Mass spectrometry in art conservation-With focus on paintings.

Conservation of historic artifacts has been a multidisciplinary field from its very beginning. Traditionally, it has been and still is associated with the history of art. It applies knowledge from technical and basic sciences, adapting their solutions to its goals. At present, however, a new tendency is clearly emerging-scientific research is starting to play an increasingly important role not only as a service, but also by proposing new solutions both in the traditional conservation areas and in new areas of conservation activities. The above trend opens up new perspectives for the field of preservation of our heritage but may also create new threats. Therefore, the conservators' caution in introducing new technologies should always be justified; after all, they are responsible for the effects of any activities on the historic objects. This, quite selective review, discusses application of mass spectrometry techniques for the detection of various components that are important to the conservators of our heritage with particular focus on paintings. The text also contains some basic knowledge of technical details to introduce the methodology to a broader group of professionals.

Graphitic nitrogen in carbon catalysts is important for the reduction of nitrite as revealed by naturally abundant 15N NMR spectroscopy.

Metal-free nitrogen-doped carbon is considered as a green functional material, but the structural determination of the atomic positions of nitrogen remains challenging. We recently demonstrated that directly-excited solid state 15N NMR (ssNMR) spectroscopy is a powerful tool for the determination of such positions in N-doped carbon at natural 15N isotope abundance. Here we report a green chemistry approach for the synthesis of N-doped carbon using cellulose as a precursor, and a study of the catalytic properties and atomic structures of the related catalyst. N-doped carbon (NH3) was obtained by the oxidation of cellulose with HNO3 followed by ammonolysis at 800 °C. It had a N content of 6.5 wt% and a surface area of 557 m2 g-1, and 15N ssNMR spectroscopy provided evidence for graphitic nitrogen besides regular pyrrolic and pyridinic nitrogen. This structural determination allowed probing the role of graphitic nitrogen in electrocatalytic reactions, such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and nitrite reduction reaction. The N-doped carbon catalyst (NH3) showed higher electrocatalytic activities in the OER and HER under alkaline conditions and higher activity for nitrite reduction, as compared with a catalyst prepared by the carbonization of HNO3-treated cellulose in N2. The electrocatalytic selectivity for nitrite reduction of the N-doped carbon catalyst (NH3) was directly related to the graphitic nitrogen functions. Complementary structural analyses by means of 13C and 1H ssNMR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and low-temperature N2 adsorption were performed and provided support to the findings. The results show that directly-excited 15N ssNMR spectroscopy at natural 15N abundance is generally capable of providing information on N-doped carbon materials if relaxation properties are favorable. It is expected that this approach can be applied to a wide range of solids with an intermediate concentration of N atoms.