First-principles Study For The Effect Of Boron And Nitrogen Co-doping And Covalent Functionalization With Oxygen-containing Functional Groups On Reactivity Of Graphene

Owing to its unique physical and chemical properties,graphene-based nanomaterials provide potential applications in nanoelectronics,novel catalysts,and senors,and attract a large of interest experimentally and theoretically.In this work,based on first-principles calculations,we investigated effect of boron and nitrogen chemical doping and covalent functionalization with oxygen-containing functional group on reactivity of graphene surface,and calculated the dissociation of molecular oxygen on BCN doped graphene and mechanisms for oxidative dehydrogenation?ODH?of propane into propene catalyzed by N-doped graphene oxides?GOs?.We revealed the structural and electronic properties of Ag nanopaticles?NP?deposited on GOs.The effect of interface interaction of Ag NP/GOs on adsorption of NH₃ and NO molecules is discussed.Present works provide basic understanding for design of novel non-metal catalysts toward ODH reaction and new sensors in experiment.The main results in this thesis are as follows:?1?The effect of different shapes?triangular or quadrangular?and edge termination?N-terminated or B-terminated?of BN cluster doping on O₂ dissociation are discussed using density functional?DFT?calculations.The calculated results showed that the edge termination and shape of BN clusters are two important factors,determining the catalytic activity of BCN graphene for the dissociation of molecular oxygen.On the one hand,the effect of triangular BN?t-BN?cluster doping on reactivity of graphene is more prominent than that of quadrangular?q-BN?.The t-BN doping can reduce the energy barrier more effectively and cause the reaction to exotherm,compared to q-BN.On the other hand,the effect of the N-terminated BN cluster doping on activation of molecular oxygen is better than that of B-terminated.In particular,the B atom neighboring the N edge,only for the N-terminated triangular BN doping,is dertemined to be the most active site for the oxygen dissociation.The electronic structure calculations reveal that in addition to the large positive charge densities,the enhanced catalytic activity of graphene by the BN doping is also attributed to the increased density of states?DOS?of?*states of active site around the Fermi level.?2?The activation of C-H bond is an important reaction process in the oxidative dehydrogenation of alkanes.Nitrogen doping may tuned the activity of graphene oxides towards ODH of propane.Using DFT calculations,we constructed different GO models with epoxy and hydroxyl functional groups,and investigated the interaction of propane with N-doped GOs for ODH to propene.The calculated results showed that activation of C-H bond by epoxy group mainly depends on the site of oxygen-containing groups relative N doping.Comparing with pristine GOs,the epoxy and hydroxyl groups located at many sites neighbor the N doping lower the energy barrier for C-H activation,and increase the reaction energies.The cleavage of the first C-H bond is rate-determined process for ODH of propane to propene.?3?Density functional calculations have been used to investigate the stability of Ag₁₃nanoparticles deposited on graphene oxides and mechanisms for the adsorption of NH₃ and NO on GOs improved by nanoparticles.The calculated results show that the epoxy functional group and its neighboring sp² carbon atoms of graphene oxides,are used as active sites to enhance the binding of Ag₁₃3 to graphene through the C–O–Ag and C–Ag chemical bonds,increasing the stability of nanoparticles deposited on graphene oxides.The electronic properties of nanoparticle can be modified by the strong interfacial interaction of Ag₁₃/GOs.The NH₃ is strongly adsorbed on deposited Ag₁₃3 through the formation of N–Ag bond and NH???O hydrogen bond.The adsorption of NO on GOs is obviously improved due to the oxidation of Ag to Ag₁₃O by neighboring oxygen.The electronic structure calculations reveal that the hybridization of HOMO orbital of NH₃ with conduction bands of Ag₁₃-GOs results in larger charge transfers from NH₃ to hybrid.On the contrary,the adsorbed NO acts as acceptor character.The calculated results show good agreement with experimental observations.