Rhodamine B Molecules Research Articles

Highly selective chemiluminescence detection of hydroxyl radical via increased π-electron densities of rhodamine B on montmorillonite matrix

The current chemiluminescence (CL) probes for hydroxyl radical (•OH) are poorly selective owing to a non-specific redox reaction. To the best of our knowledge, there have not been established on the CL probes for •OH using the strong electrophilicity of •OH. In this work, an ultrastrong CL emission is initiated by electrophilic attack of •OH towards rhodamine B (RhB) on the surface of montomorillonite (MMT). The improved CL emissions are attributed to the oriented H-type aggregation of RhB molecules on the surface of MMT by π–π stacking interactions, resulting in an increase in π-electron density of aromatic ring of RhB. The high π-electron density of benzene ring could facilitate the attack of electrophilic •OH towards RhB. In addition, a novel CL probe for •OH with high selectivity and high sensitivity has been established using the electrophilic properties of •OH rather than its common redox properties. The applicability of the proposed CL probe is evaluated by detecting •OH in untreated and gentamicin treated mouse fresh plasma samples. Our findings provide a new strategy to improve the selectivity of CL sensor of •OH.

Fluorescent Detection of Tadalafil Based on Competitive Host-Guest Interaction Using p-Sulfonated Calix[6]arene Functionalized Graphene.

A competitive fluorescence method toward tadalafil detection has been developed based on host-guest recognition by selecting rhodamine B (RhB) and p-sulfonated calix[6]arene functionalized graphene (CX6-Gra) as the "reporter pair". Upon the presence of tadalafil to the performed CX6-Gra-RhB complex, the RhB molecules are displaced by tadalafil, leading to a "switch-on" fluorescence signal. The observed fluorescence signal can be used for quantitative detection of tadalafil ranging from 1.00 to 50.00 μM with a detection limit of 0.32 μM (S/N = 3). The inclusion complex of tadalafil and CX6 was studied by molecular docking and the results indicated that a 1:1 host-guest stoichiometry had the lowest ΔG value of -7.18 kcal/mol. The docking studies demonstrated that the main forces including π-π interactions, electrostatic interactions, and hydrophobic interactions should be responsible for the formation of this inclusion compound. The mechanism of the competitive host-guest interaction was clarified. The binding constant (K) of the tadalafil/CX6 complex was more than 5 times greater than that of RhB/CX6.

Integration of ZnO with g-C3N4 structures in core–shell approach via sintering process for rapid detoxification of water under visible irradiation

We integrated ZnO with g-C3N4 nanostructures via successful core–shell formation using single step simple sintering process for photocatalysis application. Analytical tools show that the g-C3N4 shell with an average thickness of 3 nm has been coated onto surface of ZnO nanoparticles. Additionally, few ZnO particles are sporadically distributed on g-C3N4 sheets forming their nanocomposites. Further, these core–shell nanocomposites are used as photocatalysts for the degradation of Rhodamine B (RhB) under visible irradiation. As a result of photocatalysis measurements, it was found that 0.75 wt% zinc source with g-C3N4 exhibited almost two times high kinetic rate constant (k = 6.87 × 10−3 min−1) as compared with that of pure g-C3N4 (k = 3.38 × 10−3 min−1) and ZnO (k = 1.03 × 10−3 min−1) nanostructures. This enhanced photocatalytic performance of core–shell nanocomposites was aroused from effective interfacial charge separation and transportation, resulted into rapid degradation of RhB molecules. Moreover, increased optical absorption in visible region of spectrum revealed the large number of generation of charge carriers. Fabricated ZnO/g-C3N4 core–shell nanocomposites are also stable upto four cycles, indicating its good stability. Therefore, present core–shell nanocomposites can be applied to water purification devices under visible irradiation.

Study of surface-enhanced Raman scattering activity of DNA-directed self-assembled gold nanoparticle dimers

Quantitative research on the localized surface plasmon resonance of metallic nanostructures has received tremendous interest. However, most current studies have concentrated on theoretical calculation because it is difficult to obtain monodisperse metallic nanostructures with high purity experimentally. In this work, gold nanodimers (GNDs) with high uniformity are fabricated through DNA-directed self-assembly of gold nanoparticles and then used as substrates for surface-enhanced Raman scattering (SERS). The dependence of the SERS properties of the substrates on the size of the gold particles and the position of Rhodamine B (RB) molecules is systematically studied using the DNA-directed self-assembled GNDs with Raman-active RB molecules immobilized in different positions between pairs of gold nanoparticles as a model system. Theoretical simulations conducted using the finite difference time domain (FDTD) method confirm the structure-dependent SERS characteristics of the GNDs, with good agreement between the FDTD simulation data and experimental results.

Estimating pH at the Air/Water Interface with a Confocal Fluorescence Microscope.

One way to determine the pH at the air/water interface with a confocal fluorescence microscope has been proposed. The relation between the pH at the air/water interface and that in a bulk solution has been formulated in connection with the adsorption equilibrium and the dissociation equilibrium of the dye adsorbed. Rhodamine B (RhB) is used as a surface-active fluorescent pH probe. The corrected fluorescence spectrum of RhB molecules at the air/water interface with the surface density of 1.0 nmol m(-2) level shows pH-dependent shifts representing an acid-base equilibrium. Two ways to determine the unknown acid-base equilibrium constant of RhB molecules at the air/water interface have been discussed. With surface-tension measurements, the adsorption properties, maximum surface density, and adsorption equilibrium constants were estimated for both cationic and zwitterionic forms of RhB molecules at the air/water interface.

Hydrothermal synthesis of SnO 2 –Zn 2 SnO 4 –graphene composites with high activity for photodegradation of rhodamine B

The SnO2–Zn2SnO4–graphene composite photocatalysts were successfully prepared by a facile hydrothermal reaction method in an ethanol–water solvent. The as-prepared catalysts were characterised by techniques of X-ray diffraction, Raman spectroscopy, transmission electron microscopy and N2-sorption. The catalytic activity test results show that this SnO2–Zn2SnO4–graphene composite possesses higher photocatalytic degradation of rhodamine B (RhB) activity than that of pure SnO2–Zn2SnO4 under UV-light irradiation in an aqueous solution. The improved photocatalytic activity may be due to the increased adsorbability for the RhB molecule, more active sites, more photocatalytic reaction centres and the prevention of the photogenerated electron–hole pair recombination.

Silver Iodide Nanospheres Wrapped in Reduced Graphene Oxide for Enhanced Photocatalysis

AbstractWe have prepared nanocomposites of well‐defined spherical AgI nanostructures wrapped in reduced graphene oxide nanosheets (AgI@RGO). The as‐obtained AgI@RGO nanocomposites exhibit an enhanced photocatalytic activity and stability in the degradation of organic pollutants, namely, Rhodamine B (RhB), in comparison with bare AgI nanospheres. The hybridization of AgI nanospheres with RGO nanosheets affords a good adsorptive capacity for RhB molecules, facilitated charge transfer, and suppressed recombination of electron–hole pairs. These figures of merit lead to an enhanced photocatalytic performance over AgI@RGO. This work opens new possibilities for the development of highly efficient and stable visible‐light‐driven composite photocatalysts for environmental purification.

Multi-Step Host–Guest Energy Transfer Between Inorganic Chalcogenide-Based Semiconductor Zeolite Material and Organic Dye Molecules

We herein present the first case of energy transfer process in an inorganic chalcogenide-based semiconductor zeolite material (coded as RWY) serving as UV–vis light-harvesting host. A multistep vectorial energy transfer assay was fabricated by encapsulating acridine orange (AO) molecules into the RWY porous framework and further covering the formed capsules with rhodamine B (RhB) molecules. The UV high-energy excitations absorbed by RWY host were channeled to AO molecules and then onto RhB molecules to give rise to visible-light emission. The steady-state fluorescence and confocal microscope as well as fluorescent dynamics of emission reveal successfully the process of multistep vectorial energy transfer. This inorganic-host-involved energy transfer process has never been observed in an insulating oxide-based zeolite host system. Therefore, chalcogenide-based semiconductor zeolites could be a class of promising host materials to be further explored in the field of energy transfer and electron transfer bet...

Photomechanically Controlled Encapsulation and Release from pH-Responsive and Photoresponsive Microcapsules.

Poly(acrylic acid)/azobenzene microcapsules were obtained through distillation precipitation polymerization and the selective removal of silica templates by hydrofluoric acid etching. The uniform, robust, and monodisperse microcapsules, confirmed by transmission electron microscopy and scanning electron microscopy, had reversible photoisomerization under ultraviolet (UV) and visible light. Under UV irradiation, azobenzene cross-linking sites in the main chain transformed from the trans to cis isomer, which induced the shrinkage of microcapsules. These photomechanical effects of azobenzene moieties were applied to the encapsulation and release of model molecules. After loading with rhodamine B (RhB), the release behaviors were completely distinct. Under steady UV irradiation, the shrinkage adjusted the permeability of the capsule, providing a novel way to encapsulate RhB molecules. Under alternate UV/visible light irradiation, a maximal release amount was reached due to the continual movement of shell networks by cyclic trans-cis photoisomerization. Also, microcapsules had absolute pH responsiveness. The diffusion rate and the final release percentage of RhB both increased with pH. The release behaviors under different irradiation modes and pH values were in excellent agreement with the Baker-Lonsdale model, indicating a diffusion-controlled release behavior. Important applications are expected in the development of photocontrolled encapsulation and release systems as well as in pH-sensitive materials and membranes.

Adsorption and heterogeneous degradation of rhodamine B on the surface of magnetic bentonite material

A kind of imitation enzyme catalyst, Fe3O4 nanoparticles decorated Al pillared bentonite (Fe3O4/Al-B), was successfully prepared by in situ precipitation oxidization method and then applied for the adsorption and degradation of rhodamine B (RhB) in the presence of H2O2. The catalyst was characterized by XRD, SEM, XPS, BET, VSM and FTIR spectroscopy. The effects of oxidant concentration, initial RhB concentration and iron leaching on the degradation of RhB were investigated. The surface interactions with RhB in the absence and the presence of oxidant could be well described by Langmuir and Langmuir–Hinshelwood models, respectively. The Fe3O4/Al-B showed higher ability of adsorption and degradation efficiency toward RhB than bare Fe3O4 in the batch experiments. The whole degradation process of RhB followed pseudo-first-order rate law and was mainly controlled by surface mechanism reaction. The enhanced degradation efficiency of Fe3O4/Al-B might relate to the enrichment of RhB molecules by Al-B in the vicinities of active sites. Furthermore, the catalyst showed stable catalytic activity and convenient recycling. Negligible iron leaching showed the reused Fe3O4/Al-B can withstood the oxidation.

A new ratiometric electrochemical sensor for sensitive detection of bisphenol A based on poly-β-cyclodextrin/electroreduced graphene modified glassy carbon electrode

A ratiometric electrochemical sensor has been developed for highly sensitive and selective detection of bisphenol A. The assay strategy was based on the competitive host–guest interaction between poly-β-cyclodextrin/electroreduced graphene (Pβ-CD/EG) and Rhodamine B (RhB) probe or bisphenol A (BPA) target molecules. RhB can enter into the hydrophobic inner cavity of β-CD and shows an obvious oxidation peak on the Pβ-CD/EG modified glassy carbon electrode. In the presence of BPA, the RhB molecules are displaced by BPA because the host–guest interaction between β-CD and BPA is stronger than that between β-CD and RhB. As a result, the oxidation peak current of RhB (IRhB) decreases and the oxidation peak current of BPA (IBPA) increases correspondingly. The logarithmic value of IBPA/IRhB is linear with the logarithm of BPA concentration in the range of 1–6000 nM and the detection limit is 52pM (S/N=3). This strategy provides a new approach for sensitive detection of BPA, and has promising applications in the detection of organic pollutants in real environmental samples.

Rhodamine/Nanodiamond as a System Model for Drug Carrier.

In this paper we present some strategies that are being developed in our labs towards enabling nanodiamond-based applications for drug delivery. Rhodamine B (RhB) has been choosen as model molecule to study the loading of nanodiamonds with active moieties and the conditions for their controlled release. In order to test the chemical/physical interactions between functionalized detonation nanodiamond (DND) and complex molecules, we prepared and tested different RhB@DND systems, with RhB adsorbed or linked by ionic bonding to the DND surface. The chemical state of the DND surfaces before conjugation with the RhB molecules, and the chemical features of the DND-RhB interactions have been deeply analysed by coupling DND with Au nanoparticles and taking advantage of surface enhanced Raman spectroscopy SERS. The effects due to temperature and pH variations on the process of RhB release from the DND carrier have been also investigated. The amounts of released molecules are consistent with those required for effective drug action in conventional therapeutic applications, and this makes the DND promising nanostructured cargos for drug delivery applications.

Comparative Investigation on Photoreactivity and Mechanism of Biogenic and Chemosythetic Ag/C3N4 Composites under Visible Light Irradiation

A Ag/C3N4 nanocomposite with optimum Ag content is an efficient and green photocatalyst for pollutant degradation under visible light irradiation. In this study, we synthesized Ag NPs using NaBH4 and the squeezed out liquid (SOL) of plant biomass. The Ag NPs thus obtained have been loaded to C3N4 to form Ag/C3N4 nanocomposites that show superior photocatalytic performance toward Rhodamine B (RhB) under visible light irradiation. The photocatalytic activity of both biogenic and chemogenic Ag/C3N4 nanocomposites with different Ag contents is compared. Results show that the biogenically synthesized Ag/C3N4 exhibits better photocatalytic performance than the chemosynthetic composite. Of all the different nanocomposites prepared in this study, Ag48/C3N4 (0.048% of Ag content) exhibits excellent photoreactivity, with a reaction rate constant (k) 7-fold higher that the chemosynthetic Ag/C3N4. The observed improvement in the photoreactivity is mainly attributed to the high dispersion of Ag NPs on C3N4, facilitated by the organic compounds in SOLs. Besides, these organic compounds also enhance the photoreactivity of the catalyst by providing adsorption sited for RhB molecules and by shifting the Fermi level to more negative potential.

Effect of HCl and H2SO4 treatment of TiO2 powder on the photosensitized degradation of aqueous rhodamine B under visible light.

The acid treatments of TiO2 nanopowder with HCI or H2SO4 solution increase the concentration of the hydroxyl group on TiO2 surfaces compared to bare TiO2, which acts as a Brønsted acid site. For the case of the HCl-treated TiO2, the dissociation of Brønsted acid (proton donor) sites on TiO2 leads to a drop in the pH levels of rhodamine B (RhB) dye solutions (leading to the protonation of the RhB molecule), which allows the physisorption of the uncharged carboxyl acid group on the positively charged TiO2 surface. The carboxyl acid group is believed to afford a more efficient charge injection from the Visible-light-excited RhB to the conduction band of TiO2 compared to the N-ethyl group, yielding a significantly enhanced photodegradation of RhB mainly via the N-de-ethylation pathway. For the case of the H2SO4-treated TiO2, although the dissociation of Brønsted acid sites on TiO2 is also achieved, its photoactivity is much lower than that of the HCl-treated TiO2. It seems that the presence of SO4(2-) on the H2SO4-treated TiO2 behaves as an *OH scavenger to prevent the photodegradation of the dye.

A new spectrofluorimetric method for the determination of some tetracyclines based on their interfering effect on resonance fluorescence energy transfer.

A rapid, simple, inexpensive and highly sensitive spectrofluorimetric method was developed for the determination of trace amounts of some tetracyclines (TCs), namely tetracycline hydrochloride (TCH), oxytetracycline hydrochloride (OTCH) and minocycline hydrochloride (MCH). Binding rhodamine B (RhB) to gold nanoparticles (Au NPs) resulted in quenching of the fluorescence of RhB by a resonance energy transfer (FRET) mechanism, with Au NPs as the energy acceptors. The presence of TCs caused the release of RhB molecules and recovered their fluorescence, and this was used as a basis for the quantitative determination of TCs. The reaction was monitored spectrofluorimetrically by measuring the increase in fluorescence of RhB at 572 nm starting 5 min after mixing the reagents in Tris buffer solution (pH 6.5). The effect of various experimental factors such as buffer type, pH, concentrations of the involved reagents and reaction time were studied to optimize the reaction conditions. Under optimum conditions, the calibration graphs were linear within the ranges 2.08 × 10(-9) -1.04 × 10(-6) mol/L, 2.01 × 10(-9) -1.00 × 10(-6) mol/L and 2.02 × 10(-9) -1.01 × 10(-6) mol/L and detection limits (LODs) of 0.61 × 10(-9) , 0.32 × 10(-9) and 0.66 × 10(-9) mol/L were calculated for TCH, OTCH and MCH, respectively, with corresponding percent relative standard deviations (%RSDs) of 1.18, 1.21 and 1.54 (n = 5). The method was successfully applied to the determination of TCs in drinking water, human urine, bovine milk and breast milk samples.

Organic liquids-responsive β-cyclodextrin-functionalized graphene-based fluorescence probe: label-free selective detection of tetrahydrofuran.

In this study, a label-free graphene-based fluorescence probe used for detection of volatile organic liquids was fabricated by a simple, efficient and low-cost method. To fabricate the probe, a bio-based β-cyclodextrin (β-CD) was firstly grafted on reduced graphene surfaces effectively and uniformly, as evidenced by various characterization techniques such as Ultraviolet/Visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. The subsequent inclusion of Rhodamine B (RhB) into the inner cavities of the β-CD grafted on the graphene surfaces was achieved easily by a solution mixing method, which yielded the graphene-based fluorescent switch-on probe. In addition, the gradual and controllable quenching of RhB by Fluorescence Resonance Energy Transfer from RhB to graphene during the process of stepwise accommodation of the RhB molecules into the β-CD-functionalized graphene was investigated in depth. A wide range of organic solvents was examined using the as-fabricated fluorescence probe, which revealed the highest sensitivity to tetrahydrofuran with the detection limit of about 1.7 μg/mL. Some insight into the mechanism of the different responsive behaviors of the fluorescence sensor to the examined targets was also described.

Synthesis of Carbon Materials-TiO2 Hybrid Nanostructures and Their Visible-Light Photo-catalytic Activity.

Activated carbon, graphene, carbon nanotubes and fullerene were incorporated into TiO2 by a solvothermal approach and thermal annealing to produce carbon materials-TiO2 hybrid nanostructures. The carbon materials-TiO2 products were characterised by using SEM, TEM, XRD, Raman spectroscopy, X-ray photo-electron spectroscopy, UV-visible spectroscopy and photo-luminescence. The aim was to study the interactions between the main TiO2 phase and the carbon components, and the relationships between morphology, structure and photo-degradation of the rhodamine B (RhB) dye. An enhanced photo-catalytic degradation of RhB was achieved when using these nanocomposites over that for only using pure TiO2 . The superiority in photo-catalytic activities on the RhB molecules resulted from contributions from the excellent adsorption property, favourable chemical bond formation (TiOC), narrower band gap, smaller particle size and effective charge-carrier separation of the nanocomposites. Compared with the graphene-, carbon nanotube- and fullerene-TiO2 products, activated carbon-TiO2 exhibited weaker interactions between carbon and titania, lower adsorption for RhB and a larger band gap, which led to lower photo-catalytic activity of RhB.

Role of decoupled defect transitions of ZnO nanocrystals in energy transfer

Abstract We examine the quenching of the visible emission of zinc oxide (ZnO) nanocrystals (NCs) in the presence of Rhodamine B (RhB) molecules. Spectroscopic measurements reveal that the quenching is nonuniform over the entire emission envelope and this quenching could be explained by the energy transfer from NCs to RhB molecules under Forster formalism. Analysis of the steady state and time-resolved emission data of ZnO NCs demonstrate that at least three defect transitions are associated with the visible emission of ZnO NCs. These transitions are completely decoupled and thereby interact individually with the RhB molecules resulting in wavelength dependent energy transfer and hence uneven quenching of the NC fluorescence. Moreover, we determine the parameters for fluorescence resonance energy transfer (FRET) from NCs to RhB molecules.

Evaluating the sensitizing effect on the photocatalytic decoloration of dyes using anatase-TiO2

This work tries to clarify the contribution of the dye-sensitizing effect on the photocatalytic decoloration of dyes dissolved in aqueous media using an anatase TiO2 (A-TiO2) photocatalyst. The photocurrent-voltage (J–V) curves of a typical dye-sensitized solar cell (DSSC) with the A-TiO2 photoanodes adsorbed with various dyes, including methylene blue (MB), orange G (OG), rhodamine B (RhB), metanil yellow (MY), acid black 24 (AB24), and N719, are employed to demonstrate the sensitizing characteristics of dyes on A-TiO2. Unlike RhB, the MB, OG, MY, and AB24 cannot work as the photo-sensitizer on A-TiO2 from the J–V curves of DSSCs, reasonably due to the unmatched band position between dyes and A-TiO2. In the photocatalytic decoloration test of these dyes on A-TiO2 in aqueous media, dye adsorption onto A-TiO2 becomes the key factors affecting the photocatalytic decoloration rate because the generation of oxidants species (e.g., O2−, OH• or photo-excited holes) occurs on the A-TiO2 surface. The contribution of dye-sensitizing on the photocatalytic decoloration of RhB is negligible since the dye-sensitizing/electron-injection/dye-regeneration cycle cannot be completed in the degradation media while adsorbed RhB molecules are unstable when few photo-generated electrons have been injected into the conduction band of A-TiO2, probably leading to the decomposition of RhB.

PH-dependent absorbance of a centrifuged rhodamine B-TiO2 suspension, and a practical filtration method with minimized dye loss in a dye decoloration test

Although the centrifugation of a rhodamine B (RhB)-TiO2 suspension cannot separate TiO2 particles completely, the UV/Vis absorbance of the residual TiO2 in the centrifuged suspension, under neutral and basic conditions, is not fully revealed under the presence of RhB molecules. Therefore, in a dye decoloration test, the centrifuged suspension can be used for estimating the concentration of RhB molecules based on the RhB absorbance peak in a Vis light regime. From acidic suspensions, however, the elimination of TiO2 is so difficult that the centrifuged suspension results in a significant shift of the baseline of the RhB absorbance peak. An additional use of a microfilter removes not only the residual TiO2, but also a part of the dye. A practical recipe for the successful microfiltration of TiO2 powder with a minimal loss of dye from the acidic suspension has been proposed and its feasibility has been validated.