Figure 2: 13C REDOR SSNMR measurement of labelled RGO.
From: Chemical structures of hydrazine-treated graphene oxide and generation of aromatic nitrogen doping
13C MAS SSNMR spectra with a π/2-pulse excitation of 13C- and 15N-labelled RGO, (a) without and (b) with dipolar dephasing by 13C–15N REDOR during a period of 1.6 ms. (c) The difference spectrum of a and b. Note that the vertical scale in c is magnified five times, compared with that of a and b. The spectra in a and b were collected with the pulse sequence shown (d), (a) without and (b) with 15N π-pulse trains. Although the 13C signal intensities for both control and dephased spectra are mildly modulated by 13C T2 relaxation and 13C–13C J-coupling, the difference spectrum in c highlights a spectrum of 13C species within a few bonds from 15N atoms. The phase cycles in d are as follows: φ1=x, −x, y, −y; φ2=y, y, −x, −x. The receiver phase was cycled as x, −x, y, −y. The phases for φ3 and φ4 in the rotor-synchronous π-pulse trains were incremented after every π-pulse, following the XY-16 phase cycle (x, y, x, y, y, x, y, x, −x, −y, −x, −y, −y, −x, −y, −x). τR denotes one rotation period of magic angle spinning.
