Brewing up solutions: developing high-performance adsorbents from spent coffee grounds for carbon capture

Reducing the cost of post-combustion carbon capture is essential for advancing carbon capture and storage (CCS) technologies. In this study, we tackle this challenge by transforming spent coffee grounds, a widely available waste material, into low-cost, robust, regenerable adsorbents designed for CO2 capture. We employed four distinct activation methods—chemical (potassium hydroxide (KOH) and potassium oxalate (KOx)), physical (CO2), and biological (through fungal activation)—to optimise the biochars' surface area, microporosity, and nitrogen functionality, which are critical for effective CO2 adsorption. Using a systematic design of experiments approach, we varied pyrolysis conditions and activation methods to identify the most promising candidates. The CO2-activated biochar emerged as the most effective under real-world conditions, offering a balance of appreciable surface area, nitrogen functionalisation, and rapid adsorption kinetics, despite its slightly lower surface area and microporosity compared to chemically activated samples. Chemically activated samples demonstrated superior performance at higher CO2 partial pressures due to their higher surface areas. Although the novel biological activation approach showed only modest improvements in terms of surface area, it serves as a proof of concept for using green, biological methods to extract additional value from feedstocks prior to charring, offering a more sustainable alternative to traditional techniques. This study lays the groundwork in optimising biochars from spent coffee grounds for scalable carbon capture applications. Our findings underscore the importance of methodical optimisation in developing adsorbents that are not only effective but also environmentally sustainable, paving the way for integrating circular economy principles into CCS technologies.