In this contribution, an Ag/g‐C3N4 nanocomposite was synthesized and utilized as highly efficient and green photocatalyst for organic reactions under visible light irradiation. A layered, porous g‐C3N4 was synthesized following a modified solvothermal‐roasting process by using melamine and cyanuric chloride as precursor. Silver nanoparticles (NPs) were well anchored on g‐C3N4 nanosheets, which were prepared by a facile impregnation–roasting method. The inexpensive, stable g‐C3N4 coupled with the localized surface plasmon resonance (LSPR) effect of Ag NPs exhibited high photocatalytic activities toward aerobic oxidative amidation of aromatic aldehydes under visible light irradiation. Good to excellent yields were achieved for various substrates under the light of a 25 W compact fluorescent light (CFL) bulb in air. The operationally easy procedure provides an economical, green, and mild alternative for the formation of amide bonds.magnified image

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In this paper, we combine the design of band-pass frequency selective surfaces (FSSs) with polarization converters to realize a broadband frequency-selective polarization converter (FSPC) with lowbackward scattering, which consists of the top polarization conversion layer backed by a multi-layer bandpass FSS. It is numerically demonstrated that the 1 dB transmission window can be obtained from 8.5 GHz to 11 GHz with a 25.6% fractional bandwidth (FBW), and the bandwidth of reflection below -10 dB is up to 92% from 5.6 GHz to 15.13 GHz. Moreover, the proposed device can achieve two polarization conversion bands (5.66-6.9 GHz and 12.8-15.2GHz) with the polarization conversion ratio over 90%. Besides, by arranging the proposed structure in a checkerboard-like distribution, the backward scattering energy can be reduced in a wide frequency band ranging from 4 to 16 GHz. Both simulation and experimental results are in good agreements, which demonstrates our design strategy. Compared with the conventional polarization conversion designs, the proposed design presents an extra frequency-selective performance and hence can be applied to various practical situations, for instance, working as radomes to transmit the in-band signals with high-efficiency while keeping low-backward scattering for the out-of-band waves.

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A reflective metasurface based on the quasi‐spiral element is proposed to achieve broadband orbital angular momentum vortex beams for multi‐polarisations. The quasi‐spiral element can provide linear and smooth phase responses covering about 360° from 10 to 15 GHz with a relative bandwidth about 40% by adjusting the length of four phase delay lines. Additionally, the metasurface can generate vortex beams with optional charges in vertical, horizontal and circular polarisations which are determined by the polarisation of feed antenna. Finally,we have designed and fabricated a 24 × 24 cm2 metasurface prototype. The simulated and measured results show that the reflective metasurface can generate broadband vortex beams with orbital angular momentum effectively. As the structure is simple, lightweight and easy to fabricate, the proposed method is applicable to generate broadband vortex beams for multi‐polarisations.