Insights into the adsorptive application of solvent assisted hydrothermal carbonization products

Solvent-assisted hydrothermal carbonization or solvothermal carbonization (STC) is a process involving the conversion of biomass into carbonaceous materials (solvochar) with the presence of a solvent. Unlike traditional hydrothermal carbonization STC operates at lower temperatures and uses solvents rather than water. The types of solvents that are commonly reported in literature are organic and inorganic solvents, ionic liquids, and deep eutectic solvents. Solvochar has shown high effectiveness in adsorbing pollutants in both liquid phases (e.g., dyes, organic compounds, and heavy metals) and gaseous phases (e.g., CO₂). Adsorption studies suggest monolayer adsorption in most cases, based on the Langmuir isotherm, while kinetic studies highlight chemisorption via pseudo-second-order models. For gaseous applications, solvochar can be thermally regenerated, while liquid-phase applications require chemical eluents. These properties enable solvochar to be reused for multiple cycles, where solvochar could be regenerated for approximately 5 cycles using chemical eluents in liquid phase and 10 cycles thermally in gas-phase applications. Future studies should work towards developing continuous scaled-up processes, the use of real wastewater, as well as techno-economic analysis to ensure the cost effectiveness and applicability of solvochar on a commercial scale. • SA-HTC improves hydrochar adsorption via enhanced surface chemistry and porosity. • DES emerge as promising green solvents for functional solvochar production. • Solvochars show strong performance in liquid and gas phase (CO 2 ) pollutant removal. • Solvochar is regenerated thermally for gas, and chemically for liquid applications. • Pollutant adsorption on solvochar follows the Langmuir isotherm and PSO kinetics.