Carbon dioxide capture using various metal oxyhydroxide-biochar composites

Innovative and cost-effective methods are needed to capture and store CO2 to reduce anthropogenic impact on global warming. This work produced and characterized aluminum hydroxide, magnesium hydroxide, and iron oxide-biochar composites, and evaluated their ability to capture CO2 at room temperature and atmospheric pressure. Biomass feedstocks were treated with metal ions of a variety of concentrations, and were then pyrolyzed at 600 °C. Characterization experiments showed that the process not only turned the biomass into biochar, but also converted the metal ions into metal oxyhydroxide nanoparticles onto the carbon surfaces with the biochar matrix. As a result, the composites, particularly the ones with optimal metal to biomass ratios, had higher CO2 capture capacity than the unmodified biochar. All the composites had relatively large surface area and captured CO2 mainly through physical adsorption. Although Fe2O3-biochar composites had the highest surface area, the AlOOH-biochar composite showed the largest sorption. Thus, both the characteristics of the metal oxyhydroxides and the surface area contributed to the CO2 capture capacity. The maximum adsorption capacity (71 mg g−1 at 25 °C) by AlOOH-biochar is comparable to commercial adsorbents. The samples had between 90% and 99% desorption at 120 °C, so they required low cost regeneration. All these results suggested that biochar-based composites could be a high efficiency and cost-effective adsorbent for CO2 capture.