Linking the Defective Structure of Boron-Doped Carbon Nano-Onions with Their Catalytic Properties: Experimental and Theoretical Studies.

Defects are widely present in nanomaterials, and they are recognized as the active sites that tune surface properties in the local region for catalysis. Recently, the theory linking defect structures and catalytic properties of nanocatalysts has been most commonly described. In this study, we prepared boron-doped carbon nano-onions (B-CNOs) by applying an annealing treatment of ultradispersed nanodiamond particles and amorphous boron. These experimental conditions guarantee doping of CNOs with boron atoms in the entire carbon nanostructure, thereby ensuring structural homogeneity. In our research, we discuss the correlations between defective structures of B-CNOs with their catalytic properties toward SO2 and tert-butanol dehydration. We show that there is a close relationship between the catalytic properties of the B-CNOs and the experimental conditions for their formation. It is not only the mass of the substrates used for the formation of B-CNOs that is crucial, that is, the mass ratio of NDs to amorphous B, but also the process, including temperature and gas atmosphere. As it was expected, all B-CNOs demonstrated significant catalytic activity in HSO3- oxidation. However, the subsequent annealing in an air atmosphere diminished their catalytic activity. Unfortunately, no direct relationship between the catalytic activity and the presence of heteroatoms on the B-CNO surface was observed. There was a linear dependence between catalytic activity and Raman reactivity factors for each of the B-CNO materials. In contrast to SO2 oxidation, the B-CNO-a samples showed higher catalytic activity in tert-butanol dehydration due to the presence of Brønsted and Lewis acid sites. The occurence of three types of boron-Lewis sites differing in electron donor properties was confirmed using quantitative infrared spectroscopic measurements of pyridine adsorption.

What Is the Value of Water Contact Angle on Silicon?

Silicon is a widely applied material and the wetting of silicon surface is an important phenomenon. However, contradictions in the literature appear considering the value of the water contact angle (WCA). The purpose of this study is to present a holistic experimental and theoretical approach to the WCA determination. To do this, we checked the chemical composition of the silicon (1,0,0) surface by using the X-ray photoelectron spectroscopy (XPS) method, and next this surface was purified using different cleaning methods. As it was proved that airborne hydrocarbons change a solid wetting properties the WCA values were measured in hydrocarbons atmosphere. Next, molecular dynamics (MD) simulations were performed to determine the mechanism of wetting in this atmosphere and to propose the force field parameters for silica wetting simulation. It is concluded that the best method of surface cleaning is the solvent-reinforced de Gennes method, and the WCA value of silicon covered by SiO2 layer is equal to 20.7° (at room temperature). MD simulation results show that the mechanism of pure silicon wetting is similar to that reported for graphene, and the mechanism of silicon covered by SiO2 layer wetting is similar to this observed recently for a MOF.

Thermodynamics of the CMMS approach and carbon surface chemistry in SO2 adsorption.

In this study, we develop the equation describing the enthalpy of adsorption corresponding to the cooperative multimolecular sorption approach proposed by Malakhov and Volkov. For different shapes of adsorption isotherms plotted from this model (and analyzed by Rutherford and Coons), we generated the corresponding enthalpy of adsorption curves. We also discuss other enthalpy plot shapes predicted by the CMMS. The new relations are verified for simultaneous description of SO2 adsorption data, and enthalpy of sorption, measured on graphitized carbon black and on activated carbon. Finally, we apply the CMMS model to description of adsorption data of SO2 measured on the series of modified activated carbons. The porosity of adsorbents was characterized via description of low-temperature N2 isotherms applying the method of Nguyen and Do. Oxygen content in carbons was measured applying the elemental analysis. From the results of the correlations between the parameters of the CMMS and elemental analysis data, it is concluded that the interaction between SO2 molecules and carbon surface oxygen groups is crucial during adsorption of this adsorbate. Our results explain and summarize up the conclusions concerning the effect of carbon surface nitrogen functionalities on SO2 sorption mechanism presented by other authors. Finally, we conclude that the CMMS approach can be successfully applied to the description of this process.