One-Step CO₂Assisted Pyrolysis as an Efficient Route for Producing Highly Porous Biochar from Spent Coffee Grounds

Spent coffee grounds (SCG) are an abundant, carbon-rich residue suitable for converting into biochar through a thermochemical process. In this study, biochar was produced from SCG using a two-step pyrolysis-CO2 activation process and a one-step CO2 assisted pyrolysis method to compare their physicochemical and structural properties. Results showed that CO2 activation significantly increases the porosity and surface area, from 9.8 m²/g for non-activated biochar (BCK) to 550.6 m²/g for BCK-CO2 and 671.0 m²/g for SCG-CO2. FTIR and Boehm titration analyses confirmed a decrease in surface oxygenated groups after CO2 treatment, and SEM-EDX and XRD analyses indicated a structural reorganization. The one-step CO2 assisted pyrolysis produces biochar with a more uniform pore structure, a higher degree of carbonization, and better textural properties than the two-step method. Therefore, using CO2 directly during pyrolysis can be an efficient and sustainable method to obtain highly porous biochar from spent coffee grounds, reduce energy demands, and make valuable organic waste.