Saihua Wang

Spatial confinement of a Co3O4 catalyst in hollow metal-organic frameworks as a nanoreactor for improved degradation of organic pollutants.

We here first proposed a yolk-shell Co3O4@metal-organic frameworks (MOFs) nanoreactor via a facile method to accommodate sulfate radical-based advanced oxidation processes (SR-AOPs) into its interior cavity. The mesoporous and adsorptive MOFs shells allow the rapid diffusion of reactant molecules to the encapsulated Co3O4 active sites, and the confined high instantaneous concentration of reactants in the local void space is anticipated to facilitate the SR-AOPs. As a proof of concept, the nanoreactor was fully characterized and applied for catalytic degradation of 4-chlorophenol (4-CP) in the presence of peroxymonosulfate (PMS). The enhancement of SR-AOPs in the nanoreactor is demonstrated by the result that degradation efficiency of 4-CP reached almost 100% within 60 min by using the yolk-shell Co3O4@MOFs catalysts as compared to only 59.6% under the same conditions for bare Co3O4 NPs. Furthermore, the applicability of this nanoreactor used in SR-AOPs was systematically investigated in terms of effect of reaction parameters and identification of intermediates and primary radical as well as mineralization of the reaction and stability of the composite. The findings of this study elucidated a new opportunity for improved environmental remediation.

Preparation of polydopamine coated Fe3O4 nanoparticles and their application for enrichment of polycyclic aromatic hydrocarbons from environmental water samples

Core/shell structured magnetic Fe3O4/polydopamine (Fe3O4/PDA) nanoparticles have been successfully synthesized and developed as a magnetic solid-phase extraction (SPE) adsorbent in dispersion mode for the determination of trace polycyclic aromatic hydrocarbons (PAHs) in environmental samples. The Fe3O4/PDA synthetic procedure is simple and involves no organic solvents. Only 20mg of Fe3O4/PDA adsorbents are required to extract PAHs from 500mL water samples. The adsorption attains equilibrium rapidly and analysts are eluted with acetonitrile readily. The extraction efficiency is not influenced by salt concentrations up to 300mM and pH values over the range 4-11. Under optimized conditions, the detection limits of PAHs are in the range of 0.5-1.9ngL(-1). The accuracy of the method is evaluated by the recoveries of PAHs from environmental samples. Good recoveries (76.4-107%) with low relative standard deviations from 1.0% to 9.7% are achieved. Comparison study shows that the recoveries of target PAHs are low when they are extracted using traditional SPE method even with the addition of methanol or tetrabutylammonium bromide surfactants in water samples, suggesting great application potential of magnetic SPE method to preconcentrate highly hydrophobic contaminants (such as PAHs) from large volume of water samples. This new SPE method provides several advantages, such as simplicity, low environmental impact, high extraction efficiency, high breakthrough volumes, convenient extraction procedure, and short analysis time.

Assembly of a Nanoreactor System with Confined Magnetite Core and Shell for Enhanced Fenton‐Like Catalysis

Conventional solid catalysts for heterogeneous Fenton-like reactions in bulk solution usually suffer from aggregation and vulnerability, which greatly lower the catalytic efficiency and hamper their practical application. Herein, we demonstrate a promising yolk-shell nanostructure with both the core and the shell composed of magnetite (designated as yolk-like Fe3O4@Fe3O4/C) as a nanoreactor capable of accommodating the Fenton-like reaction into its void space. Benefiting from the mesoporous shell and perfect interior cavity of this composite, reactants can access and be abundantly confined within the microenvironment where Fe3O4 sites are dispersed on the entire cavity surfaces, thus leading to a higher catalytic efficiency compared with the conventional solid catalysts in bulk solution. The chosen model reaction of chlorophenols degradation in the presence of the as-prepared materials as well as hydrogen peroxide (H2O2) confirms this assumption. Under the optimal reaction conditions, more than 97 % 4-chlorophenol (4-CP) can be degraded in the Fe3O4@Fe3O4/C nanoreactor, whereas only 28 % can be achieved by using bare Fe3O4 particles within 60 min. Furthermore, owing to the existence of the outermost carbon layer and high-magnetization properties, the nanoreactor can be re-used for several runs. The synthesized nanoreactor displays superior catalytic activity toward the Fenton-like reaction compared with the bare solid catalysts, and thereby holds significant potential for practical application in environmental remediation.

A double-shelled yolk-like structure as an ideal magnetic support of tiny gold nanoparticles for nitrophenol reduction

A facile method is proposed to fabricate yolk–shell microspheres consisting of a movable silica core, a multifunctional double-layered shell, and plenty of tiny gold nanoparticles (Au NPs, ∼2 nm) confined within the interior cavity and the mesoporous shell. The presented strategy involves the one-step coating of a Fe3O4/carbon double-layered shell, the partial etching of the silica cores and the in situ immobilization of Au NPs. The inner Fe3O4 layer of the double-layered shell endows the composites with superparamagnetism and thereby simplifies the introduction procedure of a magnetic component. The outer carbon layer not only protects the Fe3O4 layer from outside harsh conditions but also provides additional adsorption sites for Au NPs besides the interior space. The large number of catalytic active sites together with the advantages of the yolk–shell architecture make the nanocomposite a perfect catalyst for the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4 (TOF value is 17.4 min−1). Moreover, the synthesized catalyst can be easily recovered and reused for at least nine cycles due to its magnetically separable feature and good stability. These confirm that the as-prepared yolk-like nanocomposites are promising candidates for catalytic application.

Sensitive colorimetric visualization of perfluorinated compounds using poly(ethylene glycol) and perfluorinated thiols modified gold nanoparticles.

In this work, we have developed a novel sensing strategy employing mixed poly(ethylene glycol)-terminated (PEG-thiols) and perfluoroalkyl-terminated (F-thiols) alkanethiols modified gold nanoparticles (Au@PEG-F NPs) as a probe to detect perfluorinated compounds (PFCs) from water samples. PEG-thiols with high density and long carbon chains make the Au NPs probe well-dispersed in solution and stable even in high concentration of salt solution; F-thiols provide specific fluorous-fluorous interactions to PFCs, which results in adsorption of PFCs on Au@PEG-F NPs. The adsorbed PFCs cause the aggregation of Au@PEG-F NPs probes and thus induce the insolubility of probes and precipitation directly from reaction solution due to the superhydrophobicity of perfluorocarbon monolayers, leading to color and absorbance response of the assay to PFCs. The preparation of the Au@PEG-F NPs probe is very simple, and the colorimetric assay based on this mechanism for the detection of PFCs is selective and convenient. Combined with UV-vis spectrophotometry, the assay demonstrates good sensitivities to PFCs with wide linear range. In the designed concentration range, the response of the colorimetric assay to long-chain PFCs (perfluoroalkyl chain ≥7) is discerned even as the concentration of these PFCs is as low as 10 μg L(-1). This low-cost and sensitive assay shows great potential to measure total PFCs in water samples. To the best of our knowledge, this is the first application of the specific fluorous-fluorous interactions and Au NPs based probes for colorimetric recognition for PFCs.

Facile Synthesis of Magnetic Covalent Organic Framework with Three-Dimensional Bouquet-Like Structure for Enhanced Extraction of Organic Targets

A facile strategy for the fabrication of novel bouquet-shaped magnetic porous nanocomposite via grafting a covalent organic framework (COF, TpPa-1) onto the surface-modified Fe3O4 nanoparticles (Fe3O4 NPs) was reported. The magnetic TpPa-1 (a COF synthesized from 1,3,5-triformylphloroglucinol (Tp) and p-phenylenediamine (Pa-1)) contains clusters of core-shell magnetic nanoparticles and interconnected porous TpPa-1 nanofibers. Thus, it possesses larger specific surface area, higher porosity, and supermagnetism, making it an ideal sorbent for enrichment of trace analytes. Its performance was evaluated by the magnetic solid-phase extraction (MSPE) of trace polycyclic aromatic hydrocarbons (PAHs) from environmental samples prior to high-performance liquid chromatographic analysis. The results indicated that the magnetic TpPa-1 possessed superior enrichment capacity of such organic compounds.

Fabrication of magnetic mesoporous carbon and its application for adsorptive removal of 2,4,6-trichlorophenol (TCP) from aqueous solution

Magnetic mesoporous (MMP) carbon has been successfully synthesized by using Fe3O4 NPs, CaCO3 and dopamine as cores, template, and carbon precursor, respectively. The synthetic procedure of MMP carbon is simple, low-cost and involves no organic solvents. The generated MMP carbon has a large surface area and strong magnetism. MMP carbon was used to remove 2,4,6-trichlorophenol (TCP) from water samples. The results show that adsorption equilibrium was observed within 10 h, and the kinetics can be described by a pseudo-second-order kinetic model. TCP adsorption is not affected by ionic strength and increases with temperature and initial concentration. When the TCP initial concentrations are 10 and 100 mg L−1, the adsorption capacities are 117 and 610 mg g−1, respectively, which are much higher than those achieved from other adsorbents. These results indicate that most of the adsorption sites on the MMP carbon are available for TCP due to its relatively large pore size.

One-pot synthesis of C-18-functionalized core-shell magnetic mesoporous silica composite as efficient sorbent for organic dye

In this work, a facile one-pot strategy was proposed for the synthesis of C18-functionalized core-shell magnetic mesoporous silica composite (Fe3O4/mSiO2-C18). The Fe3O4/mSiO2-C18 composite, with an average size of 80 nm and a functionalized mesoporous silica shell of about 30 nm in thickness, has excellent adsorption ability toward methylene blue dye (MB) due to the large surface area (303 m(2) g(-1)) and the abundant hydrophobic C18 groups. The adsorption equilibrium was achieved within 20 min and the adsorption behavior of MB on Fe3O4/mSiO2-C18 composite fitted the pseudo-second-order kinetic model well (k2=1.29×10(-2) g mg(-1) min(-1), q(e)=144.72 mg g(-1), h(o)=270.27 mg g(-1) min(-1) under 25 °C and an initial MB concentration of 10 mg L(-1)). Langmuir and Freundlich isothermal adsorption models can both be used to describe the adsorption process and the maximum Langmuir adsorption capacity of MB on Fe3O4/mSiO2-C18 at 25 °C and pH 7.5 is 363.64 mg g(-1). Thermodynamic parameters show that the adsorption reaction is exothermic and spontaneous (ΔH(0)=-63.49 kJ mol(-1), ΔG(0)=-7.80 kJ mol(-1)). Ionic strength and pH affected the adsorption slightly. In addition, the MB adsorbed sorbent can be readily separated from water solution by an external magnet because of the high magnetic saturation value (22.62 emu g(-1)). After being regenerated by treatment with acidic methanol, the sorbent could be reused for at least 5 cycles with a little decrease in adsorption capacity.

One-step fabrication of high quantum yield sulfur- and nitrogen-doped carbon dots for sensitive and selective detection of Cr(VI)

In this work, we have developed a green, simple, and low-cost hydrothermal method using wool and pig hair as the precursor to fabricate sulfur- and nitrogen-doped carbon dots (CDs). The precursors are natural and nontoxic raw materials, and the one-step strategy requires no organic solvents. The as-prepared carbon dots exhibit good water dispersibility, strong fluorescence emission with a relatively high quantum yield of 25.6% (contributed by the doped N and S elements), excellent pH stabilities and high ionic strength tolerance. More importantly, the fluorescence intensity of the CDs could be significantly and selectively quenched in the presence of Cr(VI) due to the oxidation–reduction reaction between Cr(VI) and the oxygen-containing groups and S-related species on the surface of CDs. Accordingly, the CDs are employed as a fluorescent probe for the detection of Cr(VI) ions in water. This CDs sensor exhibits high sensitivity to Cr(VI) with a limit of detection of 16.8 nM in a wide range of 50 nM to 100 μM. Furthermore, the sensor is successfully applied in the detection of Cr(VI) in real water samples.

Stable hierarchical microspheres of 1D Fe–gallic acid MOFs for fast and efficient Cr(VI) elimination by a combination of reduction, metal substitution and coprecipitation

One-dimensional Fe–gallic acid MOFs were assembled into stable hierarchical microspheres in DMF solvent taking advantage of DMF decomposition by heat. The rapid electron transfer ability and high accessibility of the multiple reaction sites on Fe–gallic acid microspheres ensure fast and complete elimination of Cr(VI) from water samples.