3,5,11,13-Tetraazacycl[3.3.3]azine: theoretical (ab initio) and experimental (x-ray and ultraviolet photoelectron spectroscopy) studies of the electronic structure

The characterization of organic nitrogen and sulfur functional groups in coals after biomethane production

To study the change characteristics of nitrogen and sulfur functional types in the raw coal and coal residues after anaerobic fermentation, three different rank coals from Baiyinhua mine (BY coal), Qianqiu mine (QQ coal), and Malan mine (ML coal) in China were collected and treated with methanogenic microorganisms, then X-ray photoelectron spectroscopy (XPS) was used to test the nitrogen and sulfur functional types in raw coals and coal residues. The results show that the pyrrolic nitrogen (N-5) and aromatic sulfur are the main nitrogen type and sulfur type in three coals. The N-5 increases by 17.42% in BY coal residue and decreases by 2.37% and 8.51% in QQ and ML coal residues, respectively. The pyridinic nitrogen (N-6) in BY, QQ, and ML coal residues decreases by 2.18%, 5.44%, and 2.75%, respectively. The aromatic sulfur increases by 2.13%, 3.14%, and 4.02% in BY, QQ, and ML coal residues, respectively. The aliphatic sulfur has obvious changes in BY and QQ coal residues with the increment of 9.17% and decrement of 11.64%, respectively. The results reveal that the nitrogen and sulfur types have changed in the coal residues after the biomethane production, and the instable types such as N-5 and aliphatic sulfur have obvious changes in the low-rank BY and QQ coals. The research provides a sight to the changes about nitrogen and sulfur types after biomethane yield and more deep thoughts about the clean and effective utilization of coals.

Pentagons and Heptagons on Edges of Graphene Nanoflakes Analyzed by X-ray Photoelectron and Raman Spectroscopy

Identifying pentagons and heptagons in graphene nanoflake (GNF) structures at the atomic scale is important to completely understand the chemical and physical properties of these materials. Herein, we used X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy to analyze the spectral features of GNFs according to the position of pentagons and heptagons introduced onto their zigzag and armchair edges. The XPS peak maxima were shifted to higher binding energies by introducing the pentagons or heptagons on armchair rather than zigzag edges, and the structures could be distinguished depending on the positions of the introduced pentagons or heptagons. Raman spectroscopic analyses also revealed that the position of edges with introduced pentagons or heptagons could also be identified using Raman spectroscopy, with characteristic bands appearing at 800-1200 cm^-1, following the introduction of either pentagons or heptagons on armchair edges. This precise spectroscopic identification of pentagons and heptagons in GNFs provides the groundwork for the analysis of graphene-related materials.

Heptagons in the Basal Plane of Graphene Nanoflakes Analyzed by Simulated X-ray Photoelectron Spectroscopy

The performance of graphene-based electronic devices depends critically on the existence of topological defects such as heptagons. Identifying heptagons at the atomic scale is important to completely understand the electronic properties of these materials. In this study, we report an atomic-scale analysis of graphene nanoflakes with two to eight isolated or connected heptagons, using simulated C 1s X-ray photoelectron spectroscopy (XPS) to estimate the XPS profiles depending on the density and the position of the heptagons. The introduction of up to 24% of isolated heptagons shifted the peak position toward high binding energies (284.0 to 284.3 eV), whereas the introduction of up to 39% of connected heptagons shifted the calculated peak position toward low binding energies (284.0 to 283.5 eV). The presence of heptagons also influenced the full width at half-maximum (FWHM). The introduction of 24% of isolated heptagons increased the FWHMs from 1.25 to 1.50 eV. However, the introduction of connected heptagons did not increase the FWHMs above 1.40 eV. The FWHMs increased to 1.40 eV for 19% of connected heptagons, but did not increase further as the percentage of connected heptagons increased to 39%. Based on the calculated results, the XPS profiles of graphene nanoflakes containing heptagons with different densities and positions can be obtained. Our precise identification of heptagons in graphene nanoflakes by XPS lays the groundwork for the analysis of graphene.

New Insights into Co-pyrolysis among Graphitic Carbon Nitride and Organic Compounds: Carbonaceous Gas Fragments Induced Synthesis of Ultrathin Mesoporous Nitrogen-Doped Carbon Nanosheets for Heterogeneous Catalysis

N-doped carbon materials are well known as promising metal-free catalysts and applied in innumerable industrial synthetics. However, most of the N-doped carbon materials obtained by conventional synthetic means exhibit generally low mesoporosity, and their reported pore volumes reached only 1-3 cm³ g^-1, which greatly limits their further industrial application in heterogeneous catalysis. Especially for oxidation reaction of alkylbenzenes, this type of reaction is almost always accompanied by many different byproducts, while the reaction activity and selectivity are mainly affected by mesoporosity of catalysts. Traditionally, graphitic carbon nitride (GCN) is commonly considered as a self-sacrificed nitrogen source together with multifarious organic compounds to obtain N-doped carbon materials by a co-pyrolysis process. However, the mechanisms of formation process are still complex and uncontrollable to date. In this work, we present a novel co-pyrolysis synthetic strategy by a facile chemical vapor deposition method for preparing a series of ultrathin N-doped carbon nanosheets with high mesoporosity. More importantly, it is found that GCN containing abundant hydrogen bonds can be irreversibly anchored by carbonaceous gas fragments (C_xH_y⁺) released from various organic substances via thermogravimetry-differential thermal analysis coupled with mass spectrometry and X-ray photoelectron spectroscopy analysis, and the C_xH_y⁺ fragments exhibit a non-negligible role during the transformation. Our results further demonstrated that the residue of incompletely decomposed GCN is a key point to enlarge porosity in final products which are obtained via mixing pyrolysis between an organic precursor and GCN (or GCN precursors). Benefitting from the outstanding mesoporosity and ultrathin morphology, the representative ABCNS-900 exhibits excellent catalytic performance for oxidizing ethylbenzene to acetophenone with extremely low dosage and high selectivity. Our findings show a universal synthetic strategy for ultrathin N-rich carbon nanosheets with a high mesopore volume, further promoting the application of N-doped carbon materials in heterogeneous catalytic industry.

Distinguishing Zigzag and Armchair Edges on Graphene Nanoribbons by X-ray Photoelectron and Raman Spectroscopies

Graphene nanoribbons (GNRs) have recently emerged as alternative 2D semiconductors owing to their fascinating electronic properties that include tunable band gaps and high charge-carrier mobilities. Identifying the atomic-scale edge structures of GNRs through structural investigations is very important to fully understand the electronic properties of these materials. Herein, we report an atomic-scale analysis of GNRs using simulated X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Tetracene with zigzag edges and chrysene with armchair edges were selected as initial model structures, and their XPS and Raman spectra were analyzed. Structurally expanded nanoribbons based on tetracene and chrysene, in which zigzag and armchair edges were combined in various ratios, were then simulated. The edge structures of chain-shaped nanoribbons composed only of either zigzag edges or armchair edges were distinguishable by XPS and Raman spectroscopy, depending on the edge type. It was also possible to distinguish planar nanoribbons consisting of both zigzag and armchair edges with zigzag/armchair ratios of 4:1 or 1:4, indicating that it is possible to analyze normally synthesized GNRs because their zigzag to armchair edge ratios are usually greater than 4 or less than 0.25. Our study on the precise identification of GNR edge structures by XPS and Raman spectroscopy provides the groundwork for the analysis of GNRs.

Development of emissive aminopentaazaphenalene derivatives employing a design strategy for obtaining luminescent conjugated molecules by modulating the symmetry of molecular orbitals with substituent effects

This communication describes the transformation of a non-emissive heterocycle into a luminophore via modulation of molecular orbitals by the introduction of dialkylamine group.

Color tuning of alternating conjugated polymers composed of pentaazaphenalene by modulating their unique electronic structures involving isolated-LUMOs

Pentaazaphenalene-containing polymers with unique conjugated systems were synthesized. Various colors can be observed from the polymer solutions.