Facile preparation of graphene nitride by irradiating MHz ultrasound.

The present study aimed at developing a simple sonochemical method to prepare graphene nitride from the mixture of graphite and aqueous ammonia solution. Ultrasound of 1.6 MHz was irradiated to the sample in a fabricated sonoreactor at predetermined ultrasonic power and duration. The one-pot method succeeded in the preparation of graphene nitride. The generation was proven by XPS analysis in finding N1S peak in the spectrum. Detail analysis of N1s peak suggested that the major nitrogen species was pyrrolic type. Furthermore, the presence of CO bond proved the oxidation by OH radical. The reaction product had the value of N/C as high as 0.08, which is comparable to reported values for ultrasonic preparation of graphene nitride. The fact indicates that the significance of chemical effects of MHz range ultrasound, and the finding of the simple preparation method will accelerate practical application of graphene nitride.

Non-uniform Excitation States in Photoinduced Deformation of Amorphous Carbon Nitride Films.

Amorphous carbon nitride (a-CNx) films prepared via reactive radio frequency magnetron sputtering deform under on-off visible light illumination. We investigate the relationship between photoinduced deformation and surface electrical states via scanning electron microscopy with Ar+ laser irradiation (SEM-L). Two samples with different levels of photoinduced deformation are prepared. For the film with small photoinduced deformation, uniform secondary electron emission is observed on the film surface, regardless of whether the laser is on or off. On the a-CNx film, which has fifty times larger photoinduced deformation than the previous film, light and dark patches, similar to a speckle pattern, appear on the film surface in SEM-L images. This anomalous phenomenon indicates non-uniformity of the electrical states excited by laser light irradiation. A size of the patches is well correlated with an inhomogeneous distribution of sp3C and sp2C, Isp3C/Isp2C, obtained using soft X-ray emission spectroscopy (SXES). Simultaneously, temporal decrease in the sp3C component under illumination is obtained via SXES.

Soft X-ray emission spectroscopy study of characteristic bonding states and its distribution of amorphous carbon-nitride (a-CNx) films.

Soft X-ray emission spectroscopy based on electron microscopy was applied to investigate bonding electron states of amorphous carbon nitride (a-CNx) films with different nitrogen contents of x. Carbon K-emission spectrum showed characteristic intensity distribution of not only sp2 bonding but also sp3 bonding. The a-CNx film with lager x, which has a larger macroscopic electric resistivity, shows a larger content of the carbon sp3: C-C bonding signal. Furthermore, the dependence of spectral intensity distribution on x suggests the presence of sp2: C-N and sp3: C-N bonding. Those results show that the relation between macroscopic electrical resistivity of a-CNx film and its nitrogen content is because of the decrease of sp2: C-C bonding and the formation of sp2: C-N and sp3: C-C and C-N bonding conformation induced by an introduction of nitrogen atoms. Spatial variation of a signal ratio of sp3/sp2 was visualized and was confirmed as a relation between sp3 boding amount and nitrogen content x.

Optical absorption and photoconductivity in iodine-excess ionic liquids: the case of 1-alkyl-3-methyl imidazolium iodides.

We investigated the optical absorption and photoconductivity of iodine-excess ionic liquids (ILs) based on 1-alkyl-3-methyl imidazolium iodide ([Cnmim][I]; n = 3, 4, and 6). The iodide concentration m was 2 ≦ m ≦ 8, which was determined by the molar fraction [Cnmim]+ : [Im]- = 1 : m. By adding iodine, an absorption edge shifted from 282 nm in the UV region to around 600 nm in the visible-light region. The optical bandgaps Eo decreased gradually from 2.3 eV to 1.9 eV with increasing m from 2 to 8. The alkyl-side chain lengths of the cations have little effect on the Eo. This experimental result was confirmed by ab initio molecular orbital calculations. The effects were reflected in the photoconductivity of the ILs, as expected. [C4mim][Im] exhibited greater photo-induced electron generation compared with [C3mim][Im] and [C6mim][Im]. The photoconductivity in both [C3mim][Im] and [C6mim][Im] increased slightly with increasing m. The trend of photoconductivity in [C4mim][Im] exhibited an N-shaped form. The highest photoconductivity 1.6 was observed in [C4mim][I8].

Polyiodides in room-temperature ionic liquids.

Polyiodides, Im-, were formed in room-temperature ionic liquids (RTILs). The RTILs were N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium iodide, [DEME][I], and 1-alkyl-3-methylimidazolium iodide, [Cnmim][I] (n = 1, 2, 3, 4, 6, and 12). In [Cnmim][Im], prepeak and intensity modulation of X-ray diffraction were caused by polyiodides. Above m = 4, polyiodide-mediated local structures were formed, although little alkyl side-chain length, n, dependence was seen in the X-ray diffraction patterns. The viscosity of the mixtures was measured as a function of m to obtain their dynamic properties. The m tendencies of the viscosity and density changed at around m = 4 when fixing n = 4. By 127I-NMR, the local environments of only polyiodides were extracted by changing n, m, and the temperature. Doublet/triplet peak splitting of pure [Cnmim][I] (n = 3, 4, and 6) occurred at low temperature. In [Cnmim][Im] (n = 2 and 4), the effect of polyiodides was clarified from the chemical shifts and peak splitting in the NMR spectra. The experimental results support a Grotthuss-type exchange mechanism of iodide between polyiodides.