Rhodamine 6G Aqueous Solutions Research Articles

Aggregation-induced emission spectral shift as a measure of local concentration of a pH-activatable rhodamine-based smart probe

Generating activatable probes that report about molecular vicinity through contact-based mechanisms such as aggregation can be very convenient. Specifically, such probes change a particular spectral property only at the intended biologically relevant target. Xanthene derivatives, for example rhodamines, are able to form aggregates. It is typical to examine aggregation by absorption spectroscopy but for microscopy applications utilizing fluorescent probes it is very important to perform characterization by measuring fluorescence spectra. First we show that excitation spectra of aqueous solutions of rhodamine 6G can be very informative about the aggregation features. Next we establish the dependence of the fluorescence emission spectral maximum shift on the dimer concentration. The obtained information helped us confirm the possibility of aggregation of a recently designed and synthesized rhodamine 6G-based pH-activatable fluorescent probe and to study its pH and concentration dependence. The size of the aggregation-induced emission spectral shift at specific position on the sample can be measured by fluorescence microspectroscopy, which at particular pH allows estimation of the local concentration of the observed probe at microscopic level. Therefore, we show that besides aggregation-caused quenching and aggregation-induced emission also aggregation-induced emission spectral shift can be a useful photophysical phenomenon.

Quenching of R6G Fluorescence by Gold Nanoparticles of Various Particle Geometries

Abstract The quenching of Rhodamine 6G in aqueous solution by citrate stabilized gold nanoparticles differing in their geometry (spheres, rods, prisms) was investigated. Static quenching was observed throughout. At constant surface area, the quenching rate diminished in the order spheres>rods>prisms. The effect is shown to be due to differing nanoparticle volumes rather than to variations in the surface area.

Gold nanoparticles modified double-tapered fiber for SERS detection

Double-tapered fiber probes modified with gold nanoparticles were fabricated for the surface-enhanced Raman scattering (SERS) sensing. Its performance was compared with the fiber SERS probes of flat end and of single-tapered structure. The remote detection performances of three fiber probe structures were compared by detecting rhodamine 6G (R6G) aqueous solutions with the different concentrations. The results of remote detection of R6G aqueous solution indicate that double-tapered fiber probe with the detection limit of 10-9 M is the most sensitive.

Facile synthesis of α-Fe2O3/diatomite composite for visible light assisted degradation of Rhodamine 6G in aqueous solution

α-Fe2O3 particle supported on diatomite (α-Fe2O3/diatomite composite) was prepared at room temperature by the chemical precipitation method using ferrous sulphate as the raw material and diatomite as supporter. α-Fe2O3/diatomite composite was characterized by XRD, FE-SEM, FT-IR and DRS. The result showed that α-Fe2O3 was uniformly loaded on the diatomite. The photocatalytic activity was investigated under visible light toward degradation of Rhodamine 6G aqueous solution and the effects of various experimental factors on Rhodamine 6G degradation were investigated. Compared with the α-Fe2O3, α-Fe2O3/diatomite composite had significantly enhanced activity in the degradation of Rhodamine 6G under visible light irradiation. Besides, the photostability of catalysts was also investigated. The experimental results indicated that the prepared composite is a promising material for the wastewater treatment for its good catalytic performance property and long-term stability.

Effect of silver nanoparticles on luminescent and generation properties of rhodamine 6G in aqueous alcohol solutions

The plasmon effect that silver nanoparticles have on the luminiscent and generation properties of rhodamine 6G molecules in aqueous alcohol solutions is studied. It is found that the intensities of absorption and emission increase when silver nanoparticles are added to aqueous solutions of rhodamine 6G. It is shown that upon the laser photoexcitation of aqueous solutions of rhodamine 6G dye, spontaneous fluorescence occurs that is converted into stimulated laser emission as the pump power grows. It is found that an increase in intensity and a drop in the generation threshold of stimulated emission are observed when silver nanoparticles are added to a solution of rhodamine 6G. It is shown that the dependence of absorbance, the intensity of fluorescence, and the dye’s generation of stimulated emission on the concentration of silver nanoparticles in solution falls as the proportion of alcohol grows.

Supramolecular polymer micelles as universal tools for constructing high-performance fluorescent nanoparticles

This study is the first attempt to encapsulate fluorescent rhodamine 6G (R6G) into supramolecular micelles as a means of manipulating the fluorescence color and quantum efficiency of R6G, and provides a quick and simple route towards the fabrication of high-efficiency fluorescent nanoparticles for next-generation lighting devices and biomedical image applications. We demonstrate that these R6G-loaded micelles exhibit a uniform size distribution, tunable R6G loading capacity and a rapid R6G release rate, in combination with excellent thermal sensitivity due to dissociation of the dynamic hydrogen bonds at environmental temperatures above the lower critical solution temperature. Importantly, R6G-loaded micelles act as an effective chromophore to greatly improve the fluorescence-color stability of R6G in aqueous solution and provide a maximum quantum yield of 0.75, which is more than two times higher than that of the equivalent concentration of free R6G; these features are highly desirable yet extremely rare in conventional polymer carriers and low-molecular-weight surfactant systems.

CsPbBr3 Perovskite Quantum Dots-Based Monolithic Electrospun Fiber Membrane as an Ultrastable and Ultrasensitive Fluorescent Sensor in Aqueous Medium.

Perovskite quantum dots with excellent optical properties and robust durability stand as an appealing and desirable candidate for fluorescence resonance energy transfer (FRET) based fluorescence detection, a powerful technique featuring excellent accuracy and convenience. In this work, a monolithic superhydrophobic polystyrene fiber membrane with CsPbBr3 perovskite quantum dots encapsulated within (CPBQDs/PS FM) was prepared via one-step electrospinning. Coupling CPBQDs with PS matrix, this CPBQDs/PS FM composite exhibits high quantum yields (∼91%), narrow half-peak width (∼16 nm), nearly 100% fluorescence retention after being exposed to water for 10 days and 79.80% fluorescence retention after 365 nm UV-light (1 mW/cm2) illumination for 60 h. Thanks to the outstanding optical property of CPBQDs, an ultralow detection limit of 0.01 ppm was obtained for Rhodamine 6G (R6G) detection, with the FRET efficiency calculated to be 18.80% in 1 ppm R6G aqueous solution. Electrospun as well-designed fiber membranes, CPBQDs/PS FM composite also possesses good tailorability and recyclability, showing exciting potential for future implementation into practical applications.

TiO2-chabazite semiconductor composites for photocatalytic degradation of rhodamine under sunlight irradiation

In this work, natural zeolite chabazite was employed to obtain semiconductor composites by mixing with commercial and sol-gel processed, anatase phase TiO2 powders. The TiO2-chabazite semiconductor composites were prepared by mixing the powders and subsequently milling at high-energy or stirring in aqueous solution at acid pH. The crystalline and morphological characteristics of the semiconductor composites were analyzed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show the polycrystalline character of the composites with good synergy between the phases. The different semiconductor composites were also tested and compared as photocatalysts in the photodegradation of rhodamine 6G in aqueous solutions under sulight irradiation. The photocatalytic properties of the semiconductor composites depend mainly on the quality of the TiO2 semiconductor, with the commercial one yielding better photocatalysts. The adsorption properties of chabazite aid the photocatalysis process by accumulating rhodamine molecules near TiO2 and allowing deeper penetration of sunlight in the solution. Both high-energy milled and acid route processed, commercial TiO2–based composites produced better results for the rhodamine photodegradation under sunlight irradiation. The percent reduction of rhodamine in solution after 90min produced by these semiconductor composites was 97.9 and 96.8%, respectively.

Decoration of silicon nanowires with silver nanoparticles for ultrasensitive surface enhanced Raman scattering

Silicon nanowires (Si NWs), produced by the chemical etching technique, were decorated with silver nanoparticles (NPs) produced at room temperature by the pulsed laser deposition (PLD) technique. Silver NPs were obtained by means of nanosecond pulsed laser ablation of a target in the presence of a controlled Ar atmosphere. Two different laser pulse numbers and Si NWs having different lengths were used to change the NP number density on the Si NW surface. The resulting Ag NP morphologies were studied by scanning electron microscopy imaging. The results show that this industrially compatible technological approach allows the coverage of the Si NW walls with Ag NPs with a strong control of the NP size distribution and spatial arrangement. The obtained Ag NP decorated Si NWs are free from chemicals contamination and there is no need of post deposition high temperature processes. The optical properties of Si NW arrays were investigated by reflectance spectroscopy that showed the presence of a plasmon related absorption peak, whose position and width is dependent on the Ag NP surface morphology. Coupling the huge surface-to-volume ratio of Si NW arrays with the plasmonic properties of silver nanoparticles resulted in a 3D structure suitable for very sensitive surface enhanced Raman scattering (SERS) applications, as demonstrated by the detection of Rhodamine 6G in aqueous solution at a concentration level of 10−8 M.

WO3/TiO2 composite coatings: Structural, optical and photocatalytic properties

WO3/TiO2 and TiO2 coatings were prepared on titania substrates using facile and cost-effective plasma electrolytic oxidation process. The coatings were characterized by X-ray diffraction, scanning electron microscopy, Raman, UV⿿vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. With increasing duration of PEO process, the monoclinic WO3 phase became dominant and new monoclinic WO2.96 phase appeared. The optical absorption edge in the WO3/TiO2 samples, enriched with WO3/WO2.96 phase, was shifted to the visible region. The photocatalytic efficiency of WO3/TiO2 and pure TiO2 samples was evaluated by performing the photodegradation experiments in an aqueous solution of Rhodamine 6G and Mordant Blue 9 under the visible and UV light. The WO3/TiO2 catalysts are much more efficient than pure TiO2 under visible light and slightly better under UV light. The improvement of photocatalytic activity in the visible region is attributed to better light absorption, higher adsorption affinity and increased charge separation efficiency.

The influence of synthesis method on size and toxicity of CeO2 quantum dots: Potential in the environmental remediation

The present study reports the investigation of photocatalysis and bacterial toxicity of cerium oxide quantum dots (CeO2 QDs) synthesized by two different approaches. The 3nm CeO2 QDs were synthesized by non-hydrolytic sol–gel method, while the 7nm QDs were prepared by hydrothermal method. The samples prepared by the sol–gel method exhibited a red shift in the absorption spectrum. In the current study, we also report the influence of size of CeO2 QDs on the antibacterial activity and photocatalysis. The antibacterial study was performed by minimum inhibitory concentration (MIC) method using Escherichia coli as model organism. The MIC of CeO2 QDs was established to be 2.5µg/mL and 5µg/mL for 3nm and 7nm CeO2 QDs respectively. Further evaluation and interpretation of bacterial viability was done by means of dual fluorescent staining. The photocatalytic activity experiment indicated that 3nm CeO2 QDs exhibited a higher photocatalytic activity for the photocatalytic decolonization of Rhodamine 6G aqueous solution under the visible-light illumination than 7nm samples. The synthesized QDs are not only photocatalysts but are potent bactericides as well. Conclusively, the size dependent antimicrobial activity of CeO2 QDs was demonstrated for the first time in this report. The disruption of bacterial cell wall mechanism was found to be the probable mechanism responsible for bacterial toxicity. Thus, the reported CeO2 QDs are promising candidates for removal of chemical and biological pollutants and thus have great potential in the environmental remediation.

SERS and FDTD simulation of gold nanoparticles grafted on germanium wafer via galvanic displacement

Uniform and dense Au nanoparticles grown on Ge (Au/Ge) were fabricated by a facile galvanic displacement method and employed as surface-enhanced Raman scattering (SERS) substrates. The substrates exhibited excellent reproducibility in the detection of rhodamine 6G aqueous solution with a relative standard deviation of <20%. The substrate showed a high Raman enhancement factor of 3.44 × 106. This superior SERS sensitivity was numerical confirmed by the three-dimensional finite-difference time-domain method, which demonstrated a stronger electric field intensity (|E/E0|2) distribution around the Au nanoparticles grown on Ge. This facile and low-cost prepared Au/Ge substrate with high SERS sensitivity and reproducibility might have potential applications in monitoring in situ reaction in aqueous solution. Copyright © 2014 John Wiley & Sons, Ltd.

Excited-state dynamics of rhodamine 6G in aqueous solution and at the dodecane/water interface.

The excited-state dynamics of rhodamine 6G (R6G) has been investigated in aqueous solution using ultrafast transient absorption spectroscopy and at the dodecane/water interface using the femtosecond time-resolved surface second harmonic generation (SSHG) technique. As the R6G concentration exceeds ca. 1 mM in bulk water, both R6G monomers and aggregates are excited to a different extent when using pump pulses at 500 and 530 nm. The excited-state lifetime of the monomers is shortened compared to dilute solutions because of the occurrence of excitation energy transfer to the aggregates, which themselves decay nonradiatively to the ground state with a ca. 70 ps time constant. At the dodecane/water interface, both monomers and aggregates contribute to the SSHG signal to an extent that depends on the bulk concentration, the pump and probe wavelengths, and the polarization of probe and signal beams. The excited-state lifetime of the monomers at the interface is of the order of a few picoseconds even at bulk concentrations where it is as large as several nanoseconds. This is explained by the relatively high interfacial affinity of R6G that leads to a large interfacial concentration, favoring aggregation and thus rapid excitation energy transfer from monomers to aggregates.

Sonocatalytic and sonophotocatalytic degradation of rhodamine 6G containing wastewaters

The present work deals with degradation of aqueous solution of Rhodamine 6G (Rh 6G) using sonocatalytic and sonophotocatalytic treatment schemes based on the use of cupric oxide (CuO) and titanium dioxide (TiO2) as the solid catalysts. Experiments have been carried out at the operating capacity of 2L and constant initial pH of 12.5. The effect of catalyst loading on the sonochemical degradation has been investigated by varying the loading over the range of 1.5–4.5g/L. It has been observed that the maximum degradation of 52.2% was obtained at an optimum concentration of CuO as 1.5g/L whereas for TiO2 maximum degradation was observed as 51.2% at a loading of 4g/L over similar treatment period. Studies with presence of radical scavengers such as methanol (CH3OH) and n-butanol (C4H9OH) indicated lower extents of degradation confirming the dominance of radical mechanism. The combined approach of ultrasound, solid catalyst and scavengers has also been investigated at optimum loadings to simulate real conditions. The optimal solid loading was used for studies involving oxidation using UV irradiations where 26.4% and 28.9% of degradation was achieved at optimal loading of CuO and TiO2, respectively. Studies using combination of UV and US irradiations have also been carried out using the optimal concentration of the catalysts. It has been observed that maximum degradation of 63.3% is achieved using combined US and UV with TiO2 (4g/L) as the photocatalyst. Overall it can be said that the combined processes give higher extent of degradation as compared to the individual processes based on US or UV irradiations.

Gold Nanoparticles-Modified Tapered Fiber Nanoprobe for Remote SERS Detection

This letter presents a surface-enhanced Raman scattering (SERS) nanoprobe based on gold nanoparticles-modified tapered optical fiber and demonstrates its ability to perform remote Raman detection. The nanoscale tapered fiber with the tip size of 40.7 nm was made by heated pulling and chemical etching methods. The gold nanoparticles, prepared beforehand by the Frens method with a microwave heating process, were deposited on the tapered surface of the nanoprobe with the electrostatic self-assembly technology. Raman spectra of Rhodamine 6G (R6G) molecules were measured, using this SERS nanoprobe in an optrode remote detection mode. Considerably high signal-to-noise ratio and high sensitivity were achieved. The detection limit for R6G aqueous solution reaches 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> mol/L.

Highly sensitive superhydrophobic Ag nanorods array substrates for surface enhanced fluorescence studies

We report a facile method to fabricate highly sensitive superhydrophobic Ag nanorods (AgNR) arrays based surface enhanced fluorescence spectroscopy (SEFS) substrates using glancing angle deposition technique at a substrate temperature of 133 K and then subsequent coating of heptadecafluoro-1-decanethiol (HDFT) molecules. The SEFS enhancement behaviour of these substrates was determined by using aqueous solution of Rhodamine 6G. The HDFT coated superhydrophobic AgNR arrays SEFS substrates exhibit more then 3-fold fluorescence signal enhancement than conventional AgNR films. These HDFT coated superhydrophobic AgNR SEFS substrates based sensors may find application for the purpose of trace analysis and biosensing.

Fabrication of SERS Active Surface on Polyimide Sample by Excimer Laser Irradiation

A possible application of excimer laser irradiation for the preparation of surface enhanced Raman spectroscopy (SERS) substrate is demonstrated. A polyimide foil of 125 μm thickness was irradiated by 240 pulses of focused ArF excimer laser beam (λ= 193 nm, FWHM = 20 ns). The applied fluence was varied between 40 and 80 mJ/cm2. After laser processing, the sample was coated with 40 nm silver by PLD in order to create a conducting layer required for the SERS application. The SERS activity of the samples was tested by Raman microscopy. The Raman spectra of Rhodamine 6G aqueous solution (c=10−3 mol/dm3) were collected from the patterned and metalized areas. For areas prepared at 40–60 mJ/cm2laser fluences, the measured Raman intensities have shown a linear dependence on the applied laser fluence, while above 60 mJ/cm2saturation was observed. The morphology of the SERS active surface areas was investigated by scanning electron microscopy. Finite element modeling was performed in order to simulate the laser-absorption induced heating of the polyimide foil. The simulation resulted in the temporal and spatial distribution of the estimated temperature in the irradiated polyimide sample, which are important for understanding the structure formation process.

Iron(III)-Based Metal–Organic Frameworks As Visible Light Photocatalysts

Herein, a new group of visible light photocatalysts is described. Iron(III) oxides could be promising visible light photocatalysts because of their small band gap enabling visible light excitation. However, the high electron-hole recombination rate limits the yield of highly oxidizing species. This can be overcome by reducing the particle dimensions. In this study, metal-organic frameworks (MOFs), containing Fe3-μ3-oxo clusters, are proposed as visible light photocatalysts. Their photocatalytic performance is tested and proven via the degradation of Rhodamine 6G in aqueous solution. For the first time, the remarkable photocatalytic efficiency of such Fe(III)-based MOFs under visible light illumination (350 up to 850 nm) is shown.

Surface‐enhanced Raman scattering sensing on black silicon

Reactive ion etching was used to fabricate black‐Si over the entire surface area of 4‐inch Si wafers. After 20 min of the plasma treatment, surface reflection well below 2% was achieved over the 300–1000 nm spectral range. The spikes of the black‐Si substrates were coated by gold, resulting in an island film for surface‐enhanced Raman scattering (SERS) sensing. A detection limit of 1 × 10−6 M (at count rate &gt; 102 s−1 . mW−1) was achieved for rhodamine 6G in aqueous solution when drop cast onto a ∼ 100‐nm‐thick Au coating. The sensitivity increases for thicker coatings. A mixed mobile‐on‐immobile platform for SERS sensing is introduced by using dog‐bone Au nanoparticles on the Au/black‐Si substrate. The SERS intensity shows a non‐linear dependence on the solid angle (numerical aperture of excitation/collection optics) for a thick gold coating that exhibits a 10 times higher enhancement. This shows promise for augmented sensitivity in SERS applications.

Photodegradation of rhodamine 6G in aqueous solution via SrCrO4 and TiO2 nano-sphere mixed oxides

Nano-sphere TiO2 and SrCrO4 (up to 5 mol%) mixed oxides were synthesized by co-precipita- tion method and investigated as catalyst in the photodegradation of rhodamine 6G (Rh6G) in aqueous solution. SrCrO4/TiO2 oxides were characterized by techniques of powdered X-ray diffraction, EDAX, BET, TEM, SEM and ESR analysis. The photocatalytic activities of degradation of dyes were measured by UV-VIS absorption spectroscopy. The results showed that the mixed oxides of TiO2 with 1 mole % of SrCrO4 (SCT1) exhibit a photocatalytic acti- vity 3 times higher than that of P25TiO2 for oxidation of various dyes (Rh6G, TB, MO and BG) under UV light irradiation (l>280nm). Among all these dyes the photodegradation of Rh6G was faster compared to other dyes. The average crystallite sizes, spherical particle sizes and grain sizes of SCT1 were found to be ~15nm, 90±5nm and 100±5nm, respectively. The EPR spectrum of SCT1 indicated that the ejection of electron helped to degrade the dye molecule faster.