Metallic 1T-MoS2 Research Articles

Interaction of Pb2+ ions in water with two-dimensional molybdenum disulfide

The removal of heavy metal contaminants from water is important for public health, and recently many two-dimensional (2D) materials with high specific surface areas are being studied as promising new active components in water purification. In particular, 2D MoS2 nanosheets have been used for the removal of various heavy metals, but usually in either in complex geometries and composites, or in the chemically exfoliated metallic 1T-MoS2 phase. However, the interaction of heavy metals dissolved in water with unmodified semiconducting 2H-MoS2 is not well studied. In this paper, we report a detailed fundamental investigation of how Pb2+ ions interact with 2H-MoS2. We observe small solid clusters that form on the MoS2 surfaces after exposing them to Pb(NO3)2 aqueous solutions as shown by atomic force microscopy and transmission electron microscopy, and for liquid phase exfoliated MoS2 we observe the nanosheets precipitating out of dispersion along with insoluble solid granules. We use a combination of x-ray photoelectron spectroscopy and x-ray diffraction to identify these solid clusters and granules as primarily PbSO4 with some PbMoO4. We put forth an interaction mechanism that involves MoS2 defects acting as initiation sites for the partial dissolution in aqueous oxygenated conditions which produces MoO42− and SO42− ions to form the solids with Pb2+. These results are an important contribution to our fundamental understanding of how MoS2 interacts with metal ions and will influence further efforts to exploit MoS2 for water remediation applications.

Construction of Hybrid MoS2 Phase Coupled with SiC Heterojunctions with Promoted Photocatalytic Activity for 4-Nitrophenol Degradation.

Phase engineering has been recognized as a promising method for boosting the catalytic activity of molybdenum sulfide (MoS2) in the field of electrocatalysts and photocatalysts. The metallic 1T-MoS2 exhibits much higher catalytic activity than natural semiconducting 2H-MoS2 but suffers from harsh synthetic conditions and metastable physical/chemical properties. The hybrid 1T/2H phase MoS2 shows higher catalytic activity than the 2H-MoS2 and exhibits better stability than the 1T-MoS2, which is more favorable than the 2H-MoS2 in the photocatalytic reactions. In this study, we report a hydrothermal synthesis of the hybrid 1T/2H-MoS2 phase coupled with SiC as a heterojunction photocatalyst for 4-nitrophenol (4-NP) degradation. SiC acts as a counterpart of the heterojunction structure and a morphology modifier, which dramatically promotes the reaction rate and visible light responsibility, providing new candidates and strategies in photocatalysis.

1T-MoS2 nanotubes wrapped with N-doped graphene as highly-efficient absorbent and electrocatalyst for Li–S batteries

A novel three-dimensional porous graphene/MoS2 hybrid is synthesized through a facile spray-drying approach. This hybrid is constructed with two-dimensional N-doped graphene nanosheets wrapping one-dimensional nanotubes self-assembled by vertically oriented few-layered 1T-MoS2. Due to its well-designed nanoarchitecture, the hybrid owns several advantages: the metallic 1T-MoS2 and highly conductive graphene skeleton facilitates electron transfer; with abundant specific area and electrocatalytic active sites, the unique hollow nano-architecture enables efficient electrolyte infiltration and Li-ion transfer. The experiments of lithium polysulfides adsorption and in-situ Raman spectra confirm that the hybrid acts as both excellent chemical absorbant and high-efficiency electrocatalyst for the transition of long-chain lithium polysulfides. Benefiting from these merits, the cathode delivers outstanding electrochemical properties with a superior reversible capacity of 1219 mAh g−1 (after 200 cycles at 0.2 C), a low long-term cycling capacity decay of 0.039% per cycle (500 cycles at 1 C), and excellent rate performances.

Carbon-Free, High-Capacity and Long Cycle Life 1D-2D NiMoO4 Nanowires/Metallic 1T MoS2 Composite Lithium-Ion Battery Anodes.

Both metallic 1T MoS2 and conductive molybdate compounds exhibit interesting electrochemical properties, however, the properties of composite electrodes based on these materials have not been investigated. Here, 1T MoS2 single crystal nanosheets and NiMoO4 single crystal nanowires are synthesized and formed into a carbon-free composite lithium-ion anode using blade- and spray-coating. The composite anodes deliver charge mass specific capacity of 940.1 mAh g-1, while the discharge mass specific capacity is up to 941.6 mAh g-1, with a capacity retention ratio of 84.2% after 750 cycles. The charge and discharge volumetric capacity (porosity of 15.6%, full electrode basis, excluding the current collector) are 1238.7 mAh cm-3 and 1240 mAh cm-3, respectively, and the active materials volume fraction is 82.5%. These capacities significantly exceed that of single 1T MoS2 or single NiMoO4 anodes we reported. We calculate if matched vs a cathode with an average discharge voltage of 4.0 V the gravimetric energy density of the composite electrodes would be 3389.8 Wh kg-1. Electrochemical measurements indicate that the composite electrode has excellent electrochemical reversibility, suggesting that the structure has played a crucial role in the cycling process.

Interface-engineered metallic 1T-MoS2 nanosheet array induced via palladium doping enabling catalysis enhancement for lithium–oxygen battery

Lacking strategy to enhance the intrinsic catalytic activity and site density of hexagonal molybdenum disulfide (2H-MoS2) is restricting their further development as viable electrocatalysts for lithium–oxygen (Li–O2) battery. Here, palladium (Pd) induced metallic (1T) MoS2 nanosheet array supported on carbon textiles (Pd-TMS/CT) was deliberately fabricated as a high-efficient freestanding cathode of Li–O2 battery. Transforming semiconducting 2H phase to the stabilized metallic 1T phase of MoS2 was induced by doping Pd using a spontaneous interfacial redox strategy. This novel class of 1T-MoS2 nanosheet array with unique electronic structures enables the electrode with fast reaction kinetics, high electrical transport rate, and proliferated catalytic active sites, which lead to a striking improvement of their intrinsic catalytic behavior in Li–O2 battery. In addition, the synergistic effect with well-designed surface chemistry of MoS2 is favorable for the reversible formation and decomposition of products and the inhibition of side reactions on Pd-TMS/CT cathode. As a result, the battery with Pd-TMS/CT exhibits outstanding electrochemical behavior in terms of high discharge capacity of 7441 mA h g−1, low overpotential, and especially the excellent electrochemical stability for over 2488 h (622 cycles). Moreover, due to its flexibility superiority, the assembled pouch-type battery based on Pd-TMS/CT cathode can stably operate in real air atmosphere under different bending and twisting conditions, which opens up a variety of potential applications of flexible devices with high energy density.

Metallic MoS2 nanosphere electrode for aqueous symmetric supercapacitors with high energy and power densities

Metallic 1T-MoS2 nanospheres composed of nanosheets were facilely synthesized by a hydrothermal method, and the moderate polyvinyl alcohol (PVA) and K+ ions were intentionally introduced in the subsequent exfoliation process. The as-prepared electrode (1T-MoS2/PVAK+), collected on the available carbon paper through vacuum filtration, exhibits a large specific capacitance of 488 F g−1 at a current density of 1 A g−1 in an aqueous electrolyte (3M KCl) because of the crosslink effect PVA to integrate the MoS2 nanospheres and interaction of K+ cation into the interlayers of MoS2. An aqueous symmetric supercapacitor was further prepared with 1T-MoS2/PVAK+ as the positive and negative electrodes. 1T-MoS2/PVAK+//1T-MoS2/PVAK+ device can work with an operating voltage of 1.6 V and manifests a high energy density of 49.0 Wh kg−1 at power density of 800 W kg−1. Remarkably, the maximum power density of 1T-MoS2/PVAK+//1T-MoS2/PVAK+ device reaches as high as 8000 W kg−1 with a corresponding energy density of 38.2 Wh kg−1. Furthermore, this type of aqueous symmetric device evidences the outstanding cycling stability with capacitance retention of 96% after 16,000 charge–discharge cycles at 1 A g−1. These excellent electrochemical performances of 1T-MoS2/PVAK+ electrode demonstrate a promising potential for application in supercapacitor with high energy density and high power density.

The influences of Mg intercalation on the structure and supercapacitive behaviors of MoS2

Metallic 1T MoS2 greatly benefits the supercapacitance of MoS2 due to its considerably higher conductivity as compared to semiconducting 2H MoS2. Alkali metals, such as Li, Na and K, are always used to prepare 1T MoS2 through intercalation of alkali metal ions into the interlayer of 2H MoS2. Nevertheless, the influences of the alkali-earth metals as the guest in the interlayer of MoS2 on its structure and electrochemical capacitor performance are rarely investigated. Herein, we introduced hydrated Mg ions as the guest into MoS2 nanosheets. The interlayer spacing was increased to 1.144 nm after the introduction of hydrated Mg ions, larger than that of the pristine MoS2 (0.620 nm) and restacking MoS2 (0.626 nm). The enlarged interlayer spacing can accommodate more ions during intercalation process. Moreover, the 1T phase concentration after the introduction of hydrated Mg ions was as high as ~ 90%, which benefits the charge transfer during the charging/discharging processes. Consequently, the specific capacitance of the MoS2 with Mg guest ions as well as the energy densities and power densities was greatly improved as compared to those of the restacking MoS2 or pristine MoS2 counterparts. The present work not only demonstrated a new strategy for engineering the physical properties and improving the electrochemical performance of MoS2 supercapacitor electrode through pre-intercalation of alkali-earth metal ions in the interlayer of MoS2, but also has directive significance for the design of other layered electrode materials for energy storage systems.

Metallic 1T MoS2 overlapped nitrogen-doped carbon superstructures for enhanced sodium-ion storage

Abstract The rational design and development of robust anode materials are important to realize high-performance sodium-ion batteries (SIBs). Herein, intrinsically conductive MoS2 supported nitrogen-doped carbon superstructures (MoS2/NC) are reported as a highly active and conductive Na-ion battery anode. The in-situ formation of nitrogen-doped carbon matrices during hydrothermal treatment significantly favours the formation and coexistence of the 2H (semiconducting) and 1T (metallic) phases of MoS2 due to the confinement effect of nitrogen and carbon. In addition, the restacking and intrinsic conductivity of MoS2 nanosheets are diminished through the generation of layered carbon structures. As an anode material for Na-ion battery, the as-prepared MoS2/NC material exhibited improved Na-ion storage with a reversible capacity of 394 mAh g−1 at a current rate of 0.1 C, and a good rate capability. The improved electrochemical performances of the MoS2/NC superstructures might be due to the coexistence of the 2H and 1T phases of MoS2. The layers of carbon in these structures act as spacers to prevent the agglomeration of MoS2 sheets, thus enhancing the conductivity by mitigating volume changes.

Understanding Phase Stability of Metallic 1T-MoS2 Anodes for Sodium-Ion Batteries

We discuss metallic 1T-MoS2 as an anode material for sodium-ion batteries (SIBs). In situ Raman is used to investigate the stability of metallic MoS2 during the charging and discharging processes. Parallel first-principles computations are used to gain insight into the experimental observations, including the measured conductivities and the high capacity of the anode.

Robust Photodetectable Paper from Chemically Exfoliated MoS2-MoO3 Multilayers.

Photodetectors, which are capable of detecting light with varied wavelength, have nowadays been widely applied onto emerging fields such as security, entertainment, healthcare, environment, and so on. As the one with a two-dimensional layered structure, molybdenum disulfide (MoS2) possesses striking optical and electrical properties that can be used in photodetecting, yet the challenges remain in terms of material processing, device fabrication simplicity, and enhancement of overall photodetection performance. In this work, a photodetectable paper based on a mixture of double-phased MoS2 (1T and 2H) and MoO3 was successfully fabricated through a straightforward route, that is, chemical exfoliation and deposition of MoS2 powder on a flexible cellulose ester membrane, followed by inkjet-printed PEDOT:PSS as electrodes. The obtained device shows varied sensitivity to the light with different wavelengths. Compared with that under green and red lights, the prepared photodetector has the highest internal quantum efficiency (0.063%) and responsivity (0.134 mA W-1), while having longest response/recovery time (17.5/15.3 s) when illuminated with purple light (405 nm). The achieved responsivity is much higher than other reported liquid exfoliation- and solution-derived MoS2 photodetectors. This is ascribed to (1) the enhanced photoelectron generation caused by both MoS2 and MoO3 and (2) the good electric conductivity and efficient charge transport caused by the metallic 1T MoS2. This work demonstrates the feasibility of fabricating the MoS2-based photodetector with excellent performance through a simple exfoliation/filtration and inject printing route, and the detailed study on the response to light with different wavelengths unveils the interaction between the device and the incident light, further broadening the potential applications of such design.

Lithium-Sulfur Batteries with a 1T MoS2/Graphene As a Highly Efficient Electrocatalyst

Advanced energy-storage technologies are urgently needed to satisfy the energy demands of the society. Lithium-sulfur (Li-S) batteries are one of the most attractive candidates for next-generation energy-storage technology.1-3 However, it is extremely crucial to suppress the inherent “polysulfide shuttle” for the Li-S batteries to be viable.4, 5 Although electrocatalysis has been shown to enhance cell stability, further performance improvement of Li-S cells is seriously hindered due to a lack of understanding of the electrocatalysis mechanism on the sulfur redox process. Herein the electrocatalysis mechanism on the sulfur redox process is revealed based on both experimental and theoretical work.6 We present the synthesis of well-designed, freestanding, three-dimensional graphene/1T MoS2 (3DG/TM) heterostructures as a highly efficient electrocatalyst for lithium polysulfide (LiPS) conversion.7 The metallic 1T MoS2 nanosheets are hydrophilic with rich active sites and high electronic conductivity that is six orders of magnitude higher than that of 2H MoS2. The high electronic conductivity facilitates fast electron transfer, the hydrophilic property benefits ion diffusion, and the dense active sites ensure sufficient catalytic activity for LiPSs. The 3DG/TM heterostructures of our designed material can maximize the aspect ratio of active catalytic sites. The freestanding, porous morphology of the 3DG/TM material facilitates electrolyte accessibility, enabling better ion transport. Benefitting from these synergistic effects (Fig. 1a), the cells with 3DG/TM exhibit excellent specific capacity and outstanding cycling stability. Furthermore, the fundamental understanding for the enhanced catalytic activity in the MoS2-supported systems is revealed via experimental characterizations and theoretical calculation, which provide new insights and opportunities to develop advanced Li-S batteries with highly efficient electrocatalysts for LiPSs. Based on the deep understanding of the electrocatalysis of LiPSs conversion, the well-designed 3DG/TM heterostructures with rich electrocatalytically active sites ensure high catalytic activity and thus significantly improve the electrochemical performance of Li-S batteries. Even with a very high sulfur loading (10 mg cm-2), the S/3DG/TM cathode not only effectively mitigates the LiPS shuttling, but also delivers excellent specific capacity, outstanding rate capability, and pronounced cycling stability for an impressive number of 500 cycles (Fig. 1b). Fig. 1 (a) The conversion process of LiPSs on a graphene surface with 1T MoS2. The 3DG/TM heterostructures work as a highly efficient electrocatalyst for LiPSs conversion. (b) Long-term cycling cyclability of 3DG/TM with catholyte at 1C rate. REFERENCES 1 Y. Fu, C. Zu, A. Manthiram, J. Am. Chem. Soc. 2013, 135, 18044. 2 J. He, Y. Chen, A. Manthiram, Energ. Environ. Sci. 2018, 11, 2560. 3 J. He, Y. Chen, A. Manthiram, iScience 2018, 36. 4 G. Tan, R. Xu, Z. Xing, Y. Yuan, J. Lu, J. Wen, C. Liu, L. Ma, C. Zhan, Q. Liu, T. Wu, Z. Jian, R. Shahbazian-Yassar, Y. Ren, D. J. Miller, L. A. Curtiss, X. Ji, K. Amine, Nature Energy 2017, 2, 17090. 5 J. He, Y. Chen, W. Lv, K. Wen, C. Xu, W. Zhang, Y. Li, W. Qin, W. He, ACS Nano 2016, 10, 10981. 6 G. Babu, N. Masurkar, H. Al Salem, L. M. R. Arava, J. Am. Chem. Soc. 2016, 139, 171. 7 J. He, G. Hartmann, M. Lee, G. S. Hwang, Y. Chen, A. Manthiram, Energ. Environ. Sci. 2019 (10.1039/C8EE03252A). Figure 1

Interfacial Design of Metallic 1T-MoS2/Carbon Nanotubes for High-Electrocatalytic Hydrogen Evolution Performance

The development of effective non-noble metal based electrocatalysts for the electrocatalytic hydrogen evolution reaction (HER) at lower overpotentials has attracted tremendous attention due to its important role for various electrochemical energy storage devices.1,2 In this study, a simple hydrothermal approach is implied for the preparation of metallic 1T-MoS2/carbon nanotubes (1T-MoS2/CNTs), which acts as an efficient electrocatalyst for HER.3 Fig. 1a, b, and c show the TEM images of 1T-MoS2/CNT composite, in that the 1T-MoS2 consists of a few-layered nanometers in structure and the CNT are well distributed homogenously in the 1T-MoS2 nanosheets, which can reduce aggregation and restacking of the 1T-MoS2 nanosheets. In addition, it can be seen from the fig. 4d that the presence of more intrinsic defects in the 1T-MoS2 nanosheets (marked as circles) was observed, which might result in an expansion of the interlayer spacing. Moreover, the HRTEM image (Fig. 1d) confirmed the presence of the octahedral 1T phase (marked as square) in 1T-MoS2/CNT composite. Besides, 1T-MoS2/CNT composite has been characterized by EDX elemental mapping analysis (Fig. 1f), which shows the existence and homogeneous distribution of Mo, S, and C elements.The tuning of catalytically more active sites and enhancement in the electron transport property can be achieved by designing of the defect-rich 1T-MoS2/CNTs composite material. The unique interfacial composition of the defect-rich 1T-MoS2/CNTs enables enhanced electrocatalytic HER performance with a low onset potential of 96 mV, a small Tafel slope of 54 mV dec-1 and low overpotential of 172 mV at a current density of 10 mA cm−2 (Fig. 1g). In addition, the 1T-MoS2/CNTs demonstrate superior long-term stability in acid conditions and the developed approach is easily applied to the large-scale production of efficient electrocatalysts. The electrocatalytic performance of 1T-MoS2/CNTs composite is also compared with the 1T-MoS2, CNTs, 2H-MoS2 modified electrodes and the commercial Pt/C catalyst. This high-electrocatalytic HER performance is likely attributed to the synergistic effects between the MoS2 nanosheets and CNTS, and rich defects.4 Moreover, DFT calculations also have proved that 1T-MoS2/CNTs show higher free energy change for hydrogen adsorption (ΔGH) than the 1T-MoS2 and CNTs. This work provides a novel and simple strategy to design 1T-MoS2/CNTs for high-performance applications in energy storage fields.

Engineering 2D Metal-Organic Framework/MoS2 Interface for Enhanced Alkaline Hydrogen Evolution.

2D metal-organic frameworks (MOFs) have been widely investigated for electrocatalysis because of their unique characteristics such as large specific surface area, tunable structures, and enhanced conductivity. However, most of the works are focused on oxygen evolution reaction. There are very limited numbers of reports on MOFs for hydrogen evolution reaction (HER), and generally these reported MOFs suffer from unsatisfactory HER activities. In this contribution, novel 2D Co-BDC/MoS2 (BDC stands for 1,4-benzenedicarboxylate, C8 H4 O4 ) hybrid nanosheets are synthesized via a facile sonication-assisted solution strategy. The introduction of Co-BDC induces a partial phase transfer from semiconducting 2H-MoS2 to metallic 1T-MoS2 . Compared with 2H-MoS2 , 1T-MoS2 can activate the inert basal plane to provide more catalytic active sites, which contributes significantly to improving HER activity. The well-designed Co-BDC/MoS2 interface is vital for alkaline HER, as Co-BDC makes it possible to speed up the sluggish water dissociation (rate-limiting step for alkaline HER), and modified MoS2 is favorable for the subsequent hydrogen generation step. As expected, the resultant 2D Co-BDC/MoS2 hybrid nanosheets demonstrate remarkable catalytic activity and good stability toward alkaline HER, outperforming those of bare Co-BDC, MoS2 , and almost all the previously reported MOF-based electrocatalysts.

Atomically engineering activation sites onto metallic 1T-MoS2 catalysts for enhanced electrochemical hydrogen evolution

Engineering catalytic sites at the atomic level provides an opportunity to understand the catalyst’s active sites, which is vital to the development of improved catalysts. Here we show a reliable and tunable polyoxometalate template-based synthetic strategy to atomically engineer metal doping sites onto metallic 1T-MoS2, using Anderson-type polyoxometalates as precursors. Benefiting from engineering nickel and oxygen atoms, the optimized electrocatalyst shows great enhancement in the hydrogen evolution reaction with a positive onset potential of ~ 0 V and a low overpotential of −46 mV in alkaline electrolyte, comparable to platinum-based catalysts. First-principles calculations reveal co-doping nickel and oxygen into 1T-MoS2 assists the process of water dissociation and hydrogen generation from their intermediate states. This research will expand on the ability to improve the activities of various catalysts by precisely engineering atomic activation sites to achieve significant electronic modulations and improve atomic utilization efficiencies.

Suppression of Electrochemically Driven Phase Transitions in Nanostructured MoS2 Pseudocapacitors Probed Using Operando X-ray Diffraction.

Pseudocapacitors with nondiffusion-limited charge storage mechanisms allow for fast kinetics that exceed conventional battery materials. It has been demonstrated that nanostructuring conventional battery materials can induce pseudocapacitive behavior. In our previous study, we found that assemblies of metallic 1T MoS2 nanocrystals show faster charge storage compared to the bulk material. Quantitative electrochemistry demonstrated that the current response is capacitive. In this work, we perform a series of operando X-ray diffraction studies upon electrochemical cycling to show that the high capacitive response of metallic 1T MoS2 nanocrystals is due to suppression of the standard first-order phase transition. In bulk MoS2, a phase transition between 1T and triclinic phases (Li xMoS2) is observed during lithiation and delithiation in both the galvanostatic traces (as distinctive plateaus) and the X-ray diffraction patterns with the appearance of the additional peaks. MoS2 nanocrystal assemblies, on the other hand, show none of these features. We hypothesize that the reduced MoS2 crystallite size suppresses the first-order phase transition and gives rise to solid solution-like behavior, potentially due to the unfavorable formation of nucleation sites in confined spaces. Overall, we find that nanostructuring MoS2 suppresses the 1T-triclinic phase transition and shortens Li-ion diffusion path lengths, allowing MoS2 nanocrystal assemblies to behave as nearly ideal pseudocapacitors.

Contact Resistance at MoS2-Based 2D Metal/Semiconductor Lateral Heterojunctions

The contact resistance at lateral 1T-MoS2/2H-MoS2 heterostructures is theoretically studied, using first-principles simulations based on density functional theory and the nonequilibrium Green’s function method. The computed contact resistance lies between 30 and 40 kΩ μm and is weakly dependent on the contact edge symmetry (armchair or zigzag). These values are about 2 orders of magnitude larger than the experimental ones reported recently on MoS2-based metal/semiconductor lateral heterojunctions. This discrepancy can be explained by considering the interaction of 1T-MoS2 with various chemical species (H, Li, or H2O) present during the local transformation of semiconducting 2H-MoS2 into metallic 1T-MoS2. The functionalization of 1T-MoS2 by these atoms or molecules results in the decrease of its workfunction, leading to contact resistances in the range of few hundred Ω μm.

Metallic 1T-phase MoS2 quantum dots/g-C3N4 heterojunctions for enhanced photocatalytic hydrogen evolution.

Recently, molybdenum disulfide (MoS2) has been regarded as an efficient non-precious-metal co-catalyst for photocatalytic hydrogen (H2) evolution, however, its inherent low-density active site and poor electron transfer efficiency have essentially limited its photocatalytic properties. Here we report that 1T-MoS2 quantum dots (QDs) can act as co-catalysts in assisting the photocatalytic H2 evolution to form heterostructures with g-C3N4 nanosheets (denoted as 1T-MoS2 QDs@g-C3N4). Benefiting from the abundance of exposed catalytic edge sites and the excellent intrinsic conductivity of 1T-MoS2 QDs, an optimized 1T-MoS2 QD@g-C3N4 composite (15 wt%) exhibits an extraordinary photocatalytic H2 evolution rate of 1857 μmol h-1 g-1 under simulated solar light irradiation, apparently 37.9 times higher than that of pure g-C3N4 NSs (49 μmol h-1 g-1). Meanwhile, the 1T-MoS2 QD@g-C3N4 composites exhibit a good stability in the cyclic runs for the photocatalytic H2 production. The high efficient photocatalytic activity and stability of the 1T-MoS2 QD@g-C3N4 composite is primarily attributed to the following reasons: (1) the introduction of 1T-MoS2 QDs results in a stronger light absorption capability in comparison with pure g-C3N4; (2) the tiny particle size of 1T-MoS2 QDs, in which edges and basal surface are catalytically active, provides a proliferated density of catalytically active sites; (3) 1T-MoS2 QD co-catalysts with metallic characteristics could act as efficient electron acceptors, which builds up a highly efficient pathway for photo-generated electrons from the CB of g-C3N4 NSs to 1T-MoS2 and thus realizes rapid spatial charge separation. The improved light harvesting ability, increased catalytically active sites, as well as increased separation of charge carriers could be responsible for the improved photocatalytic H2 evolution. This work will provide new insight for the design and fabrication of smarter, cheaper and more robust artificial photocatalysts for photocatalytic H2 evolution.

In-situ fabrication of needle-shaped MIL-53(Fe) with 1T-MoS2 and study on its enhanced photocatalytic mechanism of ibuprofen

High photocatalytic hole-electron pairs separation efficiency and the wide use of inexpensive and earth-abundant materials as cocatalysts in most semiconductor-based photocatalytic systems are desired for improving the photocatalytic activity and practical application. Herein, we report a facile one-pot solvothermal approach of integrating stable metallic nonmetal materials 1T-MoS2 nanosheets with MIL-53(Fe) to form needle-shaped 1T-MoS2@MIL-53(Fe) (TSMF) composites. Interestingly, the introduction of 1T-MoS2 turns nonspecial-structured MIL-53(Fe) into needle-like structure and the BET analysis reveals that the optimal TSMF composites possess abundant coexistence of micropores and mesopores with a large surface area of 337 m2 g−1, which is about 16 folds higher than that of the pure MOFs. Meanwhile, it is remarkable that the photocatalytic rate of ibuprofen (IBP) by optimal TSMF nanocomposites has improved 7.5 and 9.4 times compared to the pristine MIL-53(Fe) and 1T-MoS2, respectively. The photocatalytic efficiency of TSMF composites enhances due to the emerging micropores, which can provide more adsorption and reaction sites. In addition, the formed compact and uniform interface contact between 1T-MoS2 sheets and MOF may dramatically accelerate the separation of the photo-induced charges, thus enhance the photocatalytic activity. We also study the photocatalytic mechanism combined the corresponding electrochemical testing and the photo-degradation intermediates identified by ion chromatography (IC) and LC–MS-MS, indicating that superoxide radicals (O2–), hydroxyl radical (OH) and electrons (e−) are the main active radicals in IBP photocatalysis and decarboxylation and hydroxylation are the main degradation pathways of IBP.

Metallic 1T-MoS2 nanosheets in-situ entrenched on N,P,S-codoped hierarchical carbon microflower as an efficient and robust electro-catalyst for hydrogen evolution

Phosphorus contained metallic 1T-MoS2 produced from in-situ ammonium intercalation induced surface sulfur atom distortion of MoS2 rooted in N,P,S-codoped hierarchical flowerlike carbon (HCMF) hybrids were successfully prepared via a dopamine self-polymerization together with molybdate process followed by a hydrothermal reduction route. On account of the coupling effect of metallic phase, defect-rich character, heteroatomic dopants and highly conductive carbon support, the P-MoS2@HCMF demonstrates prominent performances with an overpotential of merely 86 mV to deliver a current density of 10 mA cm–2 and a small Tafel slope of 42.35 mV dec–1 for hydrogen evolution reaction (HER) in 0.5 M H2SO4, which are among the best results for molybdenum disulfide based HER catalysts. Strikingly, benefiting from S vacancies and P dopant functioning as electron donors, as well as strain arisen from the tensile of rigid carbon microflower scaffold to MoS2 nanosheets to overcome agglomeration barriers of nanosheets, P-MoS2@HCMF remained well the pristine 1 T phase and exhibited superior cycling stability with indistinguishable overpotential decay over 5000 sweeps and extraordinary HER durability during the 100 h long-term operation with negligible current deterioration. These findings highlight the prospective potential of P-MoS2@HCMF as a highly efficient and stable noble metal-free electrocatalyst towards HER.

Simultaneous Exfoliation and Functionalization of 2H-MoS2 by Thiolated Surfactants: Applications in Enhanced Antibacterial Activity.

Two-dimensional transition metal dichalcogenides (TMDs), such as MoS2, generally exist in two different polymorphic structures, metallic (1T phase) and semiconducting (2H phase). In context of their wide spectrum of applications ranging from electronic to biomedicine, the aspects of ligand conjugation and solution processability are highly significant. In addition, the assessment of their antibacterial property and biocompatibility is equally important to explore their biomedical applications. Here we report a new method for the exfoliation and direct functionalization of 2H-MoS2 using surfactant molecules with thiol functionality. We found that the exfoliated MoS2 using thiolated ligands are functionalized with desired functionality and the processing scheme can be extended to other TMDs. Functionalized 2H-MoS2 exhibits highly enhanced antibacterial efficiency compared to similarly functionalized metallic 1T-MoS2 against pathogenic bacteria. The newly synthesized functionalized 2H-MoS2 exhibits better hemocompatibility, which makes it suitable for in vivo applications. This convenient functionalization method opens the door for many other applications of functionalized semiconducting 2H-MoS2 and other TMDs.