The Preparation Of Bifunctional Polysilsesquioxane/Carbon Nanotube Magnetic Composites And Their Adsorption Properties

With the development of industrialization and urbanization,the environmental pollution caused by harmful pollutants have been increasingly emerging,water pollution caused by heavy metal ions is particularly serious,heavily threatens humans and other creatures'safety.Besides,there is also a low concentration of precious metals in industrial wastewater,discard directly causes resources waste and environmental pollution,restricting green and sustainable economy development.Therefore,it is incumbent upon researchers to find a proper way to solve the problem of water pollution.Adsorption is a very attractive approach for researchers due to its operational simplicity,less secondary pollution,low-cost,etc.At present,the common adsorption materials mainly include zeolite,activated carbon,clay ore,chitosan,macromolecular biopolymers and other traditional materials.With the continuous development of nanotechnology,nano-adsorbents have gradually replaced traditional adsorbents.Carbon nanotubes(CNTs),as a type of nanomaterials with many excellent properties,have been widely used in the adsorption field due to their large specific surface area,excellent aspect ratio,and thermal stability.Nevertheless,CNTs have few active sites,difficult to disperse and dissolve,which limit their widely application in practice.Thus,it is necessary to modify the surface of carbon nanotubes.Polysilsesquioxane(PSQ)is a type of organic-inorganic hybrid material with Si-O inorganic bond and organic group R,which has good corrosion resistance,heat resistance,and oxidation resistance.Thanks to its large surface area and good selectivity,PSQ as an adsorbent has high adsorption capacity.In this work,carboxyl carbon nanotubes as a matrix,the first step is APTMS grafted to the surface of carbon nanotubes by amidation reaction,and then the mixture of APTMS and MPTMS coated to the surface of CNTs by the condensation reaction between the alkoxy,thus bifunctional PSQ/CNTs composites will be prepared.To better explore the role of different functional groups in the composites,the single functional group PSQ/CNTs composites were prepared in the same way as the contrast materials.Simultaneously,magnetic particles Fe₃O₄ were introduced in the preparation process to improve the separation efficiency of the composites in solution to prepare PSQ/CNTs magnetic composites.The structure,morphology and properties of the composites were analyzed by FT-IR,SEM,VSM,XPS,XRD,TG,BET,and etc.The characterization results show that the bifunctional polysilsesquioxane were successfully coated on the surface of CNTs.A series of adsorption experiments,including static saturation,p H effect,adsorption thermodynamics,adsorption kinetics and etc.were carried out to investigate the adsorption properties of PSQ/CNTs magnetic composites for different metal ions.The static saturation adsorption results show that the composites have excellent adsorption performances for Au(III),Pt(IV)and Hg(II),therefore,the three metal ions have been further explored.Adsorption thermodynamics experiments show that the adsorption process is more consistent with Langmuir adsorption isotherm model,that is to say,the adsorption process is monolayer adsorption and spontaneous endothermic reaction with increased disorder.Adsorption kinetics experiments show that the adsorption process of Au(III),Pt(IV)and Hg(II)were more consistent with the pseudo-second-order kinetics model.The adsorption selectivity experiments show that the composites have good adsorption selectivity in the binary systems with other metal ions coexist.The adsorption mechanism shows that chelation reaction,ion exchange reaction or redox reaction may occur in the adsorption process.Reuse experiments show that the adsorption capacity of the composites can reach more than 78%after repeated use for three times.In conclusion,a novel bifunctional PSQ/CNTs magnetic composites were prepared by sol-gel method in this paper.This kind of new adsorbent is expected to be applied to recovery of low concentration of noble metal ions and removal of low concentration of heavy metal ions in water.