Removal of Brilliant Green from wastewater using conventional and ultrasonically prepared poly(acrylic acid) hydrogel loaded with kaolin clay: A comparative study

The present work deals with the removal of Brilliant Green dye from wastewater using a poly(acrylic acid) hydrogel composite (PAA-K hydrogel) prepared by incorporation of kaoline clay. The composite has been synthesized using ultrasound assisted polymerization process as well as the conventional process, with an objective of showing the better effectiveness of ultrasound assisted synthesis. It has been observed that the hydrogel prepared by ultrasound assisted polymerization process showed better results. The optimum conditions for the removal of dye are pH of 7, temperature of 35 °C, initial dye concentration of 30 mg/L and hydrogel loading of 1 g. The extent of removal of dye increased with an increase in the contact time and initial dye concentration. A pseudo-second-order kinetic model has been developed to explain the adsorption kinetics of dye on the PAA-K hydrogel. Thermodynamic and kinetic parameters indicate that the adsorption process is spontaneous in nature and the PAA-K hydrogel prepared by ultrasound process is a promising adsorbent compared to conventional process. The obtained adsorption data has also been fitted into commonly used adsorption isotherms and it has been found that Freundlich as well as Langmuir adsorption isotherm models fits well to the experimental results.     

Ultrasonically assisted hydrothermal synthesis of activated carbon–HKUST-1-MOF hybrid for efficient simultaneous ultrasound-assisted removal of ternary organic dyes and antibacterial investigation: Taguchi optimization

Activated carbon (AC) composite with HKUST-1 metal organic framework (AC–HKUST-1 MOF) was prepared by ultrasonically assisted hydrothermal method and characterized by FTIR, SEM and XRD analysis and laterally was applied for the simultaneous ultrasound-assisted removal of crystal violet (CV), disulfine blue (DSB) and quinoline yellow (QY) dyes in their ternary solution. In addition, this material, was screened in vitro for their antibacterial actively against Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (PAO1) bacteria. In dyes removal process, the effects of important variables such as initial concentration of dyes, adsorbent mass, pH and sonication time on adsorption process optimized by Taguchi approach. Optimum values of 4, 0.02 g, 4 min, 10 mg L⁻¹ were obtained for pH, AC–HKUST-1 MOF mass, sonication time and the concentration of each dye, respectively. At the optimized condition, the removal percentages of CV, DSB and QY were found to be 99.76%, 91.10%, and 90.75%, respectively, with desirability of 0.989. Kinetics of adsorption processes follow pseudo-second-order model. The Langmuir model as best method with high applicability for representation of experimental data, while maximum mono layer adsorption capacity for CV, DSB and QY on AC–HKUST-1 estimated to be 133.33, 129.87 and 65.37 mg g⁻¹ which significantly were higher than HKUST-1 as sole material with Q_m to equate 59.45, 57.14 and 38.80 mg g⁻¹, respectively.     

Synthesis of carbon loaded γ-Fe2O3 nanocomposite and their applicability for the selective removal of binary mixture of dyes by ultrasonic adsorption based on response surface methodology

The contemporary problems concerning water purification could be resolved by using nanosorbents. The present studies emphasis on the synthesis of γ-Fe₂O₃-activated carbon nanocomposites (γ-Fe₂O₃-NP-AC) by sol-gel method. The composition and surface morphology of them were studied by FTIR, EDS, SEM and XRD techniques. Moreover they were employed for the selective removal of binary mixture of dyes including reactive red 223 dye (RR) and Malachite Green dye (MG) by ultrasonic assisted adsorption method. Sonication is the act of applying sound energy to agitate particles in the sample. The ultrasonic frequencies (>20 kHz) were used to agitate experimental solutions in current studies. The response surface methodology based on 5 factorial central composite design (CCD) was employed to investigate the optimum parameters of adsorption. The optimum operating parameters (OOP) including sonication time, solution pH, amount of adsorbent, concentration of RR and MG were estimated for the selective removal of mixture of dyes. On OOP conditions of RR, the % removal of RR and MG were observed to be 92.12% and 10.05% respectively. While at OOP of MG, the % removal of MG and RR were observed to be 85.32% and 32.13% from the mixture respectively. Moreover the mechanisms of adsorption of RR and MG on the γ-Fe₂O₃-NP-AC were also illustrated. The significance of the RR-γ-Fe₂O₃-NP-AC and MG-γ-Fe₂O₃-NP-AC adsorption models was affirmed by ANOVA test. The Pareto plots for the selective removal of the RR and MG from the binary mixture also confirm the significance of the factors. Isothermal studies were performed and RR adsorption was observed to follow Langmuir isotherm model whereas MG adsorption was observed to follow Freundlich model. Thermodynamic studies were conducted and the outcomes suggested the spontaneous nature of adsorption processes. The kinetic models were employed to study the kinetics of the process. It was observed that the system followed pseudo second order, intra-particle diffusion and Elovich models as represented by the R² values of the respective models. The comparative study from the previously studies revealed that the proposed method is amongst them is the most efficient method to eliminate RR and MG dyes from the aqueous medium. Therefore the current study will be useful in reducing the toxicity of RR and MG contaminated effluent.     

Synthesis of a Cationic Polymer-Bentonite Composite Utilizing a Simple and Green Process for the Adsorption of Acid Orange 7 from Aqueous Solution

A one-step, green process is reported for synthesis of poly([2-(methacryloyloxy)ethyl] trimethylammonium chloride) (PMETAC) modified bentonite (Bent-PMETAC). The Bent-PMETAC was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Zeta potential, scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA). The results indicated that large amounts of PMETAC were successfully grafted on the surface and interlayers of bentonite, and changed the Zeta potential of the sample from negative to positive. Acid Orange 7 (AO 7), as adsorbate, was used to test the anionic dye adsorption of the samples. The batch adsorption results implied that this novel Bent-PMETAC adsorbent exhibited a much higher removal (95%) of AO 7 than bentonite (10%). In addition, the adsorption process was hardly influenced by pH, which is in good agreement with the results of the Zeta potential analysis. The equilibrium adsorption isotherms and the adsorption kinetics of AO 7 fitted well to the Langmuir model and pseudo-second-order kinetic model, respectively. The maximum adsorption capacity of AO 7 onto Bent-PMETAC was 208.6?mg·g^?1 at 298?K, which is much higher than for most other materials. Overall, the results indicated the Bent-PMETAC is a low-cost, simple synthesis and highly efficient adsorbent for anionic dye removal from aqueous solutions.     

Adsorptive removal of congo red dye from aqueous solution using bael shell carbon

This study investigates the potential use of bael shell carbon (BSC) as an adsorbent for the removal of congo red (CR) dye from aqueous solution. The effect of various operational parameters such as contact time, temperature, pH, and dye concentration were studied. The adsorption kinetics was modeled by first-order reversible kinetics, pseudo-first-order kinetics, and pseudo-second-order kinetics. The dye uptake process obeyed the pseudo-second-order kinetic expression at pH 5.7, 7 and 8 whereas the pseudo-first-order kinetic model was fitted well at pH 9. Langmuir, Freundlich and Temkin adsorption models were applied to fit adsorption equilibrium data. The best-fitted data was obtained with the Freundlich model. Thermodynamic study showed that adsorption of CR onto BSC was endothermic in nature and favorable with the positive ΔH° value of 13.613 kJ/mol.     

LDH of NiZnFe and its composites with carbon nanotubes and data-palm biochar with efficient adsorption capacity for RB5 dye from aqueous solutions: Isotherm,kinetic, and thermodynamics studies

In the study, the layered double hydroxide (LDH) of NiZnFe and its composites with date-palm biochar (LDH-DPb) and carbon nanotubes (LDH-cnt) were synthesized for adsorbing reactive black 5 (RB5) dye from aqueous solutions. In the first 5 min, rapid adsorption was followed by a gradual increase in both dye uptake and removal efficiency of up to 60 min of starting time. In the investigated pH range (3.0–8.0), the removal efficiency linearly decreased while the sorption capacity linearly increased for all three adsorbents as their doses increased to 0.3 or 0.4 g following a decreasing trend up to 0.6 g. By increasing the initial RB5 concentration from 10 to 100 mg L⁻¹, the removal efficiency linearly decreased. A nearly perfect fitting of the pseudo-second-order kinetic model to the adsorption data was observed; however, the Elovich kinetic model showed the heterogeneous surface of adsorbents with chemisorption. At the solid–liquid interface, from a thermodynamics point of view, we obtained the nonspontaneous nature of the adsorption of RB5 dye of the studied adsorbents with an increased disorder, which supported the endothermic nature onto the studied adsorption process. Furthermore, a nearly perfect fitting of the Langmuir model was obtained to the adsorption data, thereby suggesting the monolayer adsorption of RB5 dye onto the studied adsorbents. In the Dubinin–Radushkevich model, a good agreement of the calculated adsorption capacities to the experimental values were observed and the chemical adsorption of RB5 dye on to the studied adsorbents was proposed based on E (8 – 16 kJ mol⁻¹).     

三元LDH的改性及去除酸性橙II的光谱分析研究

吸附法由于具有效率高、成本低、无毒、简单等优点，具为最常见的废水处理方法。采用吸附法的关键是吸附剂的选择和制备。层状氢氧化物(LDH)作为一类新型吸附剂，拥有特殊的层状结构、层板元素的可调变性、层间阴离子的可交换性，近期备受关注，但其吸附能力的提升仍是亟需研究的问题。利用均苯四甲酸(PA)对三元层状氢氧化物(Ca-Mg-Al-LDH)进行插层改性，制备出新型的芳香酸阴离子改性层状氢氧化物(PA-LDH)，对其进行煅烧得到煅烧产物(PA-LDO)，并结合紫外分光光度法(UV-Vis)研究其对酸性橙II的吸附性能。通过红外光谱(FTIR)和氮气吸附-脱附实验对其进行结构表征。结果发现，PA-LDH相比LDH在1 717 cm-1处出现了一个新的峰，归属为ν(C═O)，且相对PA的C═O峰(1 668 cm-1)向高频方向移动，这可能是由于PA之间形成的缔合体被破坏，表明PA可能插层进入了LDH的间层。相比PA-LDH的红外光谱谱图，可以发现PA-LDO在3 000 cm-1附近的弱峰消失了，表明层间阴离子在煅烧过程中被破坏，但是在875和723 cm-1处与M—O和M—OH(M=Ca，Mg和Al)振动相对应的峰仍然存在，表明煅烧处理后其相似的结构依然得到了保持。通过氮气吸附-脱附实验测得PA-LDH和PA-LDO的比表面积分别为15.934 1和119.401 0 m2·g-1，说明在煅烧后，其比表面积增大，因此PA-LDO可能具有更好的吸附效果。以阴离子染料酸性橙Ⅱ为目标污染物，在pH 7.0，吸附剂用量5 mg，波长为484 nm的条件下，通过UV-Vis分析手段，分别考察了吸附时间、染料初始浓度等对PA-LDH、PA-LDO吸附性能的影响。结果表明，PA-LDH和PA-LDO对酸性橙Ⅱ的Q_max分别为561.322和1 401.639 mg·g-1，高于目前文献所报道的Q_max值。通过吸附等温实验，发现PA-LDH和PA-LDO对酸性橙II的吸附基本符合Langmuir模型，即单分子层吸附为该吸附过程的主导过程，且理论最大吸附容量分别可为588.235和1 428.571 mg·g-1，与上述实验值相接近，这说明制备的芳香酸阴离子改性层状氢氧化物对阴离子染料具有较好的吸附性能，在治理染料废水中具有一定的应用前景。     

Removal of chromium(VI) and dye Alizarin Red S (ARS) using polymer-coated iron oxide (Fe3O4) magnetic nanoparticles by co-precipitation method

The present research was conducted with an aim to develop such adsorbent system: polymer-coated magnetic nanoparticles which can remove heavy metal and dye from water of different concentration. Synthesis of magnetic iron oxide nanoparticles for contaminated water purification has been one of the outcomes of application of rapidly growing field of Nanotechnology in Environmental Science. In the present study, the efficiency of magnetic nanoparticles for removal of Cr(VI) and dye (alizarin) from water solutions of known concentrations were evaluated. The nanoparticles were prepared by co-precipitation method and characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. Polymer-coated magnetic iron oxide nanoparticles carrying functional groups on their surface were synthesized by different methods for permanent magnet-assisted removal of heavy metal (chromium) and dye (Alizarin Red S) from water. The characterization showed that synthesized nanoparticles were in the size range of 10–50 nm. The adsorption capacities of the Fe₃O₄ using polyMETAC-coated particles for dye (Alizarin Red S) removal were 80–96 % and chromium 62–91 %. The chromium concentration was determined after magnetic separation using atomic absorption spectrophotometer and dye concentration was estimated with UV–visible spectrophotometer. Nanoparticles of polymer coated showed the highest removal capacity from water for metal and dye. The developed adsorbents had higher capacity for removal of heavy metal ions and dye.     

Sono-sorption as a new method for the removal of methylene blue from aqueous solution

The sorption of methylene blue as a basic dye onto cellulosic materials such as waste newspaper was examined kinetically in the presence of ultrasound (sono-sorption) and in its absence (conventional method). The effects of various experimental parameters such as the amount of sorbent, type of cellulosic sorbents, initial dye concentration, temperature, and contact time have been investigated using a batch sorption technique. The information obtained can be used for treating effluents from the dye industry which deals with this kind of dye. The results show that as the amount of sorbent is increased, the dye removal in conventional method increases accordingly. In case of sono-sorption, it was stopped at specific amount of sorbent. More than 98% removal of the dye could be achieved in a very short period of time of sonication with respect to the conventional method. This behavior is related to the cavitation process which facilitates the removal of dye from aqueous solution. The method mentioned could be employed as a low cost alternative to the commercial activated carbon currently used in wastewater treatment for the removal of dyes.     

Effect of biotite content of hydrogels on enhanced removal of methylene blue from aqueous solution

A series of chitosan-g-poly(acrylic acid)/biotite (CTS-g-PAA/BT) hydrogels with unique clay biotite (BT) were prepared and used to remove cationic dye methylene blue (MB) from aqueous solution by batch adsorption experiments. Variables of the system including BT content, initial pH, contact time, initial concentration, and temperature affecting the adsorption efficiency of MB by CTS-g-PAA/BT hydrogels were investigated. Kinetic studies indicated that the adsorption data well followed pseudo-second-order kinetics. Langmuir and Freundlich isotherm models were applied to experimental equilibrium data of MB adsorption depending on temperature. The adsorption equilibrium data obeyed Langmuir isotherm, and the monolayer adsorption capacity calculated from the Langmuir isotherm was 2,125.70 mg/g for CTS-g-PAA/10% BT at 30 °C. The adsorption capacity was much higher compared with other hydrogels with the same content of other clays. The introduction of BT into the hydrogel could effectively improve its adsorption properties and reduce the cost. Thermodynamic parameters were evaluated for the dye-adsorbent systems and revealed that the adsorption process was spontaneous and exothermic in nature. All the information gave an indication that CTS-g-PAA/10% BT could potentially be applied as an efficient adsorbent for cationic dye removal from aqueous solution.     

A simplified method for synthesis of Fe3O4@PAA nanoparticles and its application for the removal of basic dyes

A simplified method for synthesis of polyacrylic acid-bound iron oxide magnetic nanoparticles (Fe₃O₄@PAA NPs) was reported. The as-prepared nanoparticles were characterized by TEM, FT-IR, VSM and XRD. Characterization results indicated that PAA was successfully introduced onto the surface of Fe₃O₄ and did not cause any changes in magnetic property. The Fe₃O₄@PAA NPs were used to adsorb rhodamine 6G (R6G) as a model basic dye pollutant from aqueous solution. Kinetics data and adsorption isotherms were better fitted by pseudo-second-order kinetic model and Langmuir isotherm, respectively. The adsorption equilibrium could be reached at about 20 min, showing that the as-prepared adsorbent exhibited extremely rapid adsorption rate. The aqueous solution of the Yellow River was chosen as the test sample, and the results showed that the magnetic adsorbent was efficient for the removal of the basic dye in the real sample.     

FTIR和XPS对沸石合成特性及Cr(Ⅲ)去除机制的谱学表征

以粉煤灰为原料,采用优化的水热晶化法合成沸石,使用XRD,SEM和ζ电位分析沸石产品的组成特性,借助FTIR和XPS等揭示废水中Cr(Ⅲ)的去除机制。合成产品主要为NaP1型沸石,在pH值8～12区间内,ζ电位由-8.72mV降到-24.46mV。准二级方程和Langmuir等温线对试验的拟合效果更好,理论饱和吸附量为33.557 0mg.g-1。FTIR图谱表明—OH和Si—O类官能团在反应过程中有重要贡献。XPS全谱发现:结合能576.45eV为Cr(2p3/2)的特征峰,揭示了吸附过程的有效性。吸附Cr(Ⅲ)后,沸石中Si—Si和Si—O对应的结合能增加了0.25和0.60eV,含Si官能团可能与Cr(Ⅲ)发生了配位反应。O(1s)的结合能在反应后变得更低。这些证据表明:沸石对Cr(Ⅲ)的去除过程是物理吸附和化学吸附共同作用的结果。     

Simultaneous adsorption of dyes and heavy metals from multicomponent solutions using fly ash

In wastewaters originating from dye industry there are amounts of dyes (very common methyl orange, methylene blue—MB) and heavy metals (cadmium, copper, nickel mainly from the organo-metallic dyes). They tend to adsorb in a competitive process and modify the substrate. Advanced removal is usually proposed via adsorption and the use of modified fly ash as a substrate is sustainable solution. The main constituents of fly ash (silica, alumina, iron oxide and un-burned carbon), are the priority compounds which favour the heavy metal adsorption and are active sites in dyes’ adsorption processes. The paper studies the effect of MB adsorbed on the fly ash surface on the removal efficiency of cadmium, copper and nickel ionic species from complex, multi-cationic dye solutions. The adsorption efficiency and kinetics are evaluated from the complex, multicomponent systems and possible influences are discussed. High efficiencies are obtained at low heavy metal concentrations (as it is the real case for the dyes industry) whereas at medium values, competitive processes lower the individual efficiencies of copper, nickel or cadmium from mixtures.     

Synthesis of graphene oxide-poly(2-hydroxyethyl methacrylate) composite by dispersion polymerization in supercritical CO2: adsorption behavior for the removal of organic dye

The use of a biocompatible and thermoresponsive polymer, poly(2-hydroxyethyl methacrylate) (PHEMA) grafted onto the surface of graphene oxide (GO) as an adsorbent for the removal of a cationic dye (methylene blue [MB]) from an aqueous solution is examined in this work. GO–PHEMA forms a hydrogel in water thus overcoming the problem faced by carbon-based adsorbent materials during post-treatment (i.e., separation of adsorbent from the aqueous phase). The GO–PHEMA composite was synthesized using a green approach through dispersion polymerization in supercritical CO₂. The successful preparation of this composite was confirmed by a series of characterization techniques. The adsorption behavior of the composite toward MB such as the effect of the adsorbent dosage, pH, contact time, dye concentration, and recyclability were observed. In addition, the adsorption isotherm, kinetics and thermodynamics were investigated. According to the experimental data, the adsorption parameters were found to fit well into the Freundlich adsorption isotherm with a correlation coefficient of 0.975 and a maximum predicted adsorption capacity of 39.41 mg g^?1 at 25 °C. The adsorption kinetics studies showed that the adsorption behavior followed a pseudo-second-order reaction. On the other hand, the thermodynamics studies showed that the adsorption of MB on GO–PHEMA composite followed spontaneous and endothermic adsorption process with an efficient adsorption temperature at 45 °C. The experimental results also showed that the GO–PHEMA composite could remove 99.8% of the dye in 45 min. Therefore, GO–PHEMA composite is a favorable green adsorbent for environmental applications.     

功能化石墨烯对亚甲基蓝染料吸附的密度泛函理论研究

由于染料在食品,印刷,纺织等行业的广泛应用,水中的染料被广泛发现,染料污染是造成水污染的重要原因之一,因此,对于水中染料进行前处理变得尤为重要.石墨烯和功能化石墨烯的吸附性能可以被应用于水中染料的检测和去除.本研究采用密度泛函理论方法详细探讨了纯石墨烯和功能化石墨烯对亚甲基蓝有机染料污染物的吸附机理.研究结果表明,纯的石墨烯和功能化石墨烯表面对亚甲基蓝染料均有一定程度的吸附,其中环氧原子,羧基和羟基功能化的石墨烯对亚甲基蓝的吸附能力较纯石墨烯吸附能力强,其次是环氧,羧基和羟基三者共同功能化的石墨烯吸附能力最强.研究结果有望为石墨烯材料在有机染料的吸附应用方面提供有意义的理论指导.     

Sonocatalytic oxidation of olefins catalyzed by heteropolyanion–montmorillonite nanocomposite

A Keggin-type heteropolyanion compound (HPO) was doped within the montmorillonite (MMT) structure by impregnation method. The synthesized catalyst was characterized by FT-IR, XRD, UV–vis, CV, SEM and elemental analysis. Based on chemical adsorption between HPO, and hydroxyl surface groups, HPOs nanoparticles were successfully located on the MMT. Moreover, the obtained nanocomposite was found as an efficient catalyst for oxidation of hydrocarbons under reflux and ultrasonic irradiation conditions.     

One-step fabricated Fe3O4@C core–shell composites for dye removal: Kinetics,equilibrium and thermodynamics

B-Fe₃O₄@C core–shell composites were synthesized via one-pot hydrothermal carbonization (HTC) process and used as an adsorbent for the removal of methylene blue (MB) from aqueous solution. By using sodium borate as the catalyst, the hydrothermal carbonization process of B-Fe₃O₄@C core–shell composites was optimized and a higher surface area was obtained. The adsorbent was characterized by XRD, Raman spectra, SEM, TEM and N₂ adsorption/desorption isotherms. We studied the dye adsorption process at different conditions and analyzed the data by employing the Langmuir and Freundlich models, and the equilibrium data fitted well with both models. Kinetic analyses were conducted by using the Lagergren pseudo-first-order and pseudo-second-order model and the results showed that the adsorption process was more consistent with the pseudo-second-order kinetics. To better understand the dye adsorption process from the thermodynamics perspective, we also calculated ΔH^ο, ΔS^ο, ΔG^ο and E_a, the results suggesting that the MB adsorption process was physisorption endothermic process, and spontaneous at room temperature. The as-synthesized B-Fe₃O₄@C showing high magnetic sensitivity provides a facile and efficient way to recycle from aqueous solution.     

Ultrasound assisted synthesis of polyacrylic acid–nanoclay nanocomposite and its application in sonosorption studies of malachite green dye

Synthesis of nanoclay nanocomposite has been undertaken by using polyacryalic acid (PAA) in aqueous medium and ultrasound environment and its application in dye removal has been investigated. The synthesized product was characterized by using FTIR and XRD techniques. The sonosorption capacity of the product namely PAA–nanoclay composite was determined by choosing malachite green (MG) dye as a model pollutant. The effects of various parameters such as nanocomposite loading, pH, various process conditions etc. have been studied. On comparing the results obtained with that of nanoclay as an adsorbent, it was found for an initial concentration of 500 mg/l, the PAA–nanoclay nanocomposite exhibited higher percentage of pollutant removal (68%) and for nanoclay it was 54%. The adsorption data has been correlated using Langmuir and Freundlich models. The fit of the Freundlich isotherm model was found to be good in the entire range of concentration for the experimental sorption data obtained on the nanoclay nanocomposite. A plausible reaction mechanism for use of PAA–nanoclay nanocomposite as an adsorbent is also proposed.     

Synthesis of magnetic γ-Fe2O3-based nanomaterial for ultrasonic assisted dyes adsorption: Modeling and optimization

γ-Fe₂O₃ nanoparticles were synthesized and loaded on activated carbon. The prepared nanomaterial was characterized by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transforms infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The γ-Fe₂O₃ nanoparticle-loaded activated carbon (γ-Fe₂O₃-NPs-AC) was used as novel adsorbent for the ultrasonic-assisted removal of methylene blue (MB) and malachite green (MG). Response surface methodology and artificial neural network were applied to model and optimize the adsorption of the MB and MG in their individual and binary solutions followed by the investigation on adsorption isotherm and kinetics. The individual effects of parameters such as pH, mass of adsorbent, ultrasonication time as well as MB and MG concentrations in addition to the effects of their possible interactions on the adsorption process were investigated. The numerical optimization revealed that the optimum adsorption (>99.5% for each dye) is obtained at 0.02 g, 15 mg L⁻¹, 4 min and 7.0 corresponding to the adsorbent mass, each dye concentration, sonication time and pH, respectively. The Freundlich, Langmuir, Temkin and Dubinin–Radushkevich isotherms were studied. The Langmuir was found to be most applicable isotherm which predicted maximum monolayer adsorption capacities of 195.55 and 207.04 mg g⁻¹ for the adsorption of MB and MG, respectively. The pseudo-second order model was found to be applicable for the adsorption kinetics. Blank experiments (without any adsorbent) were run to investigate the possible degradation of the dyes studied in presence of ultrasonication. No dyes degradation was observed.     

Preparation, characterization and dye adsorption properties of γ-Fe2O3/SiO2/chitosan composite

A γ-Fe₂O₃/SiO₂/chitosan composite was prepared by water-in-oil emulsification, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Effects of various factors, including adsorbent dosage, initial dye concentration, solution pH, and competing anions, on the adsorption of methyl orange from aqueous solutions by the resulting composite were studied by batch adsorption experiments. The adsorption kinetics was found to follow the pseudo-second-order kinetic model, and intraparticle diffusion was related to the adsorption, but not as a sole rate-controlling step. The equilibrium adsorption data were well described by the Freundlich isotherm model. Evaluation of the thermodynamic parameters ΔG°, ΔH°, and ΔS° revealed that the adsorption process was naturally feasible, spontaneous, and exothermic. The composite was proven to be efficient, suitable and promising for the removal of methyl orange from aqueous solutions since it has a relatively higher adsorption capacity than other low-cost adsorbents.