Demonstration of Thermally Tunable Multi-Band and Ultra-Broadband Metamaterial Absorbers Maintaining High Efficiency during Tuning Process

Metamaterial absorbers (MMAs) with dynamic tuning features have attracted great attention recently, but most realizations to date have suffered from a decay in absorptivity as the working frequency shifts. Here, thermally tunable multi-band and ultra-broadband MMAs based on vanadium dioxide (VO2) are proposed, with nearly no reduction in absorption during the tuning process. Simulations demonstrated that the proposed design can be switched between two independently designable multi-band frequency ranges, with the absorptivity being maintained above 99.8%. Moreover, via designing multiple adjacent absorption spectra, an ultra-broadband switchable MMA that maintains high absorptivity during the tuning process is also demonstrated. Raising the ambient temperature from 298 K to 358 K, the broadband absorptive range shifts from 1.194–2.325 THz to 0.398–1.356 THz, while the absorptivity remains above 90%. This method has potential for THz communication, smart filtering, detecting, imaging, and so forth

Formation of Yolk–Shell MoS₂@void@Aluminosilica Microspheres with Enhanced Electrocatalytic Activity for Hydrogen Evolution Reaction

The development of low-cost electrode materials with enhanced activity and favorable durability for hydrogen evolution reactions (HERs) is a great challenge. MoS2 is an effective electrocatalyst with a unique layered structure. In addition, aluminosilica shells can not only provide more hydroxyl groups but also improve the durability of the catalyst as a protective shell. Herein, we have designed a hard-template route to synthesize porous yolk–shell MoS2@void@Aluminosilica microspheres in a NaAlO2 solution. The alkaline solution can directly etch silica (SiO2) hard templates on the surface of MoS2 microspheres and form a porous aluminosilica outer shell. The electrocatalytic results confirm that the MoS2@void@Aluminosilica microspheres exhibit higher electrocatalytic activity for HERs with lower overpotential (104 mV at the current density of −10 mA cm−2) and greater stability than MoS2 microspheres. The superior electrocatalytic activity of MoS2@void@Aluminosilica microspheres is attributed to the unique structure of the yolk@void@shell geometric construction, the protection of the aluminosilica shell, and the greater number of active sites offered by their nanosheet subunits. The design of a unique structure and new protection strategy may set up a new method for preparing other excellent HER electrocatalytic materials

Enhanced flexural performance of epoxy polymer concrete with short natural fibers

Epoxy polymer concrete (EPC) has found various applications in civil engineering. To enhance the flexural performance of EPC, two kinds of short natural fibers with high specific strength (sisal fibers and ramie fibers) have been incorporated into EPC. The results of mechanical tests show that a small loading of natural fibers (0.36 vol%) can significantly increase the flexural strength of EPC by 25.3% (ramie fibers) or 10.4% (sisal fibers). This enhancement is achieved without any sacrifice of compressive strength of EPC. The reinforcing effects of short natural fibers on the flexural properties and compressive properties of EPC decrease with further increase in fiber content, due to the insufficient wetting of fibers by epoxy resin which results in poor interfacial bonding. The reinforcing mechanisms of short natural fibers are explored according to the observation of fracture surfaces and micromechanical modelling. It is found that the parallel model based on the rule of mixture can be a good approximation to describe the improvement in flexural strength of the short natural fiber reinforced EPC at low fiber volume fractions

Selective Catalytic Oxidation of H₂S over Well-Mixed Oxides Derived from Mg₂Al_<i>x</i>V_1–<i>x</i> Layered Double Hydroxides

A series of Mg₂Al_<i>x</i>V_1–<i>x</i>–LDH (LDH = layered double hydroxide) was synthesized by using a facile method, and well-mixed derived oxides were obtained after calcinations. These catalysts were further tested for H₂S selective oxidation. Meanwhile, the physicochemical properties of the catalysts were investigated by various methods. It was observed that vanadium species existed mainly in the form of isolated V⁵⁺ in distorted [VO₄],Mg₃V₂O₈ and VO²⁺. Significantly, these catalysts exhibited high catalytic activities in a relatively lower range of reaction temperatures (100–200 °C) as a result of the well-dispersed vanadium species and excellent moderate basicity property. A catalytic reaction mechanism was proposed as follows: H₂S was first adsorbed on the Mg–O–Mg band of MgO (moderate basic sites), forming S^2– and H₂O, then the S^2– was oxidized to S_<i>n</i> by V⁵⁺, simultaneously, forming oxygen vacancies and V⁴⁺. Finally, V⁴⁺ was oxidized to V⁵⁺ by O₂, and O^2– was incorporated into oxygen vacancies. In addition, the catalyst deactivation was mainly due to the decrease in moderate basic sites. Moreover, the formed less-active VOSO₄ also contributed to the catalyst deactivation