Chemical Engineering Journal 488 (2024) 150784 Available online 27 March 2024 1385-8947/© 2024 Elsevier B.V. All rights reserved. Bio-based and fireproof radiative cooling aerogel film: Achieving higher sustainability and safety Wei Cai a, b , Bicheng Lin b , Liangyuan Qi b , Tianyang Cui b , Zhaoxin Li b , Junling Wang c , Sicheng Li d , Chengfei Cao e , Mohammad Ziaur Rahman a , Xin Hu a , Rujun Yu a , Shuo Shi a , Weiyi Xing b, * , Yuan Hu b , Jixin Zhu b , Bin Fei a, * a School of Fashion and Textiles, The Hong Kong Polytechnic University, Kowloon 999077, Hong Kong, China b State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230026, China c Jiangsu Key Laboratory of Hazardous Chemicals Safety and Control, College of Safety Science and Engineering, Nanjing Tech University, Nanjing 211816, China d College of Materials Science and Engineering, State Key Laboratory of Bio-fibers and Eco-textiles, Shandong Collaborative Innovation Center of Marine Biobased Fibers and Ecological Textiles, Qingdao University, Qingdao 266071, China e Centre for Future Materials, University of Southern Queensland, Springfield 4300 Australia A R T I C L E INFO Keywords: Fire Safety Flame Retardant Mechanism Radiative Cooling Bio-Based Materials ABSTRACT Even though significant advantages in the energy-free regulation of temperature are presented, the practical applications of radiative cooling materials in buildings and human surfaces still involve many safety issues, especially for fire hazards of polymer-based materials. Meanwhile, renewable and environmentally friendly materials are urgently needed to develop suitable radiative cooling materials with no adverse environmental impact. Herein, a chitosan-derived composite aerogel film with high solar reflection provided by the addition of melamine-phytic acid (MA/PA) hybrids is designed and prepared, presenting radiative cooling and fireproof performances. The instinct deep-yellow color of chitosan (CS) is successfully shielded by high-reflective MA/PA hybrids, while IR emissivity of up to 90.4 % and solar reflectivity of ~ 89.3 % are achieved. In outdoor envi- ronments, this composite aerogel shows sub-ambient temperature drops of ~ 4.3 ◦ C and ~ 3.1 ◦ C in cloudless and cloudy weather, presenting a robust cooling effect. In addition, CS-MA/PA composite aerogel film with 3 mm thickness can isolate the fire of ~ 500 ◦ C, showing superior fire safety attributed to the synergistic flame retardant effects among chitosan, phytic acid, and melamine, which suppress the initial growth of fire and promote the rapid formation of protective char layer. This work provides a bio-based, fire-safe, and radiative cooling material to decrease the energy consumption of temperature regulation with a more environmentally friendly and safer approach, further promoting the practical application of radiative cooling materials. 1. Introduction At present, an enormous amount of energy and resources has been invested into the temperature regulation of spaces and buildings, composed of cooling and heating. Meanwhile, the energy consumption in building cooling is responsible for 2–3 % of the total residential en- ergy consumption, representing almost 2.9 % and 6.7 % of the total energy consumption of the residential and commercial buildings, respectively[1,2]. The huge energy consumption not only aggravates the energy shortage problem globally but also produces more CO 2 gas associated with the greenhouse effect. Obviously, the released CO 2 in turn facilitates the increase of global temperature, again lifting the requirement for cooling and energy consumption. Even worse, there is an inevitable contradiction between the energy consumption of cooling and human body comfort. In other words, turning off the energy supply to adjust the room temperature will cause health problems for people. Therefore, there is a huge challenge yet urgent target to develop a low- energy or energy-free technology to reduce the significant energy con- sumption of the cooling of spaces and buildings. Passive radiative cooling, delivering the matter heat through an infrared transparent window of the earth’s atmosphere (λ: ~8 to 13 μm) to the cold sink of outer space, has been regarded as an efficient, envi- ronmentally friendly, and energy-free technology to adjust the temper- ature of spaces and buildings, and explored by academic institutions and * Corresponding authors. E-mail addresses: xingwy@ustc.edu.cn (W. Xing), bin.fei@polyu.edu.hk (B. Fei). Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej https://doi.org/10.1016/j.cej.2024.150784 Received 8 January 2024; Received in revised form 22 March 2024; Accepted 27 March 2024