Tailored boron phosphate monolithic foam with multimodal hierarchically porous structure and its applications

The synthesis of multimodal hierarchically porous materials is of great challenge by facile approach. Herein, we assemble BPO₄ hollow spheres into macroscopic foam materials with multimodal hierarchically porous structure by combining down-to-up process and Ostwald ripening effect. Tailored monolithic B₂O₃@BPO₄ foams were obtained from a sticky hydrogel precursor by a one-step annealing process. The foam has the self-supporting frame of BPO₄ hollow spheres with covering B₂O₃ nanowires and shows excellent permeability and relatively high surface area due to hierarchical structure. The formation mechanism of monolithic B₂O₃@BPO₄ foams mainly undergoes inflation, particle aggregation, and Ostwald ripening process. Monolithic foams exhibit superior catalytic activity in oxidation dehydrogenation of alkanes due to the sufficient exposure of active sites over the special frame structure. Furthermore, various monolithic functionalized BPO₄ foam composites can be easily synthesized and exhibit superior performance in different applications including the oxidation of carbon monoxide, and the self-driven removal of organic pollutants. More interestingly, we also found the sticky hydrogel precursor possesses good heat shielding effect. This work provides a new insight for constructing multimodal hierarchically porous materials with the remaining superior property of nanoscale to cope with various challenges.