Tuning of adsorption energies of CO2 and CH4 in borocarbonitrides BxCyNz: A first-principles study

Theoretical Investigation of the BCN Monolayer and Their Derivatives for Metal-free CO2 Photocatalysis, Capture, and Utilization

In recent years, carbon capture and utilization (CCU) has been explored as an attractive solution to global warming, which is mainly caused by increasing CO2 emission levels. Many functional materials have been developed for removing atmospheric CO2 and converting it to more useful forms of carbon. Traditional metallic photocatalytic species have drawbacks-photocorrosion, low visible-light absorbance, and environmental damage; therefore, metal-free materials have attracted considerable research attention. In particular, boron nitride (BN) possesses unique B-N bonds, characterized by a large difference in the electronegativity of atoms that facilitates CO2 reduction, and catalytic CO2 reduction by boron carbon nitride (BCN) has been demonstrated under visible light; hence, these two materials can be considered potential CO2 reduction photocatalysts. However, further modification of the materials and their applicability to other CCU applications have not been extensively explored. Therefore, we decided to investigate the modification of BCN monolayers, with the aim of ensuring that the properties of the materials are better suited, first, to the requirements of CO2 photocatalysis, and second, to those of carbon capture or other optoelectronic applications. In this study, we considered various novel BCN monolayers, based on modification via metal-free substitutional doping and nitrogen vacancy creation, and performed first-principles density functional theory calculations. The effects of the modifications on band gap tuning, charge transfer, and the CO2 adsorption ability were all studied. Specifically, ON-B13C8N11 and SiC-2 × 2-BC6N were shown to possess excellent properties for photocatalytic CO2 reduction, and OC-2 × 2-BC6N and Nv-4 × 4-BN can be considered for future CO2 capture materials. These results contribute to existing CCU approaches, suggesting that BCN monolayer modification merits further investigation, and offering insights relevant to other photocatalytic applications.

Pd-Functionalized ZnO:Eu Columnar Films for Room-Temperature Hydrogen Gas Sensing: A Combined Experimental and Computational Approach

Reducing the operating temperature to room temperature is a serious obstacle on long-life sensitivity with long-term stability performances of gas sensors based on semiconducting oxides, and this should be overcome by new nanotechnological approaches. In this work, we report the structural, morphological, chemical, optical, and gas detection characteristics of Eu-doped ZnO (ZnO:Eu) columnar films as a function of Eu content. The scanning electron microscopy (SEM) investigations showed that columnar films, grown via synthesis from a chemical solutions (SCS) approach, are composed of densely packed columnar type grains. The sample sets with contents of ∼0.05, 0.1, 0.15, and 0.2 at% Eu in ZnO:Eu columnar films were studied. Surface functionalization was achieved using PdCl₂ aqueous solution with additional thermal annealing in air at 650 °C. The temperature-dependent gas-detection characteristics of Pd-functionalized ZnO:Eu columnar films were measured in detail, showing a good selectivity toward H₂ gas at operating OPT temperatures of 200-300 °C among several test gases and volatile organic compound vapors, such as methane, ammonia, acetone, ethanol, n-butanol, and 2-propanol. At an operating temperature OPT of 250 °C, a high gas response I_gas/I_air of ∼115 for 100 ppm H₂ was obtained. Experimental results indicate that Eu doping with an optimal content of about 0.05-0.1 at% along with Pd functionalization of ZnO columns leads to a reduction of the operating temperature of the H₂ gas sensor. DFT-based computations provide mechanistic insights into the gas-sensing mechanism by investigating interactions between the Pd-functionalized ZnO:Eu surface and H₂ gas molecules supporting the experimentally observed results. The proposed columnar materials and gas sensor structures would provide a special advantage in the fields of fundamental research, applied physics studies, and ecological and industrial applications.

Performance of Intrinsic and Modified Graphene for the Adsorption of H2S and CH4: A DFT Study

In this study, the adsorption performances of graphene before and after modification to H₂S and CH₄ molecules were studied using first principles with the density functional theory (DFT) method. The most stable adsorption configuration, the adsorption energy, the density of states, and the charge transfer are discussed to research the adsorption properties of intrinsic graphene (IG), Ni-doped graphene (Ni–G), vacancy defect graphene (DG), and graphene oxide (G–OH) for H₂S and CH₄. The weak adsorption and charge transfer of IG achieved different degrees of promotion by doping the Ni atom, setting a single vacancy defect, and adding oxygen-containing functional groups. It can be found that a single vacancy defect significantly enhances the strength of interaction between graphene and adsorbed molecules. DG peculiarly shows excellent adsorption performance for H₂S, which is of great significance for the study of a promising sensor for H₂S gas.