First principle study of the adsorption of formaldehyde molecule on intrinsic and doped BN sheet

Adsorption of NO2, NO, NH3, and CO on Noble Metal (Rh, Pd, Ag, Ir, Pt, Au)-Modified Hexagonal Boron Nitride Monolayers: A First-Principles Study

To investigate the application of modified hexagonal boron nitride (h-BN) in the detection and monitoring of harmful gases (NO2, NO, NH3, and CO), first-principles calculations are applied to study the geometric structure and electronic behavior of the adsorption system. In this paper, the four adsorption sites, namely, B, N, bridge, and hollow sites, are considered to explore the stable adsorption structure of metals (M = Rh, Pd, Ag, Ir, Pt, and Au) on the BN surface. The calculation results demonstrate that the geometric structures of metal at the N-site are relatively stable. Subsequently, the different adsorption structures of NO2, NO, NH3, and CO on M-BN are researched. The electron transfer, charge difference density, and work function of the stable adsorption structure are calculated. The results show that NO2, NO, and CO have the strongest adsorption capacity in the Ir-BN system, with adsorption energies of -2.705, -5.064, and -3.757 eV, respectively. The Pt-BN system has an excellent adsorption performance (-2.251 eV) for NH3. Compared with the M-BN system, the work function of the adsorption system increases after adsorbing NO2, while it decreases after adsorbing NH3. This work shows that h-BN with metal modification is a potential material for online monitoring of harmful gases.

Insights into Poisoning Mechanism of Zr by First Principle Calculation on Adhesion Work and Adsorption Energy between TiB2, Al3Ti, and Al3Zr

Al-Ti-B intermediate alloys are widely used as grain refiners in aluminum alloys owing to the presence of Al3Ti and TiB2 phases. However, the existence of Zr in aluminum alloy melts often results in coarse grain size, leading to Al-Ti-B failure called Zr poisoning. There are three kinds of poisoning mechanisms related to TiB2, Al3Ti, and a combination of TiB2 and Al3Ti for Zr. First, Zr forms ZrB2 or Ti2Zr with TiB2 in Al-Ti-B to reduce the nucleation ability. Second, Zr existing in the aluminum melt with a high melting point Al3Zr then attracts Ti to reduce the dispersion of Ti as a growth inhibitor. Third, Zr reacts with Al3Ti on TiB2 surface to form Al3Zr, thereby increasing the degree of mismatch with Al and diminishing the refiner’s ability as a nucleation substrate. To gain a better understanding of the mechanism of Zr poisoning, the first principle was used in this study to calculate the adhesion works (ZrB2∥Al3Ti), (Ti2Zr∥Al3Ti), (Al3Zr∥Al3Ti), (Al3Ti∥Al), (TiB2∥Al3Zr), and (Al3Zr∥Al), as well as the surface energy of Al3Zr and adsorption energies of Al to Al3Ti or Al3Zr. The results demonstrated that Zr poisoning originated from the second guess. Zr element exiting in aluminum melt led to the formation of an Al3Zr (001) surface. The interfacial adhesion work of Al3Zr (001)∥Al3Ti (001) was not weaker than that of TiB2∥Al3Ti. As a result, Al3Zr first combined with Al3Ti to significantly decline the adsorption of Al3Ti (001) on Al, losing its role as a nucleating agent and grain coarsening. Overall, to prevent failure of the grain refiner in Zr containing aluminum melt, the adhesion work interface between the generated phase of the grain refiner and Al3Zr must remain lower to avoid the combination of the generated phase of grain refiner with Al3Zr. In sum, these findings look promising for evaluating future effects of grain refinement in Zr containing aluminum melt.

First-principles calculations combined with experiments to study the gas-sensing performance of Zn-substituted SnS

Two-dimensional group-IV monochalcogenides MX (M = Ge, and Sn; X = S, and Se) are explored for their potential in gas-sensing applications. In this work, a combined theoretical and experimental study on pure SnS and Zn-substituted SnS for promising methanol sensors is performed. The adsorption characteristics of methanol on pure and Zn-substituted SnS were first calculated using first-principles based on density functional theory (DFT). It is clarified theoretically that the incorporation of Zn dopant could enhance the adsorption capability of the SnS surface to methanol molecules, thus achieving obvious response enhancement and selectivity improvement. Further experimental investigation is carried out based on the successful synthesis of pure and Zn-substituted SnS with hierarchical architecture via a one-step solvothermal process. Gas-sensing measurement indicates that the Zn-substituted SnS sensor is promising for selective detection of rarefied methanol. At room temperature, the as-synthesized hierarchical SnS with an appropriate amount of Zn-doping can sense methanol vapor of as low as 100 ppb. In particular, Zn-doping can enhance the sensing response of methanol significantly, with a 32.8-fold increase in response value achieved in comparison to that of the pure SnS. The underlying mechanism for the response enhancement of Zn-substituted SnS is also analyzed and demonstrated in detail. The present work demonstrates that Zn-doping is highly effective for improving the response and selectivity of SnS towards methanol vapor, and the Zn-substituted SnS is promising for highly sensitive methanol sensors with low consumption.