Visualization of the Formation and 3D Porous Structure of Ag Doped MnO₂ Aerogel Monoliths with High Photocatalytic Activity

Owing to their intriguing properties, aerogels with rich and hierarchical pore systems are best appreciated in catalysis, sensing, and separation technologies. Herein, a comprehensive study is presented for inorganic monolithic aerogel of Ag doped MnO₂ (Ag-MnO₂), synthesized solely out of nanowires of diameter ∼10 nm. We demonstrated a 3D image of the full bulk structure of the aerogel using X-ray computed tomography (μCT), providing a concise and statistical description of its porous structure for the first time. Interestingly, a flow-through supermacroporous system was observed as a result of freeze-drying. Owing to the rich pore system, the Ag-MnO₂ aerogel monolith exhibited photocatalytic degradation of organic water pollutants, which was superior in performance as compared to that of the MnO₂ powder and compressed Ag-MnO₂ pellet. A detailed study of photocatalytic mechanism was also carried out, indicating that Ag can simultaneously modulate the physical and chemical properties of MnO₂. This work highlights the significance of porous system in monolith catalysts, and provides insight into design and prepare metal oxide aerogels for environmental and energy applications.