High-efficiency adsorption removal of CR and MG dyes using AlOOH fibers embedded with porous CoFe2O4 nanoparticles

Owing to the toxicity and difficulty in degradation, how to the effective separation for the residual dyes in the aqueous solution is still an issue with great challenge in the area of environmental protection. Now, to high-efficiency removal of organic dyes from the aqueous solution, we design a unique AlOOH/CoFe₂O₄ adsorbent with porous CoFe₂O₄ nanoparticles embedded on the AlOOH fibers using a simple hydrothermal technique and calcination process. The structural properties and surface characteristics of the AlOOH/CoFe₂O₄ composites are detailedly analyzed by XRD, FTIR, XPS, TEM and SEM. Here, the high S_BET and specific porous structure are beneficial to improve the adsorption performance of AlOOH/CoFe₂O₄ adsorbents. Especially, when the molar ratio of AlOOH to CoFe₂O₄ in the AlOOH/CoFe₂O₄ fibers is 1:1, an optimal performance on adsorbing anionic Congo red (CR) and cationic methyl green (MG) dyes can be obtained at pH = 6.29, where the corresponding maximum adsorption capacities reach up to 565.0 and 423.7 mg g^-1, respectively. Factors leading to the change in the ability of adsorbing CR and MG dyes are systematically discussed, including contact time, temperature, initial concentrations, and pH values of the solutions. Meanwhile, the uptake of CR and MG dyes can best conform to Langmuir isotherm model and pseudo-second-order adsorption kinetics. The thermodynamic analysis verifies that the dye adsorption process is spontaneous and endothermic. Moreover, from the point view of practical application, the good reusability further makes the as-synthesized magnetic AlOOH/CoFe₂O₄ composite be a perfect adsorbent with efficiently removing both anionic and cationic dyes from aqueous solutions.

3D porous coral-like Co1.29Ni1.71O4 microspheres embedded into reduced graphene oxide aerogels with lightweight and broadband microwave absorption

In this work, three-dimensional (3D) porous coral-like Co_1.29Ni_1.71O₄ microspheres were successfully combined with reduced graphene oxide (rGO) to form Co_1.29Ni_1.71O₄/rGO aerogels as an efficient microwave absorber by a facile calcination and hydrothermal method. The elemental composition, microstructure, and morphology of the as-synthesized composites were characterized, and the electromagnetic wave absorption performance were analyzed in the frequency range of 2.0-18.0 GHz. The results show that adjusting the mass ratio of Co_1.29Ni_1.71O₄ microspheres and rGO in the composites can effectively tune the electromagnetic parameters, which in turn improves their microwave absorption performance. Here, the minimum reflection loss (RL_min) of the Co_1.29Ni_1.71O₄/rGO aerogels is -51.76 dB with an effective absorption bandwidth (RL < -10 dB) of 7.04 GHz (10.96-18 GHZ) at the thickness of 2.66 mm and a low filling ratio of 15 wt%. It can be demonstrated that the superior microwave absorption performance is attributed to the synergistic effect of impedance matching and dielectric loss, the unique 3D porous structure as well as the abundant interface of the composites. In brief, this study provides a new strategy for the design of magnetic/dielectric high-performance microwave absorbing materials.

3D core-shell Fe3O4@SiO2@MoS2 composites with enhanced microwave absorption performance

In this work, a 3D ternary core-shell Fe₃O₄@SiO₂@MoS₂ composite is synthesized by a hydrothermal technique and a modified Stöber method, where magnetic Fe₃O₄@SiO₂ microsphere with the core of raspberry-like Fe₃O₄ nanoparticles is completely coated by the flower-like MoS₂. Herein, the electromagnetic parameters of the composites are effectively tuned by the combination of magnetic Fe₃O₄ with dielectric SiO₂ and MoS₂. The obtained ternary composites exhibit remarkable enhancement of microwave absorption. The measurement results indicate that the minimum reflection loss (RL) of Fe₃O₄@SiO₂@MoS₂ composites reaches -62.98 dB at 1.83 mm with the effective absorption bandwidth (RL < -10 dB) of 5.76 GHz (from 11.28 to 17.04 GHz) at 1.92 mm, much higher than those of pure Fe₃O₄ particles and Fe₃O₄@SiO₂ microsphere. It is believed that the improved performances come from the specific structural design and the plentiful interfacial construction. Further, the synergistic effect of the dielectric and magnetic loss as well as the promoted impedance matching also help to enhance the microwave absorption of the composites. The microwave absorption behavior of the composites conforms to the quarter-wavelength cancellation theory. Our study offers an effective and promising strategy in the structural design and interfacial construction of the novel magnetic/dielectric composites with high-efficiency microwave absorption.

Hydrothermal Synthesis of Various Magnetic Properties of Controlled Micro/Nanostructured Powders and Films of Rare-Earth Iron Garnet

In this study, the synthesis and magnetic properties of the rare-earth iron garnets Sm₃Fe₅O₁₂, Pr₃Fe₅O₁₂, and Er₃Fe₅O₁₂ (in the form of powders and thin films) are reported. According to the composition, shape, and size of particles, the optimal precipitant for the synthesis of Sm₃Fe₅O₁₂, Pr₃Fe₅O₁₂, and Er₃Fe₅O₁₂ films is an aqueous solution. The parameters for the synthesis of powders and films of the rare-earth iron garnets with micro- and nano-particles have been investigated and selected. The magnetic properties of these materials were studied; field dependencies of the magnetic moment (hysteresis loops) of nanostructured powders of iron garnets of samarium, praseodymium, and erbium in the range of +20 kOe to −20 kOe were obtained. The structural features of the Al₂O₃ substrate on which the films were formed are also shown.