Effects of bimetallic catalysts on synthesis of nitrogen-doped carbon nanotubes as nanoscale energetic materials

Well aligned nitrogen-doped carbon nanotubes （CNx-NTs）, as energetic materials, are synthesized on a silicon substrate by aerosol-assisted chemical vapor deposition, Tungsten （W） and molybdenum （Mo） metals are respectively introduced to combine with iron （Fe） to act as a bimetallic co-catalyst layer. Cor- relations between the composition and shape of the co-catalyst and morphology, size, growth rate and nitrogen doping amount of the synthesized CNx-NTs are investigated by secondary and backscattered electron imaging in a field emission scanning electron microscope （FESEM） and X-ray photoelectron spectrometer （XPS）. Compared to pure iron catalyst, W-Fe co-catalyst can result in lower growth rate, larger diameter and wider size distribution of the CNx-NTs; while incorporation of molybdenum into the iron catalyst layer can reduce the diameter and size distribution of the nanotubes. Compared to the sole iron catalyst, Fe-W catalyst impedes nitrogen doping while Fe-Mo catalyst promotes the incorporation of nitrogen into the nanotubes. The present work indicates that CNx-NTs with modulated size, growth rate and nitrogen doping concentration are expected to be synthesized by tuning the size and composition of co-catalysts, which may find great potential in producing CNx-NTs with controlled structure and properties,

Sorption of 2,4-dinitroanisole (DNAN) on lignin

The present study describes the use of two commercially available lignins,namely,alkali and organosolv lignin,for the removal of2,4-dinitroanisole（DNAN）,a chemical widely used by the military and the dye industry,from water.Sorption of DNAN on bothlignins reached equilibrium within 10 hr and followed pseudo second-order kinetics with sorption being faster with alkali than withorganosolv lignin,i.e.k2 10.3 and 0.3 g/（mg·hr）,respectively.In a separate study we investigated sorption of DNAN between 10 and40 C and found that the removal of DNAN by organosolv lignin increased from 0.8 to 7.5 mg/g but reduced slightly from 8.5 to 7.6mg/g in the case of alkali lignin.Sorption isotherms for either alkali or organosolv lignin best fitted Freundlich equation with enthalpyof formation,H0 equaled to 14 or 80 kJ/mol.To help understand DNAN sorption mechanisms we characterized the two lignins byelemental analysis,BET nitrogen adsorption-desorption and 31P NMR.Variations in elemental compositions between the two ligninsindicated that alkali lignin should have more sites（O-and S-containing functionalities） for H-bonding.The BET surface area andcalculated total pore volume of alkali lignin were almost 10 times greater than that of organosolv lignin suggesting that alkali ligninshould provide more sites for sorption.31P NMR showed that organosolv lignin contains more phenolic-OH groups than alkali lignin,i.e.,70% and 45%,respectively.The variations in the type of OH groups between the two lignins might have affected the strength ofH-bonding between DNAN and the type of lignin used.