Optimization using response surface methodology for fast removal of hazardous azo dye by γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>@CuO nanohybrid synthesized by sol–gel combustion

An efficient adsorption system was developed for removal of hazardous Direct Blue 71 as a sample azo dye. The γ-Fe₂O₃@CuO adsorption system was synthesized based on a sol–gel combustion route and characterized by energy-dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) analysis, vibrating-sample magnetometry (VSM), and field-emission scanning electron microscopy (FESEM) techniques. The response surface methodology with Box–Behnken design was used to evaluate the effects of pH, shaking time, and adsorbent dose on dye adsorption. The results showed that solution pH was the parameter with greatest effect on dye adsorption. Adsorption equilibrium was reached quickly, within 8 min. Study of isotherms revealed adsorption capacity of 45.7 mg g^?1 according to the Freundlich model. Sorbent regeneration could be performed using methanol–NaOH (0.1 mol L^?1) solution.     

以高岭土为原料合成沸石分子筛的相变规律

以天然粘土矿物高岭土为原料, 采用水热晶化法合成了NaX, NaP和SOD三类沸石. 利用XRD、 静态饱和水吸附等测试手段详细考察了晶化温度、 初始反应混合物的碱浓度对沸石结晶的影响. 通过实验研究得到了三类沸石的结晶相区和结晶变化规律, 并优化出最佳合成工艺条件和相转变规律.     

Fabrication and characterization of CMC‐based magnetic superabsorbent hydrogel nanocomposites for crystal violet removal

In this research work, novel magnetic superabsorbent hydrogel nanocomposites (MSHNs) based on carboxymethyl cellulose were prepared via a facile “one‐pot” two step approach. Magnetic iron oxide nanoparticles were in situ synthesized and incorporated into carboxymethyl cellulose/poly(acrylic acid) polymer hydrogel. The morphology and chemical composition of MSHNs as well as the presence of magnetic iron oxide nanoparticles were evaluated by using Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, X‐Ray diffraction, ultraviolet–visible spectroscopy, thermogravimetric analysis, and vibrating sample magnetometer. The effect of different reaction parameters on the swelling capacity of MSHNs was investigated. Furthermore, batch adsorption experiments of crystal violet dye onto MSHNs were studied by varying solution pH, initial dye concentration, and temperature. Evaluation of thermodynamic parameters of crystal violet adsorption confirmed that the adsorption was spontaneous and endothermic process in nature. The equilibrium study revealed that the dye adsorption behavior of MHSNs followed the Redlich‐Peterson isotherm model. Finally, the dye adsorption experiment data was well fitted by the pseudo‐second‐order kinetic model with the regression coefficient (R²) of 0.9979. Our results suggest that the MHSNs with facile preparation method, high swelling capacity, and high dye adsorption capacity may be used as promising adsorbents for fast removal of various dyes from aqueous solutions. Copyright © 2016 John Wiley & Sons, Ltd.     

Efficient removal of MB dye using litchi leaves powder adsorbent: Isotherm and kinetic studies

Removal of Methylene Blue (MB) dye using Litchi Leaves Powder (LLP) material was carried out in batch mode. Effect of the mass of the adsorbent (0.1–2.5 g/L), pH of the solution (2−12), starting concentration of MB dye (50–150 mg/L), ionic strength using NaCl (0.1–0.5 M) as an electrolyte, contact time (0–60 min) on the adsorption of MB dye was studied. To calculate pH at which LLP material surface becomes neutral point of zero charge (pH_pzc) is also determined and found to be 6.48. Removal process best fit in the pseudo-second-order kinetic model as indicated by its higher R² value (0.999). Isotherm models (Freundlich and Langmuir) were fitted to the data obtained from the experiment to understand the adsorption behaviour. Result shows that experimental data were fitted to the both isotherm models (Freundlich and Langmuir) as indicated by higher R² value for both Freundlich (0.991) and Langmuir (0.994) model, and it was determined that LLP has a maximum adsorption capacity of 119.76 mg/g.     

Fabrication of PANI@Fe–Mn–Zr hybrid material and assessments in sono-assisted adsorption of methyl red dye: Uptake performance and response surface optimization

In recent decades, industrial wastewater discharge containing toxic or hazardous manufactured dyes has risen tremendously, creating a serious environmental threat. A new hybrid adsorbent, [email protected]–Mn–Zr synthesized by mixing Fe–Mn–Zr metal oxide composite with polyaniline (PANI), was used to study methyl red (MR) dye removal from aqueous solution. The adsorption process was observed to be influenced by the sonication time, dose of [email protected]–Mn–Zr, and initial concentration of MR dye. At an initial MR dye concentration of 25 mg/L, 0.25 g/L of [email protected]–Mn–Zr dose, 15 min of sonication, and pH 7.0, the maximum MR dye adsorption efficiency of 90.34% was achieved. Kinetic analysis was performed using five different kinetic models, which shows that the pseudo-second-order kinetic model had the best fit among the five models. The Langmuir isotherm best fits the adsorption experiments at pH 7.0, yielding a significant MR dye uptake capacity of 434.78 mgg^?1. The most significant adsorption mechanisms that have been observed in uptake of MR dye onto [email protected]–Mn–Zr were electrostatic attraction, π-π bond interactions and hydrogen bonding. Response surface optimization study was performed for optimizing the experimental conditions from which maximum dye removal of 98.19% was obtained at contact time of 12 min, initial MR dye concentration of 15 mg/L and [email protected]–Mn–Zr dose of 0.4 g/L. Use of real wastewater and water samples suggest that there is only 6–19% reduction in the dye removal efficiency as compared to the blank or controlled experiments conducted with deionized water.     

Kinetic,isothermal and thermodynamic studies on Th(IV) adsorption by different modified activated carbons

In this study, the performance of modified adsorbents obtained from activated carbon for the adsorption of thorium(IV) ions from aqueous media was investigated. The analytical and spectroscopic methods such as FT-IR, BET, SEM and UV–Vis were used to examine the properties of the modified materials. According to the analysis results, the both adsorbents had large surface areas after modification. Then, temperature, pH, mixing time and solution concentration parameters were observed to determine optimum thorium adsorption conditions on modified materials. The obtained results from the experiments were applied different three kinetic models and adsorption isotherms and thermodynamic parameters were calculated and then all of the results were interpreted. The adsorption process for both adsorption systems was observed to be compatible with the pseudo-second-order kinetic model. The adsorption equilibrium data were best described by the Langmuir model for modified adsorbent with KMnO₄ and by the Freundlich model for modified adsorbent with NaOH. Furthermore, the calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) showed that the both adsorption processes were endothermic and spontaneous. The data show that modified adsorbents can be used as influential and low-cost adsorbents to remove thorium ion. Modified new adsorbents were highly selective for thorium ion in competitive adsorption studies.

     

Evaluation and applications of a new dye affinity adsorbent

The basic properties of a new dye affinity adsorbent Toyopearl AF-Blue HC-650M and its applications to the purification of proteins were studied. The binding capacity for human serum albumin (HSA) was greater than 18 mg per ml gel. The dye leakage from Toyopearl AF-Blue HC-650M in 0.5 M NaOH and 0.5 M HCI was less compared with an agarose adsorbent. Caustic stability study also demonstrated this material withstood exposure to 0.1 M NaOH for 1 month with no significant loss of binding capacity for HSA. We purified human albumin from human serum and lactate dehydrogenase (LDH) from rabbit muscle extract in a single step. Sodium dodecylsulfate-polyacrylamide gel electrophoresis indicates that human albumin and LDH were highly purified.     

Simple Chemical Route Synthesis of Fe2O3 Nanoparticles and its Application for Adsorptive Removal of Congo Red from Aqueous Media: Artificial Neural Network Modeling

Nanocrystalline Fe₂O₃ powder was synthesized by a simple chemical route involving FeCl₃ and NaOH. The Fe₂O₃ powder thus prepared was characterized using x-ray diffraction study, scanning electron microscopy, and Fourier transform infrared spectroscopy. The adsorption properties of crystalline Fe₂O₃ powder have been investigated with an aim to explore a possible low cost and efficient way to remove Congo red (CR) from waste water. Fe₂O₃ powder was found as an excellent adsorbent for CR from aqueous medium. Adsorption capacity as much as 203.66 mg g^?1 is reported at room temperature. Effect of different experimental parameters such as reaction pH, initial CR dye concentration, adsorbent dose, and reaction temperature were studied on adsorption capacity of Fe₂O₃ powder and modeled by artificial neural network (ANN). Optimal ANN structure (4–5–1) shows minimum mean squared error (MSE) of 0.00235 and determination coefficient (R²) of 0.991 with Levenberg–Marquardt algorithm. Isotherm analysis of experimental data exhibited better fit to the Langmuir isotherm. The adsorption process was found to follow second-order kinetics as depicted by the analysis of experimental results. Thermodynamic study shows that the adsorption process is endothermic, spontaneous, and thermodynamically favorable in the temperature range of 27°C to 60°C.     

Removal of cationic methylene blue and malachite green dyes from aqueous solution by waste materials of Daucus carota

In present study adsorption capacity of waste materials of Daucus carota plant (carrot stem powder: CSP and carrot leaves powder: CLP) was explored for the removal of methylene blue (MB) malachite green (MG) dye from water. The morphology and functional groups present were investigated by scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. The operating variables studied were pH, adsorbent dose, ionic strength, initial dye concentration, contact time and temperature. Equilibrium data were analysed using Langmuir and Freundlich isotherm models and monolayer adsorption capacity of adsorbents were calculated. Kinetic data were studied using pseudo-first and pseudo-second order kinetic models and the mechanism of adsorption was described by intraparticle diffusion model.Various thermodynamic parameters such as enthalpy of adsorption ΔH°, free energy change ΔG° and entropy ΔS° were estimated. Negative value of ΔH° and negative values of ΔG° showed that the adsorption process was exothermic and spontaneous. Negative value of entropy ΔS° showed the decreased randomness at the solid–liquid interface during the adsorption of MB and MG onto CSP and CLP.     

Sorptive and thermal properties of red clay in relation to Cr(VI)

The results of Cr(VI) adsorption on the red clay modified by hexadecyltrimethylammonium bromide are given. The adsorption isotherm of Cr(VI) is determined based on the Langmuir–Freundlich model and exhibits the adsorption capacity of 0.0005 mol/g in relation to Cr(VI). The study of the pH effect showed that the optimal pH range corresponding to the Cr(VI) adsorption maximum on this clay is 2–6.5. Thermal analysis of the modified adsorbent, i.e., Na/HDTMA-clay, shows two DTG peaks at 58–61 and 241 °C. The first one is a consequence of dehydration of the modified clay sample. The other DTG peak results from evaporation and pyrolysis of HDTMA adsorbed on the clay. In the case of Na/HDTMA-Cr-clay three peaks appear at: 64, 232, and 340 °C. The third DTG peak is related to the oxidation of surfactant. Moreover, the raw mineral shows the peak at 543 °C attributed to the clay dehydroxylation.     

Preparation of activated carbon from organic fraction of municipal solid wastes by ZnCl2 activation method and use it for elimination of chromium(VI) from aqueous solutions

In this study, the use of the organic fraction of municipal solid waste as an abundant and low-cost raw material for producing activated carbon was investigated. For this purpose, ZnCl₂ was used as a chemical activation agent and the carbonization process took place at 800 °C in N₂ atmosphere. Seven sorbents were prepared by chemical activation (pyrolysis under N₂ atmosphere at temperature of 800 °C after impregnation with ZnCl₂) with different ratios of ZnCl₂. The optimum ratio of organic fraction of municipal solid waste to ZnCl₂ was inspected via methylene blue number and iodine number (ASTM Designation: D4607–94). The results showed that the adsorbent with 60 % ZnCl₂/raw material was the most appropriate one with a satisfactory adsorption capacity, 112.4 mg g^?1 for methylene blue and 134.0 mg g^?1 for iodine. In addition, the structural analysis of this sorbent was performed using FT-IR, BET surface area, SEM–EDX and thermal analysis. Application of this sorbent to remove Cr(VI) from wastewater was studied to find an adsorption capacity of 66.7 mg g^?1. The experimental adsorption equilibrium data were fitted to Langmuir adsorption model with an acceptable adsorption capacity of 66.7 mg g^?1.     

Adsorption of indigo carmine from aqueous solution using coal fly ash and zeolite from fly ash

Coal fly ash, a waste generated at the Figueira coal-fired electric power plant located in Brazil, was used to synthesize zeolite by hydrothermal treatment with NaOH solution at 100 °C for 24 h. The fly ash (FA) and this synthesized zeolite (ZM) that was characterized predominantly as hydroxy-sodalite were used as adsorbents for anionic dye indigo carmine from aqueous solutions. The samples were analyzed by instrumental neutron activation analysis (INAA) for the determination of As, Co, Fe, La, Mo, Na, Sb, Sc, Sm, Th, U and Zn. Effects of contact time and initial dye concentration were evaluated in the adsorption processes. The kinetics studies indicated that the adsorption followed the pseudo-second order kinetics and that surface adsorption and intraparticle diffusion were involved in the adsorption mechanism for both the adsorbents. The Langmuir isotherm model provided the best correlation of the experimental data. The maximum adsorption capacity was found to be 1.48 mg L⁻¹ for FA and 1.23 mg L⁻¹ for ZM. Laboratory leaching and solubilization tests conducted to classify this ZM as if was a waste residue according to the Brazilian regulation classified it as a residue non-hazardous and non-inert.     

Poly-L-Histidine Attached Poly(glycidyl methacrylate) Cryogels for Heavy Metal Removal

Poly-L-histidine immobilized poly(glycidyl methacrylate) (PGMA) cryogel discs were used for the removal of heavy metal ions [Pb(II), Cd(II), Zn(II) and Cu(II)] from aqueous solutions. In the first step, PGMA cryogel discs were synthesized using glycidyl methacrylate (GMA) as a basic monomer and methylene bisacrylamide (MBAAm) as a cross linker in order to introduce active epoxy groups through the polymeric backbone. Then, the metal chelating groups are incorporated to cryogel discs by immobilizing poly-L-histidine (mol wt ≥ 5000) having poly-imidazole ring. The swelling test, fourier transform infrared spectroscopy and scanning electron microscopy were performed to characterize both the PGMA and poly-L-histidine immobilized PGMA [P-His@PGMA] cryogel discs. The effects of the metal ion concentration and pH on the adsorption capacity were studied. These parameters were varied between 3.0–6.0 and 10–800 mg/L for pH and metal ion concentration, respectively. The maximum adsorption capacity of heavy metal ions of P-His@PGMA cryogel discs were 6.9 mg/g for Pb(II), 6.4 mg/g for Cd(II), 5.6 mg/g for Cu(II) and 4.3 mg/g for > Zn(II). Desorption of heavy metal ions was studied with 0.1 M HNO₃ solution. It was observed that cryogel discs could be recurrently used without important loss in the adsorption amount after five repetitive adsorption/desorption processes. Adsorption isotherms were fitted to Langmuir model and adsorption kinetics were suited to pseudo-second order model. Thermodynamic parameters (i.e. ΔH° ΔS°, ΔG°) were also calculated at different temperatures.     

Synthesis and performance evaluation of chitosan/zinc oxide nanocomposite as a highly efficient adsorbent in the removal of reactive red 198 from water

In this study, Chitosan and Chitosan-zinc oxide (ZnO) nanocomposite were prepared and applied as a low-cost adsorbent with high adsorption capacity for removing reactive red 198 (RR 198) dye from contaminated water. After preparation, it was characterized using FT-IR, XRD, and SEM. The effect of pH, temperature, time, adsorbent amount, and initial dye concentration were investigated in the removal efficiency of RR 198. The maximum adsorption capacity (q_m) obtained from the Langmuir equation was 172.41 mg/g in adsorbent dose of 0.1 g/L, pH: 4, temperature of 25°C, adsorption time of 40 min. The thermodynamic parameters demonstrated the spontaneous and endothermic nature of the adsorption process. Due to the high efficiency of chitosan/ZnO nanocomposite in removal of RR 198 from water and advantages such as high adsorption capacity, simple synthesis, and easy application, it can be used as an effective method in the removal of RR 198 from water.     

Adsorptive removal of tannin from aqueous solutions by cationic surfactant-modified bentonite clay

The removal of tannin from aqueous media by cationic surfactant-modified bentonite clay was studied in a batch system. The surfactant used was hexadecyltrimethylammonium chloride. Adsorbent characterizations were investigated using X-ray diffraction, infrared spectroscopy, surface area analysis, and potentiometric titration. The effects of pH, contact time, initial solute concentration, adsorbent dose, ionic strength, and temperature on the adsorption of tannin onto modified clay were investigated. The adsorbent exhibited higher tannin removal efficiency (>99.0%) from an initial concentration of 10.0 micromol/L at pH 3.0. Adsorption capacity decreased from 90.1 to 51.8% with an increase in temperature from 10 to 40 degrees C at an initial concentration of 25.0 micromol/L. The adsorption process was found to follow pseudo-first-order kinetics. Film diffusion was found to be the rate-limiting step. Tannin adsorption was found to decrease with increase in ionic strength. The tannin equilibrium adsorption data were fitted to Langmuir and Freundlich isotherm models, the former being found to provide the best fit of the experimental data. The maximum monolayer adsorption capacity for tannin was 69.80 micromol/g at 30 degrees C. Comparison of adsorption capacity of the modified clay with reported adsorbents in the literature was also presented. Adsorbed tannin on modified clay can be recovered by treatment with 0.1 M NaOH solution. Regeneration experiments were tried for four cycles and results indicate a capacity loss of <10.0%. From the results it can be concluded that the surfactant-modified clay could be a good adsorbent for treating tannin-contaminated waters.     

Evaluation of N719 amount in TiO2 films for DSSC by thermogravimetric analysis

The aim of this work is to evaluate the amount of N719 dye in TiO₂ films for DSSCs by thermogravimetric analysis coupled with mass spectrometry (TG-MS) in comparison with the traditional method based on the dye extraction in NaOH solutions. The characterization was carried out on TiO₂ films applied on FTO glasses by automatic screen printing method. For all the samples, TG-MS showed three well defined steps. The first, below 100 °C and coupled to an endothermic signal was due to water release. From 200 to about 300 °C, there was the release of CO₂ coming from decarboxylation reaction of N719. The last exothermic step was due to the combustion of organic residues. As the decarboxylation reaction occurs with release of 4 moles of CO₂ per mole of N719, it was used to determine the dye loading of the samples that resulted in the range 7?15 wt% well agreeing the relevant content of dye obtained by desorption with NaOH.     

Cellulose nanocrystals as promising adsorbents for the removal of cationic dyes

Cellulose nanocrystals (CNCs) prepared from cellulose fibre via sulfuric acid hydrolysis was used as an adsorbent for the removal of methylene blue (MB) from aqueous solution. The effects of pH, adsorbent dosage, temperature, ionic strength, initial dye concentration were studied to optimize the conditions for the maximum adsorption of dye. Adsorption equilibrium data was fitted to both Langmuir and Freundlich isotherm models, where the Langmuir model better described the adsorption process. The maximum adsorption capacity was 118 mg dye/g CNC at 25 °C and pH 9. Calculated thermodynamic parameters, such as free energy change (ΔG = ?20.8 kJ/mol), enthalpy change (ΔH = ?3.45 kJ/mol), and entropy change (ΔS = 0.58 kJ/mol K) indicates that MB adsorption on CNCs is a spontaneous exothermic process. Tunability of the adsorption capacity by surface modification of CNCs was shown by oxidizing the primary hydroxyl groups on the CNC surface with TEMPO reagent and the adsorption capacity was increased from 118 to 769 mg dye/g CNC.     

Synthesis of phosphorus-modified poly(styrene-co-divinylbenzene) chelating resin and its adsorption properties of uranium(VI)

A new phosphorus-modified poly(styrene-co-divinylbenzene) chelating resin (PS–N–P) was synthesized by P,P-dichlorophenylphosphine oxide modified commercially available ammoniated polystyrene beads, and characterized by Fourier transform infrared spectroscopy and elemental analysis. The adsorption properties of PS–N–P toward U(VI) from aqueous solution were evaluated using batch adsorption method. The effects of the contact time, temperature, pH and initial uranium concentration on uranium(VI) uptake were investigated. The results show that the maximum adsorption capacity (97.60 mg/g) and the maximum adsorption rate (99.72 %) were observed at the pH 5.0 and 318 K with initial U(VI) concentration 100 mg/L and adsorbent dose 1 g/L. Adsorption equilibrium was achieved in approximately 4 h. Adsorption kinetics studied by pseudo second-order model stated that the adsorption was the rate-limiting step (chemisorption). U(VI) adsorption was found to barely decrease with the increase in ionic strength. Equilibrium data were best modeled by the Langmuir isotherm. The thermodynamic parameters such as ?G ₀, ?H ₀ and ?S ₀ were derived to predict the nature of adsorption. Adsorbed U(VI) ions on PS–N–P resin were desorbed effectively (about 99.39 %) by 5 % NaOH–10 % NaCl. The synthesized resin was suitable for repeated use.     

Removal of Reactive Red 141 Dye from Aqueous Solution by Titanium Hydroxyapatite Pellets

The adsorption of Reactive Red 141 over the pressed and calcined pellets of TiHAp and HAp was investigated by using continuous reflux system. Langmuir isotherm model was found to be the best model to describe the equilibrium data, with maximum adsorption capacity of 20.62 and 28.41 (mg g^?1) for HAp and TiHAp, respectively. Kinetics data was best described by the pseudo-second-order model and intraparticle diffusion determined as sole controlling step of adsorption process. Possible mechanisms of the adsorption dye on the HAp and TiHAp were discussed.