Hybrid Heterostructures of a Spin Crossover Coordination Polymer on MoS2 : Elucidating the Role of the 2D Substrate

Controlling the deposition of spin-crossover (SCO) materials constitutes a crucial step for the integration of these bistable molecular systems in electronic devices. Moreover, the influence of functional surfaces, such as 2D materials, can be determinant on the properties of the deposited SCO film. In this work, ultrathin films of the SCO Hofmann-type coordination polymer [Fe(py)2 {Pt(CN)4 }] (py = pyridine) onto monolayers of 1T and 2H MoS2 polytypes are grown. The resulting hybrid heterostructures are characterized by GIXRD, XAS, XPS, and EXAFS to get information on the structure and the specific interactions generated at the interface, as well as on the spin transition. The use of a layer-by-layer results in SCO/2D heterostructures, with crystalline and well-oriented [Fe(py)2 {Pt(CN)4 }]. Unlike with conventional Au or SiO2 substrates, no intermediate self-assembled monolayer is required, thanks to the surface S atoms. Furthermore, it is observed that the higher presence of Fe3+ in the 2H heterostructures hinders an effective spin transition for [Fe(py)2 {Pt(CN)4 }] films thinner than 8 nm. Remarkably, when using 1T MoS2 , this transition is preserved in films as thin as 4 nm, due to the reducing character of this metallic substrate. These results highlight the active role that 2D materials play as substrates in hybrid molecular/2D heterostructures.

Morphological and Physicochemical Properties of Nanostructured Cellulose Obtained through Chemical and Biological Methods

The authors obtained samples of chemically pure, crystalline, micro-and nanostructured cellulose of various modifications using two approaches - biological and chemical. They studied these cellulose samples via scanning electron microscopy (SEM), thermogravimetric analysis, and infrared (IR) spectroscopy. To prepare cellulose microcrystals, they used the mild acid treatment method based on glycerol-acid mixtures for treating cotton fibers. They showed that the chemical processing of cotton fiber ensured its dispersion with generation of microcrystals surrounded by a partially preserved amorphous shell. The authors produced bacterial cellulose (BC) films using the Komagataeibacter xylinus C3 strain in surface cultivation conditions. With a view of obtaining higher-quality SEM images, they applied chemical fixation of lipids and proteins with critical drying to fix the process of nanofiber synthesis by bacterial cells. The two-step fixation method helped find the fibrillar structure of a cellulose film, while the morphology of bacterial cells was not deformed. The authors made a comparative analysis of the IR spectroscopy results between chemically synthesized cellulose microcrystals and BC. The obtained cellulose samples do not contain lignin and hemicellulose, both samples are highly crystalline. The BC has an ordered structure, higher crystallinity and gets carbonized when exposed to air pyrolysis. A thermogravimetric analysis of the samples shows the absence of thermally stable impurities. Both cellulose samples of biological and chemical origin are thermally stable, and the initial decomposition temperature is high enough for cellulose materials. These results show that the authors have managed to create nanocellulose materials that might be potentially applied in various industries, such as pharmaceuticals, functional composites, engineering, etc. The paper contains 6 Figures, 2 Tables, 29 References. The Authors declare no conflict of interest.

Synthesis of Carbon Nanotubes from High-Density Polyethylene Waste

This article presents results of carbon nanotubes synthesis from household high-density polyethylene waste by thermal decomposition. A specific feature of this work is that the decomposition of high-density polyethylene waste and synthesis of carbon nanotubes were carried out in one-step using three-zone chemical vapor deposition reactor. The effect of temperature in the range of 450‒550 °C on decomposition products of high-density polyethylene was investigated. The decomposition products of polyethylene wastes were investigated by IR Fourier spectroscopy. Cenospheres obtained from ash and slag waste from thermal power plants during coal combustion were used as a catalyst for the synthesis of carbon nanotubes. The cenospheres were impregnated with an aqueous solution of iron nitrate. It was found that as a result of thermal decomposition of high-density polyethylene waste at temperature of 450 °C, gaseous carbon-containing compounds are formed, which upon further heating to 800 °C lead to the formation of carbon nanotubes with a diameter of 16‒21 nm on the surface of catalyst. Physicochemical analysis showed that turbostratic carbon is almost completely absent in the formed product. Carbon nanotubes analysis was performed by scanning electron microscopy and Raman spectroscopy.