Multi-functional air filters with excellent flame retardancy and fire-warning capability

High fire-safe air filters are indispensable for indoor environments, such as vehicle interior, fresh air filtration system, and window screens. However, it is still challenging to afford both excellent flame retardancy and rapid fire-warning capability in air filters. In this study, we fabricate a type of high-efficient fiber filters with combined flame-retardant and fire-warning performance. Nanofibers with a specific tri-layer structure are designed to incorporate Polyacrylonitrile (PAN) matrix and two functional components, flame retardant ammonium polyphosphate (APP) and amino-functionalized carbon nanotube (A-CNTs). The resultant PAN/CNTs/APP fiber filters have high PM2.5-10 capture efficiency of > 99.99%. The filters can not be burnt in vertical burning test and exhibit high limiting oxygen index value of 30.9%. Moreover, the resultant PAN/CNTs/APP fiber filters achieve short fire-warning response time (∼5s) when encounters fire. This work offers a facile and cost-effective approach to fabricate multifunctional air filters, and shows promising applications in vehicle interior, firefighting, fresh air filtration and building materials.