Visible-Light-Driven Selective Hydrogenation of Nitrostyrene over Layered Ternary Sulfide Nanostructures

Selective hydrogenation of nitrostyrenes is a great challenge due to the competitive activation of the nitro groups (─NO2 ) and carbon-carbon (C═C) double bonds. Photocatalysis has emerged as an alternative to thermocatalysis for the selective hydrogenation reaction, bypassing the precious metal costs and harsh conditions. Herein, two crystalline phases of layered ternary sulfide Cu2 WS4 , that is, body-centered tetragonal I-Cu2 WS4 nanosheets and primitive tetragonal P-Cu2 WS4 nanoflowers, are controlled synthesized by adjusting the capping agents. Remarkably, these nanostructures show visible-light-driven photocatalytic performance for selective hydrogenation of 3-nitrostyrene under mild conditions. In detail, the I-Cu2 WS4 nanosheets show excellent conversion of 3-nitrostyrene (99.9%) and high selectivity for 3-vinylaniline (98.7%) with the assistance of Na2 S as a hole scavenger. They also can achieve good hydrogenation selectivity to 3-ethylnitrobenzene (88.5%) with conversion as high as 96.3% by using N2 H4 as a proton source. Mechanism studies reveal that the photogenerated electrons and in situ generated protons from water participate in the former hydrogenation pathway, while the latter requires the photogenerated holes and in situ generated reactive oxygen species to activate the N2 H4 to form cis-N2 H2 for further reduction. The present work expands the rational synthesis of ternary sulfide nanostructures and their potential application for solar-energy-driven organic transformations.

Synthetically Produced Isocubanite as an Anode Material for Sodium-Ion Batteries: Understanding the Reaction Mechanism During Sodium Uptake and Release

Bulk isocubanite (CuFe₂S₃) was synthesized via a multistep high-temperature synthesis and was investigated as an anode material for sodium-ion batteries. CuFe₂S₃ exhibits an excellent electrochemical performance with a capacity retention of 422 mA h g^-1 for more than 1000 cycles at a current rate of 0.5 A g^-1 (0.85 C). The complex reaction mechanism of the first cycle was investigated via PXRD and X-ray absorption spectroscopy. At the early stages of Na uptake, CuFe₂S₃ is converted to form crystalline CuFeS₂ and nanocrystalline NaFe_1.5S₂ simultaneously. By increasing the Na content, Cu⁺ is reduced to nanocrystalline Cu, followed by the reduction of Fe²⁺ to amorphous Fe⁰ while reflections of nanocrystalline Na₂S appear. During charging up to -5 Na/f.u., the intermediate NaFe_1.5S₂ appears again, which transforms in the last step of charging to a new unknown phase. This unknown phase together with NaFe_1.5S₂ plays a key role in the mechanism for the following cycles, evidenced by the PXRD investigation of the second cycle. Even after 400 cycles, the occurrence of nanocrystalline phases made it possible to gain insights into the alteration of the mechanism, which shows that Cu_xS phases play an important role in the region of constant specific capacity.

CuFeS2 as a Very Stable High-Capacity Anode Material for Sodium-Ion Batteries: A Multimethod Approach for Elucidation of the Complex Reaction Mechanisms during Discharge and Charge Processes

Highly crystalline CuFeS₂ containing earth-abundant and environmentally friendly elements prepared via a high-temperature synthesis exhibits an excellent electrochemical performance as an anode material in sodium-ion batteries. The initial specific capacity of 460 mAh g^-1 increases to 512 mAh g^-1 in the 150th cycle and then decreases to a still very high value of 444 mAh g^-1 at 0.5 A g^-1 in the remaining 550 cycles. Even for a large current density, a pronounced cycling stability is observed. Here, we demonstrate that combining the results of X-ray powder diffraction experiments, pair distribution function analysis, and ²³Na NMR and Mössbauer spectroscopy investigations performed at different stages of discharging and charging processes allows elucidation of very complex reaction mechanisms. In the first step after uptake of 1 Na/CuFeS₂, nanocrystalline NaCuFeS₂ is formed as an intermediate phase, which surprisingly could be recovered during charging. On increasing the Na content, Cu⁺ is reduced to nanocrystalline Cu, while nanocrystalline Na₂S and nanosized elemental Fe are formed in the discharged state. After charging, the main crystalline phase is NaCuFeS₂. At the 150th cycle, the mechanisms clearly changed, and in the charged state, nanocrystalline Cu_xS phases are observed. At later stages of cycling, the mechanisms are altered again: NaF, Cu₂S, and Cu_7.2S₄ appeared in the discharged state, while NaF and Cu₅FeS₄ are observed in the charged state. In contrast to a typical conversion reaction, nanocrystalline phases play the dominant role, which are responsible for the high reversible capacity and long-term stability.

An Interconnected Ternary MIn2 S4 (M=Fe, Co, Ni) Thiospinel Nanosheet Array: A Type of Efficient Platinum-Free Counter Electrode for Dye-Sensitized Solar Cells

The ternary iron-group thiospinels of metal diindium sulfides (MIn₂ S₄ , M=Fe, Co, Ni) with a vertically aligned nanosheet array structure are fabricated through an in situ solvothermal method on F-doped tin oxide (FTO) substrates, which are employed as one type of platinum (Pt)-free counter electrodes (CEs) in structure-dependent dye-sensitized solar cells (DSSCs). A DSSC assembled with ternary CoIn₂ S₄ CE achieves an photoelectric conversion efficiency (PCE) of 8.83 %, outperforming than that of FeIn₂ S₄ (7.18 %) and NiIn₂ S₄ (8.27 %) CEs under full sunlight illumination (100 mW cm^-2 , AM 1.5 G), which is also comparable with that of the Pt CE (8.19 %). Putting aside that the interconnected nanosheet array provides fast electron transfer and electrolyte diffusion channels, the highest PCE of CoIn₂ S₄ based DSSC results from its largest specific surface area (144.07 m²  g^-1 ), providing abundant active sites and the largest electron injection efficiency from CE to electrolyte.

CuV2S4: A High Rate Capacity and Stable Anode Material for Sodium Ion Batteries

The ternary compound CuV₂S₄ exhibits an excellent performance as anode material for sodium ion batteries with a high reversible capacity of 580 mAh g^-1 at 0.7 A g^-1 after 300 cycles. A Coulombic efficiency of ≈99% is achieved after the third cycle. Increase of the C-rate leads to a drop of the capacity, but a full recovery is observed after switching back to the initial C-rate. In the early stages of Na uptake first Cu⁺ is reduced and expelled from the electrode as nanocrystalline metallic Cu. An increase of the Na content leads to a full conversion of the material with nanocrystalline Cu particles and elemental V embedded in a Na₂S matrix. The formation of Na₂S is evidenced by ²³Na MAS NMR spectra and X-ray powder diffraction. During the charge process the nanocrystalline Cu particles are retained, but no crystalline materials are formed. At later stages of cycling the reaction mechanism changes which is accompanied by the formation of copper(I) sulfide. The presence of nanocrystalline metallic Cu and/or Cu₂S improves the electrical conductivity, leading to superior cycling and rate capability.

A General Strategy toward Carbon Cloth-Based Hierarchical Films Constructed by Porous Nanosheets for Superior Photocatalytic Activity

Herein, the controlled synthesis of 3D hierarchical films on carbon cloth (CC) in a high yield through a hydrothermal process and their high photocatalytic properties are reported. As representative examples, the obtained ZnIn2 S4 /CdIn2 S4 composites are composed of porous nanosheets. During the hydrothermal process, l-cysteine plays an important dual role as a coordinating agent and sulfur source, which is in favor of adjusting stoichiometry of the final product and forming the nanoporous structure. This facile method can be extended to synthesize other sulfides and oxides on CC substrates, such as CoIn2 S4 , MnIn2 S4 , FeIn2 S4 , SnS2 , and Bi2 WO6 . When evaluated the photocatalytic activity, the optimized ZnIn2 S4 /CdIn2 S4 (20%)-CC with an easily recycling feature shows higher photocatalytic degradation activity for methylene blue (MB) than ZnIn2 S4 -CC, CdIn2 S4 -CC, and ZnIn2 S4 /CdIn2 S4 (20%) powder. More importantly, ZnIn2 S4 /CdIn2 S4 (20%)-CC also exhibits superior H2 production activity. The enhanced photocatalytic activity is attributed to the unique porous sheet-like structure and the formation of heterojunction. Our results could provide a promising way to develop high-performance photocatalytic films, which makes it possible to be used in real devices.