Sustainable CO ₂ Capture Using Porous CuBDC Monoliths via Pickering Foam Templating Reinforced with Bacterial Cellulose

Metal-organic frameworks (MOFs) offer high porosity and tunable chemistry, while practical applications are often hindered by their poor processability, low packing density, and inadequate mechanical stability when used in powder form. Shaping MOFs into monoliths could dramatically solve these limitations. However, traditional methods such as sol-gel synthesis, freeze-drying, casting, or templating often involve multiple steps or organic solvents, leading to structural collapse and loss of intrinsic porosity. To overcome the aforementioned challenges, herein we report a green, one-step strategy for fabricating hierarchically porous MOF monoliths via Pickering foam templating. By using hexanoic acid (HA) to in situ modulate the surface of CuO nanoparticles (NPs), ultrastable aqueous foams could be directly prepared while subsequently serving as templates for in situ MOF conversion and growth at the air-water interface. In this work, two typical MOF monoliths based on CuBDC and HKUST-1 were synthesized by this method without the use of surfactants, polymers, or harmful solvents. Besides, backbone materials, such as bacterial cellulose (BC), could subsequently be introduced as a reinforcing scaffold to improve mechanical integrity. Structural analyses revealed that the resulting CuBDC monoliths exhibited well-defined hollow spherical shells templated from the foam bubbles, and the incorporation of BC significantly enhanced compressive strength while preserving hierarchical porosity, although the excessive BC slightly caused pore collapse and surface area reduction. The monoliths showed great potential for CO₂ adsorption achieving the highest uptake of 2.42 × 10^-1 mmol g^-1 at 298 K. This study presents the first demonstration of using Pickering wet foam as a direct template for MOF monoliths, offering a sustainable and tunable approach for scalable fabrication of porous materials suitable for gas storage, separation, and adsorption applications.