Developing cellulose nanofibrils/Na-montmorillonite composite air filter with efficient filtration ability for PM2.5 and adsorption of formaldehyde

Indoor and outdoor air treatment is one of the key issues that people focus on. However, developing green air filtration materials with high filtration efficiency (FE), low pressure drops (ΔP) and good mechanical properties is still intractable challenges. In this study, we designed a green composite aerogel air filter with double filtration mechanism, where Na-montmorillonite (NMMT) was exploited in the adsorption ability for PM2.5 due to its unique layered structure, high specific surface area, and negative charge. In the system, cellulose nanofibrils (CNF) as the structure materials were mixed with HCl acidified modified Na-montmorillonite (HMMT) as the functional particles, followed by freeze-drying to obtain CNF/HMMT composite aerogel air filter. The resulting aerogel air filter showed excellent capture ability to PM2.5 (up to 96.5 %) and adsorption performance for formaldehyde (81.97 mg/g). This was mainly due to both the mechanical interception of the three-dimensional network constructed by CNF and the surface electrostatic adsorption of HMMT. After hydrophobic modification with methyltrimethoxysilane (MTMS), the samples displayed good water resistance, recycling performance and mechanical properties. In view of its features of environment-friendly, wide source and low cost, the aerogel air filter has the possibility of wide application.