Cellulosic aerogels show great promise for diverse applications. However, their widespread adoption is hindered by energy-intensive processing and limited mechanical properties. This work presents a green and efficient approach for strong cellulosic aerogel synthesis through cell wall nano-reconstruction using one-step NaOH (10 wt%) treatment of wood at ambient temperature. The obtained cellulosic aerogel (wood aerogel) showed partially preserved hierarchical structure and nanofibril networks filled lumen, leading to a combination of high specific surface area (202 m2 g-1) and a high yield strength (4.3 MPa). The generation of mesoporosity and the building of nanofibril networks were studied in detail. NaOH provided cell wall swelling and partial extraction of deacetylated xylan, generating nanoporosity in the cell wall. The extracted xylan then aggregated and rearranged into nanofibril networks occupying the lumen. The technology developed for wood aerogel synthesis and the understanding of wood aerogel formation pave the way for green cell wall nanoengineering towards advanced materials design.

Hierarchical porous materials yield versatile functionalities by combining pores across multiple length scales, whereas their controlled bottom-up synthesis remains a challenge. This thesis presents a biomimetic strategy to fabricate hierarchical porous metal and mineral composites by utilizing and exploring the naturally developed hierarchical structure of wood. Direct use of wood as template is also environmentally and economically friendly due to its renewable source, low cost, and scalable processability. 

A sequential methodology was developed, beginning with cell wall engineering to overcome the limited accessibility and mass diffusion of bulk wood. This was first achieved by programmed removal of cell wall components. Reassembly of intrinsic biopolymers into lumina fibril networks was then investigated to create wood aerogels with high specific surface area. The engineered wood scaffolds were subsequently functionalized via metallization or mineralization. Electroless Cu plating produced compressible, electrically conductive templates, while MTMS condensation imparted hydrophobicity. ZnCl2 was also explored to simultaneously fabricate wood aerogels and precipitate ZnO in situ. The resulting composites combined the structural advantages of engineered wood scaffold (large surface area, aligned channels, mechanical robustness) with the functionality of guest materials. This synergy enables applications in pressure sensors, thermal insulation in energy-efficient buildings, and photocatalytic dye degradation. This work established a versatile and sustainable platform for transforming renewable resources into high-performance functional composites. 

Hierarkiska porösa material erbjuder mångsidiga funktionaliteter genom att kombinera porer över flera längdskalor, men deras kontrollerad bottent-uppsyntes är en stor utmaning. Denna avhandling presenterar en biomimetisk strategi för att framställa hierarkiska porösa mineraler och metaller genom att utnyttja trädets naturligta hierarkiska struktur. Direkt användning av trä som mall är dessutom miljövänlig och ekonomiskt fördelaktigt på grund av dess förnybara ursprung, låga kostnad och skalbara processbarhet.

En sekventiell metodik utvecklades, som började med att öka cellväggens begränsade tillgänglighet och massdiffusion i massivt trä. Detta uppnåddes först genom programmerad borttagning av cellväggskomponenter. Därefter undersöktes om-montering av biopolymererna till ett fibrilnätverk i lumen för att skapa träaerogeler med hög specifik ytarea. De konstruerade trästommen funktionaliserades därefter via metallisering eller mineralisering. Elektrolös kopparplätering gav komprimerbara, elektriskt ledande templat, medan MTMS-kondensation gav hydrofobicitet. ZnCl2 undersöktes också för att samtidigt framställa träaerogeler och utfälla ZnO in situ. De resulterande kompositer kombinerade de strukturella fördelarna med den konstruerade trästommen (stor ytarea, ordnade kanaler, mekanisk robusthet) med gästmaterialens funktionalitet. Denna synergieffekt möjliggör tillämpningar inom trycksensorer, termisk isolering i energieffektiva byggnader samt fotokatalytisk nedbrytning av färgämnen. Detta arbete etablerade en mångsidig och hållbar plattform för att omvandla förnybara resurser till högpresterande funktionella kompositer. 

Metallic wood combines the unique structural benefits of wood and the properties of metals and is thus promising for applications ranging from heat transfer to electromagnetic shielding to energy conversion. However, achieving metallic wood with full use of wood structural benefits such as anisotropy and multiscale porosity is challenging. A key reason is the limited mass transfer in bulk wood where fibers have closed ends. In this work, programmed removal of cell-wall components (delignification and hemicellulose extraction) was introduced to improve the accessibility of cell walls and mass diffusion in wood. Subsequent low-temperature electroless Cu plating resulted in a uniform continuous Cu coating on the cell wall, and, furthermore, Cu nanoparticles (NPs) insertion into the wood cell wall. A novel Cu NPs-embedded multilayered cell-wall structure was created. The unique structure benefits compressible metal-composite foam, appealing for stress sensors, where the multilayered cell wall contributes to the compressibility and stability. The technology developed for wood metallization here could be transferred to other functionalizations aimed at reaching fine structure in bulk wood.

ZnO is a versatile material for optoelectronics and catalysis, whose efficacy can be enhanced by a porous and self-standing matrix that ensures high accessibility. Combining ZnO with sustainable cellulose aerogels creates a promising composite that synergizes the high specific surface area (SSA) of aerogel scaffold with the multi-functional properties of ZnO. This work presents a topdown strategy for fabricating hierarchical ZnO-wood aerogel (WA) nanocomposites directly from native wood through a one-pot reaction enabled by the dual-role chemistry of ZnCl2. The process leverages a concentrated ZnCl2 solution, which simultaneously acts as an agent to reassemble intrinsic biopolymers of wood into an anisotropic, porous aerogel and as a precursor for the in-situ precipitation of ZnO. The resulting composite integrates flower-like ZnO particles within the porous cellulose matrix, inheriting the photocatalytic properties of ZnO and high SSA of the cellulosic scaffold. The ZnO-WA nanocomposite demonstrates great promise for applications such as photocatalytic dye degradation, effectively bridging the advantageous properties of its components into a sustainable and high-performance material. 

Energy-efficient buildings demand high-performance insulation materials. Wood aerogels, with their intrinsic low thermal conductivity, high porosity, and good mechanical strength, offer exceptional potential as sustainable thermal insulators. However, their moisture sensitivity restricts the practical applications. To address this, we developed a silsesquioxane-functionalized wood aerogel composite through cold alkali treatment followed by methyltrimethoxysilane (MTMS) condensation, resulting in a hierarchical mesoporous wood structure with silsesquioxane particles integrated into cell walls and lumina fibril networks. This functionalization simultaneously achieves high specific surface area (261 m2/g), robust mechanical strength (compression yield strength > 4 MPa), and superhydrophobicity (surface contact angle > 170°, interior ~156°). The composite exhibits reduced moisture uptake and great thermal insulation. These attributes make functional wood aerogel a promising solution for nearly zero-energy buildings (NZEBs), where energy performance is paramount.