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Background and purpose: Nitrate is one of the most common chemical pollutants in groundwater in the world. Adsorption has been considered as an effective and efficient method of removing pollutants, particularly nitrate from aqueous solutions and so the aim of this study was to magnetization of the carbon nanotubes with zero-valent iron and using it as an adsorbent for the removal of nitrate from aquatic environments. Materials and methods: In this study, reduction method for converting divalent iron into zero-valent iron and co-precipitation method for iron particles deposition on carbon nanotubes was used. Characteristics of absorbent were analyzed by SEM (structural equation modelling), XRD (X-ray powder diffraction), and VSM (value stream mapping) techniques. In this study, the effect of the pH, contact time, mixer speed, temperature, adsorbent dosage and the concentration of nitrate was investigated by one factor at the time method and then was optimized. Results: The pH equal to 3, 60 min contact time, 200 rpm stirring speed and 1 g/l absorbent was obtained as the optimum conditions in the adsorption of nitrate. Investigating the isothermandkinetic models showed that the experimental data correlate to the Langmuir adsorption isotherm model (R2 > 0.997) and pseudo-second order kinetic (R2 > 0.993). The reaction thermodynamic study also expressed endothermic and spontaneous reaction. Conclusion: In optimal conditions, carbon nanotubes modified by zero-valent iron has well potential to quickly and effectively remove nitrate and simply be separated from the solution by the magnet due to its magnetic property.

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Background and purpose: Cadmium is a very toxic metal that have adverse effects on human health and aquatic environments even at low concentrations, therefore, efforts should be made to eliminate this metal from aquatic ecosystem. The aim of this study was to investigate the efficacy of L-cysteine functionalized single-walled carbon nanotubes in removing cadmium from aqueous environments. This study also assessed the role of some parameters such as pH, adsorbent dose, contact time and concentration of cadmium. Materials and methods: Single-walled carbon nanotubes were functionalized with L-cysteine. Then the optimum level of pH, carbon nanotubes dose, contact time, and cadmium concentration were determined during the adsorption process. The experimental data were compared with the Langmuir and Freundlich adsorption isotherm models. Results: qe increased when the pH level increased, while contact time and Cd concentration decreased by increase in the number of carbon nanotubes. The Langmuir adsorption model agreed well with the experimental data (R2 = 0.997). Efficiency of single-walled carbon nanotubes in optimal condition was 94.26%. Conclusion: The results showed that L-cysteine functionalized single-walled carbon nanotubes could be effective for the removal of cadmium.

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Background and purpose: Mercury is a toxic heavy metal which causes irrevocable intense nerve-recognition disturbance to human. Excess contact to mercury causes diseases like tremor, losing sensation, decreasing vision and hearing or growth. WHO recommended the most amount of mercury absorption about 0.3 mg per week and the most concentration in water about 1µg/L. The purpose of this study was to investigate the efficiency of Lcysteinefunctionalized single-walled carbon nanotubes (SWCNs) in mercury removal from aqueous solutions. Materials and methods: In this study, single-walled carbon nanotubes was used as absorbent. The effects of some parameters such as pH, absorbent dose, contact time and mercury concentration were assessed. All experiments have been done according to standard methods. The sample size was determined by Box-Benkan method. Results: The result showed that absorption rate increased by increasing of pH, contact time and mass CNTs dose. The Hg removal efficiency decreased by increasing of initial Hg concentration.The maximum and the minimum of absorption rate are 95 and 22 percent, respectively. ANOVA showed that RSM has a significant relationship for single-walled carbon nanotubes with linear conditions. Conclusion: The study demonstrated that SWCNT-Cysteine is a well absorbent for Hg removal from aqueous solutions Therefore, it can be effective for the removal of mercury from aqueous solutions.

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Background and purpose: Continuous input of antibiotics to the environment causes many problems such as antibiotic resistance in pathogenic microorganisms. Therefore, researchers are aiming to find solutions to reduce antibiotics in hospital effluents and polluted waters. Amoxicillin is an antibiotic which is widely used to treat infections. Due to inappropriate use it enters the wastewater and finally the environment in almost unmetabolized form. This study was conducted to evaluate the performance of multi-walled carbon nanotubes for Amoxicillin removal from aqueous solutions. Materials and methods: In this study the efficacy of multi-walled carbon nanotubes for the removal of amoxicillin was investigated in a batch system considering pH (10-4), ionic strength (0 to 0.1 mol/ L sodium chloride), and adsorbent dose (0.4 – 1.8 g /L). Finally, isotherms and kinetics of the adsorption was analyzed. Results: The results showed that the maximum removal of amoxicillin occurred at pH 8. Also, increase in the ionic strength decreased the removal efficiency while increase in the adsorbent dose increased the removal efficiency. The equilibrium adsorption isotherm data well fitted with Langmuir model (R2= 0.9108) and adsorption kinetics fitted with pseudo second order model. Conclusion: According to the results multi-wall carbon nanotubes could be assumed as an acceptable adsorbent for Amoxicillin removal in the aquatic solutions.

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Background and purpose: Contamination of drinking water with fluoride due to natural and human activities is a serious problem that threatens human health. Long-term and excessive consumption of water containing fluoride could lead to endocrine glands diseases and Alzheimer's disease. Adsorption process is an effective and popular method for removal of fluoride, so the purpose of this research was magnetizing multiwall carbon nanotubes with nano iron oxide and using it as an adsorbent for fluoride removal from aqueous solution. Materials and methods: Co-precipitation method used for synthesized magnetic nano composite and its characteristics were investigated by SEM, TEM, XRD and VSM techniques. The effect of independent variables such as contact time, pH, temperature, adsorbent dose and initial concentration on fluoride removal was analyzed by response surface methodology (box-Behnken design method) and ANOVA. Results: The optimum condition was obtained at pH= 3, 2g/L sorbent dosage in 2h contact time and 45oC temperature. Isotherms and kinetics results showed that the Langmuir model and pseudo-second order were correlated by data with R2>0.98 and R2>0.941, respectively. Thermodynamic values revealed that fluoride adsorption process was endothermic and spontaneous. Conclusion: In this study synthesized adsorbent was found efficient in fluoride removal (98.5% adsorption in optimal condition) and due to magnetic ability it can be easily separated from the samples by an external magnet. Therefore, it can be applied in removal of fluoride from drinking water.

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Background and purpose: Removal of emerging pollutants from water and wastewater is a great concern in environmental issues. In this study the Taguchi method as one of the major methods for experimental designs was used to assess the removal of atenolol from aqueous solution by multi-wall carbon nanotubes.

Materials and methods: In an experimental study in a batch system to investigate the factors affecting atenolol absorption (pH, contact time, absorbent dose, and initial concentration of atenolol) Taguchi design was used in four levels with L-16 matrix. The properties of the absorbent were determined using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The absorption isotherm models were analyzed by Design Expert 6.

Results: The optimum conditions for pH, contact time, MWCNT dose and initial concentration of atenolol to affect the absorption on multi-walled carbon nanotubes were 7, 20 minutes, (0.5 gr/l), and (10 mg/l), respectively. The removal efficiency and absorption capacity in optimum condition were 94.8% and 16.76 mg g^-1, respectively. The data was evaluated by absorption models such as Langmuir, Freundlich and Dubinin Radeshkevich. The equilibrium data was well fitted with Freundlich model (R²=0.93).

Conclusion: This study showed that multi-walled carbon nanotubes as an effective absorbent have a high potential to remove atenolol from water and wastewater.