Investigation and Characterization of the Optical, Thermal, and Adsorption Properties of Carbon Aerogels for CO2 Capture Applications

Abstract

Climate change driven by rising atmospheric CO₂ concentrations has intensified the need for efficient, regenerable solid sorbents. Carbon aerogels are promising candidates due to their ultra-high porosity, low density, and tunable structure, yet their coupled optical, photothermal, and CO₂ adsorption behaviour as monolithic sorbents remains insufficiently characterized. This thesis investigates a disc-shaped carbon aerogel for CO₂ capture under flue-gas-like conditions to clarify how its radiative and thermal properties govern adsorption performance and photothermal regeneration.

The aerogel was characterized using UV–Vis–NIR and FTIR spectroscopy to measure reflectance, transmittance, and absorptance across the solar and thermal-infrared ranges. Mid-wave infrared thermography under a xenon arc lamp (1 Sun irradiance) quantified transient heating and cooling. Dynamic breakthrough experiments with a 11% CO₂ / 89% N₂ mixture at 25 °C, followed by photothermal desorption at 110 °C, were performed to determine CO₂ capacity and regeneration performance.

Optical measurements showed negligible transmittance and low reflectance from the ultraviolet through the mid-infrared, corresponding to broadband absorptance generally above 0.9 and high effective emissivity in the thermal-imaging band. Under 1 Sun illumination, the surface temperature rose from ~28 °C to ~64 °C within 1–2 min and cooled rapidly back toward ambient once the light source was removed, indicating efficient radiative heating and low thermal mass. Breakthrough measurements yielded a net CO₂ adsorption capacity of 1.88 mmol g⁻¹ and a photothermal desorption capacity of 1.14 mmol g⁻¹, with good reproducibility but partial hysteresis between adsorption and desorption.

Overall, the results demonstrate that carbon aerogels can combine meaningful CO₂ uptake with favourable photothermal characteristics, making them strong candidates for radiatively driven temperature-swing adsorption processes. The work provides a quantitative baseline for future material design, further characterization, and reactor-level optimisation of carbon-aerogel-based CO₂ capture systems