جستجوی مقالات مرتبط با کلیدواژه "aqueous solutions" در نشریات گروه "محیط زیست"

In the present study, cypress cone raw biochar was modified using walnut peel extract under the chemical modification process and its performance optimization on nickel (Ni) removal in aqueous solutions was affected by various factors was evaluated using the RSM. Contrary to expectation, chemical modification caused a decrease in the specific surface area and a decrease in effective functional groups in Ni removal (functional groups containing oxygen and C-C) compared to the non-modified biochar sample. The investigations of Ni removal by modified biochar also showed a significant reduction of Ni removal by this adsorbent in the same conditions compared to the non-amended sample, so that the average amount of Ni removal in the same conditions in the non-modified adsorbent was 1.8 times more than modified biochar. The investigation of the factors affecting the removal of Ni in two modified and non-modified adsorbents showed that with the increase of the initial concentration of Ni, the removal of Ni had a decreasing trend; while with the increase of other factors, Ni removal showed a relatively increasing trend. The results of the present study show that the modification and engineering of biochars by the mentioned chemical method, with the effect of reducing the physical absorption (reduction the specific surface area) and chemical adsorption (reduction of the intensity of the active groups affecting the adsorption), caused the reduction of Ni removal efficiency compared to the raw sample, which challenges the hypothesis of constant increase of heavy metal removal efficiency by chemical modification of biochar.

In recent years, research on the widespread use of biodegradable polymers, such as sodium alginate (SA), in removing pollutants from water sources has shown significant growth. The present study aims to evaluate the efficiency of SA hydrogels cross-linked with ferric chloride (for mechanical strength) in optimizing the removal of nickel (Ni) from aqueous solutions. Various factors, including Ni initial concentration, solution pH, amount of adsorbent, and contact time, were considered using response surface methodology (Box-Benken model). Based on the results of FTIR and SEM analyses, activated SA hydrogels were found to have hydroxyl and carboxyl functional groups, and their surface morphology was non-flat and prominent. The Ni removal values in the presence of SA hydrogels varied, with the minimum and maximum removal percentages being 53.39% and 85.43%, respectively. Increasing the initial Ni concentration resulted in a decreasing trend in Ni removal, while increasing contact time, solution pH, and amount of adsorbent led to an increasing trend in Ni removal. The evaluation of the data obtained from Ni removal using the Box-Benken model showed an accurate prediction (R2 higher than 0.98%) in optimizing Ni removal from aqueous solutions in the presence of SA. The possible mechanisms of Ni removal by SA hydrogel were identified as the formation of Van der waals bonds (physical adsorption), interaction with carboxylate anions, chelate formation between Ni ions and hydroxyl functional groups, and electrostatic interactions (due to the negative surface charge of SA). Overall, the results of this study demonstrate that SA has a suitable ability to remove Ni from aqueous solutions. However, future studies should investigate, compare, and integrate other activation methods, such as physical activation (combination with inorganic substances) and chemical activation (surface grafting) on the SA polymer, to improve the removal efficiency of heavy elements using this polymer.

Ibuprofen is one of the most widely used drugs in the world, which affects the health of living organisms by causing pollution in water sources. Therefore, this study was conducted with the aim of determining the effectiveness of modified carbon of straw and sesame stubble in removing ibuprofen from aqueous solutions. For this purpose, ammonium chloride, zinc chloride, and phosphoric acid were used to optimize the adsorbent. Also, the changes in the absorbent surface and its characteristics were studied using a scanning electron microscope (SEM) and infrared spectroscopy (FTIR) technique. After determining the optimal conditions of pH variables, contact time, temperature, and adsorbent dose, the surface adsorption process was investigated under three Langmuir, Freundlich, and Dubinin-Radoshkevich models. On the other hand, first-order and pseudo-second-order kinetic models were used to process the adsorption data. The results showed that the surface adsorption process followed the Freundlich isotherm model pseudo-second-order kinetics. pH, contact time, initial concentration of ibuprofen, and optimal adsorbent dose were 3, 120 min, 50 mg/l, and 0.10 g/l respectively at 25°C. The results of this study showed that agricultural residues such as straw and sesame stubble can be used as effective and cost-effective adsorbents to remove the remaining pharmaceutical compounds from aqueous solutions.

Fluoride is one of the developed compounds that can enter water resources in different ways. The World Health Organization has recommended its maximum permissible concentration in drinking water of 1.5 mg/l so that its concentration exceeding the permissible limit can be harmful to the health of living organisms and ecosystems. The aim of this study was to determine the efficiency of activated carbon modified by the thermo-chemical method from oak fruit in fluoride removal. This research was conducted in a discontinuous system on a laboratory scale, and for this purpose, the effect of effective parameters such as time, pH, concentration, adsorbent dose, and other factors was investigated. The results of the experiments showed that the maximum amount of removal takes place during 90 min, pH=3, adsorbent dose of 0.1 g/l, and pollutant concentration of 50 mg/l. The results of the synthetic models showed that the Freundlich model with the coefficient of determination (R2=0.863) is a better model than the Langmuir model with the coefficient of determination (R2=0.736) to describe the synthetic behavior of the absorber. Until now, most absorption methods have been performed to remove the pollutant concentration of 30 mg/l. In the current study, with the input pollutant concentration of 50 mg/l, it can be stated that the activated carbon modified from the oak fruit is a cheap, efficient, and effective adsorbent. It is considered available to remove fluoride from aqueous solutions.

The discharge of heavy metals from various industries has negative effects on the environment and living organisms. Conventional technologies for removing heavy metals from aqueous solutions are not economically viable and, in addition to not being effective at low concentrations of metal ions, produce large amounts of chemical sludge. Nickel's biological uptake by living, inactive, microbial or plant-derived biomass is an alternative and innovative technology to remove this contamination from aqueous solutions. It has high absorbency and reabsorption capacity.
Investigation

In this research, in a review study with the aim of introducing different types of microbial and plant-derived biological adsorbents in order to remove nickel from aqueous solution and reveal the adsorption capacity of each adsorbent, articles found between 2001 and 2020 have been used.

Research has shown that the use of these biomass as a biological adsorbent for the removal of nickel in aqueous solution is a promising and environmentally friendly prospect.

Based on thermodynamic studies in most nickel biosorption processes with different adsorbents, the value of ∆G° is negative and the value of ∆S° is positive due to the increase of random collisions between solid and solution during the process.

One of the most common methods for removing pollutants from aqueous solutions is adsorption. Currently, research on cheap adsorbents with high potential for removing pollutants is economically important. In this study, the efficiency of nano-chitosan was investigated for toluene removal from aqueous solutions by adsorption method in a laboratory scale. The effect of different pH parameters, initial concentrations of toluene, absorbent dose and contact time were investigated. Toluene concentration values ​​were analyzed by UV-Vis Array spectrophotometer Model Photonix Ar 2015 at 206 nm. The results showed that the amount of toluene adsorption increased with increasing pH, increasing the dose of adsorbent and increasing the contact time by inverse ratio and increasing the concentration of direct ratio. According to the results, the optimal amount of toluene adsorption at pH=5, concentration of 70 mg /L, absorbent dose of 0.01 g L, and contact time of 5 minutes were determined. The results of this study showed that nano-chitosan adsorbent has high efficiency in toluene adsorption from aqueous solutions.

Today, heavy metals are used in many important industries and technologies, which result in the production of polluted industrial effluents that are harmful to human health and the environment. The aim of this study was to investigate the efficiency of cadmium removal from aqueous solutions using a suitable new adsorbent for manganese dioxide nanoparticles.

In order to do this, manganese dioxide nanoparticles were synthesized using cathode electrochemical deposition method and the effect of pH, contact time, MnO2 concentration and cadmium concentration on cadmium removal efficiency were investigated in a batch system. Scanning electron microscope (SEM), XRD and FT-IR were used to identify the characterization of synthesized manganese dioxide nanoparticles.

SEM results showed that the diameters of the particles were 30 to 50 nm. The other results showed that the optimum pH value for adsorption was 7. Contact time enhancement and the concentration absorbent are omitted because they make the efficiency boost. The adsorption capacity increased and the adsorption efficiency slightly increased with increasing concentration of cadmium and reducing the concentration adsorbent. Experimental data were shown the best to follow Langmuir model. Langmuir adsorption capacity, was found to be 42/016 mgg−1. The results also showed that the absorption of cadmium was obeyed from pseudo-second-order kinetic model. The overall results showed that the use of manganese dioxide nanoparticles was a suitable method with high potential for removal of cadmium from aqueous solutions.

Nowadays, rapid development of the chemical industry has brought about environmental pollution, a serious threat, as a result of the entry of organic and inorganic chemicals, as well as heavy metals. Surface absorption by the use of biological polymers is a novel environmentally friendly technology for reducing and removing heavy metals from industrial wastewater. The objective of this study was to investigate the performance of lignocellulose nanofiber (LCNFs) adsorbents in the removal of Cu(II) from aqueous media. The test conditions are considered for two completely identical adsorbents. In the batch system, parameters of pH (4-8), adsorbent dosage (0.1- 0.5 g/l), contact time (15-120 min), Cu(II) initial concentration (5-50 mg/l), and temperature (15-40 °C) were studied. The results were analyzed by one-way ANOVA and Duncan's tests for significant evaluation of changes in parameters. Results showed that the highest percentage of removal of Cu(II) (99.8%.) for LCNFs at pH 7, Cu(II) concentration of 10 mg/l, adsorbent dosage of 0.3 g/l, contact time of 60 min at temperature of 25 °C was obtained. This study showed that LCNFs adsorbents are considered as an optimal adsorbent for removal Cu(II) by removing more than 98% of Cu(II) from aqueous solutions

Nowadays, one of the most important environmental pollution is heavy metals industrial wastewater. Among the various types of heavy metals, chromium is one of the hazardous and toxic environmental pollutants. In order to prevent damage caused by chromium, it seems essential to prevent its entrance to the environment. The purpose of this study was modelling chromium removal using iron oxide nanoparticles through artificial neural network model for estimating the best removal Cr(VI) model. The optimum conditions (more than 90% removal efficiency) achieved were at pH=3, initial concentration of Cr = 10 mg/L; dosage of Fe2O3 = 1 g/L; contact time = 60 minutes, and temperature =25 . After backpropagation (BP) training, the ANN model was able to predict adsorption efficiency with a tangent sigmoid transfer function (Tansig) at hidden layer with 11 neurons and a linear transfer function (Purelin) at out layer. The Levenberg-Marquardt algorithm (LMA) was applied, giving a minimum mean squared error (MSE) for training and cross validation at the ninth place of decimal. The high correlation coefficient (R2ANN = 0.996) between the model and its closeness to the experimental coefficient (R2Exp = 0.998) showed that the model is able to predict the removal of Cr(VI) from aqueous solutions by iron oxide nanoparticles.

The objectives of this research were to synthesize manganese dioxide nanoparticles and determine their efficiency in the removal of lead from aqueous solutions. Consequently, manganese dioxide nanoparticles were synthesized by the cathode electrochemical deposition method and the effect of pH, contact time, lead concentration and quantity of nanoparticles on lead removal efficiency were investigated through the batch system. A scanning Electron Microscope (SEM), XRD and FTIR were used to characterize the synthesized manganese dioxide nanoparticles. SEM results showed that the diameter of the particles is 30-50 nm and the results also showed that the optimum pH value for adsorption was 6. The adsorption capacity increased and the adsorption efficiency decreased with increasing concentration of lead ions and by reducing the amount of adsorbent. In a study of the adsorption isotherm, experimental data from the Langmuir model to follow. The data obtained in this study showed that the absorption of lead absorption kinetics model obeys the model of Hu and colleagues. The overall results of this study showed that the use of manganese dioxide nanoparticles was a suitable method with high potential for the removal of lead from aqueous solutions.

Environmental pollution by heavy metals is one of the most commonly-encountered problems in many areas in which biological controls have not been implemented. As these metals are non-biodegradable, they remain in the nature for a long time, and through deep percolation into underground water they can cause degradation of ecosystems. The uptake of these elements by plants and their inclusion in the chain of human and animal food is a great risk for the environment and the human being health. Due to non-biodegradable property of Cadmium and some other toxic heavy metals, these metals remain in the environment for a long time. Cadmium is one of the most toxic heavy metals and it has been reported to cause renal dysfunction, hyper-tension, lung insufficiency, bone lesions, cancer, and etc. The principal industrial sources of Cd in the environment are electroplating, smelting, alloy manufacturing, pigments, plastic, battery, mining and refining processes. In the recent years there have been some reports on the use of inorganic absorbents for separating and removing heavy metals from aqueous solutions. Due to the availability, cost-effectiveness, stability against oxidation and reduction conditions and the possibility of recycling, inorganic adsorbents are economically viable. Traditional inorganic adsorbents with a low surface area lose their ability to absorb. Thus, making high capacity adsorbents for fast and easy removal of contaminants is a necessary step. One of the outstanding characteristics of fast-emerging nanotechnology studies is the high surface area to volume ratio of nanomaterials. Because of these outstanding features and other unique properties, nanoparticles may have potential to absorb pollutants from contaminated environments. So far, many technologies to remove heavy metals from aqueous solutions including chemical precipitation, ion exchange, membrane technologies, electrodialysis, and biosorption have been developed. Many of these methods have disadvantages such as high cost of operation, the high sludge, and secondary contamination. Nanoparticles with extremely small size and high ratio of surface-area to volume, provide better kinetics for the adsorption of metal ions from aqueous solutions. Hydroxyapatite as one of the major components of bones and teeth are widely used in biomedical and dental applications, drug delivery, and waste water remediation because of biocompatibility, low solubility, ion exchange and high sorption capacity of heavy metals. Magnetic separation technology as an efficient, fast and economical method for separating magnetic materials has been widely used in textile, biology, and environmental protection. In this study, magnetic hydroxyapatite nanoparticles were synthesized by co-precipitation method. The nanoparticles were characterized by x-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared spectroscopy (FT-IR), Vibrating Sample Magnetometer (VSM). Finally, the produced nanoparticles were used as adsorbents for the removal of cadmium ions from aqueous solutions. In batch experiments, the effects of pH, evaluation time and initial concentration of Cd2+ ions on adsorption were investigated. FeCl2·4H2O, FeCl3·6H2O, NH4OH (25%), Ca (NO3) 2·4H2O and (NH4)2HPO4 were purchased from Merck. All the solutions for the metal adsorption experiments were prepared using their nitrate salts. The amount of FeCl2·4H2O (1.85 mmol) and FeCl3·6H2O (3.7 mmol) was dissolved in 30mL of deoxygenated water under nitrogen atmosphere at room temperature, and then 10mL of NH4OH solution was added to the resulting solution under vigorous mechanical stirring (300 rpm). A black precipitate was produced instantly. After 15 min, up to 50mL of Ca(NO3)2·4H2O (33.7 mmol) and 50mL of (NH4)2HPO4 (20 mmol) solutions whose pH were all adjusted to 11 were drop wise added, simultaneously to the obtained precipitate solution for 30 min with mechanical stirring. The resulting puce suspension was heated at 110 ◦C for 2 h and then the mixture was cooled to room temperature and aged for 24 h without stirring. The obtained precipitate was separated by a magnet, washed repeatedly with deionized water till neutrality, dried in the drying oven at 110◦C, and grinded with mortar. The final products were the prepared magnetic hydroxyapatite nanoparticles adsorbents. The adsorption behavior of the magnetic hydroxyapatite nanoparticles for Cd2+ions was investigated by means of the batch experiments at 24±1°C. A known amount of magnetic hydroxyapatite nanoparticles was mixed with 50 mL of the corresponding Cd2+ solution over a period of time on a shaker at 150rpm. After that, the aqueous phase was separated by magnetic decantation; the concentration of Cd2+ in the solution was determined by using an atomic absorption spectrometer. In order to determine the optimum of pH, 0.05g of magnetic hydroxyapatite nanoparticles were added to 8 flask containing cadmium and under different pH conditions, the removal efficiency of cadmiumions by the adsorbent was detected. To evaluate the optimum dosage of magnetic hydroxyapatite nanoparticles adsorbent, 3–10 mg of freshly prepared magnetic hydroxyapatite nanoparticles was added to 50.0mL of aqueous solution containing 50.0mg/L Cd2+. The results showed that increasing the amount of adsorbent, the adsorption efficiency of Cd2+ due to increased absorption of available sites, has increased the effect of contact time on the adsorption of Cd2+ by magnetic hydroxyapatite nanoparticles (pH of the solution: 5.5, amount of adsorbent: 0.1g, Cd2+ concentration 50 ppm; temperature: 25±1°C). Sorption isotherms were obtained by equilibrating magnetic hydroxyapatite nanoparticles with metal solutions of different initial concentrations: 10-300 mg/l for 30 min. After separation, the final concentrations of metal in the solutions were measured. The adsorption capacity was calculated according to the following equation: qe = (C0 − Ce)V/m The removal efficiency of lead ions was calculated by the difference of lead ion concentrations in aqueous solution using the equation expressed as follows: R% = (C0 – Ce)/C0× 100 Where, qe (mg/g) is the amount of lead ions adsorbed onto the unit amount of the adsorbent, C0 (mg/L) is the initial lead ion concentration, Ce (mg/L) is the final or equilibrium lead ion concentration, V (L) is the volume of the solution, and m (g) is the adsorbent weight in dry form. The Langmuir and Freundlich models were used to describe the relationship between the absorbed amount of Cd2+ and its equilibrium concentration in solution. To determine whether the Cd2+ adsorption process by magnetic hydroxyapatite nanoparticles is favorable or unfavorable for the Langmuir type adsorption process, the isotherm shape can be classified by a term “RL”. RL values are ranged from 0 to 1 and indicate favorable adsorption, while RL >1, RL =1,and RL =0 indicate unfavorable, linear, and irreversible adsorption isotherms. Phase composition of the samples were characterized using a X-ray diffractmeter (XRD, Model pw-18/40, Philips, Germany) with CuKα (λ = 1.5418 Å) incident radiation over the 2θ range of 10–80◦ at room temperature with a step size of 0.02◦. The morphology of particles was investigated by scanning electron microscopy (SEM, Model VEGAII, XMU, Tescan, Czech Republic). To study the chemical structure of samples, Fourier Transform Infrared spectroscopy (FTIR, Model: EQUINOX55, Bruker, Germany) was used. For this, the samples prepared from 1:80 magnetic hydroxyapatite nanoparticles -KBr mixtures (by weight) were compacted into pellet form and then scanned from 4000 to 400 cm−1. The magnetization measurements were performed at room temperature using vibrating magnetometer. The concentration of Cd2+ in the solution was determined by using an atomic absorption spectrometer (Analytic jena- verio6). In this study, magnetic hydroxyapatite nanoparticles were synthesized by co- precipitation method, and the adsorption potential of nanoparticles for the removal of Cd2+ from aqueous solutions was investigated. The experimental results confirm that this adsorbent has the potential application for removal of Cd2+ from aqueous solution. The nanoparticles were characterized by x-ray diffraction, Field emission scanning electron microscopy, FTIR, and vibrating sample magnetometer. The effect of contact time, initial metal ions concentrations, pH, adsorbent dosage was discussed. The XRD patterns of samples confirm the hexagonal structure of hydroxyapatite and tetragonal structure of maghemite. This pattern indicates that the diffraction peaks are in agreement with the standard card (0566-074-01 ICSD) of hydroxyapatite and (0566-013-01 ICSD) of the tetragonal of maghemite. FESEM image of the nanoparticles showed almost spherical shape. The average size of nanoparticles was 19±2.FTIR spectroscopyreveals expected bondsformation. Magnetic properties of nanoparticles prepared at room temperature were studied in the range of 10000 ± Oe. Hysteresis curves of nanoparticles showed that the saturation magnetization and coercivity of the nanoparticles was 2.8 emu/g and 0 Oe, respectively. The nanoparticles indicate super-paramagnetic behavior. The super-paramagnetic property of the magnetic hydroxyapatite nanoparticles is critical for their application in industrial catalysis, environmental protection, biomedical and bioengineering field, which prevents them from aggregation and enables them to re-disperse rapidly when the magnetic field is removed. Finally, the produced nanoparticles were used as adsorbents for the removal of Cd2+ from aqueous solutions. In batch experiments, the effects of pH, evaluation time, adsorbent dosage and initial concentration of Cd2+ ions on adsorption were investigated. The highest removal efficiency of Cd2+ was in the range pH = 5-7. The removal efficiency increases with time in the first 30 min. Then, the adsorption curve reached equilibrium after this time. Removal efficiency increased as the adsorbent dosage was raised. When a dosage of 0.1 g was used, the removal efficiency reached 96%, indicating that the composite adsorbent magnetic hydroxyapatite nanoparticles showed strong affinity to Cd2+. The adsorption was relatively fast and the equilibrium was established within 30 min to be considered the adsorption isotherm data could be well described by Longmuir equation. The RL values in this study were in the range from 0.045 to 0.488 which indicated the favorable adsorption between Cd2+ and magnetic hydroxyapatite nanoparticles sorbent. Maximum adsorption capacities of Cd2+ were 84.746 mg/g. The results of adsorption experiments indicated that magnetic hydroxyapatite nanoparticles have high adsorption efficiency with short reaction time (30 min) and can be very effective to remove Cd2+ ions from aqueous solution. The most prominent advantage of prepared magnetic hydroxyapatite nanoparticles adsorbents with super-paramagnetism and adsorption capacities was the separation convenience from aqueous solutions.