Methylene Blue Water Research Articles

Utilizing waste corn straw to photodegrade methyl orange and methylene blue: Photothermal effect of biochar enhances photodegradation efficiency

The burning of corn straw will cause serious air pollution, and the utilization of corn straw can avoid the burning of corn straw and reduce environmental pollution. The pyrolysis of corn straw into biochar (BC) is a promising approach to apply corn straw in environmentally sustainable development. Dye wastewater such as methyl orange (MO) and methylene blue (MB) is a pollution that poses a threat to human health and the environment. Herein, biochar/TiO2 (BC/TiO2) and biochar/ZnO (BC/ZnO) were prepared by pyrolysis of corn straw for the photodegradation of MO and MB in water. The MO removal rates of BC/TiO2 and BC/ZnO are up to 83.3 % and 76.2 %, respectively, and the MB removal rates of BC/TiO2 and BC/ZnO are 78.6 % and 71.4 %, respectively. The photothermal effect of BC improves the surface temperature of photocatalysts and promotes the separation and transfer of photogenerated electron-hole pairs, enhancing the photodegradation of MO and MB efficiencies. Three-dimensional (3D) FDTD simulations were performed to investigate the mechanism of photothermal effect in BC/TiO2 and BC/ZnO. This work provides a promising approach to the utilization of corn straw.

Characterization and Adsorption Capacity of Modified Biochar for Sulfamethylimidine and Methylene Blue in Water.

In this study, a composite of pond mud and lanthanum- and nano-zero valent iron-modified-biochar was investigated for its ability to adsorb methylene blue (MB) and sulfamethazine (SMZ). La-modified attapulgite and nano-zero valent iron (surface area enhanced by 43.7% via Brunauer-Emmett-Teller analysis) were successfully loaded onto the straw-sediment biochar (BC) surface. With the increase in pyrolysis temperature, the biocompatibility yield, the H, O, and N content, and the ratio of carbon elements decreased, while the pH value, surficial micropores, C element, and ash content increased. The biocarbon small molecules were gradually and tightly ordered, and the organic groups such as hydroxyl, carboxyl groups, and carbon oxygen double bonds were gradually lost or disappeared. The original Fe-BC had more phenolic hydroxyl groups forming an intermolecular hydrogen bond than others with a higher adsorption capacity possibly through the Schiff base reaction. The effect of various pH (2-9), temperature (15-35 °C), and initial concentration (1-25 mg L-1) on adsorption was investigated. pH and temperature were the main factors governing the adsorption process. The maximum adsorption capacity was observed at pH 4. The adsorption performances for MB followed the order Fe-BC > La-BC > BC, and the maximum removal rate was over 98.45% with pH = 7. The three types of BC dosages between 0.2 (6.67 g L-1) and 0.4 g showed a removal rate of 99% for MB. The adsorption capacity of Fe-BC, La-BC, and BC for MB was 2.201, 1.905, and 2.401 mg L-1 with pH = 4, while 4.79, 4.58, and 5.55 mg g-1 were observed with BC dosage at 0.025 g. For SMZ, the higher the temperature, the better the adsorption effect, and it reaches saturation at approximately 25 °C. To further evaluate the nature of adsorption, Langmuir/Freundlich/Temkin models were tested and the adsorption capacities were evaluated on the surface of the BC composite. The three modified materials were physisorbed to SMZ, while MB was chemisorbed. For MB, the adsorption performance of BC is the best < 0.2 g (6.67 g L-1) at pH 7.0 at 35 °C. The Elovich model was more suitable for MB, while the Freundlich and Temkin models could better fit the adsorption process of MB. The preparatory secondary dynamics equation and Langmuir equation were more compliant for SMZ, and the saturated adsorption capacities of straw-modified, La-BC, and Fe-BC reached 5.699, 6.088, and 5.678 mg L-1, respectively.

Efficient photocatalytic degradation of organic pollutants over TiO2 nanoparticles modified with nitrogen and MoS2 under visible light irradiation

Investigate the use of visible light to improve photocatalytic degradation of organic pollutants in wastewater. Nitrogen-doped titania and molybdenum sulfide nanocomposites (NTM NCs) with different weight ratios of MoS2 (1, 2, and 3 wt.%) synthesized by a solid state method applied to the photodegradation of methylene blue(MB) under visible light irradiation. The synthesized NTM composites were characterized by SEM, TEM, XRD, FT-IR, UV–Vis, DRS and PL spectroscopy. The results showed enhanced activity of NTM hybrid nanocrystals in oxidizing MB in water under visible light irradiation compared to pure TiO2. The photocatalytic performance of NTM samples increased with MoS2 content. The results show that the photodegradation efficiency of the TiO2 compound improved from 13 to 82% in the presence of N-TiO2 and to 99% in the presence of MoS2 containing N-TiO2, which is 7.61 times higher than that of TiO2. Optical characterization results show enhanced nanocomposite absorption in the visible region with long lifetimes between e/h+ at optimal N-TiO2/MoS2 (NTM2) ratio. Reusable experiments indicated that the prepared NTM NCs photocatalysts were stable during MB photodegradation and had practical applications for environmental remediation.

Fabrication of reduced graphene oxide-doped carbon aerogels from water hyacinth for removal of methylene blue in water and energy storage

The development of industries has caused severe impacts on the environment and increased the demand of using energy. In this work, reduced graphene oxide-doped water hyacinth carbon aerogels (rGO/WHCA) were synthesized by cross-linking cellulose with poly(vinyl alcohol) as a binder and addition of graphene oxide (GO) as rGO precursors, followed by freeze-drying and pyrolysis techniques. The obtained materials were studied for adsorption of methylene blue (MB) in water and applied as electrodes for the supercapacitor. The impact of GO content on the characteristics, adsorption performance, and electrochemical properties of the rGO/WHCA were investigated. Besides, the concurrent effects of the adsorption time, and MB concentration on the adsorption capacity were evaluated via the response surface methodology according to the Box–Behnken model. The obtained rGO/WHCA materials exhibited ultralow density, high porosity, and an abundance of meso- and micropores structures. Especially, rGO/WHCA materials showed a great ability for removing MB in water with the highest adsorption capacity up to 95.03 mg/g after 420 min with the initial MB concentration of 150 ppm at pH 9 and performed the electrical double-layer capacitors (EDLCs) in a three-electrode system with an outstanding specific capacitance of 272.08 F/g at current density of 0.5 A/g. The obtained results open a potential pathway of using biomass sources, like water hyacinth, for solving environmental issues and the demand for energy storage.

Incorporation of polyoxometalate in La-BTC metal-organic frameworks for fast and selective removal of methylene blue dyes in water

This study prepares Mo-doped, particulate La-BTC metal-organic frameworks (Mo/La-BTC MOFs) using polyoxometalate over a broad Mo atomic fraction (fMo) from 0 to 0.9, and examines their selective adsorption against methylene-blue (MB) dyes in water. An increased Mo concentration up to 0.61 ​at% results in the Mo/La-BTC MOFs when fMo was increased to 0.9. Raman spectroscopy reveals an enhanced MoO bond intensity. The Mo/La-BTC MOFs show a linearly dependent MB adsorption uptake with the increasing fMo; to which, the MOF particles remove up to 75% of MB in water within only 1 ​min when using an initial MB concentration of 5 ​× ​10−6 ​M. This is in significant contrast with virtually zero removal against methyl-orange dyes. Our results indicate that the selective dye-removal capability depends solely on the [PMo12O40]3- complex as active sites on the La-BTC scaffold, and the MB adsorption remains effective over a broad pH range (3–10).

Studi Adsorpsi Methylene Blue oleh Graphene Oxide Dengan dan Tanpa Penyinaran Menggunakan Sinar UV-A

Graphene oxides (GO) that has a band gap of 3.2 eV is widely applied to remove color pollutants in water using the adsorption method. Besides, GO is also widely used as a supporting material in nanocomposites for photocatalytic applications. In this study, we carried out adsorption tests of methylene blue (MB) by GO in dark conditions and with UV-A light irradiation. The adsorption tests were carried out by mixing the GO dispersion with MB solution, then stirring for a certain period of time. During the process, samples sampling was carried out at a certain time to estimate concentration of the MB permeate. The adsorption tests were carried out in dark conditions (without irradiation) and with UV-A light irradiation. The results showed an improvement of adsorption ability of GO in reducing MB permeate concentration from 74% to 92% under the UV-A light irradiation. The process of adsorption without and under UV irradiation successively also shows an increasing reduction of concentration of MB in water

Adsorption studies of KOH-modified hydrochar derived from sugarcane bagasse for dye removal: Kinetic, isotherm, and thermodynamic study

Toxicity of methylene blue (MB) in water bodies has a negative effect on environment and living organisms. The presence of MB in water could last longer in view of the non-biodegradable characteristic. In this study, hydrochar was used as adsorbent to remove MB from aqueous solution. Hydrochar derived from bagasse was successfully prepared by hydrothermal carbonization treatment at temperature of 270oC, and pressure of 10 Bar for 30 minutes. For enhancing the adsorption ability, hydrochar was activated by adding KOH that was able to increase the percent removal by ~11%. The hydrochar was characterized using FTIR before and after adsorption. The results showed that the dominant functional groups of hydrochar included O-H, C=O, -O- and aromatic compounds. Whereas, the functional group of azo groups such as N-H and N=N appeared after adsorption. The maximum adsorption capacity (Qmax) was 5.1204 mg/g, while the adsorption isotherm of MB onto hydrochar followed the Langmuir and Freundlich model. The adsorption mechanism belongs to chemical adsorption, and the rate of diffusion can be neglected because the adsorption kinetics fitted well with pseudo-second order and the value of k2 &gt; kdif &gt; k1. Thermodynamic studies indicated that the adsorption process is classified as endothermic and reversible at room temperature. The results showed that hydrochar could be the alternative adsorbent for removing MB in wastewater. In addition, sugarcane bagasse has a great potential as feedstock of hydrochar.

Studies related to changes in ionic strength due to addition of sodium chloride to an aqueous solution of cationic dye methylene blue (MB): Electronic spectra analysis for dimerization equilibria

It is well-known that methylene blue (MB),a cationic dye forms dimer and higher aggregates in aqueous solutions. For specific concentration range (1∙10−6–1∙10−4 M), a D⇌2M equilibria has been postulated and well characterized by visible electronic spectroscopy. The dye molecules can lead to formation of stacking (end on end and sandwich) type structures in solution phase stabilized by weak dispersion van der Waals forces and cation-anion-cation ion pairs and triplet interactions usually referred as hydrophobic interactions. Recent literature reports indicate that excess chemical potential of small hydrophobic particles and the strength of hydrophobic pair interactions appear to be linearly related. Our observations about precipitation of dye (MB) at higher concentrations of salt like sodium chloride (NaCl) made us to study the dimerization equilibria in detail since in the Corona health disaster; use of MB to diagnose the type of Covid variants helped Scientists in a great way. Salting-out of proteins is in general used to explain the specific protein aggregation behaviour observed in Huntington's disease. For model compound like tertiary butyl-alcohol, Geiger et al. reported enhancement of hydrophobic contacts which increase with increase in salt concentration. NaCl is an essential ingredient of biological fluids, of which concentration controls the various biological life governing processes. However, such information is non-existent for aqueous solutions of dyes.We therefore reported measured optical absorbance of aqueous solution containing NaCl (0.1–1.0 M) and dye at different concentrations (1∙10−6–1∙10−4 M) at 298 K spectrophotometrically, in the wavelength range of 550–700 nm. The spectrums are compared to those obtained for binary solutions of MB in water. Analysis of the spectral data yielded the dimer dissociation constant and individual characteristic monomer and dimer spectra. Further information about the geometry and twist angle between the dipoles of the MB molecules in the dimer species has been obtained. The results are analyzed for the monomer-dimer equilibria and salting-out effect as well applications of mass action model and exciton theories are discussed.

Nanocellulose and Graphene Oxide Aerogels for Adsorption and Removal Methylene Blue from an Aqueous Environment.

The characteristics of aerogel materials such as the low density and large surface area enable them to adsorb large amounts of substances, so they show great potential for application in industrial wastewater treatment. Herein, using a combination of completely environmentally friendly materials such as cellulose nanofibers (CNFs) extracted from the petioles of the nipa palm tree and graphene oxide (GO) fabricated by simple solvent evaporation, a composite aerogel was prepared by a freeze-drying method. The obtained aerogel possessed a light density of 0.0264 g/cm3 and a porosity of more than 98.2%. It was able to withstand a weight as much as 2500 times with the maximum force (1479.5 N) to break up 0.2 g of an aerogel by compression strength testing and was stable in the aquatic environment, enabling it to be reused five times with an adsorption capacity over 90%. The CNF/GO aerogel can recover higher than 85% after 30 consecutive compression recovery cycles, which is convenient for the reusability of this material in wastewater treatments. The obtained aerogel also showed a good interaction between the component phases, a high thermal stability, a 3D network structure combined with thin walls and pores with a large specific surface area. In addition, the aerogel also exhibited a fast adsorption rate for methylene blue (MB) adsorption, a type of waste from the textile industry that pollutes water sources, and it can adsorb more than 99% MB in water in less than 20 min. The excellent adsorption of MB onto the CNF/GO aerogel was driven by electrostatic interactions, which agreed with the pseudo-second-order kinetic model with a correlation coefficient R2 = 0.9978. The initial results show that the CNF/GO aerogel is a highly durable “green” light material that might be applied in the treatment of domestic organic waste water and is completely recoverable and reusable.

Sustainable synthesis of silver nanoparticles using Alstonia scholaris for enhanced catalytic degradation of methylene blue

The present work described a simple, green, and fast approach for the synthesis of silver nanoparticles using an aqueous fruit extract of Alstonia scholaris(AS-AgNPs). The role of plant extract was identified as both reducing as well as capping agent in the synthesis of AS-AgNPs. The formation of AS-AgNPs was confirmed through the visible color change from pale yellow to brown and the respective surface plasmon resonance (SPR) peak observed at 426 nm in the UV-Visible (UV-Vis) spectrum. Further, the synthesized AS-AgNPs were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy with Energy dispersive spectrum (SEM with EDS), High resolution transmission electron microscopy (HR-TEM), and Dynamic light scattering (DLS) with Zeta potential. The DLS derived average particle size and poly dispersion index (PDI) of AS-AgNPs are about 50 nm and 0.664 with Zeta potential of -22.4 mV, suggested the presence of mono and polydispersive AS-AgNPs with good stability. The synthesized AS-AgNPs were mainly distributed (56 %) as a quasi-spherical shape with size ranges from 5 to 50 nm revealed by SEM and TEM images. Moreover, the catalytic reduction of methylene blue (MB) by AS-AgNPs has been accessed via time-dependent UV-Vis spectroscopy. The UV-Vis results suggested that AS-AgNPs show enhanced catalytic activity on the reduction of MB by aqueous sodium borohydride with pseudo first-order kinetics and the calculated rate constant was about 0.7 × 10−3 s−1. Overall, the green synthesized AS-AgNPs have a great catalytic potential in the degradation of MB in water.

Graphene oxide incorporated amino‐functionalized iron terephthalate composite as a heterogeneous Fenton‐like catalyst

AbstractAmino‐functionalized iron terephthalate metal–organic framework (NH2‐MIL‐88B) has been studied for its adsorption and catalytic properties due to its high surface area and unique topological architecture. Functionality of the material can be improved through surface modification to increase active sites for the targeted applications. In this study, graphene oxide (GO) was incorporated to the NH2‐MIL‐88B material to obtain composite with improved adsorption and catalytic properties. The results showed that GO/NH2‐MIL‐88B in dark (as GO/NH2‐MIL‐88B/Dark system) was capable to adsorb 28.1% of methylene blue (MB) in water, which is about twice the adsorption of MB by the NH2‐MIL‐88B material in dark (as NH2‐MIL‐88B/Dark system). Furthermore, with the presence of hydrogen peroxide (H2O2), the GO/NH2‐MIL‐88B composite in dark condition (as GO/NH2‐MIL‐88B/H2O2/Dark) and the GO/NH2‐MIL‐88B composite under ultraviolet‐A (UV‐A) irradiation (as GO/NH2‐MIL‐88B/H2O2/UV‐A) have shown promising Fenton‐like behavior, which have removed 72.2% and 92.3% of MB in water, respectively. The removal of MB was well fitted to the Langmuir–Hinshelwood pseudo‐first order kinetics model with the reaction rate constant, k1 = 0.0221 min−1 and k1 = 0.0426 min−1 for GO/NH2‐MIL‐88B/H2O2/Dark and GO/NH2‐MIL‐88B/H2O2/UV‐A system, respectively. This study implies that the GO/NH2‐MIL‐88B composite can be a good catalyst for the heterogeneous Fenton‐like degradation of cationic pollutants in water.

Activated carbon and biochar from pineapple waste biomass for the removal of methylene blue

Dye pollution in water system is of concern due to its carcinogenicity and its effect on aesthetic feature. One pollutant of interest is methylene blue (MB), which is a cationic dye widely used in industries. In this study, pyrolysis process was used to convert pineapple waste biomass (PWB) into useful adsorbents such as biochar (BC) and activated carbon (AC) to remove MB in water. BC was produced from pyrolysis of PWB (340 °C, 3 hours) whereas AC was prepared from pyrolysis of PWB (500 °C, 1 hour) impregnated with zinc chloride (ZnCl2). Prior to use, AC-PWB and BC-PWB were characterized for surface area, functional groups and surface morphology. Removal of MB was investigated by varying different parameters i.e. initial MB concentration and contact time, adsorbent dosage and temperature. Results obtained showed that AC-PWB has higher adsorption capacity than BC-PWB. The adsorption capacity and adsorption rate increased with increasing initial concentration of MB, adsorbent dosage and temperature until reached equilibrium condition. As a conclusion, PWB can be used as a useful raw material to produce cheap and environmentally friendly adsorbent to remove dye from solution.

Preliminary Study of ZnO/GO Composite Preparation as Photocatalyst Material for Degradation Methylene Blue under Low UV-Light Irradiation

ZnO:Graphene Oxide composite nanopowders have been successfully prepared by sol-gel method. The study of composite preparation is discussed in this paper. Graphene oxide was added in two ways in order to study the mixed behaviour especially in photocatalytic properties. The degradation of methylene blue (MB) concentration in water was used to evaluate the photocatalytic property under low UV-light irradiation (14 μW/cm2). The results showed that all varian ZnO-GO composite samples have spherical morphology and hexagonal wurtzite crystal structure. An addition of graphene oxide (GO) in ZnO precursor solution during preparation shows a better photocatalytic property that related to reducing in particle size, thereby produce a large surface area and formed a better interfacing with GO/rGO. The existence of GO around ZnO nanoparticles gives some advantageous due to presences of hydroxyl component that directly relate to the increments in photocatalytic behavior. The photodegradation rate of MB in water using ZnO-GO composite as catalyst is significantly increase compared with pure ZnO.

Study of Methylene Blue Adsorption onto Aminated Graphene Oxides at Varied Stirring Time

Aminated graphene oxide (AGO) is one of graphene oxide (GO) derivatives that contained amine group (NH2). GO has a lot of oxygen-containing groups, such as hydroxyl, carboxyl, carbonyl, and epoxide functional groups, therefore it is hydrophilic and readily dispersed in water forming a stable colloidal suspension. This property was used to study decolorize of dye pollutant in water contamination. The presence of amine side chain in the molecule might contribute on improving hydrophilic properties of AGO compared to GO. Waste water containing harmful dyes such as methylene blue (MB) is one of the main problems in water contamination. In this work we study MB adsorption onto AGO surface. The experiments were carried out by mixing 50 mL of the MB solution in water (5 ppm; 0.25 mg) with 0.5 mL of dispersed AGO (0.5 mg / ml; 0.25 mg) in dimethylformamide (DMF), and then stirring at 1000 rpm at varied stirring times. The initial and final concentration of MB solutions after AGO adsorption were analyzed using spectroscopy. We obtained that AGO can adsorb MB in water, which the adsorption happened very fast until stirring time of 20 minutes. Addition of stirring time does not have significant change on MB concentration, which indicates that AGO adsorption capacity has saturated.

Synchronous photosensitized degradation of methyl orange and methylene blue in water by visible-light irradiation

In this work, a novel method that homogeneous degrading methyl orange (MO) with methylene blue (MB) as a photosensitizer under visible-light irradiation is proposed. MO can be efficiently degraded at a wide concentration range, and its degradation rate is significantly promoted by increasing MB concentration. The result of EPR, LC-MSMS, TOC and ion chromatography reveals that the degradation mechanism of MO consists two parts: 1O2 mediated Type II pathway and Type I photosensitization of involving direct electron transfer between 3MB* and MO. Furthermore, benefitting from the self-degradation of MB, synchronous removal of MO and MB in water can be realized by controlling the initial MB concentration in system, thus avoiding the problems faced by heterogeneous photocatalytic such as solid-liquid separation. Therefore, this cost-effective and easy method possesses great potential in the application of eliminating MO and MB from wastewater as well as provides a new strategy for sustainable water treatment.

Palladium nanoparticles decorated on ZSM-5 derived micro-/mesostructures (MMZ) for nitrophenol reduction and MB degradation in water

Palladium-based catalysts are promising for catalytic reduction in catalysis. The dispersion state of palladium nanoparticles (Pd NPs) impacts the catalytic performance, while the development of catalysts with highly dispersed Pd NPs is a major challenge. Herein, we developed ZSM-5 derived micro-/mesoporous silica MMZ to regulate Pd NPs size and dispersion. MMZ was synthesized by combined dissolution of ZSM-5 under basic condition and re-assembly of Al-or Si-containing species of ZSM-5 by cetyltrimethylammonium bromide (CTAB) instead of expensive carbon nanofiber reported earlier. The Pd precursor is introduced into MMZ by ultrasound assisted incipient wetness impregnation (U-IWI) strategy. Up to 1.0 wt% Pd was highly dispersed per g of MMZ without showing any X-ray diffraction lines (denoted as 1.0 Pd/MMZ), while obvious diffraction lines were noticed in the counterpart synthesized from ZSM-5 (denoted as 1.0 Pd/ZSM-5). Further calculation shows the size of Pd NPs in 1.0 Pd/MMZ is 3.5 nm, which is smaller than that in 1.0 Pd/ZSM-5. Our results also demonstrated that well-dispersed and smaller size Pd NPs corresponds to superior catalytic activity in reduction of p-nitrophenol (P-NP) and methylene blue (MB). The typical catalyst 1.0 Pd/MMZ exhibited complete reduction of P-NP and MB in water within 3 min. It is superior to 1.0 Pd/ZSM-5 catalyst with the same Pd content as well as to several reported catalysts. Furthermore, 1.0 Pd/MMZ not only keeps high catalytic activity for 6 consecutive cycles, but also exhibit long-term stability in hydrogenation reaction.

Monitoring of methylene blue monomers and dimers to control the bacterialogical water quality including application to photocatalysis.

In this study, we propose the development of a rapid and reliable method to control and to monitor microbial water quality. The methylene blue (MB) decolorization assay was based on the analysis of spectral profiles of dye in interaction with a different bacterial concentration. The determination of dye decolorization rate (DDR) shows a correlation between the MB reduction rate and the bacterial density. Moreover, the kinetic of the monomer and dimer equilibrium of MB in water mainly, the monitoring of bounded MB species in relationship with a knowed concentration of target bacteria, was allowed to establish a relationship between MB decolorization rate and bacterial density. Furthermore, this method was applied to evaluate the water quality after photocatalysis. Based on this method, the photocatalytic effects on bacterial density was highlighted by the decrease in DDR after photocatalytic treatment with fractioned times (0 to 5 h); this increase was followed by a decrease of bounded MB species and, an increase in free MB forms miming the reduction of bacterial density due to the biocide effects of photocatalysis process. However, the analysis of spectra profiles shows a weak but a continuous decrease in bounded MB dimer and monomer forms in the treated water samples exempt of culturable bacteria. Moreover, the MB spectra profiles were tended toward a negative control spectrum without superposition. Thus, the possibility of the presence of viable but non-culturable bacteria was expected; therefore, to optimize this tertiary water treatment process, an extending on proceeding time was recommended to avoid the bacterial resuscitation after photocatalysis.

Visible Light Spectroscopic Analysis of Methylene Blue in Water; What Comes after Dimer?

As in our previous work, most attempts to study the self-aggregation of methylene blue (MB) in water have been limited to the dimer. In the present work, we have analyzed the self-aggregation of MB in water beyond the dimeric form. For this purpose, the visible light absorption spectra of a large number of aqueous solutions of MB (1.1 × 10–6 to 3.4 × 10–3 M) and NaCl (0.0–0.15 M) at different temperatures (282–333 K) have been fed to a mathematical routine in order to determine the potential existence of a unique higher-order aggregate without any preconception about the aggregation order or about the need of counterions, such as chloride, for compensating the positive charge of the aggregates. Contrary to the common belief that the trimer is the dominant aggregate at high MB concentration, to our surprise we found that the tetramer acting alone, and without any counterion, is the higher-order aggregate that yields the best fitting to all the experimental absorbance spectra, with a very low average relative error of 0.04 ± 0.34%. Also contrary to previous assumptions, it has emerged quite evidently that this aggregate is present in the solution at MB concentrations below 3.4 × 10–5 M (11 ppm), though to a rather low extent. This has brought the need for the recalculation of the visible light absorption spectrum and the thermodynamic parameters for the dimer, which along with those for the tetramer are the main contributions of the present work.

Catalytic degradation of methylene blue using a newly engineered composite and its electrochemical performance

Herein, we reported the development of tetramethoxyphenylporphyrin (CoTPP)/reduced graphene (rGO)/multiwalled carbon nanotubes (MWCNTs) composite via an ultrasonic treatment. The engineered composite was characterized by different analytical techniques like scanning electron microscopy (SEM), energy dispersive X-ray (EDX), ultraviolet–visible spectroscopy (UV–Vis) and Fourier transform infrared spectroscopy (FT-IR). The synthesized composite was tested for the catalytic degradation of methylene blue (MB) under solar irradiation and the electrochemical performance of the CoTPP/rGO/MWCNTs was also investigated in alkaline media by using cyclic voltammetry (CV). The photodegradation efficiency of prepared CoTPP/rGO/MWCNTs composite is 92% degradation of MB in water within 60 ​min irradiation. The results of the cyclic voltammogram showed that the onset potential value was -0.4 ​V while peak potential value of CoTPP-rGO/CNTs was -0.59 ​V. The high onset peak potential values and the current values of the CoTPP/rGO/MWCNTs make it a promising candidate as a catalyst for ORR.

Effect of acidic conditions on decomposition of methylene blue in aqueous solution by air microbubbles

Methylene blue (MB) has recently been proposed as a new chemical probe to colorimetrically verify the presence of hydroxyl radicals and was applied to the microbubble technique in this report. The degradation of MB in water was observed by air microbubbles under acidic condition or adding H2O2. The discoloration of MB induced by air microbubbles supports that hydroxyl radicals are generated by the collapse of microbubbles in water. The decomposition rate of MB increases with increasing the concentration of acids (HCl, HNO3, H2SO4) and H2O2 up to ab. 2mM, and becomes almost constant above ab. 2mM. Note that the decomposition rate of MB mainly depends on pH, not the kind of acid and that adding salt slightly enhanced the decomposition of MB. The fact that the blue-shift of the absorbance band of MB was observed for not H2O2 but acids proposed that the methyl groups of MB are preferentially dissociated under acidic conditions due to the protonation of dimethylamino group.