Carbon Capture in Zeolite-Modified Hydrochar Composite: Effect of Zeolite Socony Mobil-5 Loading during Hydrothermal Carbonization

The development of efficient and sustainable materials for carbon dioxide (CO 2 ) sequestration is critical for addressing global climate change. This study investigates the potential of zeolite-modified hydrochar composites (HZCs) as effective adsorbents for enhanced CO 2 capture. The research systematically explores the hydrothermal carbonization (HTC) of loblolly pine at temperatures ranging from 200 to 260 °C, incorporating 0–10 wt % zeolite ZSM-5. The resulting hydrochars were further activated using KOH (2:1 %w/w) at 800 °C for 2 h to produce HZCs. Characterization of the HZCs revealed significant physical, chemical, and morphological alterations introduced by zeolite incorporation during HTC. Zeolite catalyzed the carbonization process, resulting in HZCs with enhanced thermal stability, higher surface area, increased microporosity, and improved surface functionalities. Notably, 5% zeolite composite showed doubled CO 2 uptake (12.20–13.24 mmol/g at 4 bar) compared to the control samples. The maximum CO 2 uptake of 13.24 mmol/g was attributed to the surface area (646.27 m 2 /g) and higher micropore volume (0.412 cm 3 /g) of the composite. In contrast, 10% zeolite composites had lower uptake (5.83–9.93 mmol/g) due to pore collapse and reduced surface area caused by excessive zeolite loading during HTC. Adsorption isotherm analysis confirmed the Freundlich model as the best fit, indicating multilayer adsorption on heterogeneous surfaces. These findings emphasize the importance of small micropores, enhanced surface area, and zeolite incorporation in the CO 2 capture performance. Furthermore, these results highlight the potential of HZCs prepared under controlled operating conditions for their application in industrial CO 2 capture and climate change mitigation.