Construction of Functional Catalysis Centers in Two Dimensional Carbon Frameworks
Author:Lv Li Bing
Supervisor:chen jie sheng li xin zuo
The unique two dimensional(2D)structure of graphene endows it many extraordinary properties,such as high conductivity,high surface area,high Young’s modulus and excellent thermal conductivity.Graphene has great application prospect in catalytic area due to its enormous surface area and the high ability of electron and mass transformation.However,perfect graphene is a zero band gap material which offers limited activity for various catalytic reactions.Thus,further functionalization of graphenes by introducing guest components,for instance,heteroatoms and metal nanoparticles or constructing graphene based composites is essential to promote the the catalytic activity.But the existing functional methods could only give limited promotion of the catalytic activity of graphene.Therefore,we constructed various functional catalysis centers in 2D carbon frameworks including triazine rings decorated graphenes rather than separated nitrogen atoms dopants,metal nanoparticles growing through the whole carbon layers and mono-atomic metal centers via one step calcination of different precursors and conditions.And experimental results confirmed that our functional methods promoted the catalytic activity of pristine graphene enormously.The results are summarized as follows:(1)The 3D graphene monolith(Gr)with very high surface area and wrinkled surface was synthesized via calcination of glucose and dicyandiamide.And it was used as superabsorbing building blocks for constructing superhydrophobic or superhydrophilic surfaces on arbitrary substrates with different surficial structures from mesoscale to macroscale.The surface wettability of a Gr-coated surface was mainly dominated by the add layers(air for superhydrophobic surface and water for superhydrophilic surface)absorbed on the surface of graphene sheets.Transforming wettability of a Gr-coated surface between both superhydrophobic and superhydrophilic was thus very easy by drying and pre-wetting with ethanol respectively.The Gr-based superhydrophobic membranes or films promised great potentials as efficient separators for fast and gravity-driven oil-water separation.(2)Triazine rings were introducted into the 2D carbon frameworks based on the superabsorbing quality and the as-obtained samples were denoted as TA-G.The introduction of triazine rings elevated the adsorption ability of TA-G for small molecules(exemplified with oxygen in this chapter).The triazine ring-decorated graphenes(TA-G)was used as an atomic-scale carbocatalyst for room-temperature activation of oxygen molecules for selective oxidation.The unique C-N complexes forming by the combination of triazine and atom-thick structure significantly endowed TA-G the capability to activate oxygen at room temperature by enhancing the preadsorption of oxygen molecules over the triazine-carbon complexes as demonstrated with both the theoretical and experiments results.A novel strategy was proposed to modify the graphene for the design of novel and functional carbocatalysts with great application potentials in various realms of green chemistry and synthesis.(3)An ultra-stable electrocatalyst with cobalt nanocrystals grown through the plane of graphene subunits of nitrogen-doped graphenes was synthesized.It is the introduction of strongly bonded cobalt nanocrystals into the network of graphenes that modulate the electronic properties of the latter,resulting in the superb electrocatalytic performance.The catalyst has more positive onset and half-wave potential than Pt/C,high methanol crossover tolerance and superior stability.(4)The scale of guest components was shrinked to atomic scale and two dimensional metal/nitrogen/carbon nanolayers with accessible mono-atomic Fe centers,which bridge the “materials gap” between heterogeneous and homogeneous catalysis,were designed for liquid-phase oxidation of alcohols using molecular oxygen under mild conditions.This approach significantly promotes the mass transfer to the Fe centers,here exemplifies with the selective oxidation of alcohols using molecular oxygen.The catalysts show also high mechanical and chemical stability for good to excellent reusability.As the method is general for the synthesis of C-N 2d nanolayers with diverse transition metals and tunable metal contents,a broad range of 2d nanocatalysts can be envisioned that bridge the gap between homogeneous and heterogeneous catalysis.Such two-dimensional graphitic nitrogen/carbon nanocatalysts,also involving other metal centers,can be considered as a novel class of catalysts with a great potential for real applications in green chemistry.