Hydrophobic Modification Of Metal-organic Framework UiO-66 And Its Adsorption Performance Of VOCs In Humid Environment

Most volatile organic compounds（VOCs）are highly toxic,carcinogenic and dangerous,which pose a long-term threat to the environment and human health,and are an important cause of atmospheric pollution and global climate change.Metal organic framework materials（MOF s）have a very attractive prospect in the field of adsorption and separation due to their high specific surface area,pore volume and uniform pore size,but poor water stability also limits the practical application of MOFs in the field of VOCs adsorption.In this paper,a series of porous adsorption materials with excellent hydrothermal stability and high adsorption performance were prepared by using three strategies for hydrophobic modification of UiO-66 materials:ligand design and functionalization before synthesis,hydrophobic modification in situ synthesis and modification after synthesis（PSM）.The VOCs adsorption characteristics of the modified UiO-66 material in dry（wet）state were studied.The adsorption kinetics model and general diffusion model were used to analyze the adsorption behavior of the adsorbent.Finally,the regeneration performance of the adsorbent was studied.This study enriched the hydrophobic modification method of UiO66,and provided theoretical basis and technical support for the application of MOFs in VOCs waste gas treatment.（1）UiO-66-NDC（X）materials with dual organic ligands were prepared using the strategy of pre-synthetic ligand design.Through this strategy,the pore structure and specific surface area of MOFs can be regulated,and a non-polar functional group naphthyl group can be introduced into UiO-66,which enhances the hydrophobicity of the material and the π-πinteraction between toluene molecules,and improves the material’s performance in wet conditions.Adsorption performance under ambient conditions.Under the relative humidity of RH=50%,UiO-66-NDC（50）has the best adsorption performance（76mg/g）,which is about 1.69 times that of pristine UiO-66（45mg/g）.And the cycle experiment proves that UiO-66-DNC（50）can still be regenerated effectively after five cycles.（2）UiO-66@MWCNT,a composite of UiO-66 and multi-walled carbon nanotubes（WMCNT）,was prepared by in situ synthesis of hydrophobic modification strategy.In the toluene dynamic adsorption experiment,UiO-66@MWCNT（10%）exhibited the best adsorption performance（355 mg/g）,which was 2.23 times that of UiO-66（159 mg/g）,which could be attributed to the composite pores The structural change and the increase of the surface dispersion force of the UiO-66@MWCNT（10%）composite enhanced the electrostatic interaction between the composite and toluene molecules.Under the relative humidity RH=50%,the toluene adsorption capacity of UiO-66@MWCNT（10%）was 159 mg/g,which was 3.53 times that of UiO-66（45 mg/g）.Under different humidity,UiO-66@MWCNT（10%）also showed much better adsorption performance than UiO-66,and the adsorption capacity was reduced from 355mg/g to 159mg/g（RH=50%）and 65mg/g（RH=50%）,respectively.RH=80%).The adsorption and desorption cycle experiments proved that the composites are reproducible,and further to the experimental industrial application.（3）UiO-66-NH₂ materials were prepared by microwave-assisted solvothermal method using a post-synthesis modification strategy,and UiO-66-PSM（CH₃）materials were prepared by trimethylbenzaldehyde grafting.UiO-66-PSM（CH₃）exhibited the highest adsorption performance（210 mg/g）in dry state,which was 32%higher than that of UiO-66,which could be attributed to the introduction of additional benzene rings and methyl groups into the material by PSM modification,increasing the π-π interactions and hydrophobic interactions between the material and toluene molecules were investigated.Under the relative humidity RH=50%,the adsorption capacity of UiO-66-PSM（CH₃）decreased,and UiO-66-PSM（CH₃）had better adsorption capacity（62mg/g）,which was higher than that of UiO-66（45mg/g）.about 38%.When the relative humidity increased from 0%to 80%,the adsorption capacity of UiO-66PSM（CH₃）decreased from 210 mg/g to 62 mg/g（RH=50%）and 52 mg/g（RH=80%）,respectively.Finally,the cycle experiments show that UiO-66-PSM（CH₃）can be effectively regenerated under the relative humidity of RH=50%,the adsorption capacity is not significantly reduced,and the saturated adsorption capacity after regeneration is maintained at about 58 mg/g.