The Preparation And Properties Of SiO₂ Aerogel Composite Membrane

Volatile organic compounds(VOCs)are harmful to human health and the environment due to their volatile and toxic property.Currently,nanofiber membrane prepared by electrospinning technology has been widely used in VOCs adsorption and attracted more and more researchers’ attention due to its simple preparation,easy formation,small fiber diameter and interconnected pore structure.Among them,the electrospun noncarbon nanofiber membranes prepared from noncarbon based materials are promising adsorption material because of easy regeneration and good adsorption performance.Nevertheless,the specific surface area of the noncarbon nanofiber membranes is only a dozen.As we know,the high specific surface area is the key to providing more active sites for the adsorption of harmful substances.Therefore,it is necessary to further increase the specific surface area of electrospun noncarbon nanofiber membrane to promote VOCs adsorption efficiency further.SiO2 aerogel is a porous material with high specific surface area and also has great potential in the application of VOCs adsorption due to its porous property.Now,the common forms of SiO2 aerogel are mainly block,powder and aerogel composite mats.But blocky aerogel is fragile and requires strict process conditions.Powdery aerogel can easily diffuse into the air,which is harmful to human health,and the dust release from aerogel composite mats also has an adverse impact on the human body and the environment.Therefore,searching for a new form of aerogel is a topic worth studying,which is necessary to control production cost and expand application.Based on the above questions,we fabricated two kinds of SiO2 aerogel/PAN composite nanofiber membranes with high area surface and different contact angles for the first time by using hydrophilic SiO2 aerogel(SA)and hydrophobic SiO2 aerogel(MSA-4h)as functional components and PAN as carrier via electrospinning technology in this paper and mainly studied their VOCs adsorption property.First,we explored the process parameters during the preparation process and fabricated SiO2 aerogel composite nanofiber membranes with different SA contents.The microscopic morphology displayed SiO2 aerogel with honeycomb porous structure assembled on the surface of PAN nanofibers,which greatly improved the specific surface area of the resultant membranes.The high surface area played an important role in promoting the VOCs adsorption performance of membranes.The adsorption results showed the PAN membrane containing 100 wt%SiO2 aerogel(based on PAN)showed the highest VOCs adsorption capacity,which was 2.5-5.3 times(for four VOCs,formic acid,chloroform,methanol and xylene respectively)greater than that of pristine PAN membrane and even higher than activated carbon,and the VOCs adsorption capacity trend of different membranes toward different hydrocarbons was similar,with the order of chloroform>formic acid>methanol>xylene.And the unchanged VOCs adsorption capacity during 10 cycles demonstrated the resultant membranes had excellent regeneration.Secondly,SA was modified for 4h by using the modification solution containing 10%hexamethyldisilazane and SA was successfully prepared into the hydrophobic aerogel MSA-4h with the contact angle of 144.4°,but the specific surface area of the aerogel decreased from 815.38 m2/g to 564.36 m2/g after modification.Finally,we fabricated hydrophobic SiO2 aerogel/PAN composite nanofiber membrane(marked as PAN+MSA 71.4%)containing 71.4%(based on PAN)MSA-4h according to the same preparation process.The morphology,specific surface area and pore structure of PAN+MAS 71.4%were similar to those of SiO2 aerogel composite nanofiber membrane containing 71.4%SA(PAN+SA 71.4%).And it was worth noting that the difference in the specific surface area and pore structure between MSA-4h and PAN+MSA 71.4%was smaller than those between SA and PAN+SA 71.4%,which meant that the hydrophobic modification of SiO2 aerogel can reduce the effect of PAN polymer and solvents on its specific surface area and pore structure to some extent.Besides,PAN+MSA 71.4%composite nanofiber membrane also had good VOCs adsorption performance and had a higher adsorption capacity for the other three VOCs than PAN+SA 71.4%except for formic acid.And the adsorption amount of PAN+MSA 71.4%for different VOCs showed the order of chloroform>methanol>formic acid>xylene.In this paper,SiO2 aerogel and PAN were successfully fabricated into a flexible membrane material.The form of the membrane can effectively solve the problem of dust-releasing of aerogel composites and is more convenient than powder or particle in practical application.And the successful preparation of the SiO2 aerogel composite not only enriches the types of VOCs adsorption materials but also provided a new design method for aerogel composites.