A mild and facile method for the construction of robust organic–inorganic hybrid magnetic microcapsules was developed by a hard-template mediated method combined with polydopamine (PDA) and Fe3O4 nanoparticles onto a CaCO3 microparticle template. More specifically, negatively charged Fe3O4 nanoparticles were adsorbed on the surface or into the lumen of porous CaCO3 microparticles through electrostatic interaction and physical absorption. Then, the magnetic sacrificial templates were coated with PDA through the self-polymerization of dopamine to obtain the magnetic PDA–CaCO3 microparticles, which was followed by template removal using EDTA to construct organic–inorganic hybrid magnetic microcapsules. Characterization confirmed that the microcapsules possess a robust hollow structure such that the enzyme inside exists in a free state. The Fe3O4 nanoparticles acted as critical factors in the microcapsules for both recyclable component and tough scaffolds to sustain the microcapsules away from collapsing and folding. Combing the merits of the organic layer and the inorganic component, the microcapsules were applied for the encapsulation of Candida Rugosa Lipase (CRL). The encapsulated CRL was demonstrated to have several advantages, including increased encapsulation efficiency, enzyme activity and long-term storage stability. Hopefully, the as-prepared microbioreactor may provide a facile and generic approach for other biochemical applications.

Rattle-type magnetic carbon nanospheres were obtained easily by annealing core–shell–shell hybrid nanospheres. The nanospheres were fabricated by combining, in a single step, a tetraethyl orthosilicate sol–gel process and the condensation polymerization of resorcinol and formaldehyde in the presence of ammonia. Subsequent annealing and silicon dioxide removal in sodium hydroxide solution resulted in materials with a high specific surface area (250.3 m2 g−1) that could be separated easily from aqueous media using an external magnetic field. Methylene blue was selected as a typical organic pollutant to test adsorption and Fenton catalytic degradation performance. The results demonstrate the potential applicability of the rattle-type magnetic carbon nanospheres. The nanospheres could remove methylene blue rapidly with an adsorption capacity of 45.15 mg g−1. They can also effectively catalyze the degradation of methylene blue because of their special structure.

High-specific-surface-area copper doped magnetic porous carbon (CuFe2O4/Cu@C) was fabricated by annealing iron, copper and 1,3,5-benzenetricarboxylic ([Cu/Fe]-BTC) metal–organic coordination polymers, which were prepared via a one-pot solvothermal method. The novel CuFe2O4/Cu@C catalyst consists of Cu (3.80%), CuFe2O4 (64.84%), and C (31.36%). Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, elemental analysis, inductively coupled plasma, Brunauer–Emmett–Teller surface area measurement, and vibrating sample magnetometer analysis were used to characterize the materials. The as-prepared materials were employed as a heterogeneous Fenton’s reagent with the addition of H2O2 for degradation of methylene blue (MB). The results showed that the materials effectively catalyzed H2O2 to generate hydroxyl radicals (˙OH). And due to their magnetism, the materials can be easily separated from wastewater to achieve repeatability. It also turned out that CuFe2O4/Cu@C had a higher catalytic activity than Fe3O4@C, which proved the importance of copper doped into the catalyst. This work indicated that porous carbon composites provide good support for the development of a highly efficient heterogeneous Fenton catalyst, which is useful for environmental pollution cleanup.

Hierarchical magnetic porous carbon fibers (MBFs) were fabricated by annealing Fe(BTC)-coated bamboo fibers, which were produced using a new synthesis route for growing Fe(BTC) on bamboo fiber materials, in a nitrogen atmosphere. The materials were characterized using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, Brunauer–Emmett–Teller surface area measurement, and vibrating sample magnetometry. The obtained MBF composites possess both high surface areas and magnetic characteristics. Their adsorption properties were preliminarily tested by the adsorptive removal of methylene blue from aqueous solution. Results demonstrated that the obtained hybrid materials possess high adsorption capacity and can be easily recycled from liquid media by using an external magnetic field. MBF adsorption reached equilibrium within approximately 1 min and the adsorption capacity rapidly reached 143 mg g−1. Most importantly, MBF can be reused after washing with ethanol. After six reuses, the removal efficiency could still reach 80%. Moreover, the low-cost raw material used (i.e., bamboo) is abundant and renewable. This study indicated that the as-prepared MBF composites show great potential for use in a wide range of applications.

Separation and recycling of noble metal nanocatalysts after catalytic reactions are significant challenges to reduce catalyst cost and avoid waste generation in industrial applications. In this study, Pd-loaded magnetic porous carbon nanospheres (Fe3O4@MC-Pd) were prepared by annealing Fe3O4@MIL-100/PdCl2, which was fabricated through a facile one-pot solvothermal method, at 450 °C in a nitrogen atmosphere. The novel Fe3O4@MC-Pd catalyst consists of a superparamagnetic Fe3O4 core and a chemically inert porous carbon layer, which can protect the Fe3O4 core from extreme external environments and prevent the loss of Pd NPs. The resultant composite material showed excellent catalytic performance in reducing methylene blue with sodium borohydride as a reducing agent and superparamagnetic behavior that enabled the magnetic separation and convenient recovery of the nanocatalysts from the reaction mixture. Moreover, the composite material also showed good thermal and acid stability, fast regeneration ability, and high cyclic stability (>10 cycles without loss of catalytic efficiency). The result shows the nanocatalysts could overcome the drawbacks of MOF catalysts (chemical unstability). This study indicated that the as-prepared Fe3O4@MC-Pd composite material shows great potential for using in a wide range of applications.

High-specific-surface-area magnetic porous carbon microspheres (MPCMSs) were fabricated by annealing Fe2+-treated porous polystyrene (PS) microspheres, which were prepared using a two-step seed emulsion polymerization process. The resulting porous microspheres were then sulfonated, and Fe2+ was loaded by ion exchange, followed by annealing at 250 °C for 1 h under an ambient atmosphere to obtain the PS-250 composite. The MPCMS-500 and MPCMS-800 composites were obtained by annealing PS-250 at 500 and 800 °C for 1 h, respectively. The iron oxide in MPCMS-500 mainly existed in the form of Fe3O4, which was concluded by characterization. The MPCMS-500 carbon microspheres were used as catalysts in heterogeneous Fenton reactions to remove methylene blue (MB) from wastewater with the help of H2O2 and NH2OH. The results indicated that this catalytic system has a good performance in terms of removal of MB; it could remove 40 mg L–1 of MB within 40 min. After the reaction, the catalyst was conveniently separated from the media within several seconds using an external magnetic field, and the catalytic activity was still viable even after 10 removal cycles. The good catalytic performance of the composites could be attributed to synergy between the functions of the porous carbon support and the Fe3O4 nanoparticles embedded in the carrier. This work indicates that porous carbon spheres provide good support for the development of a highly efficient heterogeneous Fenton catalyst useful for environmental pollution cleanup.Keywords: carbon microspheres; degradation; Fenton reaction; heterogeneous; magnetic; methylene blue; porous;

A series of uniformed mono-disperse magnetic nanoligands (MNLs) (CoFe2O4–NH2 (MNL A), Fe3O4@Si(CH2)3NH2 (MNL B), Fe3O4@Si(CH2)3NHC(O) (CH2)2PEI (MNL C) and Fe3O4@Si(CH2)3NHC(O)PEI (MNL D)) were obtained by loading two ligands, an aminosilane coupling agent and PEI-600, onto magnetic nanoparticles prepared using a solvothermal method. The catalytic applications of the synthesized MNLs were explored for the cross-coupling reaction of heterocyclic thiols with aromatic iodides. The reactions were carried out in the presence of CuI (5 mol%), MNL (10 mol% N) and K2CO3 (1.3 eq.) in DMF at 120 °C. A variety of heterocyclic sulfides were afforded in good to excellent yields (up to 98%) when MNL B was used. The magnetic, crystal, organic matter structure and morphology of MNL B exhibited no obvious changes after five consecutive cycles. XPS characterization of MNL B revealed the combination of a small amount of Cu0 nanoparticles, but this had no significant effect on catalytic performance.

Tetrabromobisphenol A (TBBPA) is the most widely used brominated flame retardant around the world. In this study, we report that iron oxide decorated on a magnetic nanocomposite (Fe3O4/MWCNT) was used as a heterogeneous Fenton catalyst for the degradation of TBBPA in the presence of H2O2. Fe3O4/MWCNT was prepared by a simple solvothermal method, whereby an iron source (Fe(acac)3) and a reductant (n-octylamine) were allowed to react in n-octanol solvent. Monodisperse Fe3O4 nanoparticles of consistent shape were uniformly dispersed on the nanotubes. Samples were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller surface area measurement, and vibrating sample magnetometry. The samples effectively catalyzed the generation of hydroxyl radicals (·OH) from H2O2, which degraded and subsequently mineralized the TBBPA. The whole process took four hours at near neutral pH. A degradation pathway for the system was proposed following analysis of intermediate products by gas chromatography-mass spectrometry. The quantification of Fe2+ and Fe3+ distribution before and after the recycling test of the composite were explored by X-ray photoelectron spectroscopy, in order to explain the stability and recyclability of the composite. Analysis of the results indicated that the magnetic nanocomposite is a potentially useful and environmentally compatible heterogeneous Fenton's reagent with promising applications related to pollution control.

A one-step thermal decomposition strategy, in which a novel reductant participated, was developed to prepare superparamagnetic nearly cubic monodisperse Fe3O4 nanoparticles loaded on multiwall carbon nanotubes (MWCNTs/Fe3O4). Subsequently, the as-prepared MWCNTs/Fe3O4 nanocomposites were modified with 3-aminopropyltriethoxysilane (APTS) (MWCNTs/Fe3O4–NH2). The materials were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM) and the BET surface area method. The results indicated that superparamagnetic Fe3O4 nanoparticles were successfully loaded onto the surface of the MWCNTs, and APTS was also modified on the MWCNTs/Fe3O4 magnetic nanocomposites. The two as-prepared magnetic nanocomposites were used as adsorbents to remove tetrabromobisphenol A (TBBPA) and Pb(II) from wastewater. The adsorption kinetics and adsorption isotherms of TBBPA and Pb(II) on the two as-prepared adsorbents were studied at pH 7.0 and 5.3, respectively. It was revealed that MWCNTs/Fe3O4–NH2 performed better than the MWCNTs/Fe3O4 nanocomposites for the adsorption properties of TBBPA and Pb(II). After adsorption, both adsorbents could be conveniently separated from the media by an external magnetic field within several seconds, and regenerated in 0.1 M NaOH solution.

In the present study, Au-loaded magnetic metal organic frameworks (MOFs)/graphene multifunctional composite were prepared. The well-dispersed nanoparticles were stabilized with 2D reduced graphene oxide and MOFs, which acts as effective substitutes for more conventional polymer ligands that are used to stabilize nanoparticles in a sol-immobilization procedure. The result shows the multifunctional composite could overcome the drawbacks of MOFs catalysts (chemical instability). This study indicated that the as-prepared Au-loaded magnetic MOFs/graphene multifunctional composite has great potential for using in a wide range of applications.In the present study, Au-loaded magnetic metal organic frameworks (MOFs)/graphene multifunctional composite were prepared. The well dispersed nanoparticles were stabilized with 2D graphene oxide and MOFs, which act as effective substitutes for more conventional polymer ligands that are used to stabilize nanoparticles in a sol-immobilization procedure.Download high-res image (152KB)Download full-size image

A mild and facile method for the construction of robust organic–inorganic hybrid magnetic microcapsules was developed by a hard-template mediated method combined with polydopamine (PDA) and Fe3O4 nanoparticles onto a CaCO3 microparticle template. More specifically, negatively charged Fe3O4 nanoparticles were adsorbed on the surface or into the lumen of porous CaCO3 microparticles through electrostatic interaction and physical absorption. Then, the magnetic sacrificial templates were coated with PDA through the self-polymerization of dopamine to obtain the magnetic PDA–CaCO3 microparticles, which was followed by template removal using EDTA to construct organic–inorganic hybrid magnetic microcapsules. Characterization confirmed that the microcapsules possess a robust hollow structure such that the enzyme inside exists in a free state. The Fe3O4 nanoparticles acted as critical factors in the microcapsules for both recyclable component and tough scaffolds to sustain the microcapsules away from collapsing and folding. Combing the merits of the organic layer and the inorganic component, the microcapsules were applied for the encapsulation of Candida Rugosa Lipase (CRL). The encapsulated CRL was demonstrated to have several advantages, including increased encapsulation efficiency, enzyme activity and long-term storage stability. Hopefully, the as-prepared microbioreactor may provide a facile and generic approach for other biochemical applications.

A one-step thermal decomposition strategy, in which a novel reductant participated, was developed to prepare superparamagnetic nearly cubic monodisperse Fe3O4 nanoparticles loaded on multiwall carbon nanotubes (MWCNTs/Fe3O4). Subsequently, the as-prepared MWCNTs/Fe3O4 nanocomposites were modified with 3-aminopropyltriethoxysilane (APTS) (MWCNTs/Fe3O4–NH2). The materials were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM) and the BET surface area method. The results indicated that superparamagnetic Fe3O4 nanoparticles were successfully loaded onto the surface of the MWCNTs, and APTS was also modified on the MWCNTs/Fe3O4 magnetic nanocomposites. The two as-prepared magnetic nanocomposites were used as adsorbents to remove tetrabromobisphenol A (TBBPA) and Pb(II) from wastewater. The adsorption kinetics and adsorption isotherms of TBBPA and Pb(II) on the two as-prepared adsorbents were studied at pH 7.0 and 5.3, respectively. It was revealed that MWCNTs/Fe3O4–NH2 performed better than the MWCNTs/Fe3O4 nanocomposites for the adsorption properties of TBBPA and Pb(II). After adsorption, both adsorbents could be conveniently separated from the media by an external magnetic field within several seconds, and regenerated in 0.1 M NaOH solution.