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The photochemical reaction of iodine and graphene induces strong new Raman modes due to the formation of trans‐oligoene substructures in graphene domains. This unique reactivity was demonstrated before on defect‐free graphene, however leaving the influence of e. g. carbon vacancies, unexplored. Here, we investigate the photochemical reaction applied on graphene with varying average distances of lattice defects and statistically analyze the characteristic Raman modes which develop with the iodination reaction. We show that the iodination reaction does not lead to Raman‐active defects and thus, the newly formed trans‐oligoene substructures do not contribute to the D‐mode of graphene. A statistical analysis reveals the correlation between the average distance of lattice defects and the intensity of the v1‐mode. For defective graphene with average defect distances below ~1 nm no new Raman modes evolve, which is the lower limit of the substructure size probed at 532 nm and explains why this observation was not possible before using common graphene oxide as graphene source. [ABSTRACT FROM AUTHOR]

Hybridizing graphene and molecules possess a high potential for developing materials for new applications. However, new methods to characterize such hybrids must be developed. Herein, the wet‐chemical non‐covalent functionalization of graphene with cationic π‐systems is presented and the interaction between graphene and the molecules is characterized in detail. A series of tricationic benzimidazolium salts with various steric demand and counterions was synthesized, characterized and used for the fabrication of graphene hybrids. Subsequently, the doping effects were studied. The molecules are adsorbed onto graphene and studied by Raman spectroscopy, XPS as well as ToF‐SIMS. The charged π‐systems show a p‐doping effect on the underlying graphene. Consequently, the tricationic molecules are reduced through a partial electron transfer process from graphene, a process which is accompanied by the loss of counterions. DFT calculations support this hypothesis and the strong p‐doping could be confirmed in fabricated monolayer graphene/hybrid FET devices. The results are the basis to develop sensor applications, which are based on analyte/molecule interactions and effects on doping. [ABSTRACT FROM AUTHOR]

Abstract: Controlled covalent functionalization of graphene remains a challenging task owing to the heterogeneous nature of materials. Functionalization approaches for graphene either lack in quantifying the degree of functionalization or they do not discriminate between covalent and non‐covalent functionalization. Here, graphite is oxidized and exfoliated in a three‐step procedure and subsequently reduced and functionalized by hexylation. Although Raman spectroscopy is powerful to determine the degree of in‐plane lattice defects (θLD) and functionalization (θFD), the method fails at detecting introduced hexyl groups at a concentration of about 0.03 %, next to the pre‐existing in‐plane lattice defects of 0.7 %. However, sensitive thermogravimetric analysis coupled with gas chromatography and mass spectrometry (TGA‐GC/MS) can prove the hexylation reaction. The efficiency of functionalization is comparable to reductive functionalization of pristine chemical vapor deposition (CVD)‐graphene and bulk graphite. [ABSTRACT FROM AUTHOR]

Abstract: Graphene oxide possesses defects of various kinds. The structure of graphene oxide is reviewed with focus on defects in the σ‐framework of the hexagonal lattice. We clearly distinguish between on‐plane functionalization defects and in‐plane lattice defects. Moreover, vacancy defects and hole defects are discriminated. In this context, Raman spectroscopy is introduced as a sensitive method for detecting and quantifying defects. Moreover, the visualization of in‐plane lattice defects by transmission electron microscopy (TEM) at atomic resolution is introduced. Understanding the type and density of defects in graphene oxide bears the potential for advancing the field of research while considering the specific types of defects as structural motifs. [ABSTRACT FROM AUTHOR]

Graphene production by wet chemistry is an ongoing scientific challenge. Controlled oxidation of graphite introduces oxo functional groups; this material can be processed and converted back to graphene by reductive defunctionalization. Although thermal processing yields conductive carbon, a ruptured and undefined carbon lattice is produced as a consequence of CO2 formation. This thermal process is not understood, but it is believed that graphene is not accessible. Here, we thermally process oxo-functionalized graphene (oxo-G) with a low (4-6 %) and high degree of functionalization (50-60 %) and find on the basis of Raman spectroscopy and transmission electron microscopy performed at atomic resolution (HRTEM) that thermal processing leads predominantly to an intact carbon framework with a density of lattice defects as low as 0.8 %. We attribute this finding to reorganization effects of oxo groups. This finding holds out the prospect of thermal graphene formation from oxo-G derivatives. [ABSTRACT FROM AUTHOR]

In this study, we use our recently prepared graphene oxide (GO) with an almost intact σ-framework of carbon atoms (ai-GO) to probe the thermal stability of the carbon framework for the first time. Ai-GO exhibits few defects because CO2 formation is prevented during synthesis. Ai-GO was thermally treated before chemical reduction and the resulting defect density in graphene was subsequently determined by statistical Raman microscopy. Surprisingly, the carbon framework of ai-GO is stable in thin films up to 100 °C. Furthermore, we find evidence for an increase in the quality of ai-GO upon annealing at 50 °C before reduction. The carbon framework of GO prepared according to the popular Hummers' method (GO-c) appears to be less stable and decomposition starts at 50 °C, which is qualitatively indicated by CO2-trapping experiments in μm-thin films. Information about the stability of GO is important for storing, processing, and using GO in many applications. [ABSTRACT FROM AUTHOR]

Twenty-two different graphite grades of the familiesnatural, synthetic,intercalated,expanded,amorphous,andturbostratic graphite, as well asplateletsandactivated carbon,were analyzed on their dispersibility inN-methylpyrrolidone, cyclohexylpyrrolidone and water-sodium cholate solution. They were characterized for their properties (grain size, density, purity, surface area, pH in water) and morphology. Thermogravimetric analysis, Raman spectroscopy studies, and electrical conductivity measurements were also used. XRPD followed by a Rietveld refinement provided information on the amounts of the rhombohedral (3R) and hexagonal (2H) phases for the crystalline part of the material and the interlayer distances. The properties of graphites favoring better dispersibility are: small grain size and bulk density, neutral pH in water. The electrical conductivity in inversely proportional to the RamanD-band intensity and is highest for the graphites with shortest interlayer spacing. TheD-,G- and2D-bands in the Raman spectra of graphites are in an exponential relation. [ABSTRACT FROM AUTHOR]

Abstract: Efficiently reducible graphene oxide (GO) was obtained, even if a high degree of functionalization is present. Graphite with few defects was used as starting material and oxidized according to Hummer’s method. An extremely high I D/I G ratio for rGO of 2.8 (532nm) was observed in the Raman spectrum as a consequence of the lower defect density in GO. It was also possible to demonstrate the impact of local defects on the structure in rGO by local laser exposure experiments on single graphene oxide flakes. Raman spectroscopy can visualize the laser impact by I D/I G ratio measurements. [Copyright &y& Elsevier]

The efficiency of reducing agents for the reduction of graphene oxide (GO) could be probed by scanning Raman spectroscopy. A film of graphene flakes derived from GO was probed to be graphene like. We also focus on the surface quality of reduced GO (rGO). [ABSTRACT FROM AUTHOR]

Etching pores in the basal plane of graphene by wet-chemical methods with a certain size-control reflects a synthetic challenge. Here, a facile and controllable method is presented to produce solution-processible porous-graphene derivatives. The derivative of graphene oxide, here oxo-functionalized graphene (oxo-G) with a controlled density of in-plane vacancy defects is chosen as a precursor. Hydroxyl radicals are generated, which etch pores into the basal plane of oxo-G, preferably starting at defect sites. Thereby, solution-processible flakes of oxo-G with μm-size lateral dimensions and pores with tunable diameters between 5 nm and 500 nm are accessible. Moreover, a plausible mechanism for the growth of pores is proposed based on AFM, TEM, UV–vis spectroscopy, FTIR spectroscopy, XPS, solid-state NMR spectroscopy and statistical Raman spectroscopy. In first approximation, the electrophilic addition and oxidation reaction between hydroxyl radicals and oxo-G close to defect-sites is the basis for etching. The porous graphene materials may act as membranes or tunable two-dimensional materials. [Display omitted] • A facile and controllable method is presented to prepare solution-processible porous-graphene derivatives. • The mechanism of the growth of pores is proposed as a defect-driven process. • The as-prepared porous graphene derivatives is a starting point to develop a controlled chemistry at the rims of pores. [ABSTRACT FROM AUTHOR]