Methylene Blue Molecules Research Articles

New insights into visible light active SnS semiconductor for the elimination of methylene blue: RSM and DFT approaches

In this study, a response surface methodology (RSM) based on a central composite design (CCD) was performed by varying five pivotal variables: concentration of pollutant (mg/L), mass of catalyst (g), time (min), temperature (°C), and pH to evaluate the degradation efficiency of Methylene Blue (MB) using nanostructured SnS under visible light irradiation. The quadratic model displayed a notable level of reliability and fitness, as evidenced by its R2 value of 0.925. The optimized conditions obtained (Concentration of pollutant: 13.38 mg/L, mass of catalyst: 0.09 g, irradiation time: 25.26 min, temperature: 47.34 °C and pH: 8.36) yielded a degradation efficiency of 99 %, which is highly remarkable. Furthermore, based on density functional theory (DFT), the adsorption energy (Eads), charge transfer, and density of states (DOS) are investigated to study the application of tin sulfide as an adsorbent for Methylene Blue adsorption. When the MB molecule was positioned in a horizontal configuration at a distance of 3.136 Å from SnS, the significant adsorption energy of −3.22 eV was obtained. Due to the bond formation between tin atoms of SnS and carbon atoms of MB, it can be stated that there is a strong chemical interaction between SnS and MB molecule in this configuration. Regarding vertical orientation, adsorption energy was obtained to be −0.45 eV and no sign of any bond formation or breaking was observed, indicating that the adsorption process may be physisorption. The computational and experimental results proved that SnS is a promising candidate for MB adsorption and degradation.

An electrochemical biosensor to assay Trop-2 of breast cancer cells fabricated by methylene blue-assisted assembly of DNA nanoparticles

Human trophoblast surface cell antigen 2 (Trop-2) on the tumor cell membrane can not only serve as the target for chemotherapy drugs, but also as a biomarker for typing and prognosis of breast cancer; however, assay of Trop-2 is seriously hampered due to the limitations of available tool. Herein, we have designed and fabricated an electrochemical biosensor for the assay of Trop-2 based on methylene blue (MB)-assisted assembly of DNA nanocomposite particles (DNPs). Specially, the recognition between Trop-2 and its aptamer may activate the primer exchange reaction (PER) on an electrode surface to produce long single-strand DNA (ssDNA) which can be self-assembled into DNPs by electrostatic interaction between negative charged DNA and positive charged and electro-active MB molecules which can also be used to give electrochemical signal. By using this electrochemical biosensor, ultrasensitive detection of tumor cells with high Trop-2 expressions can be conducted, with the limit of detection (LOD) of 1 cell/mL. Moreover, this biosensor can be further used for accurately profiling Trop-2 expression of tumor cells in mouse tissues, suggesting its great potential in the precise definition of breast cancer.

Poly(vinylidene fluoride‐hexafluoropropylene)/mesoporous graphitic carbon nitride composite membranes for photocatalytic methylene blue degradation and sensing applications

AbstractIn this work, poly(vinylidene fluoride‐hexafluoropropylene) (PVDF‐HFP)/mesoporous graphitic carbon nitride (mpg‐C3N4) composite fiber web have been prepared and characterized for photocatalytic methylene blue (MB) degradation and sensing applications. The electrospinning technique, operating at a flow rate of 1 mL/h and a voltage of 15 kV, was utilized to prepare the composite membranes of PVDF‐HFP with the uniform distribution of the mpg‐C3N4. The composite web demonstrated outstanding photocatalytic activity for the degradation of MB, reaching a quick 68% drop in MB concentration in just 45 min. The composite web furthermore worked as a sensor for MB detection. After MB exposure, the film resistance was increased, suggesting its potential as a chemiresistive sensor. The maximum resistivity of PVDF‐HFP/mpg‐C3N4 composites was found to be 90 Ω·m at 2% concentration of MB. The MB molecules' adsorption on the surface of the composite web and the existence of photocatalytic byproducts on the surface may be responsible for this shift in resistance. This dual functionality highlights the adaptability and potential of the PVDF‐HFP/mpg‐C3N4 composite web as a versatile material for environmental sensing and cleanup. This research presents a comprehensive approach to the synthesis, characterization, and evaluation of such flexible membranes for potential applications as self‐cleaning devices and chemiresistive sensor.Highlights PVDF‐HFP/mpg‐C3N4 composite membranes act as an efficient material for MB degradation (68%) with visible light exposure. mpg‐C3N4 plays the role of active material in degradation. PVDF‐HFP/mpg‐C3N4 composite membrane also act as sensors for MB detection. Composite membrane becomes chemiresistive due to notable resistivity changes with MB concentration.

A triple-signal strategy separated aptasensor for sensitive determination of aflatoxin B1 in peanut based on electrochemical and fluorescent dual-mode

It is necessary to develop accurate and sensitive AFB1 detection method due to its high toxicity of pathogenicity and carcinogenicity. The results of traditional single-mode AFB1 detection methods are easily affected by the test environment and human operation. Herein, an electrochemical and fluorescent dual-mode separated aptasensor was developed for detecting AFB1 with triple-signal readout. The AFB1 aptasensor was constructed by combining the Fc-labeled AFB1 aptamer with its complementary DNA (cDNA). Subsequently, the methylene blue (MB) was incorporated into dsDNA as another signal tag. In the presence of AFB1, the Fc tag approached to electrode surface, both of the cDNA and MB molecule released due to the interaction between AFB1 and its aptamer, resulting in “signal-on” and “signal-off” dual-signal strategy. There was a good linear relationship between the SWV electrochemical response signal and the logarithm of AFB1 concentration at 0.01–200 ng/mL (LOD 2.5 pg/mL, S/N = 3). Meanwhile, the released cDNA was designed to trigger hybridization chain reaction (HCR), and the HCR product was served as template for the formation of fluorescent copper nanoparticles (CuNPs). There was a good linear relationship between the fluorescent intensity of CuNPs and the logarithm of AFB1 concentration at 0.001–200 ng/mL (LOD 0.28 pg/mL, S/N = 3). The separated fluorescent method showed broadened linear range and lower LOD compared with SWV method, both up to 10-folds, which improved the detection sensitivity. The constructed dual-mode AFB1 aptasensor showed satisfactory selectivity, stability and reproducibility, and the good recoveries of real peanut samples indicated its practical application in food detection.

Drug Encapsulation via Peptide-Based Polyelectrolyte Complexes.

Peptide-based polyelectrolyte complexes are biocompatible materials that can encapsulate molecules with different polarities due to their ability to be precisely designed. Here we use UV-Vis spectroscopy, fluorescence microscopy, and infrared spectroscopy to investigate the encapsulation of model drugs, doxorubicin (DOX) and methylene blue (MB) using a series of rationally designed polypeptides. For both drugs, we find an overall higher encapsulation efficiency with sequences that have higher charge density, highlighting the importance of ionic interactions between the small molecules and the peptides. However, comparing molecules with the same charge density, illustrated that the most hydrophobic sequence pairs had the highest encapsulation of both DOX and MB molecules. The phase behavior and stability of DOX-containing complexes did not change compared to the complexes without drugs. However, MB encapsulation caused changes in the stabilities of the complexes. The sequence pair with the highest charge density and hydrophobicity had the most dramatic increase in stability, which coincided with a phase change from liquid to solid. This study illustrates how multiple types of molecular interactions are required for efficient encapsulation of poorly soluble drugs and provides insights into the molecular design of delivery carriers.

Heterostructured organic/MoS2 nanowall with synergistic SERS enhancement enabling direct and sensitive detection of contaminants

In recent years, the π-conjugated organic molecular system has attracted considerable attention for its surface-enhanced Raman scattering (SERS) properties. However, the practical application of π-conjugated organic materials as SERS substrates is limited due to the inefficient dissociation of excitons, weak enhancement, and poor reproducibility. Herein, we proposed a novel nanowall SERS heterocomposite based on 3D D(C7CO)-BTBT nanowalls and 2D few-layer MoS2 flakes. A significant SERS activity of the D(C7CO)-BTBT/MoS2 nanowall heterocomposite can be achieved by the charge transfer (CT) resonance enabled by the π-conjugated interactions between D(C7CO)-BTBT and MoS2 and the electromagnetic field spatial distribution induced by the D(C7CO)-BTBT nanowalls. The concentration limit of detection (LOD) of the methylene blue (MB) molecules absorbed on the heterostructured D(C7CO)-BTBT/MoS2 nanowall substrate is as low as 8.2 × 10−11 M, which is excellent among the reported organic-based substrates. A practical SERS detection for the 100 nm polystyrene (PS) nanoparticles on the D(C7CO)-BTBT/MoS2 substrates can be down to 4.5 × 105 ng/L, which is exceptional for the real-time monitoring of emerging contaminants based on SERS technology. This research not only provides a new SERS enhancement strategy for organic-based materials, but also may be helpful in exploring a potential candidate for SERS detection of emerging contaminants.

Methylene blue modified graphene film as high-performance electrode towards all-in-one flexible supercapacitors with “all-graphene” structure

The emergence of wearable electronics has raised the demand for flexible supercapacitors. However, conventional multilayer flexible supercapacitors have high interfacial resistance and unavoidable displacement among adjacent components during the bending process. Herein, a novel all-in-one flexible supercapacitor (AFSC) with “all-graphene” structure is proposed. Benefit from the additional pseudocapacitance enhancement of methylene blue (MB) molecules, the AFSC assembled with the flexible self-supporting MB modified graphene hydrogel film (MB/rGO) obtained by a simple hydrothermal as electrode and graphene oxide (GO) as separator exhibits a high specific capacitance of 317.27 F g−1 at 0.2 A g−1. Even at a high current density of 20 A g−1, the specific capacity still maintains 213.66 F g−1. Besides, the soft package AFSC device shows excellent flexibility, mechanical properties and electrochemical stability. After continuously bending from 0° to 180° for 1200 times, the AFSC device can display a high capacity retention of 90.8%, showing splendid expectation in the field of flexible wearable applications.

Nanopores limited domain and PVA film used to assist the SERS property of gold nanoparticle arrays

The combination of nanopores and noble metal nanoparticles has been the focus of research in recent years, and their synergistic effect enabled the substrate exhibit excellent SERS property. In this paper, the array porous silicon structures embedded with gold nanoparticles have been prepared by using the polystyrene (PS) microsphere template assisted gold annealing process and metal assisted chemical etching techniques (AuNPs@nanopore). Polyvinyl alcohol (PVA) thin film was introduced as a molecular adsorption layer to be spin coated on the surface and formed composite structure (AuNPs@nanopore @PVA) to enrich more detection molecules. Through the SERS analysis of different depths of gold nanoparticles by Rhodamine 6G (R6G) probe molecules, the optimal etching time, that is, the optimal depth that gold nanoparticles should be in, was determined. Under the etching time of 2 min, the AuNPs@nanopore @PVA structure base with pore depth of 245 nm and diameter of gold nanoparticles of 181 nm showed high sensitivity, high uniformity and the best SERS property. It can realize the low concentration detection of 10−10 mol/L R6G molecule and 10−11 mol/L methylene blue (MB) molecule, and the enhancement factor is up to 1.20 × 107. The substrate can also be used to detect the pesticide thiabendazole molecule, the detection limit of 10−8 mol/L.

Perovskite Type B-CaTiO3 Coupled with Graphene Oxide as Efficient Bifunctional Composites for Environmental Remediation

To prepare boron doped perovskite CaTiO3 nanocubes coupled with graphene oxide (B-CaTiO3/GO), B-CaTiO3 photocatalyst was initially synthesized by the solvothermal method and subsequently attached on GO by a simple hydrothermal process. The phase structure and optical features of the prepared materials were efficiently characterized by several techniques. The XRD patterns indicated that boron doping could not give rise to lattice disruption of CaTiO3. The results of XPS, HRTEM and Raman measurements revealed that the presence of B-CaTiO3 is anchored on the surface of GO effectively. The morphology of the B-CaTiO3/5GO was nanocube particles. The photocatalytic capacity of B-CaTiO3/GO nanocomposites was determined by investigating the degradation of a model dye, methylene blue (MB). Their degradation performance could be enhanced by altering the ratio between B-CaTiO3 and GO. The most effective GO incorporation is 5 wt%, and at this loading percentage, B-CaTiO3/GO nanocomposite showed improved photocatalytic activity compared with CaTiO3 and B-CaTiO3 photocatalyst, which could be attributed to the synergistic efficacy of the adsorbed MB molecule on the GO followed by their degradation after 180 min of visible light. Additionally, the active species trapping tests confirm the dominant role performed by ·OH and O2·− during the degradation of MB. The presence of HCO3− and Cl− indicated moderate prohibitive effect on the degradation of MB, while NO3− and SO42− negatively affected the catalytic activity in a non-significant way. In brief, the results of this study show that boron doped perovskite-type semiconductor catalysts by combining with graphene has significant efficiency in the removal of MB from aqueous solution, which can be employed as effective photocatalyst materials for the treatment of other organic pollutants.

Magnetized CNTs incorporated MBA cross‐linked guar gum nano‐composite for methylene blue dye removal

AbstractIn the present work, a magnetized multiwalled carbon nanotube dispersed in chemically cross‐linked gaur gum was developed as a nano‐composite adsorbent material for the removal of dye from wastewater. The gaur gum, a bio‐macromolecule was chemically modified by cross‐linking with methylene bis‐acrylamide in the presence of sodium hydroxide as a novel approach to prepare the gel matrix. The magnetite nanoparticles loaded multiwalled carbon nanotubes were dispersed in methylene bis‐acrylamide cross‐linked gaur gum gel during gelation. The nano‐composite was characterized for morphological, spectral, and analytical data. The solid form of the nano‐composite was evaluated as an adsorbent material for the treatment of water containing methylene blue dye molecules as pollutants by the spectrophotometric method. Adsorption isotherm studies suggested that the Freundlich model was the befitting model for adsorption, indicating the multilayered adsorption and the kinetic study revealed the adsorption to occur by a pseudo‐second‐order kinetic process. The novel nano‐composite is found to be a promising material for the adsorptive removal of dye molecules from dye‐contaminated wastewater. The adsorption capacity was observed to be 11 mg/g of the material.

ZnO nanoparticles dispersed in nitrogen-enriched carbon matrix for the efficient adsorption and photocatalytic degradation of aqueous methylene blue molecules

In the present study, ZnO nanoparticles dispersed in graphitic carbon nitride (g-C3N4) composite is synthesized via hydrothermal route at 150 °C. The synthesized material (ZnO/g-C3N4) is further heat-treated at an optimized temperature of 500 °C in an air-rich environment and the heat-treated material is denoted as the ZnO/g-C3N4-HT. Physicochemical properties of the as-synthesized material are evaluated by various analytical and spectroscopic techniques. The obtained results confirm good dispersion of the ZnO nanoparticles on the surface of the g-C3N4. The ZnO/g-C3N4-HT is further tested for its adsorption ability and photocatalytic activity towards aqueous methylene blue (abbreviated as MB). The data show that the ZnO/g-C3N4-HT possesses remarkably high MB adsorption capacity of 251.70 mg/g at the pH value of 7. The MB adsorption capacity obtained in the present study is superior to most of the carbon-based adsorbents. The kinetic curve is found to be in good agreement with pseudo-second-order kinetic model. The remarkably high MB adsorption capacity is ascribed to the combined effects of surface area, wettability characteristic, and the negative surface charge of the material. The photocatalytic MB-degradation study over the ZnO/g-C3N4-HT yields a maximum degradation efficiency of 90% with pseudo-first-order rate constant value of 0.0113 min−1. The high MB-degradation efficiency of the material is attributed to the modified band gap and morphological properties of the material. With adequate optimization, the ZnO/g-C3N4-HT may be useful in the removal of several other recalcitrant organic pollutants from water.

Femtosecond laser-induced production of ZnO@Ag nanocomposites for an improvement in photocatalytic efficiency in the degradation of organic pollutants

Green synthesis based nanoparticle production methods and water purification techniques were carried out using pulsed laser ablation and photocatalysis degradation techniques. The femtosecond laser ablation based ZnO and Ag nanoparticles were produced with different concentration ratios such as 2.0 wt%, 4.0 wt%, 6.0 wt%, 8.0 wt% and 10.0 wt% in ultra pure water to photocatalytic degradation of methylene blue dye contaminant. Following the production of nanoparticle and photocatalysis applications, FTIR, XRD and linear absorption spectra were recorded. HRTEM and FE-SEM microscopy was carried out to determine size and shape performance of nanoparticles. The crystal peak density of ZnO and its crystal size were decreased by doping Ag into ZnO nanoparticles. LSPR peak was formed due to plasmonic properties of Ag nanoparticles in ZnO. As Ag content is increased in ZnO, it has been observed that band gap of ZnO@Ag structure is decreased. The morphological structure of ZnO is partially composed of homogeneous particle mergers while ZnO@Ag can be formed from the growth of small particles on AgO clusters. The photocatalytic activity of composite photocatalysts was systematically investigated as a function of amount of Ag nanoparticles in samples. Experimental results showed that the optimal composite was Ag-ZnO composite containing 6.0 wt% Ag. This composite photocatalyst exhibited a 68.62% higher rate constant value in the degradation of methylene blue (MB) dye molecules under visible light compared to pure ZnO nanoparticles. The improved photocatalytic performance compared to pure ZnO nanoparticles was attributed to some increase in light absorption performance, more efficient charge separation due to the gradual band structure between plasmonic Ag nanoparticles and semiconductor ZnO nanoparticles. In addition, active radicals taking role in the degradation mechanism of MB were revealed by scavenger chemical experiments.

Advancing photo-electrocatalysis: Selective degradation using graphene oxide–cerium oxide functionalized synthetic nanochannels

This study introduces a novel approach using a nanofluidic-based photo-electrocatalytic system to investigate the degradation ability of synthetic nanochannels functionalized with graphene oxide – cerium oxide GO-CeO2 (GCF) for methylene blue (MB) dye. The formation of heterojunctions is achieved through the in-situ growth of CeO2 nanostructures on a GO matrix via the Sono-chemical synthesis route. The crystallographic, surface, optical, and charge transfer dynamics of GO-CeO2 nanocomposites are analyzed using various techniques. The photo-electrocatalysis process is conducted in an electrochemical cell consisting of track-etched GCF-modified nanochannels, MB solution, transmembrane voltage sweep, and irradiation of the visible light spectrum. The current-voltage (I-V) response is recorded to evaluate the selective degradation ability of GCF nanochannels. The photo-electrocatalytic activity of GCF nanochannels is determined by observing the increasing trend of cationic and anionic currents. Higher transmembrane potentials up to ± V led to an exponential increase in anionic current up to −3.69 μA and significantly affect the kinetics of the photo-electrocatalytic process. The electrocatalytic process is supported under neutral and basic pH conditions. The enhanced and selective photo-electrocatalytic activity of GCF nanochannels can be attributed to the adsorption between the nanochannel surface and the MB molecules, visible light photoexcitation resulting from a lower bandgap, effective charge transfer, and separation at heterojunctions of GO-CeO2. Additionally, the suitable alignment of band potentials of functionalized nanocomposites and the molecular orbital position of MB further contribute to the process of selective degradation.

Flexible Self-Powered Sensing System Based on Novel DNA Circuit Strategy and Graphdiyne for Thalassemia Gene by Rapid Naked-Eye Tracking and Open-Circuit Voltage.

Based on the controllable instantaneous self-assembly ability of long-chain branched DNA nanostructures and the synergistic effect between nucleic acid amplification without enzymes, a highly sensitive and highly specific self-powered biosensing platform is developed. Two-dimensional graphdiyne is prepared, modified on flexible carbon cloth, and then functionalized with gold nanoparticles. When DNA mi-tubes are applied on it, target thalassemia gene CD122 triggers a dual-catalytic hairpin assembly reaction. The generated nanoscale DNA is precisely captured by the DNA mi-tube, exposing binding sites and activating the hybridization chain reaction to form long-chain branched DNA. Double-stranded DNA, along with dendritic DNA carrying a large number of guanine bases, precisely captures the signal molecule methylene blue (MB), generating a significant electrochemical signal. The redox reaction of MB also causes a proportional change in the system's color, achieving a colorimetric detection functionality. An efficient dual-mode self-powered sensing platform, therefore, is established for detecting the thalassemia gene CD122. The linear response range of target concentration to open-circuit voltage and RGB Blue value is 0.0001-10,000 pM. The detection limit under electrochemical mode is 36.3 aM (S/N = 3), and under colorimetric mode, it is as low as 12.1 aM (S/N = 3). The new method exhibits high sensitivity, excellent selectivity, and high accuracy, providing a universal strategy for designing novel biosensing platforms that can be extended to the detection of other biomolecules.

Exploring the impact of incubation times and concentrations of self-assembled monolayers on electron transfer in biosensing

This study investigates the impact of different incubation times and concentrations of a self-assembled monolayer (SAMs) of 3-mercaptopropionic acid (MPA) on the rate of electron transfer in redox processes. The aim is to understand how these parameters can affect the sensitivity and efficiency of biosensors based on direct electron transfer in redox proteins. Through a series of experiments, different incubation times and concentrations of MPA were examined to determine their impact on the electron-transfer rate. Using methylene blue MB molecules as a model system and employing the EC-SPR technique, the reflectance differences (ΔR) between the reduced and oxidized states of MB were analyzed, serving as an indicator of the electron transfer rate. The results revealed significant variations in the rate depending on the incubation times and concentrations of the MPA. It was determined that a combination of 1 mM MPA concentration and 6-hour incubation time provided optimal conditions for maintaining a significant (ΔR). These findings have important implications for optimizing sensor surfaces in biosensors based on direct electron transfer in redox proteins.

Enhancing Methylene Blue Dye Removal using pyrolyzed Mytella falcata Shells: Characterization, Kinetics, Isotherm, and Regeneration through Photolysis and Peroxidation.

The potential of pyrolyzed Mytella falcata shells as an adsorbent for removing methylene blue dye molecules from aqueous solutions was investigated. The study found that the adsorbent produced at 600 °C of pyrolysis temperature, with an adsorbent mass of 0.5 g, particle diameter of 0.297-0.149 mm, and pH 12.0, demonstrated the highest dye molecule removal efficiency of 82.41%. The material's porosity was observed through scanning electron microscopy, which is favorable for adsorption, while Fourier-transform infrared spectroscopy and X-Ray diffraction analysis analyses confirmed the presence of calcium carbonate in the crystalline phases. The pseudo-second order model was found to be the best fit for the data, suggesting that the adsorption mechanism involves two steps: external diffusion and diffusion via the solid pores. The Redlich-Peterson isotherm model better represented the equilibrium data, and the methylene blue adsorption was found to be spontaneous, favorable, and endothermic. The hydrogen peroxide with UV oxidation was found to be the most efficient method of regeneration, with a regeneration percentage of 63% achieved using 600 mmol.L-1 of oxidizing agents. The results suggest that pyrolyzed Mytella falcata shells could serve as an ecologically viable adsorbent alternative, reducing the amount of waste produced in the local environment and at the same time removing pollutants from the water. The material's adsorption capacity remained almost constant in the first adsorption-oxidation cycles, indicating its potential for repeated use.

Proximity Amplification-Enabled Electrochemical Analysis of Tumor-Associated Glycoprotein Biomarkers.

Glycoproteins produced and secreted from specific cells and tissues are associated with several diseases and emerge as typical biomarkers to provide useful information in cancer diagnosis considering their abnormal expression levels. In this work, we design a universal method to achieve the accurate and sensitive analysis of tumor-associated glycoprotein biomarkers based on both carbohydrate recognition and protein recognition at the same protein surface. The byproduct of dual recognition-induced proximity amplification, pyrophosphate, triggers the disassembly of methylene blue-encapsulated metal-organic frameworks, MB@ZIF-90. As a result, methylene blue molecules are released to arouse amplified electrochemical responses for glycoprotein analysis. Experimental results demonstrate the high-accuracy analysis of carcinoembryonic antigen, a typical glycoprotein biomarker in cancer diagnosis, in a linear range of 0.001-100 ng mL-1 with a low limit of detection of 0.419 pg mL-1. The method also displays satisfactory specificity and recoveries in complex serum samples and proves good versatility by adopting two other tumor-associated glycoprotein biomarkers, α-fetoprotein and mucin-1, as the targets. Therefore, this work provides a valuable tool for the analysis of glycoprotein biomarkers, which may be of great potential in early warning of malignant tumors in clinical applications.

Steric and Energetic Studies on the Synergetic Enhancement Effect of Integrated Polyaniline on the Adsorption Properties of Toxic Basic and Acidic Dyes by Polyaniline/Zeolite-A Composite.

The synergetic enhancement effect of the polyaniline (PANI) integration process on the adsorption properties of the PANI/zeolite-A composite (PANI/ZA) as an adsorbent for malachite green and Congo red synthetic dyes was evaluated based on classic equilibrium modelling in addition to the steric and energetic parameters of advanced isotherm studies. The PANI/ZA composite displays enhanced adsorption capacities for both methylene blue (270.9 mg/g) and Congo red (235.5 mg/g) as compared to ZA particles (methylene blue (179.6 mg/g) and Congo red (140.3 mg/g)). The reported enhancement was illustrated based on the steric parameters of active site density (Nm) and the number of adsorbed dyes per active site (n). The integration of PANI strongly induced the quantities of the existing active sites that have enhanced affinities towards both methylene blue (109.2 mg/g) and Congo red (92.9 mg/g) as compared to the present sites on the surface of ZA. Every site on the surface of PANI/ZA can adsorb about four methylene blue molecules and five Congo red molecules, signifying the vertical orientation of their adsorbed ions and their uptake by multi-molecular mechanisms. The energetic investigation of the methylene blue (-10.26 to -16.8 kJ/mol) and Congo red (-9.38 to -16.49 kJ/mol) adsorption reactions by PANI/ZA suggested the operation of physical mechanisms during their uptake by PANI/ZA. These mechanisms might involve van der Waals forces, dipole bonding forces, and hydrogen bonding (<30 kJ/mol). The evaluated thermodynamic functions, including enthalpy, internal energy, and entropy, validate the exothermic and spontaneous behaviours of the methylene blue and Congo red uptake processes by PANI/ZA.

Pore Nanoarchitectonics of Carbon Nitrides for the Excited‐State Deactivation of Confined Methylene Blue

AbstractThe confinement of organic chromophores within mesoporous material architectures can exert a considerable alteration on their physico‐chemical properties. This study presents a detailed spectroscopic investigation of methylene blue (MB) entrapped in mesoporous polymeric carbon nitrides (mPCNs) with different pore architecturesusing transient absorption spectroscopy (TAS). The spatial confinement of MB molecules results in a prominent change in absorption spectra, characterized by both redshifts and the appearance of additional shoulder peaks, arising from the formation of MB dimers (MB2) concomitant with a distortion of the MB structure. Upon photoexcitation, entrapped MB molecules exhibit a notable altered excited‐state absorption feature, along with a drastic excited‐state quenching within 2 ns compared to molecues in bulk solutions. In contrast to the ultrafast quenching of sole MB2 with a lifetime of ~3.6 ps in highly concentrated solutions, the concentration‐dependent quenching behavior of MB aggregates in confined environments suggests the effect is caused by excimers formed in close proximity. The findings of this work highlight the impact of constrained environments and intermolecular interactions on the relaxation pathways of the excited states in photoactive molecules.

Development of methylene blue imprinted silica for detecting arsenic ions in aqueous solution

Arsenic pollution is caused by industrial activities of human beings such as the mineral product manufacturing industry and metal industries. Arsenic pollution can cause nervous system and cardiovascular diseases in humans and destroy various water-based ecosystems. So far, different chemical analysis equipment is being utilized to carry out measurements of arsenic. However, conventional chemical analysis techniques are restricted by their needs for large or expensive equipment, which prevents convenient and rapid measurement. Here, we show that convenient measurements of arsenic can be conducted through the utilization of silica that has been modified with methylene blue molecules (MB-Silica). Several studies have reported that the interaction of methylene blue (MB) with arsenic in aqueous solution leads to color variations caused by oxidation-reduction reactions. Taking these alterations in colors into consideration, we have developed a convenient approach for arsenic detection by synthesizing MB-Silica. Furthermore, by varying the MB concentration during synthesis, arsenic ions can be detected with various concentration gradients, validating the feasibility of aqueous arsenic detection. Since the possibility of detecting arsenic using MB-silica, developed in this study, was successfully confirmed, it is anticipated that the MB-silica will be extensively used to detect arsenic in the field.