A comprehensive study by Selma Kuloglija, Ilias-Maximilian Kropik, and their team, published in Separation and Purification Technology, thoroughly assessed the use of KOH-activated biochars derived from pine and birch wood for capturing atmospheric carbon dioxide (CO₂​). This research responds to the critical global need for effective, economical, and locally sourced sorbents to combat human-induced climate change. The team systematically investigated how different processing temperatures influence the structure and performance of the final activated carbon.

The researchers used pine (Pinus sylvestris) and birch (Betula pendula) biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More, carbonizing them at temperatures of 600°C, 700°C, or 800°C, followed by chemical treatment with KOH using a 3:1 impregnation ratio. Detailed characterization revealed that higher carbonization temperatures favored the development of primarily microporous frameworks. These frameworks possessed high specific surface areas, with pine-derived activated carbon reaching a maximum of 1416 m2/g at 800°C, and birch-derived material achieving 1398 m²/g at the same temperature. Both values substantially surpassed the commercial activated carbon reference (1023 m²/g). The physical development of the carbon structure due to KOH activation is critical, as it creates the ultra-micropores that CO_2​ molecules require for effective capture.

This superior structure led to excellent CO₂​ capture performance. Measured at 1 bar and 30°C, the equilibrium CO_2​  adsorption isotherms showed maximum capacities of ∼3.50 mmol/g for the pine biochar and ∼3.10 mmol/g for the birch biochar, both carbonized at 800∘C. In comparison, the commercial activated carbon showed a significantly lower capacity of ∼1.52 mmol/g under the same conditions. This highlights the value of KOH activation and high-temperature treatment for producing high-performance CO_2​  adsorbents. The adsorption data fit well to the Langmuir model (R2≥0.999), indicating monolayer adsorption and a high affinity of the activated biochar surface for CO_2​ ​.

Beyond capacity, the study evaluated the kinetics of the adsorption process, which dictates how fast the material can work in a practical setting. Time-resolved uptake experiments demonstrated that CO₂​ adsorption is rapid, with over 90% of the equilibrium capacity achieved within five minutes. The characteristic half-times, which measure the speed, decreased from approximately 1.5 min for materials carbonized at 600°C to less than 0.8 min for those treated at 800°C. The adsorption kinetics conformed to a pseudo-first-order model, corresponding with a surface-controlled physisorption mechanism. Further analysis, supported by the Weber-Morris model, confirmed that adsorption is governed by an initial rapid surface adsorption phase followed by a slower intraparticle diffusion phase.

The study also addressed the practical stability and reusability of the materials. Cyclic adsorption-desorption tests showed no measurable decline in adsorption capacity over up to ten consecutive cycles, confirming the stable performance and reusability of the biochars under repeated operation. Isosteric heats of adsorption (16−29 kJ mol−1) confirmed that the binding of CO_2​ is physical and exothermic. This exothermic nature means that adsorption capacity decreases with increasing temperature, dropping from 3.54 mmol/g at 30°C to 1.60 mmol/g at 75°C for the pine biochar.

In summary, activating pine and birch biochar at elevated temperatures via KOH creates affordable, high-surface-area adsorbents that can rapidly and efficiently capture CO₂​. The superior performance over commercial activated carbon highlights the potential of these forestry residues as sustainable, effective options for carbon sequestration technologies. While the study used pure CO_2​/He, future research must validate the materials using mixed gases, such as those found in industrial flue gas, to confirm CO₂​/N_2​ selectivity and resilience to impurities like water and SO₂​.

Source: Kuloglija, S., Kropik, I. M., El Gohary Ahmed, A., Kalman, V., Windbacher, A., Jordan, C., Konior, A., Abbaspour, N., Steinacher, N., Winter, F., Tomasetig, D., Lamprinidou, E., & Harasek, M. (2026). Isotherms and kinetics of CO2​ adsorption on biochar-based activated carbon for sustainable climate solutions. Separation and Purification Technology, 382, 136079.