Fixed-bed N-doped modified biochar for CO₂ capture integrated with a purging bubble absorber for CO₂ quantification

Carbon dioxide (CO2) is the primary greenhouse gas driving climate change and global warming, with atmospheric concentrations exceeding 400 ppm and continuously rising. Natural photosynthesis processes are insufficient to offset the high CO2 production rates, and chemical absorption methods, such as using amines, are costly and environmentally detrimental. Biochar, a product of organic waste pyrolysis, is characterized by strong adsorption power, porosity, high stability, and a richness in functional groups, making it a promising material for gas capture. Previous research demonstrated that metal-modified (MnO2) and alkaline (KOH) biochar effectively reduce CO2 emissions from oil palm plantation soils. This study aims to develop new materials for direct air CO2 capture using two types of metal-modified biochar as precursors. N-doped modified biochar was prepared by mixing the modified biochar with concentrated HNO3 in a 1:10 solid-to-nitric acid ratio, stirring for one hour, followed by centrifugation at 7000 rpm to separate solids. The solids were then washed with acid and deionized water. The CO2 capture performance of N-doped modified biochar was tested using a fixed-bed absorption column containing 3 grams of the material, fed with CO2 at a flow rate of 2.5 L/min. Unabsorbed CO2 was directed into a NaOH absorber purging bubble column. The effectiveness of the absorption column and CO2 concentration in the NaOH solution, determined by acid-base titration, were analyzed. In addition, the characterization of biochar, modified biochar, and N-doped modified biochar was performed. This study contributes to the development of sustainable materials for mitigating atmospheric CO2 levels.