First-principles study of a SiC nanosheet as an effective material for nitrosourea and carmustine anti-cancer drug delivery.

The development of novel nanosheet-based drug delivery systems requires a systematic understanding of the interactions between the drug and the nanosheet carrier under various physiological environments. In this work, we investigated electronic and quantum molecular descriptors of a SiC monolayer adsorbed with the anticancer drugs nitrosourea (NU) and carmustine (BCNU) using density functional theory (DFT). Our calculations revealed negative adsorption energies for both drugs, indicating a spontaneous and energetically favorable adsorption process. Density of states and orbital population analysis studies revealed that both drugs are capable of significantly (>30%) narrowing the gap between HOMO and LUMO, depending on the configuration of the adsorption complex. Furthermore, the electronic and quantum molecular descriptors were investigated in gas and water mediums to explore the effect of the solvent on the adsorption process. Our calculations predict a higher narrowing of the HOMO-LUMO gap in the water phase compared to the gas phase. Besides, a modest reduction in global hardness and a marked increase in the global electrophilicity index were observed after the adsorption of the drug molecules by the SiC nanosheet, indicating its high reactivity towards both NU and BCNU. Changing the medium to water showed a maximum 2× increase in the global electrophilicity index of the nanosheet for NU and a maximum 7× increase for BCNU. Additionally, the thermodynamic study of the adsorption process indicates that the formation energies at high temperatures are smaller than those at low temperatures, unfolding the potential of SiC nanosheet for application in the phototherapy of these drugs.

Photoexcited Hot Electron Catalysis in Plasmon-Resonant Grating Structures with Platinum, Nickel, and Ruthenium Coatings.

We report the electrochemical potential dependence of photocatalysis produced by hot electrons in plasmon-resonant grating structures. Here, corrugated metal surfaces with a period of 520 nm are illuminated with 785 nm wavelength laser light swept as a function of incident angle. At incident angles corresponding to plasmon-resonant excitation, we observe sharp peaks in the electrochemical photocurrent and dips in the photoreflectance consistent with the conditions under which there is wavevector matching between the incident light and the spacing between the lines in the grating. In addition to the bare plasmonic metal surface (i.e., Au), which is catalytically inert, we have measured grating structures with a thin layer of Pt, Ru, and Ni catalyst coatings. For the bare Au grating, we observe that the plasmon-resonant photocurrent remains relatively featureless over the applied potential range from -0.8 to +1.2 V vs NHE. For the Pt-coated grating, we observe a sharp peak around -0.3 V vs NHE, three times larger than the bare Au grating, and near complete suppression of the oxidation half-reaction, reflecting the reducing nature of Pt as a good hydrogen evolution reaction catalyst. The photocurrent associated with the Pt-coated grating is less noisy and produces higher photocurrents than the bare Au grating due to the faster kinetics (i.e., charge transfer) associated with the Pt-coated surface. The plasmon-resonant grating structures enable us to compare plasmon-resonant excitation with that of bulk metal interband absorption simply by rotating the polarization of the light while leaving all other parameters of the experiment fixed (i.e., wavelength, potential, electrochemical solution, sample surface, etc.). A 64X plasmon-resonant enhancement (i.e., p-to-s polarized photocurrent ratio) is observed for the Pt-coated grating compared to 28X for the bare grating. The nickel-coated grating shows an increase in the hot-electron photocurrent enhancement in both oxidation and reduction half-reactions. Similarly, Ru-coated gratings show an increase in hot-electron photocurrents in the oxidation half-reaction compared to the bare Au grating. Plasmon-resonant enhancement factors of 36X and 15X are observed in the p-to-s polarized photocurrent ratio for the Ni and Ru gratings, respectively.

A graphene-like BeS monolayer as a promising gas sensor material with strain and electric field induced tunable response: a first-principles study.

A comprehensive investigation of the gas sensing potential of BeS monolayer has been conducted using DFT calculations. Twelve common pollutant gases: NH3, NO2, NO, CO, CO2, CH4, H2, O2, N2, H2S, H2O and SO2, have been studied. Our analysis reveals defect states in the band structure near the Fermi level and strong hybridization between gas molecule orbitals and the BeS monolayer. We observe higher adsorption energies for NH3 and CO compared to other popular gas sensing materials. The optical properties of CO2 and NO2 adsorbed on the BeS monolayer show increased reflectivity and absorption coefficient in the UV and far infrared region. Tensile strain has minimal impact on adsorption energy, while biaxial compressive strains enhance the gas sensing capability of the BeS monolayer. The application of an electric field offers control over gas adsorption and desorption. We propose the BeS monolayer as a promising candidate for future gas molecule sensing applications due to its high adsorption energy, rapid recovery time, and distinct optical properties.

Adsorption of gas molecules on buckled GaAs monolayer: a first-principles study.

The design of sensitive and selective gas sensors can be significantly simplified if materials that are intrinsically selective to target gas molecules can be identified. In recent years, monolayers consisting of group III-V elements have been identified as promising gas sensing materials. In this article, we investigate gas adsorption properties of buckled GaAs monolayer using first-principles calculations within the framework of density functional theory. We examine the adsorption energy, adsorption distance, charge transfer, and electron density difference to study the strength and nature of adsorption. We calculate the change in band structure, work function, conductivity, density of states, and optical reflectivity for analyzing its prospect as work function-based, chemiresistive, optical, and magnetic gas sensor applications. In this regard, we considered the adsorption of ten gas molecules, namely NH3, NO2, NO, CH4, H2, CO, SO2, HCN, H2S, and CO2, and noticed that GaAs monolayer is responsive to NO, NO2, NH3, and SO2 only. Specifically, NH3, SO2 and NO2 chemisorb on the GaAs monolayer and change the work function by more than 5%. While both NO and NO2 are found to be responsive in the far-infrared (FIR) range, NO shows better spin-splitting property and a significant change in conductivity. Moreover, the recovery time at room temperature for NO is observed to be in the sub-millisecond range suggesting selective and sensitive NO response in GaAs monolayer.