Xiangyu Xu

Layer-by-layer assembly of layered double hydroxide/cobalt phthalocyanine ultrathin film and its application for sensors

This paper reports the preparation of cobalt phthalocyanine/layered double hydroxide ultrathin films (UTFs) through an electrostatic layer-by-layer (LBL) technique as well as its application in electrocatalysis for dopamine oxidation. UV-vis absorption and electrochemical impedance spectra indicate the uniform deposition of the LBL films. XRD measurements demonstrate the long-range ordered structure of organic/inorganic UTFs, with an average repeating distance of 1.89 nm. SEM images show that the film surface displays a continuous and uniform morphology, with the root-mean-square (rms) roughness of ∼6.4 nm revealed by AFM. The UTF modified ITO electrode exhibits significant electrocatalytic performance for the oxidation of dopamine which is related to the Co(II)/Co(III) couple in the (LDH/CoPcTs)n UTF. The dopamine biosensor shows rather high sensitivity, low detection limit and excellent anti-interference properties in the presence of ascorbic acid. Furthermore, compared with pristine organic multilayer (PDDA/CoPcTs)n modified electrodes, the (LDH/CoPcTs)nelectrodes show superior repeatability and long-term stability, due to the immobilization and dispersion of electroactive CoPcTs molecules by LDH nanosheets. Therefore, this work demonstrates a successful paradigm for the fabrication of electroactive species in an inorganic 2D matrix, which can be potentially used for practical applications in bioanalysis and biodetection.

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.

Thermal study of boehmite nanofibers with controlled particle size

Boehmite nanofiber materials with controlled particle size were synthesized without any surfactant by careful tuning of the hydrothermal temperatures, and followed by a series of characterizations. It was found that the boehmite nanofibers became shorter and coarser with the increase of temperature, and resulted in a gradual decrease of their specific surface areas. Moreover, the thermal stability of the boehmite nanofibers was studied by in situ HT X-ray diffraction and thermogravimetry–differential scanning calorimetry. All materials showed the phase transition from γ-Al2O3 to other forms. Yet the transition temperature was increased with the increase of hydrothermal temperature. The boehmite nanofibers with the largest diameter showed the best thermal stability.