Composition Optimization and Microstructure Design in MOFs-Derived Magnetic Carbon-Based Microwave Absorbers: A Review.

Magnetic carbon-based composites are the most attractive candidates for electromagnetic (EM) absorption because they can terminate the propagation of surplus EM waves in space by interacting with both electric and magnetic branches. Metal-organic frameworks (MOFs) have demonstrated their great potential as sacrificing precursors of magnetic metals/carbon composites, because they provide a good platform to achieve high dispersion of magnetic nanoparticles in carbon matrix. Nevertheless, the chemical composition and microstructure of these composites are always highly dependent on their precursors and cannot promise an optimal EM state favorable for EM absorption, which more or less discount the superiority of MOFs-derived strategy. It is hence of great importance to develop some accompanied methods that can regulate EM properties of MOFs-derived magnetic carbon-based composites effectively. This review comprehensively introduces recent advancements on EM absorption enhancement in MOFs-derived magnetic carbon-based composites and some available strategies therein. In addition, some challenges and prospects are also proposed to indicate the pending issues on performance breakthrough and mechanism exploration in the related field.

Heterogeneous Interface Induced the Formation of Hierarchically Hollow Carbon Microcubes against Electromagnetic Pollution.

Carbon materials with multilevel structural features are showing great potentials in electromagnetic (EM) pollution precaution. With ZIF-67 microcubes as a self-sacrificing precursor, hierarchical carbon microcubes with micro/mesoporous shells and hollow cavities have been successfully fabricated with the assistance of rigid SiO2 coating layers. It is found that the SiO2 layer can effectively counteract the inward shrinkage of organic frameworks during high-temperature pyrolysis due to intensive interfacial interaction. The obtained hollow porous carbon microcubes (HPCMCs) exhibit larger Brunauer-Emmett-Teller surface area and pore volume than porous carbon microcubes (PCMCs) directly derived from ZIF-67 microcubes. The unique microstructure is confirmed to be favorable for conductive loss and interfacial polarization, thus boosting the overall dielectric loss capability of carbon materials. Besides, hollow cavity will also promote multiple reflection of incident EM waves and intensify the dissipation of EM energy. As expected, HPCMCs harvest better microwave absorption performance, including strong reflection loss intensity and broad response bandwidth, than many traditional microporous/mesoporous carbon materials. This study provides a new strategy for the construction of hierarchical carbon materials and may inspire the design of carbon-based composites with excellent EM functions.

Solvent-Free Synthesis of Ultrafine Tungsten Carbide Nanoparticles-Decorated Carbon Nanosheets for Microwave Absorption.

Carbides/carbon composites are emerging as a new kind of binary dielectric systems with good microwave absorption performance. Herein, we obtain a series of tungsten carbide/carbon composites through a simple solvent-free strategy, where the solid mixture of dicyandiamide (DCA) and ammonium metatungstate (AM) is employed as the precursor. Ultrafine cubic WC1-x nanoparticles (3-4 nm) are in situ generated and uniformly dispersed on carbon nanosheets. This configuration overcomes some disadvantages of conventional carbides/carbon composites and is greatly helpful for electromagnetic dissipation. It is found that the weight ratio of DCA to AM can regulate chemical composition of these composites, while less impact on the average size of WC1-x nanoparticles. With the increase in carbon nanosheets, the relative complex permittivity and dielectric loss ability are constantly enhanced through conductive loss and polarization relaxation. The different dielectric properties endow these composites with distinguishable attenuation ability and impedance matching. When DCA/AM weight ratio is 6.0, the optimized composite can produce good microwave absorption performance, whose strongest reflection loss intensity reaches up to - 55.6 dB at 17.5 GHz and qualified absorption bandwidth covers 3.6-18.0 GHz by manipulating the thickness from 1.0 to 5.0 mm. Such a performance is superior to many conventional carbides/carbon composites.

Polyaniline: A New Metal-Free Catalyst for Peroxymonosulfate Activation with Highly Efficient and Durable Removal of Organic Pollutants.

Metal-free heterogeneous catalysts are receiving more and more attention for wastewater remediation by activating peroxymonosulfate (PMS) due to their environmental benign. However, carbon-based materials as the most typical metal-free heterogeneous always suffer from poor durability. Inspired by the fact that a conjugated system may facilitate the electron transfer during PMS activation, we innovatively select polyaniline (PANI) as a new PMS activator and investigate its catalytic performance in detail. It is found that PANI can display better catalytic performance than traditional metal-based catalysts and popular N-doped carbocatalysts in methyl orange (MO) degradation. More importantly, PANI is not only universal for various pollutants degradation but also maintains its catalytic performance in repeated degradation experiments. The stable N sites in the conjugated chains and the oxidation-resistance benzene rings as the building units are considered to be responsible for such an excellent durability. In addition, the influences of some routine factors and actual water backgrounds are comprehensively checked and analyzed. The quenching experiments and electron paramagnetic resonance confirm that MO degradation is achieved through both radical and nonradical pathways, where SO4•- and 1O2 are primary reactive species. The reaction mechanism is also proposed with the assistance of X-ray photoelectron spectroscopy.

Reduced graphene oxide decorated with carbon nanopolyhedrons as an efficient and lightweight microwave absorber.

Graphene-based composites are becoming a new kind of microwave absorbers that can overcome the challenges related to the performance and light weight in electromagnetic pollution precaution. Herein, a series of reduced graphene oxide decorated with carbon nanopolyhedrons (CNPs/rGO) composites have been successfully fabricated through in situ pyrolysis of ZIF-8/GO hybrids. It is found that GO can restrain the growth of ZIF-8 crystals and produce small-size CNPs after high-temperature pyrolysis, and CNPs will suppress the re-stacking of rGO nanosheets. More importantly, the coupling of CNPs and rGO not only generates the desirable synergistic effects, but also accounts for the profitable interfacial polarization. Therefore, the electromagnetic parameters and microwave absorption properties of these composites can be rationally modulated in terms of the amount of GO. The optimized CNPs/rGO composite exhibits strong reflection loss [-66.2 dB (6.2 GHz, 2.89 mm)] and broad qualified bandwidth (over -10 dB in 3.2-18.0 GHz with integrated absorber thickness of 1.0-5.0 mm), which are superior to many graphene-based composites with high-density magnetic components. Electromagnetic analysis reveals that good attenuation ability and impedance matching are responsible for its excellent performance. It is believed that these results may inspire the design of lightweight microwave absorbers in the future.

A simulation of current focusing and steering with penetrating optic nerve electrodes.

OBJECTIVE: Current focusing and steering are both widely used to shape the electric field and increase the number of distinct perceptual channels in neural stimulation, yet neither technique has been used for an optic nerve (ON)-based visual prosthesis. In order to evaluate the effects of current focusing and steering in penetrative stimulation, we built an integrated computational model to simulate and investigate the influence of stimulating parameters on ON fibre recruitment. APPROACH: Finite element models with extremely fine meshes were first established to compute the 3D electric potential distribution under different stimulating parameters. Then the external electric potential was fed to randomized multi-compartment cable models to predict the distribution of fibres generating an action potential. Finally a statistical process was conducted to quantify the recruitment region. MAIN RESULTS: The simulation results show that a two-electrode mode is superior to a three-electrode mode in current steering. The three-electrode mode performs poorly in current focusing, albeit the localized recruitment from both configurations implies that current focusing might be unnecessary in penetrative ON stimulation. SIGNIFICANCE: This study provides useful information for the optimized design of penetrating ON electrodes and stimulating strategies. The Monte Carlo style computation paradigm is designed to simulate neural responses of an ensemble of ON fibres, which can be immediately transferred to other similar problems.

Acoustically penetrable optical reflector for photoacoustic tomography.

Photoacoustic tomography (PAT) detects ultrasound signals generated by the objects after absorbing illuminating photons. However, the widely used piezoelectric ultrasound transducers are generally not optically transparent, which would cause conflicts between the light illumination and the ultrasonic detection in PAT. We report a different acoustically penetrable optical reflector (APOR) concept to provide a solution to this conflict. We measured the properties of an APOR and experimentally tested its performance in a PAT system. The results demonstrated that the APOR successfully allowed the transducer to detector photoacoustic signals without affecting the light illumination. Moreover, the APOR concept can be readily implemented in various PAT systems.

[Advanced research in Sclera collagen cross-linking treating progressive myopia].

Collagen can link between or within collagen molecules through the covalent bond, which leads to increasing the tension and stability of collagen fiber. Collagen cross-linking had been widely used in other industries, the recent research showed that cross-linking of scleral collagen increased the scleral biomechanical rigidity efficiently, which might become a new treatment modality for strengthening scleral tissue to prevent progressive myopia. This review describes the sclera collagen characteristics of progressive myopia, traditional treatment and sclera collagen cross-linking therapy.