Au Nanoparticles In Solution Research Articles

Surface-Enhanced Electronic and Vibrational Raman Spectroscopy of Ionic Liquid [BMI][PF6] on Au Electrode

Room-temperature ionic liquids have gathered great attention across various fields in recent years due to their fascinating physical and chemical properties. These liquids are, for example, expected as a next-generation solvent-free electrolyte. Their structure and dynamics at an electrode interface, where an electrical double layer is formed, should differ from those for conventional dilute electrolyte solutions. Because the performance of ionic liquids as electrolytes is significantly influenced by their behavior in the electrical double layer, many vibrational spectroscopic studies have been conducted to understand their properties at the molecular level. However, the interpretation of vibrational spectrum often suffers from its complicated spectral features. In this study, we observed not only the interfacial structure of ionic liquid on Au electrode but also the surface charge density of Au electrode at the same time using surface-enhanced electronic and vibrational Raman scattering (SERS) spectroscopy in a wide frequency range between 10 and over 2000 cm-1, which can provide a complete picture of the electrical double layer at the ionic liquid/Au interface.In this study, an imidazolium-based ionic liquid, 1-n-butyl-3-methylimidazoium hexafluorophosphate [BMI][PF6], with a residual water concentration below 5 ppm was used as an electrolyte. A SERS-active Au electrode was prepared by drop-casting a colloidal solution of Au nanoparticles with an average diameter of 100 nm onto the surface of a smooth Au electrode, followed by an electrochemical surface cleaning and vacuum-drying at 120°C for 1 hour. Then, the SERS-active Au electrode and the ionic liquid were sealed in a homemade three-electrode electrochemical Raman cell in an Ar-filled glovebox where H2O were below 0.1 ppm. Prior to SERS measurement, oxidation-reduction cycles were applied within the electrochemical potential window of [BMI][PF6] for further cleaning of the Au electrode surface. SERS spectra were measured with a 632.8 nm He-Ne laser under applied potential. The measured spectra were converted to the SERS susceptibility (χ”SERS) spectra using a conversion method described in previous reports1,2.Fig. 1 shows a typical SERS spectrum of [BMI][PF6] on Au electrode at open circuit potential, which includes both vibrational sharp peaks (vibrational SERS, vSERS) and a broad electronic background continuum (electronic SERS, eSERS). The observed peaks in the range of 1000 cm-1 to 1600 cm-1 are assigned to vibrational modes of BMI cation. The peak at 740 cm-1 is attributed to the symmetric stretching of PF6 anion. There is also a peak at around 180 cm-1, which can be assigned to the external mode of PF6 anion adsorbed on Au. In the THz region (10 cm-1 to 100 cm-1), there exists a broad feature, which is related to anion-cation interactions. When the applied potential was scanned to the negative direction, significant spectral changes were observed in both vSERS peaks and the eSERS background, which can be interpreted as desorption of PF6 anion, replacement of cation/anion layering structures, increase in the surface charge on Au, etc. These changes were in good agreement in capacitive current responses observed in the cyclic voltammogram.Reference(1) M. Inagaki, T. Isogai, K. Motobayashi, K. -Q. Lin, B. Ren, K. Ikeda, Chem. Sci., 11, 9807 (2020)(2) R. Kamimura, T. Kondo, K. Motobayashi, K. Ikeda, Phys. Status Solidi B, 259, 9, 2100589 (2022) Figure 1

Interrelated Roles of Multiple Key Structure-Directing Agents in Seed-Mediated Growth of Monodisperse and Multibranched Au Nanoparticles.

Detailed mechanistic investigations of the interrelated roles of multiple key structure-directing agents in the growth solution of Au nanoparticles (AuNPs) is required for the optimization of synthetic protocols. Here, we report a robust seed-mediated growth strategy for synthesizing multibranched NPs (MB-AuNPs) with monodispersed size distribution, and investigate the roles of Ag ions and 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid (HEPES) based on an overgrowth synthesis approach. The intertwining roles of Ag+, surface-capping stabilizers, and reducing agents were elucidated, and used to control the morphology of MB-AuNPs. The overgrowth of MB-AuNPs involves two distinct underlying pathways, namely, directional and anisotropic growth of Au branches on specific facets of Au seeds as well as an aggregation and growth mechanism governed by HEPES. In addition to Ag ions and HEPES, morphology tunability can also be achieved by pre-modification of the Au seeds with molecular probes. Optimized probe-containing MB-AuNPs prove to be excellent surface-enhanced Raman scattering (SERS) substrates and nanozymes. Taken together, the results of this work reveal the mechanistic evolution of nanocrystal growth which should stimulate the development of new synthetic strategies, improve the capabilities of tuning the optical, catalytic, and electronic properties of NPs, and further advance their applications in biolabeling, imaging, biosensing, and therapy.

Nonlinear optical properties of gold nanoparticles produced by laser ablation at two different radiation wavelengths

In this study, gold nanoparticles were synthesized by laser ablation of Au bulk in distilled water. The laser used is Nd: YAG laser, which has a fundamental harmonic wavelength (λ=1064nm) and second harmonic wavelength (λ=532nm). In order to control the size of Au nanoparticles (NPs), we used sodium citrate as a stabilizer. Morphology, structure and linear optical properties of Au NPs samples were characterized by transmission electron microscopy (TEM observation), XRD diffraction (XRD) and UV–Visible spectroscopy. Furthermore, the chemical structure in solution of Au NPs was studied by Fourier transform-infrared spectroscopy (FTIR). The nonlinear optical parameters of these Au NPs were studied using the Z-scan method. We found the optimal values of fluencies and laser pulse repetition rates to achieve the smallest size values and the most distribution of the produced gold nanoparticles. It is resulted that due to the very small size of NPs, the nonlinear optical parameters show larger values. It is 107 order of magnitude larger than what has been reported for the nonlinear refractive index in previous researches. In addition, gold nanoparticles that are produced with a laser wavelength of 1064 nm and have a high nonlinear refractive index can be used in chip-based sensors. Finally, the use of these Au NPs in optical switching devices was investigated by the two figures of merit method, which indicated that these Au NPs are practical tools for optical switching devices.

Quantitative colorimetric sensing of heavy metal ions via analyte-promoted growth of Au nanoparticles with timer or smartphone readout.

This work describes two new colorimetric nanosensors for label-free, equipment-free quantitative detection of nanomolar copper (II) (Cu2+) and mercury (II) (Hg2+) ions. Both are based on the analyte-promoted growth of Au nanoparticles (AuNPs) from the reduction of chloroauric acid by 4-morpholineethanesulfonic acid. For the Cu2+ nanosensor, the analyte can accelerate such aredox system to rapidly form a red solution containing dispersed, uniform, spherical AuNPs that is related to these particles' surface plasmon resonance property. For the Hg2+ nanosensor, on the other hand, a blue mixture consisting of aggregated, ill-defined AuNPs with various sizes can be created, showing a significantly enhanced Tyndall effect (TE) signal (in comparison with that produced in the red solution of AuNPs). By using a timer and a smartphone to quantitatively measure the time of producing the red solution and the TE intensity (i.e., the average gray value of the corresponding image) of the blue mixture, respectively, the developed nanosensors are well demonstrated to achieve linear ranges of 6.4nM to 100μM and 6.1nM to 1.56μM for Cu2+ and Hg2+, respectively, with detection limits down to 3.5 and 0.1nM, respectively. The acceptable recovery results obtained from the analysis of the two analytes in the complex real water samples including drinking water, tap water, and pond water ranged from 90.43 to 111.56%.

Tuning the photoluminescence of CdTe quantum dots by controllable coupling to plasmonic Au nanoparticles

A controllable variation of the photoluminescence (PL) intensity of semiconductor quantum dots (QDs) via their coupling to plasmonic nanoparticles (NPs) is the potential basis for optoelectronic and sensing applications. In this work, the effect of Au NPs on the PL of colloidal CdTe QDs is investigated in solution and solid films. An PL enhancement for the QDs synthesized in water was observed in case of spectral overlap of the plasmon absorption band of and QD PL band. In case of Au NPs synthesized in dimethyl sulfoxyl the trend is to reduction of the PL intensity. For the reference samples prepared by mixing QDs not with Au NP solutions but with corresponding pure solvent, certain PL enhancement was observed and presumably attributed to reduction of self-absorption or non-radiative interparticle interaction in less concentrated QD solution. However, the contribution of this dilution-related enhancement is expected to be independent of the spectral properties of NPs and QDs. Therefore, the observed in this work different behavior of QD PL in certain combinations of QDs and NPs is attributed to interaction between electronic excitation in the QD and plasmon.

Study of the Applicability of Colloidal Solutions of Gold and Silver Nanoparticles for Surface-enhanced Raman Spectroscopy of Blood Plasma

This work focuses on the preparation of colloidal solutions of Au and Ag nanoparticles and verification of their applicability for surface-enhanced Raman scattering spectroscopy of blood plasma. The composition of blood plasma may change due to pathobiochemical processes associated with disease development. Analysis of blood plasma might reveal these changes and thus help in the diagnostics process of various diseases. Raman spectroscopy appears to be an ideal method for rapid and non-destructive analysis of blood plasma. Moreover, surface-enhanced Raman scattering spectroscopy might allow the detection of very low levels of potential disease-specific markers. In this work, the prepared colloidal solutions of Au and Ag nanoparticles were first characterized by UV‑VIS absorption spectroscopy and their enhancing capabilities were verified using riboflavin as a model analyte. Subsequently, optimization of the measurement conditions for surface-enhanced Raman spectroscopy of blood plasma was performed. The results show that at the excitation wavelength of 785 nm, significantly higher enhancement is achieved when using Ag nanoparticles. In the case of Au nanoparticles, the enhanced blood plasma spectrum was successfully detected only once, and the addition of an aggregating agent (NaCl) was required.

Rapid Detection of Aspergillus flavus and Quantitative Determination of Aflatoxin B1 in Grain Crops Using a Portable Raman Spectrometer Combined with Colloidal Au Nanoparticles.

Aspergillus flavus and Aflatoxins in grain crops give rise to a serious threat to food security and cause huge economic losses. In particular, aflatoxin B1 has been identified as a Class I carcinogen to humans by the International Agency for Research on Cancer (IARC). Compared with conventional methods, Surface-Enhanced Raman Scattering (SERS) has paved the way for the detection of Aspergillus flavus and Aflatoxins in grain crops as it is a rapid, nondestructive, and sensitive analytical method. In this work, the rapid detection of Aspergillus flavus and quantification of Aflatoxin B1 in grain crops were performed by using a portable Raman spectrometer combined with colloidal Au nanoparticles (AuNPs). With the increase of the concentration of Aspergillus flavus spore suspension in the range of 102–108 CFU/mL, the better the combination of Aspergillus flavus spores and AuNPs, the better the enhancement effect of AuNPs solution on the Aspergillus flavus. A series of different concentrations of aflatoxin B1 methanol solution combined with AuNPs were determined based on SERS and their spectra were similar to that of solid powder. Moreover, the characteristic peak increased gradually with the increase of concentration in the range of 0.0005–0.01 mg/L and the determination limit was 0.0005 mg/L, which was verified by HPLC in ppM concentration. This rapid detection method can greatly shorten the detection time from several hours or even tens of hours to a few minutes, which can help to take effective measures to avoid causing large economic losses.

Shape influence on the ultrafast plasmonic properties of gold nanoparticles.

The aim of shape-controlled colloidal synthesis of gold (Au) is to produce Au nanoparticles (NPs) with fine control of shapes, sizes, and dispersities. We show how transient absorption spectroscopy (TAS) can be used to rapidly and accurately quantify the vast ensemble of shapes of Au NPs in solution within minutes, including the synthesized nanorods, decahedra, and nanospheres. Colloidal solutions containing Au NPs were measured in TAS and their localized surface plasmon resonance (LSPR) modes were classified according to the shape, wavelength and number of peaks. Then their excited-state relaxation dynamics were used to ascertain their electron-phonon (e-ph) coupling time constant and frequency of optomechanical modes. TAS can quickly show that an Au nanosphere sample contains a tiny fraction of Au nanorods, whereas steady-state absorbance is totally blind to the presence of nanorods. Additionally, the TAS experiments indicate that the characteristic e-ph coupling time constants in Au nanorods depend on the NPs dimensions at high excitation intensity (> 6 µJ/cm2) which can help identify if there are any elongated Au NPs in Au spheres samples. Finally, optomechanical oscillations formed by NPs breathing modes were observed, providing information related to the average size and monodispersity of Au nanospheres and nanorods.

Uncovering strong π-metal interactions on Ag and Au nanosurfaces under ambient conditions via in-situ surface-enhanced Raman spectroscopy

Uncovering strong π-metal interactions on Ag and Au nanosurfaces under ambient conditions via in-situ surface-enhanced Raman spectroscopy

Spin-casting of Micron-Scale Thick PMMA Films with Embedded Au Nanoparticles Formed by Laser Ablation in Liquid

Background: A Facile, scalable approach to fabrication of organic thin films with an embedded layer of nanoparticles in the ambient environment. The approach is based on step-bystep spin-coating of polymethylmethacrylate (PMMA) films and a nanoparticle layer. Objective: The goal of the present work is to fabricate a sandwich structure of the PMMA films for the top and bottom layers of a sandwich structure as well as a middle layer of nanoparticles formed in solution by the Laser Ablation in Liquid (LAL) method. Methods: First, a PMMA thin film was fabricated by spin-casting of PMMA solution in ethylacetate. Secondly, a solution of Au nanoparticles synthesized by laser ablation in ethanol was spin-cast on a prefabricated PMMA film. The distribution of Au nanoparticles and the morphology of the resulting film were analyzed using scanning electron microscopy (SEM), optical microscopy, and atomic microscopy (AFM). Finally, another PMMA layer was spin-cast on the nanoparticle-decorated film. Results: A hybrid organic film with the embedded layer of nanoparticles was fabricated using the spin-casting method for top and bottom layers as well as for the middle layer of Au nanoparticles fabricated by laser ablation in ethanol by a pulsed UV laser. Statistical and fractal analysis shows uniform distribution of nanoparticles on length scale above ten microns. Conclusion: Spin-cast-based layer-by-layer approach to fabrication of sandwich structures of organic films with embedded nanoparticlesis a facile and scalable method for hybrid organic - nanoparticle films. This approach can be extended for the fabrication of multi-layered hybrid structures.

Effect of laser beam propagation through the plasmonic nanoparticles suspension

Gold nanoparticles are excellent light absorbers at the surface plasmon resonance wavelength. This absorption process generates highly energetic electrons near the surface that enhances the local electric field on the gold nanoparticles surface, and results in modification of the refractive index. The present work focuses on interaction of the laser, both near and far from the resonance wavelength, with colloidal solution of plasmonic nanoparticles. For the laser beam interaction, we first prepared the gold nanoparticles by sol gel method and characterized the absorption spectrum in terms of particle size and morphology. The absorption peak in visible range confirmed to the formation of Au nanoparticles. Therefore, a laser at 532 nm was selected to study light matter interaction with Au nanoparticles in solution. The interaction produced diffraction rings, which changed shape over time due to convection of colloidal nanoparticles. In another experiment, a 405 nm laser with the same power produced only a laser spot on the screen. Thus, the 532 nm is closer to the surface plasmon excitation and is responsible for producing a pattern of diffraction rings in the far-field region. The produced diffraction rings provide a very simple and sensitive technique to find out induced nonlinear refractive index for the plasmonic nanoparticles. Finding plasmonic resonances holds importance for variety of applications in plasmonic sensing and these rings could be used to characterize the resonances.

Laser-Based Synthesis of Au Nanoparticles for Optical Sensing of Glyphosate: A Preliminary Study.

Nowadays, Au nanoparticles (AuNPs) capture great interest due to their chemical stability, optical properties, and biocompatibility. The success of technologies based on the use of AuNPs implies the development of simple synthesis methods allowing, also, the fine control over their properties (shape, sizes, structure). Here, we present the AuNPs fabrication by nanosecond pulsed laser ablation in citrate-solution, that has the advantage of being a simple, economic and eco-sustainable method to fabricate colloidal solutions of NPs. We characterized the stability and the absorbance of the solutions by Ultraviolet-Visible (UV-Vis) spectroscopy and the morphology of the AuNPs by Transmission Electron Microscopy. In addition, we used the AuNPs solutions as colorimetric sensor to detect the amount of glyphosate in liquid. Indeed, glyphosate is one of the most widely used herbicides which intensive use represents a risk to human health. The glyphosate presence in the colloidal AuNPs solutions determines the aggregation of the AuNPs causing the change in the color of the solution. The variation of the optical properties of the colloidal solutions versus the concentration of glyphosate is studied.

Slow Charge Carrier Relaxation in Gold Nanoparticles

We report on ultrafast transient absorption (TA) studies of surface plasmon-excited ∼25 nm-diameter Au nanoparticles in solution, monitoring the response of the surface plasmon resonance in the visible region (1.7–3.0 eV) and that of the inter- and intraband transitions in the deep UV region (3.4–4.5 eV). The former reflects lattice heating by electron–phonon energy transfer, while the latter monitors charge carriers, that is, excess holes and electrons, respectively, below and above the Fermi level. Although the steady-state UV absorption spectrum of Au is featureless, the TA spectra reveal three bands that appear promptly upon plasmon excitation and decay over hundreds of picoseconds (ps). Based on the band structure diagram of bulk Au, we attribute these to inter- and intraband transitions around the X and L symmetry points. The decay of the hot electrons monitored via the interband transitions takes 150–180 ps. On the other hand, probing the intraband transitions at the L symmetry points below the Fermi level reveals both electron and hole relaxation, with the latter requiring tens of ps. These results show that after the initial ultrafast electron–electron and electron–phonon scattering processes, hot charge carriers above and below the Fermi level remain in equilibrium with the hot lattice for several tens to hundreds of ps.

On-Site and Daily Stress-Measurement Using Gold-Linked Electrochemical Immuno Assay for IgA Determination

[Introduction]Mental stress is closely connected with our physical and mental wellness. In particular, depression may be associated with stress. Therefore, stress measurement can contribute to assess our lifestyle and increase our quality of life. However, objective stress-measurement is not established. To establish objective stress-measurement, an individual must indicate the stress level by obtaining numerous data continuously throughout the day. Therefore, the measurement method which can be suitable for this condition is needed. In this paper, we detect the secretory Immunoglobulin A (sIgA), which is the candidate of salivary stress-markers, with original electrochemical immunoassay: Gold-Linked Electrochemical Immuno Assay (GLEIA). This biosensor is based on a sandwich-type immunosensor, and adopt the electrochemical method to detect the reduction peak from Au nanoparticles linked to the secondary antibody. GLEIA is convenient and cost-effective that only requires low sample volume (10 µL). In addition, all devices that GLEIA needs are minimal such as note PC and portable potentiostat and printed electrode. Therefore, GLEIA method shows various advantages suitable for stress measurement as compared with other sIgA detection methods. In this paper, we aim to the on-site and continuous measurement of salivary IgA in our daily life, to determine the various concentration of sIgA in standard solution and artificial saliva using GLEIA.[Experimental]Primary Anti-IgA Antibody solution was dropped onto the working electrode for immobilizing the antibody by physical adsorption. After, the Au nanoparticle solution was mixed with the phosphate buffer (50 mM, pH=8.3). The anti-IgA to dissolve the 5 mM of phosphate buffer add the Au nanoparticle solution. For the preparing of secondary antibody modified Au nanoparticle, the antibody was conjugated with Au nanoparticle under the pH=8.3 condition and kept for 10 min at room temperature. Then, 10% BSA in PBS buffer and 1% PEG in PBS buffer were added in preparing Au solution. Finally, the concentration was adjusted for OD520=6.0 by centrifuge and exclude the supernatant. The Au Anti-IgA conjugate was diluted by 3 times with 50 w/v of trehalose (OD520=2) and dripping 5µL of this solution in the immunomodule. Then the immunomodule was dried in vacuum condition for 5 minutes. Dried immunomodule was stored at 4 ℃ until use. Different concentrations of the IgA antigen solution (0, 10, 60, 150, 300 ng/mL) were made by diluting in PBS. For the detection of Antibody-Antigen reaction, the IgA solutions were mixed in prepared immunomodule, After the 1 minute, and 1.4 µL of the solution was placed on immunosensor to incubate for 1 hour, after rinsing with PBS, and eliminate the PBS solution with the air gun. The direct redox reaction was performed in 2M KCl solution (20 µL) covering the entire three-electrode zone at room temperature.[Results and Discussion]We obtained the linear response to relate the concentration of sIgA (10-300 ng/mL) in D-PBS buffer with the artificial-saliva which includes salivary inorganic salt and typically glycoprotein (mucin). Figure 1 shows the differential pulse voltammogram of GLEIA with IgA in artificial saliva (a) and calibration curve (b). In addition, the calibration curve shows the linear range within 10-300 ng/mL and the correlation coefficient (R2) of the calibration curve for this relationship was 0.963. The peak current intensity is decreased from in standard solution. It may prevent the Antigen-Antibody reaction from artificial saliva which pH is nearly 8.5. Generally, the antibody shows the best affinity in pH= 6.5~8.4 condition. However, these results show that GLEIA is suitable for salivary IgA detection because the salivary pH is mainly neutral. Furthermore, we evaluate the selectivity of the immunosensor by comparing it with the reduction peak between IgA= 300ng/mL or 0 ng/mL and interference protein such as α-amylase, human serum albumin, immunoglobulin G (IgG), lysozyme and mucin. We acknowledge GLEIA shows the signal increasing within the existence of interference proteins. This may be the affinity of antibody and non-specific reaction between antibody and the proteins. More importantly, we recognize that the reduction peak is increasing with the concentration of sIgA in the existence of interference proteins. Therefore, GLEIA can be applied for stress measurement using salivary sIgA that can be used in daily life anywhere and anytime whenever necessary. In the future, we try to detect the sIgA in real saliva for on-site stress measurement using GLEIA and to integrate the various immunosensors for stress-markers in saliva.nd anytime whenever necessary. In the future, we try to detect the sIgA in real saliva for on-site stress measurement using GLEIA and to integrate the various immunosensors for stress-markers in saliva. Figure 1

Temperatural conductivity of diluted water solutions graphen and nanostructures of graphen nanoparticles

The purpose of this work was to study the specific thermal conductivity of aqueous graphene dispersions and the diluted aqueous solution of nanostructures based on graphene and Au nanoparticles, as well as to determine the temperature and concentration dependences of the specific thermal conductivity of these aqueous dispersions.
 The objects of study were aqueous dispersions of graphene and nanostructures based on graphene and Au nanoparticles. Graphene has characteristic dimensions of the order of 150 - 200 nm in the plane. The Au nanoparticles also have an average size of about 50 nm and a star-like shape. In dry nanocomposites, graphene is oriented parallel to the substrate plane, and nanostars are evenly distributed on the sample surface.
 The specific volumetric thermal conductivity values of aqueous graphene dispersions and aqueous solutions of graphene-based nanoparticles and Au nanoparticles were obtained in the temperature range from 30оC to 60оC. A slight increase in the specific thermal conductivity was found with increasing temperature. The absolute values a/v of aqueous graphene dispersions are 1.6 times higher than in three-component systems. The concentration dependences of the thermal conductivity of the two systems studied are linear. It is determined that the values of the specific thermal conductivity of dry graphene nanofillers are 1,62 times higher than the thermal conductivity of a mixture of graphene and Au nanoparticles.

Rapid and low-cost quantitative detection of creatinine in human urine with a portable Raman spectrometer

The creatinine concentration of human urine is closely related to human kidney health and its rapid, quantitative, and low-cost detection has always been demanded. Herein, a surface-enhanced Raman spectroscopic (SERS) method for rapid and cost-effective quantification of creatinine concentrations in human urine was developed. A Au nanoparticle solution (Au sol) was used as a SERS substrate and the influence of different agglomerating salts on its sensitivity toward detecting creatinine concentrations was studied and optimized, as well as the effect of both the salt and Au sol concentrations. The variation in creatinine spectra over time on different substrates was also examined, demonstrating reproducible quantitative analysis of creatinine concentrations in solution. By adjusting the pH, a simple liquid−liquid solvent extraction procedure, which extracted creatinine from human urine, was used to increase the SERS detection selectivity toward creatinine in complex matrices. The quantitative results were compared to those obtained with a clinically validated enzymatic “creatinine kit (CK).” The limit of detection (LOD) for the SERS technique was 1.45 mg L−1, compared with 3.4 mg L−1 for the CK method. Furthermore, cross-comparing the results from the two methods, the average difference was 5.84% and the whole SERS detection process could be completed within 2 min compared with 11 min for the CK, indicating the practicality of the quantitative SERS technique. This novel quantitative technique shows promises as a high-throughput platform for relevant clinical and forensic analysis.

Surface construction of fluorinated TiO2 nanotube networks to develop uvioresistant superhydrophobic aramid fabric.

Poor ultraviolet (UV) resistance and good hydrophilicity lead to light aging of aramid fabrics and cause heat damage to the human body. This scenario occurs when the absorbed water by the fabric evaporates and forms high-temperature water vapor in a high-temperature fire environment, which may scald the human body. Herein, a superhydrophobic hollow TNT network structure was built on surfaces of aramid fibers by surface coating fluorinated TiO2 nanotubes (TNTs) to develop an air-permeable, UV-protective, and superhydrophobic coating. The as-prepared superhydrophobic aramid fabric exhibited highly superhydrophobic properties against various solutions of sauce, coffee, methylene blue, active red, Au nanoparticles, Ag nanoparticles, HCl, and NaOH with liquid contact angles up to 152–160°. In addition, the superhydrophobic fabric exhibited excellent UV aging resistance (UV protection factor was 100+; 74.58% of strength retention for 24 h of UV radiation compared with 55.15% of untreated fabric), a self-cleaning function against solid soil, and original wearing characteristics, including good breaking strength and air permeability. The developed superhydrophobic coating technology may promote practical application in high-temperature environments for aramid fabrics due to its good UV resistance, chemical resistance, poromericity, superhydrophobicity, anti-fouling, and self-cleaning properties.

Effective up-conversion behaviors for Er3+–Yb3+-doped SrF2 phosphors synthesized by flux-assist method

Up-converting materials composed of Sr0.925−3x/2ErxYb0.05F2 (x = 0.001–0.075) were synthesized using excess NH4F flux at 950 °C for 2 h. X-ray diffraction patterns and scanning electron microscopic images were obtained from samples of Sr0.925−3x/2ErxYb0.05F2 phosphors prepared using different molar ratios of Sr((Er,Yb)O3/2)CO3:NH4F. The effective Er3+ emission spectra in the Sr0.925−3x/2ErxYb0.05F2 phosphors that depend on the concentrations of Er3+ and Yb3+ ions were explored during excitation with a 980-nm wavelength diode laser. The emission intensity of the laser diode has two dependencies that were investigated—the pump power has to be constrained within the range of 77–118 mW, and the temperature of the Sr0.91Er0.01Yb0.05F2 phosphor must range from 25 to 175 °C. The fluorescence intensity ratio and sensitivity were calculated based on the energy levels of the Er3+ dopant ions in the phosphor. When Au nanoparticle solution was dispersed on the Sr0.91Er0.01Yb0.05F2 phosphor, the luminescent intensity of the phosphor was obviously enhanced by the surface-plasmon-resonance effect.

Fabrication of Stable Nanofiber Matrices for Tissue Engineering via Electrospinning of Bare Laser-Synthesized Au Nanoparticles in Solutions of High Molecular Weight Chitosan.

We report a methodology for the fabrication of neutralized chitosan-based nanofiber matrices decorated with bare Au nanoparticles, which demonstrate stable characteristics even after prolonged contact with a biological environment. The methodology consists of electrospinning of a mixture of bare (ligand-free) laser-synthesized Au nanoparticles (AuNPs) and solutions of chitosan/polyethylene oxide (ratio 1/3) containing chitosan of a relatively high molecular weight (200 kDa) and concentration of 3% (w/v). Our studies reveal a continuous morphology of hybrid nanofibers with the mean fiber diameter of 189 nm ± 86 nm, which demonstrate a high thermal stability. Finally, we describe a protocol for the neutralization of nanofibers, which enabled us to achieve their structural stability in phosphate-buffered saline (PBS) for more than six months, as confirmed by microscopy and FTIR measurements. The formed hybrid nanofibers exhibit unique physicochemical properties essential for the development of future tissue engineering platforms.

Photocatalysis of Nickel-Based Graphene/Au/ZnO Nanocomposites

Gold (Au) nanoparticles were deposited on the 3D Nickel (Ni)/graphene composites by soaking the composites in the Au nanoparticles solutions and the ZnO nanostructures with different morphologies were fabricated on Ni/graphene/Au by the hydrothermal processing. The photocatalytic performance of Ni/graphene/Au/ZnO nanocomposites was investigated and the one with ZnO nanoplates exhibited optimal photocatalytic performance toward methyl orange (MO) under simulated sunlight, revealing superior apparent degradation rate constant Kapp about 1.5-fold higher compared with that of the nanocomposite without Au incorporated. The influence of Au nanoparticles and hydrothermal processing time on the ZnO nanostructures morphology and structure as well as the photocatalysis mechanism were discussed in detail. The incorporation of Au nanoparticles induced reduction of ZnO bandgap due to the generation of remarkable valence band tail states, and ZnO crystallinity revealed a strong dependence on its morphology. Meanwhile, the combining effect of incorporation of Au nanoparticles and optimization of ZnO nanostructures morphology would not only facilitate the electron transfer from ZnO to Au but also enhance the photo-generated electron storage, suppressing the electron-hole pairs recombination and improving the photocatalytic performance. The study provided an easy-handling way for the fabrication of noble metal incorporated, hybrid carbon–semiconductor-based photocatalysts.