S. W. Hwang

Large-scale synthesis of ZnO balls made of fluffy thin nanosheets by simple solution process: structural, optical and photocatalytic properties.

This paper reports a large-scale synthesis of ZnO balls made of fluffy thin ZnO nanosheets by simple solution process at low-temperature of 65±2°C. The synthesized ZnO structures were characterized in detail in terms of their morphological, structural, optical and photocatalytic properties. The detailed morphological characterizations, done by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), confirmed that the synthesized products are ZnO balls which are made by accumulation of hundreds of thin ZnO nanosheets. Interestingly, it is seen that the nanosheets are arranged in such a special fashion that they made ball-like morphologies. Detailed structural examinations revealed that of as-synthesized ZnO products are well-crystalline and possessing wurtzite hexagonal phase. The optical property, measured by UV-Visible spectroscopy, substantiated good optical properties for as-synthesized ZnO balls. The as-synthesized ZnO balls were utilized as an efficient photocatalysts for the photocatalytic degradation of methylene blue (MB) dye. Almost complete degradation of MB was observed in presence of ZnO balls composed of nanosheets within 70 min under UV-light irradiation. By comparing the photocatalytic performance with commercially available TiO(2)-UV-100, it was observed that the synthesized ZnO balls exhibited superior photocatalytic performance as compared to TiO(2)-UV-100 photocatalyst.

Ultra-high sensitive ammonia chemical sensor based on ZnO nanopencils.

This paper reports a very simple, reliable and facile methodology to fabricate ultra-high sensitive liquid ammonia chemical sensor using well-crystalline hexagonal-shaped ZnO nanopencils as an efficient electron mediator. A low-temperature facile hydrothermal technique was used to synthesize ZnO nanopencils. The synthesized nanopencils were characterized in detail in terms of their morphological, structural and optical properties which confirmed that the synthesized nanomaterial is well-crystalline, possessing wurtzite hexagonal phase and possess very good optical properties. A very high sensitivity of ≈ 26.58μAcm(-2)mM(-1) and detection limit of ≈ 5nM with a correlation coefficient (R) of 0.9965 and a response time of less than 10s were observed for the fabricated liquid ammonia by I-V technique. To the best of our knowledge, by comparing the literature, it is confirmed that the fabricated sensor based on ZnO nanopencils exhibits highest sensitivity and lowest detection limit for liquid ammonia. This research opens a way that simply synthesized nanomaterials could be used as efficient electron mediators for the fabrication of efficient liquid ammonia chemical sensors.

A highly sensitive ammonia chemical sensor based on α-Fe2O3 nanoellipsoids

This paper reports the facile synthesis of ?-Fe2O3 nanoellipsoids by a low-temperature hydrothermal process and their effective utilization in the fabrication of a highly sensitive aqueous ammonia chemical sensor by the I?V technique. The as-synthesized ?-Fe2O3 nanoellipsoids are characterized in terms of their morphological, structural and optical properties. The detailed structural and optical properties confirm a rhombohedral ?-Fe2O3 structure and indirect (1.87?eV) and direct (2.15?eV) band gaps, respectively, for the synthesized nanoellipsoids. The fabricated aqueous ammonia sensor based on nanoellipsoids exhibits a very high and reproducible sensitivity of ~4.678??A?cm?2?mM?1 and a detection limit of ~0.04?nM with a correlation coefficient (R) of 0.995 in a short response time (10.0?s). The presented work demonstrates that simply synthesized iron oxide nanostructures can efficiently be used for the fabrication of reliable and reproducible chemical sensors.

Structural and optical properties of CuO layered hexagonal discs synthesized by a low-temperature hydrothermal process

Layered hexagonal discs of CuO were synthesized on a large scale via low-temperature hydrothermal growth process at 130 °C using copper nitrate, hexamethylenediamine and NH4OH. The detailed morphological investigations by field emission scanning electron microscopy and transmission electron microscopy (TEM) clearly revealed that the synthesized CuO structures are made by the well layer-by-layer accumulation of several sheets which arranged themselves in such a special manner that they exhibit the hexagonal discs of CuO. The detailed structural characterizations of the hexagonal CuO discs were done by high-resolution TEM and x-ray diffraction which confirmed that the synthesized structures possessing well nanocrystalline nature and monoclinic structure. The purity and composition of the synthesized products were examined using energy dispersive spectroscopy, elemental mapping and Fourier transform infrared spectroscopy. Using UV–Vis spectroscopy at room temperature we obtained indirect and direct band gap values slightly blue shifted to the bulk values. Finally, a plausible growth mechanism has been proposed for the formation of CuO layered hexagonal discs.

Growth and photocatalytic properties of Sb‐doped ZnO nanoneedles by hydrothermal process

This paper reports a facile hydrothermal synthesis of Sb‐doped ZnO nanoneedles by using aqueous mixtures of zinc chloride, antimony (Sb) chloride, hexamethylenetetramine (HMTA) and ammonium hydroxide at low temperature of 110 °C. The morphological characterizations of as‐synthesized nanoneedles were done by field emission scanning electron microscopy (FESEM) which reveals that the nanoneedles are grown in large‐quantity and arranged in such a special manner that they made flower‐like morphologies. The structural characterization of as‐synthesized nanoneedles was investigated by X‐ray diffraction (XRD) pattern which confirm the well‐crystalline and wurtzite hexagonal phase of as‐synthesized products. The compositional characterization of as‐synthesized nanoneedles was characterized by energy dispersive spectroscopy (EDS), which verify that the synthesized nanoneedles are composed of zinc, Sb and oxygen. For application point of view, the synthesized nanoneedles were used as photocatalyst for photocatalytic...

Utilization of CuO Layered Hexagonal Disks for Room‐Temperature Aqueous Ammonia Sensing Application

In this paper, CuO layered hexagonal disks based ammonium hydroxide chemical sensor has been fabricated which demonstrated good sensitivity and detection limit. The CuO layered hexagonal disks were synthesized in large quantity via facile hydrothermal process at low‐temperature of 130 °C and characterized in detail in terms of their structural and optical properties [1]. The detailed structural and optical properties of as‐synthesized CuO layered hexagonal disks confirmed the good crystallinity with monoclinic structure and good optical properties for synthesized products [1]. The fabricated ammonium hydroxide chemical sensor based on CuO layered hexagonal disks demonstrate a good sensitivity of 0.07166 μA cm−2  mM−1, detection limit = 1.333 μM, response time less than 10 s, linear dynamic range (LDR) from 5.0 μM to 5.0 mM. This study reveals that simply synthesized CuO materials can be efficiently as an electron mediator to fabricate efficient chemical sensors.

Fabrication and Characterization of Field Effect Transistor Based on High-Aspect Ratio Sulfur-Doped ZnO Nanowires.

Well-crystalline sulfur (S) doped ZnO nanowires have been grown via a simple thermal evaporation process on Si substrate using high purity zinc and sulfur powders in presence of oxygen. The as-grown S:ZnO nanowires were characterized in terms of their morphological structural, compositional and optical properties using several techniques such as FESEM, TEM, XRD, EDS and PL. The morphological characterizations revealed that the as-grown nanowires had diameters in the range of 60-100 nm with lengths 5-15 μm. The details structural properties confirmed the well-crystallinity and wurtzite hexagonal phase for the prepared nanowires. Room temperature photoluminescence (PL) spectrum showed a strong green band with a suppressed UV emission. The electrical properties of single S:ZnO nanowire was examined by fabricating single nanowire based field effect transistors (FETs). The detailed electrical transport results showed that S:ZnO nanowires possess n-type semiconducting behavior and exhibited an electron mobility of -67.7 cm2 V(-1) s(-1) and a carrier concentration of 2 x 10(17) cm(-3), respectively.

Growth of branched In‐doped ZnO nanowires: Structural and Optical Properties

Well‐crystallized branched Indium (In)‐doped ZnO nanowires were grown on silicon substrate via simple thermal evaporation process by using metallic zinc and indium powders in the presence of oxygen. The as‐grown branched nanowires were examined in terms of their morphological, structural and optical properties using field emission scanning electron microscopy (FESEM) attached with energy dispersive spectroscopy (EDS), X‐ray diffraction and room‐temperature photoluminescence (PL) spectroscopy. The morphological and structural characterizations confirmed that the as‐grown products are branched nanowires, grown in high‐density and possessing well‐crystalline structures. The room‐temperature photoluminescence (PL) spectrum exhibited a very small UV emission and a broad band in the visible region indicating the presence of structural defects due to insertion of In‐atoms in the lattices of as‐grown nanowires. The presence of a strong green emission in the room‐temperature PL spectrum demonstrates that these str...