Tunable optical properties of Au nanoparticles encapsulated TiO2 spheres and their improved sunlight mediated photocatalytic activity

Detection of pesticide residues using flower-like silver SERS substrates based on flexible sponge

In response to the existing issues of cumbersome and time-consuming detection processes and limited application scope in current pesticide residue detection, this paper designed a novel flexible substrate for surface-enhanced Raman spectroscopy (SERS) by combining flower-like silver nanoparticles prepared by chemical reduction technology with a flexible sponge. The flexible substrate exhibits excellent SERS enhancement effects, with a minimum detection limit of 10-12 mol/L for the probe molecule rhodamine 6G (R6G) and an average enhancement factor of 6.63 × 105. For the commonly used pesticide thiram, the minimum detection limit is 0.1 mg/L, which is significantly lower than the maximum residue limits set by China and the USA for thiram. Further experiments confirmed the substrate's excellent uniformity and stability, and the use of finite difference time domain (FDTD) software revealed that the model combining flower-like silver nanoparticles with a sponge exhibited higher electromagnetic field intensity compared to the model without the sponge, resulting in abundant "hot spots". Additionally, the sparrow search algorithm (SSA) was used to optimize the backpropagation (BP) neural network for predicting the concentration of thiram pesticide. The experimental results indicated that the SSA-BP algorithm achieved a determination coefficient (R2) of 0.99974 and root mean square error (RMSE) of 300.321, demonstrating good network performance and meeting the requirements of actual detection needs.

The incident photons cut-off energy, the optical linear equations and the electron phonon interactions in ZnO thin films annealed at different temperatures

The using RF-magnetron sputtering, the ZnO thin films were deposited on glass substrates at room temperature. Then using an electrical furnace in the presence of argon gas, they were annealed at different temperatures (400-600 °C). It was found that with taking N c  = 4, Z a  = 2, N e  = 8 for ZnO films for covalently bonded crystalline and amorphous chalcogenides, the constant β has values of about 0.37 ± 0.04 and for halides and most oxides that have ionic structure the constant β has values of about 0.26 ± 0.04 eV. It can be seen that with increasing annealing temperature absorption edge these films have a shifting behavior towards larger wavelength. Due to shifting behavior of defects distribution of atoms into films, the values of the cut-off energy, E cut-off and the λ cut-off of these films were about 3.48 eV and 355 nm, respectively. The ZnO films annealed at 500 °C specially above 3 eV have maximum value of optical density. The different linears fitting of ln (⍺) for films were obtained as y = Ex + F where 10 Collapse

Key Words

• Annealing temperature
• Electron phonon interaction
• Skin depth
• Steepness parameters
• The ZnO thin films
• The optical linear equations
• The post

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Affiliation(s)

Vali Dalouji Department of Physics, Faculty of science, Malayer University, Malayer, Iran

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Fabrication of Three-Dimensional Dendritic Ag Nanostructures: A SERS Substrate for Non-Invasive Detection

This paper discusses the fabrication of three-dimensional dendritic Ag nanostructures, showcasing pronounced Localized Surface Plasmon Resonance (LSPR) effects. These nanostructures, employed in surface-enhanced Raman scattering (SERS), function as sensors for lactic acid in artificial sweat. The dendritic structures of the silver nanoparticles (AgNPs) create an effective SERS substrate, with additional hotspots at branch junctures enhancing LSPR. We achieve differential LSPR effects by varying the distribution and spacing of branches and the overall morphology. Adjustments to electrodeposition parameters, such as current and plating solution protective agents on an anodized aluminum oxide (AAO) base, allow for precise control over LSPR intensities. By pre-depositing AgNPs, the electron transmission paths during electrodeposition are modified, which leads to optimized dendritic morphology and enhanced LSPR effects. Parameter optimization produces elongated rods with main and secondary branches, covered with uniformly sized, densely packed, non-overlapping spherical AgNPs. This configuration enhances the LSPR effect by generating additional hotspots beyond the branch tips. Fine-tuning the electrodeposition parameters improved the AgNPs' morphology, achieving uniform particle distribution and optimal spacing. Compared to non-SERS substrates, our structure amplified the Raman signal for lactic acid detection by five orders of magnitude. This method can effectively tailor SERS substrates for specific analytes and laser-based detection.

Enhanced photocatalytic removal of bromate in drinking water by Au/TiO2 under ultraviolet light

The photo-reduction of bromate (BrO3 -) has attracted much attention due to the carcinogenesis and genotoxicity of BrO3 - in drinking water. In this study, a heterojunction photocatalyst was developed by depositing Au nanoparticles (NPs) onto P25 TiO2 NPs through a one-pot, solvent-thermal process. Due to the unique properties of Au, the Au NPs deposited on the TiO2 surface created a Schottky barrier between the metal and the semiconductor, leading to an effective separation of photo-generated charge carriers as the Au nanoparticles served as electron sinks. The Au/TiO2 photocatalyst demonstrated efficient reduction of BrO3 - under UV light illumination without the need for sacrificial agents. The effect of different Au loading of Au/TiO2 was systematically investigated for its influence on the generation of electrons and the reduction ability of BrO3 -. The results indicate that the 1% Au/TiO2 catalyst exhibited a higher concentration of localized electrons, rendering it more effective in BrO3 - removal. The photocatalytic efficiency for BrO3 - reduction decreased upon the addition of K2S2O8 as an electron quencher, suggesting that the primary factor in this photo-reduction process was the availability of electrons. These findings hold promise for the potential application of the Au/TiO2 catalyst in the removal of BrO3 - from drinking water through photo-reduction.

Enhanced photocatalytic and SERS performance of Ag nanoparticles functionalized MoS2 nanoflakes

We report the preparation of Ag nanoparticles functionalized MoS2 nanoflakes by using the chemical reduction method followed by the hydrothermal method. Field emission scanning electron microscopy and elemental mapping reveals the uniform functionalization of Ag nanoparticles with MoS2 nanoflakes. High density of Ag plasmonic nanoparticles onto MoS2 nanoflakes demonstrates tremendously improved charge separation behavior in Ag-MoS2 nanohybrids. Photodecomposition capability of plasmonic Ag-MoS2 nanohybrids was explored by the decomposition of industrial pollutant molecules, showing a direct correlation between the Ag content over the MoS2 surface with their photodecomposition ability. The SERS-based detection profiles of the plasmonic were investigated by the ultra-low detection of MB molecules. The Ag-MoS2 nanohybrids SERS substrate manifests the detection of MB molecules solution up to a concentration of 10-9 M with an enhancement factor of 107. In the current study, we proposed and elucidated the probable efficient charge transfer mechanism for improved photocatalytic behavior and SERS-based sensing performance.

Process monitoring of photocatalytic degradation of 2,4-dinitrotoluene by Au-decorated Fe3O4@TiO2 nanoparticles: surface-enhanced Raman scattering method

Recently, the degradation and detection of 2,4-dinitrotoluene (2,4-DNT) capable of producing 2,4,6-trinitrotoluene (TNT) for environmental and human health risks have been developed. We prepared photoresponsive Au-decorated Fe₃O₄@TiO₂ nanoparticles (Fe₃O₄@TiO₂-Au NPs) under sunlight simulated Xe lamp irradiation. The photodegradation process of 2,4-DNT by Fe₃O₄@TiO₂-Au NPs was successfully monitored by surface-enhanced Raman scattering (SERS). Since SERS monitoring shows intrinsic information about the molecular structure, it was possible to predict the photodegradation of 2,4-DNT. The 2,4-DNT photodegradation mechanism based on two-dimensional correlation spectroscopy (2D-COS), which provides very beneficial information for a deeper understanding of systems, has been identified. We confirmed that Fe₃O₄@TiO₂-Au NPs can be widely used in organic pollutant degradation under sunlight. Furthermore, the combination of SERS based process monitoring and 2D-COS can be a convincing analytical technique for photodegradation studies of organic pollutants.

Precise real-time quantification for photocatalytic reaction: integration of the sensitivein-situSERS sensor and high-efficiency photocatalyst

Recently,in-situsurface-enhanced Raman spectroscopy (SERS) is gradually becoming an important method for monitoring photocatalytic reaction processes, in which the quantification potential is a vital factor in determining whether this technology can be truly applied in the future. In order to improve the quantification performance ofin-situSERS and explore a precise operando Raman detection for photocatalytic reactions, an architecture of heterostructural Cu₂O/ZnO/Ag nano round brush has been designed and discussed in this work. This structure is an integration of sensitivein-situSERS sensor and high-efficiency photocatalyst, realizing real-time monitoring of photocatalytic reaction in a wide concentration range from 20 to 3 mg l^-1. The coefficient of determination between different detection methods is beyond 0.86 in this range, implying the high-precise quantification of this platform. Comprehensive analysis on structure effect, SERS performance, photocatalytic property, electric filed characteristic, etc were all systematically made and discussed in detail for this platform. This work presents a precise preliminar real-time photocatalytic monitoring usingin-situSERS detection, which is a new attempt and also meaningful reference for otherin-situanalytical technology.

Photocatalytic selective H2release from formic acid enabled by CO2captured carbon nitride

The selective decomposition of formic acid (FA) traditionally needs to be carried out under high temperature with the noble metal-based catalysts. Meanwhile, it also encounters a separation of H₂and CO₂for pure H₂production. The photocatalytic FA dehydrogenation under mild conditions can meet a growing demand for sustainable H₂generation. Here, we reported a photocatalytic selective H₂release from FA decomposition at low temperature for pure H₂production by Pt/g-C₃N₄. Low-cost and easy-to-obtained urea was utilized to produce carbon nitride as the metal-free semiconductor photocatalyst, along with a photodeposition to obtain Pt/g-C₃N₄. The electrochemical evidences clearly demonstrate the photocatalytic activity of Pt/g-C₃N₄to produce H₂and CO₂in one-step FA decomposition. And, the impedance is the lowest under simulated solar light of 70 mW cm^-2with a faster electron transfer kinetic. Under simulated solar light, H₂production rate is up to 1.59 mmol · h^-1· g^-1for FA with concentration at 2.65 mol l^-1, 1700 000 times larger than that under visible light and 1928 times under ultraviolet (UV) light. DFT calculations further elucidate that nitrogen (N) active site at the g-C₃N₄has an excellent adsorption towards CO₂molecule capture. Then, H₂molecules are selectively released to simultaneously separate H₂and CO₂in solution. Platinum (Pt) at Pt/g-C₃N₄as the catalytic site contributes into the acceleration of H₂production.

Green sol-gel auto combustion synthesis and characterization of double perovskite Tb2ZnMnO6 nanoparticles and a brief study of photocatalytic activity

In this work, new double perovskite Tb₂ZnMnO₆ nanoparticles were successfully synthesized by a sol–gel auto combustion method. To synthesize these nanoparticles, three known sugars, lactose, fructose, and maltose, and liquorice powder, which contains quantities of sugar and other organic compounds, were used as fuel. Images obtained from Scanning Electron Microscopy (SEM) analysis implied that maltose-based nanoparticles are homogenous and less in particle size. Further, different maltose ratios were applied to get the best size and morphology. The optimum sample was used to continue the other analysis to check other features of the nanoparticles. Also, the optimum sample was used for the removal of dye contamination under the photocatalytic process. Photocatalytic tests were performed in neutral and alkaline pH conditions under UV-light irradiation. It has been found that the decolorization percent for methyl orange was about 35% and for methyl violet about 55% at neutral pH. Also, this value for methyl violet was about 90% at pH = 8. The results obtained from the study of photocatalytic properties introduce these nanoparticles as a desirable option for removing dye contaminants from aqueous media.

In this work, new double perovskite Tb₂ZnMnO₆ nanoparticles were successfully synthesized by a sol–gel auto combustion method.