Study of adsorption of methylene blue and new methylene blue in liquid-solid interface by slab optical waveguide spectroscopy

A slab optical waveguide (SOWG) has been used for study of adsorption of both methylene blue (MB) and new methylene blue (NMB) in liquid–solid interface. Adsorption characteristics of MB and NMB on both bare SOWG and silanized SOWG by octadecyltrichlorosilane (ODS) were compared. Effect of pH on adsorption on MB and NMB was investigated. Binding rate constant analysis showed that both MB and NMB on bare SOWG demonstrates larger association constants than those on ODS-SOWG. Interactions of MB and NMB on bare SOWG and ODS-SOWG were analyzed by molecular mechanics calculation method. The binding energy change was in the following order: E_NMB–bare > E_MB–bare > E_NMB–ODS > E_MB–ODS.     

Development of a novel electrochemical cell for slab optical waveguide spectroscopy for in situ observation of methylene blue and anions on an electrode/electrolyte interface

A new spectroelectrochemical cell for slab optical waveguide (SOWG) spectroscopy was developed in order to observe in situ an electrode/electrolyte interface for bulk electrolysis. The new SOWG spectroelectrochemical cell has been evaluated by simultaneous electrochemical-absorption experiments of methylene blue (MB) using cyclic voltammetry (CV) and SOWG spectrometry. CV was performed in the SOWG spectroelectrochemical cell using indium tin oxide (ITO) coated glass as the working electrode, platinum wire as the counter electrode and a silver/silver chloride electrode (Ag/AgCl) as the reference electrode. Based on the CV and SOWG spectrometric data, it was found that the SOWG spectra showed the MB spectra on the electrode surface selectively and that SOWG with the cell would be useful as a tool for in situ study of an electrode/electrolyte interface. Using this cell, the effects of the supporting electrolytes, NaNO₃, KNO₃, CH₃COONa, and CH₃COOK on the absorbance of MB were examined at the potential of +0.8 V versus Ag/AgCl. The decrease in MB absorbance by nitrate ions was greater than that of acetate ions. Therefore the competitive adsorption of nitrate ions was stronger than that of acetate ions. Thus, the decrease in absorbance of MB in the presence of anions demonstrates the competitive adsorption of anions. These results show that the extent of specific adsorption of electrolytes was observed by measuring the SOWG absorbance intensity of MB.     

Pulse radiolysis of methylene blue and toluidine blue in PVA

Pulse radiolysis experiments were carried out with aqueous solutions of thionine dye methylene blue (MB) and toluidine blue in the presence of polyvinyl alcohol. The transient spectra obtained show maxima at 400 and 880 nm and are assigned to the respective semiquinone radical anions. The semiquinone radical decayed by a second order process. Furthermore, MB in PVA films were bleached by γ-radiolysis and the change in absorption was found to be linear with the dose.     

Sensitive measurement of methylene blue active substances by attenuated total reflection spectrometry with a trimethylsilane-modified glass slab optical waveguide

Attenuated total reflection spectrometry with a slab optical waveguide (SOWG) was explored for the simple, rapid and sensitive measurement of total anionic surfactants by the methylene blue active substance (MBAS) method. A fused-silica sheet used as a guiding layer was modified with trimethylsilane (TMS) to extract and concentrate the MBASs on the SOWG surface. Based on preliminary studies of the adsorption behavior and visible ATR spectrum of MB on the modified silica surface, a detection wavelength of 600 nm was chosen for the sensitive measurement of anionic surfactants. When the concentration of MB was set at 10 microM in the final measurement solution, the calibration curve for a typical anionic surfactant (sodium dodecylbenzenesulfonate) was linear up to 0.6 microM and the detection limit was 0.07 microM. The proposed method was applied to the determination of total anionic surfactants in river water.     

Increased cytotoxicity and phototoxicity in the methylene blue series via chromophore methylation

The cytotoxic and photodynamic activities of the commercially-available biological stains methylene blue (MB), 1,9-dimethyl MB (Taylor's Blue) and a newly synthesised compound, 1-methyl MB, were measured against the murine mammary tumour cell line, EMT-6 Both 1-methyl MB and 1,9-dimethyl MB exhibited increased dark toxicity with concomitant higher phototoxicity compared to MB at a light dose of 7.2 J cm⁻². While increasing the light dose as a function of the fluence rate increased the photocytotoxicity of MB, this had little effect on the methylated derivatives. In vitro chemical testing proved that successive methylation rendered the phenothiazinium chromophore both more resistant to reduction to its inactive leuco form, and also led to increased levels of singlet-oxygen production, thus providing a possible explanation for the increased toxicities of the methylated derivatives. Comparisons are made with the benzo[a]phenothiazinium photosensitizer, EtNBS.     

亚甲蓝在分子有序组合体中的聚集行为

研究了生物染色剂亚甲蓝(MB)在分子有序组合体(胶束、O/W微乳液和层状液晶)介质中的聚集行为。根据MB特征峰处的吸收光谱值,计算了MB的二聚平衡常数和相应单体、二聚体的摩尔消光系数。并用稳态荧光法和无外加探针的循环伏安法进一步论证了计算结果。研究发现,当MB总浓度一定时,在胶束体系中MB单体量较少,在层状液晶体系中单体量较多,在O/W微乳液体系中则介于胶束和层状液晶之间。表明层状液晶体系是获取更多MB单体的理想介质。     

Removal of methylene blue by tea wastages from the synthesis waste waters

The tea wastages could remove methylene blue（MB） as a cationic dye from waste water corresponding to second-order kinetic model.Thermodynamic studies showed that adsorption equilibrium constant（K_L） and maximum adsorption capacities(Q_max) were increased with increasing temperature.The removal efficiency of MB for Co 0.01 mmol/L at optimum conditions was about 85%. The maximum uptake capacity(Q_max) of methylene blue in a batch reactor was 0.328,0.542 and 0.659 mmol/g at 15,25 and 40℃, respectively.The enthalpy change（ΔH） and entropy change（ΔS） were 11.356 kJ/mol and 20.563 J/（mol K）,respectively.     

A sub-second, time-resolved, linear dichroism measurement system for visible attenuated total reflection spectroscopy with a slab optical waveguide

A sub-second, time-resolved, linear dichroism (LD) measurement system was constructed, fitted with a slab optical waveguide (SOWG), and utilized to observe the adsorption process of methylene blue (MB) onto silica surfaces. In the system, a semiconductor laser (670 nm) was used as the light source and the out-coupled beam from the SOWG was split by a polarizing beam splitter into two polarized beams (TE and TM modes) to allow sequential linear dichroic ratio data to be obtained; the acquisition rate was 11 data sets per second. For an MB solution that contained no sodium dodecylbenzenesulfonate (DBS), in contact with a bare silica surface, a clear decrease occurred in the average orientation angle of adsorbed MB in the initial stages of the adsorption process. This result may correspond to a change in the chemical form of MB from monomer to dimer.     

Electrochemical determination of heparin using methylene blue probe and study on competition of Ba with methylene blue for binding heparin

Cyclic voltammetric investigation of the interaction of methylene blue (MB) with heparin (hep) at a gold electrode is presented. The combination of MB with heparin formed a nonelectroactive complex MB-hep, which resulted in the peak current decrease of MB. The anodic peak current difference of MB was found to be proportional to the concentration of heparin in the range of 0.666-64.5 μg mL⁻¹ with a detection limit of 270 ng mL⁻¹ and a satisfactory result was obtained for the determination of heparin in injection samples. The equilibrium constant for MB-hep complex was calculated to be 7.32 × 10⁵. The dynamic process of competition of Ba²⁺ with methylene blue for binding heparin was monitored using quartz crystal microbalance (QCM) technique. The reaction rate constant between Ba²⁺ and MB-hep was estimated to be 0.0022 s⁻¹.     

Enthalpies of adsorption of methylene blue and crystal violet to montmorillonite

Calorimetric measurements of the enthalpy of adsorption on montmorillonite indicate different patterns for methylene blue (MB) and crystal violet (CV). The enthalpy of adsorption of MB is endothermic up to 73% of the cation exchange capacity (CEC) (i.e., about 0.6 mmol g^-1 clay), whereas at higher adsorption ratios the adsorption reaction becomes exothermic. The enthalpy of adsorption of CV is exothermic for all amounts adsorbed. These results were confirmed with adsorption experiments that prove that adsorption of MB increase with temperature, whereas CV adsorption decreases. This behavior indicates changes in the equilibrium coefficient according to Van't Hoff's equation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of NiO coated chitosan-cenosphere buoyant composite for enhanced adsorptive removal of methylene blue

The objective of the present study is to utilize fly ash cenosphere to remove methylene blue (MB) from the water streams. Nickel oxide is a typical semiconductor used as proficient adsorbent material for degradation of dye with environment friendly applications due to its excellent chemical stability and high catalytic activity. The chitosan cenosphere buoyant composite coated with NiO was synthesized with hydrothermal grafting reaction using silane coupling agent and epichlorohydrin as a cross-linking reagent. The batch adsorption experiments were carried out with a cationic dye, methylene blue as a representative organic pollutant to investigate the adsorptive capabilities of the composite as adsorbent. The influence of pH (2-12), initial concentration of dye (50–200 mg/L), temperature (37–47 °C) and contact time (0–24 h) were taken as parameters in the study. On the relative elimination of MB, the effect of time and temperature were investigated. The adsorption kinetics for MB was correlated and found to observe the pseudo-second order kinetic model, whereas the equilibrium adsorption isotherm follows the Langmuir model (R² > 0.99). The results indicate that the floating fly ash cenosphere coated with NiO proved to be more responsive for enhanced degradation of methylene blue.     

Dynamic analysis of aggregation of methylene blue with polarized optical waveguide spectroscopy

Polarized optical waveguide (POW) spectroscopy permits analysis of the changing molecular state of methylene blue (MB), including aggregate order and orientation at the waveguide surface. Monomer or dimer, dissolved randomly in MB aqueous solution, tends to aggregate at the waveguide surface during air drying. Furthermore, POW spectroscopy dynamically revealed that MB molecules became oriented vertically to the waveguide surface with increasing aggregation order.     

Comparative adsorption of methylene blue by magnetic baker’s yeast and EDTAD-modified magnetic baker’s yeast: Equilibrium and kinetic study

Magnetic baker’s yeast (MB) was prepared using glutaraldehyde cross-linking method and chemical modification with ethylenediaminetetraacetic dianhydride (EDTAD). The fabricated EDTAD-modified magnetic baker’s yeast (EMB) was then employed to remove methylene blue. Comparative adsorption of methylene blue by EMB and MB was systematically investigated with respect to pH, contact time, initial concentration and reaction temperature. The mechanism of methylene blue adsorption by EMB and MB was investigated by SEM, FTIR and Special surface area using methylene blue method. The results revealed that Fe₃O₄ nanoparticles were steadily cross-linked/incorporated with baker’s yeast biomass and the EDTA was modified on the surface of the magnetic baker’s yeast. The equilibrium adsorption data were fitted better by Langmuir isotherm, and the specific surface areas were 42.953–226.07 m²/g for MB and 94.972–499.85 m²/g for EMB, respectively. Kinetic studies suggested that the pseudo-second-order model was suitable to describe the adsorption process. Thermodynamic studies indicated that the adsorption was feasible, spontaneous and endothermic. The recovery efficiencies were above 80% by using 0.1 M HCl.     

Nucleation and Growth Mechanism of Electropolymerization of Methylene Blue: The Effect of Preparation Potential on Poly(methylene blue) Structure

Nucleation and growth mechanism of electropolymerization of methylene blue (MB) in a basic medium and the effect of preparation potential on poly(MB) film structure were investigated by using cyclic voltammetry, potentiostatic current‐time transient, scanning tunneling microscopy (STM), atomic force microscopy (AFM), and UV‐vis. absorption spectroscopy techniques. Electropolymerization of MB has been achieved by potentiodynamic (cyclic voltammetry) and potentiostatic (constant potential) techniques. The potentiostatic current‐time transients fitted with a theoretical model and morphological studies indicate that nucleation and growth mechanism of poly(MB) starts with a progressive layer‐by‐layer nucleation and growth besides random adsorption. Nucleation and growth of poly(MB) follows a process between progressive layer‐by‐layer and 3‐D instantaneous mechanism resulting in highly‐oriented poly(MB) nanofibers with increasing poly(MB) film thickness. Cyclic voltammetry and morphological studies exhibit that poly(MB) film structure changes depending on the preparation potential. Poly(MB) films prepared at the potential values of 900 and 950 mV show a well‐ordered, smooth surface but at the potential values higher than 1000 mV, rough polymer surface arises as overoxidation takes place. UV‐vis. absorption spectra of poly(MB) film and MB monomer show three peaks. The peak at 410 nm for poly(MB) shows 100 nm blue shift when compared to the MB monomer and is attributed to poly(MB) formation on the electrode.     

Intercalation of methylene blue into barium phosphate—synthesis and electrochemical investigation

Methylene blue (MB) was strongly retained inside the cavity of host layered barium phosphate, without leaching, and the intercalated compound was characterized through X-ray power diffraction (XRD), IR spectra and electrochemical measurements. The intercalated dye compound was incorporated into a carbon paste electrode and, by means of cyclic voltammetry and amperometry, its electrochemical properties were investigated. In various electrolyte solutions, changing the pH between 3 and 9, the midpoint potential remained practically constant at −0.15 V. This is not the usual behavior for MB, since it is known that in the solution phase the midpoint potential changes considerably with pH. These data suggest that methylene blue behaves as a guest molecule in the lamellar structure of the barium phosphate. The electrode formed by this host/guest composition was used to investigate NADH electrochemical oxidation.     

Reduction of methylene blue by thiocyanate: kinetic and thermodynamic aspects

This article reports the reduction of methylene blue (MB) by thiocyanate ions (SCN(-)) in aqueous and micellar solutions. Thiocyanate ions are found to be an effective reducing agent for the decolorization of methylene blue under ambient condition. Effects of salting-in and salting-out agents have been investigated for real-time application in the reduction process. The salting-in agent urea has been found to uniquely enhance the rate of the reduction of MB by thiocyanate ion in the presence of micelles. Again, the catalytic activity of nanoparticles in the reduction of MB has also been studied. Detailed kinetic and thermodynamic aspects have been considered to realize the interaction between methylene blue and thiocyanate. Kinetic studies revealed that the reaction is reversible and follows first-order reaction kinetics.     

Free‐standing Graphene/Poly(methylene blue)/AgNPs Composite Paper for Electrochemical Sensing of NADH

Highly flexible graphene/poly(methylene blue)/AgNPs composite paper was successfully prepared for amperometric biosensing of NADH. For this purpose, a dispersion including graphene oxide (GO), methylene blue (MB) and silver nanoparticles (AgNPs) was prepared and GO/MB/AgNPs paper was acquired by vacuum‐filtration of this dispersion through a suitable membrane. After peeling it off from membrane, it was transformed to rGO/MB/AgNPs paper by performing reduction with hydriodic acid. In a three‐electrode cell, which is containing 0.1 M phosphate buffer solution (pH: 9.0), rGO/MB/AgNPs paper was used as working electrode and rGO/poly(MB)/AgNPs composite paper was generated by surface‐confined electropolymerization of MB using successive cyclic voltammetry approach in a suitable potential window. Characterization of this composite paper was carried out by using scanning electron microscopy, scanning tunneling microscopy, X‐ray photoelectron spectroscopy, powder X‐ray diffraction spectroscopy, Raman spectroscopy, four‐point probe conductivity measurement and cyclic voltammetry techniques. Flexible rGO/poly(MB)/AgNPs composite paper has demonstrated high sensitivity, wide linear range and low detection limit for amperometric quantification of NADH.     

Effect of the composition and structure of titanosilicas on their photocatalytic activity in the decomposition of methylene blue

A comparison is made of the catalytic activity of the titanosilicas produced by pyrogenic synthesis and by the deposition of TiO₂ on pyrogenic SiO₂ in the photocatalytic decomposition of methylene blue (MB). The deposited titanosilicas exhibit high catalytic activity in the decomposition of MB as a result both of textural features and of the presence mainly of the anatase phase in the deposited TiO₂ compared with the pyrogenic titanosilicas. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 1, pp. 23–28, January–February, 2006.     

Determination of methylene blue by resonance light scattering method using silica nanoparticles as probe

A simple and novel method was developed to determine methylene blue(MB) by resonance light scattering(RLS) using silica nanoparticles(SiO_2NPs) as the probe.It was found that MB could enhance the RLS intensity of SiO_2NPs.Moreover,the increase in RLS intensity was linear with the concentration of MB over the range of 0.01-3.0 μg mL~(-1).The limit of detection(LOD) was as low as 4.36 ng mL~(-1)(3σ) and the relative standard deviation(RSD) was 2.4%(n=6).Under the optimum experimental conditions,this proposed method was successfully applied for the determination of MB in aquaculture samples with recoveries between 96.3% and 107%.Possible mechanisms for the RLS enhancement of SiO_2NPs in the presence of MB were also discussed.     

Study of catalytic reduction and photodegradation of methylene blue by heterogeneous catalyst

The photocatalytic degradation of methylene blue is investigated in aqueous solution containing CoS/nanoAl-MCM-41 photocatalyst under visible light. The catalyst is characterized by X-ray diffraction (XRD), UV-vis diffused reflectance spectra (UV-vis DRS) and transmission electron microscopy (TEM) techniques. The effect of CoS, nanoAl-MCM-41 support and different wt% of CoS over the support on the photocatalytic degradation and influence of parameters such as CoS loading, catalyst amount, pH and initial concentration of methylene blue on degradation are evaluated. Hypsochromic effects (i.e. blue shifts of spectral bands) resulting from N-demethylation of the dimethylamino group in methylene blue occurs in presence of CoS/nanoAl-MCM-41 under ambient condition. Meanwhile, the bleaching of methylene blue MB, by sulfide ion, in an aqueous solution is studied in the presence nanoAl-MCM-41 catalyst. In the presence of sulfide ions, MB is bleached to its colorless leuco (LMB) and MBH(2)(+) forms. In an acidified solution (pH<2) the bleaching process generates LMB and by changing pH between 2.0 and 7.0 bleaching of MB dye to MBH(2)(+) form is observed. Using nanoAl-MCM-41 with encapsulated CoS nanoparticles only causes demethylation of MB in aqueous solution.