Aerogel Network Research Articles

Versatile Three‐Dimensional Porous Cu@Cu2O Aerogel Networks as Electrocatalysts and Mimicking Peroxidases

AbstractA facile strategy is presented to form 3D porous Cu@Cu2O aerogel networks by self‐assembling Cu@Cu2O nanoparticles with the diameters of ca. 40 nm for constructing catalytic interfaces. Unexpectedly, the prepared Cu@Cu2O aerogel networks display excellent electrocatalytic activity to glucose oxidation at a low onset potential of ca. 0.25 V. Moreover, the Cu@Cu2O aerogels also can act as mimicking‐enzymes including horseradish peroxidase and NADH peroxidase, and show obvious enzymatic catalytic activities to the oxidation of dopamine (DA), o‐phenyldiamine (OPD), 3,3,5,5‐tetramethylbenzidine (TMB), and dihydronicotinamide adenine dinucleotide (NADH) in the presence of H2O2. These 3D Cu@Cu2O aerogel networks are a new class of porous catalytic materials as mimic peroxidases and electrocatalysts and offer a novel platform to construct catalytic interfaces for promising applications in electrochemical sensors and artificial enzymatic catalytic systems.

Versatile Three-Dimensional Porous Cu@Cu2 O Aerogel Networks as Electrocatalysts and Mimicking Peroxidases.

A facile strategy is presented to form 3D porous Cu@Cu2 O aerogel networks by self-assembling Cu@Cu2 O nanoparticles with the diameters of ca. 40 nm for constructing catalytic interfaces. Unexpectedly, the prepared Cu@Cu2 O aerogel networks display excellent electrocatalytic activity to glucose oxidation at a low onset potential of ca. 0.25 V. Moreover, the Cu@Cu2 O aerogels also can act as mimicking-enzymes including horseradish peroxidase and NADH peroxidase, and show obvious enzymatic catalytic activities to the oxidation of dopamine (DA), o-phenyldiamine (OPD), 3,3,5,5-tetramethylbenzidine (TMB), and dihydronicotinamide adenine dinucleotide (NADH) in the presence of H2 O2 . These 3D Cu@Cu2 O aerogel networks are a new class of porous catalytic materials as mimic peroxidases and electrocatalysts and offer a novel platform to construct catalytic interfaces for promising applications in electrochemical sensors and artificial enzymatic catalytic systems.

Application of Aqueous-Based Covalent Crosslinking Strategies to the Formation of Metal Chalcogenide Gels and Aerogels

Abstract An aqueous-based metal ion crosslinking approach for assembly of metal chalcogenide nanoparticles (NPs) into robust gels is reported. Short chalcogenide ligands (S2−) undergo crosslinking with metal salts (Sn4+) to form a gel [NP/S2−/Sn4+]n (NP=PbTe, PbS, CdS, CdSe). The corresponding aerogel networks retain the crystallinity and quantum confinement effects of the native building blocks while achieving excellent porosity [Brunauer–Emmett–Teller (BET) surface areas of 160–238 m2/g]. Treatment of sulfide-capped PbTe nanoparticles with an excess of Sn4+ leads to ion exchange and formation of an amorphous “SnTe” gel.

(Invited) Nanoscale Design and Modification of Plasmonic Aerogels for Photocatalytic Hydrogen Generation

Composite catalytic aerogels comprise a highly-flexible design motif for the creation of solar fuels photocatalysts. We exploit the compositional and interfacial design flexibility of catalytic aerogels to couple surface plasmon resonant (SPR) guests to nanometric oxidation and reduction catalysts in one hierarchical photocatalytic composite architecture. In our composite aerogels, the nanoscale TiO2 aerogel acts as a 3D-interconnected network of nanowires that couples all of the functional elements required to photogenerate molecular hydrogen from visible light and water: visible light sensitization, electron and ion transport, and oxidation and reduction catalysis. We investigate the effects of synthetically modifying the TiO2 aerogel network and the nanoparticulate Au||TiO2 interfaces in plasmonic Au–TiO2 aerogels on light sensitization, carrier (electron–hole pair) generation, and photocatalytic H2 evolution under both broadband (i.e., UV + visible) and visible excitation. We also introduce oxidation and reduction co-catalyst nanoparticles into the plasmonic aerogels, creating composite aerogels that perform visible light SPR–driven photocatalytic reduction of water to generate H2. The nanostructured high surface–area network in the aerogel spatially and effectively separates charge while electrochemically connecting plasmonic nanoparticle sensitizers and metal nanoparticle all in one mesoscale architecture and at length scales compatible with the kinetics of each reaction. Reference: "Plasmonic aerogels as a 3D nanoscale platform for solar fuels photocatalysis.” P. A. DeSario, J. J. Pietron, A. Dunkelburger, T.H. Brintlinger, O. Baturina, R. M. Stroud, J. C. Owrutsky, and D. R. Rolison, Langmuir, 2017, 33, 9444–9454; doi: 10.1021/acs.langmuir.7b01117 This work is supported by the U.S. Office of Naval Research.

3D reduced graphene oxide aerogel-mediated Z-scheme photocatalytic system for highly efficient solar-driven water oxidation and removal of antibiotics

The construction of natural photosynthesis-inspired Z-scheme tandem system has been considered as a promising strategy to fulfill efficient electron-hole separation and charge transportation in composite photocatalysts, providing a unique opportunity to achieve improved solar-driven photocatalytic water splitting performance superior to conventional heterojunctions. The presence of an ideal electron mediator is critical to promote effective electron transfer in Z-scheme semiconductor photocatalytic systems. Herein, for the first time, we report the fabrication of CeVO4/three-dimensional (3D) reduced graphene oxide (RGO) aerogel/BiVO4 ternary composites and their use as photocatalysts for visible-light-driven water oxidation and tetracycline (TC) degradation. As-prepared hybrid materials exhibit well-organized heterostructures where two vanadates with different dimensional features are surrounded by 3D aerogel networks. Under visible light irradiation, the optimal composite material revealed highly improved photocatalytic activity both in oxygen evolution from water splitting and TC degradation. The enhancement in photocatalytic efficiency is assumed to come from illuminated Z-scheme CeVO4/3D RGO/BiVO4 configuration, in which conductive 3D RGO aerogel functions as an effective electron mediator and builds the bridge between two vanadates, offering a tandem channel for more efficient charge transfer in two semiconductors. This work may provide a new clue for the design of all-solid-state Z-scheme composite photocatalytic materials in energy and environmental applications.

Complex shaped boron carbides from negative additive manufacturing

Complex shaped boron carbide with carbon (B4C/C) at near-full densities were achieved for the first time using negative additive manufacturing techniques via gelcasting. Negative additive manufacturing involves 3D printing of sacrificial molds used for casting negative copies. B4C powder distributions and rheology of suspensions were optimized to successfully cast complex shapes. In addition to demonstrating scalability of these complex geometries, hierarchically meso-porous structures were also shown to be possible from this technique. Resorcinol-Formaldehyde (RF) polymer was selected as the gelling agent and can also pyrolyze into a carbon aerogel network to act as the sintering aid for B4C. Due to the highly effective distribution of in situ carbon for the B4C matrix, near-full sintered density of 97–98% of theoretical maximum density was achieved.

Reduced graphene oxide aerogel networks with soft interfacial template for applications in bone tissue regeneration

Reduced Graphene Oxide aerogels (A-RGO), functionalized with chitosan, were found to induce and/or accelerate the mineralization of hydroxyapatite. The functionalized chitosan acts as a soft interfacial template on the surface of A-RGO assisting the growth of hydroxyapatite particles. The mineralization on these soft aerogel networks was performed by soaking the aerogels in simulated body fluid, relative to time. Polymer-induced mineralization exhibited an ordered arrangement of hydroxyapatite particles on reduced graphene oxide aerogel networks with a higher crystalline index (IC) of 1.7, which mimics the natural bone formation indicating the importance of the polymeric interfacial template. These mineralized aerogels which mimic the structure and composition of natural bone exhibit relatively higher rate of cell proliferation, osteogenic differentiation and osteoid matrix formation proving it to be a potential scaffold for bone tissue regeneration.

$$\hbox {TiO}_{2}$$ TiO 2 aerogel–metal organic framework nanocomposite: a new class of photoanode material for dye-sensitized solar cell applications

$$\hbox {TiO}_{2}$$ aerogel–metal organic framework (MOF) nanocomposite was synthesized using sol–gel method followed by subcritical drying technique and employed as a photoanode material in quasi-solid dye-sensitized solar cells (DSSCs). The nanocomposite material showed a BET surface area of $$250\hbox { m}^{2}\hbox { g}^{-1}$$ with an average pore size of 5 nm. Field emission scanning electron microscopic images revealed the continuous arrangement of pore-solid network structure. Energy-dispersive X-ray analysis shows the presence of MOF clusters on $$\hbox {TiO}_{2}$$ aerogel network. X-ray photoelectron spectroscopic analysis also supports the presence of MOF clusters in the aerogel network and indicates the presence of some oxygen vacancies in the nanocomposite material. The $$\hbox {TiO}_{2}$$ aerogel–MOF nanocomposite was used as photoanode in DSSC and an overall power conversion efficiency 2.34% along with a short-circuit current density 6.22 mA $$\hbox {cm}^{-2}$$ was achieved.

An explanation of damage and failure in cellulose aerogels: modeling approach

AbstractCellulose aerogels can be considered as foam‐like materials and have recently been modeled using micro‐mechanical approaches. The proposed microcell based models describe the constitutive response of these aerogels based primarily on the bending of the cell wall fibrils, and show good agreement with experimental data. Under compression, the cell walls are considered to undergo nonlinear bending. On the other hand, under tension the deformation in the cell walls is attributed to both, bending and stretching. Accordingly, the total aerogel network energy is divided into a bending one and a tension one. The cell walls undergoing such combined loading fail after reaching a critical normal stress value, and are then considered to no longer contribute to the total network energy. Material constants in these models are obtained from experimental observations, like for example, the pore‐size data analysis, thus resulting into physically motivated models. Finally, the models are also shown to be effective in predicting the constitutive response of other polysaccharidic aerogels. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterization of Pure and Composite Resorcinol Formaldehyde Aerogels Doped with Copper

A series of resorcinol formaldehyde aerogels (RF aerogels) composite with nanoparticles of copper has been prepared by the sol-gel method. Four samples of pure RF aerogels were prepared at different concentrations of NaOH as a catalyst (0.015, 0.017, 0.022 and 0.024 wt. %) and four samples of composite RF aerogels doped with Cu were prepared at different concentration of Cu (7.8×10-5, 1.56×10-4, 2.34×10-4, and 3.11×10-4 wt. %; NaOH concentration = 0.015 wt. %). UV-visible spectrum of Cu colloidal showes an absorbance peak at 608 nm, while UV-visible spectra of pure and composite RF aerogels show a steep decrease of absorption after 500 nm making RF aerogel color reddish brown. Results of FTIR spectra of pure and composite RF aerogels show the existence of six absorption bands ensuring the formation of RF aerogels. FTIR results ensured also that Cu particles do not affect the aerogel network. SEM images of pure and composite RF aerogels show that the textural arrangement of RF aerogels can be described as densely packed small nodules.The particle size analyzer ensured that the average particle size for Cu-RF aerogel composite increases with increasing the copper content.

Superwetting polypropylene aerogel supported form-stable phase change materials with extremely high organics loading and enhanced thermal conductivity

The development of high efficient materials or devices for storage and utilization of sustainable thermal energy should be of great importance in alleviating energy crisis. Herein, we reported the fabrication of superwetting polypropylene (PP) aerogel as the support materials for construction of form-stable phase change materials (PCMs) composites. Due to its abundant porosity, light weight of aerogel in nature, inherent superhydrophobic and superoleophilic properties, lipophilic organic PCMs can be loaded into PP aerogel (PP/PCM) with a high PCMs loading of up to 1060wt%, which is nearly two orders of magnitudes higher than those mostly reported form-stable PCMs systems. The PP/PCM composites show high latent heat in the range of 141.1kJkg−1 to 159.5kJkg−1 and excellent thermal stability and recyclability where their latent heat nearly remains unchanged even after 50 times of melting/freezing cycles. Results obtained from the X-ray diffraction (XRD) show that the incorporation of organic PCMs into PP aerogel network decreases the crystal size of PCMs in the composites. More interestingly, the PP/PCM composites show an enhanced thermal conductivity, in the case of PP/Paraffin composite, which is over two times of that of paraffin. Having the advantages of low cost and abundant resource of PP, simple preparatory process, high PCMs loading, good stability, recyclability and thermal conductivity, this the PP/PCM composites may have great potential for renewable energy saving applications.

Effects of Nanoscale Interfacial Design on Photocatalytic Hydrogen Generation Activity at Plasmonic Au–TiO2 and Au–TiO2/Pt Aerogels

We demonstrate that composite catalytic aerogels represent a superior materials design motif for the creation of solar fuels photocatalysts. We couple surface plasmon resonant (SPR) guests to the inherent compositional and interfacial design flexibility of catalytic aerogels to photogenerate molecular hydrogen (H2). We investigate the effects of synthetically modifying the TiO2 aerogel network and the nanoparticulate Au||TiO2 interfaces in plasmonic Au–TiO2 aerogels on H2 evolution under both broadband (i.e., UV + visible light) and visible excitation. We also introduce non-plasmonic Pt co-catalyst nanoparticles into our composite aerogels, creating Au–TiO2/Pt aerogels that perform visible light SPR-driven photocatalytic reduction of water to generate H2. The fuels production achieved with this multicomponent photocatalytic nanoreactor demonstrates that the nanostructured high-surface-area network in the aerogel can spatially and effectively separate charge while electrochemically connecting plasmonic nanoparticle sensitizers and metal nanoparticle. In doing so, we prove several crucial concepts: (1) integration of a plasmonic sensitizer with a separate water reduction co-catalyst within the ultraporous aerogel nanoarchitecture; (2) wiring the electron–hole pairs generated under visible light at the plasmonic Au||TiO2 interface to the co-catalyst via the nanoscale TiO2 network; and (3) combining both the photocatalytic oxidation and reduction reactions critical to solar fuels photocatalysis into one composite material at length scales compatible with the reaction kinetics. This work is supported by the Office of Naval Research.

Carbon Nitride Aerogels for the Photoredox Conversion of Water.

Aerogel structures have attracted increasing research interest in energy storage and conversion owing to their unique structural features, and a variety of materials have been engineered into aerogels, including carbon-based materials, metal oxides, linear polymers and even metal chalcogenides. However, manufacture of aerogels from nitride-based materials, particularly the emerging light-weight carbon nitride (CN) semiconductors is rarely reported. Here, we develop a facile method based on self-assembly to produce self-supported CN aerogels, without using any cross-linking agents. The combination of large surface area, incorporated functional groups and three-dimensional (3D) network structure, endows the resulting freestanding aerogels with high photocatalytic activity for hydrogen evolution and H2 O2 production under visible light irradiation. This work presents a simple colloid chemistry strategy to construct 3D CN aerogel networks that shows great potential for solar-to-chemical energy conversion by artificial photosynthesis.

Carbon Nitride Aerogels for the Photoredox Conversion of Water

AbstractAerogel structures have attracted increasing research interest in energy storage and conversion owing to their unique structural features, and a variety of materials have been engineered into aerogels, including carbon‐based materials, metal oxides, linear polymers and even metal chalcogenides. However, manufacture of aerogels from nitride‐based materials, particularly the emerging light‐weight carbon nitride (CN) semiconductors is rarely reported. Here, we develop a facile method based on self‐assembly to produce self‐supported CN aerogels, without using any cross‐linking agents. The combination of large surface area, incorporated functional groups and three‐dimensional (3D) network structure, endows the resulting freestanding aerogels with high photocatalytic activity for hydrogen evolution and H2O2 production under visible light irradiation. This work presents a simple colloid chemistry strategy to construct 3D CN aerogel networks that shows great potential for solar‐to‐chemical energy conversion by artificial photosynthesis.

Plasmonic Aerogels as a Three-Dimensional Nanoscale Platform for Solar Fuel Photocatalysis

We use plasmonic Au-TiO2 aerogels as a platform in which to marry synthetically thickened particle-particle junctions in TiO2 aerogel networks to Au∥TiO2 interfaces and then investigate their cooperative influence on photocatalytic hydrogen (H2) generation under both broadband (i.e., UV + visible light) and visible-only excitation. In doing so, we elucidate the dual functions that incorporated Au can play as a water reduction cocatalyst and as a plasmonic sensitizer. We also photodeposit non-plasmonic Pt cocatalyst nanoparticles into our composite aerogels in order to leverage the catalytic water-reducing abilities of Pt. This Au-TiO2/Pt arrangement in three dimensions effectively utilizes conduction-band electrons injected into the TiO2 aerogel network upon exciting the Au SPR at the Au∥TiO2 interface. The extensive nanostructured high surface-area oxide network in the aerogel provides a matrix that spatially separates yet electrochemically connects plasmonic nanoparticle sensitizers and metal nanoparticle catalysts, further enhancing solar-fuels photochemistry. We compare the photocatalytic rates of H2 generation with and without Pt cocatalysts added to Au-TiO2 aerogels and demonstrate electrochemical linkage of the SPR-generated carriers at the Au∥TiO2 interfaces to downfield Pt nanoparticle cocatalysts. Finally, we investigate visible light-stimulated generation of conduction band electrons in Au-TiO2 and TiO2 aerogels using ultrafast visible pump/IR probe spectroscopy. Substantially more electrons are produced at Au-TiO2 aerogels due to the incorporated SPR-active Au nanoparticle, whereas the smaller population of electrons generated at Au-free TiO2 aerogels likely originate at shallow traps in the high surface-area mesoporous aerogel.

Characterization of pure and composite resorcinol formaldehyde aerogels doped with silver

A series of Resorcinol Formaldehyde (RF) aerogels composites with nanoparticles of sliver were prepared by the sol-gel method at different concentrations doped silver. FTIR spectra of pure and composite RF aerogels show six absorption bands attributed to –OH groups bonded to the benzene ring, stretching of –CH2– bonds and aromatic ring stretching. FTIR results ensured that sliver particles do not interact with aerogel network. UV-visible spectrum of pure silver show an absorbance peak at 420 nm attributed to the surface plasmon excitation of sliver Nano spheres. UV-visible spectral of pure and composite RF aerogels shows a steep decrease of absorption with wavelength after 500 nm, making sample’s color reddish brown. TEM and SEM images of pure and composite RF aerogels revealed that the textural arrangement of RF aerogels can be described as densely packed small nodules.

Aligned α-FeOOH nanorods anchored on a graphene oxide-carbon nanotubes aerogel can serve as an effective Fenton-like oxidation catalyst

The self-assembled synthesis of a hierarchical graphene oxide (GO)-carbon nanotubes (CNTs)-α-FeOOH decorated composite aerogel (α-FeOOH@GCA) through a facile in-situ hydrolysis route is reported for the first time and the materials was tested for its performance as Fenton-like catalyst. The introduction of GO-CNTs clearly mediated the morphology to aligned α-FeOOH nanorods (ca. 100nm) within aerogel matrix comparing with pristine urchin-like α-FeOOH three-dimensional microstructures (ca. 1μm). This three dimensional porous aerogel network provided efficient charge/mass-transfer leading to great enhancement of the catalytic activity of α-FeOOH. The outstanding catalytic performance of this composite in degradation of organics with different charge and structure, i.e. Orange II (OII), rhodamine B (RhB), methylene blue (MB), phenol and endocrine disruptor bisphenol A (BPA) was demonstrated. For example, the discoloration of OII with pseudo first-order rate constant of 0.10min−1 significantly exceeded that of pristine α-FeOOH. At relatively low concentration of α-FeOOH@GCA catalyst (125mgL−1) and H2O2 (0.55mM) showed excellent catalytic activity for efficient (∼99%) discoloration of OII (40mgL−1) under a 60min UV365 irradiation in the pH range 3–10. The different charge of five target contaminats greatly determined the surface-catalyzed degradation kinetics at natural solution pH in the order of cationic>neutral>anionic organics due to the negatively charged carbon-based aerogel matrix. The new identified desulfonation intermediates elucidated through UPLC–MS analysis indicated two reaction pathways: 1) hydroxylation and 2) desulfonation by-products followed by cleavage of the azo bond as the predominant degradation pathway of OII. The elimination of the acute toxicity of the parent contaminant to luminescent bacterium Q67 was consistent with the formation of less toxic degradation by-products identified. Free radical quenching studies accessed the role of hydroxyl radical (OH), superoxide anion radical (O2−) and singlet oxygen (1O2) as the dominating reactive oxygen species (ROS). The quantitative studies to measure radical concentrations using relative molecular probes showed the effective activation of H2O2 led to high rate production of ROS accounted for OII degradation. The greatly enhanced photocatalytic property of this hybrid was correlated with the efficient conversion between Fe2+/Fe3+ and synergistic coupling between α-FeOOH and carbon-based aerogel matrix evidenced through the formation of FeOC chemical bonds was verified by X-ray photoelectron (XPS) analysis. Based on its simple and scalable preparation route as well as its excellent UV365 or visible light-responsive catalytic performance, this hybrid exhibits a high potential to be used as an efficient and environmental-friendly catalyst for water remediation.

Microwave assisted synthesis of high surface area TiO2 aerogels: A competent photoanode material for quasi-solid dye-sensitized solar cells

TiO2 aerogels are 3-dimensional interconnected network structures offer high surface area, large pores and low density. In the present work, we synthesized TiO2 aerogels by a microwave assisted sol-gel method and employed it as a photo-anode material in quasi-solid dye-sensitized solar cells (QSDSSCs). This work mainly focuses on the effect of microwave irradiation on primary TiO2 nanoparticles, the building blocks of the aerogel network. The crystallite size determined from X-ray diffraction indicates that the crystal growth was controlled, as the particle-particle attraction prevailed by the thermal effect instigated during microwave irradiation. The smaller crystals enhanced the surface area of TiO2 aerogels and the amount of dye adsorption. The porous morphology and the interconnected network structure of aerogels were ascertained by Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscopic (TEM) analysis. A maximum power conversion efficiency of 5.2% with a short-circuit current density of 15.18 mA/cm2 and an open circuit voltage of 0.62 V was realized by utilizing TiO2 aerogel as photoanode in QSDSSCs.

Self-Supporting Hierarchical Porous PtAg Alloy Nanotubular Aerogels as Highly Active and Durable Electrocatalysts

Developing electrocatalysts with low cost, high activity, and good durability is urgently demanded for the wide commercialization of fuel cells. By taking advantage of nanostructure engineering, we fabricated PtAg nanotubular aerogels (NTAGs) with high electrocatalytic activity and good durability via a simple galvanic replacement reaction between the in situ spontaneously gelated Ag hydrogel and the Pt precursor. The PtAg NTAGs have hierarchical porous network features with primary networks and pores from the interconnected nanotubes of the aerogel and secondary networks and pores from the interconnected thin nanowires on the nanotube surface, and they show very high porosities and large specific surface areas. Due to the unique structure, the PtAg NTAGs exhibit greatly enhanced electrocatalytic activity toward formic acid oxidation, reaching 19 times higher metal-based mass current density as compared to the commercial Pt black. Furthermore, the PtAg NTAGs show outstanding structural stability and elect...

Flexible Carbon Aerogels

Carbon aerogels are highly porous materials with a large inner surface area. Due to their high electrical conductivity they are excellent electrode materials in supercapacitors. Their brittleness, however, imposes certain limitations in terms of applicability. In that context, novel carbon aerogels with varying degree of flexibility have been developed. These highly porous, light aerogels are characterized by a high surface area and possess pore structures in the micrometer range, allowing for a reversible deformation of the aerogel network. A high ratio of pore size to particle size was found to be crucial for high flexibility. For dynamic microstructural analysis, compression tests were performed in-situ within a scanning electron microscope allowing us to directly visualize the microstructural flexibility of an aerogel. The flexible carbon aerogels were found to withstand between 15% and 30% of uniaxial compression in a reversible fashion. These findings might stimulate further research and new application fields directed towards flexible supercapacitors and batteries.