Top-Down Approach Making Anisotropic Cellulose Aerogels as Universal Substrates for Multifunctionalization

Highly porous, strong aerogels with anisotropicstructural properties are of great interest for multifunctionalmaterials for applications including insulators in buildings,filters for oil cleanup, electrical storage devices,etc. Contem-porary aerogels are mostly extracted from fossil resources andsynthesized from bottom-up techniques, often requiring addi-tional strategies to obtain high anisotropy. In this work, auniversal approach to prepare porous, strong, anisotropicaerogels is presented through exploiting the natural hierarchicaland anisotropic structure of wood. The preparation comprisesnanoscale removal of lignin, followed by dissolution−regener-ation of nanofibers, leading to enhanced cell wall porosity with nanofibrillated networks occupying the pore space in thecellular wood structure. The aerogels retain structural anisotropy of natural wood, exhibit specific surface areas up to 247 m2/g, and show high compression strength at 95% porosity. This is a record specific area value for wood aerogels/foams and evenhigher than most cellulose-based aerogels for its assigned strength. The aerogel can serve as a platform for multifunctionalcomposites including scaffolds for catalysis, gas separation, or liquid purification due to its porous matrix or as binder-freeelectrodes in electronics. To demonstrate the multifunctionality, the aerogels are successfully decorated with metalnanoparticles (Ag) and metal oxide nanoparticles (TiO2)byin situsynthesis, coated by the conductive polymer(PEDOT:PSS), and carbonized to yield conductive aerogels. This approach is found to be a universal way to prepare highlyporous anisotropic aerogels. QC 20200918