Mingfei Shao

Preparation of Fe3O4@SiO2@Layered Double Hydroxide Core–Shell Microspheres for Magnetic Separation of Proteins

Three-component microspheres containing an SiO(2)-coated Fe(3)O(4) magnetite core and a layered double hydroxide (LDH) nanoplatelet shell have been synthesized via an in situ growth method. The resulting Fe(3)O(4)@SiO(2)@NiAl-LDH microspheres display three-dimensional core-shell architecture with flowerlike morphology, large surface area (83 m(2)/g), and uniform mesochannels (4.3 nm). The Ni(2+) cations in the NiAl-LDH shell provide docking sites for histidine and the materials exhibit excellent performance in the separation of a histidine (His)-tagged green fluorescent protein, with a binding capacity as high as 239 μg/mg. The microspheres show highly selective adsorption of the His-tagged protein from Escherichia coli lysate, demonstrating their practical applicability. Moreover, the microspheres possess superparamagnetism and high saturation magnetization (36.8 emu/g), which allows them to be easily separated from solution by means of an external magnetic field and subsequently reused. The high stability and selectivity of the Fe(3)O(4)@SiO(2)@NiAl-LDH microspheres for the His-tagged protein were retained over several separation cycles. Therefore, this work provides a promising approach for the design and synthesis of multifunctional LDH microspheres, which can be used for the practical purification of recombinant proteins, as well as having other potential applications in a variety of biomedical fields including drug delivery and biosensors.

Directed Growth of Metal-Organic Frameworks and Their Derived Carbon-Based Network for Efficient Electrocatalytic Oxygen Reduction

A honeycomb-like carbon-based network is obtained by in situ nucleation and directed growth of metal-organic framework (MOF) arrays on the surface of layered double hydroxide (LDH) nanoplatelets, followed by a subsequent pyrolysis process, which exhibits largely enhanced electrocatalytic ORR performances. A successful paradigm for the directed growth of highly oriented MOF arrays is demonstrated, with potential applications for energy storage and conversion.

CoMn-layered double hydroxide nanowalls supported on carbon fibers for high-performance flexible energy storage devices

CoMn-layered double hydroxide (LDH) nanowalls were supported on flexible carbon fibers (CFs) via an in situ growth approach; the resulting CoMn-LDH/CF electrode delivers a high specific capacitance (1079 F g−1 at 2.1 A g−1 normalized to the weight of the active LDH material) with excellent rate capability even at high current densities (82.5% capacitance retention at 42.0 A g−1). A combined experimental and theoretical study reveals that the dramatic performance enhancement is mainly attributed to the homogeneous and ordered dispersion of metal units within the LDH framework, which enriches the redox reactions associated with charge storage by both Co and Mn. The hierarchical configuration further improves the exposure of active sites and enables a fast charge transfer to the electrode/electrolyte interface, with CFs serving as both the current collector and binderless electrode. In addition, a solid-state supercapacitor device with good flexibility was fabricated using the CoMn-LDH/CFs, which achieves a specific energy up to 126.1 W h kg−1 and a specific power of 65.6 kW kg−1. By virtue of rational design of the chemical composition and architecture, this work demonstrates a facile strategy for the fabrication of a hierarchical configuration based on CoMn-LDH nanowalls anchored to CFs, which can be potentially used in wearable and miniaturized devices for energy storage.

TiO2/graphene/NiFe-layered double hydroxide nanorod array photoanodes for efficient photoelectrochemical water splitting

The ever-increasing demand for renewable and clean power sources has triggered the development of novel materials for photoelectrochemical (PEC) water splitting, but how to improve the solar conversion efficiency remains a big challenge. In this work, we report a conceptual strategy in a ternary material system to simultaneously enhance the charge separation and water oxidation efficiency of photoanodes by introducing reduced graphite oxide (rGO) and NiFe-layered double hydroxide (LDH) on TiO2 nanorod arrays (NAs). An experimental–computational combination study reveals that rGO with a high work function and superior electron mobility accepts photogenerated electrons from TiO2 and enables fast electron transportation; while NiFe-LDH acts as a cocatalyst which accelerates the surface water oxidation reaction. This synergistic effect in this ternary TiO2/rGO/NiFe-LDH photoanode gives rise to a largely enhanced photoconversion efficiency (0.58% at 0.13 V) and photocurrent density (1.74 mA cm−2 at 0.6 V). It is worth mentioning that the photocurrent density of TiO2/rGO/NiFe-LDH, to the best of our knowledge, is superior to previously reported TiO2-based photoanodes in benign and neutral media. In addition, the method presented here can be extended to the preparation of other efficient photoanodes (WO3/rGO/NiFe-LDH and α-Fe2O3/rGO/NiFe-LDH) toward high level PEC performance.

A hierarchical heterostructure based on Pd nanoparticles/layered double hydroxide nanowalls for enhanced ethanol electrooxidation

Finely dispersed Pd nanoparticles (PdNPs) anchored to CoAl layered double hydroxide nanowalls (LDH-NWs) have been fabricated via a facile in situ redox reaction between the LDH-NWs and the PdCl42− precursor. The integrated LDH-NWs play the roles of both a hierarchical support and a reductant without any external agent, ensuring the cleanness of the metal–support interface. Based on the effective exposure of the Pd active sites and the elaborate network architecture, the Pd/LDH-NW heterogenous material yields a largely improved catalytic activity as well as robust durability towards ethanol electrooxidation in comparison with the commercial Pd/C catalyst. Moreover, a density functional theory (DFT) calculation indicates that the enhancement in the electrocatalytic properties originates from the synergistic effect between the metal and support, in which the LDH support stabilizes the PdNPs via the formation of a Pd–HO bond which is accompanied by an electron transfer from the LDH to the PdNPs. This work provides a promising approach for the design and fabrication of highly efficient metal-supported nanocatalysts which can be used in fuel cells and other related catalytic reactions.

Self-assembly of layered double hydroxide nanosheets/Au nanoparticles ultrathin films for enzyme-free electrocatalysis of glucose†

This paper reports the fabrication of layered double hydroxide nanosheets (LDH nanosheets)/Au nanoparticles (AuNPs) ultrathin films (UTFs) via the layer-by-layer (LBL) assembly technique, and their electrocatalytic performance for the oxidation of glucose was demonstrated. UV-vis absorption spectra show the uniform growth of the UTFs and the enhancement of interlayer plasmon coupling of AuNPs upon increasing deposition cycle. The XRD results indicate that the (LDH/AuNPs)n UTFs possess long-range order stacking in the normal direction of the substrate, with AuNPs accommodated between the LDH nanosheets as a monolayer arrangement. SEM, TEM and AFM images reveal a high dispersion of AuNPs on the surface of the LDH nanosheets without aggregation. The electrochemical behavior of the UTF modified fluorine-doped tin oxide (FTO) electrode was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The (LDH/AuNPs)n UTF shows improved electron transfer kinetics, owing to the formation of electron tunneling junctions resulting from the interlayer plasmon coupling. This leads to new channels for facilitating electron transfer within the UTFs. In addition, the (LDH/AuNPs)8electrode displays significant electrocatalytic performance for glucose with a linear response range (50 μM–20 mM), low detection limit (10.8 μM), high sensitivity (343 μA mM−1 cm−2), good stability and reproducibility. Therefore, this work provides a feasible method to immobilize metal nanoparticles using the LDH nanosheet as a 2D matrix, which is promising for the development of enzyme-free sensors.

Flexible hierarchical nanocomposites based on MnO2 nanowires/CoAl hydrotalcite/carbon fibers for high-performance supercapacitors

A hierarchical nanocomposite based on MnO2 nanowire/CoAl layered double hydroxide/carbon fibers is fabricated by a facile two-step method as a high-performance supercapacitor. The CoAl-LDH nanocrystals grown on flexible carbon fibers were prepared via an in situ hydrothermal method, followed by loading of MnO2 nanowires through a direct redox reaction between the Co2+ species and MnO4−. The hierarchical MnO2/LDH/CFs electrode as a supercapacitor displays a high specific capacitance (944 F g−1 at 1 A g−1) and rate capability, good stability and excellent long-term cycling life.

Hierarchical Conducting Polymer@Clay Core–Shell Arrays for Flexible All‐Solid‐State Supercapacitor Devices

A sophisticated hierarchical nanoarray consisting of a conducting polymer (polypyrrole, PPy) core and layered double hydroxide (LDH) shell are synthesized via a facile two-step electrosynthesis method. The obtained PPy@LDH-based flexible all-solid-state supercapacitor meets the requirements of both high energy/power output and long-term endurance, which can be potentially used in highly-efficient and stable energy storage.

Magnetic-Field-Assisted Assembly of Layered Double Hydroxide/Metal Porphyrin Ultrathin Films and Their Application for Glucose Sensors

The ordered ultrathin films (UTFs) based on CoFe-LDH (layered double hydroxide) nanoplatelets and manganese porphyrin (Mn-TPPS) have been fabricated on ITO substrates via a magnetic-field-assisted (MFA) layer-by-layer (LBL) method and were demonstrated as an electrochemical sensor for glucose. The XRD pattern for the film indicates a long-range stacking order in the normal direction of the substrate. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images of the MFA LDH/Mn-TPPS UTFs reveal a continuous and uniform surface morphology. Cyclic voltammetry, impedance spectroscopy, and chronoamperometry were used to evaluate the electrochemical performance of the film, and the results show that the MFA-0.5 (0.5 T magnetic field) CoFe-LDH/Mn-TPPS-modified electrode displays the strongest redox current peaks and fastest electron transfer process compared with those of MFA-0 (without magnetic-field) and MFA-0.15 (0.15 T magnetic field). Furthermore, the MFA-0.5 CoFe-LDH/Mn-TPPS exhibits remarkable electrocatalytic activity toward the oxidation of glucose with a linear response range (0.1-15 mM; R(2) = 0.999), low detection limit (0.79 μM) and high sensitivity (66.3 μA mM(-1) cm(-2)). In addition, the glucose sensor prepared by the MFA LBL method also shows good selectivity and reproducibility as well as resistance to poisoning in a chloride ion solution. Therefore, the novel strategy in this work creates new opportunities for the fabrication of nonenzyme sensors with prospective applications in practical detection.

Hierarchical CoNi-Sulfide Nanosheet Arrays Derived from Layered Double Hydroxides toward Efficient Hydrazine Electrooxidation.

A hierarchical CoNi-sulfide nanosheet array is fabricated via an in situ reduction of CoNi-layered double hydroxide (LDH) nanosheets, then a vulcanization process. The material inherits the morphology of the LDH precursor, consisting of well-distributed CoNi-alloy@CoNi-sulfide nanoparticles with a core-shell structure, and demonstrates promising performance toward hydrazine electrooxidation.