Sponge-like Aerogel Research Articles

Ultra-fast adsorption of radioactive-U(VI) and Cs(I) with high adsorption capacity towards CAA@MgAlFe spongy-like aerogel: Mechanism and application feasibility study

Secure disposal of radioactive wastewater had aroused global concerns for human health and ecological environment. Uranium (U) and Cesium (Cs) were both typical radioactive elements detected in contaminated water bodies. In response to the environmental problem, a spongy-like aerogel adsorbent was firstly prepared for the removal of radioactive U(VI) and Cs(I) and potential application in sea water. MgAlFe layered double hydroxides (LDHs) were prepared by hydrothermal method, and were then gelated by freeze-drying technique to synthesize the calcium alginate aerogels doped with MgAlFe LDHs (CAA@MgAlFe). The prepared CAA@MgAlFe was a kind of porous sponge-like aerogel, on which the LDHs dispersed uniformly. Batch adsorption experiments presented that the adsorption of U(VI) and Cs(I) could reach the equilibrium rapidly in only 4 min and 3 min, respectively. This suggested the reduction of radioactive exposure during the treatment was at a high extent. The adsorption capacities of U(VI) and Cs(I) were as high as 533 and 58 mg/g, respectively. Furthermore, the adsorption isotherms showed that U(VI) and Cs(I) matched well with the Langmuir and Freundlich models, respectively. CAA@MgAlFe could be easily separated and compressed, and its application on sea water was proved to be feasible. The adsorption mechanism of CAA@MgAlFe towards U(VI) included complexation, ion exchange and reduction, while that of Cs(I) was electrostatic attraction.

Self-assembly of mercury-ion recognizing CuS nanocrystals into 3D sponge-like aerogel towards superior mercury capturer with outstanding selectivity and efficiency

This work reports fabrication of a novel 3D sponge-like CuS aerogel (CuS AG) at room temperature by self-assembly of CuS nanocrystals and its application in recognition, capture and enrichment of mercury ions. The structure of CuS AG was characterized by SEM, TEM, XRD, FTIR and N2 adsorption − desorption isotherms, and its physicochemical properties were investigated by ICP-OES, ICP-MS, XPS, EDS elemental mapping and estimation of typical thermodynamic parameters. The highly porous Cu-S network structure has a large specific surface area (159 m2 g−1), a large pore volume (0.50 cm3 g−1) as well as abundant surface Cu-S sites and ion channels. As a result, CuS AG not only exhibits superior selectivity towards Hg2+ ions among other interfering metal ions via surface substitution reaction, but also demonstrates unprecedented capture capacity (3667 mg g−1) and superfast capture kinetics (99% removal within 30 s). These unique features endow CuS AG with a wide working range of pH (2–10) and temperature (0-45 °C) as well as suitability for practical complex samples. CuS AG was used as a new type of extracting materials for convenient enrichment and separation of ultratrace Hg2+ even at ppt level, achieving an enriching factor as high as 260. The current work may open a new avenue to the design and fabrication of high performance materials for recognition, adsorption, enrichment, separation and sensing of metal ions as well as catalysis, energy storage and bioapplications.

Development of sponge-like cellulose colorimetric swab immobilized with anthocyanin from red-cabbage for sweat monitoring

Novel sponge-like biochromic swab was developed via immobilization of natural anthocyanin (Cy) biomolecular probe into microporous cellulose aerogel. The current biosensor is characterized with simple preparation, environmentally-friendly, biocompatibility, biodegradability, flexibility, portability and reversibility. This biochromic sponge-like aerogel detector displayed a color change from pink to green-yellow in response to the biochemical changes occurs to sweat. This could be ascribed to intramolecular charge transfer occurs to the molecular system of Cy. Thus, the anthocyanin probe displayed colorimetric variations in UV–Vis absorption spectra via a blue shifting from 620 to 529 nm when raising the pH value of the prepared mimic sweat solution. Natural pH sensitive anthocyanin spectroscopic probe was extracted from red-cabbage plant, characterized by HPLC, and encapsulated into microporous cellulose. The microporous sponge-like cellulose swab was prepared by activating wood pulp utilizing phosphoric acid, and then subjected to freeze-drying. This anthocyanin probe is highly soluble in water. Thus, it was encapsulated as a direct dye into cellulose substrate during the freeze-drying process. To allow a better fixation of this water-soluble anthocyanin probe to the cellulose substrate, potash alum was added to the freeze-dried mixture to act as a fixing agent or mordant (M) generating Cy/M coordination complex. The produced Cy/M nanoparticles (NPs) were explored by transmission electron microscopy (TEM). The morphological features of the generated aerogels were investigated by scan electron microscope (SEM), energy-dispersive X-ray (EDX) spectra, and Fourier-transform infrared spectra (FT-IR). The cytotoxicity of the prepared aerogel-based biosensor was also evaluated. The naked-eye colorimetric changes were studied by exploring color strength, UV–Vis spectra and CIE Lab colorimetric coordinates.

Main-chain donor-acceptor polyhydrazone mediated adsorption of an anionic dye from contaminated water

A versatile synthetic approach was applied to synthesize a polyviologen (PV.nBr) polymer via step-growth polymerization of a tetraethylene glycol-linked trinapthyl-based dihydrazide with a bipyridinium-based dialdehyde (BIPY.2Br DA) in water under acidic conditions (pH, 2–3). The polymeric structure was constructed from alternating units of π-electron rich naphthyl and π-electron deficient bipyridinium (BIPY) moieties linked together via covalent acylhydrazone bonds. Ultraviolet-visible (UV–Vis) absorption analysis confirmed the occurrence of intramolecular donor-acceptor charge transfer (DA-CT) interactions between the electron donor and acceptor units. The synthesized polymer was subjected to lyophilization in order to produce a sponge-like aerogel with a large surface area and high porosity. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization revealed that the polymer possessed a uniform sheet-like morphology in the solid state following lyophilization. The ability of the novel polymer to adsorb Reactive Orange 122 (RO122) dye from synthetic wastewater was investigated at different operational conditions and was determined to follow pseudo-first-order kinetics. The results indicated that the novel PV.nBr can efficiently and rapidly remove RO122 under a wide range of solution pH with up to 97% uptake. The novel PV.nBr aerogel adsorbed RO122 by electrostatic attractions between the BIPY dication groups of the polymer and the anionic sulphonate groups of RO122. Adsorption isotherms revealed that the data was best fit to the Dubinin-Radushkevich model, with a calculated mean free energy of adsorption of 2.04 kJ/mol, corresponding to a physisorption dominated process.

Smart microfibrillated cellulose as swab sponge-like aerogel for real-time colorimetric naked-eye sweat monitoring

Collecting sweat sample for onsite testing is a sophisticated process as the analysis process must be completed in a real-time with a highly absorptive and sensitive device in order to gain a useful assessment of its content. Thus, we developed a chemical probe incorporated into microfibrillated cellulose to introduce a novel, simple, robust and flexible aerogel. This chromogenic sponge-like aerogel assay demonstrated a color change from yellow to orange, red and blue depending on the sweat biochemical changes. Novel pH sensitive tricyanofuran hydrazone probe was prepared, characterized and encapsulated in-situ within microfibrillated cellulose to follow up sweat pH changes. The solvatochromic performance in several solvents of different polarities and the reversible pH correlated color change of this tricyanofuran hydrazone probe in an acetonitrile solution was explored by UV–Vis absorption spectra. The microporous and microfibrillated sponge-like cellulose substrate was fabricated by activation of wood pulp using phosphoric acid followed by freeze-drying process. Morphological characterization, thermal stability and fiber crystallinity of the prepared aerogel were explored using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The visual color change was explored by studying the CIE LAB color space coordinates and color strength values. The cytotoxicity of the sponge-like aerogel sensor was also evaluated.

CHITIN LIQUID CRYSTAL- DERIVED SPONGE- LIKE AEROGEL

<p class="RSCB01COMAbstract"><span class="06CHeading"><span lang="EN-GB">Abstract: </span></span><span lang="EN-GB">Chitin nanocrystals in anisotropic liquid crystals have been used as a colloidal precursor to fabricate hydrogels and aerogels. Native chitin nanofibrils are deacetylated and hydrolyzed to generate rod-shaped chitin nanocrystals that are dispersible in water to form colloidal aqueous suspensions. Chitin nanocolloids self-organize into anisotropic liquid crystals that can solidify into layered nematic films. Chitin liquid crystals are hydrothermally gelatinized with formaldehyde crosslinkers to form homogeneous chitin hydrogels. The removal of water in the hydrogels by freeze-drying recovers ultralight chitin sponge-like aerogels with morphological retention of layered nematic chitin structure. These biocompatible chitin aerogels hold promise for developing advanced functional materials such as fabrics for antibacterial bandages and tissue engineering and hydrophobic absorbents for oil/water separation. Potentially, chitin nanocrystals assembled in the aerogels may be functionalized into hydrophobic sponges for oil/water separation or carbonized into nitrogen-doped carbon foams for supercapacitors.</span></p>

Biocompatible Chitosan-Functionalized Upconverting Nanocomposites.

Simultaneous integration of photon emission and biocompatibility into nanoparticles is an interesting strategy to develop applications of advanced optical materials. In this work, we present the synthesis of biocompatible optical nanocomposites from the combination of near-infrared luminescent lanthanide nanoparticles and water-soluble chitosan. NaYF4:Yb,Er upconverting nanocrystal guests and water-soluble chitosan hosts are prepared and integrated together into biofunctional optical composites. The control of aqueous dissolution, gelation, assembly, and drying of NaYF4:Yb,Er nanocolloids and chitosan liquids allowed us to design novel optical structures of spongelike aerogels and beadlike microspheres. Well-defined shape and near-infrared response lead upconverting nanocrystals to serve as photon converters to couple with plasmonic gold (Au) nanoparticles. Biocompatible chitosan-stabilized Au/NaYF4:Yb,Er nanocomposites are prepared to show their potential use in biomedicine as we find them exhibiting a half-maximal effective concentration (EC50) of 0.58 mg mL–1 for chitosan-stabilized Au/NaYF4:Yb,Er nanorods versus 0.24 mg mL–1 for chitosan-stabilized NaYF4:Yb,Er after 24 h. As a result of their low cytotoxicity and upconverting response, these novel materials hold promise to be interesting for biomedicine, analytical sensing, and other applications.

Highly flexible cross-linked cellulose nanofibril sponge-like aerogels with improved mechanical property and enhanced flame retardancy

Cellulose nanofibril (CNF) aerogel is highly flammable and its mechanical strength is very soft, which is unfavourable due to safety concerns and impractical when used as the thermal insulation material. In this work, we used N-methylol dimethylphosphonopropionamide (MDPA) and 1,2,3,4-butanetetracarboxylic acid (BTCA) as co-additives and then prepared lightweight flame resistant CNF sponge-like aerogels via an eco-friendly freeze-drying and post cross-linking method. The CNF/BTCA/MDPA aerogel exhibited a better flame retardant performance, outstanding self-extinguishing behaviour and significantly increased char residue (by as much as 268%) compared with the neat CNF aerogel. Meanwhile, the resilience of the aerogel samples improved significantly as the flexibility decreased slightly. Furthermore, the aerogel samples still exhibited excellent thermal insulating properties with thermal conductivity as low as 0.03258W/(m k). The combination of these characteristics makes the CNF-based aerogel a promising insulation candidate for thermal protective equipment (e.g., fire-protection clothing or advanced spacesuit elements) in the future.

Chitin Liquid-Crystal-Templated Oxide Semiconductor Aerogels.

Chitin nanocrystals have been used as a liquid crystalline template to fabricate layered oxide semiconductor aerogels. Anisotropic chitin liquid crystals are transformed to sponge-like aerogels by hydrothermally cross-linked gelation and lyophilization-induced solidification. The hydrothermal gelation of chitin aqueous suspensions then proceeds with peroxotitanate to form hydrogel composites that recover to form aerogels after freeze-drying. The homogeneous peroxotitanate/chitin composites are calcined to generate freestanding titania aerogels that exhibit the nanostructural integrity of layered chitin template. Our extended investigations show that coassembling chitin nanocrystals with other metal-based precursors also yielded semiconductor aerogels of perovskite BaTiO3 and CuOx nanocrystals. The potential of these materials is great to investigate these chitin sponges for biomedicine and these semiconductor aerogels for photocatalysis, gas sensing, and other applications. Our results present a new aerogel templating method of highly porous, ultralight materials with chitin liquid crystals.

Fabrication of Hybrid Collagen Aerogels Reinforced with Wheat Grass Bioactives as Instructive Scaffolds for Collagen Turnover and Angiogenesis for Wound Healing Applications.

The present study illustrates the progress of the wheat grass bioactive-reinforced collagen-based aerogel system as an instructive scaffold for collagen turnover and angiogenesis for wound healing applications. The reinforcement of wheat grass bioactives in collagen resulted in the design and development of aerogels with enhanced physicochemical and biomechanical properties due to the intermolecular interaction between the active growth factors of wheat grass and collagen fibril. Differential scanning calorimetry analysis revealed an enhanced denaturation temperature when compared to those of native collagen aerogels. Fourier transform infrared spectroscopy analysis confirmed that the reinforcement of bioactives in the wheat grass did not affect the structural integrity of the collagen molecule. Additionally, the reinforced biomaterial with a systematic absorptive morphology resulted in a three-dimensional (3D) sponge-like aerogel exhibiting a potent highly oriented 3D structural assembly that showed increased water retention ability and substance permeability that would enable the passage of nutrients and gaseous components for cellular growth. Furthermore, the cumulative effect of the growth factors in wheat grass and the collagen molecule augments the angiogenic ability and collagen production of the aerogel by restoration of the damaged tissue thereby making it a potential 3D wound dressing scaffold. The results were confirmed by in vivo wound healing assays. This study shows the possibility for progress of a biocompatible, biodegradable, and nonadhesive nutraceutical-reinforced collagen aerogel as an instructive scaffold with good antimicrobial properties for collagen turnover and angiogenic response for wound healing applications.

Softwood-based sponge gels

Crosslinking-aided gelation was utilized to prepare hydrogels from softwood polysaccharides, with spruce galactoglucomannans (GGM)—a group of largely unexploited hemicelluloses—as the main component, aiming at conversion into sponge-like aerogels. Cellulose nanofibrils were used for the formation of a reinforcing network, which was further crosslinked together with a GGM matrix by ammonium zirconium carbonate, an inorganic salt that is regarded as safe for use in food packaging. The hydrogels were freeze-dried into stiff, low-density aerogels with 98 % of their volume composed of air-filled pores. When immersed in water, the aerogels absorbed water up to 37 times their initial weight, demonstrating elasticity and repeatable and reversible sponge capacity. The developed concept reassembles the wood polysaccharides in a new way, creating interesting possibilities for utilizing the abundant “green gold,” GGM. The obtained biobased materials could find application potential, for example, in the field of food packaging and could contribute in the reduction of the usage of petroleum-based plastics in the future.

New soft and spongy resorcinol–formaldehyde aerogels

Novel super-flexible resorcinol–formaldehyde (RF) aerogels were synthesized via a sol–gel process followed by supercritical drying. These aerogels are soft and are reversibly deformable up to 25%. Low density of 0.06gcm−3 and low Young's modulus of about 116kPa distinguish these sponge-like aerogels from conventional RF-aerogels made especially by ambient drying. The synthesis occurs from a very diluted sol-solution and demands high accuracy during preparation. Formation of small particles and relatively big pores allow bending of pore walls without breaking and establish microstructural conditions of flexibility. The experiments show the microstructure formation leading to superflexible RF-aerogels is a very sensitive process and depends on the homogeneity of the sol and its pH value. Shrinkage during for instance ambient dyring induces a collapse of the pore structure and reduces flexibility. Additionally, a definition and calculation of the term “flexibility” is presented and discussed in this study.