Preparation Of Aramid Nanofiber Based Aerogels And Study On Their Adsorption Performance

The problem of water pollution caused by the discharge of various industrial wastewater is becoming more and more serious.The organic dyes and various metal ions in wastewater not only have a great impact on the environment,but also seriously threaten the health of human beings and various organisms.Therefore,in order to effectively adsorb and enrich pollutants and then treat them centrally,it is very necessary to develop efficient adsorbents with excellent adsorption capacity.Aramid nanofibers（ANFs）have the advantages of porosity and large specific surface area.They are ideal materials for the preparation of adsorbents,and a large number of functional groups on dendrimers can provide rich adsorption sites.In this paper,ANF was used as the base material.Different dendritic macromolecules were designed and synthesized according to different starting points.Then aerogels were prepared by blending dendrimers with ANFs,and the adsorption process and related adsorption mechanism were studied.Obtained aerogels show excellent adsorption properties for specific pollutants,and the preparation cost is low,which is conducive to industrialization.First,polyamines（PAMAM）were synthesized from ethylenediamine and then mixed with ANF solution to prepare composite aerogels.The obtained aerogels have good three-dimensional porous structure,which ensures the transport of adsorbate molecules in the aerogels.After mixing with PAMAM,the specific surface area of aerogels increased,which improved the adsorption performance by providing more adsorption sites.The adsorption experiments showed the Congo red（CR）adsorption capacity increased from 537.72 to 1842.52 mg/g,compared to pure ANF aerogels,much higher than most of the values in the literature.The performance improvement is not only due to the increase of specific surface area.The mechanism conversion from conjugation to hydrogen bond is equally important because the rotatable hydrogen bond is convenient for the adsorbed molecules to change the arrangement and make full use of the surface space of the adsorbent.However,due to the compact structure of PAMAM on the surface of ANF,their adsorption properties for metal ions are very poor.Therefore,POSS-PAMAM was synthesized using octaamino polyhedral oligomeric silsesquioxane（POSS）as the core.Through molecular dynamics simulation,it was found that the rigid core of POSS prevented the formation of compact structure of POSS-PAMAM,while the open structure allowed metal ions to enter the cavity of POSS-PAMAM and complex with internal tertiary amine groups.The adsorption experiments showed that the aerogels modified by POSS core PAMAM could adsorb CR and Cu²⁺simultaneously and effectively,with the maximum adsorption capacity of1502.95 and 248.49 mg/g,respectively.It is found the two pollutants interact with different adsorption sites respectively to achieve effective adsorption at the same time.In the field of recovery of precious metal,the selectivity is also extremely important,hence,based on the properties of Au Cl₄^-,adsorbents for selectively recovering gold were prepared.In the lower p H condition used in the experiment,the existing form of gold ion is Au Cl₄^-,so the positively charged aerogels can be prepared to interact with Au Cl₄^-through electrostatic attraction;Moreover,thiourea and Au Cl₄^-are classified as soft acid and soft base respectively in the theory of soft and hard acid-base,with high affinity.Therefore,thiourea functionalized dendrimers were prepared,and then combined with ANF to prepare positively charged adsorbents for selective adsorption of Au Cl₄^-.The maximum adsorption capacity is 719.42 mg/g,which is 6 times higher than that of pure ANF aerogels.Moreover,in the presence of a variety of common metal ions,the ratio of Au Cl₄^-adsorption capacity to other metal ions is close to 3:1.