Guozhong Wang

Highly efficient and recyclable triple-shelled Ag@Fe3O4@SiO2@TiO2 photocatalysts for degradation of organic pollutants and reduction of hexavalent chromium ions

Herein, we demonstrate the design and fabrication of the well-defined triple-shelled Ag@Fe3O4@SiO2@TiO2 nanospheres with burr-shaped hierarchical structures, in which the multiple distinct functional components are integrated wonderfully into a single nanostructure. In comparison with commercial TiO2 (P25), pure TiO2 microspheres, Fe3O4@SiO2@TiO2 and annealed Ag@Fe3O4@SiO2@TiO2 nanocomposites, the as-obtained amorphous triple-shelled Ag@Fe3O4@SiO2@TiO2 hierarchical nanospheres exhibit a markedly enhanced visible light or sunlight photocatalytic activity towards the photodegradation of methylene blue and photoreduction of hexavalent chromium ions in wastewater. The outstanding photocatalytic activities of the plasmonic photocatalyst are mainly due to the enhanced light harvesting, reduced transport paths for both mass and charge transport, reduced recombination probability of photogenerated electrons/holes, near field electromagnetic enhancement and efficient scattering from the plasmonic nanostructure, increased surface-to-volume ratio and active sites in three dimensional (3D) hierarchical porous nanostructures, and improved photo/chemical stability. More importantly, the hierarchical nanostructured Ag@Fe3O4@SiO2@TiO2 photocatalysts could be easily collected and separated by applying an external magnetic field and reused at least five times without any appreciable reduction in photocatalytic efficiency. The enhanced photocatalytic activity and excellent chemical stability, in combination with the magnetic recyclability, make these multifunctional nanostructures promising candidates to remediate aquatic contaminants and meet the demands of future environmental issues.

The influence of biochar type on long-term stabilization for Cd and Cu in contaminated paddy soils

Long-term effect of biochar on PTEs (potential toxic elements) immobilization depends upon biochar own property and its aging process in soil. To understand the role of biachar type on PTEs stabilization, two types of biochar, corn-straw-derived biochar (CB) and hardwood-derived biochar (HB), were compared for their efficacy in achieving a stable decrease in the bio-availability of Cd and Cu in soils. The 3-year pot-culture experiment showed that HB reduced the concentration of CaCl2-extractable Cd and Cu by 57.9 and 63.8% in soil, and Cd and Cu uptake by 63.6 and 56.3% in rice tissue respectively, in the first year, whereas these values increased in the next two years. On the other hand, CB decreased these values steadily year by year. At the end of the 3 years, CB at 5% level had lowered the levels of CaCl2-extractable Cd and Cu by 53.6 and 66.8%, respectively. These variations between CB and HB were due to the differences in the way the two types of biochar age in the soil. The aging process was simulated in the laboratory, and the XPS results showed that the oxidization of the biochars introduced more oxygen-containing groups (especially carboxyl) on the surface of CB than HB, leading to a correspondingly greater number of oxygenated binding sites for Cd and Cu in the case of CB. The content of lignin was the major factor resulting in the variation of oxidation degree in two biochars. These results suggest that it is important to select the right kind of biochar to stably decrease the bio-availability of potential toxic elements (Cd and Cu) in contaminated soils.

Fe/Fe2O3 nanoparticles anchored on Fe-N-doped carbon nanosheets as bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries

Electrocatalysts with high catalytic activity and stability play a key role in promising renewable energy technologies, such as fuel cells and metal-air batteries. Here, we report the synthesis of Fe/Fe2O3 nanoparticles anchored on Fe-N-doped carbon nanosheets (Fe/Fe2O3@Fe-N-C) using shrimp shell-derived N-doped carbon nanodots as carbon and nitrogen sources in the presence of FeCl3 by a simple pyrolysis approach. Fe/Fe2O3@Fe-N-C obtained at a pyrolysis temperature of 1,000 °C (Fe/Fe2O3@Fe-N-C-1000) possessed a mesoporous structure and high surface area of 747.3 m2·g−1. As an electrocatalyst, Fe/Fe2O3@Fe-N-C-1000 exhibited bifunctional electrocatalytic activities toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline media, comparable to that of commercial Pt/C for ORR and RuO2 for OER, respectively. The Zn-air battery test demonstrated that Fe/Fe2O3@Fe-N-C-1000 had a superior rechargeable performance and cycling stability as an air cathode material with an open circuit voltage of 1.47 V (vs. Ag/AgCl) and a power density of 193 mW·cm−2 at a current density of 220 mA·cm−2. These performances were better than other commercial catalysts with an open circuit voltage of 1.36 V and a power density of 173 mW·cm−2 at a current density of 220 mA·cm−2 (a mixture of commercial Pt/C and RuO2 with a mass ratio of 1:1 was used for the rechargeable Zn-air battery measurements). This work will be helpful to design and develop low-cost and abundant bifunctional oxygen electrocatalysts for future metal-air batteries.

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.

One-step fabrication of high performance micro/nanostructured Fe3S4–C magnetic adsorbent with easy recovery and regeneration properties

A magnetic Fe3S4–C composite adsorbent with micro/nanostructure was fabricated by a facile one-step solvothermal method using glucose as carbon source. The prepared products are of a tremella-like micro/nanostructure with magnetic properties and a surface area of 12 m2 g−1. The carbonaceous materials disperse uniformly on the surface of the tremella-like composites. Further experiments have revealed that glucose plays an important role in formation of such structured composites. It not only determines the morphology but also supplies functional groups which act as active sites in the adsorption process. More importantly, the composites can remove contaminants in water with high efficiency and be separated quickly at a low external magnetic field, and can be regenerated after washing with ethanol, showing good recycling performance. This work not only gives a deep insight in to the formation of novel micro/nanostructured magnetic composites but also supplies a new efficient adsorbent for water treatment.

A fluorescent chitosan hydrogel detection platform for the sensitive and selective determination of trace mercury(II) in water

In this work, a three-dimensional (3D) chitosan hydrogel with superior fluorescence properties was successfully fabricated by modifying chitosan fibers with glutaric dialdehyde (GD) via a simple cross-linking approach. The resulting three-dimensional fluorescent chitosan hydrogel (3D-FCH) with hydrophilic properties exhibited a strong blue fluorescence emission at an excitation wavelength of 337 nm. The fluorescence mechanism of the as-synthesized 3D-FCH was investigated and proposed in detail using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) techniques. As a solid-phase fluorescent probe, the 3D-FCH was used to selectively and sensitively determine mercury(II) (Hg2+) ions in aqueous media. The results demonstrated that a prominent fluorescence quenching at 401 nm was observed in the presence of Hg2+ with a linear response range of 5.0–50 nM and an estimated limit of detection of 0.9 nM. The fluorescence quenching mechanism could be ascribed to the strong complexation between Hg2+ and the GD fluorophore with a conjugate structure. Moreover, the porous structure of the chitosan hydrogel and the high adsorption capacity of the chitosan fibers in the hydrogel could be very favorable for the rapid fluorescence determination of Hg2+. This work may pave a new way to develop low-cost fluorescent chitosan hydrogels as solid-phase fluorescence determination platforms to replace traditional liquid-phase fluorophores for application in the fluorescence detection of heavy metal ions.

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.

Adsorption of Hg2+ by thiol functionalized hollow mesoporous silica microspheres with magnetic cores

Novel hollow mesoporous silica spheres with magnetic cores (HMSMCs) were successfully synthesized by using hybrid magnetic carbon (Fe3O4/C) spheres as templates. The microspheres were further functionalized with (3-mercaptopropyl)trimethoxysilane (MPTS) to produce thiol functionalized HMSMCs (SH-HMSMCs), and their ability to absorb traces of toxic Hg2+ was evaluated. The characterization results revealed that the hollow microspheres were 250–300 nm in diameter. The thickness of the shell was about 50 nm, in which contained an inner core of Fe3O4 crystallites with a size of about 10 nm. It was also found that the saturation magnetization of the sample was 62.5 emu g−1 and the BET surface area was 421 m2 g−1. These magnetic hybrid silica microspheres with thiol functional groups were found to have a high affinity to Hg2+, and were able to reduce even a low concentration of Hg2+ (<1 mg L−1) down to about 0.53 μg L−1, which was less than the Hg2+ content in the drinking water standard. The super strong affinity towards Hg2+ was attributed to the synergistic effect of the thiol groups and the unique structure of the microspheres. Moreover, the microspheres as adsorbents could be easily separated by an external magnetic field, and the adsorbed Hg2+ on the adsorbents could be removed by using hydrochloric acid, thus the adsorbents are readily reusable.

3D Fe3O4@Au@Ag nanoflowers assembled magnetoplasmonic chains for in situ SERS monitoring of plasmon-assisted catalytic reactions

One-dimensional (1D) assembled magnetoplasmonic nanochains (MPNCs) were fabricated using Fe3O4@Au core–shell nanoparticles (NPs) via a magnetic field induced assembly. With the help of a silver growth solution, the 3D Fe3O4@Au@Ag nanoflowers assembled magnetoplasmonic chains (Fe3O4@Au@Ag NAMPCs) were prepared via an in situ reduction method. A heterogeneous epitaxial growth mechanism was proposed to explain the growth process of the Fe3O4@Au@Ag NAMPCs. The Fe3O4@Au@Ag NAMPCs possessed large numbers of hot spots within the highly ordered structure and were used as a SERS substrate to enhance the sensitivity, uniformity and reproducibility of Raman signals. Subsequently, the Fe3O4@Au@Ag NAMPCs, integrating a heterogeneous catalysis and in situ SERS detection, was assessed to monitor the catalytic reduction of 4-nitrothiophenol (4-NTP) to p,p′-dimercaptoazobenzene (DMAB).