Herein we present a modified IL route using phosphonium additives, paving the way towards P-and N-co-doped carbonsa class of materials only rarely reported in the literature so far.
36BMP-dca with 40 mol% of tetrabutyl-phosphonium-bromide (TBuPBr) as a phosphorus source was therefore carbonised at 1000 1C in a constant flow of inert gas (see ESI † for details). The black solid product is a carbonaceous material exhibiting a local graphitic order that is limited in its extension. This can be derived from the powder X-ray diffraction (PXRD) patterns showing broadened, but intense, (002) and (100) reflexes typical for a stacking motif in turbostratic-like carbons (compare Fig. S1, ESI †). The black product was also characterised by means of elemental combustion analysis (EA) and inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the degree of heteroatom-doping: 4.1 wt% of N-doping (EA) and 5.7 wt% of P-doping (ICP-OES) are revealed. The material is thus successfully dually doped; especially the remarkably high degree of P-doping compared to other approaches 36-38 is noteworthy and points out the advantages of the method. To also prove the homogeneity of the material, elemental mapping based on energy dispersive X-ray spectroscopy (EDX) and wavelength dispersive X-ray spectroscopy (WDX) was performed. The data are provided in the ESI † (Fig. S2-S5, ESI †), showing clearly that the dopants are spread homogeneously throughout the material. Significant local concentration maxima cannot be found. The binding environments of both N and P could be elucidated by X-ray photoelectron spectroscopy (XPS), and the detailed N1s and P2p scans are depicted in Fig. 1. The results for nitrogen are as expected according to our previous studies:1,2,27,46 three deconvolved contributions appear at 398.13 eV, 400.88 eV and 402.80 eV that can be assigned to pyridinic and pyrollic nitrogen species, quaternary graphitic nitrogen and minor oxidised nitrogen binding motifs (due to oxidative processes on the surface of the materials), respectively. 16,34,49,50 The N doping thus occurs with N atoms firmly bound to the carbon backbone. To clearly assign the P2p XPS scan to certain chemical environments is however more difficult. Fig. 1 Deconvolved XPS scans of the N1s and P2p orbitals of the material.