| Functional materials based on β-cyclodextrin(β-CD)have great potential in application in the field of adsorption and separation because of their unique host-guest molecular-recognition properties.In the preparation of functional materials,the surface modification method is simple to operate,and the product morphology is controllable with high utilization rate of β-CD,so it has been widely applies.So far,chemical grafting and coating are generally adopted as two surface modification strategies.Among them,the mechanism of coating method is based on the weak interaction force such as van der Waals force,hydrophobic effect or π-πinteraction,coating β-CD or macromolecular materials containing β-CD component onto the substrate to achieve adsorption performance.The coating method,which does not involve complex reaction steps,is simple and fast.However,usually the coating lacks stability because it relies on weak interactions.In addition,as the coating depends on the adsorption mechanism,the coating method can only be selectively applied on those substrates with adsorption properties.Therefore,the development of coating modification methods suitable for most substrates with stable coatings is of great significance for the application of β-CD functional materials in the field of adsorption and separation.Another important point is that in the field of adsorption and separation,the coating method often fails to take into account both high adsorption performance and simple operation process.The selected substrates usually have small size and good adsorption performance,but they are difficult to be separated from the continuous phase.Although the substrates with large size are easily to be separated from continuous phase,they have fewer amount of coating as well as lower adsorption performance.Therefore,it is of great significance to select substrates with superior surface properties to build a simple and continuous adsorption separation system on the basis of ensuring high adsorption performance,to further promote the application process of β-CD functional materials in the field of adsorption separation.Compared with the coating method,the chemical grafting method has the advantage of stability,because it is a modification method based on covalent bonding.Up to now,the chemical grafting methods are usually complex and face the challenges of both high adsorption performance and simple operation process.Therefore,the development of simple chemical grafting strategies and the construction of simple and continuous separation systems for water treatment,especially for the treatment of contaminated water with complex chemical components,is also very important for the application of β-CD functional materials for adsorption and separation.To solve the abovementioned problems,two new strategies based on coating and chemical modification are proposed for the preparation of β-CD functional materials in this thesis,and affinity membrane separation systems that can be operated continuously and separated with high efficiency by adsorption are constructed.The research work of this thesis is divided into the following three parts:In order to solve the problems of poor universality and stability faced by current coating methods,dopamine(DA),which is of excellent adhesion property,is grafted onto β-CD to prepare a coating molecule dopamine-grafted-β-CD(DACD)with substrate universality and stability.First,DA is grafted onto carboxymethyl-β-cyclodextrin by dehydration condensation reaction based on carboxyl and amino groups.Next,DACD is coated on the surface of organic and inorganic substrates with various morphologies,such as silica,copper,silicon,polyurethane sponge and nickel foam.It is proved that DACD coating molecules prepared in this chapter are universal to the substrates and able to resist strong fluid erosion and mechanical shock.The coating amount of DACD on the substrate surface indicates that,the smaller the substrate size is,the higher the coating amount of DACD.Then,bisphenol A(BPA)is used as the model pollutant to test the adsorption performance of DACD-coated micropowder materials and porous materials.The results show that the adsorption performances of BPA on both micropowder and porous materials are greatly improved after coating with DACD.The larger the specific surface area of the substrate is,the higher the coating amount of DACD,and the better the adsorption performance of BPA on the composite material.This work provides a universal and stable new strategy for the coating modification of β-CD on the surface of solid substrate,and is valuable for promoting the development and application of β-CD functional materials.In order to achieve both high adsorption performance and simple operation,based on the strategy proposed in Chapter 2,graphene oxide(GO)2D nanomaterials with great specific surface areas are selected as substrates,and the resultant DACD@GO nanomaterials have high adsorption performance.With DACD@GO nanomaterials as building blocks,DACD@GO affinity membrane separation systems are established with continuous and simple operation as well as high adsorption performance.First,DACD is coated on the surface of GO nanosheets.Due to the large specific surface areas of GO nanosheets,the coating amount of DACD is as high as 20 wt%.The adsorption behavior of BPA on DACD@GO nanosheets belongs to monolayer chemical adsorption,and the adsorption speed is fast.Under the condition that the initial concentration of BPA is 0.01 mmol L-1,the adsorption equilibrium can be reached within1 min.Stable DACD@GO affinity membranes are successfully prepared by vacuum filtration.Due to the fact that DACD prevents the compact stacking of DACD@GO nanosheets,the DACD@GO affinity membranes exhibit large water flux.In addition,DACD@GO affinity membranes have good adsorption and separation performance for BPA due to the high content of β-CD in DACD@GO and the tortuous 2D channel in the DACD@GO affinity membranes.DACD@GO affinity membranes have good recycling performance and can be recycled through membrane washing.The proposed DACD@GO affinity membrane separation systems in this chapter have the characteristics of fast,simple,efficient and sustainable operation,so they are highly promising in application in the field of water pollution treatment.In order to further improve the stability of the functional layer after surface modification,and simplify the operations of conventional surface grafting methods,β-CD is grafted onto GO surface in high density and by a simpler and milder method,thus β-CD-grafted-GO(CDGO)nanocomposites are prepared wtih high content of β-CD,with which CDGO affinity membrane separation systems with continuous operation and higher adsorption efficiency are constructed.Firstly,β-CD with amino group is grafted onto the surface of GO under mild reaction conditions(40 oC aqueous phase,no catalyst)by ring-opening reaction of epoxy group on GO.The grafting amount is as high as 43.6 wt%.The adsorption behavior of BPA on CDGO nanosheets belongs to monolayer chemical adsorption,and is a fast process.Under the condition that the initial concentration of BPA is 0.01 mmol L-1,the adsorption equilibrium can be reached within 1 min,and the maximum adsorption amount of BPA is twice higher than that of DACD@GO nanosheets in Chapter 3.The CDGO affinity membranes with stable water flux are successfully prepared by vacuum filtration.Due to the high graft amount of β-CD,the CDGO affinity membrane separation systems exhibit high BPA adsorption and separation performance.CDGO affinity membranes have good reusability and can be regenerated by simple and quick washing operation.The CDGO affinity membrane separation systems constructed in this chapter have good adsorption performance,and are highly promising in application of removal of BPA and other organic pollutants in water.To sum up,based on β-CD host-guest molecular-recognition system,two new strategies of coating and chemical grafting are successfully developed for preparing β-CD functional materials in this thesis,in which the coating method is stability and has universality for various substrates and the chemical grafting method has the advantages of simple reaction and high adsorption performance.The GO composite nanosheets prepared by these two methods are used as building blocks to construct the affinity membrane separation systems,which can be operated continuously and have high efficiency of adsorption.The results in this thesis provide valuable guidance for the preparation of β-CD functional materials as well as the adsorption application in the field of water pollution treatment. |
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