Aerogel Surface Research Articles

Nanohybrid electrodes of porous hollow SnO2 and graphene aerogel for lithium ion battery anodes

In this work, we present the nanohybrid electrode (termed as p-h-SnO2/GA) of porous hollow SnO2 (p-h-SnO2) integrated on the surface of graphene aerogel (GA) for anodes with large lithium storage capacity. Selective etching of Ni from Ni3Sn2 nanoparticles produces the porous hollow nanostructure of SnO2, which is important for providing the structural flexibility that can accommodate the volume change of SnO2 during the lithiation and delithiation processes. GA also serves as a buffer for the volume change of SnO2 and induces effective charge transports through its interconnected porous network structure. These combined advantages of p-h-SnO2 and GA enable a reversible Li storage capacity as high as 620mAhg−1 with ∼100% Coulombic efficiency at a specific current of 50mAg−1 over 200 charge–discharge cycles and ∼71% of rate-retention capability over the specific currents of 100mAg−1–1Ag−1. It makes this nanohybrid electrodes an attractive candidate for high-performance lithium ion battery anode.

One-step synthesis of peanut hull/graphene aerogel for highly efficient oil-water separation

Peanut hull has been used to prepared three-dimensional self-assembled peanut hull/graphene aerogels (3D-PG) in a very simple, green and low-cost way, successfully making use of agricultural waste as well as achieving base-induced one-step synthesis of 3D-PG for oil-water separation. The addition of peanut hull has increasingly improved the properties of graphene aerogels. A 9.6 mg 3D-PG can support a 200 g counterpoise, more than 2000 times its own weight. Meanwhile, the surface of aerogel has outstanding hydrophobicity and oleophilicity due to the addition of peanut hull in the graphene oxide (GO) aqueous dispersion, with the water and oil contact angles of 141° and 0°, respectively. This endows the 3D-PGs outstanding absorbing capability with the quality factor Q from 3214% up to 7933% for organic solvents and oils. Noteworthily, the adsorption equilibrium can be achieved within 1 min. In addition, the dynamic test indicated highly efficient oil-water separation of 3D-PG. Results also showed 3D-PG with super low density, large specific surface area, excellent adsorption capacities and superior adsorption recyclability (93%). Such outstanding oleophilic properties make the agricultural waste make the 3D-PG tremendously potential applications for oil absorbing, recovery and oil-water separation.

Analysis of Hydrophobic Silica Aerogels Adsorption Properties on Toluene Vapor

The hydrophobic silica aerogels were prepared by the sol-gel method and the adsorption characteristics of their nitrogen adsorption at low temperature were analyzed. The static, dynamic and cyclic adsorption experiments of toluene vapor were carried out to study the adsorption properties of toluene vapor. The results show that the prepared silica aerogels are mesoporous adsorbents with a specific surface area of 732 m2·g-1. The surface of the silica aerogel has a hydrophobic methyl group and the adsorption capacity is up to 1.6g·g-1. The adsorption stability is strong. Dynamic adsorption temperature rises to 12 °C and the logistic model is use to fit the adsorption breakthrough curve with high similarity.

Preparation, Characterization, and Application of Silica Aerogel for Adsorption of Phenol: An In-Depth Isotherm Study

: This study evaluated silica aerogel as an adsorbent for phenol removal from aqueous solutions. Silica aerogel was prepared through the sol-gel process and characterized by different analyses. Then, it was used for phenol removal under various conditions of operational parameters. Also, twelve isotherm parameters were employed to describe the behavior of phenol-silica aerogel adsorption system. The chemical structural analysis confirmed -OH functional groups in amorphous SiO2 and proved the adsorption of phenol onto the surface of silica aerogel. The findings of the adsorptive behavior of silica aerogel toward phenol showed increasing pH, up to 8.5, and contact time, and adsorbent dose increased the phenol removal. The removal efficiency reached over 90% when phenol concentration was below 50 mg L-1. The reaction kinetics followed the pseudo-first order model. The isotherm study showed that equilibrium adsorption data were well-described by Freundlich and Halsey equations, among two-parameter isotherms, and Hill, Sips, and Koble-Corrigan, among three-parameter isotherms. Jovanovic and BET were the worst isotherm models for prediction of experimental equilibrium data. The maximum adsorption capacity of 75.23 mg.g-1 was calculated in phenol-silica aerogel adsorption system. The study showed silica aerogel as an efficient adsorbent to remove phenol from phenol-containing solutions.

1D ultrafine SnO2 nanorods anchored on 3D graphene aerogels with hierarchical porous structures for high-performance lithium/sodium storage

SnO2 is considered as one of the most promising alternative anode materials for lithium ion batteries (LIBs) and sodium ion batteries (SIBs) due to high specific capacity, low discharge voltage plateau and environmental friendliness. In this work, 1D ultrafine SnO2 nanorods anchored on 3D graphene aerogel (SnO2 NRs/GA) composite is prepared through a simple reduction-induced self-assembly method in the solution of graphene oxide (GO), Vitamin C and SnO2 nanoparticles. Vitamin C plays an important role in the reduction of GO. The structural and morphological characterizations demonstrate that 1D ultrafine SnO2 nanorods are uniformly and tightly anchored on the surface of 3D graphene nanosheet aerogels. The unique 3D network structure as well as the synergistic effect between 3D graphene nanoshhet and 1D SnO2 nanorods endows the as-prepared SnO2 NRs/GA composite with the good electrochemical lithium/sodium storage performance. It delivers the high initial discharge capacity (1713 mA h g−1 at 0.1 A g−1 for LIBs and 539 mA h g−1 at 0.05 A g−1 for SIBs) and good cycle stability (869 mA h g−1 at 0.1 A g−1 after 50 cycles for LIBs and 232 mA h g−1 at 0.05 A g−1 after 100 cycles for SIBs). Moreover, the SnO2 NRs/GA composite exhibits excellent cycle stability for SIBs with a high reversible capacity of 96 mA h g−1 at as high as 1 A g−1 for 500 cycles. This work provides a simple method to fabricate the electro-active materials-graphene aerogel composites for high-performance LIBs and SIBs.

High Efficiency Thermoacoustic Loudspeaker Made with a Silica Aerogel Substrate

AbstractThe extremely low thermal effusivity of the silica aerogel is exploited to develop a high efficiency thermoacoustic (TA) loudspeaker with solid substrate. The deposition of the electrically conductive, low heat capacity active film on the silica aerogel surface is achieved with both the spray coating of silver nanowires and the sputter coating of gold films. The uniform spray coating of the hydrophobic silica aerogel is enabled by a low pressure plasma treatment, which however impairs its robustness. The spray‐coated samples prove to be fragile when subjected to elevated temperatures and thus not suitable for TA applications. Sputter coating, not requiring any treatment of the aerogel surface, allows the fabrication of working TA loudspeaker samples with a 100 nm gold active film. The electroacoustic response of the gold‐sputtered silica aerogel TA loudspeaker is characterized at different input power levels. The experimental results are compared with those present in literature, showing an improved efficiency with respect to the other TA loudspeakers with solid substrate.

Influence of exchange scattering on superfluidHe3states in nematic aerogel

The superfluid state in bulk liquid $^3$He is realized in the form of A or B phases. Uniaxially anisotropic aerogel (nafen) stabilizes transition from the normal to the polar superfluid state which on further cooling transitions to the axipolar orbital glass state (Phys. Rev. Lett. {\bf 115}, 165304 (2015)). This is the case in nafen aerogel preplated by several atomic layers of $^4$He. When pure liquid $^3$He fills the same nafen aerogel a solid-like layer of $^3$He atoms coats the aerogel structure. The polar state is not formed anymore and a phase transition occurs directly to the axipolar phase (Phys. Rev. Lett. {\bf 120}, 075301 (2018). The substitution of $^4$He by $^3$He atoms at the aerogel surface changes the potential and adds the exchange scattering of quasiparticles on the aerogel strands. A calculation shows that both of these effects can decrease the degree of anisotropy of scattering and suppress the polar phase formation. The derived anisotropy of the spin diffusion coefficient in globally anisotropic aerogel is determined by the same parameter which controls the polar state emergence which allows one to check the effect of anisotropy change for different types of covering.

CO2-activated porous self-templated N-doped carbon aerogel derived from banana for high-performance supercapacitors

N-doped porous carbon materials derived from eco-friendly, renewable and economical biomass resources have attracted interest for applications in supercapacitors due to their porous structures and physicochemical properties. However, controlling the pore structure remains difficult and there is a need to simplify the N-doping process. Herein, we report a porous self-templated N-doped carbon aerogel derived from banana flesh obtained through one-step carbonization followed by CO2 activation. The specific surface area and pore distribution of the carbon aerogels could be controlled by changing the CO2 activation time. A specific surface area and total pore volume of 1414.97 m2 g−1 and 0.746 cm3 g−1 were achieved. The results show that raw banana flesh provides the necessary N content, which only slightly decreased following activation from 3.25% to 2.25%. On the surface of the carbon aerogel we detected pyrrolic N and pyridinic N groups, which are known to contribute to pseudo-capacitance. Furthermore, the specific capacitance of the prepared carbon aerogel reached 178.9 F g−1 at a current density of 1 A g−1. The simple preparation method and excellent electrochemical performance show great potential for application of our porous self-templated N-doped carbon aerogel as an electrode in high performance supercapacitors.

Ultrahigh selective and efficient removal of anionic dyes by recyclable polyethylenimine-modified cellulose aerogels in batch and fixed-bed systems

A new type of polyethylenimine modified cellulose (PMC) aerogels were synthesized through a chemical cross-linking process, by which plenty of amine groups were introduced to the surface of cellulose aerogels. FT-IR, SEM, EDS, BET and XPS were used to characterize the physicochemical properties of this novel composite. The prepared aerogels were used to remove anionic dyes from effluents and it exhibited excellent adsorption performance in batch and fixed-bed experiments. Adsorption results indicated that PMC could efficiently, selectively separate anionic dyes from dye mixtures and maintain the maximum absorption capacity even after ten regeneration cycles, exhibiting superior selectivity and desirable recyclability. The maximum adsorption capacities of PMC for rose bengal and methyl blue were 1310.21 and 1333.04 mg/g, respectively, which were much higher than those of previously reported results. The Kinetics and isothermal adsorption data were well described by pseudo-second-order kinetic model and Langmuir model. The breakthrough curves obtained from fixed-bed systems were well fitted by Thomas model. Most importantly, anionic dyes could be efficiently removed even with high concentrations of coexisting anions. All these results manifested that PMC could be a promising candidate for sewage treatment, profiting from the fascinating merits of easy separation, low-cost, high adsorption capacity, strong anti-environment disturbance, superior reusability and selectivity.

Silylation of sodium silicate-based silica aerogel using trimethylethoxysilane as alternative surface modification agent

Trimethylethoxysilane (TMES) has been recognized as a good co-precursor to increase the degree of hydrophobicity during the synthesis of a silica aerogel because of its methyl groups. Therefore, some physical properties of silica aerogels, including the contact angle and porosity, were investigated using TMES as a co-precursor at different molar ratios with the main precursor such as tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS). In contrast to TMES, most silylating agents such as hexamethyldisilazane (HMDZ) and trimethylchlorosilane (TMCS) have been used for surface modification because of their ability to enhance the hydrophobicity of the aerogel surface. This work examines the silylation effect, which includes increasing hydrophobicity by TMES to determine the possibility of using it as an alternative silylating agent during ambient pressure drying in the synthesis of sodium silicate-based silica aerogel. In addition, the physical properties of sodium silicate-based silica aerogels with silylation under different TMES/TMCS volume ratio are investigated. The physical properties of sodium silicate-based aerogels can be changed by the TMES/TMCS volume ratio during the surface modification step. Aerogels with a high specific surface area (458 m2/g), pore volume (3.215 cm3/g), porosity (92.7%), and contact angle (131.8°) can be obtained TMES/TMCS volume ratio of 40/60.

Recyclable biomass carbon@SiO2@MnO2 aerogel with hierarchical structures for fast and selective oil-water separation

Biomass carbon aerogels are emerging as attractive versatile materials have broad potential applications in various fields including energy storage, oil absorption and catalysts due to their abundance in nature, low cost and environmental friendliness. Here, we have successfully prepared a compressible, superhydrophobic and multifunctional hierarchical biomass carbon@SiO2@MnO2 aerogel (HBCSM aerogel) by using cost-effective and environmentally friendly sisal cellulose as main raw material. During this process, the cellulose@SiO2 aerogel (CS aerogel) was fabricated using sol-gel process, followed by carbonization to form biomass carbon@SiO2 aerogel (BCS aerogel). Then, the HBCSM aerogel was fabricated by in situ assembly of MnO2 nanosheets on the surface of the BCS aerogel under hydrothermal conditions. The incorporation of hierarchical SiO2@MnO2 structure into the HBCSM aerogel could not only improve the surface roughness and hydrophobic properties but also enhance the absorption capacity and mechanical durability. In addition, the HBCSM aerogel exhibits excellent superhydrophobicity with the water contact angle (WCA) of 155°. The as-prepared modified HBCSM aerogel exhibits a very large absorption capacity (60–120 g g−1) for different oils and organic solvents and the absorption capacity of the as-prepared aerogel shows a slight decrease after the repeated absorption and release of several oil and solvents for 9 cycles. This work provides a new procedure for fabrication of hybrid carbon aerogel with well-defined 3D hierarchical porous structures that may provide a new slight on the relationship between the structure and property of biomass carbon aerogel, making it a promising candidate for industrial oil-polluted water treatments and oil spill cleanup.

Adsorption of boron by CA@KH-550@EPH@NMDG (CKEN) with biomass carbonaceous aerogels as substrate

This research reports an innovative boron adsorbent of CA@KH-550@EPH@NMDG (CKEN) via the modification of N-methyl-d-glucosamine (NMDG) on the surface of biomass carbonaceous aerogel, which is environmentally friendly, economically inexpensive, has simple preparation process and good regenerability. SEM and FT-IR characterization results indicate that CKEN has a 3D cross-staggered structure with lots of hydroxyl groups and pore structure, which are beneficial to the diffusion of boron and the chelation interaction between boron and CKEN. The adsorption behavior of CKEN for boron was evaluated. Various parameters affecting adsorption properties, viz., pH, ionic strength, initial concentration of boron, temperature and contact time were investigated. The adsorption kinetics is fitted with pseudo-second-order kinetics model better and the adsorption of boron on CKEN is an exothermic process. The adsorption equilibrium reached within 15 h with the maximum adsorption amount of 1.42 mmol/g (298 K). Moreover, CKEN also showed excellent reusability by consecutive five cycles of adsorption-desorption. It can be used as a potential recyclable adsorbent for efficient enrichment of boron from aqueous solution.

Facile method for surface etching of silica aerogel monoliths

In this work we demonstrate the use of a commercial CO2 laser cutting system to etch the surface of silica aerogel monoliths without causing overall structural damage to the monoliths. Text, photographs and other images can be readily reproduced on an aerogel surface. The visual appearance of the etched aerogel sample depends on the orientation of the sample and the viewer relative to the light source, which renders this approach visually attractive for applications in fine art, fenestration and architecture.

Cellulose Nanofiber Biotemplated Palladium Composite Aerogels.

Noble metal aerogels offer a wide range of catalytic applications due to their high surface area and tunable porosity. Control over monolith shape, pore size, and nanofiber diameter is desired in order to optimize electronic conductivity and mechanical integrity for device applications. However, common aerogel synthesis techniques such as solvent mediated aggregation, linker molecules, sol–gel, hydrothermal, and carbothermal reduction are limited when using noble metal salts. Here, we present the synthesis of palladium aerogels using carboxymethyl cellulose nanofiber (CNF) biotemplates that provide control over aerogel shape, pore size, and conductivity. Biotemplate hydrogels were formed via covalent cross linking using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) with a diamine linker between carboxymethylated cellulose nanofibers. Biotemplate CNF hydrogels were equilibrated in precursor palladium salt solutions, reduced with sodium borohydride, and rinsed with water followed by ethanol dehydration, and supercritical drying to produce freestanding aerogels. Scanning electron microscopy indicated three-dimensional nanowire structures, and X-ray diffractometry confirmed palladium and palladium hydride phases. Gas adsorption, impedance spectroscopy, and cyclic voltammetry were correlated to determine aerogel surface area. These self-supporting CNF-palladium aerogels demonstrate a simple synthesis scheme to control porosity, electrical conductivity, and mechanical robustness for catalytic, sensing, and energy applications.

Template-Free Self-Assembly of Fluorine-Free Hydrophobic Polyimide Aerogels with Lotus or Petal Effect

Aerogels have been widely used in the fields like thermal insulation, energy storage, environmental remediation, catalysis, drug release, sensor, and cosmic dust collection, etc. Hydrophobic functionalization not only determines the surface energy and basic physical properties of the target aerogels but also be critical for their long-term stability due to their highly open-porous structures. However, there is still lack of facial and versatile methodologies for the hydrophobic functionalization of aerogels, especially for the nonsilica ones. Herein, two efficient fluorine-free strategies were developed to synthesize various hydrophobic and even superhydrophobic polyimide (PI) aerogels. First, superhydrophobic PI aerogels with contact angle higher than 150° were fabricated by the segregation self-assembly process between poly[4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride)- co- p-phenylene diamine] and poly[biphenyl-3,3',3,4'-tetracarboxylic dianhydride- co-2,2'-dimethylbenzidine] (poly(BPDA-DMBZ)). These PI aerogels exhibited a lotus effect that water droplets could not wet the surface but could easily roll off. Second, various hydrophobic PI aerogels, including the well-documented superhydrophilic PI aerogels derived from DMBZ-BPDA and 4,4'-oxydianiline-BPDA, were synthesized by the density-induced hydrophilicity-hydrophobicity transition approach. These PI aerogels exhibited a petal effect that water droplets on the aerogel surface appeared spherical in shape, which could not roll off even when the aerogel was turned upside down. These two reported strategies might open new and straightforward ways to hydrophobic functionalization of other polymeric aerogel systems.

Structure and thermal stability in hydrophobic Pluronic F127-modified silica aerogels

Hydrophobic ambient pressure drying (APD) aerogels were prepared from hydrolysis of tetraethylorthosilicate (TEOS) in solutions with different concentrations of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (F127). APD was carried out after silylation of wet gels with 20% by volume of hexamethyldisilazane (HMDZ) in n-hexane. The samples were analyzed by small-angle X-ray scattering (SAXS) and nitrogen adsorption. The APD aerogels obtained in this process were submitted to heat treatment at 300, 500, 700 and 900 °C to study the pores stability. The samples were characterized by nitrogen adsorption. Wet gels are formed by mass-fractal domains, with fractal dimension close to 2.1 and characteristic size (ξ) spanning from about 9 nm (for the gel prepared without the addition of F127) up to values that exceed the maximum limit of the SAXS experimental setup, with increasing the concentration of F127. Nitrogen adsorption data showed that the pore volume (Vp) and the mean pore size (lp) of the aerogels increased with increasing the concentration of F127. The drying process diminished the characteristic size ξ and increased the dimension D of the mass-fractal domains and the size (r0) of the primary particles of the aerogels with respect to the wet gels. The characteristic size ξ of the mass-fractal of the aerogels was found significantly larger with increasing the concentrations of F127. Thermally treated aerogels exhibited a similar general behavior with temperature independent of the concentration of F127. The porosity was found fairly stable up to about 500 °C. The porosity started to be eliminated at 700 °C and it was found practically collapsed at 900 °C. The silylation layer on the silica surface of the present APD aerogels was promptly eliminated at about 350 °C yielding complete loss of hydrophobicity.

A Co-Precursor Approach Coupled with a Supercritical Modification Method for Constructing Highly Transparent and Superhydrophobic Polymethylsilsesquioxane Aerogels.

Polymethylsilsesquioxane (PMSQ) aerogels obtained from methyltrimethoxysilane (MTMS) are well-known high-performance porous materials. Highly transparent and hydrophobic PMSQ aerogel would play an important role in transparent vacuum insulation panels. Herein, the co-precursor approach and supercritical modification method were developed to prepare the PMSQ aerogels with high transparency and superhydrophobicity. Firstly, benefiting from the introduction of tetramethoxysilane (TMOS) in the precursor, the pore structure became more uniform and the particle size was decreased. As the TMOS content increased, the light transmittance increased gradually from 54.0% to 81.2%, whereas the contact angle of water droplet decreased from 141° to 99.9°, ascribed to the increase of hydroxyl groups on the skeleton surface. Hence, the supercritical modification method utilizing hexamethyldisilazane was also introduced to enhance the hydrophobic methyl groups on the aerogel’s surface. As a result, the obtained aerogels revealed superhydrophobicity with a contact angle of 155°. Meanwhile, the developed surface modification method did not lead to any significant changes in the pore structure resulting in the superhydrophobic aerogel with a high transparency of 77.2%. The proposed co-precursor approach and supercritical modification method provide a new horizon in the fabrication of highly transparent and superhydrophobic PMSQ aerogels.

Flower-like MoS2 supported on three-dimensional graphene aerogels as high-performance anode materials for sodium-ion batteries

Flower-like MoS2 supported on three-dimensional graphene aerogel (MoS2/GA) composite has been prepared by a facile hydrothermal method followed by subsequent heat-treatment process. Each of MoS2 microflowers is surrounded by the three-dimensional graphene nanosheets. The MoS2/GA composite is applied as an anode material of sodium-ion batteries (SIBs) and it exhibits high initial discharge/charge capacities of 562.7 and 460 mAh g−1 at a current density of 0.1 A g−1 and good cycling performance (348.6 mAh g−1 after 30 cycles at 0.1 A g−1). The good Na+ storage properties of the MoS2/GA composite could be attributed to the unique structure which flower-like MoS2 are homogeneously and tightly decorated on the surface of three-dimensional graphene aerogel. Our results demonstrate that as-prepared MoS2/GA composite has a great potential prospect as anodes for SIBs.

Evaluation of Carbon Aerogel Manufacturing Process in Order to Desalination of Saline and Brackish Water in Laboratory Scale

Carbon aerogel its fabrication and characterization and its uses in this process were studied for desalinating of saline and brackish water. The carbon aerogel manufacturing process involves the polymerization and pyrolysis of the mixture of resorcinol and formaldehyde. Carbon aerogels were analyzed using BET, BJH, and T-plot after construction. The effect of various parameters (including the influent salt concentration, the intensity of electric current flow, the distance between the electrodes and pH) on salt adsorption were studied. Analysis of BET/BJH shown that the surface of aerogel was 677.8 m2/g. much of porosity in the samples of carbon aerogel were between 1-2 nm, namely micro-pour and a similar level 0f 456 m2/gr is dedicated to micro-pour, with a correlation coefficient (r) equal to 94.5. According to the results, it seems that carbon aerogel electrodes have a good structure in desalination of brackish and saline water.

Laser Surface Engineering of Hierarchy Hydroxyapatite Aerogel for Bone Tissue Engineering

Bioceramics with porous microstructure has attracted intense attention in tissue engineering due to tissue growth facilitation in the human body. In the present work, a novel manufacturing process for producing hydroxyapatite (HA) aerogels with a high density shell inspired by human bone microstructure is proposed for bone tissue engineering applications. This method combines laser processing and traditional freeze casting, in which HA aerogel is prepared by freeze casting and aqueous suspension prior to laser processing of the aerogel surface with a focused CO2 laser beam that forms a dense layer on top of the porous microstructure. Using the proposed method, HA aerogel with dense shell was successfully prepared with a microstructure similar to human bone. The effect of laser process parameters on the surface, cross-sectional morphology and microstructure was investigated in order to obtain optimum parameters and has a better understanding of the process. Low laser energy resulted in a fragile thin surface with defects and cracks due to the thermal stress induced by the laser processing. However, increasing the laser power generated a thicker dense layer on the surface, free of defects. The range of 40–45 W laser power, 5 mm/s scanning speed, spot size of 1 mm, and 50% overlap in laser scanning the surface yielded the best surface morphology and microstructure in our experiments.