Mechanism of charge transfer and its impacts on Fermi-level pinning for gas molecules adsorbed on monolayer WS2

Density functional theory calculations were performed to assess changes in the geometric and electronic structures of monolayer WS2 upon adsorption of various gas molecules (H2, O2, H2O, NH3, NO, NO2, and CO). The most stable configuration of the adsorbed molecules, the adsorption energy, and the degree of charge transfer between adsorbate and substrate were determined. All evaluated molecules were physisorbed on monolayer WS2 with a low degree of charge transfer and accept charge from the monolayer, except for NH3, which is a charge donor. Band structure calculations showed that the valence and conduction bands of monolayer WS2 are not significantly altered upon adsorption of H2, H2O, NH3, and CO, whereas the lowest unoccupied molecular orbitals of O2, NO, and NO2 are pinned around the Fermi-level when these molecules are adsorbed on monolayer WS2. The phenomenon of Fermi-level pinning was discussed in light of the traditional and orbital mixing charge transfer theories. The impacts of the charge transfer mechanism on Fermi-level pinning were confirmed for the gas molecules adsorbed on monolayer WS2. The proposed mechanism governing Fermi-level pinning is applicable to the systems of adsorbates on recently developed two-dimensional materials, such as graphene and transition metal dichalcogenides.Published versio

The use of 3-(2-pyridyl)-5, 6-diphenyl-1, 2, 4-triazine as precolumn derivatizing reagent in HPLC determination for Fe(II) in natural samples

The 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT) was used for the first time as a precolumn derivatizing reagent applied in the high-performance liquid chromatography (HPLC) method with UV-detection for the Fe (II) determination. The Fe (II) reacts with PDT to form a magenta colored chelate in the presence of sodium dodecyl sulfate (SDS) and acetic acid-sodium acetate buffer solution medium of pH 4.65. The selection of maximum absorbance detect wavelength and the optimum composition of the organic modifier in the mobile phase were investigated in detail for the quantitative determination of Fe (II) using HPLC system. The formed Fe(II)-PDT chelate was satisfactorily separated from PDT on a Agilent Shim-pack ODS column (Eclipse XDB-C8,4.6x150mm) by isocratic elution with acetonitrile and 0.02 mol L-1 acetic acid-sodium acetate buffer solution (pH 4.65, containing 0.02% of SDS and 60x10-3 mol L-1 NaClO4) as mobile phase at a flow rate of 1 mL min-1, and monitored with a multiple wavelength detector. The detection limit (S/N =3) is 0.35 ng ml-1. Due to the excellent separation ability of HPLC, the innovative introduction of PDT as the precolumn derivatizing reagent, and the proper selection of the detect wavelength, the sensitivity of our newly developed HPLC method was enhanced remarkably compared to the common spectrophotometric methods. The developed HPLC method was successfully applied to the determination of Fe(II) in lake water samples

Conjugate Heat Transfer Analysis and Heat Dissipation Design of Nucleic Acid Detector Instrument

Temperature affects both the stability of nucleic acid detectors and efficiency of DNA amplification. In this study, temperature and flow inside a nucleic acid detector were simulated and the results were used to design vents for the instrument casing. A test platform was constructed to collect experimental temperature data that were used for simulation validation. The experimental and simulation results showed that the temperature error was less than ±3 K. A total of two heat-dissipation schemes were designed based on the simulation and a new instrument casing was fabricated based on the scheme with the best results. Nucleic acid amplification was performed continuously for 120 min using a prototype with the new casing. The temperatures of the monitoring points were stable and the maximum temperature measured only 307.76 K (34.61 °C). Therefore, waste heat was effectively eliminated, which ensured safety of the electronic components and stability of the nucleic acid detection process

The characteristics and two-step reaction model of <i>p</i>-nitroacetophenone biodegradation mediated by <i>Shewanella decolorationis</i> S12 and electron shuttle in the presence/absence of goethite

<div><p>The current study mainly focused on the biodegradation process of <i>p</i>-nitroacetophenone (NP) in the presence and absence of goethite mediated by iron-reducing microbe (<i>Shewanella decolorationis</i> S12) and electron shuttle. The results showed that introduction of electron shuttle could obviously lead to an accumulation of biodegradation intermediate, especially in reaction systems containing high content of electron shuttle in the absence of goethite. Goethite could enhance the degree and rate of NP biodegradation. The microbial reductively generated Fe(II) played an active role in the biodegradation process. The relationship between the concentrations of biodegradation end product and the reaction times could be fitted by a consecutive reaction model with correlation coefficients (adjusted <i>R</i>²) in the range from 0.9241 to 0.9831 during the biodegradation stage from the beginning to about 250 h of incubation. However, during the subsequent biodegradation stages, in the presence and absence of goethite, transitions from the consecutive reaction model to zero-order reaction model and from the consecutive reaction model to exponential growth reaction model were observed, respectively. The newly proposed two-step reaction model will help understand the mechanism of the biodegradation process of nitroaromatic compounds and related pollutants.</p></div

Quinone-Mediated Microbial Goethite Reduction and Transformation of Redox Mediator, Anthraquinone-2,6-Disulfonate (AQDS)

<p>The aim of current study is to identify the kinetic characteristics and elucidate the possible transformation pathways of the interaction between the redox mediator (anthraquinone-2,6-disulfonate, AQDS) and goethite during the process of microbial goethite reduction by <i>Shewanella putrefaciens</i>, a dissimilatory iron reduction bacterium (DIRB). Speciations of both AQDS and microbially reduced ferrous iron are used to characterize the interaction process among <i>S. putrefaciens</i>, AQDS and goethite. Due to the complexities of the natural environment, two pre-incubation reaction systems of the “DIRB–goethite” and the “DIRB–AQDS” are introduced to investigate the dynamics of goethite reduction and redox transformation of AQDS. Results show that the characteristics of the microbial goethite reduction and the kinetic transformation between two species of the redox mediator are different in two pre-incubation reaction systems. Both abiotic and enzymatic reactions and their coupling regulate the kinetic process for “redox mediatoriron” interaction in the presence of DIRB. This study will help to understand the characteristics and mechanism of microbial reduction of the Fe(III) oxide and transformation of redox mediator.</p

Genome-Wide Analysis of the <i>Liriodendron chinense Hsf</i> Gene Family under Abiotic Stress and Characterization of the <i>LcHsfA2a</i> Gene

Heat shock factors (Hsfs) play a crucial role in plant defense processes. However, the distribution and functional characteristics of Hsf genes in the relict plant Liriodendron chinense are still unclear. In this study, a total of 19 LcHsfs were identified and divided into three separate subgroups, comprising 10 LcHsfA, 7 LcHsfB, and 2 LcHsfC genes, respectively, based on their phylogenetic tree and the presence/absence of conserved protein domains. Whole-genome duplication and segmental duplication led to an expansion of the LhHsf gene family. The promoters of LcHsf genes are enriched for different types of cis-acting elements, including hormone responsive and abiotic-stress-responsive elements. The expression of LcHsfA3, LcHsfA4b, LcHsfA5, LcHsfB1b, and LcHsfB2b increased significantly as a result of both cold and drought treatments. LcHsfA2a, LcHsfA2b, and LcHsfA7 act as important genes whose expression levels correlate strongly with the expression of the LcHsp70, LcHsp110, and LcAPX genes under heat stress. In addition, we found that transiently transformed 35S:LcHsfA2a seedlings showed significantly lower levels of hydrogen peroxide (H2O2) after heat stress and showed a stronger thermotolerance. This study sheds light on the possible functions of LcHsf genes under abiotic stress and identifies potentially useful genes to target for molecular breeding, in order to develop more stress-resistant varieties