Synthesis of sulfur-rich MoS2 nanoflowers for enhanced hydrogen evolution reaction performance

Construction of surface-rich MoS2 nanoflowers decorated on 2D layered MXene nanohybrid heterostructure for highly efficient and rapid degradation of oxytetracycline

In this study, we successfully developed a hybrid architecture referred to as MoS2@MX, involving the integration of MoS2 layered onto MXene using a straightforward co-precipitation method. This innovative hybrid photocatalyst exhibited remarkable efficiency in removing oxytetracycline (OTC) molecules from aqueous solutions under visible-light irradiation. During the photocatalytic process, both MoS2 and MX played distinct yet complementary roles. MoS2 facilitated efficient electron transfer, while MX contributed to the generation of radicals. This unique collaboration resulted in a noteworthy 99 % oxidation efficiency for OTC degradation within a brief 60 min of visible light exposure in an aqueous environment. The radicals 1O2 and •OH were identified as the principal drivers behind OTC degradation, underscoring the vital role of the hybrid material. Mechanistically, the degradation of OTC involved several key steps, including C-H bond cleavage, de-carboxylation, C-N bond oxidation, and de-chlorination. Importantly, the MoS2@MX hybrid composite demonstrated remarkable stability, maintaining a noteworthy photocatalytic efficiency of 89 % for targeted OTC removal after undergoing five consecutive cycles. In conclusion, this study emphasizes the potential of the MoS2@MX hybrid material as an effective agent for degrading organic OTC compounds within aquatic environments. The hybrid's multifaceted roles and exceptional performance suggest promising applications in sustainable water treatment.

Application of 2D MoS2 Nanoflower for the Removal of Emerging Pollutants from Water

Two-dimensional (2D) nanomaterial-MoS2 (molybdenum disulfide) has gained interest among researchers, owing to its exceptional mechanical, biological, and physiochemical properties. This paper reports on the removal of organic dyes and an emerging contaminant, Ciprofloxacin, by a 2D MoS2 nanoflower as an adsorbent. The material was prepared by a green hydrothermal technique, and its high Brunauer-Emmett-Teller-specific area of 185.541m2/g contributed to the removal of 96% rhodamine-B dye and 85% Ciprofloxacin. Various characterizations, such as X-ray diffraction, scanning electron microscopy linked with energy-dispersive spectroscopy, and transmission electron microscopy, revealed the nanoflower structure with good crystallinity. The feasibility and efficacy of 2D MoS2 nanoflower as a promising adsorbent candidate for the removal of emerging pollutants was confirmed in-depth in batch investigations, such as the effects of adsorption time, MoS2 dosages, solution pH, and temperature. The adsorption mechanism was further investigated based on thermodynamic calculations, adsorption kinetics, and isotherm modeling. The results confirmed the exothermic nature of the enthalpy-driven adsorption as well as the fast kinetics and physisorption-controlled adsorption process. The recyclability potential of 2D MoS2 exceeds four regeneration recycles. MoS2 nanoflower has been shown to be an effective organic pollutant removal adsorbent in water treatment.

Tuning of interfacial HGO@CLS nanohybrid S-scheme heterojunction with improved carrier separation and photocatalytic activity towards RhB degradation

Herein, we premeditated and invented the innovative hybrid photocatalyst 2D/2D CuLa2S4 on holey graphene oxide (HGO) (HGO@CLS) via the hydrothermal method. Electrochemical techniques demonstrate the action of HGO in the HGO@CLS photocatalyst as an effective medium for electron transfer. Combining bimetallic sulfides on porous HGO synergistically provides a higher negative conduction band edge (-0.141 V), greater photo response (10.8 mA/cm2), smaller charge transfer resistance (Rct = 1.79Ω), and lower photoluminescence (PL) spectral intensity. According to our research, the catalytic recitals are sped up when HGO is assimilated into CLS photocatalyst hetero-junction. Additionally, it lowers the reassimilation rate due to the combined mesh nanostructures and functionality of CLS and HGO. UV-Vis DRS, Mott-Schottky, PL, and Electrochemical impedance spectra (EIS) results manifested that the CuLa2S4/HGO makes the spatial separation competent and transference of charge carriers due to the photon irradiation and exhibits superior photocatalytic ability. Electron spin resonance (ESR) analysis confirmed that •OH and h+ were the predominant radical species responsible for Rhodamine B(RhB) degradation. Moreover, conceivable degradation ways of RhB were deduced according to the identified intermediates which are responsible for the degradation of recalcitrant products. To check the stability of the photocatalyst, revival tests were also carried out. Similarly, the oxidative byproducts created in the deprivation courses were looked at, and a thorough explanation for the mechanism of degradation was given.

Phosphorus vacancies improve the hydrogen evolution of MoP electrocatalysts

Although molybdenum phosphide (MoP) has attracted increasing attention as an electrocatalyst in the hydrogen evolution reaction (HER), it is still worth exploring an effective approach to further improve the HER activities of MoP. To date, the generation and effect of P vacancies (Pv) on MoP have been rarely investigated for the HER in both alkaline and acidic media and remain unclear. Here, MoP rich in P vacancies (MoP-Pv) was prepared by hydrogen reduction to improve the HER catalytic performances. As a result, the overpotentials of MoP-Pv were 70 mV and 62 mV lower than those of pristine MoP in 1 M KOH and 0.5 M H₂SO₄ electrolytes, respectively. What's more, the TOFs of MoP-Pv were 3.14 s^-1 and 1.19 s^-1 at an overpotential of 200 mV in 1 M KOH and 0.5 M H₂SO₄, respectively, which are 4.1-fold and 2.5-fold higher than those of pristine MoP. Even when compared with other corresponding catalysts, the TOFs of MoP-Pv still ranked at the top. Due to the surface P vacancies, MoP-Pv possesses more electrochemically active sites and faster charge transfer capability, which all favor higher HER catalytic activities. Overall, our work validates a straightforward and vigorous strategy for improving the intrinsic HER catalytic activities of P vacancies, and also provides guidance for the development of vacancy engineering in electrocatalysts.

Recent progress in 2D hybrid heterostructures from transition metal dichalcogenides and organic layers: properties and applications in energy and optoelectronics fields

Atomically thin transition metal dichalcogenides (TMDs) present extraordinary optoelectronic, electrochemical, and mechanical properties that have not been accessible in bulk semiconducting materials. Recently, a new research field, 2D hybrid heteromaterials, has emerged upon integrating TMDs with molecular systems, including organic molecules, polymers, metal-organic frameworks, and carbonaceous materials, that can tailor the TMD properties and exploit synergetic effects. TMD-based hybrid heterostructures can meet the demands of future optoelectronics, including supporting flexible, transparent, and ultrathin devices, and energy-based applications, offering high energy and power densities with long cycle lives. To realize such applications, it is necessary to understand the interactions between the hybrid components and to develop strategies for exploiting the distinct benefits of each component. Here, we provide an overview of the current understanding of the new phenomena and mechanisms involved in TMD/organic hybrids and potential applications harnessing such valuable materials in an insightful way. We highlight recent discoveries relating to multicomponent hybrid materials. Finally, we conclude this review by discussing challenges related to hybrid heteromaterials and presenting future directions and opportunities in this research field.

The first-principles study on Mo-doped monolayer ReS2

Based on the first-principles calculations, the electronic structure and optical properties of the Mo-doped monolayer rhenium disulfide (ReS₂) model are calculated, and the system stability, bond length, charge difference density, band structure, photoabsorption coefficient, system stability, and reflectivity are analyzed. The calculation results show that doping changes the structural stability of the system, which gradually decreases with an increasing concentration of doping. The calculation of band structure and density of states indicated that the band gap value of the system decreases continuously to 0 with increasing doping concentration, while the average charge population of atoms at doping sites keeps increasing with the better electron-losing ability of atoms. Compared with the intrinsic monolayer ReS₂, the peak of systemic reflectivity at different doping concentrations has corresponding degrees of redshift in a certain wavelength range, as demonstrated by the optical properties.

A visible and near-infrared light dual responsive "signal-off" and "signal-on" photoelectrochemical aptasensor for prostate-specific antigen

A visible and near-infrared light dual responsive "signal-off" and "signal-on" photoelectrochemical aptasensor was constructed for determining prostate-specific antigen (PSA) based on MoS₂ nanoflowers and gold nanobipyramids. The dual responsive photoelectrochemical aptasensor can provide accurate results for PSA determination. For the photoelectrochemical aptasensor fabrication, amino-group functionalized aptamers were immobilized on a MoS₂ nanoflowers modified glassy carbon electrode surface for the specific recognition, and thus to achieve a "signal-off" aptasensor for PSA under visible light illumination. Subsequently, gold nanobipyramids integrated with thiol-functional aptamer were introduced to the "signal-off" aptasensing interface after PSA recognition. Under excitation with near-infrared light at 808 nm, the photocurrent response can be amplified significantly due to the excellent conductivity and local surface plasmon resonance effect of gold nanobipyramids, thus to producing a "signal-on" model for determining PSA. Under the optimized conditions, the dual-responsive photoelectrochemical aptasensor shows a linear response to the logarithm of PSA concentration in the range of 0.005-100 ng/mL. The detection limits for PSA determination with a "signal-off" or a "signal-on" mode are 1.75 pg mL^-1 and 0.39 pg mL^-1, respectively. The dual-responsive photoelectrochemical aptasensor was also employed for determining PSA in clinical serum samples with satisfactory selectivity and excellent accuracy.

Three-dimensional cross-linked Co-MoS2 catalyst on carbon cloth for efficient hydrogen evolution reaction

MoS₂-Based materials are promising hydrogen evolution reaction (HER) electrocatalysts. However, their HER activities are restrained by the poor population of HER activated edge centers, the large area exposed HER inert basal planes, and low conductivity. Fixing these problems on one system is an effective strategy, but it remains a challenge due to the harsh synthetic conditions. Herein, cobalt carbonate hydroxide (CoCH) nanosheets were used as the substrate for preparing a three-dimensional self-supported cross-linked (3DSC) Co-MoS₂ nanostructured HER catalyst, which possesses abundant active centers and fast electronic transfer ability. In addition, Co activates the basal-plane sulfur atom in MoS₂ to be the HER reactive center effectively. Benefiting from these advantages, 3DSC Co-MoS₂ electrode integrated on carbon cloth (CC) shows that it can drive the current density of 10 and 100 mA cm^-2 with only 40 and 119 mV overpotentials, respectively, which is superior to other MoS₂-based HER catalysts reported recently. This research provides a facile strategy for the improvement of efficient HER electrocatalysts.

Synergistic zinc doping and defect engineering toward MoS2 nanosheet arrays for highly efficient electrocatalytic hydrogen evolution

Herein, we have demonstrated synergistic zinc doping and defect engineering toward MoS₂ nanosheet arrays assembled on carbon cloth (CC) by a one-pot hydrothermal approach for the first time, which are employed directly as a cathode for the hydrogen evolution reaction (HER). In our strategy, simultaneously doping sufficient Zn atoms and introducing a defect-rich structure into a MoS₂ nanosheet can synergistically increase active sites. Additionally, the assembly of such nanosheets on CC can achieve lower charge-transfer resistance for the highly efficient HER.

Rapid Charge Separation Boosts Solar Hydrogen Generation at the Graphene-MoS2 Junction: Time-Domain Ab Initio Analysis

Transition metal dichalcogenides and graphene hybrids hold great promise for photovoltaics and photocatalysts. Using a combination of time-domain density functional theory and nonadiabatic molecular dynamics, we investigate the interplay between forward and backward electron transfer (ET), as well as energy relaxation in a van der Waals graphene-MoS₂ heterojunction. We demonstrated that built-in potential formed at the polarized interface produces charge separation upon photoexcitation. The electron left on graphene is injected into MoS₂ on an ultrafast time scale, which is notably faster than energy losses to heat regardless of the initial state energy. Once the electron is relaxed to the conduction band edge state of MoS₂, it transfers back and recombines with the hole remaining on graphene on ultrafast time scales by considering quantum transitions among multiple k points. The obtained time scales for ET, back-ET, and energy relaxation agree well with experimental data. The study reveals that ET that is faster than energy loss makes the graphene-MoS₂ heterojunction efficient for optoelectronic applications.

A nanostructured MoO2/MoS2/MoP heterojunction electrocatalyst for the hydrogen evolution reaction

Electrocatalytic production of hydrogen from water is considered to be a promising and sustainable strategy. In this work, the low-cost nanostructured MoO₂/MoS₂/MoP heterojunction is successfully synthesized by phosphorization of the pre-prepared urchin-like MoO₂/MoS₂ nanospheres as the stable, highly efficient electrocatalysis for the hydrogen evolution reaction (HER). The MoO₂/MoS₂/MoP-800 (MoO₂/MoS₂ nanospheres are phosphated at 800 °C) displays a catalytic ability for the HER with an overpotential of 135 mV to achieve 10 mA cm^-2 and a Tafel slope of 67 mV dec^-1 in 0.5 M H₂SO₄, which is superior to MoO₂/MoS₂ nanospheres (200 °C; 24 h), MoO₂/MoS₂/MoP-700 (MoO₂/MoS₂ nanospheres are phosphated at 700 °C) and MoO₂/MoS₂/MoP-900 (MoO₂/MoS₂ nanospheres are phosphated at 900 °C). Meanwhile, the catalyst exhibits superior properties for HER with an overpotential of 145 mV to achieve 10 mA cm^-2 and a Tafel slope of 71 mV dec^-1 in 1 M KOH solution. Detailed characterizations reveal that the improved HER performances are significantly related to P-doping and the spherical nanostructure. This work not only provides a low-cost selective for electrocatalytic production of hydrogen, but also serves as a guide to optimize the composition and structure of nanocomposites.

Engineering MoS2 nanostructures from various MoO3 precursors towards hydrogen evolution reaction

MoS₂, MoO₂–MoS₂-B and MoO₂–MoS₂-R nanoflowers were prepared using α-MoO₃ particles, α-MoO₃ nanobelts and h-MoO₃ microrods, respectively; larger exposure of Mo–S and lower amounts of Mo–O were responsible for the higher HER performance.

Mass-producible 2D-WS2 bulk modified screen printed electrodes towards the hydrogen evolution reaction

A screen-printable ink that contained varying percentage mass incorporations of two dimensional tungsten disulphide (2D-WS2) was produced and utilized to fabricate bespoke printed electrodes (2D-WS2-SPEs). These WS2-SPEs were then rigorously tested towards the Hydrogen Evolution Reaction (HER) within an acidic media. The mass incorporation of 2D-WS2 into the 2D-WS2-SPEs was found to critically affect the observed HER catalysis with the larger mass incorporations resulting in more beneficial catalysis. The optimal (largest possible mass of 2D-WS2 incorporation) was the 2D-WS2-SPE40%, which displayed a HER onset potential, Tafel slope value and Turn over Frequency (ToF) of -214 mV (vs. RHE), 51.1 mV dec-1 and 2.20 , respectively. These values significantly exceeded the HER catalysis of a bare/unmodified SPE, which had a HER onset and Tafel slope value of -459 mV (vs. RHE) and 118 mV dec-1, respectively. Clearly, indicating a strong electrocatalytic response from the 2D-WS2-SPEs. An investigation of the signal stability of the 2D-WS2-SPEs was conducted by performing 1000 repeat cyclic voltammograms (CVs) using a 2D-WS2-SPE10% as a representative example. The 2D-WS2-SPE10% displayed remarkable stability with no variance in the HER onset potential of ca. -268 mV (vs. RHE) and a 44.4% increase in the achievable current over the duration of the 1000 CVs. The technique utilized to fabricate these 2D-WS2-SPEs can be implemented for a plethora of different materials in order to produce large numbers of uniform and highly reproducible electrodes with bespoke electrochemical signal outputs.

Field Emission Characterization of MoS2 Nanoflowers

Nanostructured materials have wide potential applicability as field emitters due to their high aspect ratio. We hydrothermally synthesized MoS₂ nanoflowers on copper foil and characterized their field emission properties, by applying a tip-anode configuration in which a tungsten tip with curvature radius down to 30-100 nm has been used as the anode to measure local properties from small areas down to 1-100 µm². We demonstrate that MoS₂ nanoflowers can be competitive with other well-established field emitters. Indeed, we show that a stable field emission current can be measured with a turn-on field as low as 12 V/μm and a field enhancement factor up to 880 at 0.6 μm cathode-anode separation distance.

Pyrite FeS2/C nanoparticles as an efficient bi-functional catalyst for overall water splitting

Pyrite FeS₂/C nanoparticles exhibited excellent OER/HER activity and show good overall water splitting efficiency.