Versatile Assembly of Metal–Phenolic Network Foams Enabled by Tannin–Cellulose Nanofibers

Abstract

ranging from filaments [2] and films [3] to porous aerogels and foams. [4,5] Among the latter, cellulosic foams represent green options with potential for nontoxic thermal insulation, [6] catalytic environmental remediation, [7,8] and lightweight materials, [5] among others. Although cellulose provides robust porous scaffolds, its intrinsic chemical inertness restricts applications unless it is modified with entities holding specific functionalities (e.g., magnetism, conductivity). On that note, CNFs have been chemically modified, [9,10] composited with polymers [11,12] or nanomaterials, [6] used as a template for the growth of functional nanoparticles, [13] and more recently coassembled with metal-organic frameworks (MOFs). [14] Such efforts have enhanced their processing and uses; [1] however, most of the classical challenges related to generic nanohybridization also apply to cellulosic materials, a subject that remains poorly developed in the case of CNF. In cellulose constructs, cellulose-cellulose interactions are superior to other noncovalent interactions. Therefore, modifying cellulose or adding a secondary phase typically reduces the structural cohesion. Furthermore, incorporating a functionality within a nanocellulose network often leads to uneven distribution, aggregation, and phase separation. Meanwhile, Metal-phenolic network (MPN) foams are prepared using colloidal suspensions of tannin-containing cellulose nanofibers (CNFs) that are ice-templated and thawed in ethanolic media in the presence of metal nitrates. The MPN facilitates the formation of solid foams by air drying, given the strength and self-supporting nature of the obtained tannin-cellulose nanohybrid structures. The porous characteristics and (dry and wet) compression strength of the foams are rationalized by the development of secondary, cohesive metalphenolic layers combined with a hydrogen bonding network involving the CNF. The shrinkage of the MPN foams is as low as 6% for samples prepared with 2.5-10% tannic acid (or condensed tannin at 2.5%) with respect to CNF content. The strength of the MPN foams reaches a maximum at 10% tannic acid (using Fe (III) ions), equivalent to a compressive strength 70% higher than that produced with tannin-free CNF foams. Overall, a straightforward framework is introduced to synthesize MPN foams whose physical and mechanical properties are tailored by the presence of tannins as well as the metal ion species that enable the metal-phenolic networking. Depending on the metal ion, the foams are amenable to modification according to the desired application.

Bark extractives as sources of carbon-efficient functional precursors and materials

“…[75][76][77][78][79][80] Dynamic covalent bonds (e.g., imines and boron-diols) can also be introduced to impart stimulation with small organic molecules, typically within the case of boronate-catechol interactions. [81][82][83] Materials such as foams at the macroscopic level can be achieved by the modification of cellulose fibers with metalphenolic networks. The physical and mechanical properties are governed by the composition, content, and types of polyphenols.…”

Desirable Strong and Tough Adhesive Inspired by Dragonfly Wings and Plant Cell Walls

“…Tannic acid (TA), a polyphenol generated from plants, is being studied extensively in the modification and enhancement of various materials due to its low cost, excellent interface binding, multifunctional chemical activity, and antimicrobial properties. 38,39 Rich opportunities for interfacial engineering arise from the abundant catechol/ pyrogallol groups in TA that can interact with different substrates via π−π interactions, hydrogen bonds, electrostatic forces, Schiff base/Michael addition reactions, and coordination chemistry. Notably, bulk MoS 2 can be exfoliated into superior 2D MoS 2 @TA nanosheets by the hydrophobic interaction of the hydrophobic aromatic structure of TA with MoS 2 and the concurrent breaking of weak van der Waals contacts between neighboring MoS 2 by sonication.…”

“…Molybdenum disulfide (MoS 2 ) nanosheets and other two-dimensional (2D) transition metal thionides (TMDs) have generated wide interest in the field of multifunctional nanocomposites with excellent mechanical, flame retardant, antimicrobial, and optical properties. − MoS 2 is widely found in pyromolybdenum ores, containing abundant reserves and being much more economical than graphene, black phosphorus, and MXene, being an attractive material for the application as a functional adhesive or coating material. , However, unmodified MoS 2 nanosheets are not rich in reactive groups, rendering their interfacial interactions with other substrates ineffective. Tannic acid (TA), a polyphenol generated from plants, is being studied extensively in the modification and enhancement of various materials due to its low cost, excellent interface binding, multifunctional chemical activity, and antimicrobial properties. , Rich opportunities for interfacial engineering arise from the abundant catechol/pyrogallol groups in TA that can interact with different substrates via π–π interactions, hydrogen bonds, electrostatic forces, Schiff base/Michael addition reactions, and coordination chemistry. Notably, bulk MoS 2 can be exfoliated into superior 2D MoS 2 @TA nanosheets by the hydrophobic interaction of the hydrophobic aromatic structure of TA with MoS 2 and the concurrent breaking of weak van der Waals contacts between neighboring MoS 2 by sonication. , Unlike organic solvent exfoliation, this is an efficient and green method to achieve surface modification of MoS 2 @TA nanosheets during exfoliation.…”

Nanoengineering of Vaccine Nanoparticles via Templating of Metal–Organic Frameworks for Tumor Immunotherapy

“…Polyphenols make up a category of compounds ubiquitous in the plant kingdom. Since phenolic compounds have the properties of metal chelation, pH-responsiveness, and universal adhesion, they have been widely used as building blocks to assemble functional materials through the formation of metal coordination, π–π interactions and self-polymerization. − The resulting polyphenol-based materials including coatings, capsules, nanoparticles, and hydrogels have shown potential applications in catalysis, sensing, intracellular protein, and drug delivery. − Recently, template-assisted assembly strategies have been widely used for nanoparticle fabrication . Nanoparticles obtained via template-assisted methods offer selective and uniform geometry, shape, and size. − Templates could be divided into hard (silica, metal–organic frameworks (MOFs), etc.)…”