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Chemical surface functionalization of carbon nanodots (CNDs) offers a valuable opportunity to tailor multifunctionality in these nanocarbons, by engineering the composition of their molecular surface. Therefore, it is important to elucidate the type and amount of CNDs surface functionalization to be able to design their properties accurately. CNDs are often functionalized through amide coupling without validating the degree of surface functionalization. As a measure of surface functionalization, the amounts of primary amines via Kaiser test (KT) or imine reactions of the bare CNDs is often considered. However, this may lead to overestimating the degree of surface functionalization obtained by the pure amide coupling due to different reaction mechanisms and involved intermediates. Herein, four different CNDs prepared by microwave‐assisted synthesis from arginine or citric acid with varying amounts of ethylenediamine are presented. We resorted to combining physicochemical methods to provide elemental, structural, and optical information. By that, we developed a method to quantify the degree of surface functionalization by amide coupling and show that the surface functionalization is lower than anticipated. Comparing experimental optical features of the CNDs with different computed model systems enables us to provide a more advanced vision of structure‐property relationships in these still elusive nanocarbons. [ABSTRACT FROM AUTHOR]

Non-graphitic carbons (NGCs), such as glass-like carbons, pitch cokes, and activated carbon consist of small graphene layer building stacks arranged in a turbostratic order. Both structure features, including the single graphene sheets as well as the stacks, possess structural disorder, which can be determined using wide-angle X-ray or neutron scattering (WAXS/WANS). Even if WANS data of NGCs have already been extensively reported and evaluated in different studies, there are still open questions with regard to their validation with WAXS, which is usually used for routine characterization. In particular, using WAXS for the damping of the atomic form factor and the limited measured range prevent the analysis of higher-ordered reflections, which are crucial for determining the stack/layer size (La, Lc) and disorder (σ1, σ3) based on the reflection widths. Therefore, in this study, powder WANS was performed on three types of carbon materials (glass-like carbon made out of a phenol-formaldehyde resin (PF-R), a mesophase pitch (MP), and a low softening-point pitch (LSPP)) using a beamline at ILL in Grenoble, providing a small wavelength and thus generating WANS data covering a large range of scattering vectors (0.052 Å−1 < s < 3.76 Å−1). Merging these WANS data with WANS data from previous studies, possessing high resolution in the small s range, on the same materials allowed us to determine both the interlayer and the interlayer structure as accurately as possible. As a main conclusion, we found that the structural disorder of the graphene layers themselves was significantly smaller than previously assumed. [ABSTRACT FROM AUTHOR]

A parametrization algorithm to determine chord-length distributions (CLD) from small-angle scattering data is used to characterize details of the pore structure, pore size, and morphology of porous carbon materials. This approach is applied to various carbon processing procedures, such as steam activation, tempering, and contacting with polymer binders. It is found that this CLD method reveals, compared to previous small angle x-ray scattering evaluation approaches, fine changes in the pore structure and morphology of porous carbons with higher accuracy and physical significance. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

CarbX is an open‐source program designed for the analysis of wide‐angle X‐ray scattering (WAXS) data of non‐graphitic carbons (NGCs). As knowledge of their microstructure is crucial for tuning desired properties, an `easy‐to‐use' analysis tool is essential for effective research in this field. Using CarbX one can retrieve up to 14 microstructural parameters from a single WAXS pattern without having to master the associated complicated mathematics. CarbX was developed to serve as a convenient graphical user interface, translating a complex evaluation algorithm introduced by Ruland & Smarsly [J. Appl. Cryst. (2002), 35, 624–633] into software which can be operated by non‐experts. Besides the core functionality of displaying data and manually fitting WAXS curves by user‐editable parameters, CarbX offers additional features such as visualization of the deviation between data and fit, the possibility to choose the wavelength used in the measurement, and automatic fitting (using Wolfram Mathematica). One of the key features of the comfortable usability is the functionality to display templates. This allows the user to visually compare measurement data with typical types of NGC WAXS curves which are presented graphically around the measurement data. The authors believe that this program will provide a useful tool for scientists dealing with the characterization of NGCs. [ABSTRACT FROM AUTHOR]

A detailed study is given on the synthesis of a hierarchical porous carbon, possessing both meso- and macropores, using a mesophase pitch (MP) as the carbon precursor. This carbon material is prepared by the nanocasting approach involving the replication of a porous silica monolith (hard templating). While this carbon material has already been tested in energy storage applications, various detailed aspects of its formation and structure are addressed in this study. Scanning electron microscopy (SEM), Hg porosimetry and N2 physisorption are used to characterize the morphology and porosity of the carbon replica. A novel approach for the detailed analysis of wide-angle x-ray scattering (WAXS) from non-graphitic carbons is applied to quantitatively compare the graphene microstructures of carbons prepared using MP and furfuryl alcohol (FA). This WAXS analysis underlines the importance of the carbon precursor in the synthesis of templated porous carbon materials via the nanocasting route. Our study demonstrates that a mesophase pitch is a superior precursor whenever a high-purity, low-micropore-content and well-developed graphene structure is desired. [ABSTRACT FROM AUTHOR]

Abstract: Non-graphitic carbon materials produced by pyrolyzing wood at temperatures from 400 to 2400°C and various types of commercial carbon fibers were examined by X-ray diffraction and Raman spectroscopy. The specimens cover a wide range of crystallite sizes L a, in particular also very small sizes below 2nm. The X-ray data were evaluated using the Scherrer equation and by an advanced approach using full curve fitting. The ratio of the D/G band intensities was determined from the Raman data by different evaluation techniques. A critical assessment of the classical linear relationship between 1/L a and the D/G ratio shows that the relationship breaks down for crystallite sizes below 2nm in accordance with recent theoretical predictions. The results are compared with data from the literature, showing that there are additional discrepancies between the data from various carbon types at large L a due to different methods of data evaluation. [Copyright &y& Elsevier]

In 1987, Rius, Plana & Palanques [J. Appl. Cryst. (1987), 20,457-460] devised an X-ray powder diffraction method based on the 'least-squares' determination of calibration constants using only the diffracted intensities and the calculated absorption coefficients of the components. This method was developed for 'infinitely thick' samples, a condition which is seldom met by airborne particulates because of the small amount of material normally available. Since the analysis of such samples may become one of the principal applications of the method, this condition represents a serious limitation. The simplest way to overcome this limitation is by correcting the measured intensities. This can be done either by direct measurement of the sample transmission, or alternatively, by using refined transmission values. In the latter case no experimental values are necessary. With the help of some test calculations, the viability of both possibilities has been explored. [ABSTRACT FROM AUTHOR]

The preparation of carbons for technical applications is typically based on a treatment of a precursor, which is transformed into the carbon phase with the desired structural properties. During such treatment the material passes through several different structural stages, for example, starting from precursor molecules via an amorphous phase into crystalline-like phases. While the structure of non-graphitic and graphitic carbon has been well studied, the transformation stages from molecular to amorphous and non-graphitic carbon are still not fully understood. Disordered carbon often contains a mixture of sp3-, sp2-and sp1-hybridized bonds, whose analysis is difficult to interpret. We systematically address this issue by studying the transformation of purely sp3-hybridized carbons, that is, nanodiamond and adamantane, into sp2-hybridized non-graphitic and graphitic carbon. The precursor materials are thermally treated at different temperatures and the transformation stages are monitored. We employ Raman spectroscopy, WAXS and TEM to characterize the structural changes. We correlate the intensities and positions of the Raman bands with the lateral crystallite size L a estimated by WAXS analysis. The behavior of the D and G Raman bands characteristic for sp2-type material formed by transforming the sp3-hybridized precursors into non-graphitic and graphitic carbon agrees well with that observed using sp2-structured precursors. Image 1 [ABSTRACT FROM AUTHOR]

We study the transformation from molecular to crystalline of (non-)graphitic carbons synthesized from organic precursors by heat-treatment. Easy assessment of structural properties resulting from heat-treatment protocols is mandatory for industrial process monitoring. We demonstrate that Raman spectroscopy, in particular, the Raman lineshape analysis of G and D mode, offers quick assessment of the average sheet size of such carbons. We validate this method by performing Raman, WAXS and EPR measurements of series of resin and pitch-based carbons synthesized. The crystallite sizes of the WAXS analysis for the individual samples are related to corresponding positions and linewidths of G and D Raman modes and show excellent agreement between experiment and modelling from large sizes down to 4 nm. The theoretical master curves are independent of the precursor used in the synthesis, in contrast to models for the intensity ratio of D and G band versus size. We show that the latter are not universally valid and differ for each class of precursors. For sizes below 4 nm, our lineshape model fails as it is based on the bandstructure and phonon dispersions of ideal graphene. Thus, 4 nm corresponds to the fundamental transition from molecular to crystalline character for non-graphitic carbons. Image 1 [ABSTRACT FROM AUTHOR]

The analysis of the wide-angle X-ray scattering (WAXS) data of non-graphitic carbons is challenging due to the broad and overlapped ( hk)- and (00 l)-reflections. A recently developed advanced analysis method developed by Ruland and Smarsly allows for the fitting of the WAXS data by a continuous model function, providing a detailed insight into the sp2-carbon microstructure. Obtaining parameters like the graphene layer extent La, the average stack height Lc and disorder effects permits the quantification of microstructural features. Firstly, this publication gives a brief review over historical und recent developments regarding the evaluation of the WAXS of disordered carbons. Secondly, the applicability of this algorithm to carbon samples possessing a substantial degree of disorder is tested by investigating activated carbons, heat treated coal tar pitch and furfuryl alcohol. It is seen that several structural parameters are determined with reasonable accuracy and thereby the influence of the precursor and the temperature on the resulting carbon microstructure is identified. The decrease in disorder within the 2D graphene lattice and in the stacking of the layers at higher synthesis temperatures is quantified. Moreover, this study reveals that the graphene layer extent La is only about a few nanometers in size, showing that typical non-graphitic carbons used for diverse applications possess quite small dimensions of graphene stacks. [ABSTRACT FROM AUTHOR]