Hierarchically Porous δ-MnO ₂ Aerogels for Selective Ammonia Capture in Humid Livestock Environments

Ammonia (NH3) emissions from livestock facilities represent a major source of indoor air pollution, especially under humid conditions where traditional adsorbents such as activated carbon and zeolites suffer significant performance degradation. This study reports the scalable synthesis and systematic evaluation of four MnO2-based nanomaterials, including monolayer nanosheets, ultrathin nanosheets, monolithic colloids, and aerogels, all tailored for NH3 capture in climate-relevant livestock environments. Among them, MnO2 aerogels (MA), fabricated via ice-templating and freeze-drying, exhibited superior removal efficiencies of 94.3% and 93.6% for NH3 released from pig and chicken manure, respectively, under standard conditions, and up to 98.7% under optimized low-temperature, high-humidity settings (10 °C, 75% relative humidity, 0.3 g dosage). This performance is associated with an open, sheet-assembled 3D network that enables rapid diffusion and humidity-assisted NH3 capture under climate-relevant indoor conditions. The final outlet NH3 concentrations were reduced to below 0.05 mg m–3, outperforming many advanced sorbents such as MOFs and COFs, particularly under humid conditions. Unlike these humidity-sensitive sorbents, MA combines low-cost fabrication and environmental compatibility with a physisorption mechanism conducive to low-temperature thermal regeneration, providing a strong basis for protocol development. These findings highlight MnO2 aerogels as practical, sustainable adsorbents for mitigation NH3 pollution in livestock buildings and other agricultural indoor settings. This work supports the development of climate-adaptive indoor air purification strategies aligned with sustainable agriculture and indoor environmental health under climate change.