Synthesis And Structural Control Of Graphene Oxide

Graphene oxide(GO)is a precursor of chemically converted graphene,thus it is the most intensively investigated graphene derivative.This dissertation systematically studies the new techniques for the synthesis and structural control of GO and reveals their mechanisms.The main contents are listed as follows.An improved eco-friendly Hummers method has been developed by excluding the use of Na NO3.This modification does not decrease the yield of product.The resultant GO is well-functionalized,nearly the same to that prepared by conventional Hummers method in functional groups,thickness,and lateral dimensions.The merits of this eco-friendly method are as follows:(1)eliminating the evolution of NO2/N2O4 toxic gases;(2)simplifying the disposal of waste water because of the inexistence of Na+ and NO3-ions;(3)the resultant GO and reduced graphene oxide(r GO)have better structural integrities.High-yield production of GO has been achieved by simply replacing the 325 mesh graphite flakes with 1200 mesh graphite flakes.The yield for GO1200 is as high as 171 ± 4 %,much higher than that of GO325(110 ± 3 %).The structures,qualities and size distributions of the GO sheets prepared from both graphite precursors are nearly identical.More importantly,in the case of using small graphite flakes,the GO dispersion can be directly purified without the requirement of centrifugation to remove unoxidized residuals.Considering the high yield and simplified purification procedure,this modification of using small graphite flakes is an important step towards the industry-level mass-production of GO.A water addition-modified Hummers method has been developed for synthesizing GO sheets with controlled structural integrity and species of oxygen-containing groups.GO sheets with tunable amounts of hydroxyl and epoxide groups can be prepared via oxidizing graphite at 40 oC in the presence of water,without severe destroying their structural integrity.GO sheets with more carboxyl groups and worse structural integrity can be prepared by additional 95 oC oxidation process.This water addition-modified method can further be applied for improving the yields of high-quality GO synthesized at low temperatures(0 oC).The mechanism of water-enhanced oxidation has also been studied and discussed.A one-step technique for size fractionation of GO sheets has been developed by size exclusive passing of GO sheets through size-defined pores of track-etched membranes,which can separate GO sheets into multiple portions with narrow size distributions.This technique is simple,economical,energy-saving,eco-friendly,and can be integrated with GO preparation to realize large scale production.The size-dependent properties of GO and r GO materials were also investigated.GO and r GO films prepared from large GO sheets have better mechanical performances and higher conductivity comparing with their counterparts made from small GO sheets.Moreover,this method can also be applied for size fractionation of other micron-sized materials.