Molybdate Nanosheets Research Articles

Non-noble metal thickness-tunable Bi2MoO6 nanosheets for highly efficient visible-light-driven nitrobenzene reduction into aniline

High efficiency and selectivity is significant for photocatalytic organic transformation. In this work, the efficient photocatalytic reduction of nitrobenzene into aniline is achieved on non-noble metal thickness-tunable bismuth molybdate nanosheets prepared by the simple hydrothermal reaction. The photocatalytic activity of Bi2MoO6 strongly depends on the nanosheet thickness. The Bi2MoO6 monolayer displays remarkably enhanced photocatalytic activity for selective reduction of nitrobenzene than bilayer, multilayers and bulk Bi2MoO6 due to the unique properties of 2D materials with the large fraction of surface atoms and the ultrafast charge separation. The obtained conversion rate of 487.5 μmol g−1. h-1 (>95% conversion and >99% selectivity within 60 min reaction) on Bi2MoO6 monolayers is 5 times higher than that of Bi2MoO6 bulk, far exceeding most of common photocatalysts up to date. This work provides a thickness dependent nanosheet concept in the design of newly highly efficient catalysts for the photocatalytic reduction conversion of nitroarenes to anilines.

Development of sandwich-structured cobalt porphyrin/niobium molybdate nanosheets catalyst for oxygen reduction

Abstract

Rational construction of novel rose petals-like yttrium molybdate nanosheets: A Janus catalyst for the detection and degradation of cardioselective β-blocker agent acebutolol

Metal molybdates has paid emerging attention in variety of energy and environmental applications owing to their extra-ordinary physicochemical properties. In this regard, novel rose petal-like yttrium molybdate nanosheets (YMoO4; YM NSs) was successfully designed through a simple wet chemical method and fabricated as advanced bifunctional catalytic material. The as-prepared YM NSs catalyst were systematically scrutinized in terms of their crystal structure, morphologies, and optical properties using XRD, Raman, FE-SEM, HR-TEM, XPS and UV-DRS analysis. The bifunctional electro- and photocatalytic activity of as-prepared YM NSs was investigated towards the detection and degradation of β-adrenergic receptor-blocker agent acebutolol (ACB) for the first time. Interestingly, the YM NSs modified glassy carbon electrode (YM NSs/GCE) demonstrates an excellent electrocatalytic activity towards ACB with wider linear response ranges (0.01–9.6 µM, 13–1632 µM), lower detection limit (2.5 nM), good sensitivity (2.21 µA µM−1cm−2) and excellent selectivity even in the existence of some common cations, anions and biological substances. The sensor (YM NSs/GCE) was successfully applied to determine the level of ACB in tablet, urine and water samples. Furthermore, the YM NSs was performed as superior photocatalyst for the degradation of as detected ACB. The YM NSs could degrade above 99% and mineralize above 74% of ACB aqueous suspension under visible light irradiation with superior recycling stability.

Synthesis and evaluation of three-dimensional nickel molybdate nano-sheets on nickel foam as self-supported electrodes for sodium-ion hybrid capacitors

Sodium-ion hybrid capacitors (NHCs) are novel energy storage devices between traditional capacitors and batteries; the electrode materials of NHCs have attracted increasing attention. In this study, a NiMoO4 and activated carbon (AC) have been used as the anode and cathode materials of NHCs, respectively. To the best of our knowledge, the NiMoO4//AC NHC system has been reported for the first time. The NiMoO4 was successfully synthesized by a one-step hydrothermal route. The NiMoO4//AC system has a high energy density of 62.4 Wh kg−1 and a high power density of 3500 W kg−1. It also exhibits prominent cycling stability, with a capacity retention of about 70% after 6000 cycles. This excellent electrochemical performance can be attributed to the nanosheet structure of NiMoO4, which can increase the contact area between the electrolyte and the active material, thus promoting the rapid insertion and extraction of Na ions. Therefore, the NiMoO4 are promising anode materials for NHCs.

Hierarchical architectures of bismuth molybdate nanosheets onto nickel titanate nanofibers: Facile synthesis and efficient photocatalytic removal of tetracycline hydrochloride

A huge challenge in the field of pollutant removal is the scarcity of visible-light-driven (VLD) photocatalysts that are efficient, stable, easily recyclable and capable of mineralizing organic pollutants. In this regard, a novel hierarchical architecture of Bi2MoO6 nanosheets onto NiTiO3 nanofibers for tetracycline hydrochloride (TC) removal was rationally designed and fabricated via a facile approach. In this heterojunction system, highly homogeneous-distributed Bi2MoO6 nanosheets were anchored on electrospun NiTiO3 nanofibers, endowing the heterojunction with compact interfacial contact. By virtue of the favorable interfacial contact and matched band alignment, promoted suppression of photo-generated electron-hole recombination is achieved in Bi2MoO6/NiTiO3 system, as confirmed by photoluminescence measurement. As a result, the heterojunction with Bi2MoO6/NiTiO3 molar ratio of 1:1 exhibits an outstanding VLD photocatalytic activity and good stability for tetracycline hydrochloride (TC) degradation. The photodegradation rate constant (k) is 26.0, 5.4 or 3.7 folds higher than that of pristine NiTiO3, Bi2MoO6, or the mechanical mixture (20.2 wt% NiTiO3 + 79.8 wt% Bi2MoO6). The holes and superoxide radicals are detected as the dominant active species responsible for TC removal. Moreover, this work reports an efficient VLD photocatalyst for TC removal and will open up new insights into the design of novel fiber-shaped VLD heterojunction photocatalyts for environment remediation.

Defect state of indium-doped bismuth molybdate nanosheets for enhanced photoreduction of chromium(vi) under visible light illumination.

The construction of defect states is an effective method for regulating the energy band structure of photocatalytic semiconductor materials. Establishing defect states effectively is a particularly significant strategy to improve the photoelectric conversion efficiency. Herein, we report a peculiar method to manufacture defect states in indium-doped Bi2MoO6 by changing the valence state of the doped indium element. By increasing the amount of doped indium, different doping forms and valence states are produced, which causes distortion of crystal structure, generation of oxygen vacancies and variation in the elemental valence state. Specifically, when Bi is substituted with In(3-x)+, the acceptor energy level becomes higher than the valence band due to the p-type-like doping, which widens the width of the valence band and drives the up-shift of the valence band edges, resulting in narrowed bandgap and improved photoresponse ability. In addition, the photoelectrochemical performance tests using the In-doped Bi2MoO6 show that low-valent indium doping effectively improves the carrier separation efficiency, reduces the transmission impedance, and greatly improves the photocatalytic reduction performance of Cr(vi). This study provides a new insight to the design of efficient photocatalysts for the green and sustainable treatment of Cr(vi) pollution.

Construction of Hierarchical CNT/rGO-Supported MnMoO4 Nanosheets on Ni Foam for High-Performance Aqueous Hybrid Supercapacitors.

Rationally designed conductive hierarchical nanostructures are highly desirable for supporting pseudocapacitive materials to achieve high-performance electrodes for supercapacitors. Herein, manganese molybdate nanosheets were hydrothermally grown with graphene oxide (GO) on three-dimensional nickel foam-supported carbon nanotube structures. Under the optimal graphene oxide concentration, the obtained carbon nanotubes/reduced graphene oxide/MnMoO4 composites (CNT/rGO/MnMoO4) as binder-free supercapacitor cathodes perform with a high specific capacitance of 2374.9 F g-1 at the scan rate of 2 mV s-1 and good long-term stability (97.1% of the initial specific capacitance can be maintained after 3000 charge/discharge cycles). The asymmetric device with CNT/rGO/MnMoO4 as the cathode electrode and the carbon nanotubes/activated carbon on nickel foam (CNT-AC) as the anode electrode can deliver an energy density of 59.4 Wh kg-1 at the power density of 1367.9 W kg-1. These superior performances can be attributed to the synergistic effects from each component of the composite electrodes: highly pseudocapacitive MnMoO4 nanosheets and three-dimensional conductive Ni foam/CNTs/rGO networks. These results suggest that the fabricated asymmetric supercapacitor can be a promising candidate for energy storage devices.

Self-standing MgMoO4/Reduced Graphene Oxide Nanosheet Arrays for Lithium and Sodium Ion Storage

A three-dimensional (3D) self-standing MgMoO4/reduced graphene oxide (rGO) nanosheet arrays (MMO-G NSAs) are fabricated for lithium and sodium ion storage via a facile bottom-up strategy. In the synthesized process, graphene oxide (GO) was intelligently employed as structure-directing agents to guide the interconnection of magnesium molybdate nanosheets (MMO NSs) along the vertical direction and confine the overgrowth of MMO NSs. The formation mechanism of MMO-G NSAs is proposed based on the illustrations of thermodynamic and dynamic driving forces. As an anode material for lithium ion battery, the MMO-G NSAs nanocomposite exhibits enhanced capacity (848.2mAhg−1 at 100mAg−1) than the MMO NSs electrode (582.5mAhg−1 at 100mAg−1). For sodium ion battery, the MMO-G NSAs nanocomposite also exhibits encouraging sodium ion storage capability (201.1mAhg−1 after 300 cycles at 100mAg−1). These results demonstrate that the special array architecture not only improves the charge transfer efficiency during cycling but also facilitates the electrolyte penetration and alleviates the stress induced by volume changes. Furthermore, the morphologies of the solid–electrolyte interphase (SEI) layer at different cycle stages were captured, which reveals that a dense, flexible SEI layer is crucial to the long-life cycling performance.

Formation of molybdate organic-hybrids and exfoliated molybdate nanosheets

Novel synthetic approaches for the effective construction of MoOx – organic hybrid structures and MoOx nanosheets (NSs) have been developed. A solvothermal (ST) treatment of molybdenum trioxide utilizing dodecylamine (DDA) as an intercalating agent leads to the formation of MoOx – DDA hybrid structures. Layer spacing as a function of organic molecule lengths can be controlled by changing the surfactants located between the nanosheets. Maintaining the integrity of the parent crystal, hexagonal-shaped molybdenum oxide NSs up to four micrometers in lateral size separate following sonication of the hybrid structures. Formation of MoOx–oleylamine (OAm) highly oriented nanosheets with plasmonic behavior were also achieved using a rapid ST treatment of molybdenum trioxide in the presence of OAm surfactant. The effects of time and temperature on the formation, morphology, and crystal structure of well-ordered nanosheets were explored. These synthesized hybrid nanostructures and NSs are expected to show great potential for a variety of applications including rechargeable batteries, catalysis, and nanodevices.

Microwave-assisted solvothermal synthesis of nickel molybdate nanosheets as a potential catalytic platform for NADH and ethanol sensing

Novel β-nickel molybdate (β-NiMoO4) nanosheets were synthesized by a microwave-assisted solvothermal method, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), high-resolution TEM (HRTEM), and energy dispersive spectrum (EDS). The as-prepared NiMoO4 nanosheets exhibited strong absorption property for electroactive ferricyanide ion (Fe(CN)63−) and graphite, allowing their easy and stable modification on carbon paste electrode (CPE), which was demonstrated good electrocatalytic activity toward the oxidation of β-nicotinamide adenine dinucleotide (NADH). In addition, a nonenzymatic ethanol sensor based on NiMoO4 nanosheets was also first presented in this work.

Er3+/Yb3+co-doped bismuth molybdate nanosheets upconversion photocatalyst with enhanced photocatalytic activity

In this paper, we report the microwave hydrothermal synthesis of Er3+/Yb3+ co-doped Bi2MoO6 upconversion photocatalyst. Crystal structure, morphology, elemental composition, optical properties and BET surface area were analyzed in detail. Infrared to visible upconversion luminescence at 532nm and 546nm of the co-doped samples was investigated under excitation at 980nm. The results revealed that the co-doping of Er3+/Yb3+ into Bi2MoO6 exhibited enhanced photocatalytic activity for the decomposition of rhodamine B under simulated solar light irradiation. Enhanced photocatalytic activity can be attributed to the energy transfer between Er3+/Yb3+ and Bi2MoO6 via infrared to visible upconversion from Er3+/Yb3+ ion and higher surface area of the Bi2MoO6 nanosheets. Therefore, this synthetic approach may exhibit a better alternative to fabricate upconversion photocatalyst for integral solar light absorption.

Er3+ doped bismuth molybdate nanosheets with exposed {0 1 0} facets and enhanced photocatalytic performance

Er3+ doped Bi2MoO6 nanosheets with enhanced photocatalytic activity were synthesized for the first time using a simple hydrothermal method. The morphology of Bi2MoO6 can be controlled from nanosheets to nanowires by adjusting the pH values. The samples were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), photoluminescence spectra (PL) and X-ray photoelectron spectroscopy (XPS). Er3+ doped Bi2MoO6 nanosheets selectively exposed {010} facets as the main external surfaces and the nanowires grew along the (010) direction. The nanosheets were found to be highly active for photocatalytic degradation of dyes and phenol. The activities of the Er3+ doped Bi2MoO6 nanosheets were much superior to that of commercial Degussa P25. The effect of Er3+ on the photocatalytic activity of Bi2MoO6 was investigated in detail. The enhanced photocatalytic activity of Bi2MoO6 nanosheets can be attributed to the exposed {010} facets and the dopant Er3+ which can transform visible light into ultraviolet light.