopy showed that nanostructured morphology of native Ca- and Cu-Alg-hydrogels was preserved by supercritical drying. The same apparatus was also tested to produce alginate-chitosan (Alg-Ch) aerogels; they showed an hybrid morphology characterized by the microporosity of chitosan and the nanofibers of alginate, homogeneously distributed in the gel structure. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Kinetics of supercritical drying of alginate gel particles was investigated. • A mathematical model describing mass transfer in supercritical drying of gel particles was developed. • The drying time decreased with increasing flow rate and temperature, and decreasing particle size. • A correlation for predicting external mass transfer coefficients for supercritical drying of alcogel particles was developed. Abstract Spherical calcium alginate gel particles were synthesized by dripping method. The effects of temperature, pressure, particle size and CO 2 flow rate on kinetics of supercritical drying of alginate gel particles in a packed bed were investigated. Increase in CO 2 flow rate, increase in temperature and decrease in particle size increased the drying rate and decreased the drying time. A mathematical model based on (i) the diffusion of the solvent inside the pores of gel particles, (ii) external mass transfer of the solvent from the surface of the gel particles into the flowing fluid stream, and (iii) convection and axial dispersion of the solvent in the flowing fluid stream was developed. A correlation for predicting external mass transfer coefficients for supercritical drying of alcogel particles was developed by fitting the model to experimental data. A good agreement between the experimental data and model results was achieved using the developed correlation. [ABSTRACT FROM AUTHOR]

Silica aerogels have in common with silica glass to present a random 3-dimensional network of Si(-O-)4 molecular tetrahedrons. The main difference stands on the presence of a high volume ratio of macropores and mesopores, which may exceed 90% by volume in aerogels. By comparison, silica glass is a dense material. Consequently, an aerogel can entrap relatively big macromolecules in its pores. In the present article, the work done to observe the random network structure of oxide aerogels during the last thirty years, by the present author and his co-workers, is reviewed. As an application, the entrapment of two types of enzymes in silica aerogels is summarized. The first one comprises two types of lipases, used as biocatalysts of esterification reactions in organic solvents. The second one is carbonic anhydrase, applicable in the capture of CO2 in aqueous un-dried wet gels. The influence of the gel network on the enzyme activity and of the enzymes on the aerogels network structure, are both discussed. Overall, these investigations were independent from to the work by Phalippou and co-workers, but they largely beneficiated from cross synergy with them. The work done by the author and his co-workers on the structure of oxide aerogels and their use to entrap enzymes, is reviewed Highlights: The porous network structures of silica, boehmite and montmorillonite aerogels is described. The pore volume may exceed 90% and comprise micropores, mesopores and macropores. The pores can be efficiently used to entrap enzymes and make efficient biocatalysts. The case of two types of enzyme: a lipase and a carbonic anhydrase are summarized. Proteins such as enzymes are also shown to influence the aerogel network formation. [ABSTRACT FROM AUTHOR]

Supercritical drying avoids capillary forces, but damaging stresses can be generated during solvent exchange, pressurization, and depressurization. Each of those steps has been analyzed, so the duration of the process can be minimized without risk to the sample. This work, which was initiated in collaboration with Professor Jean Phalippou's group, is reviewed. Poromechanics is the study of stresses and strains resulting from interaction of the solid and liquid phases in a porous material. For example, if a gel is immersed in another liquid for solvent exchange, the gel network may undergo a transient contraction if the original pore liquid diffuses out faster than the replacement liquid diffuses in; poromechanical analysis quantifies the resulting stresses and indicates whether there is a risk of cracking. In the preparation of aerogels, when the pressure in the autoclave is decreased, the higher pressure inside the aerogel causes it to expand, which may result in cracking. Poromechanics reveals the rate of depressurization that can be imposed without creating damaging stresses. We also show that the sensitivity of gels to pore pressure can be exploited to measure their permeability to gases and liquids by observing the response to small loads or changes in temperature. A dilatometer incorporated into the autoclave measures dilatation of the gel during the supercritical drying cycle, and poromechanical analysis allows extraction of the permeability from the measured strain. Similar analyses are used to minimize the cycle time while avoiding damaging stresses during the solvent exchange, pressurization, and heating, and depressurization steps. Highlights: Poromechanics quantifies supercritical drying stresses during solvent exchange, pressurization and heating, and depressurization. Supercritical drying duration is minimized by accounting for the pressure dependence of permeability, viscosity and compressibility. By monitoring strain of the aerogel during depressurization, permeability can be measured as a function of pressure. The permeability of gels is found from their response to small loads or changes in temperature. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Aerogels are prepared by thermal inkjet printing followed by supercritical drying. • Process has a printability region restricted by the gel precursor concentration. • Aerogel microspheres have narrow size distribution and high textural properties. • The processing technique is compatible with incorporation of bioactive compounds. • Aerogels are relevant for pulmonary administration and for personalized medicine. Abstract Inkjet printing is as an emerging technique in the biomedical field offering cost-effective solutions for flexible production and the engineering of personalized medicine solutions. Thermal inkjet printing technology in the "drop on demand" mode allows the design of fully automated deposition patterns with high spatial resolution for applications ranging from microparticles in drug formulations to cell deposition in regenerative medicine. In particular, novel formulations in the form of porous particles are sought for the treatment of respiratory disorders and the systemic administration of bioactive compounds using the pulmonary route. Aerogel particles, i.e. highly porous and light-weight nanoporous powders, are particularly promising as carriers for the pulmonary route. In this work, the preparation of aerogel microspheres by thermal inkjet printing followed by supercritical drying is presented for the first time to overcome the current processing limitations. Alginate aerogel particles were loaded with salbutamol sulphate, a bronchodilator used for the treatment of asthma attacks and chronic obstructive pulmonary disease, as a model drug for sustained pulmonary delivery. The optimized processing method allowed the preparation of reproducible nanostructured microparticles with modified salbutamol sulphate release profile and aerodynamic performance of relevance for oral inhalation purposes. [ABSTRACT FROM AUTHOR]

Lightweight cellulose II aerogels featuring densities of about 40–70 mg cm−3 were prepared from 1 to 3% solutions of different pulps in hot (60°C) tetra-n-butylammonium fluoride (TBAF)·H2O/dimethyl sulfoxide (DMSO) by (i) the coagulation of cellulose with EtOH to afford self-standing, transparent and homogeneous gels, (ii) gel ripening and washing, (iii) solvent exchange and (iv) supercritical carbon dioxide (scCO2) drying. Size exclusion chromatography (SEC) analyses confirmed that the chemical integrity of cellulose is largely preserved at short dissolution times. Dissolution of more than 2% of cellulose at a sufficiently low viscosity for solution, casting was achieved after the water content of TBAF was reduced to a value equaling that of the monohydrate. Intriguingly, the obtained aerogels featured higher specific surfaces (≤470 m2 g−1) than comparable materials prepared from other cellulose solvents. This is due to the particular morphology of TBAF aerogels, which is supposedly formed by spinodal decomposition of the cellulose/solvent mixture upon exposure to the cellulose antisolvent. As a result, largely homogeneous three-dimensional (3D) networks of agglomerated cellulose spheres were formed, which simultaneously acted as supporting scaffolds for interconnected micron-size voids. As cellulose spheres are composed of very small interwoven nanofibers, TBAF-derived aerogels contain a high portion of micropores and small amounts of mesopores, too. [ABSTRACT FROM AUTHOR]

Comparative studies of the properties of porous aerogels based on cerium and calcium alginates obtained by supercritical or cryogenic drying are performed. The properties of aerogels were analyzed by means of low-temperature adsorption of nitrogen, scanning electron microscopy, thermogravimetric analysis, and kinetics of sorption upon one-sided contact with a model fluid. The obtained aerogels can be recommended as materials for the creation of dressings for the drainage and treatment of exuding wounds. [ABSTRACT FROM AUTHOR]

Aerogels are three-dimensional ultra-light porous structures whose characteristics make them exciting candidates for research, development and commercialization leading to a broad scope of applications ranging from insulation and catalysis to regenerative medicine and pharmaceuticals. Biopolymers have recently entered the aerogel foray. In order to fully realize their potential, progressive strategies dealing with production times and costs reduction must be put in place to facilitate the scale up of aerogel production from lab to commercial scale. The necessity of studying solvent/matrix interactions during solvent exchange and supercritical CO2 drying is presented in this study using calcium alginate as a model system. Four frameworks, namely (a) solvent selection methodology based on solvent/polymer interaction; (b) concentration gradient influence during solvent exchange; (c) solvent exchange kinetics based on pseudo second order model; and (d) minimum solvent concentration requirements for supercritical CO2 drying, are suggested that could help assess the role of the solvent in biopolymer aerogel production.

Graphical abstract Highlights • A mass transfer model for the supercritical drying of aerogels was developed. • Tortuosity factors of different gels were fitted using in situ measurements. • Theoretical minimal drying times for microparticles are in seconds range. • Transition Biot number can be used to select drying conditions. Abstract A mass transport model for the supercritical drying of gels to aerogels in different sizes (monoliths or particles) and shapes (cylinder, sphere) was developed and evaluated. Physico-chemical data for the system CO 2 /ethanol from literature at relevant process conditions were analyzed for a precise description of relevant physical properties. In situ measurements of the supercritical drying kinetics of gel monoliths using Raman spectroscopy were used to fit the tortuosity factor of the gel network. Apart from the fitted tortuosity factor the presented model is predictive. The model was analyzed in detail for the case of spherical gel particles. Theoretical minimal drying times were found to range in seconds for microparticles. The mass transfer step limiting the overall drying kinetics was analyzed using the dimensionless Biot number. The transition Biot number can be used for rational selection of the drying conditions (pressure, temperature, mass flow) to achieve a fast drying with low CO 2 consumption. [ABSTRACT FROM AUTHOR]

Graphical abstract Supercritical drying kinetics and distribution of tetralin mass fraction at the central section vertical to the autoclave at various time points. Highlights • Experimental and theoretical studies of organogels drying with supercritical CO 2. • Two modelling approaches: organogel penetrable to the CO 2 flow or not. • Parametric study: CO 2 flow rate and organogel thickness. Abstract A supercritical process to dry organogels, in order to produce aerogels is studied. The organogel is firstly produced by synthesizing an amino-acid-type organogelator of fibrillary structure, which is able to trap a solvent, here tetralin. The extraction of tetralin from the organogel using supercritical CO 2 is then investigated both through experiments and simulations. Two approaches are developed in order to understand the tetralin mass transfer mechanisms. In the first approach, the organogel is regarded as an impenetrable material and the mass transfer within it is assumed to be only diffusive. In the second approach, the organogel is considered as a penetrable porous material so that CO 2 can flow across it. The tetralin transfer is thus governed both by diffusion and convection. Both approaches are implemented in Computational fluid dynamics (CFD) software ANSYS Fluent. The drying kinetics obtained by the second approach is found to agree better with the experimental results. [ABSTRACT FROM AUTHOR]

Acid and base mediated sol–gel process followed by supercritical extraction of ethanol used for the synthesis of lithium-ion doped nickel ferrite loaded silica composite aerogels using a high-temperature high-pressure autoclave. The physical-chemical properties of synthesized materials are characterized using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FE-SEM) and DC-conductivity measurements. The conductivity results suggest that maximum electrical conductivity of 8.63 × 10 −9  Scm −1 is obtained for 4% Li 2 O doped 96%{10% NiFe 2 O 4  + 90% SiO 2 } composite aerogel due to Li + migration between grain-grain interface and electron hopping between Fe 2+ and Fe 3+ . Further, the XRD result also confirms the formation of amorphous SiO 2 , Li 2 O with crystalline NiFe 2 O 4 composite aerogel. FTIR results confirm the bond formation through molecular vibration between Si-O-Si and Ni 2+ /Fe 3+ -O. FESEM micrographs reflect the three-dimensional, highly porous interconnected network formation of 4LNS composite aerogel. Aqueous supercapacitor performance of Li 2 O doped NiFe 2 O 4 –SiO 2 composite aerogels were examined in 1 molar CH 3 COONa, Na 2 SO 4 and NaOH electrolytes on respective potential regions of 0.5 to −1 V, 0.4 to −0.8 V and 0 to −1.0 V using three electrode systems. The Li 2 O addition improves the conductivity and hence improve the specific capacitance of SiO 2 and NiFe 2 O 4 –SiO 2 composite aerogels synergically within the potential window. [ABSTRACT FROM AUTHOR]

Fresh-cut salad waste was dried by means of supercritical carbon dioxide technology using ethanol as co-solvent. The obtained material was characterized by a white color and a brittle texture. Microscopic images revealed an aerated structure, with well-evident intra and inter-cellular spaces. Based on the high internal surface (>100 m 2 /g), the extremely low density (<0.5 g/cm 3 ) and the high porosity (>80%), supercritical-dried salad waste can be regarded as a bioaerogel-like material. One gram of this material absorbed 33 and 19 g of water and oil respectively. Industrial application Fresh-cut processing of salad generates large amounts of solid waste which is not suitable for conversion into biogas or fertilizers. This waste poses management issues for producers and represents an environmental burden. Fresh-cut salad waste could be valorized to produce bioaerogel-like materials with enhanced solvent uptake ability, to be exploited as food ingredients, packaging, absorbents or innovative carriers for both lipophilic and hydrophilic compounds. [ABSTRACT FROM AUTHOR]

Polyimide (PI) aerogels are open-celled materials with high porosity, low density, excellent mechanical property and high thermal stability. Linear PI aerogels exhibit drastic shrinkage during the fabrication process. Cross-linked PI aerogels were usually fabricated by utilizing the costly cross-linking agents such as 1,3,5-triaminophenoxybenzene or octa-(aminophenyl)silsesquioxane. Herein, amino functionalized multi-walled carbon nanotubes (MWCNTs-NH2) were prepared by amidation reaction; PI/MWCNTs-NH2 composite aerogels were fabricated by adding MWCNTs-NH2 to anhydride end-capped poly(amic acid) (PAA), chemical imidization of PAA and supercritical carbon dioxide drying. The microstructures, pore size, elastic modulus, thermal properties and other physical properties of the obtained PI/MWCNTs-NH2 composite aerogels were investigated. The results showed that MWCNTs-NH2 could act as a cross-linker of PI because the amino groups of MWCNTs-NH2 could react with the terminal anhydride groups of PAA. With the addition of MWCNTs-NH2, the shrinkage of PI/MWCNTs-NH2 composite aerogels decreased. The densities and Young’s moduli of PI/MWCNTs-NH2 composite aerogels also decreased. The PI/MWCNTs-NH2 composite aerogels had coralline-like structure with mesopores (average pore size: 11–20 nm). The PI/MWCNTs-NH2 composite aerogels also exhibited decent thermal stability and thermal insulating property. [ABSTRACT FROM AUTHOR]