Interlayer engineering of molybdenum disulfide toward efficient electrocatalytic hydrogenation.

Electrocatalytic hydrogenation (ECH) enables the sustainable production of chemicals under ambient condition; however, suffers from serious competition with hydrogen (H2) evolution and the use of precious metals as electrocatalysts. Herein, molybdenum disulfide is for the first time developed as an efficient and noble-metal-free catalyst for ECH via in situ intercalation of ammonia or alkyl-amine cations. This interlayer engineering regulates phase transition (2H â†’ 1 T), and effectively ameliorates electronic configurations and surface hydrophobicity to promote the ECH of biomass-derived oxygenates, while prohibiting H2 evolution. The optimal one intercalated by dimethylamine (MoS2-DMA) is capable of hydrogenating furfural (FAL) to furfuryl alcohol with high Faradaic efficiency of 86.3%-73.3% and outstanding selectivity of >95.0% at -0.25 to -0.65 V (vs. RHE), outperforming MoS2 and other conventional metals. Such prominent performance stems from the enhanced chemisorption and surface hydrophobicity. The chemisorption of H intermediate and FAL, synchronously strengthened on the edge-sites of MoS2-DMA, accelerates the surface elementary step following Langmuir-Hinshelwood mechanism. Moreover, the improved hydrophobicity benefits FAL affinity to overcome diffusion limitation. Discovering the effective modulation of MoS2 from a typical H2 evolution electrocatalyst to a promising candidate for ECH, this study broadens the scope to exploit catalysts used for electrochemical synthesis.

Revealing Facet Effects of Palladium Nanocrystals on Electrochemical Biosensing.

Noble-metal nanocrystals (NCs) are functional segments of biosensing platforms, but their sensitivity and facet effects are still challenging. Conventional synthesis using surfactants to direct crystal growth unfortunately causes adsorbate-surface hindrance, which not only reduces sensing responses but also leads to misunderstanding on facet-dependence. Herein, we utilize electrochemical CO displacement to remove residual surfactants from facet-engineered Pd NCs, and further investigate the structure-activity relationship on specific facets, for example, {100} in cubes, {111} in octahedrons, and {110} in rhombic dodecahedrons. Along with the remarkably boosted response, facet dependence is obvious for H2O2 sensing after surface cleaning. The Pd{100} shows high sensitivity, low detection limit, and wide applicable concentration range, superior to the {110} and {111}. This can be theoretically interpreted by the befitting *OH binding on {100} and thereby the facilitated H2O2 reduction kinetics. The outstanding selectivity to H2O2 ensures the high efficiency of Pd NCs to measure intracellular H2O2 and recognize different types of cancer cells. Moreover, facet effects are also evidenced in glucose detection, highlighting that this work can provide guidelines to design efficient sensing platforms.

Efficient electrochemical biosensing of hydrogen peroxide on bimetallic Mo1-xWxS2 nanoflowers.

Two-dimensional transition-metal dichalcogenides can serve as emerging biosensing platforms after rational structural optimization. Herein, we develop a series of Mo1-xWxS2 and investigate the composition-dependent sensing of hydrogen peroxide (H2O2). Among them, the Mo0.75W0.25S2 affords high sensitivity (1290 µA mM-1 cm-2), good selectivity, and wide applicable concentration range (4 × 10-1-1.0 × 104 µM). As indicated by theoretical investigations, such prominent performance stems from the bimetallic electronic configurations and the enhanced *OH binding on surface. Moreover, the Mo0.75W0.25S2 is capable of monitoring trace amounts of H2O2 released from normal cells and various cancer cells, which provides efficient cell detection for clinical diagnosis. In addition, the composition-dependence, as a result of electronic modulation on Mo1-xWxS2 surface, is further evidenced on electrocatalytic hydrogen evolution reaction, which highlights the promise in sensing and electrocatalysis that share similar electrochemical fundamentals.

Making Use of the δ Electrons in K4Mo2(SO4)4 for Visible-Light-Induced Photocatalytic Hydrogen Production.

Quadruply bonded dimolybdenum complexes with a σ2π4δ2 electronic configuration for the ground state have rich metal-centered photochemistry. An earlier study showed that stoichiometric or less amount of molecular hydrogen was produced upon irradiation by ultraviolet light (λ = 254 nm) of K4Mo2(SO4)4 in sulfuric acid solution, which was attributed to the reductive capability of the ππ* excited state. To make use of the δ electrons for visible-light-induced photocatalytic hydrogen evolution, a multicomponent heterogeneous photocatalytic system containing K4Mo2(SO4)4 photosensitizer, TiO2 electron relay, and MoS2 cocatalyst is designed and tested. With ascorbic acid added as a sacrificial reagent, irradiation by artificial sunlight (AM 1.5) on the reaction in 5 M H2SO4 has produced 13 400 µmol g-1 of molecular hydrogen (based on the Mo2 complex), which is 30 times higher than the hydrogen yield obtained from the reaction of bare K4Mo2(SO4)4 with H2SO4 under ultraviolet light irradiation. Further improvement of hydrogen evolution is achieved by addition of oxalic acid, along with an electron donor, which gives an additional 50% increase in H2 yield. Spectroscopic analyses indicate that, in this case, a junction between the Mo2 complex and TiO2 is built by the oxalate bridging ligand, which facilitates charge injection and separation from the Mo2 core. This Mo2-TiO2-MoS2 system has achieved a high hydrogen evolution rate up to 4570 µmol g-1 h-1. The efficiency of K4Mo2(SO4)4 as a metal-centered photosensitizer is also proved by parallel experiments with a dye chromophore, fluorescein, which presents comparable H2 yields and hydrogen evolution rates. Most importantly, in this study, detailed analyses illustrate that the photocatalytic cycle with hydrogen gas as an outcome of the reaction is established by involvement of the δδ* excited state generated by visible light irradiation. Therefore, this work shows the potential of quadruply bonded Mo2 complexes as photosensitizers for photocatalytic hydrogen evolution.

Molybdenum disulfide nanoflowers mediated anti-inflammation macrophage modulation for spinal cord injury treatment.

Spinal cord injury (SCI) can cause locomotor dysfunctions and sensory deficits. Evidence shows that functional nanodrugs can regulate macrophage polarization and promote anti-inflammatory cytokine expression, which is feasible in SCI immunotherapeutic treatments. Molybdenum disulfide (MoS2) nanomaterials have garnered great attention as potential carriers for therapeutic payload. Herein, we synthesize MoS2@PEG (MoS2 = molybdenum disulfide, PEG = poly (ethylene glycol)) nanoflowers as an effective carrier for loading etanercept (ET) to treat SCI. We characterize drug loading and release properties of MoS2@PEG in vitro and demonstrate that ET-loading MoS2@PEG obviously inhibits the expression of M1-related pro-inflammatory markers (TNF-α, CD86 and iNOS), while promoting M2-related anti-inflammatory markers (Agr1, CD206 and IL-10) levels. In vivo, the mouse model of SCI shows that long-circulating ET-MoS2@PEG nanodrugs can effectively extravasate into the injured spinal cord up to 96 h after SCI, and promote macrophages towards M2 type polarization. As a result, the ET-loading MoS2@PEG administration in mice can protect survival motor neurons, thus, reducing injured areas at central lesion sites, and significantly improving locomotor recovery. This study demonstrates the anti-inflammatory and neuroprotective activities of ET-MoS2@PEG and promising utility of MoS2 nanomaterial-mediated drug delivery.

Expanding the interlayers of molybdenum disulfide toward the highly sensitive sensing of hydrogen peroxide.

Expandable interlayers in two-dimensional (2D) transition metal dichalcogenides enable the regulation of physicochemical properties toward boosted applications. Herein, interlayer-expanded MoS2 (IE-MoS2) was designed as a sensitive electrochemical biosensor for H2O2via a one-step hydrothermal process employing excessive thiourea. This facile fabrication successfully avoids the complicated manipulations in conventional exfoliation-resembling strategies. The as-obtained IE-MoS2 features an expanded interlayer-spacing of 9.40 Å and metallic electronic configurations. Thereby, it possesses good conductivity and more importantly enhanced binding with the *OH intermediate, accomplishing a fast kinetics of H2O2 reduction (H2O2 + 2e- → 2OH-) and consequently a sensitive response in electrochemical H2O2 sensing. The optimal IE-MoS2 affords a high sensitivity (1706.0 µA mM-1 cm-2) and a low detection limit (0.2 µM), outperforming the non-expanded MoS2 (738.0 µA mM-1 cm-2, 1.0 µM) and most of the previously reported materials free from enzymes. Moreover, it performs well in real samples and in the presence of various interfering substances and can be used to measure the intracellular H2O2 amount of cancer cells; this suggests the possible applications of IE-MoS2 in real-time monitoring, clinical diagnosis and pathophysiology. This study will inspire the rational design of 2D sensing materials via regulation of their interlayer chemistry.

Molybdenum-Incorporated Mesoporous Silica: Surface Engineering toward Enhanced Metal-Support Interactions and Efficient Hydrogenation.

In heterogeneous catalysis, strong metal-support interactions are highly desired to improve catalytic turnover on metal catalysts. Herein, molybdenum is uniformly incorporated into mesoporous silica (KIT-6) to accomplish strong interactions with iridium catalysts, and consequently, active and selective hydrogenation of carbonyl compounds. Mo-incorporated KIT-6 (Mo-KIT-6) affords electronic interactions to improve the proportion of metallic Ir0 species, avoiding the easy surface oxidation of ultrafine metals in silica mesocavities. Owing to the effective H2 activation and subsequent hydrogenation on metallic Ir0 sites, optimal Ir/Mo-KIT-6 with a high Ir0/Irδ+ ratio delivers prominent performance in the hydrogenation of amides to amines and α,ß-unsaturated aldehydes to unsaturated alcohols. As for N-acetylmorpholine hydrogenation, the Ir/Mo-KIT-6 catalyst achieves efficient turnover toward N-ethylmorpholine with high selectivity (>99%) and exhibits activity that relies on the engineered chemical state of Ir sites. Such promotion is further proved to be universal in cinnamaldehyde hydrogenation. This work will provide new opportunities for catalyst design through surface/interface engineering.

Chemoselective Hydrogenation of Cinnamaldehyde on Iron-Oxide Modified Pt/MoO3-y Catalysts.

Hydrogenation of α,ß-unsaturated aldehydes to unsaturated alcohols suffers a huge challenge in chemoselectivity. Herein, surface decoration by FeOx is introduced to remarkably improve the selectivity of cinnamyl alcohol (COL) in cinnamaldehyde (CAL) hydrogenation on Pt/MoO3-y . The enhanced acidity on Pt-FeOx interfaces is beneficial for the chemisorption and activation of C=O bonds, promoting selective hydrogenation. The optimal catalysts with defined FeOx decoration afford efficient and chemoselective CAL hydrogenation (91.3 % selectivity) under mild conditions (PH2 =1 MPa, T=30 °C). Moreover, such innovation is further extended to develop other efficient metal (Ir, Rh and Pd) catalysts, identifying a universal promotion to Pt-group metals. This work is anticipated to inspire the rational design of high-performance catalysts via effective surface/interface engineering.

Hydrogen Doping into MoO3 Supports toward Modulated Metal-Support Interactions and Efficient Furfural Hydrogenation on Iridium Nanocatalysts.

As promising supports, reducible metal oxides afford strong metal-support interactions to achieve efficient catalysis, which relies on their band states and surface stoichiometry. In this study, in situ and controlled hydrogen doping (H doping) by means of H2 spillover was employed to engineer the metal-support interactions in hydrogenated MoOx -supported Ir (Ir/H-MoOx ) catalysts and thus promote furfural hydrogenation to furfuryl alcohol. By easily varying the reduction temperature, the resulting H doping in a controlled manner tailors low-valence Mo species (Mo5+ and Mo4+ ) on H-MoOx supports, thereby promoting charge redistribution on Ir and H-MoOx interfaces. This further leads to clear differences in H2 chemisorption on Ir, which illustrates its potential for catalytic hydrogenation. As expected, the optimal Ir/H-MoOx with controlled H doping afforded high activity (turnover frequency: 4.62 min-1 ) and selectivity (>99 %) in furfural hydrogenation under mild conditions (T=30 °C, PH2 =2 MPa), which means it performs among the best of current catalysts.

Enhancing Metal-Support Interactions by Molybdenum Carbide: An Efficient Strategy toward the Chemoselective Hydrogenation of α,ß-Unsaturated Aldehydes.

Metal-support interactions are desired to optimize the catalytic turnover on metals. Herein, the enhanced interactions by using a Mo2C nanowires support were utilized to modify the charge density of an Ir surface, accomplishing the selective hydrogenation of α,ß-unsaturated aldehydes on negatively charged Ir(δ-) species. The combined experimental and theoretical investigations showed that the Ir(δ-) species derive from the higher work function of Ir (vs. Mo2C) and the consequently electron transfer. In crotonaldehyde hydrogenation, Ir/Mo2C delivered a crotyl alcohol selectivity as high as 80%, outperforming those of counterparts (<30%) on silica. Moreover, such electronic metal-support interactions were also confirmed for Pt and Au, as compared with which, Ir/Mo2C was highlighted by its higher selectivity as well as the better activity. Additionally, the efficacy for various substrates further verified our Ir/Mo2C system to be competitive for chemoselective hydrogenation.