Public defence in Bioproduct technology, MSc Bin Zhao

Title of the thesis: Superstructured wood-based carbon materials for broadband light absorption and CO₂ capture

Thesis defender: Bin Zhao
Opponent: Prof. Sunkyu Park, NC State University, United States
Custos: Prof. Orlando Rojas, Aalto University School of Chemical Engineering

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 wood-based superblack materials by carbonizing the delignified wood at 1500 °C. This process induced the formation of 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, which exhibited high mechanical strength. In further work, 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. 

Wood-based superblack materials and broadband blackbody 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 high CO₂ adsorption capacity. This innovation in carbon capture was shown to solve the limitations of conventional nanoparticle-based systems. Overall, this thesis summarizes wood-derived solutions that go from multispectral shielding to carbon capture technologies.

Keywords: wood, delignification, lignin particles, supraparticles, carbonization, superblack, light reflectance, CO₂ capture

Thesis available for public display 10 days prior to the defence at Aaltodoc. 

Contact information: 
bin.2.zhao@aalto.fi
linkedin.com/in/bin-zhao-ba1301161
Tel: +358505012835