File Name: adsorption and desorption of atrazine on carbon nano tubes .zip
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Carbon nanotubes, specially SWCNTs, are efficient and rapid adsorbents for ethylbenzene which possess good potential applications to maintain high-quality water. Therefore, it could be used for cleaning up environmental pollution to prevent ethylbenzene borne diseases. Ethylbenzene aromatic organic compound is important on material in the chemical process industries. This material is usually used as raw material in numerous chemical productions and also often as solvent in a wide variety of manufacturing processes [ 1 ].
Ignace Agani a , Jacques K. Osseni a , Esta A. E-mail: jacquesfatombi yahoo. Response surface methodology RSM coupled with composite central design CCD were used to optimize the effects of the four independent variables, pH, initial concentration of atrazine C 0 , bed depth H , and flow rate Q , which influence the adsorption process.
The obtained breakthrough curves were fitted with four mathematical models, Thomas, Bohart—Adams, Yan and Yoon—Nelson, in order to determine the limiting step of the mass transfer of the atrazine adsorption onto the composite.
A desorption study of the composite revealed the high reuse potential for MCHAC, thus, the prepared material could be used as a low-cost and efficient adsorbent for the decontamination of polluted wastewater. Activated carbon, chitosan and their composites have mainly been used as adsorbents for organic pollutants and heavy metals in wastewater. Thus, in order to solve the problem, research has been focused on the development of new materials for this purpose, including magnetic nanoparticles.
The use of magnetic-based adsorbents in wastewater treatment has received wide attention because magnetic nanoparticles are endowed with surface charges and can be easily separated from the reaction matrix using a magnet. However, activated carbon and chitosan mainly used for their development are of commercial origin, meaning that they contribute towards an increase in the cost of water treatment.
The composite was prepared via the coprecipitation of a FeSO 4 and FeCl 3 mixture, using activated carbon AC prepared from peanut shells, and chitosan CH extracted from local crab shells. Then, the adsorption potential of MCHAC was investigated on atrazine under a fixed bed column system.
The dynamics of the adsorption process were optimized by response surface methodology RSM coupled with central composite design CCD and the modeling of the breakthrough curves was performed using mathematical models. Then, a solution of 2. After 6 h of stirring at rpm, 10 g of activated carbon was introduced into the system.
The measured pH of the resulting mixture was in the range of 11— The textural parameters determined from Fig.
This suggests that the pores of the AC particles are clogged with magnetite nanoparticles and chitosan particles. Therefore, the high specific surface area of MCHAC suggests that it has better potential for adsorption. To better understand the model's suitability to the experimental results, graphs of the normal probability as a function of the residual values were plotted and the results shown in Fig.
Finally, the reliability of the fit of the quadratic model to the response values was investigated through the regression analysis of eqn E1. The results in Fig. It can also be seen that the FBU values increase with an increase in C 0 and the bed depth. These observations can be explained by the fact that at the beginning of the adsorption process with a low concentration of atrazine there is great availability of adsorbent surface for the adsorption to take place.
Moreover, the increase in the bed depth led to the increase in the specific surface area of adsorbent, which provided more active sites available for adsorption and justified the increase in the FBU values. In addition, the increase in the values of FBU with increasing in concentration of atrazine may be explained by the higher concentration gradient which occurred at a high initial concentration of atrazine, which then resulted in faster mass transfer through the bed depth of MCHAC. Furthermore, to optimize the experimental variables involved in the adsorption of atrazine, eqn E2 and E3 were used.
Received 14th September , Accepted 2nd November Fixed-bed experiments. The experiments were performed in glass columns with an internal diameter of 1.
A fixed amount of glass wool was inserted at the bottom of the column to serve as the support material for the adsorbent. The pH of the inlet atrazine solution was adjusted with HCl 0. The volumes of the effluents of atrazine were collected at regular time intervals at the bottom of the column. The residual concentration of atrazine in the effluent samples was quantified using a UV-Vis VWR spectrophotometer at a wavelength of nm.
Breakthrough curves were obtained by continuous monitoring of the process. Four independent variables, the C 0 initial concentration of atrazine , pH of the atrazine solution, H bed depth of the composite in the column , and Q flow rate of the solution were included in the RSM-CCD measurements. The experimental ranges of the four parameters were selected after the preliminary experiments.
Their values with units and symbols are given in Table 1. In this study, the Design Expert version 11 software was used to model the adsorption capacity at equilibrium q s and the FBU. Table 1 Characteristics of the experimental variables.
Variables Symbol Values Min. Table 2 Experimental data and predicted responses. Modeling of the breakthrough curves. The shape of the breakthrough curves is an essential characteristic for the description of the adsorption dynamics.
In order to model the breakthrough curves well, four mathematical models, Thomas, 30 Bohart—Adams, 31 Yoon—Nelson 32 and Yan, 33 were tested. Statistical analysis and model fitting. The results reveals an F -value of In addition, the significance that the coefficients have on the adsorption process was explored using the P -value Tables 4 and 5. In addition, the adjusted values of R 2 0. The difference between the adjusted and the predicted values of R 2 is less than 0. The high values of the ratios of Response surface and contour plots.
The effects of the four independent variables on the adsorption process were investigated through the surface curves displayed in Fig. It can be observed from Fig. The results also reveal that q s decreases with an increase in the pH and the flow rate Q.
The decrease in the q s values with an increase in the pH may be justified by the progressive appearance of the negative loads on the adsorbent surface, which result in a low interaction between the adsorbent surface and the atrazine molecules, and a decrease in adsorption capacity.
In addition, atrazine is a weak base with a p K a value of 1. Effects of the parameters on the breakthrough curves. The effects of pH and of initial concentration were studied at pH 5, 7 and 9 and atrazine concentrations of The results depict a decrease in breakthrough time t b , saturation time t s , adsorption capacity at breakthrough q b , adsorption capacity at saturation q s and FBU, suggesting that increasing the pH results in a decrease in the adsorption efficiency of atrazine.
In addition, it was revealed from Fig. Finally, gradual increases in q b , q s and FBU were also observed upon increasing the atrazine concentration. Similar results were reported by Homem, and Wernke et al. Table 6 Effects of the parameters on the breakthrough curves. Dynamic modeling of breakthrough curves.
To better describe the dynamic behavior of the adsorption process, the Thomas, Yan, Yoon—Nelson and Bohart—Adams mathematical models were used to fit the breakthrough curves. The results of the fitting and the calculated parameters are displayed in Fig.
All of the breakthrough curves are asymmetrical S-shaped curves, suggesting that the breakthrough curves are composed of two parts corresponding to two different mechanisms of the adsorption process.
Moreover, the adsorption capacity q Th values calculated using the Thomas model are slightly higher than the experimental q s values.
In addition, the values of the Thomas parameter k Th increased with an increase in pH and Q values and then decreased with an increase in H and C 0. This observation implies that the adsorption mechanism is not controlled by the mass transfer at the interface of the adsorbent. In addition, the adsorption capacity q Y values calculated according to the Yan equation are close to the q s values. This observation also shows that the Bohart—Adams model is a good fit to the experimental results.
Therefore, surface diffusion was determined as the rate-limiting step of the adsorption process. The results of this study suggest that all of the models tested can be used to describe the adsorption dynamics of the adsorption of atrazine onto MCHAC. Table 7 Model parameters. Desorption and regeneration study. The study of the adsorption and desorption of MCHAC was performed in order to determine the applicability and cost-effectiveness of the composite for use in water treatment applications.
The columns were regenerated over three cycles using 0. The results reveal the same trend with slight changes, suggesting that the composite can be regenerated over the three cycles tested. Furthermore, the results in Table 8 indicate a decrease in the saturation time t s from to min with HCl and from to min with NaOH.
In addition, a slight increase in the q s and FBU values was noted during the process. The q s values increased from The higher desorption efficiency of the composite with HCl and NaOH suggests the existence of a high affinity between the desorbing agents and the adsorbed atrazine molecules.
In addition, the desorption results shown in Fig. These observations suggest that the use of HCl solution as a column eluent could lead to a partial dissolution of the composite material during the desorption process.
These results are in accordance with those reported by Homem et al. R pred 2. R adj 2.
Current methods for preparing magnetic composites with carbon nanotubes MCNT commonly include extensive use of treatment with strong acids and result in massive losses of carbon nanotubes CNTs. In this study we explore the potential of taking advantage of the inherent magnetic properties associated with the metal alloy or oxide incorporated in CNTs during their production. The as-received CNTs are refined by applying a permanent magnet to a suspension of CNTs to separate the high-magnetic fraction; the low-magnetic fraction is discarded with the solvent. The collected MCNTs were characterized by a suite of 10 diffraction and spectroscopic techniques. After refinement using our method, the MCNTs show saturation magnetizations up to 10 times that of the as-received materials.
Ignace Agani a , Jacques K. Osseni a , Esta A. E-mail: jacquesfatombi yahoo. Response surface methodology RSM coupled with composite central design CCD were used to optimize the effects of the four independent variables, pH, initial concentration of atrazine C 0 , bed depth H , and flow rate Q , which influence the adsorption process. The obtained breakthrough curves were fitted with four mathematical models, Thomas, Bohart—Adams, Yan and Yoon—Nelson, in order to determine the limiting step of the mass transfer of the atrazine adsorption onto the composite. A desorption study of the composite revealed the high reuse potential for MCHAC, thus, the prepared material could be used as a low-cost and efficient adsorbent for the decontamination of polluted wastewater. Activated carbon, chitosan and their composites have mainly been used as adsorbents for organic pollutants and heavy metals in wastewater.
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Metrics details. Environmental behavior of pesticide in soils is a key current research focus. Studying the adsorption characteristics of pesticides in soils as a parameter for evaluating the risk of groundwater pollution by pesticides is commonly applied in agriculture. To provide a theoretical basis for environment risk assessment and pollution remediation, the thermodynamics and kinetics of the equilibrium of atrazine adsorption in the Three-Gorges Reservoir area were assessed and analyzed via batch experiments.
Carbon Nanotubes for Clean Water pp Cite as. Removing of wastewater pollutants by novel adsorption techniques is urgent as they are continuously defiling the limited freshwater resources, seriously affecting the terrestrial, ecosystems, aquatic, and aerial flora and fauna. Emerging carbon nanotube CNT -based adsorbent materials are effective for efficient handling of wastewater pollutants. This chapter describes the mechanisms of CNT, and its forces to host the wastewater pollutants.
Carbon Nanotubes. Pretreatment is often considered to be a fundamental step in the process of successful analysis of environmental pollutants, because it helps not only to achieve low detection limits but also to clean up the sample matrix. Solid phase extraction SPE is an effective sample handling method and is used as an enrichment technique when low concentrations of analytes need to be determined.
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