Controlled Fabrication Of Carbon Nanocoils And Their Application In SERS

To date,with the development of nano-technology,many kinds of low-dimension carbon nano-materials and their nano-composites with different morphologies and structures have been designed and synthesized.These carbon nano-materials exhibit outstanding physical and chemical properties and further promote the development of society,which has been applicated in energy,sensors and electron device.Carbon nanocoils?CNCs?as a kind of carbon nano-materials have a unique 3-dimensional spiral structure,exhibiting some different physical and chemical properities from other carbon nano-materials.It has been observed that the performance of CNCs is closely linked to their morphology and structure.Therefore,developing a simple way to synthesize CNCs with controllable coil diameters and structures would be most desirable.However,controlled synthsis of CNCs with different morphology and structure is still a challenge to the world.In this paper,the dependence of catalyst particle size with its avtivity and life were obtained by analyzing the effects of reaction time on the coil diameter distribution.And the monolayered silica spheres were used to limit the size and distribution of catalyst particles for adjusting the coil diameter,pitch,and structure of CNCs.In addition,Ag nanoparticles were synthesized by a modified photocatalysis method,which combine the advantage of sputtering method and traditional photocatalysis method.On this basis,Ag nanoparticles/nanosheets hybrids were also synthesized on TiO₂ with CNCs for application in SERS:?l?Adjusting the coil diameter,pitch,and structure of CNCs:Firstly,the effects of reaction time on the distribution of coil diameter of CNCs has been analysized and a further fitting curve for the growth of CNCs was provided.It is found that the proportion of CNCs with larger coil diameter is increased with increasing the reaction time.In addition,the fitting curve has three group of parameters.It is concluded that the as-prepared catalyst particles have different sizes and activities.The catalyst particles with a small size have a higher activity,but a shorter-lifetime.While the catalyst particles with a large size have a lower activity,but a longer lifetime.Secondly,the effects of Sn/Fe catalyst film with different thickness on the sizes and aggregation of catalyst particles have been analysized.Irregular carbon nanowires,carbon nanofibers,and CNCs with different moiphology and structure were synthesized by using Sn/Fe catalyst film with different thickness.It is found that the coil diameter of CNCs is decreased with decreasing the thickness of the catalyst films.In addition,the CNCs tend to change from spring-like to plait-like and gradually change from having an amorphous carbon structure to having a nanocrystalline graphite structure as their coil diameters are decreased.It is concluded that the milnimum catalyst film thickness for the growth of CNCs in a high yield is determined to be approximately 3-7 mil.At last,we used monolayered silica spheres to limit the sizes and distribution of the catalyst particles,which would also provide the base fixation for the growth of CNCs.It is found that the average coil diameter of the CNCs is decreased by decreasing the diameter of silica spheres.In addition,the thickness of byproduct layer is reduced by using the monolyered silica spheres,leading to an improvement in the yield of the CNCs.By patterning the catalyst films using the monolayered silica spheres as mask,the average coil diameter of CNCs can be further reduced.?2?Synthesis of CNCs with small coil diameter:The effects of Sn and Fe film sputtering turns and their mole ratio on the distributiorn and morphology of the catalyst particles have been analyzed.It is found that the catalyst films prepared as Fe/Sn turns could not form suitable catalyst particles and aggregation after calcination,which is not suitable for the growth of CNCs.While the catalyst films prepared as Sn/Fe turns would form suitable catalyst particles and aggregation after calcination,from which CNCs can be synthesized by CVD method.In addition,the coil diameter of CNCs is decreasd by decreasing the thickness of Sn.On this bases,we try to synthsize CNCs with small coil diameter by using Fe as the catalyst and using monolayered silica spheres to limit the morphology and distribution of catalyst particles.In addition,the monolayered silica spheres would also provide the base fixation for the growth of CNCs.It is found that CNCs with small coil diameter counld be obtained by this method and the yeild of CNCs with small coil diameter is increased by decreasing the diameter of silica spheres.?3?The effects of CNCs on the growth of Ag nanoparticles by photocatalysis for application in SERS:Uniform Ag NP films were synthesized on TiO₂ films with pre-sputtering high density Ag seeds by photocatalytic reduction of AgNO3 for application in SERS,which combine the advantages of the spurting method?high nucleation density?and the traditional photocatalytic method?suitable particle size?.The Ag seeds synthesized by modified photocatalytic method exhibits a much more better SERS activity.We also used finite-difference time-domain to calculate the e-field on the surface of Ag nanoparticles,which have a good match with the experiment data.On the bases of these work,Ag nanoparticles/sheets hybrids were synthesized on TiO₂ substrate with CNCs by photocatalysis for application in SERS.The helical structure,electrical conductivity,and photothennal conversion properties of CNCs would affect the distribution and transport of electron,and the distribution of temperature,those would affect the distribution and morphology a lot.The Ag nanoparticles synthesized by this method exhbits outstanding SERS activity.In addition,it also has a good SERS uniformity.