L.Z. Pei

Formation of copper vanadate nanobelts and their electrochemical behaviors for the determination of ascorbic acid

Copper vanadate nanobelts have been successfully synthesized by a facile hydrothermal process using sodium vanadate and copper acetate as the raw materials, and the polymer polyvinyl pyrrolidone (PVP) as the surfactant by adjusting the pH value. The nanobelts are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). XRD and HRTEM show that the copper vanadate nanobelts are composed of a single crystalline monoclinic Cu2.33V4O11 phase. SEM observation shows that the copper vanadate nanobelts have the thickness, width and length of about 50 nm, 300 nm to 1 μm and several tens of micrometers, respectively. The pH value plays a key role in the formation of the copper vanadate nanobelts. The growth process of the copper vanadate nanobelts has been proposed as the nucleation and PVP adsorption growth mechanism under acidic and alkaline conditions. Copper vanadate nanobelts have been used as glassy carbon electrode (GCE) modified materials for the determination of ascorbic acid showing good electrochemical detection performance. The linear range is 0.001–2 mM and the detection limit is 0.14 μM and 0.38 μM for cvp1 and cvp2, respectively. The copper vanadate nanobelt modified GCE exhibits good stability and reproducibility.

Analysis of ascorbic acid by electrochemical detection

A glassy carbon electrode (GCE) modified by copper-doped titanium dioxide nanoneedles has been fabricated and used for the electrochemical detection of ascorbic acid (AA) in KCl solution. Two pairs of peak currents on quasi-reversible electrochemical cyclic voltammogram peaks (cvps) are located at +0.16 V,–0.03 V (cvp 1 and cvp 2) and +0.01 V,–0.44 V (cvp 1′ and cvp 2′), respectively. The relationship between the peak current and AA concentration is linear in the concentration range from 0.0005 to 2 mM. There is also a linear relationship between the peak current and the scan rate. The detection limit is 0.37 μM and 0.25 μM for cvp 1 and cvp 2, respectively, at a signal-to-noise ratio of 3. A GCE modified by copper-doped titanium dioxide nanoneedles exhibts good stability and has promising characteristics for the detection of AA.

Vanadium doping of strontium germanate and their visible photocatalytic properties

Vanadium-doped strontium germanate with rod-shaped morphology and different vanadium contents has been synthesized by a facile hydrothermal process. The obtained vanadium-doped strontium germanate has been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet (UV) diffuse reflectance spectra. The phase of the vanadium-doped strontium germanate depends on the vanadium content. SEM observations show that the vanadium-doped strontium germanate comprises a rod-shaped morphology with diameter and length of nanoscale/microscale size and longer than 10 μm, respectively. The band gap of the vanadium-doped strontium germanate depends on the vanadium content and increases significantly from 2.74 eV to 3.02 eV with the vanadium content increasing from 1 wt% to 10 wt%. Vanadium-doped strontium germanate shows highly efficient photocatalytic activity for the degradation of methylene blue under sunlight irradiation. The results show that vanadium-doped strontium germanate is very promising for visible-light photocatalytic applications.

Formation mechanism of manganese vanadate microtubes and their electrochemical sensing properties

Abstract Manganese vanadate microtubes have been synthesized via a simple hydrothermal process using polyvinyl pyrrolidone as the surfactant. Scanning electron microscopy observation shows that polyvinyl pyrrolidone plays an essential role in the formation and phase transformation of the manganese vanadate microtubes. A polyvinyl pyrrolidone-assisted “Ostwald ripening” growth mechanism has been proposed to explain the formation process of the manganese vanadate microtubes. The electrochemical behavior of L-cysteine at the manganese vanadate microtube modified glassy carbon electrode has been analyzed. The manganese vanadate microtube modified glassy carbon electrode exhibits the performance for the electrochemical determination of L-cysteine with a detection limit of 9.2 μM and linear range of 0.01 – 2 mM.

Electrochemical determination of ascorbic acid using Cu sulfide modified glassy carbon electrode

The electrochemical responses of ascorbic acid at the Cu-sulfide modified glassy carbon electrode have been analyzed by adjusting the scan rate, ascorbic acid concentration and species of the electrolytes. Two anodic cyclic voltammogram peaks (cvp1, cvp2) are located at +0.56 V and +0.33 V, and two cathodic cyclic voltammogram peaks (cvp1′, cvp2′) are located at +0.10 V and–0.40 V, respectively. The intensities of the cyclic voltammogram peaks increase linearly with the increase of the ascorbic acid concentration in a range of 0.0005–2 mM and scan rate ranging from 25 to 200 mV s–1. A Cu-sulfide modified glassy carbon electrode shows good determination ability for ascorbic acid in neutral solutions with the detection limit of 0.18 μM and 0.12 μM for cvp1 and cvp2, respectively, at a signal-to-noise ratio of 3. Cu sulfide modified glassy carbon electrode shows good reproducibility and stability.

Synthesis of manganese vanadate nanobelts and their visible light photocatalytic activity for methylene blue

Manganese vanadate nanobelts have been synthesised by a simple hydrothermal process using polymer polyvinyl pyrrolidone as the surfactant by adjusting the pH value. The X-ray diffraction, selected area electron diffraction and the high-resolution transmission electron microscopy (TEM) show that the manganese vanadate nanobelts are composed of a single crystalline monoclinic Mn2V2O7 phase. Scanning electron microscopy and TEM observations show that the thickness, width and length of the nanobelts are 20 nm, 350 nm–1 μm and several dozens to several hundreds of micrometres, respectively. The photocatalytic activities of the manganese vanadate nanobelts have been evaluated by the photocatalytic degradation of methylene blue (MB) in an aqueous solution as a model pollutant under the solar light irradiation. After 4 h of the irradiation by the solar light, the MB solution with the volume of 10 mL and the concentration of 10 mg·mL−1 can be totally degraded using 10 mg manganese vanadate nanobelts.

Copper germanate nanowire electrode for the electrochemical detection of glyoxalic acid using cyclic voltammetry method

Glyoxalic acid was determined by electrochemical cyclic voltammetry method using copper germanate (CuGeO3) nanowires as the modified glassy carbon electrode (GCE) materials. The CuGeO3 nanowire modified GCE exhibited good detection performance for glyoxalic acid in neutral solution. The intensities of two anodic peaks vary linearly with the increase of the scan rate from 25 to 200 mVs−1 and glyoxalic acid concentration from 0.001 to 2 mM. The detection limit was 8.5 μM and 0.78 μM for cvp1 and cvp2 with the correlation coefficient of 0.991 and 0.998, respectively. The CuGeO3 nanowire modified GCE exhibited good reproducibility and stability.

Hierarchical bismuth phosphate microspheres with high photocatalytic performance

Abstract Hierarchical bismuth phosphate microspheres have been prepared by a simple hydrothermal process with polyvinyl pyrrolidone. Scanning electron microscopy observations show that the hierarchical bismuth phosphate microspheres consist of nanosheets with a thickness of about 30 nm. The diameter of the microspheres is about 1 – 3 μm. X-ray diffraction analysis shows that the microspheres are comprised of triclinic Bi23P4O44.5 phase. The formation of the hierarchical microspheres depends on polyvinyl pyrrolidone concentration, hydrothermal temperature and reaction time. Gentian violet acts as the pollutant model for investigating the photocatalytic activity of the hierarchical bismuth phosphate microspheres under ultraviolet–visible light irradiation. Irradiation time, dosage of the hierarchical microspheres and initial gentian violet concentration on the photocatalytic efficiency are also discussed. The hierarchical bismuth phosphate microspheres show good photocatalytic performance for gentian violet removal in aqueous solution.

Calcium germanate nanowires by vanadium doping with improved photocatalytic activity

Vanadium-doped calcium germanate nanowires were prepared by a simple hydrothermal method. The samples were analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and solid UV–Vis diffuse reflectance spectrum. The photocatalytic activity of the vanadium-doped calcium germanate nanowires was investigated by the degradation of methylene blue (MB) under solar light irradiation. The results show that the vanadium-doped calcium germanate nanowires are composed of rhombohedral Ca3GeO5 and orthorhombic CaV3O7 phases. The nanowires have the diameter and length of 50–200 nm and several dozens of micrometres, respectively. The band gap of the vanadium-doped calcium germanate nanowires strongly depends on the vanadium doping mass percentage. The absorption spectrum can be broadened to visible light region. The photocatalytic activity of the vanadium-doped calcium germanate nanowires is remarkably improved. Vanadium-doped calcium germanate nanowires with the vanadium doping mass percentage of 10% have the highest photocatalytic activity for MB degradation under solar light irradiation.