Advantage of almond green hull over its resultant ash for chromium(VI) removal from aqueous solutions

The discharge of industrial effluents containing hexavalent chromium can be very harmful for the environment. Therefore, Cr(VI) should be removed from contaminated water, and especially from wastewater, to prevent its discharge into the environment. This study is aimed at analyzing the factors that affect the removal of Cr(VI) with the use of almond green hull and ash adsorbent. The effects of pH (2–10), adsorbent dose (2–24 g/L), Cr(VI) concentration (10–100 mg/L), exposure time (1–60 min), and temperature (5–50 °C) were examined. The surface morphology, pore size of adsorbent surfaces were characterized with SEM, EDX, FTIR. Maximum removal occurred at pH = 2. Results showed that the removal yield increased with the rise of exposure time and temperature. The data indicate that due to limited site on adsorbent surface, the removal efficiency decreased as initial Cr(VI) concentration increased. When the adsorbent dose was increased, the removal yield increased in the case of the bioadsorbent as well; however, in the ash adsorbent, there was an increase followed by a decreasing trend. The study highlights that almond green hull can be more efficient than its ash in the removal of Cr(VI) from aqueous solution. As a general result of study, it can be argued that almond green hull bioadsorbent and the obtained carbon are able to remove Cr(VI) from aqueous solutions; thus, they can be used as efficient and economical substitutes for existing adsorbents like activated carbon, for the removal of chromium from polluted aqueous solutions.     

Investigating the removal of ethylbenzene from aqueous solutions using modified graphene oxide: application of response surface methodology

This research focused on the application of response surface methodology (RSM) for the removal of ethylbenzene by the graphene oxide grafted with polymethyl vinyl ketone and aniline (GO-MVK-ANI) from wastewater. The adsorbent was prepared through polymerization of graphene oxide with methyl vinyl ketone using ammonium persulfate initiator and further modification by aniline. The synthesized material was characterized via Fourier transform infrared resonance spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and Brunauer–Emmett–Teller analysis. RSM was used to minimize the number of experiments and investigate the effect of three selected parameters (contact time, initial pH and adsorbent dose) on the removal efficiency of ethylbenzene. Additionally, the affecting parameters were optimized based on the selected target (ethylbenzene removal efficiency). The results show that 73% ethylbenzene could be adsorbed with initial ethylbenzene concentration of 20 mg/l under the optimum conditions (the contact time of 11 min, pH of 5.64 and adsorbent dose of 3.75 g/l). In this paper, high R ²-value (97.18%) for ethylbenzene removal and a good agreement with adjusted R ²-value (94.65%) indicated that the model was successful and the results demonstrated a reasonable proportion of the experimental and the predicted results.     

Removal of phosphates from aqueous solution by sepiolite-nano zero valent iron composite optimization with response surface methodology

In this study, sepiolite-nano zero valent iron composite was synthesized and applied for its potential adsorption to remove phosphates from aqueous solution. This composite was characterized by different techniques. For optimization of independent parameters (pH = 3–9; initial phosphate concentration = 5–100 mg/L; adsorbent dosage = 0.2–1 g/L; and contact time = 5–100 min), response surface methodology based on central composite design was used. Adsorption isotherms and kinetic models were done under optimum conditions. The results indicated that maximum adsorption efficiency of 99.43 and 92% for synthetic solution and real surface water sample, respectively, were achieved at optimum conditions of pH 4.5, initial phosphate concentration of 25 mg/L, adsorbent dosage of 0.8 g/L, and 46.26 min contact time. The interaction between adsorbent and adsorbate is better described with the Freundlich isotherm (R ² = 0.9537), and the kinetic of adsorption process followed pseudo-second-order model. Electrostatic interaction was the major mechanisms of the removal of phosphates from aqueous solution. The findings of this study showed that there is an effective adsorbent for removal of phosphates from aqueous solutions.     

Green synthesis of magnetic mesoporous silica nanocomposite and its adsorptive performance against organochlorine pesticides

Green synthesis of nanomaterials has received increasing attention as an eco-friendly technology in materials science. Here, we have used two types of extractions from green tea leaf (i.e., total extraction and tannin extraction) as reducing agents for a rapid, simple and one-step synthesis method of mesoporous silica nanoparticles/iron oxide nanocomposite based on deposition of iron oxide onto mesoporous silica nanoparticles. Mesoporous silica nanoparticles/iron oxide nanocomposite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray, vibrating sample magnetometer, N₂ adsorption and high-resolution transmission electron microscopy. Mesoporous silica nanoparticles/iron oxide nanocomposite was used as a solid adsorbent for removal of lindane pesticide from aqueous solutions. The developed system possesses the advantages of silica as core that include large surface area and advantages of iron oxide (shell) that include the capability to interact with chlorinated compounds and ability to release by using external magnetic field. UV-Vis technique was used as a simple and easy method for monitoring the removal of lindane. Effects of pH and temperature on the removal efficiency of the developed mesoporous silica nanoparticles/iron oxide nanocomposite toward lindane pesticide were also investigated. Fourier transform infrared spectroscopy, high-performance liquid chromatography and gas chromatography techniques were used to confirm the high ability of mesoporous silica nanoparticles/iron oxide nanocomposite for sensing and the capture of lindane molecules with high sorption capacity (about 99%) that could develop a new eco-friendly strategy for detection and removal of pesticide and as a promising material for water treatment.     

Synthesis of poly(amidoamine)-graft-poly(methyl acrylate) magnetic nanocomposite for removal of lead contaminant from aqueous media

Poly(amidoamine)-graft-poly(methyl acrylate) magnetic nanocomposite was synthesized via radical polymerization of methyl acrylate onto modified magnetic nanoparticles followed by the functionalization of the methyl ester groups with poly(amidoamine) dendrimer. The resulting poly(amidoamine)-graft-poly(methyl acrylate) magnetic nanocomposite was then characterized by infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, scanning electron microscope and X-ray diffraction analysis. Its application as an adsorbent for the removal of Pb(II) ions was studied. The removal capability of the adsorbent was investigated in different pH values, contact time (kinetics) and initial concentration of lead. Moreover, adsorption isotherms were investigated to describe the mechanistic feature of this nanocomposite for adsorption. Accordingly, its high adsorption capacity (310 mg/g) and efficient adsorption toward lead ions in aqueous solution were shown. To further study of the chemistry behind the adsorption process, a comprehensive density functional theory-based study was performed, and a relatively strong interaction between metal ions and adsorbent was observed based on the calculated adsorption free energies.     

Removal of organic matter from reservoir water: mechanisms underpinning surface chemistry of natural adsorbents

One of the key challenges in water treatment industry is the removal of organic compounds by cost-effective methods. This study evaluated the adsorptive removal of dissolved organic carbon (DOC) from reservoir water using fuller’s earth (FE) in comparison with natural (SQ) and modified quartz (MSQ) sands. The removal capacities of FE at different contact times, pH levels, adsorbent dosages and initial DOC concentrations were compared with both the quartz sands. The optimum DOC removals by FE and SQs were achieved at contact time of 60 and 30 min, pH level of 6 and 4, and at adsorbent dose of 1.5 g/150 mL and 10 g/100 mL, respectively. The adsorption capacity of FE (1.05 mg/g) was much higher compared to the MSQ (0.04 mg/g) and SQ (0.01 mg/g). Adsorption equilibrium data better fitted to the Freundlich model than to the Langmuir model, suggesting that adsorption occurred primarily through multilayer formation onto the surfaces of FE and SQ. The pseudo-second-order model described the uptake kinetics more effectively than the pseudo-first-order and intra-particle diffusion models, indicating that the mechanism was primarily governed by chemisorption. These observations were well supported by the physiochemical characteristics and charge behaviour of the adsorbents. In mass-transfer study, the results of liquid film diffusion model showed that the adsorption of DOC on FE was not controlled by film diffusion, but other mechanisms also played an essential role. This study demonstrates that FE is an effective adsorbent for the removal of DOC in surface water treatment.     

Non-woven polypropylene fabric modified with carbon nanotubes and decorated with nanoakaganeite for arsenite removal

Due to its harmful impact on human health, the presence of heavy metals, metalloids and other toxic pollutants in drinking or irrigation water is a major concern. Recent studies have proved that nanosized adsorbents are significantly more effective than their microsized counterparts. Particular attention has been given to nanocomposites with nanoadsorbents embedded in matrixes that could provide stability to the material and contribute to eliminating problems that may appear when using conventional granular systems. This study presents the preparation of a novel hybrid filter from a commercially available polypropylene (PP) non-woven fabric matrix modified with multiwall carbon nanotubes (MWCNT) and iron oxy(hydroxide) nanoparticles, and its use in the removal of As(III). A Box–Behnken statistical experimental design has been chosen to explore relevant variables affecting the filter performance: (1) As(III) concentration, (2) pH and (3) sorbent dose. From an As(III) concentration of 10 mg L^?1, at pH 6.5 and with a sorbent dose of 5 g L^?1, the PP filter modified with MWCNT removes 10% of the initial metalloid concentration, reaching a capacity of 0.27 mg g^?1. After modification with iron oxy(hydroxide), the performance of the material is largely enhanced. The filter, under the same conditions, removes 90% of the initial As(III) concentration, reaching a capacity almost tenfold higher (2.54 mg g^?1). This work demonstrates that the developed hybrid filter is effective toward the removal of As(III) in a wide range of pHs. A cubic regression model to compute the removal of the filter as a function of pH and sorbent dose is provided.     

Removal of humic acid from peat water using untreated powdered eggshell as a low cost adsorbent

The main objective of this study is to investigate the possibility of powdered eggshell used as an adsorbent material for removal of humic acid from peat water. The influences of contact time, dose of eggshells, pH, and temperature were the factors considered in the removal processes of humic acid from peat water. In addition, adsorption isotherms of humic acid onto the powdered eggshell were also evaluated with the Langmuir and Freundlich approximations. Our results showed that the equilibrium of the process was eventually established after 60 min of the contact time, and also found that using 5 g of the powdered eggshell nearly 95 % of humic acid has been successfully removed from the peat water. The removal of humic acid gave better result when it was conducted at low pH, and it was almost unaffected the temperatures variation. The data was well fitted to Freundlich isotherm with the correlation coefficient of not <0.999, and could uptake the humic acid about 126.58 mg/g at pH 4.01, estimated from the Langmuir model. The kinetic experimental data proportionally correlated with the pseudo-second-order kinetic model with a rate constant in the range of 0.016–0.112 g mg^?1 min^?1, while intra-particle-diffusion were the main rate determining step in the humic acid removal process. The powdered eggshell investigated in this study, thus, exhibited as a high potential adsorbent for the removal of humic acid from peat water.     

Removal of ibuprofen from aqueous solution by functionalized strong nano-clay composite adsorbent: kinetic and equilibrium isotherm studies

The functionalized nano-clay composite adsorbent was prepared, and its properties were characterized using FT-IR, XRD and SEM techniques. The synthesized nano-clay composite was studied with regard to its capacity to remove ibuprofen under different adsorption conditions such as varying pH levels (5–9), initial ibuprofen concentrations (3, 5 and 10 mg L^?1), contact time, and the amount of adsorbent (0.125, 0.25, 0.5 and 1 g). In order to evaluate the nanocomposite adsorption capacity, the adsorption results were assessed using nine isotherm models. The results showed that the optimum adsorption pH was 6 and that an increase or decrease in the pH reduced the adsorption capacity. The adsorption process was fast and reached equilibrium after 120 min. The maximum efficacy of ibuprofen removal was approximately 95.2%, with 1 g of adsorbent, 10 mg L^?1 initial concentration of ibuprofen, 120 min contact time and pH = 6. The optimal adsorption isotherm models were the Freundlich, Fritz–Schlunder, Redlich–Peterson, Radke–Prausnitz, Sip, Toth and Khan models. In addition, four adsorption kinetic models were employed for adsorption system evaluation under a variety of experimental conditions. The kinetic data illustrated that the process is very fast, and the reaction followed the Elovich kinetic model. Therefore, this nano-clay composite can be used as an effective adsorbent for the removal of ibuprofen from aqueous solutions, such as water and wastewater.     

Empirical and mechanistic evaluation of sodium exchange isotherms on natural mineral and organic adsorbents and organically functionalized nanoparticles

This study was conducted to evaluate the efficiency of low-cost adsorbents including bentonite, kaolinite and zeolite saturated with calcium and potassium, potato and wheat residues, and three metal oxide nanoparticles functionalized with an acidic extract of potato residues in improving the quality of sodic waters. The optimization of factors such as pH, contact time, and adsorbent dosage was investigated using a solution containing sodium, calcium, magnesium, and potassium. The optimal pH and contact time were 7.0 and 24 h, respectively. The optimal dosage for using functionalized nanoparticles was 0.1 g and for using other adsorbents was 1.0 g. The sodium exchange isotherms were conducted in binary sodium–calcium and sodium–potassium and quaternary sodium–calcium–magnesium–potassium systems. Zeolite saturated with potassium was the most effective adsorbent in removing sodium from aqueous solutions with an average removal efficiency of 69.2 and 66.5 % in binary and quaternary systems, respectively. Freundlich and Langmuir equations fitted well to experimental data in both binary and quaternary systems. Cation selectivity coefficients calculated based on the Gaines–Thomas convention varied with changing pH and adsorbent dosage. Graphical and statistical evaluations confirmed that the mechanistic cation exchange model using average Gaines–Thomas selectivity coefficients in geochemical PHREEQC program was able to successfully simulate the sodium exchange on different adsorbents in both systems. The Gaines–Thomas selectivity coefficient values greater than unity and as a consequence, the negative values of the Gibbs free energy change of adsorption indicated that sodium exchange reactions in the presence of different adsorbents used is this study were exergonic and spontaneous.     

Adsorption of lead using a new green material obtained from Portulaca plant

In the present study the potential of a new green material obtained from Portulaca oleracea plant was investigated. The material was used without any chemical treatment to study the adsorption behavior of lead ions from aqueous solution. Various batch experiments were carried out using different experimental conditions such as pH, contact time, adsorbent concentration, and metal ion concentration to identify the optimum conditions. The influence of these parameters on the adsorption capacity was studied. Results showed the optimum initial pH for adsorption as 6. Adsorption equilibrium was reached in 120?min. The adsorption data were modeled using both the Langmuir and Freundlich classical adsorption isotherms. Results show ~78% removal of lead from aqueous solution. The kinetic data corresponded well with pseudo second-order equation. From the initial results, the green material obtained from the waste of Portulaca seems to be a potential low-cost adsorbent for removal of lead ions from water.     

Identification of potential soil adsorbent for the removal of hazardous metals from aqueous phase

The present study attempted to identify the efficient hazardous metal-removing sorbent from specific types of soil, upper and middle layer shirasu, shell fossil, tuff, akadama and kanuma soils of Japan by physico-chemical and metal (arsenic, cadmium and lead) removal characterizations. The physico-chemical characteristics of soil were evaluated using X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy techniques, whereas metal removal properties of soil were characterized by analyzing removal capacity and sorption kinetics of potential metal-removing soils. The chemical characteristics revealed that all soils are prevalently constituted of silicon dioxide (21.83–78.58 %), aluminum oxide (4.13–38 %) and ferrous oxide (0.835–7.7 %), whereas calcium oxide showed the highest percentage (65.36 %) followed by silicon dioxide (21.83 %) in tuff soil. The results demonstrated that arsenic removal efficiency was higher in elevated aluminum oxide-containing akadama (0.00452 mg/L/g/h) and kanuma (0.00225 mg/L/g/h) soils, whereas cadmium (0.00634 mg/L/g/h) and lead (0.00693 mg/L/g/h) removal efficiencies were maximum in elevated calcium oxide-containing tuff soil. Physico-chemical sorption and ion exchange processes are the metal removal mechanisms. The critical appraisal of three metal removal data also clearly revealed cadmium > lead > arsenic order of removal efficiency in different soils, except in tuff and akadama soils followed by lead > cadmium > arsenic. It clearly signified that each type of soil had a specific metal adsorption affinity which was regulated by the specific chemical composition. It may be concluded that akadama would be potential arsenic-removing and tuff would be efficient cadmium and lead-removing soil sorbents.     

Preparation and characterization of biosorbents and copper sequestration from simulated wastewater

This paper reports the potential of chemically treated wood chips to remove copper (II) ions from aqueous solution a function of pH, adsorbent dose, initial copper (II) concentration and contact time by batch technique. The wood chips were treated with (a) boiling, (b) formaldehyde and (c) concentrated sulphuric acid and characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive analysis X-ray. pH 5.0 was optimum with 86.1, 88.5 and 93.9 % copper (II) removal by boiled, formaldehyde-treated and concentrated sulphuric acid-treated wood chips, respectively, for dilute solutions at 20 g L^?1 adsorbent dose. The experimental data were analysed using Freundlich, Langmuir, Dubinin–Radushkevich and Temkin isotherm models. It was found that Freundlich and Langmuir models fitted better the equilibrium adsorption data and the adsorption process followed pseudo-second-order reaction kinetics. The results showed that the copper (II) is considerably adsorbed on wood chips and it could be an economical option for the removal of copper from aqueous systems.     

Removal of diazinon pesticide from aqueous solutions using MCM-41 type materials: isotherms,kinetics and thermodynamics

In this research, ordered mesoporous silica, including MCM-41, was synthesized via sol–gel process and a propyl methacrylate-modified ordered mesoporous silica (MPS-MCM-41) was successfully synthesized via a postsynthesis grafting process. Then both MCM-41 and MPS-MCM-41 were characterized using FTIR, XRD, SEM and BET techniques. The synthesized materials were utilized as adsorbent for removal of diazinon pesticide from aqueous solutions. The effects of pH, contact time, adsorbent dose, initial concentration and temperature have been evaluated using removal efficiencies. Also, the kinetic, thermodynamic and isotherm models of diazinon adsorption were studied for the both MCM-41 and MPS-MCM-41. The results showed that the maximum adsorption capacities are 142 and 254 mg g^?1 for the MCM-41 and MPS-MCM-41, respectively, at the initial concentration of 50 mg L^?1, temperature of 298 K and adsorbent dose of 0.1 g L^?1. The highest percentages of diazinon removal are 56.4 and 87.2 (at adsorbent dose of 2 g L^?1 and the temperature of 318 K) for the MCM-41 and MPS-MCM-41, respectively. The Freundlich and Langmuir models are more compatible for describing equilibrium data of the diazinon adsorption capacity on the MCM-41 and MPS-MCM-41, respectively. Thermodynamic study indicated that the adsorption process of diazinon onto MCM-41 and MPS-MCM-41 is exothermic and has a spontaneous nature. The higher adsorption capacity and higher spontaneous nature of MPS-MCM-41 in comparison with MCM-41 might be due to the presence of the both hydrogen bonding and hydrophobic interaction between surface functional groups of MPS-MCM-41 (hydroxyl and propyl methacrylate) and diazinon functional groups.     

Preparation of magnetic microgels for catalytic reduction of 4-nitrophenol and removal of methylene blue from aqueous medium

This work describes the synthesis of poly(acrylic acid) microgels and fabrication of magnetic cobalt nanoparticles in the prepared microgels. Cobalt nanoparticles were fabricated by loading the cobalt (II) ions in microgels from aqueous solution and their subsequent reduction with sodium borohydride (NaBH₄). Bare and composite microgels were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The catalytic properties of the prepared microgel composites were investigated by using them as catalyst for the reduction of 4-nitrophenol and methylene blue. The effect of temperature and catalyst dose on the rate of reduction of these toxic pollutants was investigated. The reusability of prepared catalysts was also studied for the five consecutive cycles, and an increase in catalytic activity was observed after every cycle. The prepared bare and magnetic microgels were found as very effective adsorbent for the removal of methylene blue from aqueous medium. Very rapid adsorption rate was found for the removal of methylene as its 100 mg was adsorbed on per gram of dried hydrogels in about 25 min. The effects of different parameters like amount of adsorbate and concentration of adsorbent on the adsorption process were studied. Langmuir, Freundlich and Temkin adsorption isotherms were applied, and it was found that adsorption of MB follows Freundlich model better than others. Furthermore, pseudo-first-order and pseudo-second-order kinetic models were also applied and adsorption of MB was found to abide by pseudo-second-order kinetics.     

Application of dried plant biomass as novel low-cost adsorbent for removal of cadmium from aqueous solution

Heavy metals are a threat to human health and ecosystem. These days, great deal of attention is being given to green technologies for purification of water contaminated with heavy metal ions. Biosorption is one among such emerging technologies, which utilizes naturally occurring waste materials to sequester heavy metals from wastewater. Cadmium has hazardous impact on living beings; therefore, its removal through green and economical process is an important task. The aim of the present study was to utilize the locally available Portulaca oleracea plant biomass as an adsorbent for cadmium removal from aqueous solution. The biomass was obtained after drying and grinding the portulaca leaves and stem. No chemical treatment was done on the adsorbent so that it remained green in a true sense. Batch experiments were performed at room temperature. The critical parameters studied were effects of pH, contact time, initial metal ion concentration and adsorbent dose on the adsorption of cadmium. The maximum adsorption was found to be 72 %. The kinetic data were found to best fit the pseudo-second-order equation. High adsorption rates were obtained in the initial 45 min, and adsorption equilibrium was then gradually achieved in about 100 min. Adsorption increased with increase in pH for a range 2 and 6. The equilibrium adsorption results closely followed both the Langmuir and Freundlich isotherms. The values of constants were calculated from isotherms. Results indicated that portulaca plant biomass could be developed as a potential material to be used in green water treatment devices for removal of metal ions.     

Ultrafast removal of heavy metals by tin oxide nanowires as new adsorbents in solid-phase extraction technique

In the present research, the removal of lead(II) and copper(II) from aqueous solutions is studied, using SnO₂ nanowires as new adsorbent on solid-phase extraction disk and compared with pine core and buttonwood as biosorbents. Batch adsorption experiments were performed as a function of pH, adsorption time, solute concentration and adsorbent dose for biosorbents. Also, the pH, transfer rate of solution and metal concentration were selected as experimental parameters for the removal of heavy metals by SnO₂ nanowires. All of the parameters were optimized by experimental design method for sorbents. The experimental equilibrium adsorption data are tested for the Langmuir and Freundlich equations. Results indicate the following order to fit the isotherms: Langmuir > Freundlich, in case of lead and copper ions. The removal of Cu(II) and Pb(II) was performed by selected sorbents in the presence of interferences ions. This led to no remarkable decrease in the removal efficiency of SnO₂ nanowires. Using the SnO₂ nanowires in the wastewater treatment indicated 96.8 and 85.28% removal efficiency in only 7 min for Pb(II) and Cu(II), respectively. SnO₂ nanowires were found as reusable sorbent. Therefore, SnO₂ nanowires have a good potential for application in environmental protection.     

NaOH-treated dead leaves of <Emphasis Type="Italic">Ficus racemosa</Emphasis> as an efficient biosorbent for Acid Blue 25 removal

A novel biosorbent synthesized from Ficus racemosa leaves based on the treatment using NaOH was applied for removal of Acid Blue 25 from aqueous solution. The synthesized biosorbent was characterized using scanning electron microscopy, Fourier transform infrared spectroscopy and Brunauer–Emmett–Teller analysis. NaOH treatment was demonstrated to remove lignin content from the biomass and to induce the development of significant pores. Batch experiments were performed to evaluate the effect of important operating parameters such as pH (range of 2–10), biosorbent dose (range of 1–10 g/L), contact time (range of 0–5 h), initial dye concentration (range of 50–400 mg/L) and temperature (range of 293–323 K) on the extent of removal of Acid Blue 25. The established optimum conditions were pH of 2, biosorbent dose of 4 g/L, contact time of 3 h and temperature of 323 K, yielding maximum removal of dye. Pseudo-second-order model was found to best fit the kinetic data. Langmuir and Temkin isotherm models were found to best fit the equilibrium data. The obtained thermodynamic parameters confirmed endothermic and spontaneous nature of adsorption. The study established the utility of novel biosorbent for removal of Acid Blue 25 with higher adsorption capacities (83.33 mg/g) as compared to the more commonly used adsorbents. Desorption-adsorption  studies conducted for seven cycles indicated potential reusability of synthesized biosorbent for the treatment of dye effluents.     

Removal of cadmium (II) from aqueous solution and natural water samples using polyurethane foam/organobentonite/iron oxide nanocomposite adsorbent

A novel polyurethane foam/organobentonite/iron oxide nanocomposite adsorbent was successfully prepared via in situ polymerization of toluene diisocyanate and polyol in presence of 5 wt% organobentonite/iron oxide. The obtained nanocomposite was characterized in detail, and the results revealed that the clay layers are exfoliated and/or intercalated in the polymer matrix forming a nanocomposite structure. The application of the prepared nanocomposite for adsorption of cadmium ions from aqueous solution was tested as a function of various experimental parameters using batch procedures. Adsorptive removal of Cd(II) onto the nanocomposite attained maximum at adsorbent content 1.5 g/L, pH 6, and the equilibrium was established within 60 min. Kinetic studies showed that the experimental data fit very well to pseudo-second-order model, and the adsorption process proceeds through three steps. It was found that external liquid film and intraparticle diffusion steps deeply affect the rate of Cd²⁺ ions adsorption onto the synthesized nanocomposite. Langmuir isotherm model fitted the adsorption data better than Freundlich with a maximum adsorption capacity (q _m) for Cd(II) equal to 78 mg/g under the specified experimental conditions. The synthesized nanocomposite afforded effective extraction for Cd²⁺ ions from natural water samples and excellent reusability feature. This study declares the potential efficiency of a new clay/polymer nanocomposite as alternative for wastewater remediation.     

Effect of Fenton process on treatment of simulated textile wastewater: optimization using response surface methodology

A large portion of water is consumed during various textile operations thereby discharging wastewaters with pollutants of huge environmental concern. The treatment of such wastewaters has promising impact in the field of environmental engineering. In this work, Fenton oxidation treatment was engaged to treat simulated textile wastewater. Box–Behnken design and response surface methodology were employed to optimize the efficiency of Fenton process. Iron dose, peroxide dose and pH were considered as input variables while the responses were taken as chemical oxygen demand and color removal. A total of 17 experiments were conducted and analyzed using second-order quadratic model. The quadratic models generated for chemical oxygen demand and color removal efficiencies were validated using analysis of variances, and it was found that the experimental data fitted the second-order model quite effectively. Analysis of variances demonstrated high values of coefficient of determination (R ²) for chemical oxygen demand and color removal efficiencies with values of 0.9904 and 0.9963 showing high conformation of predicted values to the experimental ones. Perturbation plots suggested that the iron dosage produced the maximum effect on both chemical oxygen demand and color removal efficiencies. The optimum parameters were determined as Fe²⁺ dose—550 mg/L, H₂O₂ dose—5538 mg/L, pH—3.3 with corresponding chemical oxygen demand and color removal efficiencies of 73.86 and 81.35%. Fenton process was found efficient in treatment of simulated textile wastewater, and optimization using response surface methodology was found satisfactory as well as relevant. From the present study, it can also be concluded that if this method is used as pretreatment integrated with biological treatment, it can lead to eco-friendly solution for treatment of textile wastewaters.