Highly sensitive sensing of CO and HF gases by monolayer CuCl.

Using a first-principles approach, the adsorption characteristics of CO and HF on a CuCl monolayer (ML) are studied with Grimme-scheme DFT-D2 for accurate description of the long-range (van der Waals) interactions. According to our study, CO gas molecules undergo chemisorption and HF gas molecules show a physisorption phenomenon on the CuCl monolayer. The adsorption energy for CO is -1.80 eV, which is quite a large negative value compared to that on other previously studied substrates, like InN (-0.223 eV), phosphorene (0.325 eV), Janus Te2Se (-0.171 eV), graphene (P-graphene, -0.12 eV, B-graphene, -0.14 eV, N-graphene, -0.1 eV) and monolayer ZnS (-0.96 eV), as well as pristine hBN (0.21 eV) and Ti-doped hBN (1.66 eV). Meanwhile, for HF, the adsorption energy value is -0.31 eV (greater than that of Ti-doped hBN, 0.27 eV). For CO, the large value of the diffusion energy barrier (DEB = 1.26 eV) during its movement between two optimal sites indicates that clustering can be prevented if many molecules of CO are adsorbed on the CuCl ML. For HF, the value of the DEB (0.082 eV) implies that the adsorption phenomenon may happen quite easily upon the CuCl ML. The transfer of charge according to Bader charge analysis and the variation in the work function depend only on the properties of the elements involved, i.e., their nature, rather than the local binding environment. The work function and band-gap energy variation of the CuCl ML (before and after adsorption) show high sensitivity and selectivity of CO and HF binding with the CuCl monolayer. HF molecules give a more rapid recovery time of 1.09 × 10-7 s compared to that of CO molecules at a room temperature (RT) of 300 K, which indicates that the necessary adsorption and reusability of the CuCl ML for HF can be accomplished effectively at RT. Significant changes in the conductivity are observed due to the CO adsorption at various temperatures, as compared to adsorption of HF, which suggests the possibility of a modification in the conductivity of the CuCl ML.

A DFT study of bandgap tuning in chloro-fluoro silicene.

The structural, electronic and optical properties of silicene and its derivatives are investigated in the present work by employing density functional theory (DFT). The Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) is used as the exchange-correlation potential. Our results provide helpful insight for tailoring the band gap of silicene via functionalization of chlorine and fluorine. First, relaxation of all the materials is performed to obtain the appropriate structural parameters. Cl-Si showed the highest lattice parameter 4.31 Å value, while it also possesses the highest buckling of 0.73 Å among all the derivatives of silicene. We also study the electronic charge density, charge difference density and electrostatic potential, to check the bonding characteristics and charge transfer between Si-halides. The electronic properties, band structures and density of states (DOS) of all the materials are calculated using the PBE-GGA as well as the modified Becke-Johnson (mBJ) on PBE-GGA. Pristine silicene is found to have a negligibly small band gap but with the adsorption of chlorine and fluorine atoms, its band gap can be opened. The band gap of Cl-Si and F-Si is calculated to be 1.7 eV and 0.6 eV, respectively, while Cl-F-Si has a band gap of 1.1 eV. Moreover, the optical properties of silicene and its derivatives are explored, which includes dielectric constants ε1 and ε2, refractive indices n, extinction coefficients k, optical conductivity σ and absorption coefficients I. The calculated binding energies and phonon band structures confirm the stability of Cl-Si, Cl-F-Si, and F-Si. We also calculated the photocatalytic properties which show silicine has a good response to reduction, and the other materials to oxidation. A comparison of our current work to recent work in which graphene was functionalized with halides, is also presented and we observe that silicene is a much better alternative for graphene in terms of semiconductors and photovoltaics applications.

Exploring optoelectronic and photocatalytic properties of X2AgBiY6 (X = NH4, PH4, AsH4, SbH4 and Y = Cl, Br): a DFT study.

Ab initio calculations have been used to investigate lead-free double-perovskites (DPs) X2AgBiY6 (X = NH4, PH4, AsH4, SbH4 and Y = Cl, Br) for solar-cell-based energy sources. The most recent and improved Becke-Johnson potential (TB-mBJ) has been proposed for the computation of optoelectronic properties. Theoretical and calculated values of the lattice constants obtained by applying the Wu-Cohen generalized gradient approximation (WC-GGA) were found to be in good agreement. The computed bandgap values of (NH4)2AgBiBr6 (1.574 eV) and (SbH4)2AgBiBr6 (1.440 eV) revealed their indirect character, demonstrating that they are suitable contenders for visible light solar-cell (SC) technology. Properties like the refractive index, light absorption, reflection, and dielectric constant are all explained in terms of the optical ranges. Within the wavelength range of 620-310 nm, the maximum absorption band has been identified. Additionally, we discover that all chemicals investigated herein have photocatalytic capabilities that can be used to efficiently produce hydrogen at cheap cost using solar water splitting by photocatalysts. In addition, the stability of the compounds was examined using the calculation of mechanical properties.

Impact of reactive oxygen species on antioxidant capacity of male reproductive system.

The present research work was aimed to study the mutual interaction of reactive oxygen species (ROS) and basal cells antioxidant capacity in the male reproductive system and to further establish the association between selected heavy metals and stress markers. Total oxidant status (TOS) and total antioxidant status (TAS) of serum and seminal plasma were determined by automated photometric methods. The concentrations of Selenium (Se), Lead (Pb), and Cadmium (Cd) were determined by using atomic absorption spectrophotometer. The TOS was increased significantly (P <0.05) in seminal plasma as well as in the serum of the infertile group when compared with the fertile group. On the other hand, the TAS of the infertile group was found to be noticeably decreased (P <0.05) when compared with the TAS of the fertile group. Among the heavy metals, a noticeably lower concentration of Se was detected in the infertile group whereas markedly elevated levels of Cd and Pb were observed in the infertile group compared with the fertile group. Among the infertile group a significant inverse correlation (r = -0.521, P <0.05) was observed between Se and TOS and between Cd and Pb (r = -0.407, P <0.05). Contrarily among the infertile group a considerable positive relationship was established between Se and TAS (r = 0.507, P <0.05). It was concluded that the oxidant stress reduces the antioxidant activity in infertile men by elevating the production of ROS. A lower concentration of Se and elevated levels of Pb and Cd explain the individual's exposure to these heavy metals. The study also revealed that the heavy metal toxicity contributes significantly to male infertility.

An unusual pathogen causing microbial keratitis.

INTRODUCTION: We report a rare case of Mycobacterium fortuitum affecting the corneal graft of a patient 6 years post-graft, possibly associated with contact lens use. CONCLUSIONS: This case shows the need for careful microbiological techniques when dealing with patients presenting with microbial keratitis. It must be kept in mind that unusual and slow growing organisms may also be responsible for corneal ulceration. If a slow growing organism is suspected, a microbiological diagnosis may not be forthcoming for weeks. Misidentification of the responsible pathogen may further complicate management for the clinicians. Cases such as these, which may not respond to medical therapy as expected, may prove a difficult therapeutic challenge to physicians.