MnO2 Sheets Research Articles

Construction of Ru/MnO–Mn7C3/N-doped carbon sheets for boosting electrocatalytic hydrogen generation

Suffering from their low conductivity, Mn-base oxides are commonly inactive in H–OH activation. Generally, tailoring the coordinate environment of materials could induce variation in the atomic arrangement and further influence their chemical activity. Herein, we propose a feasible strategy to mediate the electronic structure of Mn-based oxides by facile hydrothermal method and thermal reduction route. Compared with MnO2 sheets, the as-synthesized Ru/MnO–Mn7C3/N-doped carbon sheets (Ru/MnO–Mn7C3/NC) exhibit the higher activity for both acidic (73 mV) and alkaline water reduction reaction (44 mV@10 mA/cm2). Benefitting from unique structures, Ru/MnO–Mn7C3/NC sheets show the better freshwater/seawater oxidation reactivity, exceeding RuO2. The strong interaction of MnO–Mn7C3 heterostructures, Ru, and N-doped carbon endows Ru/MnO–Mn7C3/NC with the good freshwater and seawater dissociation performance, outperforming most of the reported Mn-based oxides.

Sr2MnO2Na1.6Se2: A Metamagnetic Layered Oxychalcogenide Synthesized by Reductive Na Intercalation to Break [Se2]2- Perselenide Dimer Units.

Recent advances in anion-redox topochemistry have enabled the synthesis of metastable mixed-anion solids. Synthesis of the new transition metal oxychalcogenide Sr2MnO2Na1.6Se2 by topochemical Na intercalation into Sr2MnO2Se2 is reported here. Na intercalation is enabled by the redox activity of [Se2]2- perselenide dimers, where the Se-Se bonds are cleaved and a [Na2-x Se2](2+x)- antifluorite layer is formed. Freshly prepared samples have 16(1) % Na-site vacancies corresponding to a formal oxidation state of Mn of +2.32, a mixed-valence between Mn2+ (d5) and Mn3+ (d4). Samples are highly prone to deintercalation of Na, and over two years, even in an argon glovebox environment, the Na content decreased by 4(1) %, leading to slight oxidation of Mn and a significantly increased long-range ordered moment on the Mn site as measured using neutron powder diffraction. The magnetic structure derived from neutron powder diffraction at 5 K reveals that the compound orders magnetically with ferromagnetic MnO2 sheets coupled antiferromagnetically. The aged sample shows a metamagnetic transition from bulk antiferromagnetic to ferromagnetic behavior in an applied magnetic field of 2 T, in contrast to the Cu analogue, Sr2MnO2Cu1.55Se2, where there is only a hint that such a transition may occur at fields exceeding 7 T. This is presumably due to the higher ionic character of [Na2-x Se2](2+x)- layers compared to [Cu2-x Se2](2+x)- layers, reducing the strength of the antiferromagnetic interactions between MnO2 sheets. Electrochemical Na intercalation into Sr2MnO2Se2 leads to the formation of multiphase sodiated products. The work shows the potential of anion redox to yield novel compounds with intriguing physical properties.

Two-Dimensional MnO2 Nanozyme-Mediated Homogeneous Electrochemical Detection of Organophosphate Pesticides without the Interference of H2O2 and Color.

Traditional peroxidase-like nanozyme-based sensors suffer from self-decomposition and high toxicity of H2O2, as well as the interference of color from nanozymes themselves and testing samples. In this work, we adopt nanozymes (two-dimension (2D) MnO2 sheets, manganese dioxide nanosheets (MnNS)) with oxidase-like and peroxidase-like properties as advanced catalysts to develop a novel homogeneous electrochemical sensor for organophosphate pesticides (OPs) using dissolved O2 as a coreactant without the interference of H2O2 and color. Owing to the large surface area and unique catalytic activity of MnNS, a large amount of tetramethylbenzidine (TMB) is catalyzed oxidation, leading to a significantly declined differential pulse voltammetry (DPV) current. Obviously, MnNS display an excellent response to thiocholine, deriving from the catalyzing hydrolysis of acetylthiocholine (ATCh) by acetylcholinesterase (AChE), which switches a homogeneous electrochemical OP detection process based on the depressing AChE activity with a limit of detection (LOD) of 0.025 ng mL-1. The as-proposed strategy on using nanozymes with oxidase-like and peroxidase-like properties to develop a homogeneous electrochemical sensor will provide a new pathway for improving the performance of nanozyme-based sensors, and the established MnNS-based homogeneous electrochemical sensor will find more applications for OP residue determination in food samples.

1-D NiO nanorods pillared 2-D MnO2 nanosheets as lithium-free cathode materials for charged-state lithium batteries

Theoretically monolayer MnO2 sheets have an impressive high capacity of 616 mAh/g, but practically monolayer MnO2 sheets have poor performances due partially to monolayer restacking. In this paper, we report the preparation of three-dimensional porous NiO nanorod pillared δ-MnO2 nanosheets as integrated nanoarchitectures as lithium-free cathode materials. The as-synthesized NiO pillared δ-MnO2 nanosheets have resulted in a moderately high specific capacity of 185 mA h g−1, with more than 63% capacity retention after 200 cycles. In comparison, 2D MnO2 nanosheets without NiO pillared structures only achieved a low initial capacity of 137 mA h g−1, with just 17% capacity retention after 200 cycles. The dramatically improved electrochemical performances could be attributed to high surface areas with excellent porosity which provides more electrochemically active sites and thermodynamically favorable insertion pathways for the lithium ions. Our results reveal that insertion of pillars is a promising strategy to explore in order to mitigate the restacking issues and achieve electrochemical performances close to theoretical values for monolayer MnO2.

Confined Tuning Hierarchical Core–Shell Architectures of Multi-Walled Carbon Nanotubes Wrapped by MnO2 Sheets with High-Performance Microwave Absorption

Hierarchical core–shell architectures with multi-walled carbon nanotubes as core and MnO2 sheets shaped in an array mode as shell (MWCNTs@MnO2) were successfully synthesized via a simple wet chemical method. X-ray diffraction patterns and X-ray photoelectron spectroscopy analysis revealed that the composites were successfully prepared. Morphological characterizations were made by scanning electron microscopy and transmission electron microscopy. Vector network analyzer was employed to investigate the electromagnetic parameters of the composites. A possible attenuation mechanism was discussed, and the high-performance microwave absorption properties were attributed to the porous microstructure, polarization effect, dielectric loss and the synergistic action between MWCNTs and [Formula: see text]-MnO2. A minimum reflection loss (RL) of [Formula: see text]50.6[Formula: see text]dB was achieved at a thickness of 1.4[Formula: see text]mm, and an effective absorption bandwidth ([Formula: see text][Formula: see text]dB) covered 4.2[Formula: see text]GHz (from 13.8[Formula: see text]GHz to 18[Formula: see text]GHz) at a thickness of 1.3[Formula: see text]mm. Therefore, these results suggested that the MWCNTs@[Formula: see text]-MnO2 composites can be an excellent candidate for microwave absorption materials.

Antiferromagnetic fluctuations and charge carrier localization in ferromagnetic bilayer manganites: electrical resistivity scales exponentially with short-range order controlled by temperature and magnetic field

The compound La2−2xSr1+2xMn2O7, x = 0.30–0.40, consists of bilayers of ferromagnetic metallic MnO2 sheets that are separated by insulating layers. The materials show colossal magnetoresistance—a reduction in resistivity of up to two orders of magnitude in a field of 7 T—at their three-dimensional ordering temperatures, TC = 90–126 K, and are the layered analogues of the widely studied pseudo-cubic perovskite manganites, R1−xAxMnO3 (R = rare earth, A = Ca, Sr, Ba, Pb). Two distinct short-range orderings—antiferromagnetic fluctuations and correlated polarons, which are related to the magnetic and the lattice degrees of freedom respectively—have previously been discovered in La2−2xSr1+2xMn2O7, x = 0.40, and have each been qualitatively connected to the resistivity. Here, in a comprehensive study as a function of both temperature and magnetic field for the different hole-concentrations per Mn site of x = 0.30 and 0.35, we show that antiferromagnetic fluctuations also appear at temperatures just above TC, and that the intensities of both the antiferromagnetic fluctuations and polaron correlations closely track the resistivity. In particular, for x = 0.35 we show that there is a simple scaling relation between the intensities of the antiferromagnetic fluctuations and the in-plane resistivity that applies for the temperatures and magnetic fields used in the experiments. The results show that antiferromagnetic fluctuations are a common feature ofLa2−2xSr1+2xMn2O7 with ferromagnetic bilayers, and that there is a close connection between the antiferromagnetic fluctuations and polarons in these materials.

Renewable carbon foam/δ-MnO2 composites with well-defined hierarchical microstructure as supercapacitor electrodes

Composite electrodes containing both carbon and transition metal oxides have attracted tremendous interest because of their great potential as prominent electrodes for supercapacitors. Herein, direct growth of δ-MnO2 on wheat flour-derived carbon foam (WFCF) with well-developed hierarchical microstructure is readily carried out through an easy, scalable, and reliable two-step synthesis (also referred to as "foaming and cooking" technique), thereby achieving dual goals of environmental sustainability and remarkable electrical energy storage. The unique electrode architecture closely assembled between the prepared sponge-like carbon foam and nanostructured δ-MnO2 affords not only large exposed electroactive surface area but also rapid electrons and ions transport pathway, benefiting from the 3D interconnected hierarchical porous texture as well as considerable open channels between the anchored MnO2 sheets. As a result, the symmetric supercapacitor device based on the WFCF/MnO2-2.0 composite delivers a capacitance of 146Fg−1 and an impressive energy density of 20.3Whkg−1 at 1Ag−1 with good cycling stability in 6M KOH electrolyte. The kinetic analysis indicates a combination of capacitive and battery-like electrochemical response. The proposed "foaming and cooking" strategy renders a prospective way for facile construction of high-performance supercapacitor electrodes with fast kinetics, good reversibility and structure stability.

Holey graphene/MnO 2 nanosheets with open ion channels for high‐performance solid‐state asymmetric supercapacitors

Holey graphene/MnO2 (HG/MnO2) composites with open ion channels are synthesized by an electrostatic self-assembly method. The HG with rich in-plane nanopores is prepared via a mild etching reaction first, followed by modified with poly-diallyldimethylammoniumchloride (PDDA) to transfer the surface charge of HG nanosheets from negative to positive, which are eventually assembled on the negatively charged MnO2 nanosheets via electrostatic attraction. As a result, the HG allows ions to pass through the graphene sheet, improving the ion transport channels. Besides, the electrostatic self-assembly between HG and MnO2 enables the composite a high conductivity, providing effective electron transport pathways. The HG and MnO2 sheets are observed to be tightly bounded by the transmission electron microscope (TEM), and the HG content in the composites is determined to be 9.6% to 20% by the thermogravimetric (TG) test. The HG/MnO2-2 electrode with the HG content of around 14.8% displays the large specific capacitance of 219.3 F g−1 at 0.5 A g−1 and the high rate capacity of 134.7 F g−1 at 10 A g−1. Furthermore, the as-prepared solid-state asymmetric supercapacitors (SSAS) achieve a wide stable operating voltage of 1.8 V, a high energy density of 16.8 Wh kg−1 at the power density of 224.6 W kg−1, and low capacitance degradation of only 6.3% after 5000 cycles.

Manganese oxides supported on ACFN by a one‐step redox method for the low‐temperature NOx reduction with NH3: effect of acid addition

AbstractBACKGROUNDIn this study, manganese dioxide (MnO2) was formed in situ on the surface of ACFN (nitric acid modified activated carbon fibres) by a one‐step redox method for the selective catalytic reduction (SCR) of nitric oxides (NOx) with ammonia (NH3) at low temperature. Meanwhile, the water and sulfur dioxide (H2O and SO2) deactivation mechanism were investigated.RESULTSEach acid, including hydrochloric, nitric and acetic (HCl, HNO3 and CH3COOH), released H+ in solution at different rates, which lead to distinct pH environments. As the driving force, it has an effect on the redox reaction, resulting in the different MnO2 amount and performance of the MnO2/ACFN catalysts. The MnO2/ACFN (CH3COOH) catalyst exhibited good NH3‐SCR activity, water resistance and sulfur resistance.CONCLUSIONThe MnO2/ACFN (CH3COOH) catalyst showed 3D growth and uniform distribution of MnO2 sheets on the surface of the support, which resulted in a larger specific surface area and better redox properties. The CH3COOH can gradually decompose H+ so that H+ is given priority to internal diffusion. The redox reaction preferentially took place in the interior, thereby promoting the formation of more MnO2, which is beneficial to the NH3‐SCR reaction. © 2019 Society of Chemical Industry

1D flower-like Fe3O4@SiO2@MnO2 nanochains inducing RGO self-assembly into aerogels for high-efficient microwave absorption

One-dimensional (1D) microwave absorbing materials (MAMs) can induce self-assembly of graphene into aerogels, which provides ideas for the preparation of new MAMs. In here, 3D flower-like Fe3O4@SiO2@MnO2@reduced graphene oxide (RGO) (FSMG) composite aerogels have been fabricated via hydrothermal method, in which 1D Fe3O4@SiO2 (FS) nanochains and two-dimensional (2D) MnO2 sheets form a nano-scale core-shell structure on the surface of the RGO nanosheets. The unique microstructure of aerogels greatly enhances the microwave absorption capability. Particularly, the addition of RGO regulates the complex permittivity and improves the impedance matching of 1D Fe3O4@SiO2@MnO2 (FSM) nanochains. Results demonstrate that the well-designed 3D conductive networks with significant oxygen vacancy defects powerfully favor the electromagnetic wave (EMW) absorption. The as-prepared FSMG composite aerogels show efficient microwave absorption (MA) properties with the maximum effective absorption bandwidth (EAB) of 4.26 GHz (7.13–11.39 GHz) at the corresponding coating thickness of 3.2 mm, accompanied by the minimum reflection loss (RLmin) of about −55.01 dB. This work indicates that the FSMG composite aerogels are excellent absorbers with wide bandwidth, strong absorption, thin thickness and light weight, which can become a hopeful candidate in the field of MA.

Annealing induced a well-ordered single crystal \u03b4-MnO2 and its electrochemical performance in zinc-ion battery

Herein, the formation and electrochemical performance of a novel binder-free turbostratic stacked/ well-ordered stacked δ-MnO2-carbon fiber composite cathodes in deep eutectic solvent (DES) based zinc-ion battery (ZIB) is reported. Results of morphological, elemental, and structural analyses revealed directly grown and interconnected δ-MnO2 crumpled nanosheets on a carbon fiber substrate. Moreover, an improvement via a simple annealing strategy in the stacking, surface area and conductivity of the δ-MnO2 sheets was observed. Annealing induces the rearrangement of δ-MnO2 sheets resulting in the transformation from turbostratic stacking to a well-ordered stacking of {delta }-MnO2 sheets, as indicated by the selected area electron diffraction (SAED) hexagonal single crystal pattern. Besides, the formation of the well-ordered stacking of {delta }-MnO2 sheets exhibited improved electrochemical performance and cyclability, as cathode material for ZIB. The novel strategy described in this study is an essential step for the development of binder-free δ-MnO2-C fiber composite with a well-ordered stacking of δ-MnO2 sheets. This study also demonstrated comparable electrochemical performance between the turbostratic {delta }-MnO2 sheets and the well-ordered stacked δ-MnO2 sheets.

Rational design of MnO2-nanosheets-decroated hierarchical porous carbon nanofiber frameworks as high-performance supercapacitor electrode materials

A hierarchical structure is proved to be important for the improvement of electrochemical performances of MnO2-based electrode materials used in supercapacitors. However, the rational design of materials’ structure and its real performance served as electrode materials are still facing challenges. Herein, hierarchical porous carbon nanofibers using ZIF-8 nanoparticles as pore templates are designed to provide one-dimensional hollow frameworks for the growth of ultrathin MnO2 nanosheets (referred as HPCNF/MnO2). The as-prepared HPCNF/MnO2 samples have a hierarchical coaxial core-shell structure, with HPCNFs as the core and MnO2 sheets as the shell. The novel nanostructure of this hybrid provides abundant electrochemical active sites for Faradic reactions and short diffusion channels for ions/electron transport. The utilization of HPCNF/MnO2 active material with such a structure can be significantly enhanced, especially at the high current density. When evaluated as electrode materials, HPCNF/MnO2 exhibits a specific capacitance of 269 F g−1 at 0.5 A g−1 (308 F g−1 for MnO2), a high capacitive retention of 98% even after 5000 cycles at 50 mV s−1 by cyclic voltammetry (86.7% capacitance retention at 1 A g−1 after 2000 cycles) and a rate capability of 58% from 0.5 to 10 A g−1. Especially at the current density of 10 A g−1, the specific capacitance of HPCNF/MnO2 has increased by 133% compared with that of non-porous carbon fiber/MnO2 composites, demonstrating a great superiority of hierarchical porous carbon nanofibers as frameworks to support pseudocapacitive materials.

Dual-modal Colorimetric and Fluorometric Method for Glucose Detection Using MnO2 Sheets and Carbon Quantum Dots

A novel dual-modal fluorometric and colorimetric method was developed for glucose detection using MnO2 sheets and carbon quantum dots(CQDs). The glucose could be oxidized by glucose oxidase, in accompanied with the formation of H2O2 intermediate, which resulted in the decomposition of MnO2 sheets, as well as the MnO2 sheets(brown) changed to Mn2+ ions(colorless), which induced the absorption of MnO2 sheet decreased and the fluorescence of CQDs increased, consequently. The linear detection ranges of glucose are 5–1000 µmol/L by fluorescent method and 5–60 µmol/L by colorimetric method. The limits of detection of these two measurements are 2.11 and 2.18 µmol/L, respectively. This method is easy to conduct, has reasonable sensitive and selectivity, and could be applied for the glucose detection in real human serum.

Multilevel Nanoarchitecture Exhibiting Biosensing for Cancer Diagnostics by Dual-Modal Switching of Optical and Magnetic Resonance Signals.

In this research, the fabrication and application of a multifunctional core-shell nanoarchitecture are proposed. NaYF4:Yb,Er@NaYF4:Yb,Nd exhibits upconversion luminescence (UCL) of erbium ions but has quenched UCL emission when it is coated with MnO2 nanosheets. This hierarchical multilevel UCNP-MnO2 exhibits restoration of UCL and generation of a magnetic resonance imaging (MRI) signal when it is exposed to a microenvironment containing glutathione (GSH)/H2O2, which strips the MnO2 sheets by converting them to paramagnetic Mn2+ ions. This dual-modal switching feature of the optical emission and MRI signals provides a platform for stimuli-responsive biosensing of GSH/H2O2. Our new formulation as a dual-modal biosensor for detecting aberrant levels of intracellular GSH/H2O2 associated in cancer cells could be a potential diagnostic probe to distinguish tumor cells from normal cells.

A MnO2 nanosheet/single-wall carbon nanotube hybrid fiber for wearable solid-state supercapacitors

Carbon nanotubes based fiber supercapacitor is considered as one of the most promising power sources for wearable electronic devices because of their remarkable mechanical and electrical properties. However, how to obtain flexible and highly conductive fibers with a high active material loading to give the supercapacitor high energy and power densities remains a great challenge. Here, we report a highly conductive hybrid fiber consisting of single-wall carbon nanotubes and ultrathin MnO2 nanosheets prepared by a scalable wet-spinning method. The mass percentage of active MnO2 in the hybrid fiber is as high as 75% and the intimate contact between the MnO2 sheets and the single-wall carbon nanotubes provides highly conductive pathways, while the abundant pores in the material enable fast ion transport. As a result, a flexible solid-state supercapacitor assembled from the hybrid fiber exhibits a very high volumetric capacitance of 74.8 F cm−3, an energy density of 10.4 mWh cm−3, and good cycling stability. This all-solid-state fiber supercapacitors with excellent flexibility are also woven into a textile demonstrating its ability of lighting wearable electronics.

Flexible ultra-thin Fe3O4/MnO2 core-shell decorated CNT composite with enhanced electromagnetic wave absorption performance

Abstract High reflection loss, wide bandwidth and low density are desirable attributes of electromagnetic wave absorption materials. Here, an ultra-thin MnO2/Fe3O4/carbon nanotube film has been synthesized in two steps using solvothermal deposition and electrochemical deposition. The Fe3O4 nanoparticles and the MnO2 sheets form a nano-scale core-shell structure on the surface of the carbon nanotube film. A series of this hierarchical composite film with different shell structures and MnO2 weight ratios were successfully synthesized. Their unique micro-structure greatly enhances the electromagnetic wave absorption capability of the composites. Instrinsic ferromagnetism is confirmed by the magnetic hysteresis loops. The strong couplings among dielectric loss, hysteresis loss and multiple scattering resulted in the reflection loss up to −42.2 dB with the bandwidth of 7.1 GHz at 10% MnO2 weight ratio for a flexible composite film of 1 mm thick.

DNA-templated Au nanoclusters and MnO2 sheets: a label-free and universal fluorescence biosensing platform

A label-free and universal fluorescence biosensing paltform has been constructed for probing and recognizing biomolecular interactions based on the excellent fluorescent properties of poly(adenine) (poly A) DNA templated-Au nanoclusters (DNA-AuNCs) and the good quenching ability of MnO2 sheets. Due to the high quenching efficiency of MnO2 sheets, the luminescence of DNA-AuNCs was decreased. Because single-stranded DNA-AuNCs was adsorbed onto the surface of MnO2 sheets through the physical absorption behavior between nucleobases of single-stranded DNA and the basal plane of MnO2 sheets. When the target DNA was introduced, the DNA-AuNCs could hybridize with the target DNA and form double-stranded duplex DNA structures, which resulting in the desorption of DNA-AuNCs from the surface of MnO2 sheets. Thus, the fluorescence signal of system was recovered. Similarly, in the presence of target substrate, aptamer-substrate complexes formed and resulted in the luminescence of DNA-AuNCs. By exploring DNA-AuNCs as signal reporter and MnO2 sheets as the quencher, this strategy could avoid the complex labelling process of the DNA probe and offer the advantages of simplicity and cost efficiency.

Preparation of magnetically recoverable bentonite–Fe3O4–MnO2 composite particles for Cd(II) removal from aqueous solutions

In this study, bentonite–Fe3O4–MnO2 composite was synthesized by combining bentonite with Fe3O4 and MnO2 through co-precipitation. Vibrating-sample magnetometry, scanning electron microscopy with energy-dispersive X-ray spectrometry, transmission electron microscopy, Brunauer–Emmett–Teller measurements, and X-ray powder diffraction techniques were used to characterize the composite. The composite consists of Fe3O4 nanoparticles orderly assembled on the surface of bentonite and an outer layer of MnO2 sheets. The composite’s particles possess a saturation magnetization of 13.4–30.5 emu/g and a high specific surface area (203.89 m2/g). The adsorption behaviors of the composite in Cd(II) removal were evaluated by batch equilibrium experiments. Kinetic and isothermal data fit well the pseudo-second-order and the Freundlich models, respectively. Adsorption reached equilibrium within 30 min, and the Freundlich capacity of the composite was 35.35 mg/g. The adsorption capacity of Cd(II) increased with increasing pH and was dependent on the ionic strength. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy showed the combination of surface hydroxyl groups of the composite and Cd(II) in the solution. The prepared composite can be easily recycled and reused by taking advantage of its magnetic properties. The results show that the designed composite is a promising absorbent for the treatment of Cd-contaminated water.

Electrostatic-Interaction-Assisted Construction of 3D Networks of Manganese Dioxide Nanosheets for Flexible High-Performance Solid-State Asymmetric Supercapacitors.

A three-dimensional (3D) macroscopic network of manganese oxide (MnO2) sheets was synthesized by an easily scalable solution approach, grafting the negatively charged surfaces of the MnO2 sheets with an aniline monomer by electrostatic interactions followed by a quick chemical oxidizing polymerization reaction. The obtained structure possessed MnO2 sheets interconnected with polyaniline chains, producing a 3D monolith rich in mesopores. The MnO2 sheets had almost all their reactive centers exposed on the electrode surface, and combined with the electron transport highways provided by polyaniline and the shortened diffusion paths provided by the porous structure, the deliberately designed electrode achieved an excellent capacitance of 762 F g-1 at a current of 1 A g-1 and cycling performance with a capacity retention of 90% over 8000 cycles. Furthermore, a flexible asymmetric supercapacitor based on the constructed electrode and activated carbon serving as the positive and negative electrodes, respectively, was successfully fabricated, delivering a maximum energy density of 40.2 Wh kg-1 (0.113 Wh cm-2) and power density of 6227.0 W kg-1 (17.44 W cm-2) in a potential window of 0-1.7 V in a PVA/Na2SO4 gel electrolyte.

Palladium nanoparticles supported on SiO2@Fe3O4@m-MnO2 mesoporous microspheres as a highly efficient and recyclable catalyst for hydrodechlorination of 2,4-dichlorophenol and reduction of nitroaromatic compounds and organic dyes

In this study, magnetic SiO2@Fe3O4@m-MnO2 microspheres with uniform morphology and mesoporous MnO2 shell were successfully prepared. The MnO2 sheets structured mesoporous shell could provide a large specific surface area, thereby increasing the catalytically active sites. Thus, magnetic SiO2@Fe3O4@m-MnO2 microspheres were used as a catalyst support. Palladium nanoparticles (Pd NPs) were successfully anchored with high dispersion on SiO2@Fe3O4@m-MnO2 surface, successfully obtained Pd(6%)/SiO2@Fe3O4@m-MnO2 nanocatalyst with a Pd weight percentage of 6%. The obtained nanocatalyst was employed in the hydrodechlorination of highly toxic 2,4-dichlorophenol and catalytic reduction of the widely used nitroaromatics and organic dyes under ambient conditions. In these catalytic reactions, the Pd(6%)/SiO2@Fe3O4@m-MnO2 nanocatalyst with large and accessible pore surface area exhibited excellent catalytic activity as compared to other noble metal supported catalysts. The Pd(6%)/SiO2@Fe3O4@m-MnO2 nanocatalyst could also be easily and conveniently recovered from the reaction mixture by using an external magnet, attributed to its magnetism, thus preventing the catalyst loss. Moreover, it could also be reused for at least six times without significant decrease in the catalytic activity, indicating its excellent reusability and stability. This study provides a useful platform and a new perspective for fabricating mesoporous MnO2 microspheres based noble metals modified catalysts for environmental catalysis.