Chitosan-Induced Synthesis of Hierarchical Flower Ridge-like MoS2/N-Doped Carbon Composites with Enhanced Lithium Storage

PEG-PVP-Assisted Hydrothermal Synthesis and Electrochemical Performance of N-Doped MoS2/C Composites as Anode Material for Lithium-Ion Batteries

Molybdenum disulfide shows promise as an anode material for lithium-ion batteries. However, its commercial potential has been constrained due to the poor conductivity and significant volume expansion during the charge/discharge cycles. To address these issues, in this study, N-doped MoS2/C composites (NMC) were prepared via an enhanced hydrothermal method, using ammonium molybdate and thiourea as molybdenum and sulfur sources, respectively. Polyethylene glycol 400 (PEG400) and polyvinylpyrrolidone (PVP) were added in the hydrothermal procedure as soft template surfactants and nitrogen/carbon sources. The crystal structure, morphology, elemental composition, and surface valence state of the N-doped MoS2/C composites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS), respectively. The results indicate that the NMC prepared by this method are spherical particles with a nanoflower-like structure composed of MoS2 flakes, having an average particle size of about 500 nm. XPS analysis shows the existence of C and N elements in the samples as C-N, C-C, and pyrrolic N. As anodes for LIBs, the NMC without annealing deliver an initial discharge capacity of 548.2 mAh·g-1 at a current density of 500 mA·g-1. However, this capacity decays in the following cycles with a discharge capacity of 66.4 mAh·g-1 and a capacity retention rate of only 12% after 50 cycles. In contrast, the electrochemical properties of the counterparts are enhanced after annealing, which exhibits an initial discharge capacity of 575.9 mAh·g-1 and an ultimate discharge capacity of 669.2 mAh·g-1 after 70 cycles. The capacity retention rate decreases initially but later increases and elevated afterward to reach 116% at the 70th cycle, indicating an improvement in charge-discharge performance. The specimens after annealing have a smaller impedance, which indicates better charge transport and lithium-ion diffusion performance.

Molybdenum Oxynitride Atomic Nanoclusters Bonded in Nanosheets of N-Doped Carbon Hierarchical Microspheres for Efficient Sodium Storage

Transition metal nitrides have attracted considerable attention as great potential anode materials due to their excellent metallic conductivity and high theoretical specific capacity. However, their cycling performance is impeded by their instability caused by the reaction mechanism. Herein, we report the engineering and synthesis of a novel hybrid architecture composed of MoO_2.0N_0.5 atomic nanoclusters bonded in nanosheets of N-doped carbon hierarchical hollow microspheres (MoO_2.0N_0.5/NC) as an anode material for sodium-ion batteries. The facile self-templating strategy for the synthesis of MoO_2.0N_0.5/NC involves chemical polymerization and subsequent one-step calcination treatments. The design is beneficial to improve the electrochemical kinetics, buffer the volume variation of electrodes during cycling, and provide more interfacial active sites for sodium uptake. Due to these unique structural and compositional merits, these MoO_2.0N_0.5/NC exhibits excellent sodium storage performance in terms of superior rate capability and stable long cycle life. The work shows a feasible and effective way to design novel host candidates and solve the long-term cycling stability issues for sodium-ion batteries.

One-Pot Synthesis of Pyrite Nanoplates Supported on Chitosan Hydrochar as Fenton Catalysts for Organics Removal from Water

The Fenton reaction is a powerful method for removing refractory pollutants from water, yet it is restricted by shortcomings such as pH adjustments and generation of iron-containing sludge. In this study, a highly dispersed pyrite nanoplate supported on chitosan hydrochar was prepared through a simple one-pot hydrothermal method. The interactions between chitosan and Fe3+ suppressed the accumulation of FeS2 in the crystal growth period and led to the formation of pyrite nanoplates with many exposed (210) facets. Thus, it showed excellent Fenton-like activity and the removal efficiency of AR 73 reached 99.9% within 60 min. The catalyst could be used in a wide pH range of 3~10. Hydroxyl radicals are the main reactive oxygen species in this catalytic system. The self-reduction of generated Fe(III) species by sulfur via inner electron transfer promoted the Fe(II)/Fe(III) redox cycle, and the presence of graphene facilitated the adsorption of pollutants. This catalyst also showed good reuse performances as well as stability, which has promising prospects for practical use in wastewater treatment.

Glucose-Assisted One-Pot Hydrothermal Synthesis of Hierarchical-Structured MoS2/C Quasi-Hollow Microspheres for High-Performance Lithium Ion Battery

In this work, hierarchical MoS2/C quasi-hollow microspheres are prepared by a one-pot hydrothermal process with the addition of glucose. The glucose is not only inclined to form the roundish sphere in the completion of the synthesis of MoS2, but at the same time the microspheres formed by the glucose can act as the nuclei on which the MoS2 grows. Glucose, acting as a nucleating agent, has the advantages of being low-cost and environmentally friendly, which can simplify the fabrication process. The interiors of the MoS2/C samples are multi-hole and quasi-hollow, which is beneficial for the insertion and extraction of lithium ions. For the first time, we demonstrate that hierarchical-structured MoS2/C quasi-hollow microspheres exhibit an excellent cycling stability and rate capability in lithium ion batteries (LIBs) and are significantly superior to the bulk MoS2. The method presented in this article may provide a simple, clean. and economical strategy for the preparation of MoS2/C microspheres as a feasible and promising anode material for LIBs.

One-pot synthesis of N-doped carbon intercalated molybdenum disulfide nanohybrid for enhanced adsorption of tetracycline from aqueous solutions

Nitrogen-doped carbon intercalated molybdenum disulfide nanohybrid (NC-MoS₂) with well-interconnected nanosheets was successfully fabricated using a one-pot hydrothermal method and applied as a novel adsorbent to remove tetracycline (TC) from aqueous solutions. Series material characterizations indicated that the intercalation of nitrogen-doped carbon into MoS₂ nanosheets could produce widened interlayer spacing, enlarge the specific surface area and create more extensive functional groups. The adsorption kinetics and isotherms investigations revealed that the pseudo-second-order model and Langmuir isotherm model could fit well the TC adsorption behavior of NC-MoS₂. Particularly, NC-MoS₂ possessed a high maximum adsorption capacity (1128.4 mg/g) that was approximately 2.8 times that of pristine MoS₂ (409.84 mg/g) at 308 K and pH = 6.0 ± 0.1. Furthermore, the relevant thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic. The adsorption process was dependent on multiple interactions including hydrophobicity, π-π stacking interaction and hydrogen bond. These findings demonstrated that NC-MoS₂ had potential applications for treating TC-containing water and broadened the application of metal sulfides in the environmental field.

Hierarchical Microtubes Constructed by MoS2 Nanosheets with Enhanced Sodium Storage Performance

Emerging sodium-ion batteries (SIBs) have aroused great attention in large-scale energy storage. However, it is still a great challenge to develop suitable electrode materials due to the large radius of Na⁺. This work demonstrates a strategy to synthesize hierarchical tubular MoS₂ via a facial hydrothermal method with the assistance of tetramethylammonium bromide (TMAB). The results show that sufficient amounts of TMA⁺ ions are necessary to form the hierarchical tubular structures of MoS₂. The obtained tubular MoS₂ displays a high diffusion coefficient of Na⁺ ions, a high specific capacity of 652.5 mAh/g at the current density of 100 mA/g after 50 cycles, and a good cycling stability (94.2% of the initial capacity can be retained after 100 cycles at 1000 mA/g). In situ XRD during the discharge/charge process displays a reversible intercalation/deintercalation of Na⁺ into MoS₂ layers followed by a conversion-type reaction. Systematic analyses reveal that the enhanced electrochemical performance is attributed to its tubular hierarchical structures with the wall composed of loosely stacked nanosheets, which can provide nearly unobstructed ion transportation paths, sufficient active sites, and enough space to mitigate the effects of the volume change during the discharge/charge process. This synthetic approach can be easily extended to other metal oxides and metal sulfides with hierarchical structures for versatile applications.

Hierarchical Octahedra Constructed by Cu2 S/MoS2 ⊂Carbon Framework with Enhanced Sodium Storage

Metal sulfides have aroused considerable attention for efficient sodium storage because of their high capacity and decent redox reversibility. However, the poor rate capability and fast capacity decay greatly hinder their practical application in sodium-ion batteries. Herein, a self-template-based strategy is designed to controllably synthesize hierarchical microoctahedra assembled with Cu₂ S/MoS₂ heterojunction nanosheets in the porous carbon framework (Cu₂ S/MoS₂ ⊂PCF) via a facile coprecipitation method coupled with vulcanization treatment. The Cu₂ S/MoS₂ ⊂PCF microoctahedra with 2D hybrid nanosubunits reasonably integrate several merits including facilitating the diffusion of electrons and Na⁺ ions, enhancing the electric conductivity, accelerating the ion and charge transfer, and buffering the volume variation. Therefore, the Cu₂ S/MoS₂ ⊂PCF composite manifests efficient sodium storage performance with high capacity, long cycling life, and excellent rate capability.

Ni12P5 nanoparticles bound on graphene sheets for advanced lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have been regarded as potential energy storage devices by virtue of their high theoretical capacity, natural abundance of materials and low cost. However, the notorious shuttle effect and sluggish reaction kinetics are still significant challenges for further development. Herein, Ni₁₂P₅ nanoparticles are devised and grown on a reduced graphene oxide (Ni₁₂P_5@rGO) framework via a self-template and recrystallization-self-assembly strategy, as the modifier for separators in LSBs for the first time. The support of rGO for Ni₁₂P₅ nanoparticles could solve the self-aggregation problem. Ni₁₂P₅ nanoparticles not only effectively adsorb polysulfides by polar interaction, but also supply active sites to ameliorate the kinetics of the redox reaction of sulfur. Consequently, when a sulfur-containing commercial acetylene black material (70 wt% sulfur content) is used as the cathode composite without complicated fabrication or surface modification, an LSB with Ni₁₂P₅@rGO modified separator shows excellent cycling stability and a capacity degradation of 0.074% per cycle at the current density of 1 C for 500 cycles. When the areal mass of sulfur further increases to 3.5 mg cm^-2, the capacity degradation is only 0.071% per cycle at 150 cycles. This study could accelerate the application of phosphides in LSBs.

Hierarchically Porous MoS2-Carbon Hollow Rhomboids for Superior Performance of the Anode of Sodium-Ion Batteries

It is always challenging to fabricate two-dimensional transition-metal dichalcogenides into multiple hollow micro-/nanostructures with improved properties for various potential applications. Here, hierarchically porous MoS₂-C hollow rhomboids (MCHRs) have been creatively synthesized via a facile self-templated solvothermal approach. It has been clarified that the obtained MCHRs assembled beneath ultrathin γ-MnS and carbon cohybridized MoS₂ nanosheets under the structural direction of the MnMoO₄·0.49H₂O self-template. The prepared MCHR anode of sodium-ion batteries exhibited a reversible capacity of 506 mA h g^-1 at 0.1 A g^-1, ultrahigh rate capabilities up to 10 A g^-1 with 310 mA h g^-1, and exceptional stability over 3000 cycles. This study provides inspiration for the rational design of hierarchically porous hollow nanostructures with specific geometries as an excellent electrode material for outstanding performance energy storage equipment.

One-Step Construction of MoS0.74Se1.26/N-Doped Carbon Flower-like Hierarchical Microspheres with Enhanced Sodium Storage

Despite the fulfilling advancement in preparing two-dimensional (2D) layered transition-metal dichalcogenide (TMD)-based hybrid architectures, most methods lie on additional template-based procedures for obtaining the expected structure. Here, we present a self-template and in situ synchronous selenization/vulcanization strategy for the synthesis of flower-like hierarchical MoS_0.74Se_1.26/N-doped carbon (MoS_0.74Se_1.26/NC) microspheres by morphology-preserved thermal transformation of a Mo-polydopamine precursor. Introducing element S into the MoSe₂ crystal structure can enhance the electron and ion transportation and lift the ability of MoSe₂ to store Na⁺; the presence of Se can expand the interlayer spacing in contrast to MoS₂. Moreover, carbon composition can also favor the electrical conductivity, and the rigid micro/nanostructure is better for preventing the stacking of MoS_0.74Se_1.26 nanoflakes. The Mo-polydopamine-derived MoS_0.74Se_1.26/NC hybrid exhibits much better performance as the sodium-ion battery (SIB) anode than MoS₂/NC and MoSe₂/NC counterparts, confirming that the advanced electrode material can be attained via the rationalization of the synthetic method. The work provides a new design configuration for novel 2D layered TMDs in the promising application of SIBs as anode materials.