Removal of heavy metals from aqueous solution using platinum nanopartcles/Zeolite-4A
© Mehdizadeh et al.; licensee BioMed Central Ltd. 2014
Received: 1 October 2012
Accepted: 15 October 2013
Published: 7 January 2014
The effects of varying operating conditions on metals removal from aqueous solution using a novel platinum nanopartcles/Zeolite-4A adsorbent are reported in this paper. Characterization of the adsorbent showed successful production of platinum nanopartcles on Zeolite-4A using 3 Wt% platinum. The effects of operation conditions on metals removal using this adsorbent were investigated. The optimal metals adsorption was observed at pH 7, 0.1 g/10 mL dosage and 30 min contact time. Sorption data have been interpreted in terms of Langmuir and Freundlich isotherms.
KeywordsPlatinum nanopartcles Zeolite-4A Heavy metals Adsorption
Water contaminated by heavy metal ions had become much more serious with a rapid development of industries and competitive use of fresh water in many parts of the world . Heavy metals are not biodegradable and tend to accumulate in living organisms, causing various diseases and disorders [2–4].Therefore, the removal of heavy metal ions from water has become an important subject today.
Several conventional methods exist for the removal of heavy metal pollutants from wastewater. These methods include precipitation, electroplating, chemical coagulation, ion-exchange, membrane separation, and electro kinetics. However, most of these methods have limitations, which include high cost, unavailability, and generation of large volumes of secondary waste and poor removal efficiency [5–7]. Considering from the economy and efficiency point of view, adsorption is regarded as the most promising and widely used method among all these . The efficiency of adsorption depends on many factors, including the surface area, pore size distribution, polarity, and functional groups of the adsorbent . One of the main limitations of the sorption techniques is the massive mass transport resistance due to the size of the adsorbents. To overcome this limitation, the use of new adsorbents has attracted considerable attention in recent years.
The application of nanotechnology to the purification and treatment of wastewater may potentially revolutionize water treatment processes because of their unusual physical and chemical properties owing to their extremely small size and large specific surface area. Due to these characteristics, nanomaterials have found wide applications in adsorption and the removal of heavy metal ions from aqueous solutions .
Zeolites are microporous crystalline solids with well-defined structures, which have unique ion exchange and sorption properties, and are widely used in a large number of water treatment processes .
The objective of the present study is to investigate the adsorption potential of Pt on zeolite in the removal of heavy metal ions from aqueous solution. The effects of pH, adsorbent dosage, contact time and temperature on adsorption capacity of Pt/Zeolite have been investigated. The Langmuir and Freundlich isotherms models are applied to the sorption data to calculate the different parameters and the best fittings achieved.
Material and instrument
The particle size of the nanocrystalline particle was examined using transmission electron microscopy (TEM, Philips EM208S at 100KV). The X-ray diffraction (XRD) pattern of the catalyst powders was provided by a (Philips PW 1800) diffractometer. To determine the concentration of component, Inductively Coupled Plasma (ICP, Perkin Elmer 5500) was used. Different pH of Samples was measured with pH meter (Schott CG-841) and centrifuge (Beckman J-21C device) was applied for separating solid particles from the solution. The Shaker bath (Infors AG) was used for the stirring system at constant temperature to determine the distribution coefficients.
Zeolite4A were obtained from Pars zeolite Co. (Tehran, Iran) and Hexachloroplatinic acid: H2PtCl6.6H2O (99.9%, metals basis) and Poly vinylpyrrolidone (PVP, Mw= 29 000) was purchased from Merck All the compounds used to prepare the reagent solutions were of analytic reagent grade. The heavy metal ions solutions containing 50, 100, 250 and 500 mg/L each of La3+, C02+, Ba2+ and Ni2+ ions were prepared by dissolving a weighed quantity of the respective nitrate salts in distilled water.
Synthesis of the platinum nanoparticle
The synthesis procedure was started by adding 133 mg PVP into a mixture of 20 cm3 of 6.0 mM H2PtCl6.6H2O aqueous solution and 180 cm3 pure ethanol. The mixture then was refluxed for 3 h. Afterward, the solvent was evaporated, and the obtained black precipitate was thoroughly washed with water and ethanol, and dried at ambient condition.
Preparation of Pt/Zeolite
About 20 cm3 of H2PtCl6.6H2O aqueous solution (6 mM) was mixed with 133 mg PVP and 180 cm3 of ethanol. The mixture was quickly added to 1.5 g of the zeolite 4A, and refluxed for 3 h. The solvent then was evaporated and the obtained granules were calcined at 450°C for 12 h in a stream of muffle furnace.
Batch adsorption experiments
Where Ci and Ce are the initial and final metal ion concentrations, respectively.
Results and discussion
Preparation and characterization of adsorbent
4A with a pore diameter of 9.0 nm was used as a support due to its high surface area and ordered mesoporous structure. Platinum/zeolite adsorbent was prepared as discussed in section 2. The loading of the platinum on the zeolite sample was measured by dissolving the sample in aqua regia, and analyzing of the Pt content of the supernatant by ICP method. The loading was found to be around 3 Wt%.
The removal efficiency (R%) of the metal ions on Pt/zeolite 4A with zeolite 4A
To optimize the adsorption system, the effects of various parameters such as adsorbent dose, pH, and time on the adsorption of Co (II), Ba (II), La (III) and Ni (II) ions were studied.
Effect of adsorbent dosage
Effect of contact time
Effect of pH on adsorption
At low pH the concentration of protons was high and metal binding sites became positively charged repelling the Co (II), Ba (II), La (III) and Ni (II) cations. With an increase in pH, the negative charge density on the adsorbent increases due to deprotonation of the metal binding sites, thus increasing metal adsorption. The maximum adsorption observed in the pH 7 and the subsequent reduction in adsorption capacity was probably due the partial hydrolysis of metal ions. Furthermore, the low solubility of hydrolyzed metals species would have resulted into precipitation of metals at pH above 7, thereby reducing adsorption capacity of Pt/zeolite 4A.
The adsorption isotherms are very important in describing the adsorption behavior of solutes on the specific adsorbents. In this work, two important isotherm models such as Langmuir and Freundlich were selected and studied.
where qe (in mg/mg) is the adsorbate amount adsorbed by 1 g of adsorbent, Ce (in mg/L) is the equilibrium concentration of adsorbate in the solution, Qo is the monolayer adsorption capacity (mg/mg), b is the constant related to the adsorption intensity, Kf is constant indicative of the relative sorption capacity of Pt/zeolite 4A (mg/g) and 1/n is the constant indicative of the intensity of the sorption process.
Isothermal adsorption models for the adsorption of Co (II), Ba (II), La (III) and Ni (II) adsorption on Pt/zeolite 4A
K f (mg/g)
It was observed that results fitted better in the Freundlich model in terms of the correlation factor (R2) value, recording 0.99 for Ba (II) and the higher Langmuir correlation factor (R2) values of 0.996, 0.992 and 0.983 for the adsorption Co (II), La (III) and Ni (II) respectively, strongly suggests that the Langmuir model gives a better fit to the experimental data and so the nature of adsorption of metal ions on the adsorbent is more compatible with Langmuir assumptions.
Pseudo-second order kinetic parameters for Co (II), Ba (II), La (III) and Ni (II) ions onto Pt/zeolite 4A
The removal of heavy metals from aqueous solution was carried out in a batch adsorption mode using platinum nanopartcles/Zeolite-4A adsorbent. The platinum nanopartcles/Zeolite-4A exhibited effectiveness in the removal of Co (II), Ba (II), La (III) and Ni (II) ions from aqueous solutions. The removal efficiency was controlled by solution pH, adsorbent concentration and contact times. Adsorption data fitted well with the Freundlich model for Ba (II), while Langmuir isotherm adsorption model having higher R2 value for Co (II), La (III) and Ni (II) ions, described the adsorption process better than Freundlich model for the three metals. This novel material opens new door for various usage of the nanomaterials in different fields of application in the wastewater treatment.
The author is thankful from Nuclear Science and Technology Research Institute and Department of Energy Engineering of Sharif University of Technology for the financial support of this project.
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