Biomimetic Oxygen Activation by MoS2/Ta3N5Nanocomposites for Selective Aerobic Oxidation

Chemical fixation of atmospheric CO2 in tricopper(II)-carbonato complexes with tetradentate N-donor ligands: reactive intermediates, probable mechanisms, and catalytic and magneto-structural studies

In the present era, the fixation of atmospheric CO2 is of significant importance and plays a crucial role in maintaining the balance of carbon and energy flow within ecosystems. Generally, CO2 fixation is carried out by autotrophic organisms; however, the scientific community has paid substantial attention to execute this process in laboratory. In this report, we synthesized two carbonato-bridged trinuclear copper(II) complexes, [Cu3(L1)3(μ3-CO3)](ClO4)3 (1) and [Cu3(L2)3(μ3-CO3)](ClO4)3 (2) via atmospheric fixation of CO2 starting with Cu(ClO4)2·6H2O and easily accessible pyridine/pyrazine-based N4 donor Schiff base ligands L1 and L2, respectively. Under very similar reaction conditions, the ligand framework embedded with the phenolate moiety (HL3) fails to do so because of the reduction of the Lewis acidity of the metal center, inhibiting the formation of a reactive hydroxide bound copper(II) species, which is required for the fixation of atmospheric CO2. X-ray crystal structures display that carbonate-oxygen atoms bridge three copper(II) centers in μ3syn-anti disposition in 1 and 2, whereas [Cu(HL3)(ClO4)] (3) is a mononuclear complex. Interestingly, we also isolated an important intermediate of atmospheric CO2 fixation and structurally characterized it as an anti-anti μ2 carbonato-bridged dinuclear copper(II) complex, [Cu2(L2)2(μ2-CO3)](ClO4)2·MeOH (2-I), providing an in-depth understanding of CO2 fixation in these systems. Variable temperature magnetic susceptibility measurement suggests ferromagnetic interactions between the metal centers in both 1 and 2, and the results have been further supported by DFT calculations. The catalytic efficiency of our synthesized complexes 1-3 was checked by means of catechol oxidase and phenoxazinone synthase-like activities. While complexes 1 and 2 showed oxidase-like activity for aerobic oxidation of o-aminophenol and 3,5-di-tert-butylcatechol, complex 3 was found to be feebly active. ESI mass spectrometry revealed that the oxidation reaction proceeds through the formation of complex-substrate intermediations and was further substantiated by DFT calculations. Moreover, active catalysts 1 and 2 were effectively utilized for the base-free oxidation of benzylic alcohols in the presence of air as a green and sustainable oxidant and catalytic amount of TEMPO in acetonitrile. Various substituted benzylic alcohols smoothly converted to their corresponding aldehydes under very mild conditions and ambient temperature. The present catalytic protocol showcases its environmental sustainability by producing minimal waste.

Bridging Atom Engineering for Low-Temperature Oxygen Activation in a Robust Metal-Organic Framework

Achieving active site engineering at the atomic level poses a significant challenge in the design and optimization of catalysts for energy-efficient catalytic processes, especially for a reaction with two reactants competitively absorbed on catalytic active sites. Herein, we show an example that tailoring the local environment of cobalt sites in a robust metal-organic framework through substituting the bridging atom from -Cl to -OH group leads to a highly active catalyst for oxygen activation in an oxidation reaction. Comprehensive characterizations reveal that this variation imparts drastic changes on the electronic structure of metal centers, the competitive reactant adsorption behavior, and the intermediate formation. As a result, exceptional low-temperature CO oxidation performance was achieved with T25(Temperature for 25 % conversion)=35 °C and T100 (Temperature for 100 % conversion)=150 °C, which stands out from existing MOF-based catalysts and even rivals many noble metal catalysts. This work provides a guidance for the rational design of catalysts for efficient oxygen activation for an oxidation reaction.

Polypyrrole-induced active-edge-S and high-valence-Mo reinforced composites with boosted electrochemical performance for the determination of 2,4,6-trichlorophenol in the aquatic environment

With the extensive application of halogenated aromatic compounds, including 2,4,6-Trichlorophenol (2,4,6-TCP), improper treatment or discharge contribute to persistently harmful effects on humans and the ecosystem, rendering the identification and monitoring of 2,4,6-TCP in the aquatic environment urgently required. In this study, a highly sensitive electrochemical platform was developed using active-edge-S and high-valence-Mo rich MoS₂/polypyrrole composites. MoS₂/PPy illustrates superior electrochemical performance and catalytic activity and has not been explored for detecting chlorinated phenols previously. The local environment of polypyrrole induces the richness of active edge S and a high oxidation state of Mo species in the composites, both of which endorse a sensitive anodic current response due to the favored oxidation of 2,4,6-TCP through nucleophilic substitution. Also, the higher complementarity between pyrrole and 2,4,6-TCP with respective electron-rich and electron-poor features through π-π stacking interactions enhances the specific detection capability of 2,4,6-TCP by the MoS₂/polypyrrole-modified electrode. The MoS₂/polypyrrole-modified electrode achieved a linear range of 0.1-260 μM with an ultralow limit of detection of 0.009 μM. Additionally, the structural stability boosted by the linkage of polypyrrole and MoS₂ results in good resistance and satisfactory recovery in real water samples. The compiled results demonstrate that the proposed MoS₂/polypyrrole composite opens up a new potential to advance a sensitive, selective, facile fabrication, and low-cost platform for the on-site determination of 2,4,6-TCP in aquatic systems. The sensing of 2,4,6-TCP is important to monitor its occurrence and transport, and can also serve to track the effectiveness and adjust subsequent remediation treatments applied to contaminated sites.

Synthesis and Aerobic Oxidation Catalysis of Mesoporous Todorokite-Type Manganese Oxide Nanoparticles by Crystallization of Precursors

The pursuit of a high surface area while maintaining high catalytic performance remains a challenge due to a trade-off relationship between these two features in some cases. In this study, mesoporous todorokite-type manganese oxide (OMS-1) nanoparticles with high specific surface areas were synthesized in one step by a new synthesis approach involving crystallization (i.e., solid-state transformation) of a precursor produced by a redox reaction between MnO₄^- and Mn²⁺ reagents. The use of a low-crystallinity precursor with small particles is essential to achieve this solid-state transformation into OMS-1 nanoparticles. The specific surface area reached up to ca. 250 m² g^-1, which is much larger than those (13-185 m² g^-1) for Mg-OMS-1 synthesized by previously reported methods including multistep synthesis or dissolution/precipitation processes. Despite ultrasmall nanoparticles, a linear correlation between the catalytic reaction rates of OMS-1 and the surface areas was observed without a trade-off relationship between particle size and catalytic performance. These OMS-1 nanoparticles exhibited the highest catalytic activity among the Mn-based catalysts tested for the oxidation of benzyl alcohol and thioanisole with molecular oxygen (O₂) as the sole oxidant, including highly active β-MnO₂ nanoparticles. The present OMS-1 nanomaterial could also act as a recyclable heterogeneous catalyst for the aerobic oxidation of various aromatic alcohols and sulfides under mild reaction conditions. The mechanistic studies showed that alcohol oxidation proceeds with oxygen species caused by the solid, and the high surface area of OMS-1 significantly contributes to an enhancement of the catalytic activity for aerobic oxidation.

Fabrication of a novel ternary heterojunction composite Ag2MoO4/Ag2S/MoS2 with significantly enhanced photocatalytic performance

A novel ternary heterojunction Ag₂MoO₄/Ag₂S/MoS₂ was successfully fabricated via a facile two-step method. The prepared ternary heterojunction showed much enhanced catalytic activity compared with monomers and binary heterojunctions.

Ta3N5 nanorods encapsulated into 3D hydrangea-like MoS2 for enhanced photocatalytic hydrogen evolution under visible light irradiation

Tantalum nitride (Ta₃N₅) with an appealing band gap (∼2.1 eV) has emerged as a promising catalyst in the photocatalysis field. However, Ta₃N₅ application in the photocatalytic hydrogen evolution reaction (HER) is limited due to disadvantages such as unsatisfactory separation and transfer of photogenerated carriers. Here we utilize MoS₂ as co-catalysts to promote the kinetics of photocatalytic H₂ evolution over Ta₃N₅. The Ta₃N₅ nanorods were encapsulated into 3D hydrangea-like MoS₂ for maximizing the contact areas between Ta₃N₅ and MoS₂ and offering rich active sites. More importantly, spectroscopic analysis and theoretical calculations consistently reveal that the unique interfacial interaction, as well as the matching band alignment between Ta₃N₅ and MoS₂, accelerates the photogenerated charge extraction from Ta₃N₅ to MoS₂, reducing charge recombination losses in Ta₃N₅. Thus, the optimized Ta₃N₅/MoS₂ hybrid exhibits a substantially enhanced hydrogen evolution rate (56.5 μmol h^-1), over 22 times higher than that of pristine Ta₃N₅. This work may provide a general strategy to overcome the low photocatalytic activity of nitrides for hydrogen evolution.

pH-Universal Water Splitting Catalyst: Ru-Ni Nanosheet Assemblies

Although electrochemical water splitting is an effective and green approach to produce oxygen and hydrogen, the realization of efficient bifunctional catalysts that are stable in variable electrolytes is still a significant challenge. Herein, we report a three-dimensional hierarchical assembly structure composed of an ultrathin Ru shell and a Ru-Ni alloy core as a catalyst functioning under universal pH conditions. Compared with the typical Ir/C-Pt/C system, superior catalytic performances and excellent durability of the overall water splitting under universal pH have been demonstrated. The introduction of Ni downshifts the d-band center of the Ru-Ni electrocatalysts, modulating the surface electronic environment. Density functional theory results reveal that the mutually restrictive d-band interaction lowers the binding of (Ru, Ni) and (H, O) for easier O-O and H-H formation. The structure-induced eg-dz² misalignment leads to minimization of surface Coulomb repulsion to achieve a barrier-free water-splitting process.

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A facile method for the synthesis of 3D hierarchical assembly Ru-Ni NA catalyst

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Superior catalytic reactivity and stability of water splitting in universal pH

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The introduction of Ni can modify the d-band and surface electronic environment

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Minimization of the surface Coulomb repulsion leads to barrier-free catalysis process

2D-MoS2 photocatalyzed cross dehydrogenative coupling reaction synchronized with hydrogen evolution reaction

The chemically exfoliated 2D-MoS₂ has a mixture of 1T (metallic) and 2H (semiconducting) phases.

Heterogeneously Catalyzed Aerobic Oxidation of Sulfides with a BaRuO3 Nanoperovskite

A rhombohedral BaRuO₃ nanoperovskite, which was synthesized by the sol-gel method using malic acid, could act as an efficient heterogeneous catalyst for the selective oxidation of various aromatic and aliphatic sulfides with molecular oxygen as the sole oxidant. BaRuO₃ showed much higher catalytic activities than other catalysts, including ruthenium-based perovskite oxides, under mild reaction conditions. The catalyst could be recovered by simple filtration and reused several times without obvious loss of its high catalytic performance. The catalyst effect, ¹⁸O-labeling experiments, and kinetic and mechanistic studies showed that substrate oxidation proceeds with oxygen species caused by the solid. The crystal structure of ruthenium-based oxides is crucial to control the nature of the oxygen atoms and significantly affects their oxygen transfer reactivity. Density functional theory calculations revealed that the face-sharing octahedra in BaRuO₃ likely are possible active sites in the present oxidation in sharp contrast to the corner-sharing octahedra in SrRuO₃, CaRuO₃, and RuO₂. The superior oxygen transfer ability of BaRuO₃ is also applicable to the quantitative conversion of dibenzothiophene into the corresponding sulfone and gram-scale oxidation of 4-methoxy thioanisole, in which 1.20 g (71% yield) of the analytically pure sulfoxide could be isolated.

Polyoxometalate-Based Metal-Organic Frameworks for Selective Oxidation of Aryl Alkenes to Aldehydes

Polyoxometalates (POMs) show considerable catalytic performance toward the selective oxidation of alkenes to aldehydes, which is commercially valuable for the production of pharmaceuticals, dyes, perfumes, and fine chemicals. However, the low specific surface area of POMs as heterogeneous catalysts and poor recyclability as homogeneous catalysts have hindered their wide application. Dispersing POMs into metal-organic frameworks (MOFs) for the construction of POM-based MOFs (POMOFs) suggests a promising strategy to realize the homogeneity of heterogeneous catalysis. Herein, we report two new POMOFs with chemical formulas of [Co(BBTZ)₂][H₃BW₁₂O₄₀]·10H₂O (1) and [Co₃(H₂O)₆(BBTZ)₄][BW₁₂O₄₀]·NO₃·4H₂O (2) (BBTZ = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene) for the selective oxidation of alkenes to aldehydes. Compound 1 possesses a non-interpenetrated three-dimensional (3D) cds-type open framework with a 3D channel system. Compound 2 displays a 3D polyrotaxane framework with one-dimensional channels along the [100] direction. In the selective oxidation of styrene into benzaldehyde, compound 1 can achieve a 100% conversion in 4 h with 96% selectivity toward benzaldehyde, which is superior to that of compound 2. A series of control experiments reveal that the co-role of [BW₁₂O₄₀]^5- and Co²⁺ active center as well as a more open framework feature co-promote the catalytic property of the POMOFs in this case. This work may suggest a new option for the development of POMOF catalysts in the selective oxidation of alkenes.

Superior adsorption and photoinduced carries transfer behaviors of dandelion-shaped Bi2S3@MoS2: experiments and theory

The enhanced light-harvesting capacity and effective separation of photogenerated carriers in fantastic hierarchical heterostructures enjoy striking attention for potential applications in the field of solar cells and photocatalysis. A three-dimensional (3D) dandelion-shaped hierarchical Bi₂S₃ microsphere compactly decorated with wing-shaped few layered MoS₂ lamella (D-BM) was fabricated via a facile hydrothermal self-assembly process. Especially, polyethylene glycol (PEG) has been proven as the vital template to form D-BM microsphere. Importantly, the as-prepared D-BM microsphere presents pH-dependent superior adsorption behavior and remarkable visible light photocatalytic activity for degradation of organic dyestuffs (Rhodamine B/RhB and Methylene blue/MB), far exceeding those for the pure Bi₂S₃ and MoS₂. It is understandable that D-BM with high surface area possesses more active sites and promotes light utilization due to the unique porous structure with outspread wings. Besides, based on the experiments and theoretical calculations, the staggered type II band alignment of D-BM permits the charge injection from Bi₂S₃ to MoS₂, subsequently accelerates the separation and restrains the recombination of carriers, leading to excellent photocatalytic activity, as well as the photoconductance and photoresponse performance (with I_light/I_dark ratio 567).

MoOx–pyridine organic–inorganic hybrid wires as a reusable and highly selective catalyst for the oxidation of alcohols: a comparison study between reaction-controlled phase-transfer catalysis and heterogeneous catalysis

The different catalytic behaviors of Mo₃O₁₀(C₅H₆N)₂·H₂O wires (MoO_x–pyridine) in the selective oxidation of alcohols by means of molecular oxygen (O₂) and hydrogen peroxide (H₂O₂) as green oxidants were investigated.

Theoretical study on the surface stabilities, electronic structures and water adsorption behavior of the Ta3N5(110) surface

DFT calculations were performed to study the surface stabilities, electronic structures and water adsorption behavior of the Ta₃N₅(100) surface.

(Fe1−xNix)3N nanoparticles: the structure, magnetic and photocatalytic properties for water splitting

Fe₃N and (Fe_1−xNi_x)₃N nanoparticles (NPs) were prepared via a simple sol–gel method.

Molybdenum-doped α-MnO2 as an efficient reusable heterogeneous catalyst for aerobic sulfide oxygenation

In the presence of Mo⁶⁺-doped α-MnO₂ (Mo–MnO₂), various sulfides could efficiently be oxidized to the corresponding sulfoxides as the major products. In addition, Mo–MnO₂ could repeatedly be reused.

Controlled nitridation of tantalum (oxy)nitride nanoparticles towards optimized metal-support interactions with gold nanocatalysts

Optimized metal-support interactions were achieved on ionothermally prepared tantalum (oxy)nitrides with controlled nitridation, and the as-formed Auδ⁻ species on TaON is efficient for nitrobenzene hydrogenation.

Nitrogen-doped nanotubes-decorated activated carbon-based hybrid nanoarchitecture as a superior catalyst for direct dehydrogenation

Nitrogen-doped activated carbon-based nanoarchitecture fabricated through a facile pyrolysis approach demonstrates enhanced catalysis in the oxidant- and steam-free dehydrogenation of ethylbenzene.

Metal non-oxide nanostructures developed from organic-inorganic hybrids and their catalytic application

The rational design of metal non-oxides is important for their catalytic application, which is however limited by the fact that the current synthetic strategies are short of effective control over formation reactions. Recently, the hybrids evenly integrating organic with inorganic molecules on a nanoscale significantly provided quasi-homogeneous reactions towards well-defined nanocatalysts of metal non-oxides, in which their structures and properties can be modulated in a wide range. Focusing on the nanostructures and the related catalytic behaviors, this feature article seeks to provide some control on the key structures and properties of metal non-oxides (e.g. carbides, nitrides, sulfides and selenides). It is thus anticipated to shed some light on the development of emerging materials for efficient catalysis, especially those used in energy utilization.

The synergetic effect of MoS₂ and graphene on Ag₃PO₄ for its ultra-enhanced photocatalytic activity in phenol degradation under visible light

The photo-degradation of organic pollutants using solar light is an attractive chemical process for water pollution control. In this study, we synthesized a new composite material consisting of silver phosphate (Ag₃PO₄) sub-microcrystals grown on a layered molybdenum disulfide (MoS₂) and graphene (GR) hybrid as a high-performance photocatalyst for the degradation of toxic organic pollutants. This composite photocatalyst was prepared via a simple two-step hydrothermal process that used sodium molybdate, thiourea and graphene oxide as precursors for the MoS₂/GR hybrid and silver nitrate for the Ag₃PO₄ sub-microcrystals. The composite Ag₃PO₄-0.02(MoS₂/0.005GR) was found to be the most effective catalyst for the photo-decomposition of 2,4-dichlorophenol under simulated solar light and visible light (λ ≥ 420 nm). The photocatalyst was also highly active for the degradation of nitrophenol and chlorophenol. The ultra photocatalytic activity of the novel catalyst arose from the synergetic effects of MoS₂ and GR as cocatalysts in the composite. MoS₂/GR nanosheets served as electron collectors for the interfacial electron transfer from Ag₃PO₄ to electron acceptors in the aqueous solution and thus enhanced the separation of the photo-generated electron-hole pairs and made the holes more available for organic oxidation. In addition, the presence of MoS₂ and GR provided more active adsorption sites and allowed for the activation of dissolved O₂ for organic degradation in water.

Constructing 2D porous graphitic C3 N4 nanosheets/nitrogen-doped graphene/layered MoS2 ternary nanojunction with enhanced photoelectrochemical activity

A 2D porous graphitic C3 N4 nanosheets/nitrogen-doped graphene/layered MoS2 ternary nanojunction is synthesized using a simple pyrolysis process followed by a hydrothermal treatment. The 2D ternary nanojunction exhibits significantly enhanced photoelectrochemical and photocatalytic activities due to the large contact area, efficient light absorption, and rapid charge separation and transport.