Cellulose Nanofiber Biotemplated Palladium Composite Aerogels

Revealing the Importance of Iron Aerogel Features as Electrocatalysts for the Oxygen Reduction Reaction

Metal nanoparticles supported in carbon materials are the traditional electrocatalyst currently used in many applications. However, these composite materials have many problems associated with the optimization of both components for the specific application, besides the stability of the mixture. Self-supported metallic materials may be an interesting strategy in order to avoid the traditional carbon supports; however, these metallic materials should present highly active surface area. Iron aerogels are presented in this work as effective and affordable unsupported electrocatalysts. The combination of their metallic structure with high porosity (i.e., 85 m2 g-1 and 0.45 cm3 g-1 of mesopore volume), due to their interconnected tridimensional structure, leads to a great activity versus the oxygen reduction reaction. A method for producing iron aerogels based on microwave-assisted sol-gel methodology is presented. The incorporation of carbon functionalities to the iron aerogels seems to clearly influence the mechanism of the reaction, favoring the direct mechanism of the oxygen reduction reaction and thus notably improving the performance of the electrocatalysts. Chemical vapor deposition seems to be an adequate methodology for incorporating carbon functionalities to the transition metal structure without affecting the tridimensional network and leading to current densities over 4 mA cm-2 and great stability even after 10,000 s.

Cellulose Nanofiber-Alginate Biotemplated Cobalt Composite Multifunctional Aerogels for Energy Storage Electrodes

Tunable porous composite materials to control metal and metal oxide functionalization, conductivity, pore structure, electrolyte mass transport, mechanical strength, specific surface area, and magneto-responsiveness are critical for a broad range of energy storage, catalysis, and sensing applications. Biotemplated transition metal composite aerogels present a materials approach to address this need. To demonstrate a solution-based synthesis method to develop cobalt and cobalt oxide aerogels for high surface area multifunctional energy storage electrodes, carboxymethyl cellulose nanofibers (CNF) and alginate biopolymers were mixed to form hydrogels to serve as biotemplates for cobalt nanoparticle formation via the chemical reduction of cobalt salt solutions. The CNF-alginate mixture forms a physically entangled, interpenetrating hydrogel, combining the properties of both biopolymers for monolith shape and pore size control and abundant carboxyl groups that bind metal ions to facilitate biotemplating. The CNF-alginate hydrogels were equilibrated in CaCl2 and CoCl2 salt solutions for hydrogel ionic crosslinking and the prepositioning of transition metal ions, respectively. The salt equilibrated hydrogels were chemically reduced with NaBH4, rinsed, solvent exchanged in ethanol, and supercritically dried with CO2 to form aerogels with a specific surface area of 228 m2/g. The resulting aerogels were pyrolyzed in N2 gas and thermally annealed in air to form Co and Co3O4 porous composite electrodes, respectively. The multifunctional composite aerogel's mechanical, magnetic, and electrochemical functionality was characterized. The coercivity and specific magnetic saturation of the pyrolyzed aerogels were 312 Oe and 114 emu/gCo, respectively. The elastic moduli of the supercritically dried, pyrolyzed, and thermally oxidized aerogels were 0.58, 1.1, and 14.3 MPa, respectively. The electrochemical testing of the pyrolyzed and thermally oxidized aerogels in 1 M KOH resulted in specific capacitances of 650 F/g and 349 F/g, respectively. The rapidly synthesized, low-cost, hydrogel-based synthesis for tunable transition metal multifunctional composite aerogels is envisioned for a wide range of porous metal electrodes to address energy storage, catalysis, and sensing applications.

Versatile nanocellulose-based nanohybrids: A promising-new class for active packaging applications

The food packaging industry is rapidly growing as a consequence of the development of nanotechnology and changing consumers' preferences for food quality and safety. In today's globalization of markets, active packaging has achieved many advantages with the capability to absorb or release substances for prolonging the food shelf life over the traditional one. Therefore, it is critical to developing multifunctional active packaging materials from biodegradable polymers with active agents to decrease environmental challenges. This review article addresses the recent advances in nanocelluloses (NCs)- baseds nanohybrids with new function features in packaging, focusing on the various synthesis methods of NCs-based nanohybrids, and their reinforcing effects as active agents on food packaging properties. The applications of NCs-based nanohybrids as antioxidants, antimicrobial agents, and UV blocker absorbers for prolonging food shelf-life are also reviewed. Overall, these advantages make the CNs-based nanohybrids with versatile properties promising in food and packaging industries, which will impact more readership with concern for future research.

P. S. AK, Olaiya NG, Abdullah CK, Alfatah T, Gopakumar DA, Pasquini D. Improved Hydrophobicity of Macroalgae Biopolymer Film Incorporated with Kenaf Derived CNF Using Silane Coupling Agent

Hydrophilic behaviour of carrageenan macroalgae biopolymer, due to hydroxyl groups, has limited its applications, especially for packaging. In this study, macroalgae were reinforced with cellulose nanofibrils (CNFs) isolated from kenaf bast fibres. The macroalgae CNF film was after that treated with silane for hydrophobicity enhancement. The wettability and functional properties of unmodified macroalgae CNF films were compared with silane-modified macroalgae CNF films. Characterisation of the unmodified and modified biopolymers films was investigated. The atomic force microscope (AFM), SEM morphology, tensile properties, water contact angle, and thermal behaviour of the biofilms showed that the incorporation of Kenaf bast CNF remarkably increased the strength, moisture resistance, and thermal stability of the macroalgae biopolymer films. Moreover, the films’ modification using a silane coupling agent further enhanced the strength and thermal stability of the films apart from improved water-resistance of the biopolymer films compared to unmodified films. The morphology and AFM showed good interfacial interaction of the components of the biopolymer films. The modified biopolymer films exhibited significantly improved hydrophobic properties compared to the unmodified films due to the enhanced dispersion resulting from the silane treatment. The improved biopolymer films can potentially be utilised as packaging materials.

Preparation and characterization of cellulose nanofiber cryogels as oil absorbents and enzymatic lipolysis scaffolds

Cellulose nanofiber (CNF) materials have received much attention as sustainable "green" materials with high mechanical properties. Their application in oil absorption and enzymatic lipolysis makes them further attractive from the perspective of environmental issues including marine pollution preservation. Herein, we prepared CNF cryogels with various surface properties, evaluated their capacities as oil absorbents and applied them as lipase-lipolysis scaffolds. Their obtained cryogels consisted of various modified CNFs and their structure and properties were investigated. Moreover, lipase-supported CNF cryogels were prepared for enzymatic lipolysis. The cryogels of protonated TEMPO-oxidized CNF showed the highest absorption capacity for olive oil, while all the CNF cryogels possessed similar absorption abilities towards water. In enzymatic lipolysis with lipase, the TEMPO-oxidized CNF (TOCN-Na⁺) cryogel showed the highest specific activity. The specific activities of lipase in TOCN-Na⁺ cryogels remained unchanged after being stored at 40 °C for 3 days.

An Opinion Paper on Aerogels for Biomedical and Environmental Applications

Aerogels are a special class of nanostructured materials with very high porosity and tunable physicochemical properties. Although a few types of aerogels have already reached the market in construction materials, textiles and aerospace engineering, the full potential of aerogels is still to be assessed for other technology sectors. Based on current efforts to address the material supply chain by a circular economy approach and longevity as well as quality of life with biotechnological methods, environmental and life science applications are two emerging market opportunities where the use of aerogels needs to be further explored and evaluated in a multidisciplinary approach. In this opinion paper, the relevance of the topic is put into context and the corresponding current research efforts on aerogel technology are outlined. Furthermore, key challenges to be solved in order to create materials by design, reproducible process technology and society-centered solutions specifically for the two abovementioned technology sectors are analyzed. Overall, advances in aerogel technology can yield innovative and integrated solutions for environmental and life sciences which in turn can help improve both the welfare of population and to move towards cleaner and smarter supply chain solutions.

Noble Metal Composite Porous Silk Fibroin Aerogel Fibers

Nobel metal composite aerogel fibers made from flexible and porous biopolymers offer a wide range of applications, such as in catalysis and sensing, by functionalizing the nanostructure. However, producing these composite aerogels in a defined shape is challenging for many protein-based biopolymers, especially ones that are not fibrous proteins. Here, we present the synthesis of silk fibroin composite aerogel fibers up to 2 cm in length and a diameter of ~300 μm decorated with noble metal nanoparticles. Lyophilized silk fibroin dissolved in hexafluoro-2-propanol (HFIP) was cast in silicon tubes and physically crosslinked with ethanol to produce porous silk gels. Composite silk aerogel fibers with noble metals were created by equilibrating the gels in noble metal salt solutions reduced with sodium borohydride, followed by supercritical drying. These porous aerogel fibers provide a platform for incorporating noble metals into silk fibroin materials, while also providing a new method to produce porous silk fibers. Noble metal silk aerogel fibers can be used for biological sensing and energy storage applications.

Salt-Mediated Au-Cu Nanofoam and Au-Cu-Pd Porous Macrobeam Synthesis

Multi-metallic and alloy nanomaterials enable a broad range of catalytic applications with high surface area and tuning reaction specificity through the variation of metal composition. The ability to synthesize these materials as three-dimensional nanostructures enables control of surface area, pore size and mass transfer properties, electronic conductivity, and ultimately device integration. Au-Cu nanomaterials offer tunable optical and catalytic properties at reduced material cost. The synthesis methods for Au-Cu nanostructures, especially three-dimensional materials, has been limited. Here, we present Au-Cu nanofoams and Au-Cu-Pd macrobeams synthesized from salt precursors. Salt precursors formed from the precipitation of square planar ions resulted in short- and long-range ordered crystals that, when reduced in solution, form nanofoams or macrobeams that can be dried or pressed into freestanding monoliths or films. Metal composition was determined with X-ray diffraction and energy dispersive X-ray spectroscopy. Nitrogen gas adsorption indicated an Au-Cu nanofoam specific surface area of 19.4 m²/g. Specific capacitance determined with electrochemical impedance spectroscopy was 46.0 F/g and 52.5 F/g for Au-Cu nanofoams and Au-Cu-Pd macrobeams, respectively. The use of salt precursors is envisioned as a synthesis route to numerous metal and multi-metallic nanostructures for catalytic, energy storage, and sensing applications.