Self-cleaning semiconductor heterojunction substrate: ultrasensitive detection and photocatalytic degradation of organic pollutants for environmental remediation

Eco-Friendly Spiking Approach Based on Microfluidics for Preparation of Matrix Reference Materials

Medicated bath is the most common spiking method used in the development of matrix reference materials for aquatic products; however, the environmental issues caused by the treatment of waste liquid after medicated bath cannot be ignored. We proposed an environmentally friendly spiking method based on microfluidics, which significantly improved the drug utilization rate without the need for subsequent drug residue treatment. Finely processed minced fish samples were fully mixed with quinolone drugs, and minced fish gel microspheres were prepared by microfluidic technology, utilizing the gel's water-locking function to enhance the drug-loading capacity. The results showed that this method can significantly increase the drug-loading capacity of the matrix (2.33-4.03 times) compared with the traditional spiking methods. In addition, the matrix reference material prepared by this method has good stability, and the drug concentration was adjustable and controllable.

Simultaneous photocatalytic degradation and SERS detection of tetracycline with self-sustainable and recyclable ternary PI/TiO2/Ag flexible microfibers

Facile and efficient photocatalysts using sunlight, as well as fast and sensitive surface-enhanced Raman spectroscopy (SERS) substrates, are urgently needed for practical degradation of tetracycline (TC). To meet these requirements, a new paradigm for PI/TiO2/Ag organic‒inorganic ternary flexible microfibers based on semiconducting titanium dioxide (TiO2), the noble metal silver (Ag) and the conjugated polymer polyimide (PI) was developed by engineering a simple method. Under sunlight, the photocatalytic characteristics of the PI/TiO2/Ag flexible microfibers containing varying amounts of Ag quantum dots (QDs) were evaluated with photocatalytic degradation of TC in aqueous solution. The results demonstrated that the amount of Ag affected the photocatalytic activity. Among the tested samples, PI/TiO2/Ag-0.07 (93.1%) exhibited a higher photocatalytic degradation rate than PI/TiO2 (25.7%), PI/TiO2/Ag-0.05 (77.7%), and PI/TiO2/Ag-0.09 (63.3%). This observation and evaluation conducted in the present work strongly indicated a charge transfer mechanism. Moreover, the PI/TiO2/Ag-0.07 flexible microfibers exhibited highly sensitive SERS detection, as demonstrated by the observation of the Raman peaks for TC even at an extremely low concentration of 10-10 moles per liter. The excellent photocatalytic performance and SERS detection capability of the PI/TiO2/Ag flexible microfibers arose from the Schottky barrier formed between Ag and TiO2 and also from the outstanding plasmonic resonance and visible light absorptivity of Ag, along with immobilization by the PI. The successful synthesis of PI/TiO2/Ag flexible microfibers holds significant promise for sensitive detection and efficient photocatalytic degradation of antibiotics.

Ni and O co-modified MoS2 as universal SERS substrate for the detection of different kinds of substances

Surface-enhanced Raman scattering (SERS) has attracted extensive attention as an ultrasensitive detection method. However, the poor biocompatibility and expensive synthesis cost of noble metal SERS substrates have become non-negligible factors that limit the development of SERS technology. Metal chalcogenide semiconductors as an alternative to noble metal SERS substrates can avoid these disadvantages, but the enhancement effect is lower than that of noble metal substrates. Here, we report a method to co-modify MoS₂ by Ni and O, which improves the carrier concentration and mobility of MoS₂. The SERS effect of the modified MoS₂ is comparable to that of noble metals. We found that the improved SERS performance of MoS₂ can be attributed to the following two factors: strong interfacial dipole-dipole interaction and efficient charge transfer effect. During the doping process, the incorporation of Ni and O enhances the polarity and carrier concentration of MoS₂, enhances the interfacial interaction of MoS₂, and provides a basis for charge transfer. During the annealing process, the introduction of O atoms into the S defects reduces the internal defects of doped MoS₂, improves the carrier mobility, and promotes the efficient charge transfer effect of MoS₂. The final modified MoS₂ as a SERS substrate realizes low-concentration detection of bilirubin, cytochrome C, and trichlorfon. This provides promising guidance for the practical inspection of metal chalcogenide semiconductor substrates.

Synthesis of recyclable SERS platform based on MoS2@TiO2@Au heterojunction for photodegradation and identification of fungicides

Surface-enhanced Raman spectroscopy (SERS) substrates based on metal/semiconductors have attracted much attention due to their excellent photocatalytic activity and SERS performance. However, they generally exhibit low light utilization and photocatalytic efficiencies. Herein, molybdenum disulfide coated titanium dioxide modified with gold nanoparticles (MoS₂@TiO₂@Au) as a heterojunction-based recyclable SERS platform was fabricated for the efficient determination of fungicides. Results showed that the MoS₂@TiO₂@Au platform could rapidly degrade 90.7% crystal violet in 120 min under solar light irradiation and enable reproducible and sensitive SERS analysis of three fungicides (methylene blue, malachite green, and crystal violet) and in-situ monitor of the photodegradation process. The platform could also be reused five times due to the unique integrated merits of the MoS₂@TiO₂@Au heterojunction. Meanwhile, experiments in determining methylene blue in prawn protein solution achieved a limit of detection of 1.509 μg/L. Therefore, it is hoped that this work could expand detection applications of photocatalytic materials.

Al/TiO2 composite as a photocatalyst for the degradation of organic pollutants

TiO₂ is a catalyst that can effectively degrade organic pollutants with the following advantages, low cost, simplicity, and pollution-free nature. In recent years, the non-noble plasmonic metal Al has effectively improved the photocatalytic performance of TiO₂. However, the current reports are limited to the photocatalytic performance of Al/TiO₂ on the substrate, which requires expensive large-scale vacuum equipment. In this study, monodispersed Al particles were proposed to enhance the photocatalysis of TiO₂. The localized surface plasmon resonance (LSPR) effect of Al is proven by finite difference time domain method (FDTF) simulation. Then, Al/TiO₂ composites were prepared by combining monodispersed Al and TiO₂. The influence of ligand (glutathione (GSH), glutamic acid (GAG), or 3-mercaptopropane acid (MPA)), Al size (40 to 300 nm), and the ratio of Al to TiO₂ (0.5:1 to 10:1) on the photocatalytic degradation of methylene blue (MB) by Al/TiO₂ were discussed. The obtained results showed that the Al/TiO₂ composite which were prepared with 200 nm Al particles, GSH as the ligand bridge, and an Al:TiO₂ ratio of 1:1 had the best MB degradation effect. It can degrade 97.7% of 10 mg/L MB in 100 min. The reaction rate of the Al/TiO₂ composite with the optimal photocatalytic performance is k=3.36×10^-2 min^-1, which is 10 times that of P25 TiO₂. In addition, Al/TiO₂ has a good photocatalytic effect on rhodamine B (RhB) and crystal violet (CV). Therefore, Al/TiO₂ composites with the advantage of high efficiency are a type of potential photocatalytic material that can be used for the photocatalytic treatment of organic pollutants in water.

Synergistic Effect of Paraffin-Incorporated In2O3/ZnO Multifold Smart Glazing Composite for the Self-Cleaning and Energy-Saving Built Environment

The thermal performance of window glazing requires improvement for a sustainable built environment at an acceptable cost. The current work demonstrates a multifold smart composite consisting of an optimized In₂O₃/ZnO-polymethyl methacrylate-paraffin composite to reduce heat exchange through the combined self-cleaning and energy-saving envelope of the smart built environment. This work has attempted to develop a smart composite coating that combines photosensitive metal oxide and phase change materials and investigate their thermal comfort performance as a glazed window. It is observed that the In₂O₃/ZnO (5 wt %) multifold composite film experienced better transmittance and thermal performance compared to its other wt % composite samples. Moreover, the multifold composite-coated glass integrated into a prototype glazed window was further investigated for its thermal performance, where a steady average indoor temperature of ∼30 °C was achieved when the outside temperature reached ∼55 °C, while maintaining good visibility. Interestingly, the transparency reached ∼86% at 60 °C and exhibited a hydrophobic water contact angle (WCA) of ∼138°. In contrast, a similar film exhibits ∼64% transparency at 22 °C, where the WCA becomes moderately hydrophilic (∼68°). Temperature dependency on transparency and wettability properties was examined for up to 60 cycles, resulting in excellent indoor thermal comfort. In addition, a thermal simulation study was executed for the smart multifold glazing composite. Moreover, this study offers dynamic glazing development options for energy saving in the smart built environment.

Surface Plasmon Resonance from Gallium-Doped Zinc Oxide Nanoparticles and Their Electromagnetic Enhancement Contribution to Surface-Enhanced Raman Scattering

In recent years, semiconductor-based surface-enhanced Raman scattering (SERS) substrates have received considerable attention and led to a forefront in the SERS field. However, the lack of electromagnetic (EM) enhancement contributions highly precludes the development of semiconductive-substrate-based SERS. In this study, Ga-doped ZnO nanoparticles (NPs) were fabricated and employed as novel SERS substrates based on the EM enhancement contribution of surface plasmon resonance (SPR). The obtained Ga-doped ZnO NPs exhibited obvious SPR absorptions in the visible and near- and mid-infrared regions. SPR absorption can be readily tuned by changing the doping ratios of Ga³⁺ ions. The SERS spectra of Ga-doped ZnO/4-mercaptopyridine (MPy) were investigated at different excitation wavelengths of 488, 532, 633, and 785 nm. The spectral enhancement of Ga-doped ZnO substrates depended on the doping ratios, excitation wavelengths, and nearby SPR absorption. Ga-doped ZnO NPs with the highest free charge carrier density and the doping ratio of 5% showed the strongest SERS spectra. For the fixed doping ratio of 5%, the better is the match between excitation wavelengths and SPR absorption, the higher is the SERS spectral enhancement. This study showed the feasibility of EM contributions to SERS by using semiconductive substrates and can contribute to the development of the semiconductor-based EM mechanism.