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 SBET 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 Co1.29Ni1.71O4 microspheres were successfully combined with reduced graphene oxide (rGO) to form Co1.29Ni1.71O4/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 Co1.29Ni1.71O4 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 (RLmin) of the Co1.29Ni1.71O4/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.

Achieving super-broad effective absorption bandwidth with low filler loading for graphene aerogels/raspberry-like CoFe2O4 clusters by N doping.

A unique three-dimension (3D) porous network structure where N-doped reduced graphene oxide aerogels (N-rGA) are decorated by raspberry-like CoFe2O4 (CFO) clusters. Super-broad effective microwave absorption bandwidth (7.28 GHz) of the CFO/N-rGA composite is obtained at 2.53 mm by changing N contents. Here, the dipolar relaxation loss and conduction loss are highly sensitive to the presence of pyridinic, pyrrolic and graphitic N in the CFO/N-rGA composites. A minimum reflection loss of the CFO/N-rGA composites reaches up to -55.43 dB at 15.36 GHz with a matching thickness (2.3 mm) and low filler loading (10 wt%). Its effective absorption bandwidth completely covers X-band from 7.76 to 12.72 GHz at 3.3 mm. The high-efficiency microwave absorption of the composites mainly results from the enhanced polarization relaxation, the specific design of conductive network and the superior impedance matching. This study offers a promising technical route to explore new N-doped magnetic/dielectric composites as ideal microwave absorbers.