Optimizing CO₂ capture: Effects of chemical functionalization on woodchip biochar adsorption performance

As atmospheric CO₂ concentrations rise, primarily due to fossil fuel combustion and deforestation, the urgent need for effective carbon capture solutions becomes increasingly critical to mitigate global warming. This study investigates the enhancement of CO₂ adsorption in woodchip biochar (WBC) through targeted chemical functionalization with potassium hydroxide (KOH), sodium hydroxide (NaOH), and ferrous sulfate (FeSO₄). Using Central Composite Design (CCD) and Response Surface Methodology (RSM), it is systematically possible to identify optimal functionalization conditions to maximize the biochar's adsorption efficiency. The KOH-treated biochar exhibited the highest adsorption capacity (Qmax of 9.89 mmol/g), substantially improving over untreated biochar (Qmax of 4.54 mmol/g). Adsorption analysis through Langmuir and Freundlich isotherm models highlighted a strong alignment with the Langmuir model, suggesting a predominantly monolayer adsorption surface. Additionally, kinetic studies using pseudo-first-order (PFO) and pseudo-second-order (PSO) models indicated a favourable chemisorption process, with the PSO model showing a superior fit. These results demonstrate the potential of chemically functionalized biochar, especially when treated with KOH, as a viable material for CO₂ capture, presenting an environmentally sustainable pathway for addressing the pressing issue of atmospheric CO₂. Utilizing biochar derived from organic waste also promotes waste valorisation and supports a circular economy. Optimised biochar could mitigate CO₂ emissions, potentially serving as a complementary solution in climate change mitigation strategies, especially in scenarios where biochar can be deployed at scale in industrial or agricultural settings.