Imaging and analysis of covalent organic framework crystallites on a carbon surface: a nanocrystalline scaly COF/nanotube hybrid

Synthesis of covalent organic frameworks (COFs) is well-advanced but understanding their nanoscale structure and interaction with other materials remains a significant challenge. Here, we have developed a methodology for the detailed imaging and analysis of COF crystallites using carbon nanotube substrates for COF characterisation. Detailed investigation using powder X-ray diffraction, infrared spectroscopy, mass spectrometry and scanning electron microscopy in conjunction with a local probe method, transmission electron microscopy (TEM), revealed details of COF growth and nucleation at the nanoscale. A boronate ester COF undergoes preferential growth in the a–b crystallographic plane under solvothermal conditions. Carbon nanotubes were found to not impact the mode of COF growth, but the crystallites on nanotubes were smaller than COF crystallites not on supports. COF crystalline regions with sizes of tens of nanometres exhibited preferred orientation on nanotube surfaces, where the c-axis is oriented between 50 and 90° relative to the carbon surface. The COF/nanotube hybrid structure was found to be more complex than the previously suggested concentric core–shell model and can be better described as a nanocrystalline scaly COF/nanotube hybrid

Modern Trends of Organic Chemistry in Russian Universities

© 2018, Pleiades Publishing, Ltd. This review is devoted to the scientific achievements of the departments of organic chemistry in higher schools of Russia within the past decade

PERSPECTIVES OF NANOPOWDERS APPLICATION FOR MANUFACTURING OF MODIFYING ALLOYING COMPOSITIONS

Application of nanomaterials for grain refining of metals and its allac is of great interest as it aimis achieveto higher physicalmechanical properties in finished parts. Analysis shows that to gain high effectiveness of nanoparticles it is important to provide proper input of these particles into alloying alloy. The aim of present research is study of initial nanoparticles structure on the base of titanium, boron, yttrium and carbon nanotubes as well as development of method to manufacture alloying alloys containing nanoparticles.Investigations of nanopowders phase compositions on the base of titanium, boron and yttrium have shown that active elements such as boron carbide, titanium carbide and nitride, yttrium oxide are base compounds of these nanopowders. Powder particles are formed by primary structural elements having mainly plate state (titanium and boron carbides) and containing equiaxial inclusions with sizes of 5–200 nm. Chemical composition of specimens synthesized is uniform and contains 98.0 – 99.5% of main compound.Results of metal-protector and nanoparticles mixing have revealed that the increase of mixing duration from 2 to 6 hours assist to more uniform elements distribution through the pellet volume. Applying extrusion method specimens of alloying alloys have been produced and elements distribution in cross-section and longitudinal directions were determined.Analysis of research implemented has shown that distribution of active nanopowders in matrix is more uniform in extruded alloying alloys specimens compared to ones produced by methods of sintering or pressing of powder mixtures