Electrospun graphene oxide/MIL-101(Fe)/poly(acrylonitrile-co-maleic acid) nanofiber: A high-efficient and reusable integrated photocatalytic adsorbents for removal of dye pollutant from water samples.

The electrospun graphene oxide/MIL-101(Fe)/poly(acrylonitrile-co-maleic acid) nanofibers (E-spun GO/MIL-101(Fe)/PANCMA NFs) were fabricated by a facile electrospinning method and used as integrated photocatalytic adsorbents (IPAs) to remove dye pollutant from water samples. Compared with E-spun GO/PANCMA and E-spun MIL-101(Fe)/PANCMA NFs, the fabricated E-spun GO/MIL-101(Fe)/PANCMA NFs exhibited higher adsorption ability and excellent photocatalytic activity towards a model pollutant Rhodamine B (RhB). Under the optimized conditions, the as-prepared IPAs achieved almost complete adsorption of RhB within 15 min with the maximum adsorption capacity of 10.46 mg/g. Under visible-light irradiation, 93.7% of RhB in 20 mL water sample was degraded within 20 min, and the degradation kinetics of RhB fitted well with the first-order kinetic model. In addition, LC-MS analysis of the RhB degradation products confirmed the degradation pathways, and the generated •OH radicals played important roles in the degradation process. Importantly, the E-spun GO/MIL-101(Fe)/PANCMA NFs exhibited good reusability and could be reused for consecutive 20 cycles, which make them promising candidate materials in the field of industrial applications and environmental remediation.

All-Dielectric Terahertz Plasmonic Metamaterial Absorbers and High-Sensitivity Sensing.

Two types of plasmonic metamaterial absorbers (PMAs) formed from patterned all-dielectric resonators are designed and demonstrated experimentally in the terahertz (THz) range. Both PMAs use a simple grating design on highly N-doped silicon. The first shows broadband absorption with near-perfect peak absorbance at 1.45 THz and a bandwidth of 1.05 THz for 90% absorbance, while the second is a dual-band absorber. Experiments show that the second absorber has two distinct absorption peaks at 0.96 and 1.92 THz with absorption rates of 99.7 and 99.9%, respectively. A fundamental cavity mode coupled to coaxial surface plasmon polaritons is responsible for the characteristics of both PMAs. Additionally, the optically tunable responses of these all-dielectric absorbers demonstrate that the absorption behavior can be modified. The quality factor (Q) values of the dual-band resonances are 4.6 and 7.8 times larger than those of the broadband PMAs, respectively, which leads to a better sensing performance. As an example, the two proposed PMAs act as high-sensitivity sensors and demonstrate considerable potential for chlorpyrifos detection. These results show that these PMAs can be used as sensors that can detect the presence of trace pesticides in adsorption analyses, among other practical applications.

Development of frequency-tunable multiple-band terahertz absorber based on control of polarization angles.

Controlling and tuning the spectral absorption response of metamaterial absorbers fabricated by arranging a set of resonators in a regular array is challenging. Polarization tunable multi-band terahertz resonant absorbers were developed using anisotropic microstructure arrays. The unit cell consisted of four pairs of H-shaped resonators of different sizes and a metallic ground plane separated by a dielectric layer. Discrete operating frequency shifts and dynamic amplitude tuning were observed by changing the polarization angle. The effect of the polarization angle on the absorption amplitude was evaluated. This work provides a concise approach to realize tunable absorption characteristics, which can be applied in sensors, detectors, and switches.

Multiband terahertz absorber and selective sensing performance.

Multiband terahertz absorbers are essential photonic components for responding to, manipulating, and modulating terahertz waves. In this work, improved electric split resonant ring arrays are used to demonstrate multiband terahertz wave absorption. The proposed design strategy is simple, practical, and significant. Experiments and simulations reveal perfect absorption at 0.918 THz and 1.575 THz for the transverse magnetic (TM) polarization and at 0.581, 1.294, and 1.556 THz for the transverse electric (TE) polarization. In addition, the weak resonant peaks that occurred in the experiments in both polarization states have been verified by the simulations. Furthermore, five concentration gradients of 2, 4-dichlorophenoxyacetic acid solutions and six concentration gradients of chlorpyrifos have been detected using the absorber. The lowest detectable concentration that could be monitored was 0.1 ppm. The absorption, intensity, and frequency shift values for the different solution concentrations at the resonant peaks were analyzed. The highest linear regression coefficients were 0.9862 and 0.9565 for the TE and TM polarizations, respectively. This multi-band absorber was demonstrated to be highly efficient in detecting pesticides for food safety applications.

Tailoring terahertz surface plasmon wave through free-standing multi-walled carbon nanotubes metasurface.

Surface plasmons have a fundamental role in the dynamics of photon-electron interactions and in optical metamaterials. Terahertz (THz) time-domain spectroscopy was used to characterize the complex dielectric constant, index of refraction, and conductivity of super-aligned, free-standing, multi-walled carbon nanotube films over the range 0.2-2.5 THz. These complex parameters were in excellent agreement with Maxwell-Garnett and Drude-Lorentz models. In addition, surface plasmon excitations in engineered, subwavelength, multi-walled carbon nanotube metasurfaces were examined. The observed surface plasmon resonances, reproduced by simulation, could be changed over the THz frequency range by altering the lattice constant of the arrays. The THz transmission was enhanced at the resonance peak. Overall, the results indicate potential applications for THz metasurfaces based on super-aligned, free-standing multi-walled carbon nanotubes.