Initial Methylene Blue Research Articles

Highly Active under VIS Light M/TiO2 Photocatalysts Prepared by Single-Step Synthesis

A single-step impregnation approach is investigated as a synthetic route for photocatalyst synthesis active under visible light. The as-derived photocatalysts exhibited very high degradation rates towards methylene blue (MB) decolorization under visible light despite the high concentration of the initial MB solution concentration. The TiO2-based photocatalysts were prepared using nitrate precursor compounds for copper and silver; thus, Ag/TiO2 and Cu/TiO2 photocatalysts were prepared. The photocatalyst’s physicochemical properties were determined by XRF, BET, and XRD analysis. The metal nature of the titania substrate, the titania matrix effect, and the metal concentration parameters were studied, while the catalyst concentration in the MB initial solution was optimized.

Promising photocatalytic activity under visible light of ZnWO4 nanocrystals prepared via green synthesis approach

In this work, we report on the biosynthesis of zinc tungstate ZnWO4 nanocrystals using Hyphaene thebaica L. Mart, fruit extracts for visible light photocatalytic application. The structure, nanostructure, and optical properties, as well as the photocatalytic activities of for biosynthesized zinc tungstate on Methylene blue, were investigated in detail. The zinc tungstate was in a pure crystalline phase without the presence of any impurities or secondary phases. The morphological analysis indicates the presence of spherical and uniformly distributed nanoparticles with an average crystallite particle size of 24 nm, and additionally the presence of rod-like particles. The bandgap energy value has been estimated to be 2.8 eV.The photocatalytic activities of ZnWO4 were investigated by the degradation of Methylene blue (MB) under visible light irradiation. A series of reactions, with different initial MB concentrations (1.10−5mol/L, 2.10−5mol/L and 3.10−5mol/L) were implemented using 1 g/L of ZnWO4 catalyst under visible light irradiation. The biosynthesized ZnWO4 achieved an outstanding degradation activity of 98.4% for methylene blue dye after 90 min under visible light emission. The green chemistry was an efficient route to prepare ZnWO4 with high photocatalytic efficiency under visible light irradiation and this improvement is related to oxygen deficiency.

Breakthrough studies for the sorption of methylene blue dye from wastewater samples using activated carbon derived from waste banana peels

In the current study, an activated carbon derived from waste banana peel using H2SO4 was applied for the first time in a packed-bed column for methylene blue (MB) dye removal from wastewater. The pore structure and surface of banana peel activated carbon (BPAC) were investigated using X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and Brunauer-Emmett-Teller analysis to discover the mechanism of MB sorption. The produced BPAC by H2SO4 activation agent has surface area of 361.86 m2/g and exhibits good thermal stability. The extent of MB breakthrough performance was examined by optimizing flow rate, bed mass, and initial concentration at pH 9. The column’s dynamics revealed a strong dependence of breakthrough curves as a function of process conditions. The breakthrough time (tb), volume of liters processed (L), and adsorption exhaustion rate all increased as bed mass increased but decreased as flow rate and initial concentration increased. Applying linear regression to the experimental data, Yoon-Nelson and Thomas’ kinetic model was used to extract column characteristic parameters that could be used in process design. Using environmental water, the waste banana peel activated carbon material demonstrated effectiveness in removing MB to below acceptable levels by processing 1.16 L of water with an initial MB concentration of 40 mg/L using 8 g of sorbent. Nitric acid (3M) was able to regenerate the exhausted bed. Moreover, the sorbent was reused four times with no significant capacity loss. It can be concluded that waste banana peel activated carbon medium is an alternative solution to remediate MB-contaminated wastewater.

Efficient removal of methylene blue from water using magnetic Alyssum homolocarpum seed gum-based matrix

In this study, we fabricated magnetic Fe3O4 nanoparticles conjugated with anionic hydroxypropyl starch-graft-acrylic acid (Fe3O4@AHSG) for the efficient removal of methylene blue (MB) dye from aqueous solutions. The synthesized nanoconjugates were characterized using various techniques. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analysis revealed that the particles exhibited homogeneously distributed nanosized spherical shapes with a mean diameter of 41.72 ± 6.81 nm. The EDX analysis confirmed the absence of impurities, with the Fe3O4 particles comprising 64.76 % iron and 35.24 % atomic oxygen. Dynamic light scattering (DLS) measurements showed a monodisperse particle system with a mean hydrodynamic size of 135.4 nm (polydispersity index, PI = 0.530) for the Fe3O4 nanoparticles and 163.6 nm (PI = 0.498) for the Fe3O4@AHSG adsorbent. Vibrating sample magnetometer (VSM) analysis indicated superparamagnetic behavior for both Fe3O4 and Fe3O4@AHSG, with higher saturation magnetization (Ms) observed for Fe3O4. The dye adsorption studies demonstrated that the adsorbed dye capacity increased with increasing initial MB concentration and adsorbent dose. The pH of the dye solution significantly influenced the adsorption, with the highest adsorption observed at basic pH values. The presence of NaCl reduced the adsorption capacity due to increased ionic strength. Thermodynamic analysis indicated the thermodynamically favorable and spontaneous nature of the adsorption process. Kinetic studies revealed that the pseudo-second-order model provided the best fit to the experimental data, suggesting chemisorption as the rate-limiting step. Overall, Fe3O4@AHSG nanoconjugates exhibited excellent adsorption capacity and could be a promising material for effective removal of MB dye from wastewater.

Artificial Neural Network Modeling for Basic Dye Adsorption onto Montmorillonite

This research focused on the use of montmorillonite (Mt) clay to eliminate methylene blue (MB) from water and the modeling of the process with an artificial neural network (ANN). The effects of initial MB concentration, contact duration, pH, and temperature on the adsorption efficiency were examined. Maximum adsorption capacity, with 91.3 wt% MB removal at the selected optimum parameters (pH: 12, contact duration: 90 min, temperature: 25 °C, adsorbent dosage: 2 g/L, and initial MB concentration (Ci ): 650 mg/L), was measured as 296.6 mg/g. Langmuir isotherm and pseudo-second-order kinetic models showed the highest correlation coefficients (0.9935 and 0.9999, respectively) to explain the mechanism of the adsorption of MB cations onto Mt. In addition, the maximum adsorption capacity at 25 °C calculated by using the Langmuir isotherm model was determined as 400 mg/g. In the developed ANN model, pH, C i, temperature, and time were considered the input data, and the equilibrium MB concentration (C e) was the output data. While obtaining the ANN model, the data were processed using fivefold cross-validation. Comparing the estimation results with the experimental studies, R 2 = 0.9987 and mean square error (MSE) = 0.00084654 were obtained. Therefore, the C e value estimations were performed with high success rates by using the developed ANN model.

Box-Behnken modeling and optimization of visible-light photocatalytic removal of methylene blue by ZnO-BiFeO3 composite.

Box-Behnken experimental design was utilized to model and optimize the photocatalytic removal of methylene blue (MB) using ZnO-BiFeO3 composite under visible light (LED). Three catalysts with different ZnO:BiFeO3 molar ratios (2:1, 1:2, and 1:1) were synthesized successfully using the hydrothermal method. The structural, morphological, and optical properties of the synthesized photocatalysts were analyzed by X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray Spectroscopy (EDX), Fourier Transform Infrared Spectra (FT-IR), Ultraviolet Visible Spectrometer (UV-vis), Transmission Electron Microscopy(TEM), High-Resolution Transmission Electron Microscopy (HR-TEM), and Photoluminescence (PL) Spectrophotometry. FESEM showed the relatively uniform distribution of BiFeO3 crystalline particles on ZnO ones. UV-vis analysis showed that the photocatalytic performance of pure ZnO and BiFeO3 under visible light irradiation is weak, while ZnO-BiFeO3 with a 2:1 molar ratio composite with a bandgap of about 2.37eV showed high performance. This improved photocatalytic activity may be due to the heterogeneous synergistic effect of the p-n junction. In order to optimize the experimental conditions, four factors of initial MB concentration (5 to 20mg/L), pH (3 to 12), catalyst dosage (0.5 to 1.25mg/L), and light intensity (4 to 18 W) were selected as independent input variables. Box-Behnken experimental design method (BBD) suggested a quadratic polynomial equation to fit the experimental data. The results of the analysis of variance (ANOVA) confirmed the goodness of fit for the suggested model (predicted- and adjusted-R2 0.99). The optimum conditions for maximizing the photocatalytic MB degradation were found to be an initial MB concentration of 11mg/L, pH of 11.7, catalyst dosage of 0.716mg/L, and light intensity of 11.4 W. Under the optimum conditions, the highest photocatalytic MB degradation of 62.9% was obtained, which is in reasonable agreement with the predicted value of 69%.

Metilen mavisi boyasının aljinat-biyocam membranlara adsorpsiyonu: Cevap yüzey yöntemi, izoterm ve kinetik çalışmalar

In this research, environment-friendly composite membranes based on alginate (ALG) and bioglass nanoparticles (BGs) were prepared by the solvent casting technique and utilized as adsorbents for the elimination of methylene blue (MB) from water. Zeta potential of the particles was determined to be -24.9 mV by laser dynamic light scattering (DLS), and their sizes were found to be 773 and 777 nm by transmission electron microscopy (TEM) and DLS analysis, respectively. Atomic force microscope (AFM) analysis revealed that increasing the BGs content from 1 to 5% w/v caused the root mean square roughness of membranes to increase from 159.38 to 182.03 nm. The adsorption process was successfully modeled and optimized using a hybrid response surface methodology integrated central composite design (RSM-CCD). A statistical analysis was utilized to examine and optimize the effects of three important independent variables (concentration of BGs (1-5% w/v), pH of the solution (3-9), and initial dye level (15-45 mg L-1)) on MB adsorption performance. The findings indicated that the quadratic model was suitable for prediction of MB's removal. Optimized experimental parameters were found to be a pH of 9, a contact time of 120 min, an initial MB concentration of 45 mg L-1, and a BGs concentration of 1% (w/v). Freundlich isotherm and pseudo-second-order kinetic models were found to be the best-fitting models in isotherm and kinetic studies, respectively. Dubinin-Radushkevich (D-R) isotherm model predicted a chemical mechanism for MB adsorption onto the composite alginate membranes.

Eco-Friendly Semi-Interpenetrating Polymer Network Hydrogels of Sodium Carboxymethyl Cellulose/Gelatin for Methylene Blue Removal.

The present work describes the potential application of environmentally friendly sodium carboxymethylcellulose/gelatin (CMC/Gel) semi-interpenetrating hydrogels prepared by citric acid as a nontoxic cross-linking agent to adsorb dyes. The prepared hydrogels were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA/DTG), and swelling study. The adsorption performance of CMC/Gel2 (C/G2) hydrogel on methylene blue (MB) was investigated. The results showed the better adsorption conditions: adsorption time of 300 min, initial MB concentration of 500 mg/L, adsorbent dosage of 1.2 g/L, solution pH of 7, and temperature of 30 °C. The adsorption kinetics fit the pseudo-second order kinetics model, and the adsorption isotherm fit the Langmuir isotherm model. The maximum adsorption capacity reached 943.40 mg/g. The adsorption process is a spontaneous exothermic process. After three adsorption-desorption cycles, the removal rate of MB by hydrogel still reached 85%, with good reusability. Consequently, the hydrogel can be used as an environmentally friendly, stable, and efficient adsorbent for dyes in wastewater treatment.

Green iron oxide-modified biochar for methylene blue removal from aqueous solutions

Textile industrial wastewater, a major source of effluent coloration, has been identified as a threat to human and animal health. A difficult and significant challenge is the complete removal of poorly biodegradable dyestuffs from complex environmental matrices. We synthesized a green iron oxide-loaded Douglas fir biochar (FDBC) hybrid using commercially available biochar, DBC, to effectively remove aqueous methylene blue (MB). Both modified and pristine adsorbents are microporous, and their MB removal speeds are very high (equilibrate in 5 min) at an initial MB concentration of 25 ppm. Large surface areas (640 m2/g versus 248 m2/g) and pore volumes (0.13 cm3/g versus 0.07 cm3/g) of DBC and FDBC partially facilitate MB surface physisorption. Compared to DBC, the maximum Langmuir adsorption capacity of FDBC is higher (634.0 mg/g versus 740.5 mg/g), indicating the hybrid adsorbent design that involves the iron oxide phase plus the biochar backbone (1500 ppm initial [MB], t = 5 min, and pH 6.8). The addition of Fe3O4 nanoparticles (∼11.0 nm) promotes the adsorption of MB on FDBC (due to the increase in the surface Fe3O4 concentration), while allowing small adsorbent particles of spent FDBC to be easily removed from batch treatments using a magnet. The magnetic variant (FDBC) simultaneously adsorbs three co-existing BP, BG, and MB with over ∼90% efficiency. Spent FDBC could be regenerated easily by stirring in Methanol. FDBC would be more economical in terms of its facile synthesis, efficient and fast MB adsorption, convenient recovery, pH-independent MB uptake, and treatment of variety of wastewaters etc.

Adsorption of methylene blue from textile industrial wastewater using activated carbon developed from Rumexabyssinicus plant

Methylene blue (MB) is abundantly found in textile industrial effluent which can cause severe health problems for public and environmental ecology. Therefore, this study aimed to remove MB from textile wastewater using the activated carbon developed from Rumexabyssinicus. The adsorbent was activated using chemical and thermal methods, and then it was characterized by SEM, FTIR, BET, XRD, and pH zero-point charge (pHpzc). The adsorption isotherm and kinetics were also investigated. The experimental design was composed of four factors at three levels (pH (3, 6, and 9), initial MB concentration (100, 150, and 200 mg/L), adsorbent dosage (20, 40, and 60 mg/100 mL), and contact time (20, 40, and 60 min)). The adsorption interaction was evaluated using response surface methodology. The characterization of a Rumexabyssinicus activated carbon was found to have multiple functional groups (FTIR), an amorphous structure (XRD), crack with ups and down morphology (SEM), pHpzc of 5.03 and a high BET-specific surface area of 2522 m2/g. The optimization of MB dye removal was carried out using the Response Surface methodology coupled with the Box Behnken approach. The maximum removal efficiency of 99.9% was recorded at optimum conditions of pH 9, MB concentration of 100 mg/L, the adsorbent dosage of 60 mg/100 mL, and contact time of 60 min. Among the three adsorption isotherm models, the Freundlich isotherm model was the best fit with an experimental value at R2 0.99 showing the adsorption process was heterogeneous and multilayer whereas the kinetics study revealed that pseudo-second-order at R2 0.88. Finally, this adsorption process is quite promising to be used at an industrial level.

Synthesis of cubic Mn2O3 and its catalytic performance in activating peroxymonosulfate for degradation of MB

In this study, uniform Mn2O3 cubic with a size of 0.6–1.1 µm was prepared using a simple carbonate precipitation-calcination method, and its performance in activating peroxymonosulfate (PMS) for degradation of methylene blue (MB) was investigated. A single factor experiment was conducted to investigate the degradation of MB by taking process parameters as variables, such as catalyst amount, PMS dosage, initial MB concentration, reaction temperature and co-existed anions. The results showed that a MB degradation rate of 81.49% was achieved within 50 min under the reaction conditions: Mn2O3 amount of 0.1 g/L, PMS dosage of 0.6 mmol/L, MB concentration of 10 mg/L, a total volume of 500 mL and reaction temperature of 25 °C. In addition, it was found that the introduction of C2O42- or PO43- had a negative effect on MB degradation, with inhibition ratio reaching 33.08% and 17.47%, respectively. However, Cl- had no inhibitory effect on MB degradation. Furthermore, reactive species in the system of Mn2O3/PMS were identified by electron paramagnetic resonance (EPR) tests, and results showed that •OH, SO4•-, •O2– and 1O2 all participated in the MB degradation process. Moreover, Mn2O3 exhibited stable catalytic performance during four consecutive cycling runs, indicating that the as-prepared cubic Mn2O3 is expected to be a potential catalyst for PMS activation and dye wastewater treatment.

Adsorption of methylene blue from aqueous solution by biochar prepared from jackfruit peel: isotherm model studies

In this study, biochar derived from Jackfruit peel (JA) via the pyrolysis at 500 °C for 2 h was used as an adsorbent to remove Methylene Blue (MB) from aqueous solution. Effects of pH, contact time, and initial MB concentration were investigated. Isotherm models, such as Langmuir, Freundlich, Sips, and Dubinin-Radushkevich, were applied to estimate the adsorption in nature. The results indicated that the Sips and Freundlich models gave the best fit with experimental datas. The maximum adsorption capacity of MB calculated from Langmuir was 39.87 mg/g at 306K, pH = 11, and time = 60 min. The E value evaluated from Dubinin-Radushkevich smaller than 8 kJ/mol indicated that the MB adsorption of JA followed a physical process.

Efficient Photocatalytic Degradation of Methylene Blue Dye from Aqueous Solution with Cerium Oxide Nanoparticles and Graphene Oxide-Doped Polyacrylamide.

A cerium oxide nanoparticles (CeO2-NPs)/graphene oxide (GO)/polyacrylamide (PAM) ternary composite was synthesized through free-radical polymerization of acrylamide in the presence of CeO2 nanoparticles and GO in an aqueous system. The synthesized composite material was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy techniques and applied for the photocatalytic degradation of methylene blue (MB) dye from an aqueous solution. Tauc's model for direct transition was used to model for the optical band gap. The key operating parameters such as the amounts of CeO2-NPs and GO, pH, initial MB concentration, type of light irradiation, and contact time have been optimized to achieve the highest MB degradation percentage. The photocatalysis process was pH-dependent, and the optimum pH value was found to be 12.0. Under UV-A light, 90% dye degradation occurred in 90 min. The degradation of MB was also specified in terms of total organic carbon (TOC) and chemical oxygen demand (COD). Free-radical capture experiments were also performed to determine the role of radical species during the photocatalytic oxidation process. The photocatalytic process showed that the equilibrium data is in good agreement with the Langmuir-Hinshelwood kinetic model. A rate constant of 0.0259 min-1 was obtained. The hydrogel was also tested to assess its reusability, which is an important key factor in practical wastewater treatment. The photocatalytic activity only decreased to 75% after nine uses.

Preparation of stimuli-responsive hydrogel vitrimers as recyclable dye adsorbent for water purification

The concept of water purification by recyclable vitrimers through topology control has been introduced new class of polymeric materials called covalent adaptable networks (CAN), with great interest of production. Meantime, for applying the feature of stimuli-responsivity and recyclability, we synthesized poly(glycidyl methacrylate-co-methacrylic acid) copolymers (P(GMA-co-MAA)) with different molar ratios of GMA to MAA. Synthesis of copolymers and their compositions were confirmed by proton nuclear magnetic resonance 1HNMR analysis. Vitrimer hydrogels were prepared by using citric acid as crosslinker through solution casting method. Successful formation of vitrimer hydrogels was confirmed by Fourier transform infrared (FT-IR) analysis. Physical and thermal characteristics of vitrimers were investigated by differential scanning calorimetry (DSC), thermal gravimetric (TGA) analysis, and field emission scanning electron microscopy (FE-SEM). The swelling ratio behaviors of hydrogels was investigated, and the results showed that V(GMA5-co-MAA95) had maximum swelling ratio. Finally, methylene blue (MB) adsorption and desorption behavior of vitrimers and their recycled samples was investigated. The results showed that samples with the highest molar ratio of MAA had the most methylene blue adsorption in all pH values (2, 4, 7.4, and 10). The as-prepared and recycled V(GMA-co-MAA) vitrimers exhibited maximum adsorption efficiency (99.9%) at pH= 10 and initial MB concentration of 5 mg/L. Also, minimum adsorption efficiency was dedicated to pH= 2 and initial MB concentration of 2 mg/L. For both conditions adsorbent dosage and aqueous solution volume was 0.7 g and 100 mL, respectively. Also, the kinetics of adsorption was investigated by pseudo-first-order, pseudo-second-order, and intraparticle diffusion models and kinetic isotherm was evaluated by Langmuir and Freundlich models. Results showed that unlike intraparticle diffusion, pseudo-second-order and Langmuir models correlated experimental data better than on other models, suggesting these two models as the depiction for our adsorption process. SynopsisPrepared dye adsorbents are based on recyclable vitrimers which can be applied in water purification without extra plastic pollution.

Chromochloris zofingiensis microalgae as a potential dye adsorbent: Adsorption thermo-kinetic, isothermal, and process optimization

In this study, the microalgae Chromochloris zofingiensis (ChZ) was harvested and used as a biosorbent for the removal of methylene blue (MB) as a model cationic dye from water. The ChZ was characterized via FTIR, FESEM-EDX, XRD and BET analyses. Response Surface Methodology, based on Central Composite Design was employed to optimize the batch adsorption process, including independent variables of biosorbent dosage, initial MB concentration and pH of the solution to maximize the MB removal percentage. The maximum removal of 97 % was obtained at the optimal conditions i.e., biosorbent dosage of 0.72 g/L, pH of 10 and initial MB concentration of 15.12 mg/L, with >97 % confidence limit. Pareto sensitivity analysis uncovered that the biosorbent dosage has the greatest impact (50 %) on MB removal. The adsorption kinetic was better described by the pseudo-second-order model among the different kinetic models applied i.e., pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models. The adsorption equilibrium was also modeled using the Langmuir, Freundlich, Dubinin–Radushkevich and Temkin isotherms. The Langmuir model provided the best fit and the maximum sorption capacity of 135.42 mg/g was recorded. Principle thermodynamic criteria including ΔGo, ΔHo and ΔSo were computed for the biosorption. The results uncovered that the biosorption of MB using ChZ is spontaneous and exothermic. Generally, the results indicated that ChZ microalga can be considered an effective biosorbent for dye-contaminated water remediation.

Adsorption Performance of Methylene Blue by KOH/FeCl3 Modified Biochar/Alginate Composite Beads Derived from Agricultural Waste

In this study, high-performance modified biochar/alginate composite bead (MCB/ALG) adsorbents were prepared from recycled agricultural waste corncobs by a high-temperature pyrolysis and KOH/FeCl3 activation process. The prepared MCB/ALG beads were tested for the adsorption of methylene blue (MB) dye from wastewater. A variety of analytical methods, such as SEM, BET, FTIR and XRD, were used to investigate the structure and properties of the as-prepared adsorbents. The effects of solution pH, time, initial MB concentration and adsorption temperature on the adsorption performance of MCB/ALG beads were discussed in detail. The results showed that the adsorption equilibrium of MB dye was consistent with the Langmuir isothermal model and the pseudo-second-order kinetic model. The maximum adsorption capacity of MCB/ALG-1 could reach 1373.49 mg/g at 303 K. The thermodynamic studies implied endothermic and spontaneous properties of the adsorption system. This high adsorption performance of MCB/ALG was mainly attributed to pore filling, hydrogen bonding and electrostatic interactions. The regeneration experiments showed that the removal rate of MB could still reach 85% even after five cycles of experiments, indicating that MCB/ALG had good reusability and stability. These results suggested that a win-win strategy of applying agricultural waste to water remediation was feasible.

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.

Response Surface Modelling of Methylene Blue Adsorption onto Seaweed, Coconut Shell and Oak Wood Hydrochars

Adsorption of methylene blue (MB) dye from an aqueous solution onto hydrochars produced from brown seaweed (Fucus Serratus) (FS-HC), coconut shell (CS-HC), and oak wood (Oak-HC) at different temperatures (200–250 °C) was investigated in a batch system. Response surface modelling (RSM) was used to investigate the effect of initial MB concentration (50–300 mg/L), contact time (0–240 min), and solution pH (2–12) on the adsorption process. RSM was also used to model and optimise these parameters for efficient adsorption. Kinetic and isotherms studies were carried out to study the adsorption mechanism onto the hydrochars. It was found that the best adsorbent from the RSM model was FS-HC200, and the optimal conditions for greater MB dye uptake were lower initial MB concentration (50 mg/L), pH 6 and contact time of 84 min; removing >99% of MB. Langmuir and Redlich–Peterson isotherm models fitted the adsorption of MB onto hydrochars prepared at 200 and 250 °C. Freundlich and Redlich–Peterson isotherms were suitable for hydrochars produced at 220 °C. FS-HCs have the highest maximum adsorption capacity of MB of about (8.60–28.57) mg/g calculated from the Langmuir isotherm. The adsorption process for all the hydrochars followed a pseudo-second-order model (R2 = 0.96–1.00), and film diffusion and intraparticle diffusion were the rate-determining steps. Therefore, this work identifies cheap adsorbents from biowaste that are effective for the removal of cationic pollutants from wastewater.

Green synthesis, characterization, and application of Fe3O4 nanoparticles for methylene blue removal: RSM optimization, kinetic, isothermal studies, and molecular simulation

Methylene Blue (MB) is a cationic dye causing various health problems such as asthma, heartbeat, eye and skin irritation, nausea, and distress during prolonged exposure. In this regard, the green magnetite nanoparticle was synthesized using the extract of Prosopis farcta. The synthesized Fe3O4nanoparticle was characterized by X-ray powder diffraction (XRD), Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transforms Infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), and Brunauer-Emmett-Teller (BET). The corresponding parameters, including the primary concentration of MB (5–65 mg/L), the dose of synthesized nanoparticle (0.025–0.925 g/L), solution pH (3–11), and contact time (20–60 min), were considered. Also, central composite design (CCD), as one of the response surface methodologies (RSM), was used for the related modelling and optimization. The particle size of the adsorbent was between 5 and 70 nm, and the nanoparticle has 206.75 m2/g of a specific surface, 6.1 nm of average pore size, and 0.3188 cm3/g of the total pore volume. The optimal conditions for MB removal by the nanoparticle were found to follow an initial MB concentration of 20 mg/L, 0.7 g/L of the nanoparticle dose, pH = 9, and a contact time of 50 min. The pseudo-second-order (PSO) and Freundlich models were the best kinetic and isothermal models for MB removal by the synthesized nanoparticle. Molecular modelling was used to optimize the MB molecular configuration and compute HOMO-LUMO energies, quantum-chemical descriptors, and molecular electrostatic potential to evaluate the nature reactivity of the MB molecule.

Synthesis of AgInS2-ZnS quantum dot/TiO2 nanocomposites as efficient photocatalysts for methylene blue degradation

Photocatalytic degradation has been demonstrated to be an efficient and eco-friendly method for the removal of dye pollutants. Herein, we report the synergetic effect of glutathione (GSH)-capped AgInS2-ZnS (AIS-ZnS) core–shell quantum dots (QDs) and titanium dioxide (TiO2) as a novel nanocomposite for the efficient photocatalytic treatment of methylene blue (MB). The AIS-ZnS core–shell QDs and the corresponding QD/TiO2 nanocomposites were synthesized directly in an aqueous medium followed by annealing. The optical properties of the AIS-ZnS core–shell QDs showed strong yellow photoluminescence, which decreased gradually with the addition of TiO2. Fourier transform infrared (FTIR) spectroscopy confirmed the GSH capping on the QDs and nanocomposites. X-ray diffraction and transmission electron microscopy revealed the nanocrystalline nature and shape of the as-synthesized materials and showed the integration of the QDs (3.9 nm) on the TiO2 particles after annealing. These materials were then investigated as a photocatalyst for MB degradation using visible light irradiation. The effect of TiO2 content in the catalyst, calcination, photoirradiation period, catalyst dose, and initial MB concentration on photodegradation of MB was studied. The results indicated that the AIS-ZnS QD/TiO2 nanocomposite exhibited better photodegradation performance compared to AIS-ZnS QDs and TiO2. The increasing TiO2 concentration in the nanocomposite also enhanced MB degradation efficiency (up to 99%). The kinetics of MB degradation follows a pseudo-first-order process. The prepared AIS-ZnS QD/TiO2 nanocomposite would serve as an effective and eco-friendly photocatalyst for MB degradation.