Application Of Nanofibrillated Cellulose Supported HKUST-1 Hierarchically Porous Membranes

More than 300 kinds of volatile organic compounds can be emitted from interior decoration materials,furniture,and newly purchased interior of passenger vehicles.Organic pollution(VOCs)will produce olfactory stimulation,mucous membrane stimulation,and carcinogenicity in the human body.Formaldehyde is one of the VOCs that attracts the most attention because it has serious harm,such as cancer and potential leukemia.In addition,formaldehyde is also widely present in many closed environments,such as passenger cars,airplanes,public Spaces,some production workshops,etc.Therefore,many people are exposed to formaldehyde in the background or the profession,making the control of indoor formaldehyde pollution a more urgent task.Nanofibrillated cellulose(NFC)has presented great potential as substantial 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 on NFC membrane through a green DMF-free 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/m~3).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 weight),which was considerably higher than support-free HKUST-1 powders.In addition,carbon nitride with elemental doping and nitrogen defect structure was constructed in this study to improve its photocatalytic activity,which is conducive to improving its application potential in air pollution control.K doping was introduced into bulk carbon nitride(CN)to form a nitrogen-deficient structure using KOH solution.The size of the majority of CN was reduced by secondary calcination to prepare CN_Xwith a large specific surface area,small particle size,and nitrogen-deficient structure.A composite membrane for photocatalytic degradation of formaldehyde in visible light was designed using modified CN_Xand HKUST-1@NFC.The composite membrane can improve the specific surface area of NFC by forming a hierarchical porous structure in the NFC membrane.SEM images of CN_Xand CN_X@HN composite membranes show that the accumulation of CN_Xis weaker and smaller than that of CN.Moreover,CN_Xwas attached to the surface of HKUST-1,which increased the absorption efficiency of CN_X.Moreover,as a porous material,HKUST-1 had a strong adsorption capacity for formaldehyde,which enriched more formaldehyde around CN_X@HN composite membrane,conducive to improving the photocatalytic efficiency of formaldehyde in CN_X@HN composite membrane.The photocatalytic performance of CN_X@HN-5 composite membrane was studied under the irradiation of a dark box and xenon lamp.The results showed that the total removal rate of formaldehyde was 86.7%,and the photocatalytic degradation rate was 48.45%under the irradiation of a xenon lamp.And the photocatalytic degradation ability of CN_X@HN-5 composite membrane to formaldehyde remains unchanged at more than 40%after ten times of recycling.Therefore,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.Consequently,the modified carbon nitride was loaded on the NFC/MOFs composite membrane,providing a new photocatalytic composite membrane material for formaldehyde treatment in a closed environment.