A solar cell is an electrical device that converts light energy into electricity. One of the crucial parts of realizing high-performance thin-film-based solar cells is an n-type buffer layer. Instead of the widely used, but toxic CdS buffer layer, we investigated the possibility of using Zn(O,S) as an alternative material grown by atomic layer deposition (ALD). First of all, structural, electrical, chemical, and optical properties of Zn(O,S) thin films were studied. In addition, this new buffer layer was applied for earth-abundant Cu 2 ZnSn(S,Se) 4 solar cells and the highest power-conversion efficiency (PCE, η) of ~2.7% was achieved by optimizing oxygen-to-sulfur (O/S) ratio.
Mesoporous carbon nitride (MCN) with well-ordered porous structures is a promising anode material for secondary ion batteries owing to their unique physico- and electrochemical properties. However, the practical application of these MCNs in sodium-ion batteries (SIBs) is still limited because of their confined interlayer distance, which results in restricted accommodation of Na ions inside the lattice. Here, we report on the synthesis of highly ordered sulfur-doped MCN (S-MCN) through a hard template approach by employing dithiooxamide (DTO) as a single molecular precursor containing carbon, nitrogen, and sulfur elements. The interlayer distance of carbon nitride is significantly expanded upon the introduction of larger S ions on the MCN lattice, which enables high capability of Na ion accommodation. We also demonstrate through the first-principles density functional theory calculation that the present S-MCN is highly optimized not only for the chemical structure but also for uptaking abundant Na ions with high adsorption energy. The specific discharge capacity of SIBs appears to be remarkably enhanced for S-MCN (304.2 mA h g-1) compared to the nonporous S-CN (167.9 mA h g-1) and g-C3N4 (5.4 mA h g-1), highlighting the pivotal roles of the highly ordered mesoporous structure and S-doping in enhancing the electrochemical functionality of carbon nitride as an anode material for SIBs.
The porous structure of a Co-Al-LDH–graphene–layered MnO2 nanohybrid is compared with the agglomerated structure of MnO2-free-Co-Al–LDH–graphene by S.-J. Hwang and co-workers. On page 3921, the Co-Al-LDH–graphene–layered MnO2 nanohybrid shows a porous morphology formed by the house-of-cards-type stacking of sheet-like crystallites. The incorporation of the MnO2 nanosheets provides more sites for the intercalation of potassium ions and also creates more open sites by preventing the agglomeration of rGO nanosheets.
Mesoporous layer-by-layer ordered nanohybrids highly active for visible light-induced O(2) generation are synthesized by self-assembly between oppositely charged 2D nanosheets of Zn-Cr-layered double hydroxide (Zn-Cr-LDH) and layered titanium oxide. The layer-by-layer ordering of two kinds of 2D nanosheets is evidenced by powder X-ray diffraction and cross-sectional high resolution-transmission electron microscopy. Upon the interstratification process, the original in-plane atomic arrangements and electronic structures of the component nanosheets remain intact. The obtained heterolayered nanohybrids show a strong absorption of visible light and a remarkably depressed photoluminescence signal, indicating an effective electronic coupling between the two component nanosheets. The self-assembly between 2D inorganic nanosheets leads to the formation of highly porous stacking structure, whose porosity is controllable by changing the ratio of layered titanate/Zn-Cr-LDH. The resultant heterolayered nanohybrids are fairly active for visible light-induced O(2) generation with a rate of ∼1.18 mmol h(-1) g(-1), which is higher than the O(2) production rate (∼0.67 mmol h(-1) g(-1)) by the pristine Zn-Cr-LDH material, that is, one of the most effective visible light photocatalysts for O(2) production, under the same experimental condition. This result highlights an excellent functionality of the Zn-Cr-LDH-layered titanate nanohybrids as efficient visible light active photocatalysts. Of prime interest is that the chemical stability of the Zn-Cr-LDH is significantly improved upon the hybridization, a result of the protection of the LDH lattice by highly stable titanate layer. The present findings clearly demonstrate that the layer-by-layer-ordered assembly between inorganic 2D nanosheets is quite effective not only in improving the photocatalytic activity of the component semiconductors but also in synthesizing novel porous LDH-based hybrid materials with improved chemical stability.
Highly efficient photocatalysts for visible light-induced O2 generation are synthesized via an electrostatically derived self-assembly of Zn–Cr-LDH 2D nanoplates with graphene 2D nanosheets. In the obtained nanohybrids, the positively charged Zn–Cr-LDH nanoplates are immobilized on the surface of negatively charged graphene nanosheets with the formation of a highly porous stacked structure. A strong electronic coupling of the subnanometer-thick Zn–Cr-LDH nanoplates with reduced graphene oxide (RGO)/graphene oxide (GO) nanosheets gives rise not only to the prominent increase of visible light absorption but also to a remarkable depression of the photoluminescence signal. The self-assembled Zn–Cr-LDH–RGO nanohybrids display an unusually high photocatalytic activity for visible light-induced O2 generation with a rate of ∼1.20 mmol h−1 g−1, which is far superior to that of the pristine Zn–Cr-LDH material (∼0.67 mmol h−1 g−1). The fact that pristine Zn–Cr-LDH is one of the most effective visible light photocatalysts for O2 production with unusually high quantum efficiency of 61% at λ = 410 nm highlights the excellent functionality of the Zn–Cr-LDH–RGO nanohybrids as visible light active photocatalysts. The Zn–Cr-LDH–RGO nanohybrid shows a higher photocatalytic activity than the Zn–Cr-LDH–GO nanohybrid, providing strong evidence for the superior advantage of the hybridization with RGO. The present findings clearly demonstrate that graphene nanosheets can be used as an effective platform for improving the photocatalytic activity of 2D nanostructured inorganic solids.
The study proposed a method for seawater quality criteria of HNS (Hazardous and Noxious Substances) using human risk assessment and ecotoxicological risk assessment. HNS is internationally designated under conventions such as MARPOL 73/78 and OPRC-HNS 2000, due to its harmfulness and risk. As an international regulation, it can be enacted as a law in Korea. This allows for partial improvement and revision of existing laws related to toxicants for HNS regulation, as well as the addition of HNS regulations through special laws. Traditionally, environmental and water quality standards have focused on drinking water or freshwater ecosystems. However, deriving seawater quality criteria requires considering specific differences such as reactions when exposing salts, dilution rates, and toxicity differences to marine organisms. National differences, including the physical and cultural characteristics of the Korean population, marine and coastal environments, and industrial characteristics, should also be taken into account. Therefore, the study proposed a method for establishing coastal seawater quality criteria for human health by referencing methods used by major countries. Research on the distribution of HNS in coastal areas and the concentration of HNS in effluents from marine industrial facilities or land is still in its early stages. Future studies should focus on HNS-related aspects such as bioaccumulation coefficients and dilution rates specific to each marine region. This information will be crucial in determining coastal seawater quality criteria and establishing seawater quality standards. Furthermore, the establishment of an international information sharing system for future research findings is considered necessary.
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