Magnetic Recyclability Research Articles

Rational design of direct Z-scheme magnetic ZnIn2S4/ZnFe2O4 heterojunction toward enhanced photocatalytic wastewater remediation.

The rationally designed heterojunction photocatalysts with magnetic semiconductors and easy recyclability have received considerable attention due to their great advantages in practical application. In our work, a series of ZnIn2S4/ZnFe2O4 Z-scheme heterojunction photocatalysts with superior magnetic properties were synthesized by a gentle chemical bath method and utilized for the effective photodegradation and Cr(VI) reduction under irradiation. Systematic evaluation experiments revealed that the derived ZnIn2S4/ZnFe2O4 photocatalysts exhibited enhanced photocatalytic efficiency for RhB degradation and Cr(VI) reduction as compared with pristine ZnIn2S4 and ZnFe2O4, which was primarily due to the close contact interface and the formation of Z - scheme charge transfer mechanism between ZnFe2O4 rods and ZnIn2S4 nanosheets. Moreover, the as-synthesized photocatalyst could be easily recycled with a remarkable photocatalytic performance because of its magnetic separation characteristic. The present work opens up a vast prospect for the design of highly efficient and magnetically separable photocatalysts for environmental remediation.

Acetic acid leaching of neodymium magnets and iron separation by simple oxidative precipitation

Neodymium-iron-boron (NdFeB) has become the most prominent permanent magnet alloy, with a wide variety of applications and an ever-increasing demand. Their recycling is important for securing the supply of critical raw materials used in their manufacturing. The use of organic acids such as acetic acid has been of recent interest for the recycling of waste NdFeB magnets. Despite achieving good leaching efficiencies, the published literature has not properly investigated the effects of key factors influencing the acetic acid leaching process and their respective interactions, which has led to conflicting findings as to what conditions are optimal. The present work goes to show that no such optimum exists by taking a look at the major factors (concentration, solid-to-liquid ratio, time, and temperature) and their interactions. The results show that leaching efficiencies >95% and even up to 100% can be achieved using a variety of different conditions showing that the leaching reaction is quite flexible, which is helpful for a potential upscaling of the process. The separation of the leached elements presents another problem in NdFeB magnet processing. As a novel application, this work investigated iron separation from the acetic acid leachate by the means of simple and inexpensive aeration. It was found that up to 99% of iron could be precipitated as FeO(OH) (goethite) within 2 h at pH 5 and 80 °C, while only minor neodymium co-precipitation was observed (5%). Separation of iron from the leachate can help obtain purer REE products in further processing. • An environmentally friendly acetic acid leaching process for NdFeB magnets. • Main effects and interactions of key factors illuminated - flexible leaching process. • Iron precipitated as FeO(OH) using a simple and inexpensive aeration method.

Metal–organic framework-derived porous metal oxide/graphene nanocomposites as effective adsorbents for mitigating ammonia nitrogen inhibition in high concentration anaerobic digestion of rural organic waste

Anaerobic digestion (AD) is an efficient technology that can efficiently convert organic waste into biofuel, but excessive ammonia nitrogen concentration will lead to failure of AD. In this study, a metal–organic framework (MOF)-derived porous metal oxide/graphene nanocomposite (FeMn-MOF/G) was first applied in AD to investigate the mitigation effect of ammonia nitrogen inhibition. Five total solids (TS) concentrations of 8 %, 10 %, 12 %, 15 % and 20 % were set up for AD experiment to investigate the effect of FeMn-MOF/G on AD. The results showed that the average ammonia nitrogen adsorption capacity of FeMn-MOF/G in AD with different TS concentrations was 102.68 mg/g, and the ammonia nitrogen adsorption effect decreased with the increase of TS. When FeMn-MOF/G was added to AD, the ammonia nitrogen concentration of the experimental group could be reduced to 2,086.00 mg/L, and the VFAs concentration was reduced to 1,510.34 mg/L. The methane production in each experimental group increased significantly, and the experimental group MOF-8 obtained the highest cumulative methane production of 321.35 mL/gVS, indicating that FeMn-MOF/G effectively mitigated the ammonia nitrogen inhibition,which promoteed the successful operation of AD. We characterized the prepared FeMn-MOF/G. The results of the vibrating sample magnetometer show that FeMn-MOF/G has excellent superparamagnetic properties. Magnetic recycling is a promising method for the recycling of FeMn-MOF/G materials, which provides a broad prospect for the application of FeMn-MOF/G in AD.

Ag NPs decorated on the magnetic Fe3O4@PDA as efficient catalyst for organic pollutants removal and as effective antimicrobial agent for microbial inhibition

In this paper, Ag NPs-decorated magnetic Fe3O4 @PDA nanocomposites have been successfully prepared. The spherical Fe3O4 nanoparticles with an average size approximately 340 nm were modified by dopamine under mild conditions. Dopamine was self-polymerized surrounding Fe3O4 nanoparticles and transformed into poly dopamine (PDA) layers. The PDA-encapsulated magnetic (Fe3O4 @PDA) nanoparticles could in-situ reduce silver ammonium ions by the catechol groups in PDA layers. The Ag NPs with an average size ranging from 20 nm to 36 nm were densely decorated on the thin PDA shell. The resultant Fe3O4 @PDA-Ag nanocomposites were employed as highly efficient catalysts for the reduction of different organic pollutants in the appearance of sodium borohydride. The Fe3O4 @PDA-Ag nanocomposites also demonstrated extraordinary cycling stability when the catalyst was recycled several times for the reduction of MB. The antimicrobial tests indicated Fe3O4 @PDA-Ag nanocomposites could efficiently prohibit the growth of microorganism, including various bacteria and fungi. The minimal inhibitory concentrations (MIC) for Fe3O4 @PDA-Ag nanocomposites against different bacteria and fungi were also determined. The excellent catalytic activity, magnetic recyclability, and antimicrobial performance make Fe3O4@PDA-Ag a feasible candidate for the remediation of wastewater which contains multiple water soluble organic pollutants and pathogenic microorganism.

Popcorn-like ZnFe2O4/CdS nanospheres for high-efficient photocatalyst degradation of rhodamine B

The popcorn-shaped ZnFe2O4 (ZFO) nanospheres has been produced by one-pot synthesis method. CdS nanoparticles (NPs) were subsequently loaded onto the surface of porous ZnFe2O4 through the successive ion layer adsorption (SILAR) process. The microstructure, composition, and degradation ability of ZFO/CdS NPs composites have been examined in-depth. Under the four SILAR cycles, the resulting ZFO/CdS NPs (FS4) composite displayed the maximum degradation efficiency of 93.2% for rhodamine B (RhB) in 40 min, and which maintained high photocatalytic activity and a stable structure after five reuse. The heterojunction between CdS and ZFO can dramatically improves the separation efficiency of photo-generated electron-hole pairs, thus boosts catalytic activity. Meanwhile, the radical scavenging investigations have demonstrated that the superoxide radicals as the principal reactive group participate in the photocatalytic reactions. The proposed ZFO/CdS NPs composites shows high photocatalytic ability and convenient magnetic recycling. This work not only provide a practical green synthesis path, but also offers new insight onto the formation of high-efficiency heterojunction photocatalysts.

Possibilities in Recycling Magnetic Materials in Applications of Polymer-Bonded Magnets

Polymer-bonded magnets have increased significantly in the application of drive technology, especially in terms of new concepts for the magnetic excitation of synchronous or direct current (DC) machines. To satisfy the increasing demand of hard magnetic filler particles and especially rare earth materials in polymer-bonded magnets, different strategies are possible. In addition to the reduction in products or the substitution of filler materials, the recycling of polymer-bonded magnets is possible. Different strategies have to be distinguished in terms of the target functions such as the recovery of the matrix material, the filler or both materials. In terms of polymer-bonded magnets, the filler material—especially regarding rare earth materials—is important for the recycling strategy due to the limited resource and high costs. This paper illustrates two different recycling strategies relative to the matrix system of polymer-bonded magnets. For thermoset-based magnets, a thermal strategy is portrayed which leads to similar magnetic properties in terms of the appropriated atmosphere and process management. The mechanical reusage of shreds is analyzed for thermoplastic-based magnets. The magnetic properties are reduced by about 20% and there is a change in the flow conditions and with that, an influence on the pole accuracy.

Heterometal modified Fe3O4 hollow nanospheres as efficient catalysts for organic transformations

Iron oxides (e.g. Fe3O4) are ideal support materials for catalytic organic transformations owing to their sufficient natural abundance, excellent thermal stability and magnetic recycling property. Herein, we report the synthesis of active heterometal (M = Pd, Cu) modified Fe3O4 (M-Fe3O4) hollow nanospheres via a two-step solvothermal/annealing method. Due to the uniformly dispersed active heterometal species in the spherical shell of Fe3O4 hollow nanospheres, the as-prepared Pd-Fe3O4 catalyst exhibits remarkable catalytic activity toward 4-nitrophenol reduction with a turnover frequency of 145 min−1, and shows excellent stability and magnetic recyclability. The catalytic efficiency surpasses most of the similar Fe3O4 supported metal catalysts reported in literatures. Particularly, Cu-Fe3O4 exhibited 5 times higher activity for benzyl alcohol oxidation compared to that of bare Fe3O4 synthesized by the same procedure. An impressive conversion of 49.66% and an outstanding selectivity of 100% can be achieved. Moreover, the positive effects of Pd or Cu elements on the 4-NP molecule adsorption were further confirmed via both experimental results and theoretical studies. Our work demonstrate that the activity boost of iron oxides by heterometal modification is a promising strategy for performance improvement.

High Recyclability Magnetic Iron Oxide‐Supported Ruthenium Nanocatalyst for H2 Release from Ammonia‐Borane Solvolysis

AbstractWe report the high capacity of recycling of a technologically simple, easily recoverable, Ru@Fe3O4 magnetic nanocatalyst, efficient in the release of H2 from ammonia‐borane (AB) solvolysis, using H2O or methanol at room temperature (25 °C). The initially oxidized Ru small nanoparticles (2–4 nm) are well‐dispersed on an iron oxide support (i. e. super paramagnetic iron oxide of spinel structure, SPIO, as aggregates of 20 nm to a few μm). As nanocatalyst, this composite achieved short‐time (<10 min) AB full hydrolysis (3 equiv. H2, no NH3, [AB]=0.1 mol L−1) with a turnover frequency (TOF) of ca 20 min−1 (86 min−1 at 50 °C). The post‐catalysis characterization of the composite showed the formation of well‐defined crystalline hcp Ru(0) dispersed on the SPIO. The activity for full H2 release from AB is conserved over ten cycles, which is among the most effective recycling processes reported to date (a magnetic recycling is achieved in <2 min). Pleasingly, an even superior activity was found in the more challenging AB methanolysis, with a TOF up to ca 30 min−1 for full H2 release, achieved in a recycling process repeated over 8 cycles.

Polyaniline enwrapped CoFe2O4/g-CN ternary nanocomposite for adsorption driven photocatalytic degradation of explicitly diverse organic pollutants

The present study strives to unlock the potential of CoFe2O4 supported over graphitic carbon nitride (g-CN) and polyaniline (PANI) as photocatalyst for wastewater decontamination. For this purpose, a series of PANI@CoFe2O4/g-CN (PA-CNC) nanocomposites were fabricated by varying PANI: CoFe2O4/g-CN ratio (0.25:1, 0.5:1, 1:1 and 2:1) employing in-situ oxidative polymerization method. The structure, morphology, optical and magnetic properties of the nanocomposites were characterized using FT-IR, Raman, XRD, FE-SEM, HR-TEM, XPS, UV-DRS, PL, EIS, VSM and BET analysis. The ternary nanocomposites were investigated for the removal of ofloxacin (OFX), sulfamethoxazole (SFX), p-nitrophenol (PNP) and malathion (MT) as model pollutants. Under optimized reaction conditions, the pseudo-first order rate constant value of PA-CNC (0.5:1) nanocomposite for the degradation of OFX (5.3 × 10−2 min−1) was observed to be nearly 4 times to that of pristine CoFe2O4 (1.3 × 10−2 min−1). The incorporation of PANI has improved the adsorption capacity of nanocomposites owing to synergistic effect of different interactions between pollutant molecules and PANI that subsequently augmented the rate of photocatalytic degradation of pollutants. Moreover, PANI improved the visible light absorption capacity and promoted the separation of photogenerated charge carriers across the ternary heterojunction. The magnetic recyclability up to four cycles highlighted the desirability of PANI@CoFe2O4/g-CN nanocomposites for the abatement of wide range of pollutants.

Magnetically recyclable nanocomposites via lanthanide-based MOFs grown on natural sea sponge: Screening hydrogenation of nitrophenol to aminophenol

Catalysts have played a significant role in chemical industries and received significant attention as a result. Unfortunately, many common catalytic systems are comprised of a small number of elemental species or use similar synthetic strategies, which potentially limit innovation in areas such as the discovery of new transformations. Metal-organic frameworks (MOFs) have been established as versatile materials employed in various applications that include catalysis; however, the majority of MOFs have been synthesized using transition metal building blocks, possibly hindering advances towards innovative materials with unique properties. This work reports the synthesis of MOFs based on lanthanide elements (Ln = Ce, Gd, La, and Sm), which demonstrate great potential yet are often overlooked. The Ln-based MOFs were grown in situ on natural sea sponge supports and Fe ion containing solution, followed by a thermal carbonization treatment to generate FeLn metal nanoparticles (NPs) embedded on carbon support (FeLn@C). These nanostructured products exhibited good crystallinity and well-confined particle sizes. We then demonstrate that these hybrid materials can be used as effective heterogeneous nanocatalysts for the hydrogenation of nitrophenol to aminophenol in aqueous media. Besides, FeLn@C catalysts had a magnetic property due to Fe atoms in the NPs, which can be mechanically separated out from the aqueous solution since the catalysts are magnetically attracted to the external magnets. This magnetic recyclability combined with the usage of the natural materials highlight the importance of sustainability in the design of Ln-based MOFs and their catalytic applications.

Super-paramagnetic polymer composite-supported dendrimer–Mn catalyst: Fabrication, characterization and catalytic evaluation in selective aerobic oxidation of ethylbenzene and oximes derivatives

Design of strategy and catalytic for oxidation ethylbenzene, toxic petroleum, to high value-added via hydrogen-atom-transfer process is lately attracting a renewed interest from both environmentally and economic view. Herein, novel manganese-based dendritic catalysts supported on the polymer-magnetic core-shell were synthesized, fully identified and evaluated with initiator NDHPI for selective and easy-to-handle aerobic oxidation of ethylbenzene (EB) and oximes to acetophenone (ACP) & carbonyl compounds (AH/KO), respectively. Besides mild condition reaction, the supported dendrimer-encapsulated Mn NPs also exhibited outstanding catalytic performance, such as selective oxidation of ethylbenzene and oximes using O2 as green and cheaper oxidant with excellent reactivity, selectivity, stability, and magnetic recyclability. Additionally, the effect of operating parameters such as the amount of catalyst, nature of solvent, temperature and reaction time, and role of several N-hydroxyimides were studied in the catalytic efficiency of the synthesized dendritic catalyst. The results illustrated that the enhanced catalytic efficiency of the catalyst is derived from the magnetic dendritic structures, high Mn(II) content, hydrophobic arm of dendrimers, and interaction of Mn and the dendritic framework. Finally, the reaction pathway for EB and oxime has been deduced, and the crucial role of dendritic catalyst, NDPHI, and electronic effect has been elucidated.

In-situ reduction-passivation synthesis of magnetic octahedron accumulated by Fe@Fe3O4-C core@complex-shell for the activation of persulfate

The iron-based heterogeneous catalysts, especially the zero valent iron (ZVI) is an eco-friendly and cost-effective activator for persulfate (PS) excitation. However, the oxidation of surface ZVI reduces its service lifetime. Herein, a series of magnetic octahedrons accumulated by Fe@Fe3O4-C core@complex-shell were constructed by in-situ reduction-passivation of the MIL-101(Fe). The catalysts exhibited good activity, high stability and magnetic recyclability. The optimized Fe@Fe3O4-C-60 with largest proportion of active iron achieved a 100 % conversion of Rhodamine B (RhB) within 4 min and high mineralization efficiency of 667.34 % in 30 min. Moreover, Fe@Fe3O4-C-60 maintained its activity even after 3 times of cycling test and could be easily magnetic separation. The rate constant was 1.23 min−1 for Fe@Fe3O4-C-60+PS in first 3 min, which was 1.6, 5 and 323 times of Fe0+PS, FeSO4+PS and Fe3O4+PS. Fe0 and Fe2+ were identified as active sites for SO4•- generating, while the carbon shell was responsible for the high stability. The synergistic effect between Fe0 core and Fe3O4-C complex shell realized the sustained regeneration of active surface Fe2+ and inhibition leaching of Fe.

Encapsulation of Zn/Co nanocrystals into sponge‐like 3D porous carbon for Escherichia coli inactivation coupled with ultrasound: Characterization, kinetics and inactivation mechanism

A sponge-like 3D Zn/Co co-doped porous carbon composite (Zn/Co-MPC) was successfully prepared using edible fungus residues as a template through a facile pyrolysis method in the current design. The optimized Zn/Co-MPC-0.3 composite was characterized by controllable release of bactericidal particles, fine sterilization ability and excellent magnetic recycle performance. The zinc oxide nanoparticles (ZnO NPs) and cobalt within the composite acted as an efficient killer of germs, while biochar could effectively achieve a controllable release of ZnO NPs and cobalt, endowing the Zn/Co-MPC composite with long-lasting antibacterial performance and eco-friendliness. High-frequency ultrasound, coupled with Zn/Co-MPC-0.3 composite, brought synergistic sterilization, contributing to the enhanced sterilization. The synergistic sterilization of Zn/Co-MPC-0.3 assisted with ultrasound caused a about 1.02-log CFU/mL reduction in Escherichia coli. Four kinetics models fitted well (R2 > 0.9), and the statistical parameters (R2 > 0.95 and smallest RMSE) of Log-linear and Weibull models fitting ultrasound-enhanced Zn/Co-MPC-0.3 treatment were fine. The sterilization mechanism of Escherichia coli by ultrasound-enhanced Zn/Co-MPC-0.3 treatment included the decreased enzyme activity, the broken cell membrane, and the loss of intracellular matter (protein, ATP, DNA). We argue that the ultrasound in combination with Zn/Co-MPC-0.3 treatment has a promising application in bacterial decontamination due to its advantages in eco-friendly characteristics and long-lasting antibacterial performance.

Preparation and performance of magnetic phase change microcapsules with organic-inorganic double shell

Magnetic microcapsulated phase change materials can achieve rapid magnetic localization temperature regulation and magnetic separation recycling. However, the efficient encapsulation of both inorganic magnetic material and organic phase change material is a challenge due to their poor compatibility. In this work, an aqueous dispersion containing methylol melamine and sodium alginate loaded with magnetic Fe 3 O 4 nanoparticles (SA-Fe 3 O 4 ) was prepared and mixed with a paraffin emulsion. After methylol melamine was initiated to in-situ polymerize at the interface of the paraffin emulsion droplets, primary magnetic phase change microcapsules (P-MPCM) composed of a paraffin core and SA-Fe 3 O 4 /melamine formaldehyde resin composite shell were formed. Then, SiO 2 sol particles were adsorbed on the surface of P-MPCM to form the final MPCM with a polymer-SiO 2 double-shell (PS-MPCM). The magnetic polymer-SiO 2 double-shell endows the PS-MPCM with rapid magnetic responsiveness (can be quickly collected under magnetic fields), high phase change enthalpy (184.4 J·g-1) and excellent structural stability. The phase change enthalpy and saturation magnetization of PS-MPCM have changed little after 200 thermal cycles. At the same time, the excellent photothermal conversion efficiency (93.9%) of PS-MPCM benefits for solar energy conversion utilization in actual application. This work provides a new way to obtain MPCM with high thermal conductivity (0.64 W·m-1·K-1), rapid magnetic response and excellent reusability, which can be potentially applied for directional temperature regulation. Magnetic polymer-SiO 2 double-shell phase change microcapsule (PS-MPCM) was prepared. PS-MPCM exhibits high encapsulation ratio of paraffin and Fe 3 O 4 nanoparticles (NPs). Sodium alginate was introduced to achieve efficient and stable loading of Fe 3 O 4 NPs. PS-MPCM exhibits excellent thermal conductivity, magnetic response and reusability. PS-MPCM can be potentially applied for magnetic localization temperature regulation.

Synthesis of ferroferric oxide@silicon dioxide/cobalt-based zeolitic imidazole frameworks for the removal of doxorubicin hydrochloride from wastewater

Due to its low-cost, eco-friendliness and easy mode of separation biosynthesized magnetic ferroferric oxide (Fe3O4) can be successfully used for the removal of organic contaminants from wastewater. However, there are some challenges that to date have limited this compound’s practical removal efficiency. Thus, in this study, a cobalt-based zeolitic imidazole frameworks (ZIF-67) coated biosynthesized ferroferric oxide@silicon dioxide (Fe3O4@SiO2) magnetic composite (Fe3O4@SiO2/ZIF-67) was prepared to address these issues and subsequently used to remove doxorubicin hydrochloride (DOX). Characterization results showed that the fabricated composite exhibited significant magnetic properties (16.1 emu·g−1) with a size ranging between 50 and 250 nm. The amount of DOX adsorbed by the composite (90.7 mg·g−1) was much higher than either of the component parts, which were only 35.7 and 82.5 mg·g−1 for Fe3O4@SiO2 and ZIF-67 respectively. This indicated enhanced DOX adsorption by Fe3O4@SiO2/ZIF-67. The DOX adsorption best fit a pseudo-second order kinetic and Langmuir adsorption model. These studies suggested that the DOX adsorption mechanism involved a combination of electrostatic interactions, π-π stacking, hydrogen bonding and pore filling. Regeneration and application studies, exposing Fe3O4@SiO2/ZIF-67 to real water samples, practically demonstrated that Fe3O4@SiO2/ZIF-67 with propensity for magnetic separation and recycle is a promising nanomaterial for DOX removal.

Preparation of rambutan-shaped hollow ZnFe2O4 sphere photocatalyst for the degradation of tetracycline by visible-light photocatalytic persulfate activation

With the extensive abuse of antibiotics, antibiotics can be detected in various water bodies, endangering the human living environment and leading to human health problems. Photocatalytic technology can achieve an efficient and stable removal of antibiotics in the water environment. In this work, solvothermal-calcination method prepared the rambutan-shaped hollow ZnFe2O4 photocatalysts composed of different thickness sheets at different temperatures. The as-prepared materials were applied for the photocatalytic degradation of tetracycline (TC) in the activation of persulfate (PS) under visible light irradiation. The results exhibit that when the calcination temperature is 400 °C, the ZFO-400 sample exhibits optimal photocatalytic activity based on the PS activation due to the high specific surface area, which can present more active sites. In addition, the modified ZFO-400 material can show better visible light absorption, light under the same conditions, can stimulate more light raw charge, and further enhance its photocatalytic effect. Furthermore, by adjusting the pH value of the system, more superior degradation effect was obtained, and the degradation rate of TC is up to 100% within 60 min visible light irradiation. Finally, the as-prepared photocatalytic material showed good magnetic recycling utilization.

Hydrometallurgical recycling of waste NdFeB magnets: design of experiment, optimisation of low concentrations of sulphuric acid leaching and process analysis

ABSTRACT Efficient recovery of rare earth elements (REEs) from scrap NdFeB magnets is a significant requirement for a circular economy. Therefore, the development of a cost-effective and environmentally friendly leaching process for the dissolution of iron and REEs has received extensive interest. In this study, the dissolution of NdFeB magnet powders in sulphuric acid solution was investigated in detail. Taguchi orthogonal array was employed for the first time to define and optimise the influence of sulphuric acid concentration, solid-to-liquid ratio and stirring speed on the extraction of iron and rare earth elements (REEs). The acid concentration of sulphuric acid was determined as a key factor for iron and REEs dissolution, while solid-to-liquid ratio and stirring speed slightly affected the dissolution of REEs and iron. Maximum iron and REEs extraction were achieved under optimal conditions as the sulphuric acid concentration of 1 M, solid-to-liquid ratio of 1/15 and stirring speed of 350 rev min−1. Consequently, after the validation experiment, it was proved that the design of experiments based on Taguchi orthogonal array is an efficient way for the optimisation of process parameters.

Porous core–shell Fe3O4@CuSiO3 microsphere as effective catalyst for styrene epoxidation

The porous core–shell Fe3O4@CuSiO3 catalyst were synthesized via a multi-step preparation method including StÖber method and hydrothermal process. The morphological, magnetic and physicochemical studies demonstrated a successful fabrication of the targeted material. This catalyst possessed a spherical morphology with a magnetic core and protective porous shell. The Fe3O4 core not only offered a convenient way for magnetic recycling, but also worked as an electron donor to increase the electron density on the CuSiO3 shell. The catalytic performance of the synthesized material was investigated in the styrene epoxidation with tert-butyl hydroperoxide as oxidant. On account of the synergy effect between Fe3O4 and CuSiO3, the porous core–shell Fe3O4@CuSiO3 catalyst showed styrene conversion significantly higher compared to those of pure Fe3O4, pure CuSiO3 and physically mixed catalyst (Fe3O4 + CuSiO3). In particularly, the catalytic activity of the Fe3O4@CuSiO3 was retained after the recyclability test and re-calcination, which confirmed that the Fe3O4@CuSiO3 catalyst was easily separated, highly stable and could be used six times without significantly affecting its structural order. Moreover, the kinetic study revealed the activation energy of Fe3O4@CuSiO3 in styrene epoxidation was 45.4 kJ/mol. The possible free radical mechanism for the styrene epoxidation based on the Fe3O4@CuSiO3 catalyst was proposed.

Three-Dimensional Hierarchical HRP-MIL-100(Fe)@TiO2@Fe3O4 Janus Magnetic Micromotor as a Smart Active Platform for Detection and Degradation of Hydroquinone.

A novel multifunctional Janus magnetic micromotor was designed and constructed by using MIL-100(Fe)@TiO2@Fe3O4 multicore-shells modified with horseradish peroxidase (HRP) as a smart active platform to realize detection and degradation of hydroquinone (HQ). The obtained micromotor showed a unique three-dimensional (3D) hierarchical architecture with highly exposed active sites and could autonomously move at a speed of 140 ± 7.0 μm·s-1 by O2 bubbles generated from the catalytic decomposition of H2O2 fuel. Benefiting from the combination of active self-propulsive motion, high peroxidase-like activity, tuned heterojunctions with matching band structures, and a 3D hierarchical structure, an effective platform involving dynamically sensitive detection and quick removal of HQ from water was established by using the multifunctional HRP-integrated MIL-100(Fe)@TiO2@Fe3O4 Janus micromotor. The proposed multifunctional Janus magnetic micromotor had advantages of simple and feasible fabrication, sensitive detection and effective photo-Fenton degradation of HQ in a wide pH range of 4-7, and magnetic recycling, revealing potential for environmental remediation applications.

Effect of Cu grain boundary modification on microstructure and corrosion resistance in recycled Nd-Fe-B sintered magnets

In order to realize the secondary use of Nd-Fe-B magnet scraps, Nd-Fe-B recycled magnets have been widely applied. However, the poor corrosion resistance due to the rare earth oxide (RE-O) in grain boundary limits their application. In this work, 0.3 wt% of Cu powder with average grain size of 1 μm was added to improve the corrosion resistance of Nd-Fe-B recycled magnet. In comparison with the initial Nd-Fe-B recycled magnet, mass loss of accelerated corrosion test after 168 h for the Cu-modified Nd-Fe-B recycled magnet dramatically drops from 30.35 mg/cm2 to 0.0078 mg/cm2. Correlated with XRD Rietveld refinement and TEM results shows that the improved corrosion resistance is attributed to the crystal structure of RE-O change at the grain boundary phase from hcp/amorphous with high oxygen content to the Cu-rich GB phase with lower oxygen content at triple junctions after Cu modification. The formed new grain boundary phase in the Cu-modified magnet possesses low relatively Volta potentials, contributing to the enhancement of anti-corrosive properties. This work paves an effective way to obtain optimal corrosion resistance and maintain high magnetic properties simultaneously in Nd-Fe-B recycled magnet, which is beneficial to recycling of waste magnets.