Cellulose nanocrystals as renewable materials for suppressing hazardous PM 2.5 pollution

The application of cellulose nanocrystals (CNCs) as a PM 2.5 capture agent is demonstrated. CNCs are prepared using sulfuric acid hydrolysis of laboratory filter paper. The obtained CNCs are characterized to obtain their molecular information, morphology, and crystallinity using ATR FT-IR spectroscopy, transmission electron microscopy, and X-ray diffraction, respectively. The negatively charged surfaces of the CNCs with an average zeta potential of −51 mV could strongly interact with PM 2.5 particles, and are principally utilized for PM 2.5 capture. In order to evaluate the PM 2.5 removal efficiency of the CNCs, they are fabricated into an air filter by dip-coating onto a cotton mesh fabric employed as the substrate. The CNCs could be homogeneously coated onto the cotton fibers, as observed via scanning electron microscopy. The air filter fabricated using the optimized conditions possesses a PM 2.5 removal efficiency of 94%. The CNC-coated air filter has good air penetrability, with a low pressure drop of 20.7 Pa. The surfaces of the air filters before and after PM 2.5 capture are characterized using optical microscopy and scanning electron microscopy. The PM 2.5 capture mechanism of the CNC-based air filter is also proposed. Our findings reveal the important discovery that negatively charged CNCs can be directly employed as a renewable PM 2.5 capture agent.