火焰法制备螺旋碳纳米纤维及其亲水改性

Preparation of Helical Carbon Nanofibers by Flame Method and Its Hydrophilic Modification

目的利用乙醇火焰法制备螺旋碳纳米纤维,并考查不同表面改性方法对螺旋碳纳米纤维亲水性的影响。方法首先研究不同烧制时间、镍片-火焰距离、SnCl4溶液浓度对制备螺旋碳纳米纤维的影响,然后用水蒸气、聚乙烯吡咯烷酮K30(PVP)溶液以及氢氧化钠-浓硝酸溶液改性螺旋碳纳米纤维。通过扫描电镜、透射电镜、拉曼光谱仪、X射线衍射仪对所制备的螺旋碳纳米纤维进行表征,利用红外光谱分析、X射线光电子能谱分析和沉降实验评价不同改性方法的改性效果。结果随着镍片-火焰距离的增加,螺旋碳纳米纤维含量增加,均匀度逐渐下降;随着烧制时间的延长,螺旋碳纳米纤维的均匀度先增加后降低;SnCl4的浓度会影响碳纳米纤维的形貌和均匀度。制备均匀的螺旋碳纳米纤维的最佳条件为:73%SnCl4溶液,镍片-火焰距离1.5 cm,烧制9 min。通过红外光谱分析发现,三种改性方法都使螺旋碳纳米纤维表面接上亲水基团。沉降实验表明,PVP溶液和氢氧化钠-浓硝酸改性的螺旋碳纳米纤维在水溶液中静置48 h后的沉降率均为26.7%,而未改性的螺旋碳纳米纤维的沉降率为58.3%。结论通过乙醇火焰法可以制备出均匀的螺旋碳纳米纤维,其中烧制时间、镍片-火焰距离、SnCl4溶液浓度对制备的螺旋碳纳米纤维的形貌和均匀度影响很大,需要在特定的条件下才能制备出均匀的螺旋碳纳米纤维。通过三种方法对螺旋碳纳米纤维进行改性,发现PVP溶液和氢氧化钠-浓硝酸改性的螺旋碳纳米纤维的表面亲水性更好,其中PVP溶液改性操作简单,且对螺旋碳纳米纤维的形貌没有破坏,对于螺旋碳纳米纤维改性会更有利。

The work aims to prepare helical carbon nanofibers by the ethanol flame method,and examine the effect of different surface modification methods on the hydrophilicity of the as-synthesized helical carbon nanofibers.Firstly,the effects of different burning time,nickel-flame distances and SnCl4 solution concentrations on preparation of helical carbon nanofibers were studied;and then the helical carbon nanofibers were modified with water vapor,polyvinylpyrrolidone K30(PVP)solution and sodium hydroxide-concentrated nitric acid solution(KOH-HNO3),respectively.The prepared helical carbon nanofibers were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),Raman spectroscopy and X-ray diffraction(XRD),and the influences of different modifications were evaluated by infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and sedimentation experiments.The experimental results showed that increasing the nickel-flame distance could extend the yield of spiral carbon nanofibers,but deteriorate the uniformity gradually,while burning time lead to fluctuation of the uniformity.In addition,the concentration of SnCl4 could also affect the morphology and uniformity of the carbon nanofibers.The optimal parameter for preparing uniform helical carbon nanofibers was:73%SnCl4 solution,1.5 cm of nickel flakes-flame distance and burning for 9 min.The FTIR revealed that hydrophilic groups can be grafted on the surface of the helical carbon nanofibers by all the three modification methods.The sedimentation experiments showed that the PVP solution or KOH-HNO3 modified helical carbon nanofibers possessed better hydrophilicity than water vapor modification,and after standing for 48 h,their sedimentation rate in aqueous solution decreased from 58.3%to 26.7%compared with unmodified helical carbon nanofibers.In conclusion,ethanol flame method can be used to prepare uniform helical carbon nanofibers whose morphology and uniformity can be controlled by burning time,nickel-flame distance and SnCl4 solution concentration.Uniform helical carbon nanofibers could be prepared under special conditions.It is found in modification through the three methods that PVP solution or KOH-HNO3 modified nanofibers show better hydrophilicity than ones modified using water vapor.The modification of PVP solution is easy to be operated and does not damage the morphology of helical carbon nanofibers.It is more beneficial to the modification of spiral carbon nanofibers.