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Tetracycline antibiotics (TCs) are widely present in wastewater and surface water due to their extensive use. Removal of TCs from water is urgent. In this study, magnetic cellulose (MC) composites were prepared from cattailresidues to adsorb oxytetracycline hydrochloride (OTC·HCl), chlortetracycline hydrochloride (CTC·HCl), and tetracycline hydrochloride (TC·HCl) from water. The influence of Fe3O4content on the antibiotics removal was studied. The synthesized MC composites were characterized using FTIR, XPS, zeta potential, SEM, and XRD. Adsorption mechanisms and characteristics were explored using classic isotherm models (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models) and common kinetic models (pseudo-first-order, pseudo-second-order, Elovich and Intraparticle diffusion models). Optimum adsorption capacity was achieved by MC2–1 (mass ratio of cellulose to Fe3O4was 2:1), with a larger specific surface area (18.24 m2g−1) and mesoporous structure. The adsorption processes were well described by the pseudo-second-order and Langmuir models. MC2–1 demonstrated maximum adsorption capacities of CTC·HCl (194.29 mg g−1), OTC·HCl (168.25 mg g−1), and TC·HCl (41.10 mg g−1). The results of models fitting and characterizations of the MC composites before and after the adsorption processes revealed that the main adsorption mechanisms were pore filling, hydrogen bonding, electrostatic interactions, and metal complexation. This study proposes a practical approach for utilizing wetland plant residues as an effective adsorbent for tetracycline antibiotics removal.

An efficient thermal emitter for selective radiative cooling is realized with vanadium dioxide metamaterials. The novel structure consists of patterned VO_2 metamaterials on the multilayer substrate and a composite layer on it. To obtain the enhanced emissivity, the influence of the top composite layer and external thermal stimuli are comprehensively optimized. The emissivity can reach up to 0.952 in the metallic phase of VO_2 with a composite layer in the atmospheric window, which is due to strong localization of the electric field in the cavity. The influence on the emissivity with different incident angles and geometric parameters is investigated elaborately. Finally, the cooling power is calculated and achieves a high value of 710W/m^2 at 383 K, which is significantly higher than that of previous works. Thus, our proposed tunable emitter with high performance will be beneficial to the dynamic radiative cooling system and may open a potential application in building cooling and intelligent windows.

In this work, actively tunable and enhanced optical properties are investigated elaborately with graphene metamaterials, which consists of a π-shaped resonator and a hollow rectangular resonator. The unit cell is periodically arranged on the dielectric substrate. An obvious plasmon-induced transparency (PIT) effect is achieved through destructive interference between these two resonators. The tunable transparency window can be well regulated with the Fermi energy and polarization angle. Specifically, padding a gain medium onto the graphene metamaterials, the intrinsic loss of the system can be greatly compensated, and the resonant intensity gets amplified to achieve a dramatic stimulated emission of radiation with a low gain threshold. Meanwhile, tunable radiation emission is also realized by adjusting the polarization angle. This gain-assisted double-resonant amplification is intensively investigated to compensate the system loss and demonstrate the brilliant performance of the lasing spaser. To the best of our knowledge, these bifunctional plasmonic metamaterial-enabled tunable and enhanced optical properties are rarely investigated. This work demonstrates a novel modulation strategy to get tunable PIT resonance and paves the way toward designing adjustable lasing spasers with metamaterials.

A distinct plasmon-induced transparency (PIT) window has been realized in our novel design of |+|-shaped graphene metamaterials, which consist of two identical graphene strips and a cross-shaped graphene resonator in the right middle. The two strips serve as the dark resonator, and the cross-shaped graphene plays the bright one. Active control of the PIT window can be modulated from the on state to the off state only by breaking structure symmetry. Furthermore, the PIT window can be dynamically adjusted with different Fermi energies in a non-contact way. More importantly, the proposed metamaterial structure achieves a maximum group delay of 13.28 ps, which is much higher than that in the previous paper. In the case of sensing application, the position of the PIT window has been investigated with different embedded media, and it shows a linear function of the refraction index. This study may open up new avenues for the development of highly integrated optical filters, optical sensors, or integrated optical switches.

We present diffractive optical elements with an extended depth of focus, namely, fractal spiral zone plates (FSZPs), which combine a fractal structure and spiral zone plates (SZPs) to generate a sequence of coaxial vortices in the focal volume along the propagation direction. The axial irradiance of the FSZPs is examined both experimentally and in a simulation and is compared with that of SZPs and that of fractal zone plates. The focusing properties of the FSZPs with different parameters are investigated, and a potential application to edge-enhancement images is also shown.

Silver rod nanoparticles with three different aspect ratios were obtained adopting the seed mediated growth method, where the seed solution of the silver nanoparticles is 0.06, 0.15, and 0.2 mL, respectively. Utilizing the plasmon resonance of the silver rod nanoparticles, we fabricate the SERS substrate with the superparamagnetic nanoparticles, which renders the substrate with magnetic field controllability. By tuning the magnitude of the magnetic field from 1450, 1900, 2500 to 3500 gauss, Raman optical activity was carried out with the crystal violet (CV) as a probed molecule. The experimental results show that enhanced and repeatable Raman spectra can be obtained with increased magnetic field and the detection limit can reach 10−10M, which was caused by the uniform array of the metallic nanoparticles. Moreover, the aspect ratio was another factor to tune the plasmon resonant properties of the silver rod nanoparticles. Thus, controllable SERS activity can be obtained based on our prepared composite SERS substrate, which renders it a feasible way to broaden its application in the single molecule detection and biomedicine diagnostic in a controlled way.

We demonstrate theoretically an analogue of electromagnetically induced transparency (EIT) at visible frequencies in an all-dielectric metamaterial-waveguide (ADMW) system that consists of a two-dimensional silicon nanopillar array on top of a dielectric slab waveguide. By varying the lattice period of the array, we show that the transmission feature of the hybridized ADMW system can be efficiently engineered due to the period-dependent guided modes. For ADMW systems with different lattice periods, the EIT-like transparency windows are confirmed either from the two detuned guided modes in the waveguide layer or from the Fano-type interference between the guided modes and the magnetic dipole mode in silicon nanopillars. We have also demonstrated the significant electric field enhancement in the waveguide layer and the remarkable slow-light effect associated with the EIT-like transmission. Compared with the hybrid waveguide-plasmon system including a metal-resonator array, the silicon-based ADMW system enables production of high Q-factor resonances with low absorption losses, thereby having promising applications in low-loss slow-light devices, bio/chemical sensing, enhancing emission rate, and optical modulation.

A tunable multiple band THz metamaterial perfect absorber (MPA) is proposed and investigated numerically, which is believed to be applicable for both temperature and refractive index sensing in THz region. Distinct from previous designs, the proposed MPA is only consisted of a structured indium antimonide (InSb) metamaterial layer, a dielectric layer and a metallic layer. Numerical results demonstrate that three resonant peaks with 100% absorptance at 1.17 THz, 1.60 THz and 2.17 THz can be achieved simultaneously. The impedance matching theory, the electric field, surface current and magnetic field distribution are used to explain the physical mechanism of the MPA. It is worth to mention that the number of perfect absorption peaks can be flexibly tuned from two to five band though breaking the symmetry of patterned InSb array. Furthermore, the absorption property of the designed MPA is found to be highly sensitive to the variations of the surrounding mediums and fluctuations of external environment temperature. Thus, the proposed MPA can not only operate as a temperature sensor with a sensitivity of 22.0 GHz/K, but also a refractive index sensor with a sensitivity of 287 GHz/RIU (refractive index unit). Due to its high sensing performance, our proposed tunable multiple band THz MPA can be widely applied into the material detection, thermal biosensing and other related optoelectronic fields.

We demonstrate theoretically an analog of electromagnetically induced transparency (EIT) in the plasmonic metamaterial with the unit cell consisting of three parallel metallic rods. The electromagnetic mechanism for the EIT-like transmission is discussed based on our investigation of the localized surface plasmon resonances in three trirod configurations. We find that the transmission minima surrounding the transparency window on both sides correspond to two detuned magnetic resonances, which arise respectively from the antiphase plasmon couplings between a long rod and a short rod and between two short rods. A decrease of more than 10 times in the group velocity can be achieved for the trirod structure at the transparency window in the optical regime, and the EIT-like response can be well described by the theoretical model of two harmonic oscillators. This work not only reveals the EIT-like transmission in plasmonic metamaterial consisting of detuned magnetic “atoms,” but also provides further insight into the plasmons’ interactions, especially for metallic nanostructures comprising multiple metallic elements.

Chlortetracycline (CTC) contamination of aquatic systems has seriously threatened the environmental and human health throughout the world. Conventional biological treatments could not effectively treat the CTC industrial wastewater and few studies have been focused on the wastewater systematic treatment. Firstly, 40.0 wt% of clay, 30.0 wt% of dewatered sewage sludge (DSS), and 30.0 wt% of scrap iron (SI) were added to sinter the new media (cathode-anode integrated ceramic filler, CAICF). Subsequently, the nontoxic CAICF with rough surface and porous interior packed into ME reactor, severing as a pretreatment step, was effective in removing CTC residue and improving the wastewater biodegradability. Secondly, expanded granular sludge bed (EGSB) and sequencing batch reactor (SBR), serving as the secondary biological treatment, were mainly focusing on chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) removal. The coupled ME-EGSB-SBR system removed about 98.0% of CODcr and 95.0% of NH3-N and the final effluent met the national discharged standard (C standard of CJ 343-2010, China). Therefore, the CTC industrial wastewater could be effectively treated by the coupled ME-EGSB-SBR system, which has significant implications for a cost-efficient system in CTC industrial systematic treatment and solid wastes (DSS and SI) treatment.