Template-free synthesis of Bi2O2CO3 hierarchical nanotubes self-assembled from ordered nanoplates for promising photocatalytic applications

Modulating Surface-Adsorbed Oxygen Species of Bismuth Silicate by a Solid Solution Strategy for Efficient Adsorption and Photocatalytic Activity

Bismuth silicate photocatalysts suffer from insufficient photocatalytic activity due to an insufficient number of surface active sites and low carrier separation and transport efficiency, which can be solved by defect modulation. Herein, Bi12SiO20/Bi2O2SiO3-BiOClxBr1-x (BSOCB) photocatalysts with a high concentration of surface-adsorbed oxygen species (SAOS) are synthesized by introducing a BiOClxBr1-x solid solution to modify nonhomogeneous BSO via an ion exchange strategy. The introduction of a solid solution enables the generation of dispersed nanoflowers and the regulation of SAOS due to the fact that anion-cation copolymerization guides the crystal growth, and the defects generated by the lattice distortion modulate the concentration of SAOS on the catalysts during the solid solution process. The obtained typical BSOCB photocatalyst possesses both high adsorption and photocatalytic properties, and the results show that it not only can almost completely degrade the traditional pollutant RhB within 20 min but also strongly degrades antibiotics, such as CIP (light for 150 min, 96%), NFX (light for 150 min, 87%), and TC (light for 150 min, 77%). This work provides a new approach for obtaining bismuth-based photocatalysts with controllable morphology and a large number of surface active sites and provides a theoretical and experimental basis for expanding the application scenarios of photocatalysts.

Multi-band perfect absorber based on an elliptical cavity coupled with an elliptical metal nanorod

We proposed a triple-band narrowband device based on a metal-insulator-metal (MIM) structure in visible and near-infrared regions. The finite difference time domain (FDTD) simulated results illustrated that the absorber possessed three perfect absorption peaks under TM polarization, and the absorption efficiencies were about 99.76%, 99.99%, and 99.92% at 785 nm, 975 nm, and 1132 nm, respectively. Simulation results matched well with the results of coupled-mode theory (CMT). Analyses of the distributions of the electric field indicated the "perfect" absorption was due to localized surface plasmon polaritons resonance (LSPPR) and Fabry-Perot resonance. We developed a multi-band absorber with more ellipsoid pillars. The four band-absorbing device presented perfect absorption at 767 nm, 1046 nm, 1122 nm, and 1303 nm, and the absorption rates were 99.45%, 99.41%, 99.99%, and 99.94%, respectively. By changing the refractive index of the surrounding medium, the resonant wavelengths could be tuned linearly. The maximum sensitivity and Figure of Merit were 230 nm RIU-1 and 10.84 RIU-1, respectively. The elliptical structural design provides more tuning degrees of freedom. The absorber possessed several satisfactory performances: excellent absorption behavior, multiple bands, tunability, incident insensitivity, and simple structure. Therefore, the designed absorbing device has enormous potential in optoelectronic detection, optical switching, and imaging.

Experimental and theoretical revealing of piezo-photocatalyst Bi2O2CO3 for degradation of ciprofloxacin in water

In this report, we have attempted to experimentally and theoretically reveal a new piezo-photocatalyst Bi2O2CO3 for efficient removal of ciprofloxacin (CIP) from water. Bi2O2CO3 nanoplates were synthesized to evaluate their photocatalytic (irradiation source: simulated-sunlight), piezocatalytic (irradiation source: ultrasonic) and piezo-photocatalytic (irradiation source: simulated-sunlight and ultrasonic) performances for CIP elimination. Under the condition CCIP = 10 mg/L and Ccatalyst = 1 g/L, the piezo-photodegradation rate constant is obtained as kapp = 0.07811 min-1, which surpasses that of photocatalysis (kapp = 0.04686 min-1) and piezocatalysis (kapp = 0.01233 min-1); this phenomenon manifests an obvious piezo-enhanced photocatalytic behavior in terms of the "1 + 1 > 2" principle. The ultrasonic-induced piezoelectric behavior in Bi2O2CO3 nanoplates and involved piezo-photocatalytic mechanism were theoretically elucidated by density functional theory (DFT) and finite-element method (FEM) studies. Additionally, the effects of various factors on the CIP degradation, decomposition mechanism of CIP and toxicity of the decomposition intermediates were also analyzed.

Novel electrospun bead-like Ag2MoO4 nanofibers coated on Ni foam for visible light-driven heterogeneous photocatalysis and high-performance supercapacitor electrodes

Novel Ag2MoO4 nanocomposite fibers were designed to enhance the photocatalytic response and supercapacitor performance of MoO3 grown via the sol-gel electrospinning technique. The Ag2MoO4 nanocomposite fibers exhibit a high specific surface area of 49.3 m2 g-1 comprising nanobeads that aggregate in the fibrous structure. The photodegradation efficiency of Ag2MoO4 was evaluated as 62% under visible light irradiation which improved to 71% with heterogeneous photocatalysis. The Ag2MoO4@Ni foam exhibited a low Rct of 19.6 Ω, and an enhanced specific capacitance of 1445 F g-1 was obtained at 1 A g-1, with 93% of its initial capacitance remaining after 5000 cycles. In addition, the Ag2MoO4//activated carbon asymmetric supercapacitor possesses an excellent energy density of 76.6 W h kg-1 at 743.2 W kg-1 and a noteworthy cycling durability of 91% after 5000 cycles. Our findings demonstrate that the electrospun Ag2MoO4@Ni foam is an important and inexpensive electrode material for supercapacitor applications and visible light-driven heterogeneous photocatalysis, drawing on the synergic effects of Ag and Mo to exhibit much better performance.

Boosted Tetracycline and Cr(VI) Simultaneous Cleanup over Z-Scheme WO3/CoO p-n Heterojunction with 0D/3D Structure under Visible Light

In this study, a Z-Scheme WO₃/CoO p-n heterojunction with a 0D/3D structure was designed and prepared via a simple solvothermal approach to remove the combined pollution of tetracycline and heavy metal Cr(VI) in water. The 0D WO₃ nanoparticles adhered to the surface of the 3D octahedral CoO to facilitate the construction of Z-scheme p-n heterojunctions, which could avoid the deactivation of the monomeric material due to agglomeration, extend the optical response range, and separate the photogenerated electronhole pairs. The degradation efficiency of mixed pollutants after a 70 min reaction was significantly higher than that of monomeric TC and Cr(VI). Among them, a 70% WO₃/CoO heterojunction had the best photocatalytic degradation effect on the mixture of TC and Cr(VI) pollutants, and the removing rate was 95.35% and 70.2%, respectively. Meanwhile, after five cycles, the removal rate of the mixed pollutants by the 70% WO₃/CoO remained almost unchanged, indicating that the Z-scheme WO₃/CoO p-n heterojunction has good stability. In addition, for an active component capture experiment, ESR and LC-MS were employed to reveal the possible Z-scheme pathway under the built-in electric field of the p-n heterojunction and photocatalytic removing mechanism of TC and Cr(VI). These results offer a promising idea for the treatment of the combined pollution of antibiotics and heavy metals by a Z-scheme WO₃/CoO p-n heterojunction photocatalyst, and have broad application prospects: boosted tetracycline and Cr(VI) simultaneous cleanup over a Z-scheme WO₃/CoO p-n heterojunction with a 0D/3D structure under visible light.

High confidence plasmonic sensor based on photonic crystal fibers with a U-shaped detection channel

In order to improve the performance of optical fiber sensing and expand its application, a photonic crystal fiber (PCF) plasmonic sensor with a U-shaped channel based on surface plasmon resonance (SPR) is proposed. We have studied the general influence rules of structural parameters such as the radius of the air hole, the thickness of the gold film and the number of U-shaped channels using COMSOL based on the finite element method. The dispersion curves and loss spectrum of the surface plasmon polariton (SPP) mode and the Y-polarization (Y-pol) mode as well as the distribution of the electric field intensity (normE) under various conditions are studied using the coupled mode theory. The maximum refractive index (RI) sensitivity achieved in the RI range of 1.38-1.43 is 24.1 μm RIU^-1, which corresponds to a full width at half maximum (FWHM) of 10.0 nm, a figure of merit (FOM) of 2410 RIU^-1 and a resolution of 4.15 × 10^-6 RIU. The results show that the proposed sensor combines the SPR effect, which is extremely sensitive to changes in the RI of the surrounding medium and realizes real-time detection of the external environment by analyzing the light signal modulated by the sensor. In addition, the detection range and sensitivity can be extended by adjusting the structural parameters. The proposed sensor has a simple structure with excellent sensing performance, which provides a new idea and implementation method for real-time detection, long-range measurement, complex environment monitoring and highly integrated sensing, and has a strong potential practical value.

Tunable broadband absorber based on a layered resonant structure with a Dirac semimetal

With the development of science and technology, intermediate infrared technology has gained more and more attention in recent years. In the research described in this paper, a tunable broadband absorber based on a Dirac semimetal with a layered resonant structure was designed, which could achieve high absorption (more than 0.9) of about 8.7 THz in the frequency range of 18-28 THz. It was confirmed that the high absorption of the absorber comes from the strong resonance absorption between the layers, and the resonance of the localised surface plasmon. The absorber has a gold substrate, which is composed of three layers of Dirac semimetal and three layers of optical crystal plates. In addition, the resonance frequency of the absorber can be changed by adjusting the Fermi energy of the Dirac semimetal. The absorber also shows excellent characteristics such as tunability, absorption stability at different polarisation waves and incident angles, and has a high application value for use in radar countermeasures, biotechnology and other fields.

Construction of Z-Scheme Ag2MoO4/ZnWO4 Heterojunctions for Photocatalytically Removing Pollutants

Facilitation of the photocarrier separation is a crucial strategy for developing highly efficient photocatalysts in eliminating environmental pollutants. Herein we have developed a new kind of Ag2MoO4/ZnWO4 (AMO/ZWO) composite photocatalysts with a Z-scheme mechanism by anchoring AMO nanoparticles onto ZWO nanorods. Multiple characterization methodologies and density functional theory (DFT) calculations were employed to study the performances of the AMO/ZWO heterojunctions as well as the underlying photocatalytic mechanism. Simulated-sunlight-driven photodegradation experiments for removing methylene blue (MB) demonstrates that the 8%AMO/ZWO heterojunction can photocatalytically remove 99.8% of MB within 60 min, and the reaction rate constant is obtained as 0.10199 min-1, which is enhanced by 6.8 (or 4.9) times when compared with that of pure ZWO (or AMO). On the base of the experimental results and DFT calculations, the enhanced photocatalytic mechanism of the AMO/ZWO heterojunctions was revealed to be the efficient separation of photocarriers via a Z-scheme transfer process. In addition, photodegradion of various organic pollutants over 8%AMO/ZWO was further compared and aimed at incorporating it into industrial application in pollutant removal.

Effect of H2O2 @CuONPs in the UV Light-Induced Removal of Organic Pollutant Congo Red Dye: Investigation into Mechanism with Additional Biomedical Study

Hazardous dyes in industrial wastewater are an internationally recognized issue for community health. Nanoparticles synthesized through green protocols are a fascinating research field with numerous applications. The current study mainly aimed to investigate the degradation of Congo red (CR) dye under UV light in the presence of H2O2 and the photocatalytic activity of copper oxide nanoparticles (CuONPs). For CuONP formation, Citrus maxima extract contains a high number of phytochemical constituents. The size of CuONPs ranges between 25 and 90 nm. The photocatalytic activity of CuONPs with the addition of H2O2 was observed and analyzed under UV light to eliminate CR dye. The UV light caused the decomposition of H2O2, which produced ·OH radicals. The results revealed a significant increment in dye degradation during the presence of H2O2. The effect of concentration on the degradation of the CR dye was also studied. The degradation pathway of organic pollutants was reputable from the hydroxy radical medicated degradation of CR. Advanced Oxidation Treatment depends on the in situ production of reactive ·OH species and is presented as the most effective procedure for decontamination. The biological activity of CuONPs was evaluated against Escherichia coli Bacillus subtillis, Staphylococcus aureus, Shigella flexenari, Acinetobacter Klebsiella pneumonia, Salmonella typhi and Micrococcus luteus. The newly synthesised nanomaterials showed strong inhibition activity against Escherichia coli (45%), Bacillus subtilis (42%) and Acinetobacter species (25%). The activity of CuONPs was also investigated against different fungus species such as: Aspergillus flavus, A. niger, Candida glabrata, T. longifusus, M. Canis, C. glabrata and showed a good inhibition zone against Candida glabrata 75%, Aspergillus flavus 68%, T. longifusus 60%. The materials showed good activity against C. glaberata, A. flavus and T. longifusus. Furthermore, CuONPs were tested for antioxidant properties using 2, 2 diphenyl-1-picrylhydrazyl) (DPPH).

The Ultrahigh Adsorption Capacity and Excellent Photocatalytic Degradation Activity of Mesoporous CuO with Novel Architecture

In this paper, mesoporous CuO with a novel architecture was synthesized through a conventional hydrothermal approach followed by a facile sintering procedure. HR-TEM analysis found that mesoporous CuO with an interconnected pore structure has exposed high-energy crystal planes of (002) and (200). Theoretical calculations indicated that the high-energy crystal planes have superior adsorption capacity for H⁺ ions, which is critical for the excellent adsorption and remarkable photocatalytic activity of the anionic dye. The adsorption capacity of CuO to methyl orange (MO) at 0.4 g/L was approximately 30% under adsorption equilibrium conditions. We propose a state-changing mechanism to analyze the synergy and mutual restraint relation among the catalyst CuO, H⁺ ions, dye and H₂O₂. According to this mechanism, the degradation rate of MO can be elevated 3.5 times only by regulating the MO ratio in three states.

Construction of a Z-scheme Ag2MoO4/BiOBr heterojunction for photocatalytically removing organic pollutants

How to facilitate photogenerated-carrier separation is an important step in developing excellent semiconductor photocatalysts for environmental pollutant removal. Herein, Ag₂MoO₄ (AMO) nanoparticles were assembled onto the surface of BiOBr (BOB) nanosheets to construct a highly efficient Z-scheme AMO/BOB heterojunction photocatalyst. Several analytical techniques were used to elucidate the characteristics and photocatalytic mechanism of the AMO/BOB heterojunction. Photodegradation experiments for removing methylene blue under simulated-sunlight irradiation reveal that a 20%AMO/BOB heterojunction exhibits excellent photodegradation activity with η(30 min) = 93.8% and k_app = 0.08638 min^-1, which were greater by 4.5 and 5.6 times in comparison with that of pure BOB and AMO, respectively. Based on the experimental and density functional theory (DFT) calculation results, it is proposed that the Z-scheme carrier transfer/separation mechanism dominates the enhanced photodegradation performance of the composite photocatalysts. Additionally, the potential application of AMO/BOB photocatalysts in degrading various organic pollutants (including organic dyes, antibiotics and other serious organic pollutants) was also investigated.

Upconversion boosting pollutants degradation efficiency in wide-spectrum responsive photocatalysts

Recently, the composite photocatalysts coupled with upconversion materials have received widespread attention due to higher utilization efficiency of solar energy in a wide-spectrum range. Novel heterojunction photocatalysts of CoWO₄@NaYF₄:Yb³⁺,Er³⁺ were designed and developed herein. The structural characterization, morphology and elemental composition analysis demonstrated that heterojunctions between CoWO₄ and NaYF₄:Yb³⁺,Er³⁺ were indeed formed in the composite photocatalysts. Moreover, CoWO₄@NaYF₄:Yb³⁺,Er³⁺ heterojunction photocatalysts exhibited higher pollutants degradation efficiency. Especially, a great enhancement of +87% on the photocatalytic activity was achieved in the heterojunction photocatalyst of 60CoWO₄-NaYF₄:Yb³⁺,Er³⁺ compared with pure CoWO₄. The dominant radicals generated from the heterojunction photocatalysts were confirmed as the photo-generated holes (h⁺) and hydroxyl radicals (⋅OH) through the radical species trapping experiments and fluorescence detection, which is fully in line with the expected band structure characteristics of CoWO₄. Eventually, an underlying mechanism was proposed that the enhanced photocatalytic activity should be attributed to the wide-spectrum responsive features of CoWO₄@NaYF₄:Yb³⁺,Er³⁺ heterojunction photocatalysts. Within the heterostructures, CoWO₄ photocatalyst can absorb both the UV-Vis light due to its narrow bandgap and the Near-Infrared energy through the upconversion NaYF₄:Yb³⁺,Er³⁺, thereby utilizing solar energy more efficiently in a wide-spectrum range for photocatalytic reactions.

Synthesis of Co3O4 Nanoparticles-Decorated Bi12O17Cl2 Hierarchical Microspheres for Enhanced Photocatalytic Degradation of RhB and BPA

Three-dimensional (3D) hierarchical microspheres of Bi₁₂O₁₇Cl₂ (BOC) were prepared via a facile solvothermal method using a binary solvent for the photocatalytic degradation of Rhodamine-B (RhB) and Bisphenol-A (BPA). Co₃O₄ nanoparticles (NPs)-decorated BOC (Co₃O₄/BOC) heterostructures were synthesized to further enhance their photocatalytic performance. The microstructural, morphological, and compositional characterization showed that the BOC microspheres are composed of thin (~20 nm thick) nanosheets with a 3D hierarchical morphology and a high surface area. Compared to the pure BOC photocatalyst, the 20-Co₃O₄/BOC heterostructure showed enhanced degradation efficiency of RhB (97.4%) and BPA (88.4%). The radical trapping experiments confirmed that superoxide (^•O₂^-) radicals played a primary role in the photocatalytic degradation of RhB and BPA. The enhanced photocatalytic performances of the hierarchical Co₃O₄/BOC heterostructure are attributable to the synergetic effects of the highly specific surface area, the extension of light absorption to the more visible light region, and the suppression of photoexcited electron-hole recombination. Our developed nanocomposites are beneficial for the construction of other bismuth-based compounds and their heterostructure for use in high-performance photocatalytic applications.

Tunable high-sensitivity sensing detector based on Bulk Dirac semimetal

This paper proposes a tunable sensing detector based on Bulk Dirac semimetals (BDS). The bottom-middle-top structure of the detector is a metal-dielectric-Dirac semimetal. The designed detector is simulated in the frequency domain by the finite element method (FEM). And the simulation results indicate that the detector achieves three perfect absorption peaks with absorptivity greater than 99.8% in the range of 2.4-5.2 THz. We analyze the cause of the absorption peak by using random phase approximation theory. The device exhibits good angular insensitivity in different incident angle ranges, and the three absorption peaks can reach 90% absorption rate when the incident angle is in the ranges of 0-60°. And when adjusting the Fermi level of BDS in the ranges of 0.1-0.5 eV, our detector can realize the frequency regulation of the ultra-wide range of 3.90-4.56 THz and realize multi-frequency controllable sensing while maintain the absorption efficiency above 96%. The detector has maximum sensitivity S of 238.0 GHz per RIU when the external environment of the refractive index changes from 1.0 to 1.8, and the maximum detection accuracy is 6.5. The device has broad development prospects in the field of space detection and high-sensitivity biosensing detection.

Highly sensitive sensing of a magnetic field and temperature based on two open ring channels SPR-PCF

A surface plasmon resonance (SPR) sensor comprising photonic crystal fiber (PCF) is designed for magnetic field and temperature dual-parameter sensing. In order to make the SPR detection of magnetic field and temperature effectively, the two open ring channels of the proposed sensor are coated with gold and silver layers and filled with magnetic fluid (MF) and Polydimethylsiloxane (PDMS), respectively. The sensor is analyzed by the finite element method and its mode characteristics, structure parameters and sensing performance are investigated. The analysis reveals when the magnetic field is a range of 40-310 Oe and the temperature is a range of 0-60 °C, the maximum magnetic field sensitivity is 308.3 pm/Oe and temperature sensitivity is 6520 pm/°C. Furthermore, temperature and magnetic field do not crosstalk with each other's SPR peak. Its refractive index sensing performance is also investigated, the maximum sensitivity and FOM of the left channel sensing are 16820 nm/RIU and 1605 RIU^-1, that of the right channel sensing are 13320 nm/RIU and 2277 RIU^-1. Because of its high sensitivity and special sensing performance, the proposed sensor will have potential application in solving the problems of cross-sensitivity and demodulation due to nonlinear changes in sensitivity of dual-parameter sensing.

Novel scheme towards interfacial charge transfer between ZnIn2S4 and BiOBr for efficient photocatalytic removal of organics and chromium (VI) from water

Construction of Z-scheme heterostructure is an effective strategy to enhance the charge carriers' separation. However, successfully achieving this on the defect heterojunction to improve the photocatalytic activity remains challenging. This work successfully obtained sulfur vacancy in the ZnIn₂S₄/BiOBr (SZIS/BOB) heterojunction composites with S-O covalent bonding using a hydrothermal method. As a result, they exhibited superior photocatalytic and stability performance. The optimized SZIS/BOB-10 exhibited excellent rhodamine B degradation (95.2%) and chromium (VI) reduction (97.8%) within 100 min under visible light. The enhanced composites with S-vacancies, S-O bond, and internal electric field induced the Z-scheme charge transfer mechanism. We had verified this mechanism based on the surface photovoltage spectra, electron spin response spectra, and density functional theory calculations. This work not only provides valuable insights into designing photocatalysts with a direct Z scheme heterostructure but also delineates a promising strategy for developing efficient photocatalysts to degrade organic pollutants.

Two-channel photonic crystal fiber based on surface plasmon resonance for magnetic field and temperature dual-parameter sensing

In this paper, a dual-parameter sensor based on surface plasmon resonance (SPR)-photonic crystal fiber (PCF) is proposed, which can be applied in detecting the magnetic field and temperature. In this sensor, two elliptical channels are designed on both sides of the fiber core. The left channel (Ch 1) is coated with gold film and filled with magnetic fluid (MF) to achieve a response to the magnetic field and temperature using SPR. The right channel (Ch 2) is coated with gold film as well as Ta₂O₅ film to improve the SPR sensing performance. Finally, Ch 2 is filled with polydimethylsiloxane (PDMS) to achieve a response to the temperature. The mode characteristics, structural parameters and sensing performance are investigated by the finite element method. The results show that when the magnetic field is in the range of 50-130 Oe, the magnetic field sensitivities of Ch 1 and Ch 2 are 65 pm Oe^-1 and 0 pm Oe^-1, respectively. When the temperature is in the range of 17.5-27.5 °C, the temperature sensitivities of Ch 1 and Ch 2 are 520 pm °C^-1 and 2360 pm °C^-1, respectively. By establishing and demodulating a sensing matrix, the sensor can not only measure the temperature and magnetic field simultaneously but also solve the temperature cross-sensitivity problem. In addition, when the temperature exceeds a certain value, the proposed sensor is expected to achieve dual-parameter sensing without a matrix. The proposed dual-parameter SPR-PCF sensor has a unique structure and excellent sensing performance, which are important for the simultaneous sensing of multiple basic physical parameters.

Design of Ultra-Narrow Band Graphene Refractive Index Sensor

The paper proposes an ultra-narrow band graphene refractive index sensor, consisting of a patterned graphene layer on the top, a dielectric layer of SiO₂ in the middle, and a bottom Au layer. The absorption sensor achieves the absorption efficiency of 99.41% and 99.22% at 5.664 THz and 8.062 THz, with the absorption bandwidths 0.0171 THz and 0.0152 THz, respectively. Compared with noble metal absorbers, our graphene absorber can achieve tunability by adjusting the Fermi level and relaxation time of the graphene layer with the geometry of the absorber unchanged, which greatly saves the manufacturing cost. The results show that the sensor has the properties of polarization-independence and large-angle insensitivity due to the symmetric structure. In addition, the practical application of testing the content of hemoglobin biomolecules was conducted, the frequency of first resonance mode shows a shift of 0.017 THz, and the second resonance mode has a shift of 0.016 THz, demonstrating the good frequency sensitivity of our sensor. The S (sensitivities) of the sensor were calculated at 875 GHz/RIU and 775 GHz/RIU, and quality factors FOM (Figure of Merit) are 26.51 and 18.90, respectively; and the minimum limit of detection is 0.04. By comparing with previous similar sensors, our sensor has better sensing performance, which can be applied to photon detection in the terahertz band, biochemical sensing, and other fields.

Effect of Higher Carrier Mobility of the Reduced Graphene Oxide-Zinc Telluride Nanocomposite on Efficient Charge Transfer Facility and the Photodecomposition of Rhodamine B

The synthesis of solar-light-responsive zinc telluride (ZnTe) nanoparticles and their composite with reduced graphene oxide (rGO-ZnTe) via a simple hydrothermal reaction is reported. The synthesized nanostructures were comprehensively characterized by a combination of X-ray diffraction and photoelectron spectroscopy, electron microscopy, UV-vis spectroscopy, photoluminescence spectroscopy and thermogravimetric analysis. The effects of graphene oxide on the crystallinity, microstructure, photo-excitation, light absorption, surface area and thermal stability of ZnTe were studied. The current-voltage (I-V) characteristics for both as-synthesized ZnTe and rGO-ZnTe composite-based Schottky devices were measured to estimate the charge transport parameters such as dc conductivity, photosensitivity, carrier's mobility and lifetime. The photocatalytic performance of both the materials in the degradation of an azo dye (Rhodamine B) was subsequently investigated using simulated solar light. The rGO-ZnTe composite exhibited a higher photocatalytic activity (66%) as compared to the as-synthesized ZnTe (23%), essentially due to the synergy between rGO sheets and ZnTe nanoparticles. The role of the carrier's mobility in the transportation of photo-induced charges (electrons and holes) through the complex network of the composite materials and thus facilitating the photo-degradation process is explained. In the end, the responsible reactive species for the decomposition of Rhodamine B was also interpreted.

High-Q refractive index sensors based on all-dielectric metasurfaces

Possessing fantastic abilities to freely manipulate electromagnetic waves on an ultrathin platform, metasurfaces have aroused intense interest in the academic circle. In this work, we present a high-sensitivity refractive index sensor excited by the guided mode of a two-dimensional periodic TiO2 dielectric grating structure. Numerical simulation results show that the optimized nanosensor can excite guided-mode resonance with an ultra-narrow linewidth of 0.19 nm. When the thickness of the biological layer is 20 nm, the sensitivity, Q factor, and FOM values of the nanosensor can reach 82.29 nm RIU-1, 3207.9, and 433.1, respectively. In addition, the device shows insensitivity to polarization and good tolerance to the angle of incident light. This demonstrates that the utilization of low-loss all-dielectric metasurfaces is an effective way to achieve ultra-sensitive biosensor detection.

Perfect Absorption of Fan-Shaped Graphene Absorbers with Good Adjustability in the Mid-Infrared

This paper presents a graphene metamaterial absorber based on impedance matching. A finite difference in time domain (FDTD) method is used to achieve a theoretically perfect absorption in the mid-infrared band. A basis is created for the multiband stable high absorption of graphene in the mid-infrared. The designed graphene absorber is composed of graphene, a dielectric layer, a gold plane, and a silicon substrate, separately. The incident source of mid-infrared can be utilized to stimulate multiband resonance absorption peaks from 2.55 to 4.15 μm. The simulation results show that the absorber has three perfect resonance peaks exceeding 99% at λ1 = 2.67 μm, λ2 = 2.87 μm, and λ3 = 3.68 μm, which achieve an absorption efficiency of 99.67%, 99.61%, and 99.40%, respectively. Furthermore, the absorber maintains an excellent performance with a wide incident angle range of 0°–45°, and it also keeps the insensitive characteristic to transverse electric wave (TE) and transverse magnetic wave (TM). The results above indicate that our perfect graphene absorber, with its tunability and wide adaptability, has many potential applications in the fields of biosensing, photodetection, and photocell.

Metamaterial Solar Absorber Based on Refractory Metal Titanium and Its Compound

Metamaterials refers to a class of artificial materials with special properties. Through its unique geometry and the small size of each unit, the material can acquire unique electromagnetic field properties that conventional materials do not have. Based on these factors, we put forward a kind of high absorption near-ultraviolet to near-infrared electromagnetic wave absorber of the solar energy. The surface structure of the designed absorber is composed of TiN-TiO2-Al2O3 with rectangles and disks, and the substrate is Ti-Al2O3-Ti layer. In the study band range (0.1–3.0 μm), the solar absorber’s average absorption is up to 96.32%, and the designed absorber absorbs more than 90% of the electromagnetic wave with a wavelength width of 2.577 μm (0.413–2.990 μm). Meanwhile, the designed solar absorber has good performance under different angles of oblique incident light. Ultra-wideband solar absorbers have great potential in light absorption related applicaitions because of their wide spectrum high absorption properites.

Natural Volcanic Material as a Sustainable Photocatalytic Material for Pollutant Degradation under Solar Irradiation

Recently, photocatalysis has been demonstrated as a solid approach for efficient wastewater cleaning. Using natural materials as photocatalysts means a promising solution to develop green catalysts for environmental purposes. This work aimed to study the suitability of a natural volcanic material (La Gomera, Canary Islands, Spain) as a photocatalytic material for the degradation of pollutants in wastewater with solar energy. After analysing the properties of the natural material (BET surface 0.188 m²/g and band-gap of 3 eV), the photocatalytic activity was evaluated at laboratory and pilot plant scale for the degradation of methylene blue (MB) in water (50 mg L⁻¹), at 20 °C, during a period of 4 h, under UV/Vis light and solar irradiation. Photolytic and adsorption studies were developed to distinguish the photocatalytic contribution to the wastewater decontamination process by photocatalysis. Our results enable us to determine the viability of black sand as a photocatalytic material activated by solar irradiation (photodegradation of MB up to 100% by using solar energy), developing a natural and green photocatalytic system with significantly high potential for application in a sustainable wastewater cleaning process.

S-Scheme BiOCl/MoSe2 Heterostructure with Enhanced Photocatalytic Activity for Dyes and Antibiotics Degradation under Sunlight Irradiation

Semiconductor photocatalysis is considered to be a promising technique to completely eliminate the organic pollutants in wastewater. Recently, S-scheme heterojunction photocatalysts have received much attention due to their high solar efficiency, superior transfer efficiency of charge carriers, and strong redox ability. Herein, we fabricated an S-scheme heterostructure BiOCl/MoSe₂ by loading MoSe₂ nanosheets on the surface of BiOCl microcrystals, using a solvothermal method. The microstructures, light absorption, and photoelectrochemical performances of the samples were characterized by the means of SEM, TEM, XRD, transient photocurrents, electrochemical impedance, and photoluminescence (PL) spectra. The photocatalytic activities of BiOCl, MoSe₂, and the BiOCl/MoSe₂ samples with different MoSe₂ contents were evaluated by the degradation of methyl orange (MO) and antibiotic sulfadiazine (SD) under simulated sunlight irradiation. It was found that BiOCl/MoSe₂ displayed an evidently enhanced photocatalytic activity compared to single BiOCl and MoSe₂, and 30 wt.% was an optimal loading amount for obtaining the highest photocatalytic activity. On the basis of radical trapping experiments and energy level analyses, it was deduced that BiOCl/MoSe₂ follows an S-scheme charge transfer pathway and •O₂⁻, •OH, and h⁺ all take part in the degradation of organic pollutants.

Grating Structure Broadband Absorber Based on Gallium Arsenide and Titanium

We designed a broadband absorber based on a multilayer grating structure composed of gallium arsenide and titanium. The basic unit is a grating structure stacked on top of a semiconductor of gallium arsenide and titanium metal. We used the finite difference time domain method to simulate the designed model and found that the absorber absorption efficiency exceeded 90% in the range from 736 nm to 3171 nm. The absorption efficiency near perfect absorption at 867 nm was 99.69%. The structure had good angle insensitivity, and could maintain good absorption under both the TE mode and TM mode polarized light when the incident angle of the light source changed from 0° to 50°. This kind of metamaterial grating perfect absorber is expected to be widely used in optical fields such as infrared detection, optical sensing, and thermal electronics.

Study of Optical Information Recording Mechanism Based on Localized Surface Plasmon Resonance with Au Nanoparticles Array Deposited Media and Ridge-Type Nanoaperture

To verify the possibility of multiple localized surface plasmon resonance based optical recording mechanism, the present study has demonstrated that an Au nanoparticles array deposited with media combined with a ridge-type nanoaperture can amplify the |E|² intensity of the incident optical light transmitted into the media under specific conditions. Using a numerical Finite-Difference Time-Domain method, we found that the optical intensity amplification first occurred in the near-field region while penetrating the ridge-type nanoaperture, then the second optical amplification phenomenon was induced between the metal nanoparticles, and eventually, the excitation effect was transferred to the inside of the media. In a system consisting of a Gold (Au) NPs deposited media and nanoaperture, various parameters to increase the |E|² intensity in the near-field region were studied. For an Au nanoparticle size (Cube) = 5 nm × 5 nm × 5 nm, an inter-particle space = 10 nm, and a gap (between nanoaperture and media) = 5 nm, the |E|² intensity of a ridge-type nanoaperture with an Au nanoparticles array was found to be ~47% higher than the |E|² intensity of a ridge-type nanoaperture without an Au nanoparticles array.