Preparation And Performance Of Smart Polymeric Microspheres Loaded Magnetic Graphene Oxide

Metal ions play an important role in life activities.Various metabolic activities in organisms require metal ions to work normally.Moreover,some heavy metal ions,such as Pb²⁺,Hg²⁺,Cd²⁺,and Cr⁶⁺,are the serious sources of environmental pollutants.Based on the importance of metal ions and the serious issue of heavy metal pollution to environment,it is highly desireable to design and construct a fast and effective method to detect and remove heavy metal ions in wastewater.Crown ether compounds can form host-guest complexes with many metal ions,thus demonstrate excellent ion-recognition performance.And they can selectively accommodate various metal ions according to the size of crown ether cavities.Therefore,ion-responsive host-guest systems based on crown ether play a significant role in the field of ion detection,especially in treatment of trace metal ions as well as the adsorption and separation of metal ions.Poly?N-isopropylacrylamide??PNIPAM?is a well-known thermo-sensitive smart material that can respond to an external temperature stimulus.A small temperature change would cause a reversible phase transition of polymer chains from swelling to shrinkage,and thus showing thermosensitivity.It has a lower critical solution temperature?LCST?of about 32°C in aqueous solution.It can be tuned by copolymerizing with some appropriate hydrophilic/hydrophobic monomers.Therefore,such an excellent thermosensitivity of PNIPAM can be utilized as a microenvironmental actuator for metal ions detection and adsorption.Graphene oxide?GO?is one new type of carbon material,and has been widely used for adsorption and separation because of its large specific surface area and abundant active groups such as hydroxyl,carboxyl,carbonyl,epoxy groups.However,it can not be used for the specific recognition and adsorption of pollutants.Moreover,the separation of GO from aqueous solution is significantly difficult,which limits its practical applications to some extent.Magnetic nanoparticles,typically Fe₃O₄,have good magnetic responsiveness and show favourable application prospects in detection and adsorption.Dopamine?DA?can oxidize and polymerize to form polydopamine?PDA?under weak alkaline conditions?pH 8.5⁸.8?,and thus bind stably into almost all solid substrates.This provides a new strategy for functionalization of GO.In this thesis,a series of Poly(NIPAM-co-B₁₈C₆Am)?PNB-1?smart polymeric microspheres,which exhibit both excellent thermo-responsive and ion-recognition properties,are prepared by free-radical copolymerization of N-isopropylacrylamide?NIPAM?and benzo-18-crown-6-acrylamide(B₁₈C₆Am)monomers.The effects of species and concentrations of metal ions as well as crown ether contents in copolymers on the ion-responsive behaviors of these microspheres are systematically investigated.In order to further improve the properties of microspheres,A two-step reaction method is adopted to prepare smart polymer microspheres.First,Poly?NIPAM-co-AAc??PNA?polymeric microspheres are prepared by free radical polymerization using NIPAM and AAc as functional monomers.Following the Poly(NIPAM-co-AmB₁₈C₆)?PNB-2?polymeric microspheres are prepared by the condensation reaction of the amino group of 4'-aminobenzo-18-crown-6(AmB₁₈C₆)and the carboxyl groups of with PNA.The dual stimuli-responsive characteristics of temperature and metal ions are systematically studied.The results show that the PNB-2 smart microspheres fabricated through two-step reaction method exhibit better Pb²⁺-responsive properties than the microspheres synthesized by one-step method.In addition,the regulation of PNA feed ratio and reaction time are also systematically studied to develop the optimal smart microspheres with best temperature sensitivity and Pb²⁺-responsive properties.Based on the above studies,we design and engineer two kinds of intelligent graphene nanomaterials?MGO@PNB?that can rapidly and specifically recognize and remove Pb²⁺from water.The MGO@PNB are fabricated by loading superparamagnetic Fe₃O₄ nanoparticles and PNB microspheres onto GO nanosheets.The 18-crown-6 units serve as hosts that can selectively recognize and capture Pb²⁺from aqueous solution and the PNIPAM chains act as a microenvironmental actuator for the inclusion constants of 18-crown-6/Pb²⁺host-guest complexes.When Pb²⁺ions present in water environment,18-crown-6 units on nanomaterials recognize Pb²⁺ions,and at low temperature,when Pb²⁺ions are saturatedly adsorbed by18-crown-6 units,Pb²⁺can be released from the intelligent nanomaterials by increasing environmental operational temperature.Moreover,the loaded Fe₃O₄ NPs endow the MGO@PNB with convenient magnetic separability.The synthesized MGO@PNB demonstrates high ion-recognition selectivity of Pb²⁺among the coexisting metal ions since the formation of stable 18-crown-6/Pb²⁺inclusion complexes.More interestingly,the MGO@PNB shows excellent thermosensitive adsorption ability toward Pb²⁺due to the incorporation of PNIPAM functional chains on the GO.The synthesized MGO@PNB is systematically characterized by IR,TEM,TGA,VSM and DLS.The effects of solution pH,contact time,solution concentrations and temperature on the adsorption of Pb²⁺onto the MGO@PNB are also investigated.Moreover,the adsorption kinetics,adsorption thermodynamics and adsorption isotherms are also studied.The results show that the MGO@PNB developed in this study show a high adsorption selectivity of Pb²⁺.It can easily adsorb Pb²⁺at low temperature and desorb the adsorbed Pb²⁺at high temperature.This functional material still demonstrates good adsorption selectivity for Pb²⁺after several recyclings.Such crown ether-based ion recognition smart materials have potential applications in ion detection and wastewater treatment.In summary,two kinds of smart polymeric microspheres?PNB-1 and PNB-2?are successfully prepared,and their thermo-responsive and ion-recognition properties are systematically investigated.The temperature-,ion-and magnetic responsive smart nanomaterials are designed and fabricated.Such ion-recognition responsive nanocomposites based on crown ether have great application potentials in the fields of ions detection and wastewater treatment,and so on.