Hierarchical porous alumina ceramics as multi-functional support with excellent performance

Abstract

Hierarchical porous nanostructure alumina ceramics (HP-Al2O3) were prepared through a novel approach involving polymer-assisted freeze-drying and subsequent calcination. The resulting material exhibits interconnected micro-meso-macro pores, distinguishing it from traditional Al2O3 nanoparticles (Al2O3-Nps) prepared without freeze-drying. By manipulating freeze-drying precursors and calcination temperatures, we tailor the morphology and structure of HP-Al2O3. Notably, the HP-Al2O3 demonstrates a remarkable 5.3-fold increase in adsorption efficiency for Congo red compared to Al2O3-Nps, attributed to its significantly larger specific surface area. The HP-Al2O3 is a versatile platform for building multi-functional composites, proved by immobilizing silver nanoparticles (AgNps) and graphitized carbonitride (g-C3N4) through chemical reduction and gas-solid reaction methods, respectively. When employed for the reduction of 4-nitrophenol and the degradation of Rhodamine B, Ag/HP-Al2O3 and g-C3N4/HP-Al2O3 display approximately 2.5 and 2.4 times higher reaction rate constants compared to Ag/Al2O3-Nps and g-C3N4/Al2O3-Nps. This enhanced catalytic performance is attributed to several key factors: the 3D porous framework of the HP-Al2O3 facilitates efficient catalyst immobilization, the microporous and mesoporous nature increases the active site and specific surface area, and the hierarchical porous structure enhances mass diffusion and light capture. Moreover, the self-supporting nature of the HP-Al2O3 simplifies separation and recovery from reaction solutions. With the integration of its hierarchical porous structure and commendable recovery properties, HP-Al2O3 emerges as a promising candidate for various functional applications, particularly in catalysis.