No abstract

EM pollution, because they can convert the EM energy into thermal energy or dissipate the EM waves through interference. [ 4,5 ] Among many kinds of microwave absorbers, carbon materials are always the most attractive candidates due to their tunable properties, relative low density, abundant resource, easy preparation, and low cost. Various carbon materials, e.g., carbon nanotubes (CNTs), carbon nanofi bers (CNF), carbon nanocoils, and mesoporous carbon, have been utilized to construct highly effective microwave absorbers in the past decades. [6][7][8][9][10][11][12] Although these carbon-based materials have made signifi cant progress in the fi eld of microwave absorption, some elaborate innovations on structure and components are still paving the way for exciting performance to satisfy the requirements of practical applications.Recently, graphene appeared as a fascinating material and grabbed worldwide attention, whose unprecedented physical and chemical properties derived from its unique 2D structure have promised great potential in many research fi elds. [ 13 ] Notably, high charge carrier mobility, extraordinary electrical and thermal conductivity also rendered graphene as a new microwave absorber, and it was found that reduced graphene oxide (rGO) provided superior microwave absorption to graphene oxide (GO). [ 14,15 ] However, sole graphene material suffers from limited loss mechanism caused by interfacial impedance mismatching, [ 15,16 ] thus it is usually employed as EM interference shielding material rather than EM absorbing material. [17][18][19] Incorporation of other lossy materials, especially magnetic metal and metal oxides, has been widely studied as the imperative solution to improve the matching of characteristic impedance and enhance the microwave absorption performance. [20][21][22][23][24][25][26][27][28][29] For example, graphene-coated Fe nanocomposites and Ni/graphene composites showed enhanced microwave absorption due to the charge transfer at metal/graphene interface and the polarization of free carriers; [ 20,21 ] Fe 3 O 4 /graphene, rGO-Fe 2 O 3 , and rGO/CNT-Fe 3 O 4 materials demonstrated optimum characteristic impedance and compatible dielectric and magnetic loss, which resulted in their strong refl ection loss in the frequency range of 12.0-16.0 GHz; [21][22][23] Graphene decorated with coreshell Fe@Fe 3 O 4 @ZnO nanoparticles was also fabricated, and Graphene-based composites offer immense potential for overcoming the challenges related to the performance, functionality, and durability in microwave absorption. In this study, a sandwich-like graphene-based composite is successfully fabricated by an interfacial engineering of amorphous carbon microspheres (ACMs) and reduced graphene oxide (rGO), with a structure of rGO/ACMs/rGO. The as-prepared rGO/ACMs/rGO composite presents comparable/superior refl ection loss characteristics in the frequency range of 2.0-18.0 GHz to previous composites of graphene and high-density magnetic particles. Electromagnetic parameters and simulation resu...

Developed from rotating zigzag bed (RZB), the counterflow concentric-ring rotating bed uses a rotor composed of stationary–rotating discs, a set of concentric circular rotating rings with perforations, and a liquid distribution at the eye of the rotor, preserving the outstanding characteristics of RZBs consisting of intermediate feeding and multirotors coaxially installed in series in a casing. A mass-transfer model was proposed from which the local gas- and liquid-side mass-transfer coefficients, gas–liquid effective interfacial area, and height equivalent to theoretical plate (HETP) can be calculated. Total reflux distillation experiments were conducted in a counterflow concentric-ring rotating bed at atmospheric pressure using an ethanol–water system, and the mass-transfer end effects were also investigated. The experimental values of overall volumetric gas-side mass-transfer coefficient and HETP agree with the calculated values very well. Obvious end effects exist in the distillation process, and a correlation which takes inner and outer end effects into consideration is given. Compared with RZB, the counterflow concentric-ring rotating bed has lower mass-transfer efficiency, but it has gas–liquid throughput at least 5.576 times greater than that of RZB. Compared with rotating packed bed, the concentric-ring rotating bed has a much higher local gas-side mass-transfer coefficient.

Alloy/perovskite composites prepared by exsolution of Fe-based perovskite have attracted wide attention due to their embedded and well-anchored structure, which have broad applications in heterogeneous catalysis and energy conversion. Herein, we use Co-doped lanthanum ferrite as a model to study the effect of doping on the B-site exsolution of Fe-based perovskite. CoFe alloy can be exsolved from La0.9Fe0.9Co0.1O3 (LFCO) after heat treatment at 500 °C in a reduced atmosphere, whereas Fe will not be exsolved from La0.9FeO3 (LFO). Density functional theory calculations revealed that the stability of LFCO decreased after Co is doped into the lanthanum ferrite perovskite lattice and the formation energy of the Co–Fe bond on the surface of LFCO is lower than that of Fe–Fe in LFO, which promises an easier exsolution of CoFe alloy than the pristine Fe cluster. In addition, owing to the strong interaction and charge transfer between the exsolved CoFe alloy and parent perovskite, as well as the longer Fe–O bond after exsolution, the exsolved composite can act as an excellent bifunctional electrocatalyst for oxygen evolution and oxygen reduction reactions. Our work not only reveals the mechanism of the alloy exsolution in Fe-based perovskites but also provides a potential route to prepare the highly efficient electrocatalysts.