Xianggui Kong

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.

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.

Layer-by-layer assembly of bi-protein/layered double hydroxide ultrathin film and its electrocatalytic behavior for catechol.

This paper reports the fabrication of a bi-protein/layered double hydroxide (LDH) ultrathin film in which hemoglobin (HB) and horseradish peroxidase (HRP) molecules were assembled alternately with LDH nanosheets via the layer-by-layer (LBL) deposition technique, and its electrocatalytic performances for oxidation of catechol were demonstrated. The results of XRD indicate that the HB-HRP/LDH ultrathin film possesses a long range stacking order in the normal direction of the substrate, with the two proteins accommodated in the LDH gallery respectively as monolayer arrangement. SEM images show that the film surface exhibits a continuous and uniform morphology, and AFM reveals the Root-Mean-Square (RMS) roughness of ∼10.2 nm for the film. A stable direct electrochemical redox behavior of the proteins was successfully obtained for the HB-HRP/LDH film modified electrode. In addition, it exhibits remarkable electrocatalytic activity towards oxidation of catechol, based on the synergistic effect of the two proteins. The catechol biosensor in this work displays a wide linear response range (6-170 μM, r=0.999), low detection limit (5 μM), high sensitivity and good reproducibility.

Layer-by-layer assembly of electroactive dye/inorganic matrix film and its application as sensor for ascorbic acid.

A novel inorganic-organic composite ultrathin film was fabricated by layer-by-layer assembly of naphthol green B (NGB) and layered double hydroxides (LDHs) nanoplatelets, which shows remarkable electrocatalytic behavior for oxidation of ascorbic acid. LDHs nanoplatelets were prepared using a method involving separate nucleation and aging steps (particle size: 25±5 nm; aspect ratio: 2-4) and used as building blocks for alternate deposition with NGB on indium tin oxide (ITO) substrates. UV-vis absorption spectroscopy and XRD display regular and uniform growth of the NGB/LDHs ultrathin film with extremely c-orientation of LDHs nanoplatelets (ab plane of microcrystals parallel to substrates). A continuous and uniform surface morphology was observed by SEM and AFM image. The film modified electrode displays a couple of well-defined reversible redox peaks attributed to Fe(2+)/Fe(3+) in NGB (ΔE(p)=68 mV and I(a)/I(c)=1.1). Moreover, the modified electrode shows a high electrocatalytic activity towards ascorbic acid in the range 1.2-55.2 μM with a detection limit of 0.51 μM (S/N=3). The Michaelis-Menten constant was calculated to be K(M)(app)=67.5 μM.

CoOOH ultrathin nanoflake arrays aligned on nickel foam: fabrication and use in high-performance supercapacitor devices

CoOOH ultrathin nanoflake arrays grown on nickel foam (NF) have been fabricated by a two-step soft chemical procedure. The ultrathin nanoflakes with a thickness of about 2.7 nm were interconnected with each other and formed a loose and open 3D network structure, providing sufficient exposure of the active sites to an electrolyte. Moreover, the growth mechanism was also investigated. Furthermore, as a supercapacitor material, the CoOOH/NF electrode exhibited ultrahigh specific capacitance (2550 F g−1 at 1.25 A g−1) and good cycling stability (83% of its initial capacitance value was preserved after 5000 charge/discharge cycles at 10 A g−1). Meanwhile, an asymmetric supercapacitor device was assembled with CoOOH/NF as the positive electrode and reduced graphene oxide (rGO) as the negative electrode, displaying an energy density of 49.8 W h kg−1 at a power density of 435 W kg−1. Furthermore, the capacitance retention of the asymmetric supercapacitor after 3000 cycles of charge–discharge at a current density of 7.7 A g−1 is 86%, showing good stability of the asymmetric pseudocapacitor.

Three-dimensional potassium niobate nanoarray on vermiculite for high-performance photocatalyst fabricated by an in situ hydrothermal process

Three-dimensional (3D) potassium niobate nanoarray/vermiculite (KNbO3/VMT) was synthesized by an in situ hydrothermal method using niobium chloride as the niobium resource. Scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, Fourier transform infrared and X-ray photoelectron spectroscopy tests were used to confirm that KNbO3 nanoneedles have been grown both on the outer and inner surfaces of natural layered VMT and the growth mechanism of the well-aligned KNbO3 nanoarray grown on mineral VMT was attributed to the existence of Nb species. The photocatalytic performance of the as-prepared composite was investigated using the photodegradation of methylene blue (MB) under illumination. MB was removed from aqueous solution by fully taking advantage of the good absorption property of VMT and photocatalytic property of KNbO3, and visible light was used in the process. After illumination for 105 min, the removal rate of MB in aqueous solution could be higher than 81%. The removal of MB via adsorption–degradation synergy of the structured composite was much better than that of pristine VMT and KNbO3 powder with the same amount of addition, respectively. Moreover, the environmentally friendly KNbO3/VMT material is easy to synthesize and is expected to be a promising structured photocatalyst for the removal of dyes.

Green removal of pyridine from water via adsolubilization with lignosulfonate intercalated layered double hydroxide

In this work, lignosulfonate intercalated Mg2Al layered double hydroxide was fabricated by coprecipitation method, which was used as a functional adsorbent for removing pyridine from wastewater. The X-ray powder diffraction and Fourier transformed infrared were carried out to investigate the structure of the product. In the removal process, the as-prepared lignosulfonate intercalated Mg2Al layered double hydroxide sample exhibited good adsolubilization property for pyridine, with maximum capacity of 400.8 mg g−1 in initial pyridine concentration of 400 mg/l and the removal percentage achieved about 87.9%. In addition, the influence of pH, time, and initial concentration of pyridine on the adsorption capacity was also examined. Moreover, the adsorption kinetic followed the pseudo-second-order model. Furthermore, after regeneration, the adsorbent can still show high adsorption capacity even for 10 cycles of desorption–adsorption. It hoped that lignosulfonate intercalated Mg2Al layered double hydroxide can be used as adsorbent for the removal of organic pollutants in wastewater.