Controllable fabrication of nanofibrillated cellulose supported HKUST-1 hierarchically porous membranes for highly efficient removal of formaldehyde in air

Nanofibrillated cellulose (NFC) has presented great potential as supports for functional membrane materials owing to its unique advantages. In this work, NFC-supported MOF hierarchically porous membranes were synthesized by anchoring HKUST-1 (copper 1,3,5-benzenetricarboxylate open-framework) on NFC membrane through a green DMF-free (N,N-Dimethylformamide) method at room temperature and afterward, the as-prepared composite membrane was used to remove formaldehyde from the air. The addition of HKUST-1 particles significantly increased the specific surface area of NFC membrane without affecting the NFC properties. Meanwhile, the nucleation and growth process of HKUST-1 on the NFC membrane could be effectively regulated, which further controlled the morphology of HKUST-1 as well as the anchored position of HKUST-1. When HKUST-1 was anchored on the interior and surface of the membrane, HKUST-1 reduced the compactness of the arrangement between fibers, which resulted in a hierarchical porous structure and then exposed more active adsorption sites of HKUST-1 particles. Thus, the flexible composite membranes exhibited effective formaldehyde adsorption from a low formaldehyde concentration environment (3.0 mg/m3). Under the optimum conditions, the maximum adsorption capacity of the HKUST-1@NFC-1 for formaldehyde reached 378.09 mg/g (based on HKUST-1 wt), which was considerably higher than support-free HKUST-1 powders. Consequently, the present work offers a green and controllable route to prepare NFC-supported MOF composite membranes with highly effective formaldehyde adsorption capacity and thus provides a promising option for NFC application as a flexible adsorbent support.