two types of cnt were investigated , nc7000 from nanocyl and mwnt  sa from sigma  aldrich ( catalog reference 659258 ) , both produced by chemical vapor deposition ( cvd ) .
nc7000 has a diameter of 710  nm , and mwnt  sa has a diameter of 110170  nm .
the cnt were functionalized by a 1,3-dipolar cycloaddition reaction of azomethine ylides using a one - pot functionalization procedure described elsewhere13 leading to the formation of pyrrolidine - type groups bonded to the cnt surface .
the functionalization was carried out at 250  c over 5  h. the unzipping of the cnt was performed using an ultrasonic processor up100h from hielscher , equipped with a sonotrode ms2 .
cnt suspensions were prepared by mixing functionalized cnt ( 5  mg ) in ethanol ( 8  ml ) .
a control experiment was conducted using pristine cnt ( 5  mg ) in ethanol ( 8  ml ) .
the suspensions were centrifuged ( 8000  rpm , 1  h ) to separate the unzipped cnt , and the gnr supernatant solutions were collected .
these solutions were analyzed by uv - visible spectroscopy on a shimadzu uv-240 1 pc , using 10  mm light path quartz cells .
the micro - raman analysis was conducted in the backscattering configuration on a jobin yvon hr800 instrument ( horiba , japan ) , using a 1800  l  mm grating and the 532  nm laser line from a nd : yag dpss laser ( ventus , laser quantum , uk ) . a 50x objective ( spot size : 3  m , na=0.75 , olympus , japan )
was used to focus the laser light onto the sample ( < 0.15  mw  m ) and to collect the backscattered raman radiation to be detected by a peltier cooled ( 223  k ) ccd sensor .
the spectrometer was operated in the confocal mode , setting the iris to 300  m , while the acquisition time was set to 30  s with 2  accumulations .
transmission electron microscopy ( tem ) of the gnr mwnt  sa was performed on an energy filtered 200  kv transmission electron microscope hr-(ef)tem 
tem analysis of the gnr nc7000 was carried out on a titan chemistem 80200  kv probe  cs corrected microscope .
low - magnification tem and high - resolution tem ( hrtem ) images were acquired with a gatan ultrascan 1000  p camera controlled with digital micrograph software integrated in the microscopes user interface .
the samples were prepared by adding a drop of the gnr solution onto a lacey carbon cu grid ( 300  mesh , ted pella ) and allowing it to dry under vacuum .
x - rays diffraction experiments were performed on a panalytical xpert pro xrd system using the cu k1 wavelength of 0.15406  nm from a copper x - ray tube operated at 45  kv and 40  ma .
a pixcel-3d detector was used , and the scan range was from 4 to 40 in 2. the gnr samples were deposited on glass lamellae by solvent evaporation .
the unzipping process produces functionalized gnrs with widths equal or larger than 35  nm for gnr nc7000 and 350  nm for gnr mwnt  sa . for this reason , a model of functionalized graphene ( see figure  6 ) , as opposite to finite gnr , was chosen .
graphene layers and their intermolecular interactions were modelled with the mm3 force field that has been found to give accurate intermolecular structures.17 all the calculations were performed with the tinker molecular mechanics suite18 using three - dimensional periodic boundary conditions.19 the shape and dimensions of unit cells containing five functionalized graphene layers with different concentrations of functional groups were systematically obtained by energy minimization .
additional data for the characterization for the gnr : thermogravimetric analysis ( tga ) and fourier - transform infrared spectroscopy ( ftir ) , is provided as supporting information .
as a service to our authors and readers , this journal provides supporting information supplied by the authors .
such materials are peer reviewed and may be re - organized for online delivery , but are not copy - edited or typeset . technical support issues arising from supporting information ( other than missing files ) should be addressed to the authors .
 graphene nanoribbons ( gnr ) were generated in ethanol solution by unzipping pyrrolidine - functionalized carbon nanotubes under mild conditions . 
 evaporation of the solvent resulted in regular few - layer stacks of graphene nanoribbons observed by transmission electron microscopy ( tem ) and x - ray diffraction . 
 the experimental interlayer distance ( 0.490.56  nm ) was confirmed by computer modelling ( 0.51  nm ) . 
 computer modelling showed that the large interlayer spacing ( compared with graphite ) is due to the presence of the functional groups and depends on their concentration . 
 stacked nanoribbons were observed to redissolve upon solvent addition . 
 this preparation method could allow the fine - tuning of the interlayer distances by controlling the number and/or the nature of the chemical groups in between the graphene layers . 