The Ball-milling Preparation Of Zwitterionic Graphene/Casein Nanohybrids And Its Application

Graphene,the most unique new material,has attracted much attention since its discovery.However,there are still many challenges to produce processable graphene nanosheets in large quantities and achieve suitable applications.Typically,liquid-phase exfoliation of graphite by shear force or sonication is considered to be more suitable for preparing high-quality graphene on a large scale.Compared with organic solvents,using exfoliating agent for producing graphene in aqueous media is more environmentally friendly and low-cost.However,it should be pointed out that many aqueous exfoliating agents are synthesized by chemical method,which is unfavorable to the sustainable development of society.Using biomass materials which have special interaction with graphene as exfoliating agents to exfoliate graphene is not only green but also can endow graphene with some unique properties.In this paper,we used a zwitterionic protein-casein as exfoliating agent to exfoliate graphite in liquid phase and prepared a high-concentration zwitterionic graphene/casein nanohybrids aqueous dispersion by one-pot ball milling,and the graphene exfoliation and the hybridization of casein and graphene were realized synchronously during ball milling.Based on the unique molecular structure and physical properties of casein,we explored the properties of the graphene hybrids and successfully prepared a new material for application-microencapsule phase change material（PCM）based on its excellent Pickering emulsification properties.The paper contains four chapters.In the first chapter,the structure,properties,preparation methods and applications of graphene and casein are briefly introduced.In chapter two,we charactered the morphology of prepared graphene and proved the few-layered graphene.Then we systematically studied the effects of ball milling process parameters（ball milling time,concentration of casein dispersion,the pH of casein dispersion and assist-exfoliation of sodium dodecyl sulfate）on the concentration and yield of prepared graphene.We found that the concentration of graphene could reach as high as 2.14 mg mL^-1 and the yield could reach 21.4%.Then,in chapter three,we explored the properties of the graphene/casein hybrids and found its pH responsiveness,excellent redispersibility and excellent Pickering emulsification characteristics and cytotoxicity experiments proved the good biocompatibility.In chapter four,graphene hybrids were used in the preparation of graphene/stearic acid microcapsule phase change materials by a Pickering emulsion method,and we proved the good encapsulation effect and high phase change enthalpy of the graphene/stearic acid microcapsules.