Methylene Blue Adsorption Capacity Research Articles

Pyrolysis characteristics, kinetics, and biochar of fermented pine sawdust-based waste.

The objective of current study is to explore the energy recovery potential of fermentation residues. In this perspective, pyrolysis characteristics, kinetics, and modified biochar derived from pine sawdust after fermentation (FPD) were determined, and comparison was established with pine sawdust (PD). The variation range of comprehensive pyrolysis index (CPI) values of FPD was found 6.51 × 10-7-16.38 × 10-7%2·min-2·°C-3, significantly higher than that of untreated samples determined under the same experimental conditions. The average activation energy of FPD was 367.95kJ/mol, 389.45kJ/mol, and 346.55kJ/mol calculated by Flynn-Wall-Ozawa (FWO) method, Kissinger-Akahira-Sonuse (KAS), and Starink method respectively, and importantly, these values are much higher than those of PD. Additionally, fermentation could enhance the adsorption capacity for methylene blue of biochar from 0.76mg/g to 1.6mg/g due to the abundant surface functional groups and three-dimensional internal pore structure. The adsorption pattern of fermented pine wood shifted from chemisorption dominated to the synergetic adsorption of surface functional groups adsorption and intragranular filling. These results show that FPD has favorable pyrolytic properties, and the derived biochar has adsorption properties, which is the basis for designing pyrolysis process and reusing fermentation residues. HIGHLIGHTS: The FPD has higher values of CPI and activation energy than the PD. FPD-derived biochar has higher adsorption capacity than PD-derived biochar. The fermentation improves the pyrolysis performance. The fermentation enhances adsorption capacity due to unique structure of biochar.

Understanding association between methylene blue dye and biosorbent: Palmyrah sprout casing in adsorption process in aqueous phase

Water pollution caused by industrial dyes has become a severe problem in the modern world. Biosorbents can be used in an eco-friendly manner to remove industrial dyes. In this study, five biosorbents were selected: palmyrah sprout casing (PSC), manioc peel, lime peel, king coconut husk, and coconut kernel. Batch adsorption experiments were conducted to identify the best biosorbent with the highest ability to adsorb methylene blue (MB) from wastewater. The detailed mechanisms of PSC used in the adsorptive removal of MB in aqueous phase were investigated. Of the five biosorbents, PSC exhibited the best removal performance with an adsorption capacity at equilibrium (qe) of 27.67 mg/g. The qe values of lime peel, king coconut husk, manioc peel, and coconut kernel were 24.25 mg/g, 15.29 mg/g, 10.84 mg/g, and 7.06 mg/g, respectively. To explain the mechanisms of MB adsorption with the selected biosorbents, the Fourier transform infrared (FTIR) spectrometry and X-ray diffraction (XRD) analyses were performed to characterize functional properties, and isotherm, kinetic, rate-limiting, and thermodynamic analyses were conducted. The FTIR analysis revealed that different biosorbents had different functional properties on their adsorptive surfaces. The FTIR and XRD results obtained before and after MB adsorption with PSC indicated that the surface functional groups of carbonyl and hydroxyl actively participated in the removal process. According to the isotherm analysis, monolayer adsorption was observed with the Langmuir model with a determination coefficient of 0.998. The duration to reach the maximum adsorption capacity for MB adsorption with PSC was 120 min, and the adsorption process was exothermic due to the negative enthalpy change (−9.950 kJ/mol). Moreover, the boundary layer thickness and intraparticle diffusion were the rate-limiting factors in the adsorption process. As a new biosorbent for MB adsorption, PSC could be used in activated carbon production to enhance the performance of dye removal.

Bamboo Nanocellulose/Montmorillonite Nanosheets/Polyethyleneimine Gel Adsorbent for Methylene Blue and Cu(II) Removal from Aqueous Solutions

In recent years, the scarcity of pure water resources has received a lot of attention from society because of the increasing amount of pollution from industrial waste. It is very important to use low-cost adsorbents with high-adsorption performance to reduce water pollution. In this work, a gel adsorbent with a high-adsorption performance on methylene blue (MB) and Cu(II) was prepared from bamboo nanocellulose (BCNF) (derived from waste bamboo paper) and montmorillonite nanosheet (MMTNS) cross-linked by polyethyleneimine (PEI). The resulting gel adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (SEM), X-ray photoelectron spectroscopic (XPS), etc. The results indicated that the MB and Cu(II) adsorption capacities of the resulting gel adsorbent increased with the solution pH, contact time, initial concentration, and temperature before equilibrium. The adsorption processes of MB and Cu(II) fitted well with the fractal-like pseudo-second-order model. The maximal adsorption capacities on MB and Cu(II) calculated by the Sips model were 361.9 and 254.6 mg/g, respectively. The removal of MB and Cu(II) from aqueous solutions mainly included electrostatic attraction, ion exchange, hydrogen bonding interaction, etc. These results suggest that the resulting gel adsorbent is an ideal material for the removal of MB and Cu(II) from aqueous solutions.

A 'green' adsorbent: effect of chemical modification of biosorbents on the adsorption of methylene blue and malachite green.

The dyes methylene blue and malachite green were adsorbed onto the as-prepared and chemically-modified biosorbents obtained from the mesocarp of crushed calabash (Lagenaria siceraria). The aim was to investigate the adsorption capacity of the natural biosorbent, neutralized biosorbent (0.1 mol L-1 NaOH, followed by 0.1 mol L-1 HCl), acid biosorbent (0.1 mol L-1 HCl) and basic biosorbent (0.1 mol L-1 NaOH). The maximum adsorption capacities for methylene blue were, in ascending order: 11.37 mg g-1 for acid biomass < 11.87 mg g-1 for basic biomass < 16.55 mg g-1 for neutralized biomass < 18.83 mg g-1 for natural biomass. In ascending order, for malachite green the maximum adsorption capacities were: 12.80 mg g-1 for basic biomass < 13.31 mg g-1 for acid biomass < 18.74 mg g-1 for natural biomass < 19.67 mg g-1 for neutralized biomass. A comparison of the thermodynamic parameters Gibbs free energy, enthalpy and entropy obtained for the natural biosorbent with those obtained for the chemically-modified biosorbents indicated that the chemical modification proposed led to a change in the materials. The removal capacity, the Freundlich isotherms and the pH of the biosorbents underwent changes with the chemical modification carried out, promoting a novel approach for the use of this biosorbent.

Graphene oxide crosslinked chitosan composites for enhanced adsorption of cationic dye from aqueous solutions

BackgroundsIn this study, we combined chitosan (CS) – considered a green adsorbent, and graphene oxide (GO) – an excellent adsorbent, to synthesize CS/GO composites with different GO contents. These composites promised the synergic effect of two materials and broadening the adsorption ability for water treatment. MethodsThe characteristic data proved the successful cross-linking between CS and GO where CS molecules might deposit on GO sheets via amide linkage and hydrogen bonding. The effects of operating conditions and co-existing ions on batch-mode adsorption performance of methylene blue (MB) on the composites were studied. Significant findingsThe experimental results indicated that the combination of CS and GO could not only improve the surface area by reducing agglomeration of GO sheets but also enhance significantly the adsorption capacity of cationic dye on CS. The Langmuir adsorption capacity of MB reached 259.5 mg/g at a pH of 8 and 30 °C for CS/GO12 material. The effect of common matrix ions such as Na+, Ca2+, Fe3+, and NO3− was examined, suggesting that the adsorption of MB over the composite was dominated by electrostatic interaction and pore space occupation. The removal of MB by the composite still achieved over 75% after the fourth adsorption-regeneration cycle.

Interlayer adsorption of cationic dye on cationic surfactant-modified and unmodified montmorillonite.

Water pollution by toxic organic dyes is one of the most critical health and environmental problems worldwide. By means of molecular dynamics method, the present work aims to evaluate the applicability of montmorillonite (Mt) modified by hexadecyltrimethylammonium cations (HDTMA+) compared to unmodified Na-Mt for the adsorption of cationic methylene blue (MB) dye. The results showed that the adsorption energy of MB on both HDTMA-Mt and Na-Mt absorbent ranged from -100 to -250kJ/mol, indicating the effectiveness of two types of adsorbents in dye water treatment. The highest adsorption energy was found at w =50% in each adsorbent system. Adsorption mechanisms of MB depend on molecular orientations, which is influenced by the surfactant and water content. The adsorption mechanism of MB is chemisorption dominated by strong electrostatic interaction between CH3 groups of MB and oxygen atoms of Mt surfaces. Besides, physisorption also plays a minor role in MB orientations. It is found that the existence of cationic surfactants can slightly improve the adsorption capacity of MB only at higher water content through enlarging the interlayer space of Mt and reducing mobility of MB. However, there will be a negative impact on the reduction of adsorption sites for dyes especially at low water content. Our results provide a possible application for swelling clay minerals being a promising adsorbent for dyes-surfactants co-existing wastewater treatment.

Adsorption Characteristics and Electrochemical Behaviors of Methyl Blue onto Magnetic MgxCoyZn(1-x-y)Fe2O4 Nanoparticles

Magnetic MgxCoyZn(1-x-y)Fe2O4 nanoparticles were successfully prepared by the rapid combustion approach, and SEM, XRD, VSM, EDX, and FTIR techniques were applied for their characterization. The influence of the element ratios (Mg2+, Co2+, and Zn2+) in magnetic MgxCoyZn(1-x-y)Fe2O4 nanoparticles on their properties was explored. To acquire a larger specific surface area for better adsorption of methyl blue (MB), magnetic Mg0.4Co0.5Zn0.1Fe2O4 nanoparticles calcined at 400°C for 2 h with 25 mL anhydrous ethanol were selected, and their average particle size and the saturation magnetization were about 81.3 nm and 13.5 emu·g-1, respectively. Adsorption kinetics models and adsorption isotherm models were applied to research the adsorption characteristics of MB onto magnetic Mg0.4Co0.5Zn0.1Fe2O4 nanoparticles. The pseudo-second-order kinetics model ([Formula: see text]) and Temkin isotherm model ([Formula: see text]) were the most consistent with the data, indicating that the adsorption was the chemical multilayer adsorption mechanism, and the process was an exothermic reaction. The E of the Dubinin-Radushkevich (D-R) isotherm model was 0.2347 KJ·mol-1, indicating the adsorption involved physical adsorption besides chemical adsorption. The [Formula: see text] and [Formula: see text] ([Formula: see text] KJ·mol-1) of the adsorption process of MB adsorbed onto magnetic Mg0.4Co0.5Zn0.1Fe2O4 nanoparticles measured through the thermodynamic experiment were both less than 0, which proved that the process was a spontaneous exothermic reaction. The adsorption capacity of MB onto magnetic Mg0.4Co0.5Zn0.1Fe2O4 nanoparticles increased with the pH of MB solution increasing from 2 to 4 at room temperature, and it had no significant change when the pH of MB solution was 4-12, while the relative removal rate was 98.75% of the first one after 2 cycles. The electrochemical impedance spectroscopy (EIS) and the cyclic voltammetry (CV) data further demonstrated that MB was adsorbed onto magnetic Mg0.4Co0.5Zn0.1Fe2O4 nanoparticles.

Chitosan/Silica Nanocomposite Preparation from Shrimp Shell and Its Adsorption Performance for Methylene Blue

In this study, novel chitosan/silica composites with different mass ratios were prepared by in-situ hydrolysis using chitosan (from shrimp shell) as a carrier, triblock copolymer (P123) as the structure-directing agent, and ethyl orthosilicate as a silicon source. These nanocomposites were characterized by different techniques, including the FT-IR, XRD, TGA, SEM, TEM and N2 adsorption–desorption. The results indicated that the morphology and properties of composites changed with the introduction of silica. When the CS/TEOS mass ratio was 0.0775, the CS−2/SiO2 composite displayed a coral-like three-dimensional porous structure with specific surface area of 640.37 m2/g and average pore size of 1.869 nm. The adsorption properties for methylene blue (MB) were investigated as well and the CS−2/SiO2 showed better adsorption performance. The removal rate for MB reached 94.01% with absorbents dosage of 6 g/L, initial concentration of 40 mg/L, initial pH value of 7, temperature of 35 °C, and adsorption time of 40 min. The adsorption process well fitted the Langmuir isothermal model and quasi-second-order adsorption kinetics model. The maximum adsorption capacity for MB was 13.966 mg/g based on Langmuir fitting. The surface functional groups of the composites can play an important role in the adsorption. The adsorption mechanism of CS−2/SiO2 on MB involved electrostatic interaction, hydrogen bonding and functional group complexation. In addition, the prepared chitosan/silica composites showed good reusability at six cycles, making them a promising material in the application of removing dyeing wastewater.

Facile, green approach for aqueous methylene blue dye adsorption: Coconut vinegar treated Trema orientalis wood biochar

Biochar is widely utilized in low-cost water treatment. However, chemicals used in most of the recorded activation techniques are corrosive, may cause secondary pollution, and not accessible by rural communities, reducing their value of being cost-effective. In this study, &lt;i&gt;Trema orientalis&lt;/i&gt; wood biochar (WB) was successfully activated with natural coconut vinegar employing a facile technique to produce a green adsorbent for efficient aqueous methylene blue (MB) removal. Batch studies showed a three-fold higher MB adsorption capacity of coconut vinegar treated wood biochar (CVWB) compared to WB. Percentage removal ranged between 98-79% at lower dye concentrations (50-100 mg/L) and 79-48% at higher dye concentrations (100-300 mg/L). Isotherm data best fitted to the Freundlich model. Kinetic data fitted to both pseudo second order and intraparticle diffusion models, suggesting that the adsorption was governed by a pore filling mechanism with predominant electrostatic attractions, and the reaction rate was diffusion controlled. FTIR, XPS, and water contact angle measurements confirmed increased surface oxygenated groups of CVWB. XPS showed a three-fold increase in O/C atomic ratio. BET and AFM studies gave evidence to the increased porosity. Therefore, the enhanced MB adsorption capacity of CVWB was attributed to both the increased surface oxygenated functional groups and porosity.

Exploitation of Bauhinia forficata residual fruit powder for the adsorption of cationic dyes

This paper analyzes the adsorption of two potential toxic dyes, i.e. methylene blue (MB) and crystal violet (CV) onto Bauhinia forficata residual fruit powder (BFRFP) as a new promising adsorbent. The experiments aimed at retrievement of adsorption data are carried out at T = 298–328 K and are coupled with an adsorbent characterization to better highlight the MB and CV dyes adsorption mechanism. MB adsorption capacity at saturation (ACS) varies from 181.48 to 201 mg.g−1, while for CV dye, it ranges from 263.06 to 282.61 mg.g−1. This difference is not very significant but reflects that the BFRFP has a higher affinity to remove CV dye. Comparing with some alternative adsorbents, the BFRFP adsorbent shows to be a competitive material for the removal of MB and CV dyes from polluted water. A model assuming that MB and CV dyes are removed via a formation of two layers on BFRFP is chosen as the one that, from a physical point of view, better interpret their adsorption mechanisms. The prediction of the number of dyes adsorbed on BFRFP is approximately equal to 1 for both the dyes, testifying that they are removed without an aggregation process and with slanted position. The physical model generates two energies to describe the interactive effects between both dyes and BFRFP adsorbent (dye- BFRFP) and between dyes (dye-dye). Results show that physical interactions occur during the adsorption process.

Magnetic Activated Biochar Fe3O4-MOS Made from Moringa Seed Shells for the Adsorption of Methylene Blue

In recent years, more and more biochars have been employed to treat dye wastewater. In order to increase the utilization of moringa seed shell resources and enrich the removal method of methylene blue (MB) in solution, in the current study, the magnetic moringa seed shells biochar was prepared through ultrasonic-assisted impregnation and pyrolysis, while Fe3O4 was used to activate the material to obtain adsorption (Fe3O4-MOS). The prepared adsorbents were characterized by SEM-EDS, XRD, XPS, FTIR, N2 adsorption and desorption and VSM. Under the suitable experimental conditions, the removal rate can be close to 100% and the maximum adsorption capacity of MB could be 219.60 mg/g. The Freundlich model provided a good match to the data presented by the adsorption isotherm, and the adsorption of MB on Fe3O4-MOS was a spontaneous and endothermic reaction. Study of the mechanism indicated that pore adsorption, electrostatic interaction, hydrogen bond, and π-π interaction were the major adsorption mechanisms. After five cycles, it was found that Fe3O4-MOS had a high removal rate for MB, which was close to 90%. This work provides a new idea for moringa seed shells and the results confirm that Fe3O4-MOS has substantial potential for dye wastewater treatment.

Removing methylene blue from water: A study of sorption effectiveness onto nanoparticles-doped activated carbon

In this present study, silver (Ag) and titanium dioxide (TiO2) nanoparticles were successfully deposited on coconut shell-derived activated carbon (CSAC), to synthesize a novel nanocomposite (CSAC@AgNPs@TiO2NPs) for the adsorption of Methylene Blue (MB) dye from aqueous solution. The fabricated CSAC@AgNPs@TiO2NPs nanocomposite was analyzed by Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscope (TEM) equipped with Energy Dispersive X-ray spectroscopy (EDS) detector, X-ray Photoelectron Spectroscope (XPS), and Brunauer–Emmett–Teller (BET). The successful deposition of AgNPs and TiO2NPs on CSAC surface was revealed by the TEM/EDX, SEM, and XPS analysis. The mesopore structure of CSAC@AgNPs@TiO2NPs has a BET surface area of 301 m2/g. The batch adsorption studies were conducted and the influence of different parameters, i.e., adsorbent dose, adsorption time, initial dye concentration, pH and temperature were investigated. The nonlinear isotherm and kinetic modelling demonstrated that adsorption data were best fitted by Sips isotherm and pseudo-second-order models, respectively. The maximum adsorption capacity of MB onto CSAC@AgNPs@TiO2NPs by the Sips model was 184 mg/g. Thermodynamic results revealed that the adsorption was endothermic, spontaneous and physical in nature. CSAC@AgNPs@TiO2NPs revealed that MB absorption by CSAC@AgNPs@TiO2NPs was spontaneous and endothermic. The uptake capacity of MB was influenced significantly by the presence of competing ions including, NO3−, HCO3, Ca2+, and Na+. Repeated tests indicated that the CSAC@AgNPs@TiO2NPs can be regenerated and reused six times before being discarded. The primary separation mechanism between MB dye and CSAC@AgNPs@TiO2NPs was the electrostatic interaction. Thus, CSAC@AgNPs@TiO2NPs was an outstanding material, which displayed good applicability in real water with ≥ 97% removal of MB dye.

Adsorption capacity of activated carbon derived from date seeds: Characterization, optimization, kinetic and equilibrium studies

Agricultural wastes have the potential to be reused in applications such as water/wastewater treatment. Several studies have focused on activating organic waste, such as date seeds, to produce activated carbon. However, these studies have always assumed that all date seeds behave similarly to each other. In this study, we evaluated different types of date seeds and characterized their physical-chemical properties. The results showed variation in the seed-to-fruit weight percentage, ash content, and moisture content among different seed types. Different activation procedures were performed to find the optimum combination of physical and chemical interventions. KOH impregnation yielded better results than H3PO4 impregnation. The maximum adsorption capacity was measured for nine different types of date seeds, and the Khalas seed type yielded the highest methylene blue (MB) adsorption capacity of 165 mg of MB/g of activated date seeds (ADS), which is 71% of the capacity of commercial activated carbon (CAC). Kinetics model was fitted to the experimental data, and the pseudo-second-order model provided the best fit, indicating that the adsorption process occurred following a chemical process rather than being controlled by intraparticle diffusion only. The results showed no significant difference among the three isotherm models used to fit the experimental data. The results indicated that there is a significant difference among various types of seeds regarding adsorption performance. The application of ADS in treating synthetic produced water showed that its performance is one third that of CAC. ADS showed promising potential in comparison with CAC, mostly considering the costs involved with CAC.

Photocatalytic study of TiO2 thin films modified with Anderson-type polyoxometalates (Cr, Co and Ni): Experimental and DFT study

In this work, three Anderson-type polyoxomolybdates (POMs) with general formula (NH4)6-n[XMo6O24H6]−6+n where X = Co3+, Cr3+, and Ni2+ were deposited on TiO2 thin films Furthermore, the methylene blue (MB) dye adsorption capacity and photocatalytic degradation were studied. Morphological results show that the POMs/TiO2 films have a more heterogeneous surface in terms of particle size and distribution than bare TiO2 films. Optical characterization indicated that the CrMo6/TiO2 material had the lowest band gap energy with a value of 2.8 eV. The adsorption results show that the maximum percentage of MB adsorption was 37 % for NiMo6/TiO2 while bare TiO2 has only 9.2 %. The MB adsorption on POMs-TiO2 was modeled using and the Freundlich model showed the best fit in all studied films for MB removal. The MB photodegradation values shows this tendency 12 % for bare TiO2, 55 % for NiMo6/TiO2, 73 % for NiMo6/TiO2 and, 83 % for CrMo6/TiO2. Finally, DFT calculations were performed to characterize the geometry and electronic structure of the all compounds studied in this work, with the aim to explain the observed experimental results.

Removal of methylene blue from aqueous solution by magnetic hydrogel nanocomposite absorbents

Currently reported adsorbents for wastewater purification generally have only limited adsorption capacity and low adsorption rate towards dye contaminants. In this work, KH570-modified magnetic hydrogel nanocomposites (KH570-mHNCs) with semi-IPNs structure were prepared based on poly (acrylamide-co-acrylic acid), polyvinyl pyrrolidone (PVP), and KH570-modified magnetic nanoparticles, and it exhibited high absorption capacity and absorption rate for methylene blue dye. KH570-mHNCs had a rough surface with many porous and gully structures, and FTIR results preliminarily confirmed the target structure of KH570-mHNCs. KH570-mHNCs could rapidly absorb methylene blue by approaching absorption equilibrium at 90 min. Dye absorption of KH570-mHNCs had maximum dye absorption capacity at pH = 8, and methylene blue adsorption capacity was 255.4 mg/g, 326.3 mg/g, and 418.5 mg/g in the condition of initial dye concentrations of 700 mg/L, 900 mg/L, and 1100 mg/L, respectively. Methylene blue adsorption isotherms and kinetics conformed to the Langmuir model and pseudo-second-order kinetic model, respectively. Methylene blue adsorption for KH570-mHNCs was a spontaneous, exothermal, and entropy reduction process. In addition, KH570-mHNCs had good magnetic response, desorption, and reusability, which made it a potential application in the field of methylene blue removal from the aqueous solution.

Composite modification of starch and adsorption capacity of starch microspherical aerogel

Starch microspherical aerogel (SMA) prepared by enzymatic hydrolysis of starch with α-amylase was demonstrated to be higher adsorption capacity for methylene blue. Proper cleavage of α-1,4 glycosidic bonds could enhance the adsorption capacity of SMA, while the cleavage of α-1,6 glycosidic bonds showed an opposite effect. Compared with tapioca starch (TS), α-amylase hydrolyzed starch exhibited a 9.46 % decrease in amylose content, a 25.40 % increase in adsorbability, and significant decreases in weight-average molecular weight (Mw) of different amylases. When the Mw of enzymolysis starch was 6.39 × 106 g/mol, it was suitable for the preparation of SMA, and could significantly increase its adsorption capacity. The adsorbability of the crosslinked starch microspherical aerogel (CSMA) was 1.816 ± 0.026 mg/g, which was increased by 100.60 % relative to that of native starch microspherical aerogel (NSMA). CSMA had the best adsorption effect on oil and could be applied to the adsorption and removal of vegetable oil.

Experimental Design, Equilibrium Modeling and Kinetic Studies on the Adsorption of Methylene Blue by Adsorbent: Activated Carbon from Durian Shell Waste.

For the first time, activated carbon from a durian shell (ACDS) activated by H2SO4 was successfully synthesized in the present study. The fabricated ACDS has a porous surface with a specific surface area of 348.0017 m2·g-1, average capillary volume of 0.153518 cm3·g-1, the average pore diameter of 4.3800 nm; ash level of 55.63%; humidity of 4.74%; density of 0.83 g·cm-3; an iodine index of 634 mg·g-1; and an isoelectric point of 6.03. Several factors affecting Methylene Blue (MB) adsorption capacity of ACDS activated carbon was investigated by the static adsorption method, revealing that the adsorption equilibrium was achieved after 90 min. The best adsorbent pH for MB is 7 and the mass/volume ratio is equal to 2.5 g·L-1. The MB adsorption process of ACDS activated carbon follows the Langmuir, Freundlich, Tempkin, and Elovich isotherm adsorption model, which has determined the maximum adsorption capacity for MB of ACDS as qmax = 57.47 mg·g-1. The MB adsorption process of ACDS follows the of pseudo-second-order adsorption kinetic equation. The Weber and Morris Internal Diffusion Model, the Hameed and Daud External Diffusion Model of liquids have been studied to see if the surface phase plays any role in the adsorption process. The results of thermodynamic calculation of the adsorption process show that the adsorption process is dominated by chemical adsorption and endothermic. The obtained results provide an insight for potential applications of ACDS in the treatment of water contaminated by dyes.

Synthesis and Characterization of Alginate/Bentonite Hydrogels

AbstractThe use of bentonite for organic dyes removal in the water system is an economical and highly efficient alternative against the usually applied purification methods. However, during the post‐treatment stage bentonite swells and forms highly stable colloidal suspensions, being difficult to separate from the aqueous system. In this work, calcium alginate hydrogels beads with 5 and 10% w/w of bentonite are synthetized and their capacity to adsorb methylene blue, as model dye, from aqueous media is evaluated. Structure and mechanical properties of hydrogels beads are determined, showing that hydrogels beads with bentonite present higher viscosity and hardness. Regarding methylene blue adsorption capacity, the effect the contact time (0–32 h) and the initial cadmium ion concentration (0.2–3.0 mg L−1) are studied employing hydrogel beads. The equilibrium adsorption time is reached at 300 min for all studied hydrogels and experimental data are fitted well with a pseudo‐second order kinetic model. As conclusion, alginate/bentonite hydrogel beads are accepted as a promising candidate to remove methylene blue dye from aqueous solutions.

Modification of covalent organic framework by hydrolysis for efficient and selective removal of organic dye

The efficient removal of organic dyes from wastewater is still a major challenge, especially for the massive production of dyeing technology. Herein, polyimide-based covalent-organic frameworks (COFs) with a highly ordered conjugated architecture are synthesized through the condensation reaction of pyromellitic dianhydride (PMDA) with tris (4-aminophenyl) amine (TAPA). Due to a repeated cyclic structure, COFs subjected to alkaline hydrolysis can offer a high density of negatively charged carboxylate anions as adsorption sites for cationic methylene blue (MB) dye through electrostatic interactions. The maximum adsorption capacity of MB on hydrolyzed COFs is measured to be 315.6 mg/g at pH = 10 and room temperature. Significantly, hydrolyzed COFs exhibit superior adsorption selectivity for MB in a mixture solution with methyl orange (MO) and rhodamine B (RhB). Overall, hydrolyzed COFs are good candidates to serve as an efficient adsorbent for the removal of MB with a high selectivity in the posttreatment of the dyeing process. The employment of COFs with a highly active surface in this study provides new insights for the future development of efficient adsorbents for organic dyes.

Dual template using P123-gelatin for synthesized large mesoporous silica for enhanced adsorption of dyes

Mesoporous Silica with a large mesopore channel was synthesized using the sol-gel method for dye adsorption. A dual template consisting of P123 and gelatin at different ratios was employed in the sol-gel synthesis to enhance surface area and mesopore diameter. Gelatin is a green pore directing agent that strengthens P123 thermal stability during the calcination of silicate gel. Optimization of P123:gelatin ratio to 1:0.02 increased the surface area of mesoporous silica to 561.9 m2/g and expanded the pore diameter to 10 nm. The large pore diameter and surface area enhanced methylene blue adsorption capacity to 363.63 mg/g. The adsorption of methylene blue on mesoporous silica follows the pseudo second-order kinetic and the Langmuir model. Regeneration studies using thermal and chemical treatments exhibited the potential of mesoporous silica as an adsorbent for multiple adsorption-desorption of dyes.