Adsorption Properties And Mechanisms Of Organic Pollutants Onto Structure-controlled Graphene Nanosheets

Graphene,an atomic thick 2-Dimensional layer of sp²-bonded carbon,is currently one the most intensively studied functional materials in the world.Thanks to the outstanding properties of graphene,it has been widely used in various applications such as electronics,energy storage,biomedicines and environmental applications.In this dissertation,the published methods to regulate graphene structure for water remediation were firstly summarized.However,the mechanisms driving the adsorption of organic molecules onto graphene nanomaterials were still not well understood.In addition,the adsorption capability of active sites on graphene for different organic molecules was also lack of study.To study the adsorption behavior of graphene-based nanomaterials with different properties,a series of graphene-based nanomaterials with different functional groups,sizes or wrinkles structures were synthesized and characterized.Firstly,the adsorption behavior of the synthetic graphene-based materials to typical organic pollutants including naphthalene,phenanthrene,and pyrene were investigated.Secondly,the co-adsorption of naphthalene,1-naphthol and Cd²⁺ onto the graphene sheet surfaces with different polarities was illustrated.Thirdly,hydrophobic organic contaminants（HOCs）were chosen to probe the potential adsorption sites on the graphene sheet surfaces with various wrinkles and lateral sizes.The results are essential for determining the effect of graphene materials on the fate and transport of organic contaminants and for designing novel adsorbents for organic pollutants.The main novelties and findings of the study were listed below:（1）The adsorption of PAH molecules significantly changed the morphologies of graphene（GNS）and graphene oxide（GO）sheets,which were observed from the TEM and SEM images.The high affinities of PAHs to GNS are dominated by the π-πinteractions and the sieving effect of the groove regions formed by wrinkles on the GNS surface.By contrast,the polar GO nanosheet surface indicated lower affinity to PAHs because the carboxyl groups on the edges of GO sheet not only smoothen the groove regions but also weaken the π-π interactions.（2）Adsorption and co-adsorption behaviors and mechanisms of graphene interface to organic,inorganic molecules with different polarities were elucidated.Three types of graphene sheets including GO>CRG>ARG with decreasing polarity were prepared.It was found that the adsorption capability of the graphene-based materials to organic pollutants was increasing with the decreased polarity.In addition,all the three adsorbents showed stronger adsorption to 1-naphthol than to naphthalene.The strong adsorption of 1-naphthol onto graphene nanosheets could be attributed to the n-π electron-donor-acceptor（EDA）interaction between-OH of 1-naphthol and the electron-depleted sites on graphene nanosheets.The adsorption of 1-naphthol on the reduced graphene materials was increasing with the increasing pH and reached the maximum around its pKa,supporting the n-π EDA interaction mechanism.On the other hand,GO with more functional groups on the nanosheets over CRG and ARG exhibited a higher affinity to Cd²⁺.The co-adsorption of Cd²⁺ on GO and CRG facilitated the adsorption of naphthalene and 1-naphthol via surface-bridging mechanism such as cation-π interaction.Notably,though ARG showed insignificantly adsorption to Cd²⁺,the suppressed co-adsorption of naphthalene onto ARG might be attributed to the sieving effect of the hydrated Cd²⁺ binding to the edge of micropores on ARG.（3）Morphology regulation of graphene-based materials by KOH etching was applied to selectively remove or separate organic pollutants with different sizes.A positively linear correlation between organic molecule uptake and the micro pore volume of AGN indicated that the pore-filling mechanism may play an important role in adsorption.Notably,with the increasing of lateral size,GO contained more hydroxyl groups as well as more defects.When it was reduced by N₂H₄,the larger lateral size the heavier aggregation of reduced graphene oxide（rGO）was observed,indicating that the lateral size may dramatically affect the structure and properties of graphene nanosheets in different conditions.