Shenghong Kang

Low-temperature synthesis of Mn3O4 hollow-tetrakaidecahedrons and their application in electrochemical capacitors

Mn3O4 hollow-tetrakaidecahedron micro/nano structures are synthesized basing on a structure-shrinkage-assisted Kirkendall effect under the hydrothermal condition. The Mn powders are transformed into Mn(OH)2 micro tetrakaidecahedron and substantially oxidized to Mn3O4 during the filtration under the flow of oxygen. The Kirkendall effect was proposed to have important responsibility on the formation of voids. Due to the structural shrinkage while transformation, the diffusion of substances from core to shell was found to be accelerated and thus larger holes formed. Electrochemical behavior of such hollow structure electrode was 148 F g−1. Mn2O3 and Mn5O8 micro hollow tetrakaidecahedron could also be obtained by annealing the corresponding Mn3O4 tetrakaidecahedrons in the air at different temperature.

Synthesis and characterization of nanostructured Fe3O4 micron-spheres and their application in removing toxic Cr ions from polluted water

We present a simple and effective method for the synthesis of nanostructured Fe(3)O(4) micron-spheres (NFMSs) by annealing hydrothermally formed FeCO(3) spheres in argon. The phase structure, particle size, and magnetic properties of the product have been characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and by means of a superconducting quantum interference device (SQUID). The results have shown that the as-obtained NFMSs have a diameter of about 5 μm and are composed of nanometer-sized porous lamellae. The NFMSs have a large specific surface area (135.9 m(2) g(-1)), reductive Fe(2+) incorporated into their structure, and intense magnetic properties. These properties suggest that NFMSs have potential application in removing toxic Cr(6+) ions from polluted water. At 25°C, each gram of NFMSs product can remove 43.48 mg of Cr(6+) ions, as compared to just 10.2 mg for nanometer-sized Fe(3)O(4) and 1.89 mg for micron-sized Fe(3)O(4). The enhanced removal performance can be ascribed to the structural features. Moreover, the Cr(6+) ion removal capacity of the NFMSs can reach up to 71.2 mg g(-1) at 50°C. The influencing parameters in the removal of Cr(6+) ions, such as contact time, pH, and temperature, have been evaluated. The Cr(6+)-removal mechanism has been investigated. We have found that the NFMSs product not only serves as an effective adsorbent to remove toxic Cr(6+) ions from polluted water, but also as an effective reductant in reducing the adsorbed toxic Cr(6+) ions to much less toxic Cr(3+) through the Fe(2+) incorporated into its structure.

Modified natural diatomite and its enhanced immobilization of lead, copper and cadmium in simulated contaminated soils.

Natural diatomite was modified through facile acid treatment and ultrasonication, which increased its electronegativity, and the pore volume and surface area achieved to 0.211 cm(3) g(-1) and 76.9 m(2) g(-1), respectively. Modified diatomite was investigated to immobilize the potential toxic elements (PTEs) of Pb, Cu and Cd in simulated contaminated soil comparing to natural diatomite. When incubated with contaminated soils at rates of 2.5% and 5.0% by weight for 90 days, modified diatomite was more effective in immobilizing Pb, Cu and Cd than natural diatomite. After treated with 5.0% modified diatomite for 90 days, the contaminated soils showed 69.7%, 49.7% and 23.7% reductions in Pb, Cu and Cd concentrations after 0.01 M CaCl2 extraction, respectively. The concentrations of Pb, Cu and Cd were reduced by 66.7%, 47.2% and 33.1% in the leaching procedure, respectively. The surface complexation played an important role in the immobilization of PTEs in soils. The decreased extractable metal content of soil was accompanied by improved microbial activity which significantly increased (P<0.05) in 5.0% modified diatomite-amended soils. These results suggested that modified diatomite with micro/nanostructured characteristics increased the immobilization of PTEs in contaminated soil and had great potential as green and low-cost amendments.

Micro/nanostructured porous Fe–Ni binary oxide and its enhanced arsenic adsorption performances

A simple method is presented to synthesize micro/nano-structured Fe-Ni binary oxides based on co-precipitation and subsequent calcination. It has been found that the Fe-Ni binary oxides are composed of the porous microsized aggregates built with nanoparticles. When the atomic ratio of Fe to Ni is 2 to 1 the binary oxide is the micro-scaled aggregates consisting of the ultrafine NiFe2O4 nanoparticles with 3-6nm in size, and shows porous structure with pore diameter of 3nm and a specific surface area of 245m(2)g(-1). Such material is of abundant surface functional groups and has exhibited high adsorption performance to As(III) and As(V). The kinetic adsorption can be described by pseudo-second order model and the isothermal adsorption is subject to Langmuir model. The maximum adsorption capacity on such Fe-Ni porous binary oxide is up to 168.6mgg(-1) and 90.1mgg(-1) for As(III) and As(V), respectively, which are much higher than the arsenic adsorption capacity for most commercial adsorbents. Such enhanced adsorption ability for this material is mainly attributed to its porous structure and high specific surface area as well as the abundant surface functional groups. Further experiments have revealed that the influence of the anions such as sulfate, carbonate, and phosphate, which commonly co-exist in water, on the arsenic adsorption is insignificant, exhibiting strong adsorption selectivity to arsenic. This micro/nano-structured porous Fe-Ni binary oxide is hence of good practicability to be used as a highly efficient adsorbent for arsenic removal from the real arsenic-contaminated waters.

A facile synthesis of single crystal TiO2 nanorods with reactive {100} facets and their enhanced photocatalytic activity

High-energy {100} faceted single crystal TiO2 nanorods were synthesized by a facile hydrothermal method. An interesting phase transition from the orthorhombic hydrogen titanate to anatase TiO2 was observed during the reaction process. A structural formation model of the TiO2 nanorods was proposed based on experimental evidence. The resultant {100} faceted TiO2 nanorods exhibited considerably enhanced photocatalytic activity towards degradation of organic pollutants and removal of heavy metal ions owing to the special one-dimensional structure with the reactive {100} facets, thus showing a great potential in the field of water treatment. At the same time, the synthetic route provided guidance for the synthesis of high-energy {100} facets using EDTA and urea as effective modifiers. This approach may be extended to synthesize other functional oxide crystals with well-defined morphologies and to increase the percentages of certain exposed facets.

Enhanced degradation performances of plate-like micro/nanostructured zero valent iron to DDT.

Micro/nanostructured zero valent iron (MNZVI) is successfully mass-synthesized by ball-milling the industrially-reduced iron powders. The as-prepared MNZVI is plate-like in morphology with about 2-5μm in planar size and 35-55nm in thickness, and ∼16m(2)/g in specific surface area. Such plate-like MNZVI has demonstrated much higher degradation performances to DDT [or 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane] in the aqueous solution than the commercial ZVI powders under acidic conditions. The MNZVI-induced DDT degradation is also much faster than the previously reported results. The time-dependent DDT removal amount can be described by the pseudo first-order kinetic model. Further experiments have shown that more than 50% of DDT can be mineralized in 20min and the rest is dechlorinated to DDX (the products with less chlorine). It has been revealed that the DDT degradation could be attributed to the acid assisted ZVI-induced mineralization and dechlorination. The mineralization process is dominant during the initial stage within 20min, and the dechlorination is the main reaction in the anaphase of the degradation. This work not only deepens understanding of DDT degradation but also could provide a highly efficient material for the practical treatment of the DDT in a real environment.

Photoelectrochemical manifestation of intrinsic photoelectron transport properties of vertically aligned {001} faceted single crystal TiO2 nanosheet films

In this work, vertically aligned anatase TiO2 single crystal nanosheets with laterally exposed {001} facets onto a conducting FTO substrate (VATN) were successfully synthesised using hydrofluoric acid (40 wt%) as a crystal facet controlling agent by a simple hydrothermal method. The as-synthesised VATN without calcination exhibited a good crystalline structure, and was used as a photoanode showing superior photoelectrocatalytic activity toward water oxidation under UV irradiation. After thermal treatment at 550 °C for 2 h, the photoelectrocatalytic activity of the VATN photoanode was almost 2.6 times that for unsintered VATN under the same experimental conditions, which could be mainly due to the surface passivation role of surface fluorine in unsintered VATN to decrease the photoelectrocatalytic activity. A photoelectrochemical method was used to manifest the photoelectron transport properties inside VATN photoanodes and concurrently quantify the inherent resistances (R0) of UV illuminated photoanodes before and after calcination. The results demonstrated that the determined R0 values were respectively 155 Ω and 66 Ω for VATN photoanodes before and after calcination, inversely proportional to their photoelectrocatalytic activities. Compared to VATN before calcination, a significantly decreased R0 value of VATN after calcination further confirmed the presence of surface fluorine in VATN unfavorable for photoelectron transport inside a photocatalyst film. This work provided direct evidence to prove the intrinsic photoelectron transport properties of {001} faceted anatase TiO2 nanosheet array film photoanodes in the presence and absence of surface fluorine.

Magnetically recyclable catalytic activity of spiky magneto-plasmonic nanoparticles

Spiky magnetoplasmonic nanoparticles (NPs) with an Fe3O4 core and epitaxial Au branches have been successfully fabricated for the magnetically recyclable catalysis of the 4-nitrophenol reduction. The epitaxial Au branches in the spiky magnetoplasmonic NPs lead to enhanced catalytic activity. Because of high magnetization, the spiky NPs exhibit good separation ability and reusability, which can be repeatedly applied for the nearly complete reduction of 4-nitrophenol for at least four successive cycles. The unique properties make spiky magnetoplasmonic NPs an ideal platform to study various heterogeneous catalytic processes that can be potentially applied in a wide variety of fields in bio-separation, catalysis, and sensing devices.

One pot microwave-assisted synthesis of Ag decorated yolk@shell structured TiO2 microspheres

A facile and economical one-pot microwave-assisted approach for the synthesis of Ag decorated yolk@shell structured TiO2 microspheres (Ag-TS) is reported. The rapid and uniform microwave heating could reduce the reaction time to 30 min, an order of magnitude shorter than that of conventional methods. The characterization data confirmed that the resultant mesoporous structured Ag-TS were highly uniform in size with an average diameter of ∼0.5 μm, which was constructed by small anatase TiO2 nanoparticles, along with Ag nanoparticles ranging from 10 to 50 nm homogeneously dispersed on the microspheres. Nitrogen adsorption–desorption measurement revealed that all the Ag-TS samples had high specific surface areas (>100 m2 g−1) and abundant mesoporous structures. The growth model of Ag-TS was proposed based on a series of contrast experiments, the unique selective heating of reaction solvent (deionized water and ethanol) by the microwave method was found to be critical. At the initial stage, amorphous solid microspheres were formed by heating of ethanol molecules through absorbing microwave energy due to the better microwave absorbing performance. Then water molecules were heated by the microwave irradiation, the crystallization of anatase TiO2 on the surface of the solid microspheres started, followed by the Ti species diffusing spontaneously towards the outer surface of the solid microspheres and leading to the formation of the outer shell due to the Ostwald ripening process. Finally, water continuously diffused through the outer shell and guided the subsequent crystallization of anatase TiO2, resulting in the formation of the core. Besides, the application of Ag-TS for the removal of water contaminants including toxic heavy metal hexavalent chromium (Cr(VI)) ions and organic dye methylene blue (MB) were also evaluated.

Semiconductor-metal transition of titanium sesquioxide nanopowder

Titanium sesquioxide (Ti2O3) nanopowders have been successfully synthesized using TiCl4 assisted hydrogen reduction method from P25 (TiO2) powders at 970 °C. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy reveal its high purity. The temperature dependent XRD, resistance, and infrared absorption investigations exhibit Z-shaped curves (cell parameter a, resistance, and infrared transmittance) indicating the semiconductor-metal transition (SMT) in the range of 135–220 °C. With prolonging the annealing time, the starting temperature of SMT is found to move toward the low-temperature side, and this was also discussed. The c/a ratio alteration is considered to result in the modulation of property. Besides, the results are verified comparing with the theoretical calculation of band structure.