B. Zhao: Superstructured wood-based carbon materials for broadband light absorption and CO2 capture

Content of the thesis: 

Light is an abundant resource; however, stray light can significantly impact the performance and

longevity of optical systems. Adverse effects such as reduced image contrast and signal degradation

highlight the need for advanced solutions to effectively mitigate these challenges. Superblack

materials, with near-zero light reflectance, are in high demand to enhance several light-based

technologies. In this study, we developed wood-based spectral shielding materials with exceptionally

low reflectance across the UV-VIS-NIR (250–2500 nm) and MIR (2.5–15 μm) ranges. Using a

straightforward top-down approach, we produced robust superblack materials by removing lignin

from wood and carbonizing the delignified wood at 1500 °C. This process induced shrinkage

stresses in subwavelength severed wood cells, forming vertically aligned carbon microfiber arrays

(~100 μm thick) with light reflectance as low as 0.36 %.

We further synthesized multiscale carbon supraparticles (SPs) through a soft-templating process

involving lignin nano- and microspheres bound with cellulose nanofibrils (CNFs). Following oxidative

thermostabilization, these lignin SPs exhibited high mechanical strength due to their interconnected

nanoscale networks. In further work, by inserting lignin particles (LPs) into delignified wood and

carbonizing the structure, we created a carbonized reconstituted wood (cRW) system with enhanced

dimensional fidelity and finely tuned light-absorbing fibrillar microstructures. They resulted in

broadband light traps that achieved superabsorbance, exceeding 99.8% across a wide range of

wavelengths, from infrared to ultraviolet.

Tiled cRW structures, optically welded for customizable size and shape, demonstrated superior laser

beam reflectivity compared to commercial light stoppers, eliminating thermal ghost reflections. This

makes them promising candidates as reference infrared radiators for thermal imaging device

calibration. Beyond optical applications, the carbon SPs also offer hierarchical adsorption sites,

achieving a CO₂ adsorption capacity of 77 mg CO2·g-1. This innovation in the area of carbon capture

was shown to solve the diffusion and kinetic limitations of conventional nanoparticle-based systems.

Overall, this thesis summarizes wood-derived solutions that go from multispectral shielding to

carbon capture technologies.

Opponent: Prof. Sunkyu Park, North Carolina State University, United States

Supervisor: Prof. Orlando Rojas, Aalto University School of Chemical Engineering

Link to electronic thesis: LINK

Link to the remote defense: LINK