Enhanced electrochemical sensing performance for trace Hg(II) by high activity of Co3+ on Co3O4-NP/N-RGO surface.

Constructing a highly sensitive and selective electrochemical interface is of great significance for the effective detection of Hg2+ in water and biological samples. Herein, Co3O4 nanopolyhedron (NP) anchored on nitrogen-doped reduced graphene oxide (N-RGO) is utilized as the electrode material for the detection of Hg2+ in the range of 0.1 µM-1.0 µM, with high sensitivity (1899.70 µA µM-1 cm-2) and low detection limits (0.03 µM) in natural water. Moreover, the Co3O4-NP/N-RGO modified electrode possesses reasonable anti-interference ability for Hg2+ in the presence of inorganic ions and glucose, which is the basis of its good response to trace Hg2+ in serum. Besides, combined with X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations, the electron transfer tendency is revealed. Additionally, combined with the electron state density of Co-p, it is speculated that Co3+ is an optimum active site for catalytic reaction. The above results elucidate an electrochemically sensitive interface is constructed to realize the efficient detection of Hg2+, which provides some theoretical guidance for the development of electrochemical sensors.

Preferred Film Orientation to Achieve Stable and Efficient Sn-Pb Binary Perovskite Solar Cells.

The preferred orientation of crystalline films in hybrid perovskite materials is known to influence the performance of perovskite solar cells (PSCs). Although the preferred growth along the (112) directions has been reported to promote charge transport within the Pb-based polycrystalline perovskite films, the preferred orientation growth of this facet is still difficult to be achieved due to the higher formation energy compared with the (110) plane. Herein, Sn-Pb binary perovskite films with a well-controlled orientation along the (224) plane were achieved by introducing a simple ultrasonic treatment (UST) into the additive engineering fabricated method. UST is used to process the perovskite precursor solutions of tartaric acid (TA) modified Sn-Pb binary polycrystalline perovskite films to regulate the interactions between PbI2/SnI2 and TA in the intermediate phases. Meanwhile, TA-modulated MA0.9Cs0.1Pb0.75Sn0.25I3-based perovskite films with a preferred orientation of (224) crystal plane were obtained by precisely controlling the UST time to 15 min. The highest power conversion efficiency (PCE) of 15.59% with less hysteresis and improved stability was achieved, while realizing 8.64 and 25.32% enhancements of PCE compared with that of TA-based and control counterparts with (110) preferred orientation, respectively. Our work provides a promising route to obtain preferred orientation growth of polycrystalline perovskite films. In particular, we have shown that this approach improves the performance of Sn-Pb binary PSCs, while such methodology is quite flexible and could also be applied to other low-/non-toxic PSCs.

In-situ surface-enhanced Raman scattering based on MTi20 nanoflowers: Monitoring and degradation of contaminants.

Real-time and in-situ monitoring of chemical reactions has attracted great attention in many fields. In this work, we in-situ monitored the photodegradation reaction process of methylene blue (MB) by Surface enhanced Raman scattering (SERS) technique. An effective and versatile SERS platform assembled from MoS2 nanoflowers (NFs) and TiO2 nanoparticles (NPs) was prepared successfully. The optimized MoS2/TiO2 substrate (MTi20) exhibits not only an ultra-high SERS response but also the excellent catalytic degradation performance to the contaminant MB, which provided a new material for real-time and in-situ monitoring the photodegradation process. Experiments prove that the detection limit is as low as 10-13 M, and degradation rate is as high as 97.2% in 180 s, respectively. And the activity of the substrate kept in the air for 90 days is almost unchanged. Furthermore, as a practical SERS substrate, MTi20 can also detect trace amounts of other harmful substances including malachite green (MG), bisphenol A (BPA) and endosulfan. Thus, this study come up with a new orientation at the real-time and in-situ monitoring of photocatalytic reaction and may be applied in environmental monitoring and food security fields in the future.

Monitoring the charge-transfer process in a Nd-doped semiconductor based on photoluminescence and SERS technology.

Surface-enhanced Raman scattering (SERS) and photoluminescence (PL) are important photoexcitation spectroscopy techniques; however, understanding how to analyze and modulate the relationship between SERS and PL is rather important for enhancing SERS, having a great effect on practical applications. In this work, a charge-transfer (CT) mechanism is proposed to investigate the change and relationships between SERS and PL. Analyzing the change in PL and SERS before and after the adsorption of the probe molecules on Nd-doped ZnO indicates that the unique optical characteristics of Nd3+ ions increase the SERS signal. On the other hand, the observed SERS can be used to explain the cause of PL background reduction. This study demonstrates that modulating the interaction between the probe molecules and the substrate can not only enhance Raman scattering but also reduce the SERS background. Our work also provides a guideline for the investigation of CT as well as a new method for exploring fluorescence quenching.

Detect, remove and re-use: Sensing and degradation pesticides via 3D tilted ZMRs/Ag arrays.

The objective of this study was to design a versatile and reusable pesticide detection surface-enhanced Raman scattering (SERS) substrate in combination with SERS enhancement and self-cleaning properties. In this paper, we present an inexpensive way to synthesize three-dimensional tilted ZnO micron rods with an Ag hierarchical structure (ZMRs/Ag arrays). Although expensive materials and complex methods were not used, the detection limit of thiram residue was 10-11 M, with a quantitative relationship (R2 = 0.9929) between the thiram concentration and the intensity of the SERS peaks. Additionally, the substrates exhibited fast and efficient photocatalytic activity for the degradation of adsorbed thiram, and the degradation rate in 30 min was close 100 % under visible-light irradiation. The enhancement and photocatalytic mechanism of this substrate were meticulously analyzed in detail. Furthermore, the residues of several mixed pesticides (e.g., thiram and methamidophos compounds) in various juices (such as grape, pear, orange, apple, and cherry juices) were quickly detected using ZMRs/Ag substrates. The main advantages of this substrate are recyclability, stability, selectivity, handiness, and cost-eff ;ectiveness. The substrate can prevent single-use problems associated with conventional SERS substrates and can be applied in pesticide residue and food security.

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

Emerging technologies in the field of environmental remediation are becoming increasingly significant owing to the increasing demand for eliminating significant amounts of pollution in water, soil, and air. We designed and synthesized MoS2/Fe2O3 heterojunction nanocomposites (NCs) as multifunctional materials that are easily separated and reused. The trace detection performance of the prepared sample was examined using bisphenol A (BPA) as the probe molecule, with limits of detection as low as 10-9 M; this detection limit is the lowest among all reported semiconductor substrates. BPA was subjected to rapid photocatalytic degradation by MoS2/Fe2O3 NCs under ultraviolet irradiation. The highly recyclable MoS2/Fe2O3 NCs exhibited photo-Fenton catalytic activity for BPA and good detection ability when reused as a surface-enhanced Raman scattering (SERS) substrate after catalysis. The SERS and photocatalysis mechanisms were proposed while considering the effects of the Z-scheme charge-transfer paths, three-dimensional flower-like structures, and dipole-dipole coupling. Moreover, the prepared MoS2/Fe2O3 NCs were successfully applied in the detection of BPA in real lake water and milk samples. Herein, we present insights into the development of MoS2/Fe2O3 materials, which can be used as multifunctional materials in chemical sensors and in photocatalytic wastewater treatments for the removal of recalcitrant organic pollutants.

Plasmon-coupled Charge Transfer in FSZA Core-shell Microspheres with High SERS Activity and Pesticide Detection.

A commercial SERS substrate does not only require strong enhancement, but also can be reused and recycled in actual application. Herein, Fe3O4/SiO2/ZnO/Ag (FSZA) have been synthesised, which consisted of Fe3O4 core with strong magnetic field response and an intermediate SiO2 layer as an electronic barrier to keep the stability of magnetite particles and outer ZnO and Ag as the effective layers for detecting pollutants. The SERS enhancement factor (EF) of the FSZA was ~8.2 × 105. The enhancement mechanism of the FSZA core-shell microspheres were anatomized. The electromagnetic enhancement of surface deposited Ag, charge transfer, and molecular and exciton resonances act together to cause such high enhancement factors. For practical application, the FSZA core-shell microspheres were also used to detect thiram, moreover, which was collected and separated by an external magnetic field, and maintained the SERS activity without significant decline during multiple tests. So the good enhancement performance and magnetic recyclability make the FSZA core-shell microspheres a promising candidates for practical SERS detection applications.

ZnO nanoparticles on MoS2 microflowers for ultrasensitive SERS detection of bisphenol A.

A heterojunction microcomposite was synthesized that consists of ZnO nanoparticles (ZnO NPs) anchored on MoS2 microflowers (MoS2 MFs). The material is shown to enable trace level detection of the pollutant bisphenol A (BPA). The microcomposite was characterized by XRD, XPS, SEM and TEM. In addition, coupling reaction between phenolic estrogens and Pauly's reagents was adopted to greatly enhance the SERS signal. BPA display a characteristic Raman band at 1592 cm-1 which can be used for its selective detection. The assay is highly sensitive and has a 1 nM detection limit which is the lowest among the reported semiconductor substrates. Graphical abstract MoS2/ZnO MCs SERS substrate broke through the application barrier of semiconductor composite materials in SERS substrates. It also sheds light on a deeper understanding of the charge-transfer based enhancement mechanism.

Improved Charge Transfer and Hot Spots by Doping and Modulating the Semiconductor Structure: A High Sensitivity and Renewability Surface-Enhanced Raman Spectroscopy Substrate.

Here, we develop a new method to improve the surface-enhanced Raman spectroscopy (SERS) activity of ZnO using Mg doping combined with noble metals. Highly aligned silver nanoparticles (AgNPs) decorated on an array of Mg-doped ZnO (MZO@Ag) were fabricated. Using rhodamine 6G as the probe molecule, SERS indicated that the MZO@Ag substrate possesses perfect sensitivity, homogeneity, and chemical stability. The enhancement mechanism of this substrate was analyzed in detail, and finite-difference time-domain (FDTD) simulations were used to examine "hot spot" distribution which generated gaps between the balls, the rods, and the stems. FDTD simulation calculated ( E/ E0)4 to be 2.5 × 106. Furthermore, the prepared substrates could degrade the target molecules in situ irradiated by visible light irradiation over the course of 40 min and then efficiently recover detectability through a recycling process. Our substrates were easy to fabricate, self-cleaning, and reusable. They are expected to provide new opportunities for the use of SERS in biological sensors, biomedical diagnostics, and food safety.