Sustainable silylated bacterial cellulose/MgAl-LDH composite aerogel integrating radiative cooling and thermal insulation for building energy saving

Passive daytime radiative cooling provides a promising zero-energy solution to reduce energy consumption and carbon emissions in building cooling. While cellulose-based radiative coolers have gained research focus, their efficiency remains constrained by inadequate spectral properties and parasitic heat gain. Herein, a novel silylated bacterial cellulose/MgAl-layered double hydroxide (MBC/LDH) composite aerogel with multi-scale architecture and nano/micro porous structure was fabricated via facile freeze-drying. Within this architecture, 1D bacterial cellulose (BC) nanofibers serve as the matrix, while methyltrimethoxysilane (MTMS) silylation simultaneously enables crosslinking, hydrophobization, and enhanced emissivity through Si-O-Si/Si-O-C bonding. Incorporating 2D MgAl-LDH imparts flame retardancy and further modulates infrared emissivity. This synergistic design yields robust mechanical strength and exceptional optical properties with 96.5 % solar reflectivity and 92.3 % infrared emissivity. Outdoor testing (493.2 W·m −2 solar intensity) achieved a 6.3 °C sub-ambient cooling effect, significantly surpassing pure BC aerogel (1.9 °C). The aerogel also exhibits outstanding flame resistance (LOI = 34.1 %), ultralow thermal conductivity (0.03478 W·m −1 ·K −1 ) and high water contact angle (142°), providing essential thermal insulation, flame retardancy and self-cleaning properties. Year-round simulations demonstrate 41.2 % cooling energy savings when applied to roofs and walls. This work provides a pathway for developing advanced sustainable BC-based composite aerogels for energy-efficient building cooling.