Hierarchically magnetic Ni–Al binary layered double hydroxides: towards tunable dual electro/magneto-stimuli performances

Magnetorheological properties of Fe-Co nanoparticles with high saturation magnetization and low coercivity

Fe-Co alloys exhibit an excellent saturation magnetization, which makes them become a potential candidate for the high property magnetic particles in magnetorheological fluids (MRFs). How to decrease their coercivity and residual magnetization without sacrificing the saturation magnetization is a crucial problem to be solved. In this study, Fe-Co nanoparticles were prepared by DC arc discharge and further disposed through low temperature annealing in Ar atmosphere. The successful synthesis of Fe-Co nanoparticles was proved by x-ray diffraction and EDS. The vibrating sample magnetometer results revealed that the prepared Fe-Co nanoparticles had a saturation magnetization of 208 emu g^-1, while the coercivity and remanent magnetization were 58 Oe and 5.8 emu g^-1, respectively. The MR properties of Fe-Co nanoparticles based MRFs (FeCoNP-MRFs) with 10% particles by volume fraction were systematically investigated. The FeCoNP-MRFs showed up to 4.61 kPa dynamic shear stress at 436 kA m^-1magnetic field and an excellent reversibility. The MR properties of FeCoNP-MRFs were fitted well by Bingham and power law model, and described by Seo-Seo and Casson fluid model. Meanwhile, the sedimentation ratio of FeCoNP-MRFs was still 87.3% after 72 h, indicating an excellent sedimentation stability.

Magnetizing Polymer Particles with a Solvent-Free Single Stage Process Using Superparamagnetic Iron Oxide Nanoparticles (SPION)s

Magnetic polymer composites are used in a variety of applications in many industries. Their production methods are usually time-consuming and solvent-intensive as they are performed in liquid phase processes, such as emulsion polymerization or precipitation. In this work, a quick, easy, and solvent-free method is presented to coat polymer particles with a discrete, non-coherent coating of superparamagnetic nanoparticles. The results of the dry coating process are evaluated optically, by means of scanning electron microscopy (SEM), via powder X-ray diffraction and thermally by means of differential scanning calorimetry, before finally demonstrating the effectiveness of dry coating by means of a vibrating sample magnetometer.

Synergistic Effect of NiLDH@YZ Hybrid and Mechanochemical Agitation on Glaser Homocoupling Reaction

Herein, we report the synthesis of nickel-layered double hydroxide amalgamated Y-zeolite (NiLDH@YZ) hybrids and the evaluation of the synergistic effect of various NiLDH@YZ catalysts and mechanochemical agitation on Glaser homocoupling reactions. Nitrogen adsorption-desorption experiments were carried out to estimate the surface area and porosity of NiLDH@YZ hybrids. The basicity and acidity of these hybrids were determined by CO₂ -TPD and NH₃ -TPD experiments respectively and this portrayed good acid-base bifunctional feature of the catalysts. The NiLDH@YZ-catalyzed mechanochemical Glaser coupling reaction achieved best yield of 83 % for the 0.5NiLDH@0.5YZ hybrid after 60 min of agitation, which revealed the highest acid-base bifunctional feature compared to all the investigated catalysts. The developed catalyst has proven itself as a robust and effective candidate that can successfully be employed up to four catalytic cycles without significant loss in catalytic activity, under optimized reaction conditions. This work demonstrated a new strategy for C-C bond formation enabled by the synergy between mechanochemistry and heterogeneous catalysis.

Magnetic Polymer Composite Particles: Design and Magnetorheology

As a family of smart functional hybrid materials, magnetic polymer composite particles have attracted considerable attention owing to their outstanding magnetism, dispersion stability, and fine biocompatibility. This review covers their magnetorheological properties, namely, flow curve, yield stress, and viscoelastic behavior, along with their synthesis. Preparation methods and characteristics of different types of magnetic composite particles are presented. Apart from the research progress in magnetic polymer composite synthesis, we also discuss prospects of this promising research field.

Enhanced electrochemical performance by nickel-iron layered double hydroxides (LDH) coated on Fe3O4 as a cathode catalyst for single-chamber microbial fuel cells

The improvement of cathode performance has always been the bottleneck and research hot spot for microbial fuel cells (MFCs). An Fe₃O₄@NiFe-LDH composite with a nanoscale core-shell structure containing an Fe₃O₄ magnetic core and a layered double hydroxide (LDH) shell was prepared by the hydrothermal method. The Fe₃O₄@NiFe-LDH was characterized by FT-IR, XRD, SEM and EDS. The characterization results showed that the composite had a unique cauliflower-like nanoflake structure and special pore size distribution, which greatly improved the ORR performance. Moreover, the use of the synthesized Fe₃O₄@NiFe-LDH core-shell structure as an electrode in an MFC was characterized by CV and LSV, which showed that the Fe₃O₄@NiFe-LDH exhibited excellent ORR catalytic properties. The voltage output of the Fe₃O₄@NiFe-LDH MFC was maintained at approximately 0.39 V, with insignificant variations over 110 h. The maximum power density was 211.40 ± 2.27 mW/m², which was 34 times that of the blank control group MFC and was caused by the many electroactive sites, good rate capability and remarkable cycling stability of LDH. This study provides the possibility for using Fe3O4@NiFe-LDH in cathodes to operate continuously and at low cost in fuel cells.

Layered Double Hydroxides Applications in the High-Performance Magnetic Nanomaterials

Layered double hydroxides (LDHs), which is related to magnetic nanomaterials’ have promising applications due to their unique structural and chemical properties. The easy tunability of cationic metals without changing the LDH structure as well as anion exchange features of LDH interlayer make them potential applications in supercapacitors, batteries, catalysis, water splitting, etc. Moreover, due to the high dispersion of active compounds in the matrix of LDH layers, LDHs have been used to construct various nanostructures such as nanoparticles, 2D monolayer nanosheets and 3D hierarchical’ which are valued in wide nanotechnological applications. Magnetic nanomaterials are an important research area because they have been applied to a wide range of disciplines such as biotechnology, data storage, magnetic fluids, magnetic resonance imaging, environmental remediation and catalysis. LDHs as starting materials including Ni, Fe or/and Co, can be used as magnetic nanomaterials. The combination between LDHs and magnetic nanostructures has improved the magnetic properties of those materials, hence can be used in more applications.

Recent development of electro-responsive smart electrorheological fluids

The characteristics of an electrorheological (ER) fluid, as a class of smart soft matter, can be actively and accurately tuned between a liquid- and a solid-like phase by the application of an electric field. ER materials used in ER fluids are electrically polarizable particles, which are attracting considerable attention in addition to further research. This perspective reports the latest ER materials along with their rheological understanding and provides a forward-looking summary of the potential future applications of ER technology.

Reversible Actuation Ability upon Light Stimulation of the Smart Systems with Controllably Grafted Graphene Oxide with Poly (Glycidyl Methacrylate) and PDMS Elastomer: Effect of Compatibility and Graphene Oxide Reduction on the Photo-Actuation Performance

This study is focused on the controllable reduction of the graphene oxide (GO) during the surface-initiated atom transfer radical polymerization technique of glycidyl methacrylate (GMA). The successful modification was confirmed using TGA-FTIR analysis and TEM microscopy observation of the polymer shell. The simultaneous reduction of the GO particles was confirmed indirectly via TGA and directly via Raman spectroscopy and electrical conductivity investigations. Enhanced compatibility of the GO-PGMA particles with a polydimethylsiloxane (PDMS) elastomeric matrix was proven using contact angle measurements. Prepared composites were further investigated through the dielectric spectroscopy to provide information about the polymer chain mobility through the activation energy. Dynamic mechanical properties investigation showed an excellent mechanical response on the dynamic stimulation at a broad temperature range. Thermal conductivity evaluation also confirmed the further photo-actuation capability properties at light stimulation of various intensities and proved that composite material consisting of GO-PGMA particles provide systems with a significantly enhanced capability in comparison with neat GO as well as neat PDMS matrix.

Ultra-fast and highly efficient removal of cadmium ions by magnetic layered double hydroxide/guargum bionanocomposites

Finding effective methodologies for the removal of heavy metals from contaminated water are really significant. Facile and "green" techniques for adsorbents fabrication are in high demand to satisfy a wide range of practical applications. This report presents of an efficient method for preparing Fe₃O₄@ layered double hydroxide@ guargum bionanocomposites (GLF-BNCs). First of all, the LDH coated Fe₃O₄ nanoparticles were simply synthesized, using ultrasonic irradiation. The citrate coated Fe₃O₄ nanoparticles which were under negative charging and LDH nanocrystals which were charged positively make electrostatic interaction which formed a stable self-assembly component, and then guargum as a biopolymer were linked onto Fe₃O₄@LDH via an in situ growth method. Furthermore, the GLF-BNCs had the ability to remove cadmium ions (Cd²⁺) from the aqueous solutions. Adsorption studies indicate that the Langmuir isotherm model and the kinetic model in pseudo-second order were appropriate for Cd(II) removal. The maximum Cd(II) adsorption capacity of the GLF8% was 258 mg g^-1. The Cd(II) was adsorbed from aqueous solutions very quickly with the contact time of 5 min by the GLF 8%, suggesting that GLF-BNCs may be a promising adsorbent for removing Cd(II) from wastewater. The effect of Fe₃O₄@LDH contents (2, 4 and 8 wt.%) on the thermal, physicomechanical, and morphological properties of guargum were investigated by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), field emission scanning electron microscopy, transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy and Brunauer-Emmett-Teller (BET) specific surface area techniques. The TEM results indicated that the LDH platelets are distributed within the polymer matrix.