DFT Based Material Computations of Metal-doped and Pure Carbon Nanodots for Examining their Enhancement of Sulfur Dioxide Adsorption

Carbon nanodots, one of the last members of the nanocarbon family, show superior properties, such as low-cost production, good conductivity, and optical properties, nontoxic behavior, high biocompatibility, and eco-friendly nature. Understanding the effect of metal doping on the modification of the electronic structure of carbon nanodots is critical for enlarging its potential applications. In the present study, in terms of structural, energetic, and electronic analyses, X-doped carbon nanodot structures (X = B, N, Si, Al, Co, Au, Pd, and Pt) and their SO2 adsorption abilities were examined comprehensively by employing DFT. Results depict that embedding the heavy impurity metals (Pd, Pt) to the nanodot structures does not improve the SO2 sensing ability of carbon nanodot materials relatively. However, the doping of the low concentrated metals to the carbon nanodots may be one of the best ways for enhancing the SO2 trapping ability of the carbon nanodot materials since the calculated results having high adsorption energy values indicate SO2 gas molecule is easily adsorbed on the surface of doped carbon nanodots. This means higher adsorption capability compared to pure ones. Thus, it is suggested that the doped carbon nanodots consisting of B, Si, and N impurity atoms may be good candidates for effective SO2 sensing (adsorptions).

A First-Principles Study of Gas Molecule Adsorption on Carbon-, Nitrogen-, and Oxygen-Doped Two-Dimensional Borophene

A first-principles study was performed to investigate the adsorption properties of gas molecules (CO, CO2, NO, and NO2) on carbon- (C-), nitrogen- (N-), and oxygen-doped (O) borophene. The adsorption energies, adsorption configurations, Mulliken charge population, surface work functions, and density of states (DOS) of the most stable doped borophene/gas-molecule configurations were calculated, and the interaction mechanisms between the gas molecules and the doped borophene were further analyzed. The results indicated that most of the gas molecules exhibited strong chemisorption at the VB site (the center of valley bottom B–B bond) of the doped borophene (compared to pristine borophene). Electronic property analysis of the C-doped borophene/CO2 and the NO2 adsorption system revealed that there were numerous charge transfers from the C-doped borophene to the CO2 and NO2 molecules. This indicated that C-doped borophene was an electron donor, and the CO2 and NO2 molecules served as electron acceptors. In contrast to variations in the adsorption energies, electronic properties, and surface work functions of the different gas, C-, N-, and O-doped borophene adsorption systems, we concluded that the C-, N-, and O-doped borophene materials will improve the sensitivity of CO, CO2, and NO2 molecule; this improvement of adsorption properties indicated that C-, N-, and O-doped borophene materials are excellent candidates for surface work functions transistor to detect gas molecules.

Gas molecules (CH4, CO, H2O and H2S) adsorption on VC (001)surface: a first principles study

The first principle plane wave pseudo-potential method based on density functional theory system is used to calculate and simulate the geometric structure, density of states and optical properties of intrinsic VC materials. And we further studied the adsorption performance of small gas molecules (CH4, CO, H2O, H2S) on the surface of VC(001). The most stable adsorption geometry of CH4, CO, H2O and H2S on the intrinsic VC(001) was determined, and the electronic structure and differential charge were calculated by the first principle method. The results show that the adsorption stability of the same molecule on the surface is related to the interaction position between the molecule and the surface after adsorption. According to the analysis of the differential charge density and the charge layout number, the charge layout number of the central atom C, O, S of the gas molecule increases after adsorption, and the adsorption strength of the gas molecule on the surface is CO>H2S>H2O>CH4. The H2S adsorbed on VC surface has the strongest adsorption energy (-1.442 eV) and more transfer charge (-0.12 e). The calculated dielectric function results shows that the existence of gases molecules inhibited the photon adsorbed on VC(001) surface. Our research provide a theoretical basis for further research on the gas sensing properties of material.

Multispecies and individual gas molecule detection using Stokes solitons in a graphene over-modal microresonator

Soliton frequency combs generate equally-distant frequencies, offering a powerful tool for fast and accurate measurements over broad spectral ranges. The generation of solitons in microresonators can further improve the compactness of comb sources. However the geometry and the material’s inertness of pristine microresonators limit their potential in applications such as gas molecule detection. Here, we realize a two-dimensional-material functionalized microcomb sensor by asymmetrically depositing graphene in an over-modal microsphere. By using one single pump, spectrally trapped Stokes solitons belonging to distinct transverse mode families are co-generated in one single device. Such Stokes solitons with locked repetition rate but different offsets produce ultrasensitive beat notes in the electrical domain, offering unique advantages for selective and individual gas molecule detection. Moreover, the stable nature of the solitons enables us to trace the frequency shift of the dual-soliton beat-note with uncertainty <0.2 Hz and to achieve real-time individual gas molecule detection in vacuum, via an optoelectronic heterodyne detection scheme. This combination of atomically thin materials and microcombs shows the potential for compact photonic sensing with high performances and offers insights toward the design of versatile functionalized microcavity photonic devices.

Effect of metal decoration on sulfur-based gas molecules adsorption on phosphorene

Based on first-principles calculation, the adsorption of sulfur-based gas molecules (H2S, SO2, SO3) on various metal-decorated phosphorenes is researched systematically. Eleven metals (Li, Na, K, Rb, Cs, Ca, Sr, Ba, Ni, La, Tl) which can avoid the formation of clusters on the phosphorene are considered. Noticeably, all metal decorations can enhance the adsorption strength of phosphorene to sulfur-based gas molecules except for H2S on Tl-decorated phosphorene. Meanwhile, the adsorption energy (Eads) shows the trend of Eads(H2S) < Eads(SO2) < Eads(SO3) for the same metal decoration case. In addition, some metal-decorated phosphorene systems exhibit intriguing magnetic and electrical variation after sulfur-based gas molecule adsorptions, indicating that these systems are promising to be candidates for the detection and removal of sulfur-based gas molecules.

Simulation of an Industrial Carbon Black Reactor Using Collision Kinetics

Purpose: Objective of the work was to test efficacy of the proposed flame chemistry and collision kinetics for prediction of process parametres through determination of the effect of basic process parameters on yield (which includes but not limited to grade of carbon black produced). Methodology: The research methodology in this work was simulation of an industrial Carbon Black Reactor based on reaction kinetics from flame chemistry which assumes that primary particle formation and particle growth is strictly by collision of molecular nuclei with gas molecule as proposed by the collision theory. Decant oil from the Fluid Catalytic Cracking Unit (FCCU) of the Warri Refinery and Petrochemical Company Limited of Nigeria represented by naphthalene was used as feedstock in the simulation while methane gas is the fuel for combustion needed to attain the reaction temperature. Findings: Results showed an excellent quantitative prediction of trends by models. Qualitative predictions gave far higher parameter values, something easily attributable to the excessively high values of kinetic data used for model testing. Recommendation: The simplifying assumptions of these models completely ignored microscopic phenomena such as interface mass and heat transfer and other similar processes. Consequently, the model can be improved upon by introducing some of these processes as identified.

DFT Study of Chemical Adsorption of NO2 Gas on Graphene Nano Material

In the current study, the density function theory (DFT) is used to investigate the chemical adsorption strength of NO2 gas molecule. The relaxation structure, molecular orbital energy, energy gap and adsorption energy are calculated at ground state. The time dependent DFT (TD-DFT) used to simulate excitation provides UV-Visible spectrum. There was a perpendicular geometrical orientation of the gas molecule around the surface and an adsorption distance of 2.58 Å. The adsorption distance shows the chemical reaction between the gas molecule and the surface. The result of adsorption energy indicates that the gas molecule that closed to the surface has high interaction and it decreases gradually when gas molecule goes further from the graphene nano-ribbon surface. The UV-Visible measurement indicates that the system interaction with gas molecule has red shifting in electromagnetic radiation. The final result concludes that graphene nano-ribbon has high reactivity for NO2 gas molecule. The theoretical calculations provide the ability to design optical sensor which has useful applications in an environmental monitoring.