科研之友
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摘要
Single-wall carbon nanohorns (SWNHs) with dahlia flowerlike structures were treated with H2SO4 and H2O2/ H2SO4 mixture. The SWNH samples before and after acid treatment were characterized using a transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, temperature-programmed desorption (TPD), and N-2 adsorption at 77 K. According to TEM and SEM observation, the SWNH bundles were coalesced after H2SO4 and H2O2/H2SO4 treatments, growing up to the bundle size of several micrometers. The Raman spectra provided evidence that the H2O2/H2SO4 treatment leads to intercalation of the H2SO4 molecule into interstitial spaces of individual SWNHs as well as defect formation by oxidation reaction. The H2O2/H2SO4 treatment also altered markedly the N-2 adsorption isotherms of SWNH from type II to type I, accompanied with an enhanced N-2 adsorption uptake at low relative pressure due to the development of microporosity. Heat treatment at 873 K on H2O2/H2SO4-treated SWNHs additionally increased the N2 adsorption amount at the low relative pressure range. The H2O2/H2SO4 treatment remarkably increased the total surface area and micropore volume. In particular, micropore volume increased almost 5.5 times after H2O2/H2SO4 treatment and successive heat treatment (from 0.11 to 0.60 mL g(-1)), whereas mesopore volume dramatically decreased (from 0.28 to 0.06 mL g(-1)). Thereby micropore volume percent remarkably increased from 28 to 91%. The H2O2/H2SO4 treatment of SWNHs enhanced the microporosity due to increase not only of internal pore volume but also interstitial pore volume, which can be achieved by both opening of nanohorn particles and H2SO4 intercalation into the interstitial space between nanohorns. Moreover, the coalescence of SWNH assemblies by H2O2/H2SO4 treatment should transform the mesopores to micropores, and it decreases the external surface area.
- 出版日期2004-11-18
