Two-dimensional molybdenum boride coordinating with ruthenium nanoparticles to boost hydrogen generation from hydrolytic dehydrogenation of ammonia borane.

The coordination between carrier and active metal is critical to the catalytic efficiency of ammonia borane (AB) hydrolysis reaction. In the present study, we report a new type of catalytic support based on molybdenum boride (MBene) MoAl1-xB and demonstrate that the effective combination of MoAl1-xB with Ru nanoparticles can realize the significantly enhanced performance for hydrogen generation. Owing to the efficient activation and dissociation of reactants, the optimal Ru/MoAl1-xB catalyst achieves the large turnover frequency of 494 molH2 molRu-1 min-1, high hydrogen generation rate of 119817 mL min-1 gRu-1 and favorable apparent activation energy of 39.2 kJ mol-1 for the catalytic hydrolysis of AB under alkaline-free condition. The isotopic test suggests the cleavage of OH bond in H2O is the rate-determining step for hydrolysis reaction, while the fracture of B-H bond in AB is also well revealed by attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy. Significantly, the flexible on-demand hydrogen generation is achieved by using chemical switches for on-off AB hydrolysis. This study provides a new support platform based on two-dimensional MBene to exploit efficient catalysts to boost AB dehydrogenation.

Facile construction of robust Ru-Co3O4 Mott-Schottky catalyst enabling efficient dehydrogenation of ammonia borane for hydrogen generation.

Developing efficient catalysts for the dehydrogenation of ammonia borane (AB) is important for the safe storage and controlled release of hydrogen, but it is a challenging task. In this study, we designed a robust Ru-Co3O4 catalyst using the Mott-Schottky effect to induce favorable charge rearrangement. The self-created electron-rich Co3O4 and electron-deficient Ru sites at heterointerfaces are indispensable for the activation of the B-H bond in NH3BH3 and the OH bond in H2O, respectively. The synergistic electronic interaction between the electron-rich Co3O4 and electron-deficient Ru sites at the heterointerfaces resulted in an optimal Ru-Co3O4 heterostructure that exhibited outstanding catalytic activity for the hydrolysis of AB in the presence of NaOH. The heterostructure had an extremely high hydrogen generation rate (HGR) of 12238 mL min-1 gcat-1 and an expected high turnover frequency (TOF) of 755 molH2 molRu-1 min-1 at 298 K. The activation energy needed for the hydrolysis was low (36.65 kJ mol-1). This study opens up a new avenue for the rational design of high-performance catalysts for AB dehydrogenation based on the Mott-Schottky effect.

Superwettable and photothermal all-in-one electrocatalyst for boosting water/urea electrolysis.

Developing multifunctional all-in-one electrocatalysts for energy-saving hydrogen generation remains a challenge. In this study, a simple and feasible thermal phosphorization strategy is explored to rationally construct P-doped MoO2-NiMoO4 heterostructure on nickel foam (NF). The heterointerfaced P-MoO2-NiMoO4/NF can simultaneously realize the integrated all-in-one functionalities, innovatively introducing superwettable surfaces, photothermal conversion capabilities and electrocatalytic functions. The superwettability gives P-MoO2-NiMoO4/NF sufficient electrolyte permeation and smooth bubble detachment. The plasmonic MoO2 with photothermal performance greatly elevates the local surface temperature of in P-MoO2-NiMoO4/NF, which is conducive to improve the electrocatalytic efficiency. The favorable in-situ surface reconstruction brings abundant active sites for electrocatalytic reactions. As an advanced multifunctional electrocatalyst, the superwettable and photothermal P-MoO2-NiMoO4/NF exhibits significantly improved performances in oxygen evolution reaction (OER) and urea oxidation reaction (UOR). More importantly, the highly efficient and stable overall water-urea electrolysis assisted by photothermal fields can be simply achieved by exposing P-MoO2-NiMoO4/NF to near-infrared (NIR) light.

Facile fabrication of Ni5P4-NiMoOx nanorod arrays with synergistic thermal management for efficient interfacial solar steam generation and water purification.

Interfacial steam generation by harnessing renewable solar energy has been recognized as a sustainable solution to global freshwater crisis. A promising evaporator with key components of high spectral absorption, efficient thermal management and adequate water transport is highly desired. In the present study, an integrated design for three-in-one functionality is achieved by simply loading Ni5P4-NiMoOx (P-NMO) on a macroporous nickel foam (NF) carrier. In situ embedding broadband Ni5P4 absorber into insulating NiMoOx enables efficient photothermal conversion and heat localization. Benefiting from proper thermal management and abundant water transmission, P-NMO/NF exhibits the excellent performance for interfacial steam generation with a high evaporation rate of 1.49 kg m-2h-1 and evaporation efficiency of 93.0 % under one sun irradiation. Furthermore, the obtained P-NMO/NF is proven to be applicable for high-efficiency freshwater production in seawater desalination and wastewater purification, showing great potential for practical solar evaporator under natural environmental conditions.

In Situ Implantation of Bi2S3 Nanorods into Porous Quasi-Bi-MOF Architectures: Enabling Synergistic Dissociation of Borohydride for an Efficient and Fast Catalytic Reduction of 4-Nitrophenol.

Catalytic hydrogenation reduction based on sodium borohydride (NaBH4) has gained attention as an appealing "one-stone-two-birds" approach for the simultaneous elimination of nitroaromatic pollutants and the production of high-value aminoaromatics under mild conditions. However, the slow kinetics of NaBH4 dissociation on the surface of catalysts restrict the catalytic hydrogenation reduction efficiency. Herein, we report an intelligent localized sulfidation strategy for an in situ implantation of Bi2S3 nanorods within quasi-Bi-MOF architectures (Bi2S3@quasi-Bi-MOF) by fine-tuning the pyrolysis temperature. In this novel Bi2S3@quasi-Bi-MOF, the porous quasi-Bi-MOF enables efficient adsorption of BH4- and 4-nitrophenol (4-NP), while Bi2S3 facilitates the BH4- dissociation to form Hads* species adsorbed on the catalyst surface. Benefiting from the synergistic structure, Bi2S3@quasi-Bi-MOF exhibits excellent performance for the catalytic reduction of 4-NP, delivering a high turnover frequency (TOF) of 1.67 × 10-4 mmol mg-1 min-1 and an extremely high normalized rate constant (knor) of 435298 s-1 g-1. The kinetic analysis and electrochemical tests indicate that this catalytic hydrogenation reduction follows the Langmuir-Hinshelwood mechanism. This study enriches the synthetic strategy of MOF-based derivatives and offers a new catalytic platform for hydrogenation reduction reactions.

Spinel-type oxygen-incorporated Ni3+ self-doped Ni3S4 ultrathin nanosheets for highly efficient and stable oxygen evolution electrocatalysis.

Spinel-type structured materials have attracted considerable attention and been regarded as promising alternative catalysts for oxygen evolution reaction (OER). However, the regulation of catalytically active octahedral sites in spinel structure to realize high activity and good stability for OER electrocatalysis is still a great challenge. Herein, we propose a self-doping strategy to boost OER performance of spinel-type Ni3S4 enriched high valence Ni3+ as active sites. By sacrificing Ni-based metal-organic framework, the ultrathin Ni3S4 manosheets are topologically grown on conductive Ni foam substrate and realize the simultaneous Ni3+ self-doping and surface oxygen incorporation during in situ sulfidation conversion process. These compositional and structural characteristics endow it with enhanced adsorption binding strength, enabling the highly efficient OER. As a result, the Ni3S4/NF exhibits excellent activity and outstanding stability toward OER electrocatalysis in alkaline medium, which only demands an ultralow overpotential of 266 mV to deliver a current density of 10 mA cm-2 and manifests the stable OER process for at least 75 h. Moreover, when used as an effective overall water splitting electrolyzer, the Ni3S4/NF achieves a current density of 10 mA cm-2 at only 1.638 V with good long-term stability.

Rational Design of Ruthenium and Cobalt-Based Composites with Rich Metal-Insulator Interfaces for Efficient and Stable Overall Water Splitting in Acidic Electrolyte.

The great promise of hydrogen energy and hydrogen production from water through proton exchange membrane (PEM) or membrane-free electrolysis drives the pursuit of highly active and acid-stable electrocatalysts with dual functionality and reduced cost for overall water splitting in acidic media. Here, we report a new Ru-modified cobalt-based electrocatalyst embedded in a nitrogen-doped carbon (NC) matrix with rationally designed Mott-Schottky heterostructure to realize high activity and stability toward overall water splitting in a strongly acidic environment. Such a composite was facilely prepared by carbonization of cobalt-based MOF, followed by galvanic exchange between cobalt and Ru, and then controlled partial oxidation. The partial oxidation of RuCo implanted inside the NC matrix led to the formation of a class of RuO2/Co3O4-RuCo@NC composites with rich metal-semiconductor interfaces to facilitate the charge-transfer process. As a result, the composite displayed remarkable electrocatalytic activity toward both oxygen/hydrogen evolutions in acidic media. Significantly, they also afforded low overpotentials of 247 and 141 mV for OER and HER, respectively, and a cell voltage of 1.66 V for overall water splitting at 10 mA cm-2. In addition, excellent operation stability in 0.5 M H2SO4 solutions, comparable to those of them working in alkaline conditions, is demonstrated due to the protection of a coated carbon thin film. The presented work opens a new opportunity toward designing bifunctional electrocatalysts for acidic water electrolysis.

Interlayer Expansion of Layered Cobalt Hydroxide Nanobelts to Highly Improve Oxygen Evolution Electrocatalysis.

The water oxidation reaction is known to be energy-inefficient and generally considered as a major bottleneck for water splitting. Exploring electrocatalysts with high-efficiency and at low cost is vital to widespread utilization of this technology, but is still a big challenge. Here we report an effective strategy based on an expanding interlayer of layered structures to realize a great enhancement of the catalytic performance of the oxygen evolution reaction from water splitting. Well-defined nanobelts of layer-structured cobalt benzoate hydroxide (Co(OH)(C6H5COO)·H2O) are successfully prepared in terms of a simple hydrothermal process. Intercalation with benzoate ions induces the interlayer expansion of the cobalt hydroxide, which is useful for the accommodation of more electrolyte ions and favorable for their diffusion and transport. The as-prepared Co(OH)(C6H5COO)·H2O nanobelts need significantly smaller overpotential (∼0.36 V) to reach 10 mA·cm-2 of current density compared with their Co(OH)2 (∼0.44 V) and Co3O4 (∼0.387 V) counterparts, and even favorably compare with most of the layered hydroxide-based electrocatalysts. Moreover, the Co(OH)(C6H5COO)·H2O nanobelts retain a much higher stability than the RuO2 reference in alkaline solution. This approach would be utilized to design and develop high-performance layered hydroxide-based electrocatalysts.

Bioinspired Cobalt-Citrate Metal-Organic Framework as an Efficient Electrocatalyst for Water Oxidation.

Efficient and cost-effective oxygen evolution reaction (OER) electrocatalysts are closely associated with many important energy conversion technologies. Herein, we first report an oxygen-evolving cobalt-citrate metal-organic framework (MOF, UTSA-16) for highly efficient electrocatalytic water oxidation. Benefiting from synergistic cooperation of intrinsic open porous structure, in situ formed high valent cobalt species, and existing Co4O4 cubane, the UTSA-16 exhibits excellent activity toward OER catalysis in alkaline medium. The UTSA-16 needs only 408 mV to offer a current density of 10 mA cm-2 for OER catalysis, which is superior to that of most MOF-based electrocatalysts and the standard Co3O4 counterpart. The present finding provides a better understanding of electroactive MOFs for water oxidation.

When Layered Nickel-Cobalt Silicate Hydroxide Nanosheets Meet Carbon Nanotubes: A Synergetic Coaxial Nanocable Structure for Enhanced Electrocatalytic Water Oxidation.

Developing robust earth-abundant electrocatalysts for oxygen evolution reaction (OER) is an ongoing scientific challenge, which is coupled with a number of important electrochemical processes and many key renewable energy systems, such as water splitting, rechargeable metal-air batteries, and regenerative fuel cells. Here, we proposed a rational design and fabrication of the synergetic coaxial nanocable structures by intimate growth of the layered nickel-cobalt silicate hydroxide nanosheets on the outer surfaces of multiwalled carbon nanotubes (MWCNTs@NCS) and demonstrated their high efficiency in electrocatalytic OER from water splitting. The electrocatalytic activities of the MWCNTs@NCS were found to be significantly higher than that of bare NCS and pristine MWCNTs, synergetically determining by such the constituted individual components. Among them, the MWCNTs@NCS-2 exhibited best electrocatalytic OER performance, showing a small OER onset potential, large anodic current and long-term durability, which was favorably comparable to the previously reported NiCo-based OER electrocatalysts in alkaline electrolytes. To the best of our knowledge, this was a first example on the earth-abundant metal silicate hydroxides utilized in electrochemical water splitting.

Hierarchical {001}-faceted BiOBr microspheres as a novel biomimetic catalyst: dark catalysis towards colorimetric biosensing and pollutant degradation.

In recent years, considerable effort has been devoted to finding novel enzyme mimetics with improved catalytic activities. However, the insightful understanding of such catalytic process is still elusive. In this paper, we report for the first time a typical photoactive layer-structured BiOBr as a novel biomimetic catalyst possessing highly efficient intrinsic peroxidase-like activity. Moreover, we have experimentally achieved high dark peroxidase-like catalytic activity in BiOBr microspheres and provided some new insights into the light-enhanced peroxidase-like catalytic property. On the basis of a typical color reaction derived from catalytic oxidation of peroxidase substrates over BiOBr microspheres with H2O2, the simple and sensitive colorimetric assays for detection of H2O2, glucose and ascorbic acid were successfully established. More interestingly, the BiOBr microspheres showed strong ability towards activation of H2O2, displaying excellent dark catalytic activity for the degradation of organic dye. It is therefore believed that our findings in this study could open up the possibility of utilizing BiOBr as enzymatic mimics in biotechnology and environmental remediation.

Catalytic reduction of 4-nitrophenol by silver nanoparticles stabilized on environmentally benign macroscopic biopolymer hydrogel.

The direct use of macroscopic biopolymer alginate hydrogels (AHs) as a green and effective carrier to stabilize silver nanoparticles (Ag NPs) is presented. The Ag@AHs were characterized by UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electronic microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). The Ag@AHs showed excellent catalytic performance for the reduction of 4-nitrophenol by NaBH4 in aqueous solution, which can be easily separated after catalytic reaction and readily reused for three successive reaction cycles, attributing to the high stability of the Ag NPs supported by AHs. Our findings shed light on the design and fabrication of new heterogeneous catalyst with high performance based on the environmentally benign biopolymer hydrogel.

Synthesis of α-Fe2O3 nanofibers for applications in removal and recovery of Cr(VI) from wastewater.

PURPOSE: Nanomaterials such as iron oxides and ferrites have been intensively investigated for water treatment and environmental remediation applications. The purpose of this work is to synthesize α-Fe(2)O(3) nanofibers for potential applications in removal and recovery of noxious Cr(VI) from wastewater. METHODS: α-Fe(2)O(3) nanofibers were synthesized via a simple hydrothermal route followed by calcination. The crystallographic structure and the morphology of the as-prepared α-Fe(2)O(3) nanofibers were characterized by X-ray diffraction, scanning electron microscope, and transmission electron microscope. Batch adsorption experiments were conducted, and Fourier transform infrared spectra were recorded before and after adsorption to investigate the Cr(VI) removal performance and adsorption mechanism. Langmuir and Freundlich modes were employed to analyze the adsorption behavior of Cr(VI) on the α-Fe(2)O(3) nanofibers. RESULTS: Very thin and porous α-Fe(2)O(3) nanofibers have been successfully synthesized for investigation of Cr(VI) removal capability from synthetic wastewater. Batch experiments revealed that the as-prepared α-Fe(2)O(3) nanofibers exhibited excellent Cr(VI) removal performance with a maximum adsorption capacity of 16.17 mg g(-1). Furthermore, the adsorption capacity almost kept unchanged after recycling and reusing. The Cr(VI) adsorption process was found to follow the pseudo-second-order kinetics model, and the corresponding thermodynamic parameters ΔG°, ΔH°, and ΔS° at 298 K were calculated to be -26.60 kJ mol(-1), -3.32 kJ mol(-1), and 78.12 J mol(-1) K(-1), respectively. CONCLUSIONS: The as-prepared α-Fe(2)O(3) nanofibers can be utilized as efficient low-cost nano-absorbents for removal and recovery of Cr(VI) from wastewater.

Self-sacrificial templating synthesis of porous quaternary Cu-Fe-Sn-S semiconductor nanotubes via microwave irradiation.

Uniform quaternary Cu(2)FeSnS(4) (CITS) nanotubes of outer diameter 400-800 nm and thickness 100-200 nm have been synthesized for the first time by a simple, rapid and easily scaled-up microwave nonaqueous route using benzyl alcohol as the microwave absorbing solvent. An interesting in situ generated one-dimensional Cu(Tu)Cl nanorod acting as a self-sacrificial template was crucial for the formation of the well-defined CITS nanotubes. Based on the designed time-dependent experiments, a formation mechanism for the CITS nanotubes was also proposed. The resulting CITS nanotubes had a strong absorption in the visible region with a bandgap of 1.71 eV that was optimal for photovoltaic applications. Our study provided a microwave nonaqueous route generally applicable for the synthesis of quaternary chalcogenide semiconductor nanotubes.

Sacrificial template-directed synthesis of mesoporous magnesium oxide architectures with superior performance for organic dye adsorption [corrected].

Mesoporous MgO architectures were successfully synthesized by the direct thermal transformation of the sacrificial oxalate template. The as-prepared mesoporous architectures were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption-desorption techniques. The MgO architectures showed extraordinary adsorption capacity and rapid adsorption rate for removal of Congo red (CR) from water. The maximum adsorption capacity of the MgO architectures toward CR reached 689.7 mg g⁻¹, much higher than most of the previously reported hierarchical adsorbents. The CR removal process was found to obey the Langmuir adsorption model and its kinetics followed pseudo-second-order rate equation. The superior adsorption performance of the mesoporous MgO architectures could be attributed to the unique mesoporous structure, high specific surface area as well as strong electrostatic interaction.

Removal of methylene blue from aqueous solution with magnetite loaded multi-wall carbon nanotube: kinetic, isotherm and mechanism analysis.

In this study, we have demonstrated the efficient removal of cationic dye, methylene blue (MB), from aqueous solution with the one-pot solvothermal synthesized magnetite-loaded multi-walled carbon nanotubes (M-MWCNTs). The as-prepared M-MWCNTs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. The effects of contact time, initial dye concentration, and solution pH on the adsorption of MB onto M-MWCNTs were systematically studied. It was shown that the MB adsorption was pH-dependent. Adsorption kinetics was best described by the pseudo-second-order model. Equilibrium data were well fitted to the Langmuir isotherm model, yielding maximum monolayer adsorption capacity of 48.06 mg g(-1). FTIR analysis suggested that the adsorption mechanism was possibly attributed to the electrostatic attraction and π-π stacking interactions between MWCNTs and MB.

Removal of methylene blue from aqueous solution by a solvothermal-synthesized graphene/magnetite composite.

In this study, we have demonstrated a facile one-step solvothermal method for the synthesis of the graphene nanosheet (GNS)/magnetite (Fe(3)O(4)) composite. During the solvothermal treatment, in situ conversion of FeCl(3) to Fe(3)O(4) and simultaneous reduction of graphene oxide (GO) into graphene in ethylene glycol solution were achieved. Electron microscopy study suggests the Fe(3)O(4) spheres with a size of about 200 nm are uniformly distributed and firmly anchored on the wrinkled graphene layers with a high density. The resulting GNS/Fe(3)O(4) composite shows extraordinary adsorption capacity and fast adsorption rates for removal of organic dye, methylene blue (MB), in water. The adsorption kinetics, isotherms and thermodynamics were investigated in detail to reveal that the kinetics and equilibrium adsorptions are well-described by pseudo-second-order kinetic and Langmuir isotherm model, respectively. The thermodynamic parameters reveal that the adsorption process is spontaneous and endothermic in nature. This study shows that the as-prepared GNS/Fe(3)O(4) composite could be utilized as an efficient, magnetically separable adsorbent for the environmental cleanup.

Multifunctional polypyrrole/strontium hexaferrite composite microspheres: preparation, characterization, and properties.

Polypyrrole (PPY)/SrFe12O19 composites with tunable electrical and magnetic properties were synthesized by in situ polymerization of pyrrole in the presence of SrFe12O19 particles. The structure of PPY/SrFe12O19 composites was characterized by means of Fourier transform infrared spectroscopy and X-ray diffraction. Transmission electron microscope and scanning electron microscope images illustrated that the spherical composites consisted of SrFe12O19 hexagonal plates sheathed by PPY. In the electromagnetic measurments, it was found that the ac conductivity of SrFe12O19 particles increased while the saturation magnetization, remanent magnetization, and coercivity decreased after PPY coating; moreover, the desired electrical and magnetic properties of PPY/SrFe12O19 composites can be modulated simply by controlling the contents of SrFe12O19 particles. A possible mechanism was also proposed to interpret the formation of the PPY/SrFe12O19 composites.