جستجوی مقالات مرتبط با کلیدواژه « desorption » در نشریات گروه « علوم پایه »

Carbonization of Zea mays roots at 600˚C in the presence of nitrogen atmosphere and its activation at 800˚C under the hydraulic environment for an hour was used for mercury adsorption studies. Activated carbon (AC) was characterized by P-XRD, Raman, SEM, EDX, BET, and pH methods. By the inductively coupled plasma-mass spectrometer technique, mercury adsorption on AC was investigated under optimum conditions (at a pH of 5, 1mg/mL of adsorbent, 10 ppm of mercury, and 60˚C for 60 min). Evaluation of the statistical parameters for non-linear isotherm and kinetic models has disclosed that mercury adsorption on AC obeyed a pseudo-first-order kinetic model and Freundlich adsorption isotherm which was further confirmed by the Sips isotherm at equilibrium. The surface area of AC is 422 m2/g and has shown an adsorption capacity of 40.8 mg/g mercury and 99.43% removal efficiency. The dimensionless separation factor (RL) was 0.018 which pronounces favorable adsorption of mercury. The larger C value (7.3675 mg/g) and not passing the plot through the origin (R2 =0.9872) in Web Morris intraparticle diffusion model evidenced that IPD is not only rate-limiting step and other kinetic models (PFO) were also involved in the mercury sorption on AC. Desorption experiments were carried out in warm water and the percentage of mercury that has been restored was 6% due to the quasi-chemical bond between AC and mercury.

Heavy metal pollution in aquatic environments has increased significantly in the last few decades. Therefore, different technologies have been used to deal with this problem. In these technologies, different adsorbents are used to adsorb and separate heavy metals from the aqueous medium. In this regard, the use of new technologies such as nanomaterial technology which uses nanomaterials as adsorbents with the potential for adsorption capacity and fast recovery and low cost, especially magnetite nanoparticle adsorbents, has provided efficient and cost-effective solutions for the extraction and removal of heavy metals from water. In the present study, the separation of vanadium (V) in an aqueous medium was studied using an adsorbent of magnetite nanoparticles that was successfully synthesized by the co-precipitation method. The synthesized nanoparticles were tested without functionalization to remove vanadium. The maximum adsorption percentage of vanadium by non-functionalized magnetite nanoparticles was 99.6 percent in optimum conditions: pH equal to 3.5, at ambient temperature (20 °C), contact time 30 minutes, 5000 mg/L adsorbent amount, and 50 mg/L initial concentration of vanadium (V). The Langmuir, Freundlich, and Temkin isotherm models were evaluated for the vanadium adsorption process. It was observed that the Langmuir isotherm fitted better onto the laboratory data than other models. The kinetics of the experiment showed that the data obtained were more consistent with the pseudo-second-order kinetic model.

MicroPlastics (MPs) are plastic materials of micro-size dimension, often between the ranges of 1μm to 5mm. MPs are potential carriers that can adsorb metal ions in aquatic environments due to their specific surface areas. MPs and their associated contaminants can reach humans in many ways and are found in drinking water sources, foods, and beverages. The metal ions associated with MPs on their surfaces can desorb into the food materials and enter humans. The current research investigates the physicochemical parameters (pH, temperature, time, and type of plastic) affecting the desorption of metal ions from MPs into aqueous solutions using Inductively Coupled Plasma-Mass-Spectrometry (ICPMS). The MP surface characterization was studied using Fourier Transform Infrared (FT-IR) spectroscopy, X-Ray Diffraction (XRD), and The Brunauer-Emmett-Teller (BET) analysis. An experiment was conducted on three metal ions Lead, Cadmium, and Chromium on PET (polyethylene terephthalate), PP (polypropylene), PS (polystyrene), and PVC (polyvinyl chloride). In this work, PP showed the highest desorption efficiency, while PVC was the lowest one. Acidic pH 3.0 favored the desorption process and with an increase in temperature and time of contact with metal ions, the desorption efficiency also increased. The Scanning Electron Microscopic (SEM) characterization of MPs disclosed the presence of wrinkles and pits which encouraged both adsorption and desorption. The BET analysis revealed the role of high specific surface area (10.6±0.3 m2/g) and higher total pore volume (Vtotal) 1.58±0.09 cm3/g in significant adsorption and desorption of metal ions on PP.  The study findings provide a better perception of the desorbing efficiency of metal ions in the surrounding environment and the optimal conditions favoring this process.

The rubber product manufacturing industry generates large volumes of wastewater containing on average 10 ppm of zinc. Presently, zinc is removed via a chemical precipitation process generating hazardous precipitate that requires secure disposal. This study evaluated the removal of zinc through adsorption on Palm Shell Activated Carbon (PSAC) and subsequent desorption in hydrochloric, nitric (0.1 and 0.2 M), and citric (0.2 and 0.5 M) acids to produce solutions for the electrodeposition of zinc to achieve the permissible discharge level of 2 ppm.  The highest desorption efficiency was achieved using HCl. Cyclic Voltammetry (CV) was applied to determine the reduction potential of zinc in desorption solutions. The presence of KCL and a buffer solution improved the electrodeposition of zinc. The chloride-based solution showed the best electroreduction behavior of zinc with a well-defined reduction peak as compared to the nitrate and citrate-based solutions, with a wider reduction peak and no peak, respectively. The chloride-based solution, selected for theelectrodeposition experiments, showed 64 % reduction in zinc concentration within 10 min. The prolonged to 30 min electrodeposition resulted in only 7 % of further increment. Overall, the obtained results confirm the feasibility of zinc removal through the electrodeposition from the adsorption-desorption solution, which provides an effective alternative to the currently industrially used chemical precipitation method.

The presence of heavy metals in water sources is worrisome because heavy-metal pollutants are associated with severe health problems. The resultant health challenges as a result of heavy metal pollution have necessitated the removal of these pollutants from wastewater before being discharged into the environment. This research was carried out to investigate the potentials of avocado pear (Persea americana) seed coat as biosorbent of lead(II) and cadmium(II), in single and binary metal systems, from aqueous solutions. Biosorbent particle sizes and dosage were varied in the study. Desorption of biosorbed metal ions was studied using sodium salt of ethylene diaminetetraacetic acid (EDTA) and hydrochloric acid (HCl). Biosorbent of 106 µm particle size gave the best uptake of lead and cadmium from aqueous solutions than those of 850, 1180, 1400 and 2000 µm particle sizes. Biosorption of lead (II) and cadmium(II) increased with an increase in biosorbent dosage (up to threshold dosage). The uptakes of lead(II) and cadmium(II) in single systems are higher than those of binary systems. Biosorption capacities of lead(II) were higher than those of cadmium(II) for both single and binary systems. The observation could be linked to low hydration energy of lead(II) compared with that of cadmium(II). Biosorbed lead(II) and cadmium(II) were desorbed using 1.0 mol/L EDTA (for single system) and 1.0 mol/L HCl (binary system). Lead and cadmium ions were easily desorbed from single metal system unlike binary system. In overall, the avocado pear biosorbent could be used for treatment of wastewater contaminated with lead(II) and cadmium(II).

This paper explores the adsorptive properties of CaF2 nanoparticles for the removal of Pb(II) and Zn(II) from aqueous solutions and their selective recovery. CaF2 nanoparticles were synthesized by a facile one-step reaction and characterized by N2 physisorption at 77 K, XRD, and TEM. The adsorption of Zn(II) and Pb(II) fits well with Elovich and Langmuir isotherm models, respectively. Kinetic data are well described by the pseudo-second-order model. Our results show that Zn(II) and Pb(II) could be totally and selectively desorbed with HCl solution (0.01 M). The results of the competitive adsorption and desorption of Pb(II) and Zn(II) show that Zn(II) is desorbed before Pb(II) leading to a good separation. The desorption yield reaches 89% for Zn(II) and 95% for Pb(II), which opens the route to regenerate the adsorbent for other cycles.

Polycyclic aromatic hydrocarbons (PAHs), abundant in mixed contaminant sites, often coexist with heavy metals. The fate and remediation of PAHs depend heavily on the sorption and desorption behavior of these contaminants. The sorption behavior can in turn be highly affected by certain soil components and properties, such as soil organic matter (SOM) and the presence of heavy metals. Through review of the literature focused on research from 2006 to 2018, this paper discusses interactions, challenges, influencing factors and potential synergies in sorption/desorption of mixed PAHs and heavy metal contamination of soil. The presence of either natural organic matter or heavy metals can enhance the sorption capability of fine soil, retarding the PAHs in the solid matrix. The co-existence of SOM and heavy metals has been reported to have synergistic effect on PAHs sorption. Enhanced and surfactant desorption of PAHs are also affected by the presence of both SOM and metals. Remediation techniques for PAHs removal from soil, such as soil washing, soil flushing and electrokinetics, can be affected by the presence of SOM and heavy metals. More detailed studies on the simultaneous effects of soil components and properties on the sorption/desorption of PAHs are needed to enhance the effectiveness of PAHs remediation technologies.

Four diverse chlorides layered double hydroxides with diverse ratios, i.e. Mg-Al (3:1), Mg-Al (4:1), Zn-Al (4:1), and Zn-Al (3:1) LDHs, were prepared to evaluate their efficiency and selectivity towards nitrate removal from aquatic solutions. A batch experiment was done at the initial nitrate concentration of 5-1000 mg/L, pH 5 to 12, and contact time of 5-180 min. Isotherms of nitrate adsorption on LDHs, soil and soil-LDH mixtures were studied. Kinetics of adsorption, temperature effect, nitrate adsorption in nitrate adsorption, simulated soil solution and desorption on Mg-Al-LDH (4:1) were measured. At an optimum speed of 250 rpm, pH value of 7 and adsorbent dosage of 2 g/L, the amounts of nitrate adsorption on Mg-Al- LDH (3:1) and Mg-Zn-LDH (3:1) and also on Mg-Al- LDH (4:1) and Mg-Zn-LDH (4:1) were obtained after 30 and 60 min, respectively. Isotherm studies indicated that nitrate adsorption on soil, soil-LDH mixture, and LDH fitted Langmuir linear isotherm. The highest nitrate adsorption on Mg-Al-LDH (4:1) and a mixture of soil-Mg-Al-LDH (4:1) were 188.67 and 107.52 mg/g, respectively. Among the studied kinetic equations for nitrate adsorption on Mg-Al-LDH (4:1), the pseudo-second-order with R2=0.998 had the best fitness. Negative values of ∆H in different nitrate concentrations indicated the exothermic process of nitrate adsorption on Mg-Al-LDH (4:1). In the presence of other anions, Mg-Al-LDH (4:1) removed nitrate preferentially. Moreover, Mg-Al-LDH (4:1) could exchange nitrate 20 times in different concentrations with no reduction in its adsorption capacity.

Adsorption of Chromium ions (VI) and (III) in aqueous solution was investigated using activated carbon prepared from olive wastes, by one step physical activation with steam. After adsorbent material characterization using adsorption capacity of methylene blue, iodine and phenol, BET surface area, Fourier Transform InfraRed (FT-IR) spectroscopy, pHpzc, surface functions based on the Boehm method and, Scanning Electron Microscopy (SEM), the effect of different parameters (initial pH, absorbent dosage, initial concentration of solutes, time) on the adsorption of chromium ions were carried out in a batch system. The obtained activated carbon has a large specific surface area of 1050,9 m2/g and good adsorption capacity for iodine (1017 mg/g) and methylene blue MB (349 mg/g), which confirm that its structure is essentially composed of micropores (61 % of the surface) and mesopores. It has a basic chemical nature. Experimental results showed that the adsorption capacity of the prepared activated carbon was strongly dependent on solution pH. It was found that the initial pH of 2.0 was most favorable for Cr(VI) adsorption, and basic pH was best for Cr(III) removal. The adsorption process was studied using two kinetic models (pseudo-first order and pseudo-second order) and three functions isotherms (Langmuir, Freundlich, Temkin). The results showed that the adsorption process follows the pseudo-second order kinetics and the adsorption data were found to agree with the Langmuir isotherm model. Maximum adsorption capacity for Cr (VI) was 74,9 mg/g at pH 2, and 14,3 mg/g at pH 9 for Cr (III), and was comparable to results reported by other researchers working on activated carbon prepared from various solid wastes. Temperature effect was determined using the thermodynamic parameters. Negative values of ΔH0 and ΔG0 proved the feasibility of the adsorption process with its spontaneous and exothermic natures. Tests of desorption were performed in three different media: neutral (distilled water), acidic (2N hydrochloric and acetic acid solutions) and alkaline (2N NaOH solution). The magnitudes of desorption efficiency in the acetic acid medium were 94% and 71% for Cr(VI) and Cr(III) respectively.

This paper discusses the biosorption of Ni(II) ions from aqueous solutions by Bacillus sphaericus biomass. The biosorption process was affected by the solution pH, biomass concentration, contact time, temperature and initial Ni(II) concentration respectively. The sorption kinetics and equilibrium data were described well with the pseudo-second order kinetic model and the Freundlich isotherm model. The maximum monolayer biosorption capacity value of Bacillus sphaericus biomass for Ni(II) ions was calculated at 55.55 mg/g using the Langmuir isotherm model. The thermodynamic study shows the Ni(II) biosorption was spontaneous and exothermic in nature. The change in heat of sorption (ΔHo) and the isosteric heat of sorption (ΔHr) values indicate the physical sorption as the predominant mechanism for Ni(II) biosorption. The Ni(II) ions were recovered effectively from Bacillus sphaericus biomass using 0.1 M HNO3 and can be recycled. FTIR results showed that carboxylic and amine groups of Bacillus sphaericus cells were responsible for Ni(II) binding.

The potential of six economically cheap agricultural waste materials, viz. rice husk, betel nut peels, sugarcane molasses, tea waste, mustard oil cake and saw dust, was investigated for copper and lead removal from aqueous solutions under batch and continuous conditions. The effect of pH, contact time, sorbent dose and initial metal ion concentration on the uptake of copper and lead was first examined in batch mode. Rice husk was found to be the best among the tested biosorbents with a maximum removal of 72.17 % and 85.87 % for copper and lead, respectively. The batch sorption data correlated well with SIPS, Redlich- Peterson, Freundlich and Langmuir isotherms models. Heavy metal sorption kinetics was best explained by the diffusion based second order kinetics model. Fourier transform infrared analysis of rice husk, before and after heavy metal sorption, revealed the involvement of mainly hydroxyl, amine, and carboxyl functional groups in lead and copper removal by rice husk. Dynamic removal of lead and copper by rice husk was examined as a function of different bed height and flow rate using fixed-bed columns, which yielded a maximum saturation time of 14 hours. The metal breakthrough curves obtained were analysed using the Thomas, BDST, Yoon-Nelson and Clark breakthrough models. The simulation of breakthrough curve for the metals was successful with BDST, Yoon-Nelson and Clark models. Removal of bound lead/copper from the loaded column was finally achieved by using 0.1M HCl as the eluant, which yielded complete desorption of the metals in nearly 60 min.

The textile effluents are considered as potential source of water contaminations. Thus the effective methods were adopted for the removal of dyes and colorants from the textile effluents. In the present research, the removal of textile dye Congo red was carried out by bentonite clay blend with kaolin. The kaolin-bentonite clay (KBC) was used as adsorbent. The adsorption properties of KBC towards Congo red were investigated, at various temperatures 303-318 ±2 K under the optimized conditions. The adsorption equilibrium data were fitted in Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherm models and the values of the respective constants were evaluated by employing standard graphical method. From the graph, it was founded that Langmuir model is the best fitted isotherm. Feasibility of adsorption process (RL) and sorption energy (Es) was also determined. The pH of adsorbent was estimated by pH drift method. Kinetics of dye removal was investigated that it follows pseudo second order rate constant. The surface morphology of adsorbent was observed by the Scanning Electron Microscope (SEM).

Polypyrrole (PPy/Cl) and polyaniline (PAni/Cl) synthesized chemically onto sawdust (SD)was used for removal of thiocyanate (SCN-) ions from aqueous solutions. The effect of some important parameters such as pH, initial concentration, sorbent dosage, and contact time on uptake of SCN- was investigated. PPy/SD was found to be much more effective sorbent than PAni/SD for uptake SCN- from aqueous solutions. Removal of SCN- ions using PPy/Cl is supposed to be occurred mostly via ion exchange process at the surface of polymer coated onto sawdust as a very thin film. Desorption studies were also carried out for figuring out the possibility of the regeneration and reuse of the exhausted adsorbent. A proposed mechanism based on interesting anion exchange properties of the PPy/Cl has been discussed. It was found that polypyrrole conducting polymers doped with releasable counterions can be used for used to remove some anions via ion exchange process under simple open circuit conditions. The finding in this paper shows the promising application of polypyrrole conducting polymers in future water or wastewater purification technology.

The discovery of mesoporous molecular sieves, MCM-41, which possesses a regular hexagonalarray of uniform pore openings, aroused a worldwide resurgence in this field. This is not onlybecause it has brought about a series of novel mesoporous materials with various compositionswhich may find applications in catalysis, adsorption, and guest-host chemistry, but also it hasopened a new avenue for creating of the zeotype materials. This paper presents a comprehensiveoverview of recent advances in the field of MCM-41. Adsorption of drug molecules such asPseudeoephedrine hydrochloride onto mesoporous molecular sieves (MCM-41) from aqueoussolution has been investigated systematically using batch experiments in this study. Resultsindicate that Pseudeoephedrine hydrochloride adsorption is initially rapid and the adsorptionprocess reaches a steady state after 2 min. The adsorption isotherms are well described by theLangmuir model. Based on the results, it suggests that the adsorption is primarily brought about byhydrophobic interaction between drug molecules and MCM-41 surface.