The novel two-dimensional photocatalyst SnN3 with enhanced visible-light absorption for overall water splitting.

Herein, we proposed a novel excellent two-dimensional photocatalyst, the SnN3 monolayer, using first-principles calculations. The stability of the SnN3 monolayer was examined via formation energy, phonon spectroscopy and ab initio molecular dynamics simulations. The SnN3 monolayer has an ultra-high optical absorption capacity of the order of 105 cm-1 in the visible region, which is 3, 4 and 10 times those of SnP3, MoS2 and g-C3N4 monolayers, respectively. Moreover, it has a higher carrier mobility, 769.19 cm2 V-1 s-1, than the other monolayers; the available electrostatic potential of -5.02 eV and the appropriate band gap of 1.965 eV indicate its applicability as a catalyst for overall water splitting over a wide strain range. The electronic properties of the SnN3 monolayer could also be engineered effectively by altering the external strain and electric field.

Theoretical Insights into Two-Dimensional IV-V Compounds: Photocatalysts for the Overall Water Splitting and Nanoelectronic Applications.

Two-dimensional (2D) materials have attracted enormous attention in many fields because of their appealing performances. In this contribution, we perform first-principles calculations on the photocatalytic properties of IV-V compounds, along with the design of a functional Schottky device based on a graphene/SiAs van der Waals heterostructure (vdWH). Our results indicate that eight IV-V compound materials are all excellent photocatalysts for water-splitting reactions with high efficiency of visible light, with the conduction band minimum (CBM) and valence band maximum (VBM) both involving the corresponding band-gap region. It is examined whether a weak acid environment is beneficial for the hydrogen production process. Monolayer GeAs is characterized by an excellent absorption coefficient of up to 105-2 × 105 cm-1 in the visible region. The other nanostructures also have a considerable optical absorption as high as approximately half of 105 cm-1. These illustrate fascinating application prospectives for IV-V compounds in photocatalysis for water splitting under the irradiation of visible light, predicting tremendous significance in the fields of energy conversion and hydrogen production. The graphene/SiAs vdWH nanocomposite at the equilibrium state is featured for an n-type Schottky contact. External strain and electric-field applications are employed to practically present the transition for interface contact between the n- and p-type Schottky contacts or between the Schottky and ohmic contacts, which suggests appealing applications for the graphene/SiAs vdWH as a competitive candidate for functional Schottky devices and nanoelectronic materials.

Investigation on photocatalytic mechanism of graphitic SiC (g-SiC)/MoS2 van der Waals heterostructured photocatalysts for overall water splitting.

Two-dimensional MoS2-based heterostructures have been given great attention due to their excellent properties. In this work, using first-principles calculations, the photocatalytic performances for overall water splitting and the photocatalytic mechanism of graphitic SiC (g-SiC)/MoS2 van der Waals heterostructures (vdWHs) have been deeply studied compared with the previous report. We align common type-II band edges for the g-SiC/MoS2 vdWH in different configurations, which demonstrates that the reduction and oxidation reactions are conducted on different parts in the g-SiC/MoS2 vdWHs. Besides, the built-in electric field induced by the charge transfer at the interface region can be used to hinder photogenerated e-/h+ from recombining, which is advantageous to the availably enhanced carrier mobility and extended lifetimes. More meaningfully, the g-SiC/MoS2 vdWHs all have considerable optical absorption as high as 105 cm-1 in the visible zone and enhanced absorption capacity in contrast to the separate g-SiC and MoS2 monolayers. Furthermore, owing to the contribution of built-in electric field, the g-SiC/MoS2 vdWH in diverse patterns can be used as an outstanding photocatalyst even under near-infrared light with high efficiency. Overall, these findings predict a promising application prospective for the g-SiC/MoS2 vdWHs as extraordinary photocatalysts for overall water splitting reactions, suggesting the valuable significance in the fields of hydrogen production and energy conversion.

Efficient polycrystalline silicon solar cells with double metal oxide layers.

Crystalline silicon solar cells can achieve high power conversion efficiency and can be successfully commercialized; however, the exploration of optimization strategies is still necessary. Here, we demonstrated improved performance of a polycrystalline silicon solar cell by depositing Sb2Ox/CdO double layers onto a Si wafer via a low-cost route. The metal oxide layers, forming effective heterojunctions, suppressed carrier recombination and reduced surface reflection. Additionally, the heterojunctions of Sb2Ox/CdO/Si enhanced the transmission of electrons and holes and simultaneously, a wider response range in the solar spectrum was realized. The power conversion efficiency improved from 12.6 to 16.7% in a polycrystalline silicon solar cell, with relative increase of 33%. It is expected that the metal oxide-enhanced devices will have tremendous potential in commercial applications.

The Health Risk assessment of Pb and Cr leached from fly ash monolith landfill.

As of 2004, nearly two hundred thousand tons of fly ash monoliths are created each year in Taiwan to confine heavy metals for reducing the leaching quantity by precipitation. However, due to abnormal monolith fracture, poorly liner quality or exceeding usage over designed landfill capacity, serious groundwater pollution of the landfills has been reported. This research focuses on Pb and Cr leaching from monolithic landfill to assess the risk of groundwater pollution in the vicinity. The methodology combines water budget simulations using HELP model with fate and risk simulations using MMSOILS model for 5 kinds of landfill structures and 2 types of leaching models, and calculates the risk distribution over 400 grids in the down gradient direction of groundwater. The results demonstrated that the worst liner quality will cause the largest risk and the most significant exposure pathway is groundwater intake, which accounted for 98% of the total risk. Comparing Pb and Cr concentrations in the groundwater with the drinking water standards, only 14.25% of the total grids are found to be under 0.05 mg/L of Pb, and over 96.5% of the total grids are in the safety range of Cr. It indicates that Pb leaching from fly ash monolithic landfills may cause serious health risks. Without consideration of the parameters uncertainty, the cancer and noncancer risk of Pb with the sanitary landfill method was 4.23E-07 and 0.63, respectively, both under acceptable levels. However, by considering the parameters uncertainty, the non-carcinogenic risk of Pb became 1.43, exceeding the acceptable level. Only under the sealed landfill method was the hazard quotient below 1. It is important to use at least the sealed landfill for fly ash monoliths containing lead to effectively reduce health risks.