Study On Surface Modification And Electrophoresis Behavior For Nanodiamond And Graphene

Nanodiamond （ND） and graphene are two kinds of new carbon materials, which haveexclusive physical and chemical properties. ND possesses excellent chemical andelectrochemical stability, high hardness, and high heat conductivity besides nanomaterials’ characteristics; graphene is an important two dimensional nano material, with alarge specific surface area, favourable conductivity, and chemical stability. These twokinds of nano materials have extensively application in nanofluid, electrochemicaldetection, and photocatalyst.Nano materials’ movement modes can be controlled by electrophoresis technology.Electrophoresis technology is the most effective method for operating commendablynanopowder owing to the advantages of simple equipment, controllable speed, uniformdepositing suitable for the irregular surface etc. Suspension stability of nano particles isthe key factor for operating nano materials by electrophoresis technology. Nevertheless,ND and graphene have poor suspension stability because of their aggregated or laminated.Usually, modifying nanoparticle surface is the effective way to solve the problem.In this paper, the low concentration ND suspension was prepared owing to diamondhas good thermal conductivity. Using the transient hot wire method, thermal conductivityof nanofluids was measured. The results showed that the thermal conductivity ofnanofluids increased with increasing particle amount or decreasing particle size. Brownianmovement of ND particles became directional movement by exerting DC electric field toND nanofluid. The phenomenon of electrophoretic compulsive convection heat transfer innanofluid was discovered. The results showed that the heat transfer performance ofnanofluids increased with improving electric field strength, decreasing particle size orincreasing suspension concentration in the experiments of electrophoretic compulsiveconvection heat transfer.In order to realize EPD of ND, high concentration suspension was prepared. In thispaper, the surface of ND powders was fluorinated by the method of cycledvacuum-feeding fluorine gas, and F-ND obtained. The results of TEM showed aggregation of ND microfied, ND powder disaggregated, and the stability of ND suspension improvedby fluorination.The EPD of F-ND on positive pole was realized under DC electric field of10⁹0V/cm, and deposited layer was even and smooth. The F-ND was electrophoresisdeposited on the surface of glassy carbon electrode for preparing modified electrode, andits electrochemical properties were studied. Electrochemical experimental results showedthat the potential window range of modified electrode expanded0.6V than the originalglassy carbon electrode in0.5mol/L Na2SO4solution, broadened its potential window.The redox couple of Fe（CN）63-/Fe（CN）64-was semi-reversible reaction on modifiedelectrode.Because of electric field shielding effect, EPD layer was homogeneous and controllable.The diamond micro powder were electrophoresis deposited on the surface of nickel foams,then diamond particles were consolidated by chemical plating nickel and phosphorus alloy.The porous polishing tools with controllable aperture were prepared by this method. Theresults showed that diamond particles could be distributed uniformly on the nickel foamssubstrate, and was hard binded in nickel and phosphorus alloy by controlling the conditionof EPD and chemical plating. When the rate of weight gain of composite coating was220%, the bending strength was100MPa, which increasing to50times than the originalnickel foams. It found that coating and substratum combined closely by observing themorphologies after grinded.Graphene was suitable for supporter of catalyst owing to its large specific surfacearea and favourable conductivity. The compound powders of graphene loading LaMnO₃nanocrystalline were prepared by sol-gel method. The grain size of LaMnO₃wasapproximately20nm, and pore size of compound powders was about3nm. Thecompound powders were electrophoretic deposited on the surface of ITO glass using DCelectric field. The degradation experiment of acid red A solution was performed using thecompound film as photocatalyst. The research revealed that film has good photo-catalysis.The decolorization rate of acid red A could be up to96.8%in10h. The photocatalyticperformance of compound film was the best when graphene mass fraction was10%.