Cyclodextrin Polymers And MOFs With Ripid Formaldehyde Adsorbed At Low Concentrations And Their Electrospun Membrane Properties

Indoor air quality is directly related to human health.As one of the pollutants strictly controlled by indoor air quality standards,formaldehyde shows low concentration but great harm to human health.Adsorption technology is one of the mainstream technologies for the treatment of indoor low concentration formaldehyde,and the adsorbent is the core of the technology.However,the existing adsorbents have the limitation of low formaldehyde adsorption capacity and adsorption rate.In this paper,a rigid structure cyclodextrin POPs material and a series of nitrogen/oxide functionalized MOFs materials were synthesized.The adsorption performance and adsorption mechanism of formaldehyde in low concentration were studied.MOF-74 and other MOFs powder materials were further shaped by electro-spinning to enhance the comprehensive air purification capability and practical application capability.The main research content and results are summarized as follows:1)The P-CDP with permanent mesoporous structure was prepared,and the adsorption performance,cycle stability,and adsorption mechanism of formaldehyde at low concentrations were investigated,resulting that the P-CDP shows 2.52 mg/g of formaldehyde adsorption capacity for 1ppm and 4.44 mg/g for 10 ppm at 303 K.The average adsorption rate of formaldehyde in the first ten minutes at a low concentration of 1ppm is 9.11 times faster than that of commercial coconut shell activated carbon,reaching 0.17 mg·g^-1·min^-1,which means that it can achieve large and rapid adsorption of indoor low-concentration formaldehyde at room temperature.Compared with the reported formaldehyde adsorbents,the adsorption performance of P-CDP is at the international advanced level.Besides,P-CDP shows no significant difference in adsorption capacity and adsorption rate after 5 cycles of 1 ppm formaldehyde absorption and desorption,which indicates good cycle stability.The hydrogen bond and electrostatic interaction between formaldehyde and P-CDP are the main effects that cause its rapid adsorption.2)The series of UiO-66 functionalized with hydroxyl and amino groups were synthesized,and the difference in formaldehyde adsorption performance and adsorption mechanism were explored.Both amino and hydroxyl functionalization can effectively improve the adsorption performance of UiO-66 series materials,and the adsorption promotion effect in different formaldehyde concentrations is different.At a low concentration of 1 ppm,the promoting effect of hydroxyl groups is the most obvious.UiO-66-（OH）₂ can quickly adsorb formaldehyde,with an average adsorption rate of 0.29 mg·g^-1·min^-1 in the first 10 minutes and an adsorption capacity of 9.16 mg/g,UiO-66-NH₂ and UiO-66 show adsorption capacities of 1.65 and 1.09mg/g for1 ppm formaldehyde,respectively.At 10 ppm formaldehyde,the promoting effect of amino groups is slightly higher than that of hydroxyl groups.The adsorption capacities of UiO-66-（OH）₂,UiO-66-NH₂,and UiO-66 for 10 ppm formaldehyde are 12.25,14.17 and 3.75 mg/g,respectively.Molecular simulation shows that UiO-66 mainly forms hydrogen bonds with formaldehyde molecules through theμ₃-OH of the Zr metal cluster,and has the lowest adsorption binding energy with formaldehyde;UiO-66-NH₂ forms a strong hydrogen bond with formaldehyde mainly through the amino group;UiO-66-（OH）₂ forms the strongest hydrogen bond and CH···O interaction with formaldehyde through the hydroxyl group and due to the small steric hindrance and the dense adsorption area,the overall framework has the highest adsorption binding energy for formaldehyde,so it shows the strongest ability to capture low concentrations of formaldehyde.However,UiO-66-（OH）₂ has few adsorption sites,which limits the further improvement of the adsorption capacity.Therefore,the adsorption capacity for 10 ppm formaldehyde is lower than that of UiO-66-NH₂.3)MOF-74 and MIL-101-NH₂ with the same ligands but different metals as the UiO-66series were synthesized,and their fast adsorption performance of formaldehyde and its mechanism were explored.The adsorption performance of MOF-74 and MIL-101-NH₂,which are rich in unsaturated metal sites,is much better than that of UiO-66-（OH）₂ and UiO-66-NH₂.Among them,MOF-74 has an adsorption capacity of 60.40 mg/g for 1 ppm formaldehyde,a PC value of 20.13mol·kg^-1·Pa^-1,and an average adsorption rate of 0.53 mg·g^-1·min^-1 in the first ten minutes.It is currently one of the most excellent materials for formaldehyde adsorption at low concentrations.MOF-74 generates electrostatic interaction with formaldehyde through Mg unsaturated metal sites,and the interaction is much stronger than that between the hydroxyl group and formaldehyde in UiO-66-（OH）₂.At the same time,formaldehyde molecules are adsorbed in the vicinity of the metal clusters at the vertices of the hexagonal pores of MOF-74.The small steric hindrance and the large number of sites make it an obvious advantage in the adsorption of low-concentration formaldehyde.4)The MOF-74/PAN membrane with MOF-74 loading of 20%-72%was synthesized by an electro-spinning method.The membrane can maintain the complete crystal form of MOF-74.The actual loading capacity of the membrane is almost the same as the theoretical value.The adsorption capacity of 72%-MOF-74/PAN to 1 ppm formaldehyde is up to 36.39 mg/g,which retains 78.6%of the adsorption capacity of MOF-74 particles.In addition,the loose fiber membrane structure makes it a better initial formaldehyde adsorption rate than MOF-74particles.Therefore,the adsorption performance of the MOF-74/PAN membrane has surpassed most powder materials currently reported.At the same time,MOF-74/PAN membrane has excellent air filtration performance,showing an air permeability of 64 mm/s under 200 Pa and a filtration efficiency of non-oily NaCl particles higher than 99.5%.It reaches the GB/T 32610-2016 Class I standard.