MgO Nanobelts Research Articles

MgO nanobelt-modified graphene-tantalum wire electrode for the simultaneous determination of ascorbic acid, dopamine and uric acid

ABSTRACT A promising electrochemical biosensor for simultaneous detection of ascorbic acid (AA), dopamine (DA) and uric acid (UA) was fabricated by electrochemical deposition of MgO nanobelts on a graphene-modified tantalum wire (denoted as MgO/Gr/Ta) electrode. The MgO nanobelts and graphene were verified by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Electrochemical performances of the electrodes were characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The CV results show that AA, DA and UA could be detected simultaneously using MgO/Gr/Ta electrode with peak-to-peak separation of 300 mV, 147 mV and 447 mV for AA-DA, DA-UA and AA-UA, respectively. In the threefold co-existence system, the linear calibration plots for AA, DA and UA were obtained over the concentration range of 5.0–350 μM, 0.1–7 μM and 1–70 μM with detection limits of 0.03 μM, 0.15 μM and 0.12 μM, respectively. The modified electrode shows excellent selectivity, good sensitivity and good stability, making it attractive as a sensor for simultaneous detection of AA, DA and UA in biological fluids.

Synthesis and characterization of MgO nanocrystals for biosensing applications

MgO nanocrystals were prepared using a simple direct current arc plasma jet chemical vapor deposition method. Magnesium nitrate was used as source material and Mo film was used as a substrate and catalyst. The high-temperature plasma produced ensured rapid synthesis of the MgO nanocrystals. The as-prepared nanocrystals were characterized by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, energy-dispersive spectroscopy, Fourier transform infrared spectrometry, ultraviolet–visible spectrophotometry, and photoluminescence measurements. The as-synthesized samples were found to consist of cubic MgO nanobelts and nanosheets with large surface areas and low coordination oxide ions, and contained numerous contacts, rough edges, vacancies, and doping defects. The nanostructures exhibited excellent electrochemical sensing properties with high-sensing sensitivity toward ascorbic acid. Their high electrocatalytic activity was attributed to the effect of defects and the surface electron transfer ability of the one-dimensional MgO nanobelts.

Electrochemical biosensor based on one-dimensional MgO nanostructures for the simultaneous determination of ascorbic acid, dopamine, and uric acid

One-dimensional (1D) MgO nanostructures of various morphologies including tadpole-like nanobelts (tadpoles), nanobelts, and nanorods were synthesized via direct current (DC) arc plasma jet chemical vapor deposition (CVD). The effect of morphology on the biosensing properties of the nanostructures was investigated by comparing their electrochemical properties. Compared with tadpoles and nanorods, the MgO nanobelts had excellent electrocatalytic activity toward ascorbic acid (AA), dopamine (DA) and uric acid (UA). The response of the MgO nanobelts to the analytes was twice that of the tadpoles. A MgO nanobelt-modified electrode was thus fabricated for the simultaneous determination of AA, DA, and UA. The peak separations between AA and DA, DA and UA, and AA and UA for this electrode were 111, 161, and 272mV, respectively. The linear response ranges of the electrodes were 2.5–15 and 25–150μM for AA, 0.125–7.5μM for DA, and 0.5–3 and 5–30μM for UA. The calculated detection limits were 0.2, 0.05, and 0.04μM (S/N=3), respectively. The excellent electrocatalytic activity of the MgO nanobelts can be attributed to various surface defects such as low-coordination anions (O5C2− and O4C2− at the terrace and edge sites, and O3C2− at the corner and kink sites). Additionally, electron tunneling between these surface defects is possible. These defects have a strong adsorption capacity toward AA, DA, and UA. This affinity improves sensitivity and decreases the detection limits of the MgO nanobelt electrodes.

The effect of microstructure and crystal defect on electrochemical performances of MgO nanobelts

The electrochemical properties of one-dimensional (1-D) nanomaterials are highly sensitive to their surface microstructure and crystal defects. MgO nanobelts were obtained by magnesium nitrate decomposition using the direct arc plasma jet chemical vapor deposition technique, with a molybdenum substrate at 950°C for 5min. The structural details, defects, and electrochemical properties of MgO nanobelts were determined. From high-resolution transmission electron microscopy, the nanobelts contain numerous contacts, rough edges, vacancies, and doping defects. Nanobelts with large surface area and oxide ions in low coordination (with O5C2− and O4C2−, for terrace and edge sites, and O3C2− for corner and kink sites) were seen by various analytical studies. The electrochemical performances of the MgO nanobelts-modified electrode were investigated using standard techniques. The unique nanostructural features and crystal defects endow MgO nanobelt with excellent electrochemical performance as demonstrated in their application in the selective determination of hydroquinone (HQ) and catechol (CC); both can be oxidized at the MgO nanobelt-modified electrode. This nanomaterial allows the sensitive determination of HQ and CC without cross-interference. The MgO nanobelts/glassy-carbon electrode exhibited high sensitivity in the selective determination of HQ and CC, with detection limits of 1×10−8M.

Electrochemical properties of tadpole-like MgO nanobelts

Tadpole-like MgO nanobelts have been grown on Mo substrates via DC arc plasma jet chemical vapor deposition. The 10−30nm wide nanobelts have spherical caps of 30−50nm diameter. The nanobelts contain numerous contacts and oxide ions in low coordination (with O5C2− and O4C2−, for terrace and edge sites, and O3C2− for corner and kink sites). Hydroquinone (HQ) and catechol (CC) can be oxidized on MgO nanobelt-modified electrodes. The electrochemical properties of the modified electrode were investigated using cyclic voltammetry and differential pulse voltammetry techniques. This modified electrode exhibited high sensitivity in the determination of HQ and CC, with the limits of detection for HQ and CC being 1×10–11M and 1×10−9M, respectively. The strong electrocatalytic properties were correlated with large surface area and presence of numerous defects.

Synthesis and optical properties of single-crystal MgO nanobelts

MgO nanobelts were obtained by the decomposition of magnesium nitrate in a direct current arc plasma jet chemical vapor deposition process, with a Mo substrate at 950°C for different durations. The products formed in the first 0.5min were nanobelts, some of which possessed spherical particles on tips of nanobelts, forming “tadpole-like” nanostructures. When the reaction time was extended to 1min, nanobelts become longer although spherical particles were still observed. When the reaction time was 3min, nanobelts became even longer, and no spherical particles were observed. Extending the reaction time to 5min significantly widened the nanobelts, with widths ranging from 10 to 100nm. The MgO nanobelt growth occurred along the 〈100〉 and the 〈111〉 axes. The growth mechanism of the MgO nanobelts was a combination of axial VLS and side VS growth. Nanobelts exhibited strong ultraviolet–blue photoluminescence emission under excitation at 350nm.

Structural Features and Electronic Properties of MgO Nanosheets and Nanobelts

On the basis of first principles calculations, we systematically investigate the structural features, stabilities, and electronic properties of the MgO nanosheets and corresponding nanobelts with different widths. For the MgO(100) sheet, two new kinds of structures characterizing rumpling and wavelike features are found to be more stable than the flat one. Our calculations predict that these two kinds of MgO(100) and MgO(111) nanosheets exhibit semiconductive properties, with the band gaps varying from 4.23 to 4.38 eV. Moreover, their band gaps vary as different functions of the applied strain. In addition, we find that the MgO(111) nanobelts with zigzag edges show metallic behavior whereas the MgO(111) nanobelts with armchair edges and MgO(100) nanobelts exhibit semiconductive properties. In particular, the band gaps for the semiconductive nanobelts can be manipulated from 2.75 to 3.95 eV by the width of the nanobelts. These aspects provide these nanobelts with promising applications in spintronics and nanoscaled ultraviolet photoelectronic devices.

MgO nanobelts using a reactive and auto-removed ZnO nanobelt template

A newly developed chemical conversion route has been used to manufacture MgO nanobelts by using prefabricated ZnO nanobelts as a template. The converted MgO nanobelts are composed of small nanocrystals with an average diameter of 12 nm. Room-temperature photoluminescence measurement shows two emission bands centered at 392 and 478 nm which are attributed to various structural defects with different densities in the MgO nanobelts. Our approach here is effective and facile without additional etching agents being introduced. Other novel MgO nanostructures may be further fabricated by this method, depending on the morphologies of ZnO nanostructure templates.

Nanocatalysis on Tailored Shape Supports: Au and Pd Nanoparticles Supported on MgO Nanocubes and ZnO Nanobelts

Active gold and palladium nanoparticles supported on MgO nanocubes and ZnO nanobelts and transition-metal-containing MgO nanobelts were synthesized by combining evaporation and deposition-precipitation techniques. The high activity and stability of the Au/CeO2 and Pd/CeO2 nanoparticle catalysts deposited on the MgO cubes are remarkable and imply that a variety of efficient catalysts can be designed and tested using this approach. The significant increase in the concentration of corner and edge sites in MgO nanocubes make them well-defined supports to study the detailed mechanism of the catalytic activity enhancement.

Uniform MgO nanobelts formed from in situ Mg 3N 2 precursor

MgO nanobelts with a pure morphology and high yield were generated by the direct evaporation of Mg metals under initial N 2 gas at 650 °C and subsequent N 2/O 2 atmosphere at 800 °C. The growth of these MgO nanobelts is explained in a VS route in which the in situ formed Mg 3N 2 slowly decomposes and reacts with oxygen. Mg 3N 2 is therefore a very effective precursor for the fabrication of high-purity one-dimensional (1D) MgO nanostructures.

Intensive green light emission from MgO nanobelts

Large-scale synthesis of crystalline MgO nanobelts was achieved through a simple thermal evaporation method. The products consist of a large quantity of single-crystalline MgO nanobelts with the cubic structure. A strong and broad green emission band centered at 508 nm and a weak ultra-light emission band centered at 383 nm were observed in the photoluminescence spectrum of the MgO nanobelts, which is attributed to the singly ionized oxygen vacancies in the MgO nanobelts. Another red-light emission band centered at 721 nm was also observed, which may be assigned to the relaxation luminescence of defect centers in the MgO nanobelts.

Preparation of network-like MgO nanobelts on Si substrate

Cubic-structure MgO nanobelts were synthesized on silicon wafers in a simple CVD process, using infrared irradiation to heat the Mg/Al target under mediate vacuum. The nanobelts were 100–200 nm wide with a width/thickness ratio of 1–2. Most of the nanobelts were connected with others to form networks. The direction of nanobelt lengths is along 〈1 0 0〉 and the surfaces are enclosed by {1 0 0} planes. The individual network has a single-crystal structure, resulting in high-network stiffness. The formation mechanism of the nanostructures was proposed. This provides an efficient way to prepare MgO one-dimensional nanostructures on different substrates over a large-area.

Fabrication of MgO nanobelts using a halide source and their structural characterization

MgO nanobelts have been fabricated by chemical vapor deposition using MgCl3 as starting material. The products consist of a large quantity of belt-like nanostructures with typical lengths in the range of several tens to several hundreds of micrometers; some of them even have lengths on the order of a millimeter. The typical thickness and width-to-thickness ratio of the MgO nanobelts are in the range of 20 to 100 nm and about 5 to 10, respectively. The size and morphology of the MgO nanobelts were measured by transmission electron microscopy. Investigations of X-ray diffraction patterns and using high-resolution transmission electron microscopy indicate that the nanobelts have a cubic structure and are single-crystalline.