Adnan Khalil

Gram‐Scale Aqueous Synthesis of Stable Few‐Layered 1T‐MoS2: Applications for Visible‐Light‐Driven Photocatalytic Hydrogen Evolution

Most recently, much attention has been devoted to 1T phase MoS2 because of its distinctive phase-engineering nature and promising applications in catalysts, electronics, and energy storage devices. While alkali metal intercalation and exfoliation methods have been well developed to realize unstable 1T-MoS2 , but the aqueous synthesis for producing stable metallic phase remains big challenging. Herein, a new synthetic protocol is developed to mass-produce colloidal metallic 1T-MoS2 layers highly stabilized by intercalated ammonium ions (abbreviated as N-MoS2). In combination with density functional calculations, the X-ray diffraction pattern and Raman spectra elucidate the excellent stability of metallic phase. As clearly depicted by high-angle annular dark-field imaging in an aberration-corrected scanning transmission electron microscope and extended X-ray absorption fine structure, the N-MoS2 exhibits a distorted octahedral structure with a 2a0 × a0 basal plane superlattice and 2.72 Å Mo-Mo bond length. In a proof-of-concept demonstration for the obtained materials applications, highly efficient photocatalytic activity is achieved by simply hybridizing metallic N-MoS2 with semiconducting CdS nanorods due to the synergistic effect. As a direct outcome, this CdS:N-MoS2 hybrid shows giant enhancement of hydrogen evolution rate, which is almost 21-fold higher than pure CdS and threefold higher than corresponding annealed CdS:2H-MoS2.

Stable Metallic 1T‐WS2 Nanoribbons Intercalated with Ammonia Ions: The Correlation between Structure and Electrical/Optical Properties

Stable metallic 1T-WS2 nanoribbons with zigzag chain superlattices, highly stabilized by ammonia-ion intercalation, are produced using a facile bottom-up process. The atomic structure of the nanoribbons, including W-W reconstruction and W-S distorted octahedral coordination, results in distinctive electrical transport and optical Raman scattering properties that are very different from semiconducting 2H-WS2 . The correlations between structure and properties are further confirmed by theory calculations.

In situ Integration of a Metallic 1T-MoS2/CdS Heterostructure as a Means to Promote Visible-Light-Driven Photocatalytic Hydrogen Evolution

The replacement of expensive noble‐metals cocatalysts with inexpensive, earth‐abundant, metallic nonmetal materials in most semiconductor‐based photocatalytic systems is highly desirable. Herein, we report the fabrication of stable 1T‐MoS2 slabs in situ grown on CdS nanorods (namely, 1T‐MoS2@CdS) by using a solvothermal method. As demonstrated by ultrafast transient absorption spectroscopy, in combination with steady‐state and time‐resolved photoluminescence, the synergistic effects resulting from formation of the intimate nanojunction between the interfaces and effective electron transport in the metallic phase of 1T‐MoS2 largely contribute to boosting the photocatalytic activity of CdS. Notably, the heterostructure with an optimum loading of 0.2 wt % 1T‐MoS2 exhibits an almost 39‐fold enhancement in the photocatalytic activity relative to that exhibited by bare CdS. This work represents a step towards the in situ realization of a 1T‐phase MoS2‐based heterostructure as a promising cocatalyst with high performance and low cost.

Stable metallic 1T-WS2 ultrathin nanosheets as a promising agent for near-infrared photothermal ablation cancer therapy

In this study, we present the preparation of stable 1T-WS2 ultrathin nanosheets with NH4+ intercalation using a bottom-up hydrothermal method and the potential application of this material in light-induced photothermal cancer therapy. Our results revealed that nanosheets with a size of 150 nm were highly hydrophilic and exhibited strong light absorption and excellent photostability in the broad near-infrared wavelength region. The in vitro experimental results indicated good biocompatibility of the nanosheets. More notably, our in vivo antitumor experiments illustrated that light-induced photothermal ablation originating from irradiation of the 1T-WS2 nanosheets with an 808 nm laser could efficiently kill tumor cells; these effects were obtained not only at the cellular level but also in the living organs of mice. This result may lead to new applications of two-dimensional layered materials in novel photothermal therapies and other photothermal related fields.

Stable 1T-MoSe2 and Carbon Nanotube Hybridized Flexible Film: Binder-Free and High-Performance Li-Ion Anode

Two-dimensional stable metallic 1T-MoSe2 with expanded interlayer spacing of 10.0 Å in situ grown on SWCNTs film is fabricated via a one-step solvothermal method. Combined with X-ray absorption near-edge structures, our characterization reveals that such 1T-MoSe2 and single-walled carbon nanotubes (abbreviated as 1T-MoSe2/SWCNTs) hybridized structure can provide strong electrical and chemical coupling between 1T-MoSe2 nanosheets and SWCNT film in a form of C-O-Mo bonding, which significantly benefits a high-efficiency electron/ion transport pathway and structural stability, thus directly enabling high-performance lithium storage properties. In particular, as a flexible and binder-free Li-ion anode, the 1T-MoSe2/SWCNTs electrode exhibits excellent rate capacity, which delivers a capacity of 630 mAh/g at 3000 mA/g. Meanwhile, the strong C-O-Mo bonding of 1T-MoSe2/SWCNTs accommodates volume alteration during the repeated charge/discharge process, which gives rise to 89% capacity retention and a capacity of 971 mAh/g at 300 mA/g after 100 cycles. This synthetic route of a multifunctional MoSe2/SWCNTs hybrid might be extended to fabricate other 2D layer-based flexible and light electrodes for various applications such as electronics, optics, and catalysts.

Metallic 1T-WS2 nanoribbons as highly conductive electrodes for supercapacitors

Layered tungsten disulfide (WS2) has attracted great attention because of its high potential for electrochemical energy applications. However, the semiconducting nature of WS2 with a 2H phase largely hinders its electrochemical performance due to poor electronic conductivity. In this study, we have successfully synthesized a metallic 1T-WS2 nanoribbon with stable ammonia-ion intercalation as a highly conductive electrode for high-performance supercapacitors. The specific capacitance using the metallic 1T-WS2 electrode exhibits significant enhancement upto the value of 2813 μF cm−2. This value is 12 times higher compared to semiconducting 2H-WS2. Moreover, the 1T-WS2 electrode has good stability even under high current scans, which is ascribed to the stable ammonia-ion interaction. The correlation between the 1T-WS2 structure and its electrochemical performance has also been discussed.

Engineering interfacial charge-transfer by phase transition realizing enhanced photocatalytic hydrogen evolution activity

Thin, planar nanojunctions between layered 2H/1T-MoS2 and graphitic C3N4 (g-C3N4) were fabricated and 1T phase nanojunctions allowed faster photogenerated electrons across the junction interfaces to facilitate hydrogen evolution. This research represents a proof of concept for the rational fabrication of thin 1T phase interfacial junctions and the importance of the 1T phase for further improving the HER perfomance.

In situ growth of metallic 1T-WS2 nanoislands on single-walled carbon nanotube films for improved electrochemical performance

Layered tungsten disulfide (WS2) is a potential electrode material for electric double layer capacitance (EDLC) and hydrogen evolution reaction (HER). However, the electrochemical performance of WS2 has been hindered by the semiconducting nature and poor active sites. Herein, we have demonstrated a bottom-up hydrothermal approach to fabricate metallic 1T-WS2 nanoislands in situ grown on flexible single-walled carbon nanotube nonwovens (1T-WS2@SWCNT). The robust hybrids with a tight interface possess nanoscopic few-layered WS2 pieces with an abundance of exposed sites, along with a unique woven-architecture originating from the high conductive carbon nanotube network. The in situ-growing enhanced interface between metallic WS2 nanoislands and SWCNTs provides a relatively strong electrical coupling integrity, which facilitates charge transfer during electrochemical reactions. The merits of rich active sites, excellent conductivity and well bonding-interactions are significantly beneficial to improve the electrochemical performance. Particularly, in contrast to the pure material, the as-obtained hybrids are found to exhibit higher EDLC capacity (226 mF cm−2), almost 646-fold higher than pure 1T-WS2, smaller Tafel slope (57 mV per decade) and lower HER overpotential (∼25 mV) than any WS2-based materials reported so far.

Synthesis of Ni9S8/MoS2 heterocatalyst for Enhanced Hydrogen Evolution Reaction

We demonstrate a heterostructure Ni9S8/MoS2 hybrid with tight interface synthesized via an improved hydrothermal method. As compared to pure MoS2, the increased surface area and the shorten charge transport pathway in the layered hybrid significantly promote the photocatalytic efficiency for hydrogen evolution reaction (HER). In particularly, the optimized Ni9S8/MoS2 hybrid with 20 wt % Ni9S8 exhibits the highest photocatalytic activity with HER value of 406 μmolg-1h-1, which is enhanced by 70% compared to that of pure MoS2 nanosheets (285.0 μmolg-1h-1). Moreover, the value is 4 times more than the commercial MoS2 (92.0 μmolg-1h-1), indicating the high potential of the hybrid in the catalytic fields.