Synthesis Of Petroleum Coke Based Graphene Materials For Metal-free Catalysis

Graphene has become a new star in the field of nanotmaterial for its expetional physical and chemical properties granted by its unique two-dimensional structure.It has been widely applied in fields such as energy,environment and catalysis.Thus far,natural graphite flake is the main raw material for preparation of graphene and its derivatives.It is of great significance to develop new raw materials and technical preparation methods for graphene materials.Petroleum coke is a largely produced by-product in oil refining process.With the densification of crude oils,high value-added utilization of petroleum coke has become a major problem in refining and chemical industry.Petroleum coke has a similar layer-by-layer structure to graphite,showing great potential in preparing graphene materials.Therefore,based on the structural characteristics of petroleum coke,the dissertation focuses on the development of feasible technical methods to prepare graphene materials,which can be further surface-modified and act as efficient metal-free catalysts.It not only provides a new avenue for the utilization of petroleum coke,but also contributes to the green preparation and application of graphene materials.In this dissertation,modified chemical oxidation methods were developed to prepare petroleum coke based graphene oxide(PCO)with distinct structural properties,which were further chemical modified to syntheize novel metal-free catalysts.Their catalytic performance towards epoxide opening reaction and electrocatalytic oxygen reduction reaction(ORR)were investigated.The specific research contents and conclusions are shown as follows:(1)Firstly,by employing petroleum coke as raw material,three routes were developed to prepare PCO by modifying traditional chemical oxidation method.The influence of critical factors on oxidation and exfoliation,such as oxidant species,oxidant amount and oxidation time were detailedly investigated.The results reveal that all of the three methods can achieve PCO.The oxidant species show great influence on the structure of PCO.Nitrate ions result in PCO with abundant wrinkles and defectss,while phosphoric acid can achieve flat and well-ordered PCO.(2)Secondly,PCO was reduced to reduced PCO(RPCO)via chemical reduction method.RPCO were further sulfonated by concentrated sulfuric acid and sulfanilic acid(SPCO),which were evaluated as catalysts for ring opening reaction of epoxides.Catalytic results showed that SPCO serve as efficient solid acid catalysts for ring opening reaction of styrene oxide.The basal plane structure of RPCO plays a significant role on the catalytic sites and corresonding catalytic performance of SPCO.When concentrated sulfuric acid is choosen as the sulfonating agent,sulfonate group is readily introduced to the wrinkles and defects of RPCO.While para-anilinesulfonic acid tend to graft onto the surface of flat and well-ordered PCO.(3)In the end,nitrogen,sulfur and phosphorus co-doped graphene(N,S,P-PCO)was prepared by using thiourea and phytic acid as the dopants via high-temperature calcination.The influence of calcining temperature and PCO structure on ORR performance of N,S,P-PCO was studied.Compared with thiourea doped PCO,N,S,P-PCO showed promoted ORR activity.This result should be attributed to the formation of supermolecular polymer by thiourea and phytic acid,which can effectively avoid structural collapse and stacking during carbonization.The three-dimensional structure is also beneficial to mass and electron transfer in the ORR process.N,S,P-PCO obtained at 900 ~oC showed an initial potential of-0.05 V and limiting current comparable to that of commercial Pt/C electrode.