Methyl Orange Aqueous Solution Research Articles

Influence of nitrogen doping on visible light photocatalytic activity of TiO2 nanowires with anatase-rutile junction

TiO2 nanowires with a multi-phase structure synthesized by a hydrothermal method and doped with nitrogen by using annealing process in N2 atmosphere at different temperatures. The effects of nitrogen content on the structural, optical, and catalytic properties were studied by XRD, XPS, SEM, and UV–Vis diffuse reflectance spectroscopy. XRD patterns showed the presence of both anatase and rutile phases in doped products. UV–Vis diffuse reflectance spectroscopy revealed a red shift in the optical absorption edge. The photocatalytic activity was studied by the degradation of methyl orange aqueous solution under visible light irradiation and higher photocatalytic activity was found in N-doped materials.

Facile synthesis, characterization, and decolorization activity of Mn2+ and Al3+ co‐doped hexagonal‐like ZnO nanostructures as photocatalysts

A good photocatalyst with high efficiency can be synthesized easily using eco‐friendly materials and processes. Our synthesized samples exhibit all of the aforementioned features. In this work, manganese co‐doped ZnO at different weight percentages (3, 6, 9, and 15 wt.%) with and without 1.5 wt.% aluminum was synthesized by hydrothermal method, and their photocatalytic activity in aqueous solutions of methyl orange (MO) was investigated under visible light. The structural and optical properties of the samples were characterized using X‐ray powder diffraction, Fourier‐transform infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray analysis, and diffuse reflectance spectroscopy. In this work, Mn2+ ions in the 9%Mn/ZnO sample and Mn2+, Al3+ ions in the (9%Mn, 1.5%Al)/ZnO sample calcined at 800 °C were replaced instead with some Zn2+ ions in hexagonal wurtzite structures of ZnO. These structures were found next to each other in the form of a hexagonal shape that created 3D‐hexagonal‐like ZnO nanostructures. Finally, nanoparticles (NPs) and nano hexagonal‐like ZnO nanostructures were, respectively, dispersed on the surface of 3D‐hexagonal‐like structure of 9%Mn/ZnO and (9%Mn, 1.5%Al)/ZnO. Diffuse reflectance spectroscopy analysis showed that the (9%Mn, 1.5%Al)/ZnO sample had more light absorption than 9%Mn/ZnO. However, contrary to our expectations, the 9%Mn/ZnO sample had better decolorization efficiency (94%) after 60 min under visible light, which could be attributed to a significant increase in the level of recombination by the aluminum ions.

Efficient removal of methyl orange by a flower-like TiO2/MIL-101(Cr) composite nanomaterial.

Nano-scale MOF composite materials prepared by combining inorganic semiconductors with controllable pore structures and functional active sites for the effective removal of organic dyes will exhibit more excellent adsorption activity. In this paper, MIL-101(Cr) was used as a carrier and two-step hydrothermal methods were successfully used to prepare flower-like TiO2/MIL-101(Cr) composite nano-adsorbents with different sizes. The results of XRD, SEM, XPS and other characterization methods showed that when the molar ratio of Ti : Cr was 0.2 : 1, the composite nano-adsorbent exhibited better adsorption performance and removal efficiency for methyl orange (MO) in aqueous solution. By assembling TiO2 on MIL-101(Cr), Ti replaced part of Cr, and the positively-charged TiO2/MIL-101(Cr) nanocomposite and negatively-charged MO in aqueous solution formed a strong interaction force. In addition, the π-π packing interactions of the benzene ring of MIL-101(Cr) and the electrostatic force between TiO2 and MIL-101(Cr) also enhanced the performance and adsorption efficiency of the adsorbent to a certain extent. The BET results showed that the large specific surface area and average pore diameter of the TiO2/MIL-101(Cr) nanocomposites effectively improved the adsorption performance of the composites. The results showed that the MO removal efficiency of 20% TiO2/MIL-101(Cr) can reach 93.03% at 80 min. But when 20% TiO2/MIL-101(Cr) was used to adsorb 70 mg·L-1 MO, the experimental maximum adsorption capacity was 242.02 mg·g-1.

Enhanced visible-light photocatalytic activity of anatase-rutile mixed-phase nano-size powder given by high-temperature heat treatment.

Nano-size EVONIK AEROXIDE® P25 titanium dioxide, TiO2, powder was heat-treated at temperatures, 700–900°C, in air. An X-ray diffraction study showed that the P25 powder is composed of approximately 20 and approximately 80 mass% of rutile and anatase phases, respectively. It was also shown that the transformation from anatase to rutile induced by high-temperature heat treatment was almost completed at 750°C, whereas a small amount (less than 3 mass%) of anatase phase was still left even in the powder heat-treated at 900°C. The transformation behaviour was consistent with results obtained by Raman scattering spectroscopy. Raman experiments also indicated that high-temperature heating induced the formation of oxide ion vacancies. Powders were dispersed in methyl orange (MO) aqueous solution, and the bleach rate of MO was measured to evaluate photocatalytic activity under ultraviolet (UV)- and visible-light irradiation. After the heat treatment, the UV-light photocatalytic performance sharply deteriorated. Interestingly, visible-light photocatalytic activity was enhanced by high-temperature heating and reached the highest performance for an 800°C-heated sample, indicating that the P25 powder obtained high visible-light photocatalytic performance after heat treatment. Even after 900°C heat treatment, the photocatalytic performance was higher than that of as-received powder. Enhancement of photocatalytic activities was discussed in relation to visible light absorption and charge carrier transfer.

Preparation and Photocatalytic Performance of Dumbbell Ag2CO3-ZnO Heterojunctions.

Dumbbell Ag2CO3–ZnO heterojunctions were synthesized for the first time via a simple in situ precipitation method. The as-prepared Ag2CO3–ZnO heterojunction showed high photocatalytic activity in the decomposition of methyl orange aqueous solution under simulated solar irradiation. The high improvement of photocatalytic activity compared to that of pure ZnO can be attributed to the formation of the Ag2CO3–ZnO heterojunction. Furthermore, the mechanism of photocatalytic activity was investigated in detail. The free radical trapping experiments indicated that the superoxide radical (·O2–) was an important active species in the photocatalytic process. This paper provides a new prospect for the preparation of photocatalysts with high catalytic performance in the degradation of dye wastewater.

Photocatalytic Degradation Dynamics of Methyl Orange Using Coprecipitation Synthesized Fe3O4 Nanoparticles

This study aims to investigate the photocatalytic degradation performance, mechanism, and dynamics of methyl orange (MO) which is a widely used organic dye in textile industries as well a hazardous wastewater pollutant. The degradation process was catalyzed by employing a synthesized Fe3O4 magnetic nanoparticle (NP) using the coprecipitation method. The structural and morphological properties of the synthesized Fe3O4 NPs were investigated by employing XRD, HR-SEM, and XPS, which proved that acquired Fe3O4 NPs were in a pure phase. Moreover, the crystallite sizes fall in the range of 28–31.8 nm and were estimated by applying the Scherrer equation on the XRD spectrum as well as calculated independently by applying a statistical approach on the SEM micrographs. The UV–Vis maximum in the visible range at 468.8 nm consists of two absorption frequency bands due to the effect of the hydrogen-bond interaction between water and the azo nitrogens in the MO. A non-monotonic spectral dynamic accompanied by peak wavelength shifts, as well as the absolute signal amplitude and signal area of the MO band, suggests that a cleavage of the azo bond is not the only and/or the dominant process in the photocatalytic oxidization of the MO in a protic solvent. The overall absorbance process is a complicated response to a combination of nonspecific and specific solute-solvent interactions, dipole-dipole interactions, hydrogen-bonding networks, and other possible intermolecular interactions such as hydrophobic/hydrophilic interactions. A bi-exponential decay was found to be the best fitting function to model the decay of the time-dependent electrical conductivity of the MO aqueous solution under photocatalytic oxidization. The Fe3O4 NPs exhibited a 98.3% removal of MO within 110 min. Photocatalytic degradation of methyl orange can be modeled to the first-order model with a rate constant k of 0.037 min−1 taking into account the initial concentration of 1175 ppm of MO. The degradation/decolorization efficiency deduced from the low-frequency band of the visible spectra is around 99.4% after 110 min. The real-time degradation/decolorization efficiencies deduced from the overall absorbance maxima and the low-frequency band have a discrepancy of 50.1% at 20 min and 12.3% at 60 min representing the progressive attenuation of the H-bond impact dissociation of MO (degradation/decolorization).

ZnO (Ag-N) Nanorods Films Optimized for Photocatalytic Water Purification

ZnO nanorods (NRs) films, nitrogen-doped (ZnO:N), and ZnO doped with nitrogen and decorated with silver nanostructures (ZnO:N-Ag) NRs films were vertically supported on undoped and N doped ZnO seed layers by a wet chemical method. The obtained films were characterized structurally by X-ray diffraction. Morphological and elemental analysis was performed by scanning electron microscopy, including an energy dispersive X-ray spectroscopy facility and their optical properties by Ultraviolet-Visible Spectroscopy. Analysis performed in the NRs films showed that the nitrogen content in the seed layer strongly affected their structure and morphology. The mean diameter of ZnO NRs ranged from 70 to 190 nm. As the nitrogen content in the seed layer increased, the mean diameter of ZnO:N NRs increased from 132 to 250 nm and the diameter dispersion decreased. This diameter increase occurs simultaneously with the incorporation of nitrogen into the ZnO crystal lattice and the increase in the volume of the unit cell, calculated using the X-ray diffraction patterns and confirmed by a slight shift in the XRD angle. The diffractograms indicated that the NRs have a hexagonal wurtzite structure, with preferential growth direction along the c axis. The SEM images confirmed the presence of metallic silver in the form of nanoparticles dispersed on the NRs films. Finally, the degradation of methyl orange (MO) in an aqueous solution was studied by UV-vis irradiation of NRs films contained in the bulk of aqueous MO solutions. We found a significant enhancement of the photocatalytic degradation efficiency, with ZnO:N-Ag NRs film being more efficient than ZnO:N NRs film, and the latter better than the ZnO NRs film.

Synthesis of heterostructure δ-MnO2/h-MoO3 nanocomposite and the enhanced photodegradation activity of methyl orange in aqueous solutions

The growing extent of dye pollution by human activities has engendered an urgent need for removing of them through adjustable approaches. The adsorption–photocatalytic technique is attractive and widely employed to address the above issue, since it could achieve pollutant mineralization by the reactive species generated under the light irradiation without other chemicals. In this paper, a series of δ-MnO2/h-MoO3 nanocomposites was successfully synthesized by a simple two-step method. The structure and morphology of the as-prepared nanocomposite have been assessed by XRD, FESEM, TEM, XPS and BET surface area measurements, and the optical properties were detected by the UV–Vis diffuse reflectance, photoluminescence (PL) and photocurrent measurements. Photocatalytic performances of the prepared δ-MnO2/h-MoO3 nanocomposite were evaluated through photodegradation of dyes in solution under simulated sunlight irradiation. After a simple two-step preparation process, the specific surface area (SBET) of the δ-MnO2/h-MoO3 composite was increased by about 4.5 times compared to the pure δ-MnO2 and h-MoO3, and this may result in a great adsorption property for the nanocomposite. With a broader absorption edge, high electron transfer efficiency and lower recombination efficiency of the photogenerated electrons and holes, the photocatalytic activity of the heterostructure δ-MnO2/h-MoO3 composites was improved heavily compared to the single-phase samples. Especially, when 20 mg of δ-MnO2 (0.6 g)/h-MoO3 composite was used to degrade methyl orange (MO) aqueous solution (100 mL, 15 mg L−1), the degradation efficiency could reach 80.55% within 115 min under simulated sunlight irradiation. Additionally, the photodegradation cyclic tests showed that the nanocomposite exhibited excellent stability, as the degradation efficiency reaches 71.02% within 95 min after four cycles, which makes it to have a bright prospect of industrial application. Finally, the reasonable mechanism for the enhanced photocatalytic activity of the heterostructure δ-MnO2/h-MoO3 composites was investigated by active species trapping experiments, and the results showed that the synergistic effect between δ-MnO2 and h-MoO3 as well as the unique flower ball-stick morphology of composites lead to an excellent photocatalytic performance.

Synthesis and characterization of cubic Ag/TiO2 nanocomposites for the photocatalytic degradation of methyl orange in aqueous solutions

Using a hydrothermal strategy combined with photoreduction process, Ag/TiO2 nanocomposites in which ultra-small metallic Ag anchored on nano-TiO2 were synthesized. The SEM, TEM, EDS, XRD, as well as UV–Vis-NIR spectrum were used to characterize the Ag/TiO2 nanocomposites. It can be drawn the conclusion that the TiO2 exhibited irregular cube with a diameter of 20–30 nm, and metallic Ag anchored on the surface of nano-TiO2. The addition of metallic Ag successfully broaden the photoresponse range from UV region to visible light region. Photocatalytic activity of Ag/TiO2 was evaluated by degradation of methyl orange in aqueous solution. The results showed that the degradation rate of methyl orange by Ag/TiO2 reached 65.4% in 120 min, indicating a higher photocatalytic activity of Ag/TiO2 than that of pure TiO2 nanomaterials. The additional absorption of Ag/TiO2 in visible region was attributed to the plasmonic absorption of Ag. Moreover, the kinetic behavior could be described in terms of Langmuir-Hinshelwood pseudo-first-order kinetic equation.

The electrochemical performance and catalytic properties of Ytterbium substitution on Manganese oxide nanoparticles: BET study; preparation and characterization

Pure and Yb-doped Mn3O4 nanostructures with different amounts of Yb3+ were synthesized via a facile hydrothermal route. The as-synthesized samples have been distinguished via scanning electron microscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction, UV–Vis spectroscopy, and Brunauer–Emmett–Teller (BET) techniques. Powder XRD patterns indicate that the Mn3-xYbxO4 (x = 0.00–0.08) samples are isostructural with spinel Mn3O4. The incorporation of Yb3+ into the Mn3O4 lattice was approved successfully through energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) technique. The pore volume and BET specific surface area of mesoporous Mn3O4 notably exceeds in comparison to Yb-doped Mn3O4 samples. The electrochemical properties of all the prepared materials as supercapacitance were investigated. Among different contents of Yb, 2% Yb-doped Mn3O4 displayed the enhanced specific capacitance. For photocatalytic degradation of Methyl Orange in aqueous solution, Yb-doped Mn3O4 nanoparticles were employed under visible light irradiation. Considering various amounts of dopant agent, 8% Yb-doped Mn3O4 nanoparticles showed the highest decolorization. In the occurrence of various radical scavengers, the inhibitory effect trend was benzoquinone > I− > buthanol > oxalate.

Improved visible-light photocatalytic activity of Mn3O4-based nanocomposites in removal of methyl orange

In this work, Mn3O4 nanoparticles were synthesized using hydrothermal and precipitation methods. Furthermore, the composites of Mn3O4 with graphene oxide alone and also with graphene oxide and clinoptilolite zeolite simultaneously were constructed. The products were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) scanning electron microscopy (SEM) and Diffuse Reflectance Spectroscopy analysis (DRS). Their photocatalytic activities were investigated using the photocatalytic degradation of Methyl Orange (MO) aqueous solution under visible light irradiation of 9 W LED lamp. According to the results, Mn3O4 nanoparticles showed no activity in removal test under visible light. In natural pH medium (pH = 7), (Mn3O4/GO)H composite revealed the best efficiency of 95.25% in MO removal process. However, (Mn3O4/GO/Clin) composite exhibited the best photocatalytic proficiency of 99.23%, in the removal of the dye in acidic medium (pH = 2).

Synthesis, characterization and photocatalytic activity of ZSM-5/ZnO nanocomposite modified by Ag nanoparticles for methyl orange degradation

In this study, ZSM-5/ZnO/Ag nanocomposite was synthesized with different amounts of silver and used for photocatalytic degradation of methyl orange aqueous solution. ZnO nanoparticles were initially precipitated on the surface of ZSM-5 zeolite, and the obtained ZSM-5/ZnO nanocomposite was modified by silver nanoparticles to increase the photocatalytic efficiency of the nanocomposite. The synthesized nanocomposites were characterized by FESEM, EDX, FTIR, XRD, UV–vis and TGA analyses. Furthermore, the effect of various parameters affecting the dye degradation as the initial dye concentration (2–20 mg/L), the photocatalyst amount (0.01-0.07 g) and initial pH (3–11) were studied. The band gap investigations showed that ZSM-5/ZnO modification with silver nanoparticles increases the photocatalytic activity of the resulting nanocomposite. The highest value of dye decomposition was obtained about 90% with an initial concentration of 5 ppm, pH = 11, 0.07 g photocatalyst under UV exposure for 2 h. Increasing photocatalyst amount in the solution and increasing silver amount in the photocatalyst structure (ZSM-5/ZnO/Ag ratio equal to 3:3:1, 3:3:5 and 3:3:10) increased the dye removal from the solution. Additionally, dye degradation of dye in alkaline conditions (pH values of 7–11) was more than that of the acidic conditions (pH values of 3–7). Investigation of different dye removal kinetic models showed the conformance of the pseudo-second-order model to the process of methyl orange dye degradation with R2>0.99 by synthetic nanocomposites.

Construction of Z-scheme g-C3N4/Ag/P3HT heterojunction for enhanced visible-light photocatalytic degradation of tetracycline (TC) and methyl orange (MO)

Constructing a conductive interface is crucial for the transfer of photoexcited charges in the photocatalytic heterojunction system. In this study, we introduced Ag into g-C3N4/P3HT system to construct a conductive interface which benefits for transfer of photoexcited charges between g-C3N4 and P3HT. A series of characterizations were employed to investigate the chemical structure, morphology and optical property of the obtained catalysts. And the photocatalytic activity of the as-prepared g-C3N4/Ag/P3HT composites were evaluated by the degradation of tetracycline (TC) and methyl orange (MO) aqueous solution under visible light irradiation. Results show that the g-C3N4/Ag/P3HT exhibits a broad absorption band in the region of 400–700 nm and the photocatalytic activity of g-C3N4/Ag/P3HT obtains a great improvement comparing with that of g-C3N4, g-C3N4/Ag and g-C3N4/P3HT. In addition, the optimized loading content of P3HT is 0.3 mass% based on g-C3N4. The enhanced photocatalytic performance is due to the introduction of Ag, which improves the transfer of photoexcited charges between g-C3N4 and P3HT. The active species trapping experiment shows that the main active specie is O2−. After five recycling experiments, the g-C3N4/Ag/P3HT shows high stability in the photocatalytic performance.

Enhanced photocatalytic activities of Nd-doped TiO2 under visible light using a facile sol-gel method

Titanium dioxide nanoparticles modified with neodymium in the range of 1 mol% to 5 mol% were prepared with template-free sol-gel method. The structures of obtained samples were characterized by X-ray powder diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and diffuse reflectance spectroscopy. The photocatalytic activity of the obtained samples was evaluated by photodegradation of methyl orange in aqueous solution under ultraviolet–visible (λ > 350 nm) and visible (λ > 420 nm) irradiation. The experimental results show that the 1 mol% Nd-doped TiO2 exhibits the highest photocatalytic activity, of which the degradation can reach to 96.5% under visible irradiation. According to the XRD results, the pristine samples are combined with anatase TiO2 and rutile TiO2, while the Nd-doped TiO2 samples are anatase TiO2 only. This transformation has made an obvious promotion of photocatalyst activity after modification.

Hydrothermal Synthesis of Novel Hierarchical Flower-Like SnO₂ with Enhanced Visible-Light-Driven Photocatalytic Activity.

The novel hierarchical flower-like SnO₂ (HFL-SnO₂) nanostructures with the diameter of about 500 nm, which are composed of regular-shaped nanosheets, are synthesized with a solvothermal method in the presence of 1 ml of Triethylamine (TEA) and the 0.2 mmol of Hexamethylene tetraamine (HMT) at 160 °C for 6 h. The SnO₂ has a high specific surface area of about 38.5 m²g-1. Based on the nucleation and self-assembly process, possible formation process of the new hierarchical flower-like nanostructures can be presented. The effects of TEA and HMT on the product are also studied. In addition, the product exhibits excellent photocatalttic activity to Methyl orange (MO) aqueous solution and possess good stability and reusability under visible light. This study will provide valuable experimental data for further study of nanomaterials and their photocatalytic properties.

Photocatalytic performance of BiFeO3 based on MOFs precursor

BiFeO3 (BFO) is considered to be a potential visible light photocatalytic material for organic degradation due to its narrow band gap. In this work, the BFO with smaller band gap and better photocatalytic performance was prepared by thermal decomposition of we prepared smaller band gap and better photocatalytic performance BFO by thermal decomposition of MOFs precursor Bi[Fe (CN)6]·5H2O. Among them, BFO‐0.5 has the best photocatalytic activity, which the photocatalytic degradation rate of methyl orange (MO) aqueous solution is 98.1% within 60 minutes. The photocatalytic activity is almost unchanged after four cycles of use. The enhanced photocatalytic activity of BFO could be attributed to the enhanced optical absorption and smaller particles. It may be conducive to design more efficient photocatalysts for photocatalytic degradation of organic dyes.

The effect of different physicochemical properties of titania on the photocatalytic decolourization of methyl orange

Due to the high variation in the reported photocatalytic activity results related the use of titania; the most famous photocatalyst, the reasons for such variation are investigated in the current article. Seven samples of commercial titania (TiO2) which produced from different sources were obtained and carefully characterized by XRD, N2 adsorption measurements Raman spectroscopy, DR UV–vis spectroscopy, and elemental analysis, to establish the physical properties and chemical structure of those samples. The photocatalytic behaviour of the investigated samples was evaluated through the decolourization reaction of methyl orange (MO) aqueous solution under black light illumination (wavelength = 367 nm) as a light source. The results showed that several parameters can affect the photocatalytic activity such as the morphological structure, the texture properties, the presence of contaminations, and the –OH density of the surface. Amongst the investigated samples, the sample with two different phases (anatase and rutile) exhibited the highest photocatalytic activity per gram catalyst.

UiO-66-supported Fe catalyst: a vapour deposition preparation method and its superior catalytic performance for removal of organic pollutants in water.

A vapour deposition (VD) method was established for preparation of the UiO-66-supported Fe (Fe/UiO-66) catalyst, which provided the first case of the metal-organic framework (MOF)-supported Fe catalyst prepared by using the vapour-based method. The Fe loading was around 7.0–8.5 wt% under the present preparation conditions. The crystal structure of UiO-66 was not obviously influenced by the Fe loading, while the surface area significantly decreased, implicating most of the Fe components resided in the pores on UiO-66. The results for the methyl orange (MO) removal tests showed that MO in aqueous solution can be removed by UiO-66 by adsorption, and in contrast, it can be oxidized by H2O2 with the catalysis of Fe/UiO-66. Further catalytic tests showed that Fe/UiO-66 was rather effective to catalyse the oxidation of benzene derivatives like aniline in water in terms of chemical oxygen demand (COD) removal efficiency. The catalytic test results for Fe/UiO-66 were compared to those of Fe/Al2O3 with the same Fe loading and to the catalysts reported in the literature. This paper provides a general strategy for VD preparation of MOF-supported Fe catalyst on the one hand, and new catalysts for removing organic pollutants from water, on the other hand.

Enhanced photocatalytic property of Fe doped ZnO nanoparticles prepared by sol-gel

Fe doped ZnO nanoparticles with different Fe concentrations 0.5%-2% were synthesized by sol-gol route. X-ray diffraction (XRD) results revealed that the prepared nanoparticles presented the hexagonal wurtzite structure. No impure peaks were found. Scanning electron microscope (SEM) and transmission electron microscopy (TEM) confirmed the nanoparticle morphology of Fe doped ZnO. UV-vis spectrophotometer showed the high asorption both in UV and visible region. Photocatalytic activity was calculated by degrading methyl orange (MO) aqueous solution under solar light. ZnO with 0.5 at% Fe showed the highest photocatalytic performance. It was observed that MO dyes undergo 91% photodegradation under 4 h solar irradiation. The results show that the prepared Fe doped ZnO nanoparticles can be efffectively helpful for the photocatalytic applications.

Visible-light-driven selectively photocatalytic performance of an open-framework based on T3 Supertetrahedral clusters

An open-framework (Heta)5(H3O)[In10S4Se14]·2H2O based on T3 supertetrahedral was synthesized by solvothermal method. It can be used as efficient and selective photocatalytic materials for the decomposition of organic cationic dyes Methylene Blue and cationic quinoid form of Methyl Orange against anionic Methyl Orange in aqueous solutions.