Classical Concept of Semiconductor Heterojunctions in the Approach to Nanohybrid Catalysts.

Recalling the well-established theory of heterojunction formation between two different semiconductors or a semiconductor and a metal can elucidate the remarkable catalytic properties of nanohybrid systems employed in thermal catalysis. Upon the creation of heterojunctions, involved nanoparticles or nanometer-sized thin films, as a result of their dimensions, may become entirely filled with space charges generated from the development of depletion or accumulation regions. This phenomenon dictates the nature of catalytic sites and consequently affects the catalytic activity of such nanohybrids. The following perspective presents this concept and examples of experimental results that substantiate its validity, along with an extremely effective tool, cold plasma deposition, for designing and realizing in a controlled manner the structure of nanohybrids with heterojunctions. This approach will undoubtedly broaden the view of the contemporary "alchemy" of nanocatalysts.

Tailoring the active phase of CoO-based thin-film catalysts in order to tune selectivity in CO2 hydrogenation.

In this study, we prepared CoO-based thin films deposited on Kanthal steel wire gauze meshes by plasma-enhanced chemical vapor deposition. X-ray photoelectron spectroscopy (XPS) analysis revealed a structure characterized by a combination of cobalt oxide and metallic cobalt embedded within a carbon matrix. Our primary objective was to gain insights into the roles of Co0 and CoO in CO2 hydrogenation reactions. To achieve this, the performance of the thin-film CoO-based catalyst with an initial atomic ratio of CoO/Co0 at 10.2 was compared with two series of the thin-film catalysts that underwent pre-reduction processes at 350 °C for durations of 30 and 60 minutes, resulting in atomic ratios of CoO/Co0 at 3.1 and 1.1, respectively. Subsequently, catalytic tests were conducted in a continuous flow stirred tank reactor operating at temperatures ranging from 250 °C to 400 °C. Our findings indicate that CoO plays a significant role in activating the CO2 methanation reaction which can be due to the high hydrogen coverage of CoO, while Co0 is the active phase in the reverse water-gas shift reaction. Results highlight the importance of oxidized cobalt for hydrogen adsorption and dissociation in CO2 hydrogenation for CH4 formation.

Carbon dioxide removal from flue gases by absorption/ desorption in aqueous diethanolamine solutions.

The carbon dioxide (CO2) desorption rate from CO2- loaded aqueous diethanolamine (DEA) solutions was measured using a stirred cell with a flat gas-liquid interface. The measurements were performed in the temperature range of 293.15-313.15 K and an amine concentration range of 10-20% mass DEA. Measurements were based on a semibatch isothermal absorption of the gas until the equilibrium state was reached, followed by desorption, which was initiated by the pressure release in the system. A simplified mass transfer model based on the film theory coupled with CO2, mass balance was developed to interpret the experimental data. On the basis of the proposed model, the initial mass transfer rates were calculated from the experimental results. The calculated initial desorption rates enabled estimation of the enhancement factor for CO2 mass transfer from aqueous DEA solutions. Analysis of the experimental data showed that desorption took place in the diffusive mass transfer regime.

Low-Temperature Plasma Modification of Styrene-Butadiene Block Copolymer Surfaces for Improved Adhesion-A Kinetic Approach.

This paper proposed a kinetic model that can describe the changes in the adhesion properties of styrene-butadiene (SBS) block copolymer surfaces under the influence of low-temperature plasma treatment. As a measure of these changes, the peel strength of joints formed between the copolymer surface and the polyurethane adhesive was chosen. Five types of low-temperature low-pressure RF plasma, two inert plasmas (Ar and He), and three reactive plasmas (O2, CO2, and CCl4) were tested. It was found that for all these types of plasma, the peel strength with the plasma treatment time first increases rapidly reaching a maximum value, and then there is a visible decrease in peel strength, after which the peel strength increases again. This dependence of the peel strength on the plasma treatment time is very well described by the proposed model, which considers three processes: (1) the generation of radical states followed by the creation of functional groups involved in the adhesive bonding process, (2) the surface cross-linking that decreases the concentration of these functional groups, and (3) the formation of nano-roughness. The model analysis revealed differences between the action of reactive and inert plasmas in the SBS surface cross-linking mechanism and preferential etching process, as well as differences in the generation of radical states between the O2 plasma (electron process) and other plasmas tested (ionic processes).