Resonance Band Research Articles

Silver nanoparticles enhanced luminescence of dysprosium ions doped silica sol-gel

Silver (Ag) nanoparticles/dysprosium (Dy3+) ions co-doped in silica Xerogel having the composition of 5Ag-5Dy-90SiO2 (mol%) have been prepared using the sol-gel method. Spectral diagnosis of Ag NPs in both collide solutions and silica Xerogels shows a typical surface plasmon resonance (SPR) band centered around 431 nm and 426 nm, respectively. The nanoscale and polycrystalline structure of AgNPs was revealed through FE-SEM and XRD. Fourier transform infrared spectroscopy (FTIR) analysis illustrates the distribution of these ions (Ag, Dy3+) in the porous structures of silica Xerogels, in which this spectrum did not display bands arising from the bonding of such ions with the silica structure. The absorption and photoluminescence (PL) spectra, as a function of Dy3+ concentrations, have been recorded at room temperature. Prominent emission bands of Dy3+ ions have been observed for 4F9/2 → 6H13/2: 575 nm and 4F9/2 → 6H15/2: 482 nm at 350 nm excitation. The PL of the Dy3+ doped and AgNPs/Dy3+ co-doped silica xerogel clearly showed that silver NPs improve the (PL) intensity of the Dy3+ions spectra, and this is due to the strong local electric field induced by SPR of silver NPs in order to energy transfer from the silver NPs to Dy3+ ions. The emission cross-section (σem.) and the radiative lifetime (τrad) of the transtion4F9/2 → 6H13/2 have been determined for doped and co-doped samples. The white light emission has been investigated and observed through the Commission International deI’Eclairage (CIE) chromaticity diagram, where the colour coordinates are in the white range for all co-doped samples.

A Novel Method for Identifying Resonance Frequency Band in Weak Bearing Fault Diagnosis of Electric Driving System

Because of the uncertainty of the structure and environment of the electric driving system (EDS), the fault signature of the rotating mechanism is complicated. A novel method based on Hilbert transform with modified fast kurtogram (HTMFK), which is used for identifying the bearing faults in the EDS, is proposed. The modified principle and algorithm flow of the proposed method are derived. A high pass filter based on the frequency band identified by HTMFK is constructed and applied to fault diagnosis. Simulation signals demonstrate the ability of demodulating signals and identifying the fault resonance band. The bearing fault bench experiment of EDS is carried out in a semianechoic chamber. The corresponding fault tests are conducted according to different operating conditions. The applicability of HTMFK is verified by comparing the square envelope spectrums. Compared with other methods, the proposed method identifies the fault resonance frequency band more effectively and expands the application range of bearing fault diagnosis in EDS.

Optical pH Sensor Based on a Long-Period Fiber Grating Coated with a Polymeric Layer-by-Layer Electrostatic Self-Assembled Nanofilm.

An optical fiber pH sensor based on a long-period fiber grating (LPFG) is reported. Two oppositely charged polymers, polyethylenimine (PEI) and polyacrylic acid (PAA), were alternately deposited on the sensing structure through a layer-by-layer (LbL) electrostatic self-assembly technique. Since the polymers are pH sensitive, their refractive index (RI) varies when the pH of the solution changes due to swelling/deswelling phenomena. The fabricated multilayer coating retained a similar property, enabling its use in pH-sensing applications. The pH of the PAA dipping solution was tuned so that a coated LPFG achieved a pH sensitivity of (6.3 ± 0.2) nm/pH in the 5.92-9.23 pH range. Only two bilayers of PEI/PAA were used as an overlay, which reduces the fabrication time and increases the reproducibility of the sensor, and its reversibility and repeatability were demonstrated by tracking the resonance band position throughout multiple cycles between different pH solutions. With simulation work and experimental results from a low-finesse Fabry-Perot (FP) cavity on a fiber tip, the coating properties were estimated. When saturated at low pH, it has a thickness of 200 nm and 1.53 ± 0.01 RI, expanding up to 310 nm with a 1.35 ± 0.01 RI at higher pH values, mostly due to the structural changes in the PAA.

Investigation on the band narrowing and shifting effects of micro-perforated panel absorbers.

Micro-perforated panel (MPP) absorbers exhibit multiple resonance bands with increased bandwidth narrowing and shifting in higher frequencies, limiting their effectiveness. This study investigates the effects of narrowing and shifting in higher-order resonance bands of MPP absorbers. First, an acoustic impedance model for MPP absorbers is introduced, and the narrowing and shifting coefficients are defined and modeled to quantify these effects. It is observed that a larger ratio of acoustic resistance to acoustic mass is favorable for reducing the narrowing and shifting effects. Subsequently, the theoretical model is validated using a numerical model, and a parametric study is conducted to explore the influence of geometric parameters on the narrowing and shifting effects. The study reveals that decreasing aperture and panel thickness, while increasing perforation ratio and cavity depth, reduces the narrowing and shifting coefficients. Remarkably, ultra-micro-perforated panels (UMPPs) with an aperture below 0.1 mm and perforation constant below 0.0046, having relatively larger acoustic resistance and smaller acoustic mass, demonstrate near-zero band narrowing and shifting. Finally, UMPPs are fabricated using micro-electro-mechanical systems (MEMS) technology, and their normal absorption coefficients are measured. Results align with theoretical predictions, confirming UMPPs' ability to achieve zero narrowing and shifting compared to ordinary MPPs and verifying the study's findings.

Magnetic vortex configuration in Fe3O4 nanorings/nanotubes for aspect ratio and magnetic orientation regulated microwave absorption

Morphological structure can greatly affect the magnetic domain of magnetic materials, which plays a significant role on regulating the magnetic characteristics and electromagnetic properties. Herein, Fe3O4 nanorings/nanotubes with adjustable aspect ratio were fabricated through a hydrothermal route followed by reduction annealing treatment. The magnetic flux distributions in radial and axial direction were characterized by electron holography, suggesting that the Fe3O4 nanorings/nanotubes show magnetic vortex structure. The magnetic vortex-domain structure is favored to break the Snoek’s limit of Fe3O4, improving the high-frequency permeability and boosting the natural resonance band to 1 ∼ 10 GHz. Meanwhile the complex permittivity is highly sensitive to the aspect ratio. The Fe3O4 nanorings/nanotubes perform excellent comprehensive microwave absorption properties, owing to the special magnetic vortex structure, tunable complex permittivity, big complex permeability, large magnetization and high natural resonance. The Fe3O4 nanorings with the smallest aspect ratio show a minimum reflection loss (RL) value of −47.9 dB at 2.6 mm and EAB of 4 GHz at 3 mm. Besides, rotational orientation by an external magnetic field can cause the parallel arrangement of nanorings/nanotubes, which can increase both the complex permittivity and broad the resonance band. Rotational orientation can realize effective absorption efficiency at a broader frequency range with a thinner thickness, further improving the comprehensive microwave absorption. These findings not only suggest that designing particular magnetic-domain structures by morphologies can break the Snoek’s limit of magnetic materials, but also demonstrate that aspect ratio and magnetic field-assisted rotational orientation is promising ways to regulate the electromagnetic parameters, resulting in high-performance microwave absorption.

Formulation of silver nanoparticles using Duabanga grandiflora leaf extract and evaluation of their versatile therapeutic applications.

The current research focused on the green synthesis of silver nanoparticles (AgNPs) using Duabanga grandiflora leaf extract. The green synthesis of AgNPs was confirmed by the surface plasmon resonance band at 453nm in a UV-Visible analysis. The formulated AgNPs had a diameter of around 99.72nm with a spherical shape. Fourier transform infrared (FTIR) spectrum revealed the bio-reducing potential of phytochemicals present in D. grandiflora, which fundamentally influenced the synthesis of AgNPs. Zeta potential, dynamic light scattering (DLS), scanning electron microscopic (SEM), energy-dispersive X-ray spectroscopic (EDX), X-ray diffraction (XRD), and transmission electron microscopic (TEM) analyses were executed to reveal the physicochemical attributes of the AgNPs. The AgNPs were further investigated for their antioxidant, antidiabetic, anticancer, and antibacterial potential. The DPPH free radical assay revealed the potential radical scavenging capacity (IC50 = 76.73μg/ml) of green synthesized AgNPs. α-Amylase inhibitory assay displayed significant inhibitory potential (IC50 = 162.11μg/ml) of this starch-breaking enzyme by AgNPs, revealing the antidiabetic potential of AgNPs. AgNPs exhibited potential cytotoxic activity (IC50 = 244.57µg/ml) against malignant human kidney cells. In addition, AgNPs showed outstanding antibacterial activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial strains. Interestingly, AgNPs showed cytotoxic and antimicrobial activities at much higher concentrations than radical scavenging and α-amylase inhibitory concentrations. Thus, our finding elaborated the scope of green synthesized AgNPs for diverse therapeutic applications (dose-dependent) for further clinical translation.

Biosynthesis of gold nanoparticles mediated by medicinal phytometabolites: An effective tool against Plasmodium falciparum and human breast cancer cells

Gold nanoparticles (AuNPs) were synthesized using leaf extracts obtained from the medicinal plants Abutilon theophrasti Medik., Origanum majorana L., Euphorbia hirta L., and Senna auriculata (L.) Roxb. The in vitro antiplasmodial and anticancer activities of AuNPs were assessed against blood-stage malaria parasites and human breast cancer cells, respectively. AuNPs were examined using UV-VIS spectroscopy, HRTEM, DLS, zeta potential, XRD, and FTIR. All the AuNPs exhibited the surface plasmon resonance (SPR) band around 530 nm, which supports the formation of gold particles. The FTIR indicated possible bioactive molecules as constituents of the AuNPs formed. The fluorescence based SYBR Green I assay was utilized to investigate the anti-plasmodial action of AuNPs on the erythrocytic phases of 3D7 (chloroquine drug-sensitive) and INDO (chloroquine drug-resistant) strains of Plasmodium falciparum. The anti-plasmodial IC50 values of the synthesized A. theophrasti AuNPs (N1), O. majorana AuNPs (N2), E. hirta AuNPs (N3), and S. auriculata AuNPs (N4) were 76, 60, 32, and 20 against Pf3D7, and >100, 48, 72, and 36 μg/mL against PfINDO, respectively. N4 showed the highest activity against both P. falciparum strains and also exhibited a high CC50 (480 μg/mL) against human embryonic kidney (HEK293) cells, which leads to a great selectivity index of 24. The in vitro anticancer potential of AuNPs (N1, N2, N3, and N4) was assessed using MCF-7 cells, and the IC50 values were 8.25, 20.25, 20.40, and 24.49 μg/mL, respectively. The present study demonstrated that AuNPs derived from plant extracts may be useful therapeutic agents for treating human breast cancer and malaria.

In Vitro Antioxidant Activity of Green-Synthesized Zinc Oxide (ZnO) Nanoparticles Utilizing Extracts From Allium sativum.

The primary objective of this study was to develop an environmentally friendly and efficient method for synthesizing zinc oxide (ZnO) nanoparticles (NPs), utilizing extracts from Allium sativum (garlic) plants, characterizing the synthesized ZnO NPs using various analytical techniques, and assessing their antibacterial and antioxidant properties. The synthesis process involved utilizing extracts from garlic plants to create ZnO NPs. The NPs were subjected to comprehensive characterization through UV-visible (UV-vis) spectroscopy, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Antibacterial properties were assessed against different microbial strains. In vitro antioxidant properties were evaluated through 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) assays. Bioactive compounds in the synthesized NPs were also identified. Analysis of the UV-visspectrum confirmed the synthesis of ZnO NPs with an approximate size of 280 nm, as indicated by the absorption peak in the surface plasmon resonance band. FTIR spectroscopy revealed the presence of functional groups such as hydroxyl and carboxyl groups. SEM analysis determined the dimensions of the NPs to be around 11 nm. XRD patterns exhibited distinct Bragg reflections, confirming specific crystallographic planes. In vitro antioxidant assays demonstrated a reduction in absorbance at 517 nm and 734 nm, indicating antioxidant activity. Antibacterial testing revealed inhibition zones against Escherichia coli, Staphylococcus aureus, Streptococcus mutans,and Enterococcus faecalis. The study successfully synthesized ZnO NPs using an eco-friendly method with garlic plant extracts. Characterization techniques confirmed the structural and chemical properties of the NPs. The synthesized NPsexhibited antioxidant and antibacterial activities, showcasing their potential for various applications. The identification of bioactive compounds further contributes to the understanding of the biological properties of the synthesized NPs.

Guidance of ultraviolet light down to 190 nm in a hollow-core optical fibre.

We report an anti-resonant hollow core fibre with ultraviolet transmission down to 190 nm, covering the entire UV-A, UV-B and much of the UV-C band. Guidance from 190 - 400 nm is achieved apart for a narrow high loss resonance band at 245 - 265 nm. The minimum attenuation is 0.13 dB/m at 235 nm and 0.16 dB/m at 325 nm. With an inscribed core diameter of ∼12 µm, the fibre's bend loss at 325 nm was 0.22 dB per turn for a bend radius of 3 cm at 325 nm.

Selective Colorimetric Detection of Pb(II) Ions by Using Green Synthesized Gold Nanoparticles with Orange Peel Extract

Gold nanoparticles (AuNPs) were prepared by using a green approach that employed orange (citrus sinensis) peel water extract (OPE) as a reducing agent. In this case, the organic compounds present in orange peel were able to reduce Au(III) to Au(0) and, at the same time, to act as a capping agent, functionalizing the surface of the AuNPs, stabilizing them in a water solution. This “green” approach valorizes orange peel waste as a resourceful material and makes the synthetic process of AuNPs more environmentally sustainable, safe, and economically feasible than the traditional methods. The obtained gold nanoparticles (AuNPs@OPE) were characterized by FT–IR, DLS, SEM analysis, and UV–Vis spectroscopy; the latter showed a characteristic surface plasmon resonance (SPR) band at 530 nm, typical of spherical gold nanoparticles. The AuNPs@OPE were then tested as colorimetric sensors for heavy metals in water, showing an affinity and selectivity toward Pb2+. In fact, in the presence of Pb2+, the added cation favors the aggregation process, and, in this case, nanoparticles form clusters due to the interactions between Pb2+ and the carboxyl/hydroxyl groups on the surface of the AuNPs@OPE, increasing the size of the nanostructure. This process is accompanied by a change in color of the AuNPs@OPE from pink to violet, with a formation of a second, new SPR band, at a higher wavelength, relative to the aggregate formation. The colorimetric assay was tested at different times with the addition of Pb2+ ions showing different LOD values of 13.31 µM and 0.05 µM after 15 min and 90 min, respectively. The proposed colorimetric assay was also tested for analyzing Pb2+ in drinking water samples demonstrating the reliability to use AuNPs@OPE with real samples.

In Situ Preparation of Dehydrodieugenol-Loaded Silver Nanoparticles and their Antischistosomal Activity.

Schistosomiasis is a major neglected disease that imposes a substantial worldwide health burden, affecting approximately 250 million people globally. As praziquantel is the only available drug to treat schistosomiasis, there is a critical need to identify new anthelmintic compounds, particularly from natural sources. To enhance the activity of different natural products, one potential avenue involves its combination with silver nanoparticles (AgNP). Based on this approach, a one-step green method for the in situ preparation of dehydrodieugenol (DHDG) by oxidation coupling reaction using silver and natural eugenol is presented. AgNP formation was confirmed by UV-Vis spectroscopy due to the appearance of the surface plasmon resonance (SPR) band at 430 nm which is characteristic of silver nanoparticles. The nanoparticles were spherical with sizes in the range of 40 to 50 nm. Bioassays demonstrated that the silver nanoparticles loaded with DHDG exhibited significant anthelmintic activity against Schistosoma mansoni adult worms without toxicity to mammalian cells and an in vivo animal model (Caenorhabditis elegans), contributing to the development of new prototypes based on natural products for the treatment of schistosomiasis.

Experimental and Theoretical Studies on Ag Nanoparticles with Enhanced Plasmonic Response, Formed Within Al2O3 Thin Films Deposited by Magnetron Sputtering

AbstractReactive magnetron sputtering was employed to prepare nanocomposite thin films of Ag/Al2O3, on a glass substrate. The films are characterized by the formation of Ag nanoparticles embedded in the Al2O3 matrix, after thermal treatment at 600 °C, which are responsible for the appearance of an outstanding pronounced and narrow localized surface plasmon resonance (LSPR) band. Electron microscopy analysis also revealed the presence of larger Ag fractal aggregates at the film’s surface, responsible for a broad band absorption. Noteworthily, the LSPR band maximum remains at the same position (about 412 nm) for Ag concentrations ranging from 23 to 34 at.%, despite some discernible alterations in both LSPR band intensity and width. An optimized thin film is characterized by full transparency in non-resonant wavelengths due to suppression of Ag aggregates at the film’s surface, while maintaining the LSPR behavior. To better explain the plasmonic behavior of the Ag/Al2O3 films, discrete dipole approximation was used to determine the extinction, scattering, and absorption efficiencies of Ag spheres surrounded by an Al2O3 cap layer. This allowed to ascertain some nanostructural features of the films, pointing to the formation of Ag nanoparticles with average sizes in the order of 40 nm.

Green Synthesis of Zinc Oxide Nanoparticles Using Clove Oil Extract (Syzygium aromaticum) and Evaluate their Antibacterial Activity against MRSA

There is a crucial need for the development of effective antimicrobial agents due to the rising incidence of hospital-acquired bacterial infections caused by multidrug-resistant microbes, leading to significant mortality and morbidity worldwide. Therefore, the current study aimed to synthesize zinc oxide nanoparticles (SaZnONPs) using clove extract through an environmentally friendly technique and to investigate their antibacterial activity against MRSA (Staphylococcus aureus). Clove extract acts as both a capping and reducing agent in the formation of ZnO-NPs. The formation of SaZnONPs was confirmed using various analytical techniques. Initially, clove extract was incubated with a zinc nitrate solution, and the subsequent change in color of the solution indicated the reduction of zinc nitrate ions to ZnO nanoparticles. UV-visible spectroscopy revealed a surface plasmon resonance band of SaZnONPs at 329.26 nm. Additionally, SEM imaging indicated that the nanoparticles had an average size of 41 nm and exhibited a spherical shape. The antibacterial activity of SaZnONPs was evaluated against MRSA using agar well diffusion and minimum inhibitory concentration assays. The phytochemicals present in clove extract facilitated the synthesis of stable ZnO-NPs, demonstrating promising antibacterial properties.

Silver Nanoparticles Biosynthesis Using White Nest-Swiftlet Extract: A Sustainable Pathway for Nanomedicine Applications

Demand of antibacterial-based metal nanoparticles biomaterials against broad ranges of pathogenic microorganisms show unique functionality in a wide range of applications. Silver nanoparticles (AgNPs) play a major role especially in nanomedicine field; thus, there are urge to find more economic and eco-friendly synthesis method without harming the consumers and/or patients. In this study, an aqueous of white nest-swiftlet (Aerodramus fuciphagus) extract was used as bio-reductant and stabilizing agent to synthesis the AgNPs. The changes colour from colourless to reddish brown within 15 minutes under heat condition, 50 mM AgNO3 concentration and 3, 4, and 5 % (w/v) edible bird nest (EBN) dose indicated the successful of AgNPs biosynthesis by using visual indication. Further characterization of AgNPs was carried out by UV-visible spectroscopy through presence of plasmon resonance band between 410 nm to 430 nm. Infrared spectroscopy technique was used to analyse the involvement of biomolecules in EBN reduced the AgNPs. Their morphology and particle size analysed by field emission scanning electron microscopy (FESEM) showed nearly spherical in size with average diameter of 35 nm. Energy dispersive X-ray (EDX) attached with FESEM evaluate the composition of silver in the solutions. The content of silver increasing with the concentration of EBN extract. On the basis of results and facts, the green approach on AgNPs synthesis through EBN can be proposed as ecologically and economically feasible approach to become antibacterial wound dressing.

Insights into the impact of surfactants on the kinetics of selenium nanoparticles formation via lemon juice-assisted methodology, followed by their antibacterial and antioxidant assessment

Selenium nanoparticles (Se NPs) fabrication utilizing active species of natural lemon juice represents a promising pathway in the biosynthesis of nanoparticles. The reduction of Se4+ to Se(0) could be attributed to the presence of natural lemon juice, which was considered a supplier of vitamin C, polyphenolic compounds, flavonoids, and sugars. The synthesized spherical Se NPs exhibited a characteristic surface plasmon resonance band (SPR) at λ = 320 nm. The values of the rate constant for the reduction of Se (IV) to Se (0) by lemon juice were estimated to be kobs = 0.0011 s−1 for a Se concentration of 0.75 mmol.dm−3 and a lemon content of 0.001 mol.dm−3 at room temperature. Various conditions have been studied on the kinetics of Se NPs formation, such as the doses of SeO2 and lemon juice, and the presence of cationic and/or anionic surfactants like cetyltrimethyl ammonium bromide (CTABr) and sodium dodecyl sulfate (SDS), respectively. The synthesized Se particles were characterized by physicochemical techniques such as FT-IR, XRD, TEM, DLS, and zeta potential to investigate their main functional groups, crystallinity, chemical composition, particle size, and surface morphology. Moreover, the antioxidant power of Se NPs was tested in terms of their DPPH free radical scavenging activity. Finally, the antibacterial activity of the studied nanoparticles was confirmed against gram-positive and gram-negative bacteria (Staphylococcus aureus and Pseudomonas aeruginosa, respectively). In short, this study introduced the impact of surfactants on the formation of biocompatible Se NPs as an active antibacterial and antioxidant.

Research on Nonlinear Vibration of Dual Mass Flywheel Considering Piecewise Linear Stiffness and Damping

Nonlinear torsional vibration differential equation of the nested arc-shaped short spring dual mass flywheel (DMF) is established, considering the piecewise linear stiffness and damping of the spring. The first-order approximate analytical solution under sinusoidal excitation and the amplitude–frequency characteristic function are obtained by means of the average method which verified by the Runge–Kutta (R–K) method. The effects of the parameters of input excitation, inertia, and piecewise linear stiffness and damping of DMF on the resonant amplitude, resonant frequency band, and equivalent linear natural frequency of the system are analyzed. The results show that the amplitude–frequency characteristic curve bending and jumping with the changes of excitation frequency and the peak of resonant amplitude can be obviously reduced by increasing the inertia of the primary flywheel and decreasing the inertia of the secondary flywheel. The complex nonlinear dynamic phenomena such as Period 1, quasi-periodic, and chaos are obtained by analyzing the forced vibration response under the different excitation frequencies.

An Adaptive Deconvolution Method with Improve Enhanced Envelope Spectrum and Its Application for Bearing Fault Feature Extraction

To address the problem that complex bearing faults are coupled to each other, and the difficulty of diagnosis increases, an improved envelope spectrum–maximum second-order cyclostationary blind deconvolution (IES-CYCBD) method is proposed to realize the separation of vibration signal fault features. The improved envelope spectrum (IES) is obtained by integrating the part of the frequency axis containing resonance bands in the cyclic spectral coherence function. The resonant bands corresponding to different fault types are accurately located, and the IES with more prominent target characteristic frequency components are separated. Then, a simulation is carried out to prove the ability of this method, which can accurately separate and diagnose fault types under high noise and compound fault conditions. Finally, a compound bearing fault experiment with inner and outer ring faults is designed, and the inner and outer ring fault characteristics are successfully separated by the proposed IES-CYCBD method. Therefore, simulation and experiments demonstrate the strong capability of the proposed method for complex fault separation and diagnosis.

Experimental Study of Transverse Mode Suppression on Wideband Hetero Acoustic Layer Surface Acoustic Wave Resonator.

Transverse mode suppression is a great challenge for high-performance surface acoustic wave (SAW) resonators. Conventional methods work well on narrowband resonators, but their performances on wideband resonator have not been demonstrated. In this article, we give an in-depth study on the transverse mode suppression of wideband resonators using 11° YX-LiNbO3 (LN)/70 °Y90°X -quartz (Qz) hetero acoustic layer structure as a platform. Two groups of design, including new dummy electrode and zigzag shape apodization, are proposed. The measured results show that the shape of the dummy electrode is not the dominant factor to affect the transverse mode. The proposed zigzag shape apodization can effectively suppress the transverse, at the same time maintain the quality ( Q ) factor at the same level with the normal type. Additionally, stronger suppression ability can be realized with a tiny tradeoff of Q -factor.

Impact of the outer‐sphere and inner‐sphere association in the surface enhanced Raman spectra of metal complexes and gold nanoparticles

AbstractTransition metal complexes, such as the low‐spin bis (phenylterpyridine) (A) and bis (pyridylterpyrazine)iron (II) (B) complexes, provide didactic chromophore species for demonstrating the Raman, resonance Raman, and the surface‐enhanced Raman scattering (SERS) behavior in coordination chemistry, as well as for elucidating the nature of inner‐sphere and outer‐sphere association with plasmonic nanoparticles. Their electrostatically stabilized ion pairs with citrate–gold nanoparticles have been studied in an aqueous solution, from the pronounced changes in the plasmonic band at 540 nm. Complex A, lacking any coordinating site, can only generate outer‐sphere complexes with citrate–gold nanoparticles, but they are stable enough to give a strong SERS response, even at 10−8 M. At 10−6 M, agglomeration accompanies the decrease of the electrostatic repulsion, resulting in a sharp decay of the plasmon resonance band at 540 nm. This is followed by the rise of a plasmon coupling band above 700 nm. However, at 10−4 M, the excess of the complex in the adsorption layer produces a reverse effect, decreasing agglomeration. The observed Raman spectra are essentially similar for the several concentrations employed because the outer‐sphere interaction implies a SERS electromagnetic mechanism. In contrast, complex B exhibits several pyridine and pyrazine N‐atoms available to form inner‐sphere‐associated species. A selective enhancement of the SERS signals is observed at 10−8 M, clearly indicating a chemical mechanism, consistent with a bridging mode. At 10−6 M and above, the agglomeration leads to a plasmon coupling band at 800 nm, while the SERS response indicates a change in the binding modes dictated by the excess of the complexing molecules.

Photocatalytically active Ag-doped TiO2 coatings developed by plasma electrolytic oxidation in the presence of colloidal Ag nanoparticles

The plasma electrolytic oxidation process of Ti foil in the presence of a colloidal solution of Ag nanoparticles was used for the synthesis of exceptionally photocatalytically active Ag-doped TiO2 coatings. UV–Vis absorption spectroscopy was applied to follow the changes in the surface plasmon resonance band of the Ag nanoparticles as a function of the Ag:PO43− ratio in a phosphate-based electrolyte solution. Transmission electron microscopy revealed the size of the Ag nanoparticles in the range of 3–12 nm. The XRD patterns of the Ag-doped TiO2 coatings confirmed the crystalline anatase TiO2 phase regardless of the dopant concentration and without metallic Ag or crystalline Ag oxide forms. The typical porous morphology of the Ag–TiO2 coatings was observed by scanning electron microscopy. A significantly improved photocatalytic activity of the Ag–TiO2 coatings in the degradation process of the insecticide lindane (gamma isomer of benzene hexachloride) and test molecule methyl orange compared to pure TiO2 was determined using the GC technique. The degradation efficiency of Ag-doped TiO2 coatings is higher for lindane than for methyl orange.