Yuhao Xiong

Synthesis of magnetic porous γ-Fe2O3/C@HKUST-1 composites for efficient removal of dyes and heavy metal ions from aqueous solution

A novel and inexpensive approach was adopted to develop magnetic porous γ-Fe2O3/C@HKUST-1 composites for the adsorption of dyes and heavy metal ions from aqueous solution. The γ-Fe2O3/C with unique functional groups present such as –OH and –NH2 was used as the support to directly grow HKUST-1 by a stepwise liquid-phase epitaxy process. The crystallographic, morphology, and magnetic properties as well as porosity of the as-synthesized γ-Fe2O3/C @HKUST-1 composites were carefully studied by XRD, SEM, TEM, XPS, TGA, and BET. The results indicated that the BET surface area, micropore volume, and saturation magnetization of the γ-Fe2O3/C @HKUST-1 are 993.4 m2 g−1, 0.69 cm3 g−1, and 12.6 emu g−1, respectively. In addition, a uniform distribution of ultrafine γ-Fe2O3 nanoparticles with an average diameter of 2–3 nm was observed in the γ-Fe2O3/C@HKUST-1 composites. Our results showed that methylene blue (MB) and Cr(VI) (used as a model for typical dye pollutants and heavy metal ions) are effectively removed from aqueous solutions by γ-Fe2O3/C@HKUST-1. The maximum adsorption capacities were 370.2 and 101.4 mg g−1 of adsorbent for MB and Cr(VI), respectively. Moreover, a removal efficiency of about 90% was retained after five cycles of consecutive adsorption–desorption. The adsorption kinetics data were well described by a pseudo-second-order model (R2 > 0.99), and equilibrium data were well fitted to the Langmuir isotherm model (R2 > 0.99). Finally, our results suggested that the γ-Fe2O3/C@HKUST-1 composites have a great potential to be employed for treatment of wastewater containing MB and Cr(VI).

From metal–organic frameworks to magnetic nanostructured porous carbon composites: towards highly efficient dye removal and degradation

A magnetic nanostructured porous carbon material (γ-Fe2O3/C) was easily synthesized using a microwave-enhanced high-temperature ionothermal method with an iron terephthalate metal–organic framework-MIL-53(Fe), as a template. The structure, morphology, magnetic properties, and porosity of γ-Fe2O3/C were characterized by powder X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, vibrating sample magnetometry, and Brunauer–Emmett–Teller surface area analysis. The obtained porous carbon materials (γ-Fe2O3/C), possessed a high specific surface area (397.2 m2 g−1) and pore volume (0.495 cm2 g−1). The adsorption properties were tested by removal of malachite green (MG) from an aqueous solution. After reaching adsorption equilibrium, the maximum adsorption capacity was 499 mg g−1 at 30 °C, and reached 863 mg g−1 at 60 °C. The excellent magnetism (20.10 emu g−1) provided an ideal magnetic-separation performance. Analysis of the sorption kinetics and isotherms showed that these sorption processes were better fitted to the pseudo-second-order and Langmuir equations than pseudo-first-order and Freundlich equations. Various thermodynamic parameters, such as ΔGθ, ΔSθ, and ΔHθ, were also calculated, and indicated that the present system was spontaneous and endothermic. It was further demonstrated that γ-Fe2O3 showed powerful photocatalytic activity for the degradation of MG under sunlight in the presence of H2O2.

Colorimetric detection of uric acid in human urine and serum based on peroxidase mimetic activity of MIL-53(Fe)

The porous metal–organic framework MIL-53(Fe) was prepared using a simple solvothermal method, using FeCl3·6H2O and 1,4-benzenedicarboxylic acid as the precursor, and characterized by X-ray diffractometry, Fourier transform infrared spectroscopy and scanning electron microscopy. The MIL-53(Fe) was demonstrated to possess an intrinsic peroxidase-like activity, and it could catalyze the oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine into a blue colored product in the presence of H2O2. Based on this phenomenon, MIL-53(Fe) was developed as a colorimetric sensor for the detection of uric acid (UA) in human urine and serum. This provided a simple and effective method for UA detection using uricase and MIL-53(Fe), with a linear range from 4.5 to 60 μM, and a detection limit of 1.3 μM (S/N = 3). Moreover, the proposed method can be successfully applied to the determination of UA in human urine and serum samples with recoveries and relative standard deviations between 1.2–4.8% and 89.50–101.44%, respectively.

Prussian blue nanoparticles encapsulated inside a metal–organic framework via in situ growth as promising peroxidase mimetics for enzyme inhibitor screening

Artificial enzyme mimics are of current research interest owing to their remarkable advantages over natural enzymes. Herein, as a novel peroxidase mimic material, MIL-101(Cr)@PB was fabricated by encapsulating Prussian blue (PB) nanoparticles into the host matrix of MIL-101(Cr) via a facile and mild in situ growth synthetic strategy. The crystallographic characteristics, morphology, and porosity of the as-synthesized MIL-101(Cr)@PB composites were carefully studied using XRD, SEM, TEM, TGA, and BET. The results show that the synthesized MIL-101(Cr)@PB possesses a reproducible and impressive intrinsic peroxidase-like activity even under extreme conditions. Exploiting this, a colorimetric platform for screening xanthine oxidase inhibitors was constructed. We hope that this work will elucidate the applications of metal-organic frameworks as carriers for enzyme mimics and enable a wider application in drug screening.

Sphere-like CoS with nanostructures as peroxidase mimics for colorimetric determination of H2O2 and mercury ions

CoS, which was prepared using a facile solvothermal method, and characterized using various analytical techniques, was demonstrated for the first time to exhibit intrinsic peroxidase-like activity. CoS catalyzed the oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine in the presence of H2O2 rendering the reaction solution blue, which is the principle used for H2O2 sensing. The mechanism of the CoS catalysis was also investigated. Under optimal conditions, the linearity of H2O2 detection ranged from 0.05 to 0.8 mM (R2 = 0.9965). More importantly, using the reducibility of glutathione and the strong affinity to thiol compounds exhibited by mercury ions (Hg2+), a novel “off–on” colorimetric sensor for Hg2+ determination was designed using CoS as a peroxidase mimics. The analytical platform for Hg2+ determination was developed, ranging from 0.25 to 3 μM (R2 = 0.9965). The limit of detection was 0.1 μM. CoS exhibited several advantageous features including good chemical stability, ease of preparation, simple purification, and excellent reproducibility.

Fabrication of copper sulfide using a Cu-based metal organic framework for the colorimetric determination and the efficient removal of Hg2+ in aqueous solutions

CuS (PCuS) particles were facilely synthesized by the wet-treatment of a Cu-based metal organic framework (HKUST-1). PCuS possesses an impressive intrinsic peroxidase-like activity. As a result of this affinity, PCuS readily binds to 3,3′,5′,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2) (Km values of 29 μM and 150 μM toward TMB and H2O2, respectively). Interestingly, when Hg2+ was added, HgS produced in conjunction with the specific binding sites on the surface of PCuS remarkably inhibited the peroxidase-like activity of PCuS. Based on this unique property, a sensing platform for the colorimetric detection of Hg2+ was established. In addition, high surface area and strong affinity for Hg2+ make PCuS an excellent adsorbent for Hg2+ (2105 mg g−1). These results indicate that PCuS could be a useful material for the facile detection and the efficient removal of Hg2+ using HKUST-1 as a precursor in environmental abatement applications.

Colorimetric detection of mercury ions using MnO2 nanorods as enzyme mimics

In this study, a simple and novel “off–on” colorimetric sensor for the detection of mercury ions (Hg2+) in aqueous solution was developed. The homogeneous MnO2 nanorods as oxidase-like mimetics could catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) into a blue colored cation radical without the requirement for additional oxidizing agents. Glutathione (GSH) could successfully hinder the cation radical production and restore them to colourless TMB molecules. Hg2+ had a strong affinity to thiolated compounds. If GSH and Hg2+ were pre-incubated, the solution would be recovered to blue colored solution in the presence of MnO2 nanorods. Based on this phenomenon, a simple and rapid colorimetric path for the sensing of Hg2+ was developed. A good linear relationship could be obtained from 0.1 to 8.0 µM. The limit of detection was estimated to be 0.08 µM. The proposed method was successfully applied for the determination of Hg2+ in real water samples with recoveries ranging from 82% to 114%. And this method was allowed for the monitoring of Hg2+ directly by the naked eye.

Preparation of magnetic core–shell nanoflower Fe3O4@MnO2 as reusable oxidase mimetics for colorimetric detection of phenol

In this paper, magnetic core–shell nanoflowers Fe3O4@MnO2 were fabricated via a solvothermal method. We demonstrated that the as-synthesized magnetic nanoflowers Fe3O4@MnO2 possess intrinsic oxidase-like activity in a wide pH range and can catalytically oxidize 4-aminoantipyrine (4-AAP) and phenol substrates to form pink color products without the requirement for additional oxidizing agents. On the basis of this phenomenon, a simple colorimetric method for the determination of phenol was developed. A wide linear detection range can be obtained from 1.0 μM to 120 μM (R2 = 0.9962) with a detection limit of 0.15 μM. And the method was applied to determine phenol in wastewater with good recoveries ranging from 96.0 to 101.5%. Furthermore, benefitting from chemical stability and easy recovery (by simple magnetic separation) of Fe3O4@MnO2, the oxidase mimetics have excellent reusability and reproducibility in cycle analysis.

Facile synthesis of low-cost biomass-based γ-Fe2O3/C for efficient adsorption and catalytic degradation of methylene blue in aqueous solution

In this study, a novel and low-cost method was developed for synthesizing magnetic porous γ-Fe2O3/C as an adsorbent and catalyst for removal of methylene blue (MB) from aqueous solution. Using FeCl3·6H2O and bagasse as the precursor, the biomass-based material was synthesized rapidly using a microwave heating process. Fe ions were introduced to achieve both adsorption and catalytic degradation by the Fenton reaction. Characterization by BET, XRD, SEM, and TEM indicated that the prepared γ-Fe2O3/C material exhibited homogeneous mesoporosity with a BET surface area, mesoporous volume, and saturation magnetization of 764.116 m2 g−1, 0.54 cm3 g−1, and 17.1 emu g−1, respectively. The material exhibited excellent adsorption and catalytic degradation abilities for removal of MB from aqueous solution (up to 352.96 mg g−1), with complete degradation of MB within 30 min. Moreover, γ-Fe2O3/C had good stability over 5 cycles. Therefore, this biomass-based γ-Fe2O3/C material can be used as a highly effective and low-cost adsorbent and catalyst and has great potential application in clean-up processes for environmental pollutants.

Facile one-pot preparation of chiral monoliths with a well-defined framework based on the thiol–ene click reaction for capillary liquid chromatography

A novel chiral cyclodextrin (CD) monolith was easily prepared via a one-pot process based on the thiol–ene click reaction of allyl-β-CD with pentaerythritol tetra-(3-mercaptopropionate) in a fused-silica capillary. The effects of both the composition of prepolymerization solution and reaction temperature on the morphology, permeability, and selectivity of the β-CD chiral monolith were investigated in detail. The conditions were optimized to fabricate a homogeneous and permeable chiral monolith. In this study, the β-CD monolith was used as the stationary phase of capillary liquid chromatography for the chiral separation of several pharmaceutical enantiomers including flavanone, flurbiprofen, naproxen, synephrine, isoprenaline sulfate, ketoprofen, and atropine sulfate monohydrate. Compared to the previously reported two-step method, this one-pot method for the preparation of a β-CD chiral monolith is simple and time-saving. Moreover, good resolutions were obtained for chiral isomers in a shorter analysis time compared to that reported in the literatures. These results indicate that the thiol–ene click chemistry provides a simple and robust method for the preparation of a chiral β-CD monolith.