| Carbon material is one of the first materials that is dealt with and used by human being,and has been applied in many fields.Compared with bulk diamond,nano-diamond has intrinsic properties of bulk diamond,also unique excellent performances such as high surface activity,large number of surface atoms.Large specific surface area and easy modification by chemical groups,which make it potential in the fields of composite materials,precision components,biomedicine and electrochemical degradation.As a P-type semiconductor material,low-dimensional boron carbide is considered as one of the most promising inorganic materials.At present,the application of two-dimensional boron carbide nanomaterials in high energy density batteries,nanoelectronics,and optics has attracted extensive attention and research.Up to date,there are various shortcomings in traditional methods for the synthesis of nanodiamonds.Developing a safer,reliable and efficient synthesis method is a difficult problem and challenge for industrial production at present.Nano-structured B4C materials,especially ultra-thin two-dimensional B4C films,have attracted great interest and attention,but no effective synthesis method has been formed so far.In particular,the synthesis of ultrathin boron carbide films has not yet been reported.In this paper,nano-diamond materials were successfully prepared by a simple and efficient DC arc plasma method using transition metal catalysts(Ni,Co,Mn)and the raw materials of silicon and carbon.Two-dimensional boron carbide materials were successfully prepared from bulk boron and carbon by controlling the atmosphere of reaction system.Based on the experimental results,the formation mechanisms of nano-diamond and two-dimensional boron carbide are analyzed,and the photocatalytic properties of two-dimensional boron carbide films were also tested.The main research contents and results are as follows:(1)Under the condition of less than atmospheric pressure,magnetic ?B group metals(Ni,Co)and non-magnetic ?B group metals(Mn)were used as catalysts to synthesize nano-diamond particles in situ by thermal plasma.The analysis shows that the metal Ni,Co,Mn and C can form supersaturated Ni(C),Co(C)and Mn7C3(C)solid solution respectively,and the C atom precipitated with the decrease of external temperature can provide the carbon source needed for the formation of diamond phase.By reacting with gaseous atoms(C,Si)vaporized from the bulk graphite and the silicon target,the betac-sic crystal nuclei with diamond structure are formed,providing growth sites for effective carbon sources,and nano-diamond particles with complete cubic crystal structure are prepared.The results show that the free C atoms can form graphite layer on the surface of the diamond and hinder the further growth of diamond phase.The increase of Si content can lead to the increase of by-products of metal-silicon compound,which is not conducive to the increase of diamond yield.Further analysis showed that the metal catalyst components can be orderly and C form short-range Ni3C,Co3C and Mn3C structure,which contains of C-C atoms w ith diamond growth interface similar crystal structure and electronic structure,under the condition of high temperature of C-C atoms can be separated,and on the diamond phase interface have been generated for stacking,promote the growth of diamond particles.The experiment revealed the formation rules of diamond phase in the process of transient quenching by using metal component high temperature solid solution C as an effective carbon source,using in situ formed beta-sic phase as crystal core seed.The key role of carbon solubility in metal solid solution changing with temperature in the formation process of diamond was verified.(2)Using thermal plasma as heat source and amorphous boron powder and graphite powder as mixed raw materials,multiform B4C nanosheets,hollow spheres and ultra-thin B4C films were prepared.Compared with compared particles.B4C nanocrystals have improved their common properties and have a high potential for application in the field of electronics.Analysis shows that B4C particles with layered structure can be synthesized in H2:Ar=1:2 atmosphere.Change the ratio of mixed atmosphere(H2:Ar=1:6)to synthesize B4C nanocrystals with a thickness of about 10 nm,which is caused by the growth of B4C's initial crystal nucleus along two-dimensional anisotropy.In the arc method,the morphology and size of B4C nanocrystals can be controlled by changing the atmosphere,which makes the arc method of preparing B4C nanocrystals of certain significance.When boron oxide and graphite powder were mixed as raw materials,hollow spheres of B4C with a diameter of 50-200 nm were prepared due to the participation of oxygen atoms,and the shell was composed of B4C nanocrystles growing along(021)crystal surface with a thickness of 5-7 nm.MgO framework was successfully prepared by arc method.Using MgO,amorphous boron powder and graphite powder as raw materials,ultra-thin two-dimensional B4C film with a thickness of about 1.5 nm was prepared for the first time.This is of great significance to the application of B4C in other fields.Analysis shows that the formation of this ultrathin B4C film is based on the MgO nanofibers formed in situ as the template framework,and the two-dimensional structure B4C aggregates are formed on the surface of the composites,which have the growth characteristics along the(021)crystal plane.Bound by the MgO framework,the aggregates are granular,and the generated B4C film cannot be extended.When the MgO framework is removed,it can be stretched,forming an ultra-thin B4C film.The experimental results show that the optical band gap is 1.37ev,and the photocatalytic degradation rate of methylene blue can reach 99.4%,which opens up the application of B4C in the field of photocatalysis. |
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