Synthesis and application of Amberlite xad-4 functionalized with alizarin red-s for preconcentration and adsorption of rhodium (III)
© Sid Kalal et al.; licensee BioMed Central Ltd. 2012
Received: 7 June 2012
Accepted: 20 July 2012
Published: 18 September 2012
A new chelating resin was prepared by coupling Amberlite XAD-4 with alizarin red-s through an azo spacer, characterized by infra-red spectroscopy and thermal analysis and studied for Rh(III) preconcentration using inductively coupled plasma atomic emission spectroscopy (ICP-AES) for rhodium monitoring in the environment. The optimum pH for sorption of the metal ion was 6.5. The sorption capacity was found 2.1 mg/g of resin for Rh(III). A recovery of 88% was obtained for the metal ion with 1.5 M HCl as eluting agent. Kinetic adsorption data were analyzed by adsorption and desorption times of Rh(III) on modified resin. Scat chard analysis revealed that the homogeneous binding sites were formed in the polymers. The linear regression equation was Q/C = –1.3169Q + 27.222 (R2 = 0.9239), for Rh were formed in the SPE sorbent,Kd and Qmax for the affinity binding sites were calculated to be 0.76 μmol/mL and 20.67 μmol/g, respectively. The equilibrium data and parameters of Rh(III) adsorption on modified resin were analyzed by Langmuir, Freundlich, Temkin and Redlich–Peterson models. The experimental adsorption isotherm was in good concordance with Langmuir and Freundlich models (R2 > 0.998) and based on the Langmuir isotherm the maximum amount of adsorption (qmax) was 4.842 mg/g. The method was applied for rhodium ions determination in environmental samples. with high recovery (>80%).
The interest in ligand immobilized solid phase like silica gel [1, 2], organic polymer or copolymers, cellulose [3, 4] and polyurethane foam  continues because of their several applications, for example in solid phase metal extraction , designing hybrid organic–inorganic catalysts  and heterogenization of homogeneous catalysts . Solid phase extraction of metal ions present at trace level in environmental samples, high purity materials, biological samples and other complex matrices, makes the analytical techniques possible, such as flame atomic absorption spectrometry (FAAS) and inductive couple plasma atomic emission spectroscopy (ICP-AES). Solid phase extraction is preferable over ion exchange and solvent extraction due to its advantages like selectivity by controlling pH, reusability, high pre concentration factors, durability, versatility and metal loading capacity [9–13].
Adsorption of metal ions is widely used in the removal of contaminants from wastewaters. The design and efficient operation of adsorption processes require equilibrium adsorption data. The equilibrium isotherm plays an important role in predictive modeling for analysis and design of adsorption systems.
Amberlite XAD resin are widely used for modification with chelating materials due to its good physical and chemical properties such as porosity, high surface area, durability and purity. Many ligands, such as chronotropic acid , α-nitrozo β-naphtol , salicylic acid , pyrocathecol , 1-(2-pyridiazo)-2-naphtol , O-amino benzoic acid , 2-(methylthio) aniline , 3,4-dihydroxybenzoic acid , 2-aminothiophenol , and succinic acid  were covalently coupled with a polymer backbone through an azo (-N = N-) [24, 25], methylene (-CH2-)  or other groups [27, 28]. There are many reports of functionalized Amberlite XAD 2, 4 and 7 resins in this respect [29–37].
rhodium (Rh) is present at about 0.001 mg/L in the earth’s crust. Metallic rhodium metal is known for its stability in corrosive environments, physical beauty and unique chemical properties. It commands a premium price because of its low abundance in nature. Rhodium is now widely used in combination with platinum. Rhodium is commonly used for alloying platinum in thermocouples, crucibles, evaporating dishes, weighing boats windings for high-temperature furnaces. It finds applications as a coating material because of the hardness and luster of its surface. Because of its commercial importance, a wide variety of reagents have been proposed for preconcentration of Rh before spectrophotometric determination.
In this work, Amberlite XAD-4 alizarin red-s was prepared by chemically bonding to be used as an adsorbent. Alizarin red-s could form chelates with metallic ions on the surface of the resin. Adsorption of Rh(III) from aqueous solution and isotherm study using modified Amberlite XAD-4 was investigated under different experimental conditions to assess its affinity towards the chelator.
Materials and methods
pH measurements were made with Metrohm model 744 (Switzerland) pH meter. IR spectra were recorded on a FT-IR spectrometer (Jasco/FT-IR-410) by KBr pellet method. Elemental analysis was carried out on an elemental analyzer from Thermo-Finnegan (Milan, Italy) model Flash EA. ICP-AES Varian, Vista-pro (Salt lake city, USA) was used for measuring the concentration of Rh (III). Thermo gravimetric analysis (TGA) was carried out by using TGA-50 H (Shimadzu, Japan).
Reagents and solutions
Acetic acid, sodium acetate, sodium hydrogen phosphate, sodium dihydrogen phosphate, rhodium chloride, tin (II) chloride, hydrochloric acid, sulfuric acid, nitric acid, sodium nitrite, sodium hydroxide, alizarin red, and iodide-starch paper were products of Merck Co. (Darmstadt, Germany).
All of the solutions were prepared in demonized water using analytical grade reagents. The stock solution (500 mg/L) of Rh(III) was prepared by dissolving appropriate amounts of rhodium chloride respectively in demonized water. 10 mL 0.01 M acetic acid acetate buffer (pH = 3-5) and 0.01 M phosphate buffer (pH = 6-9) were used to adjust pH of the solutions, wherever suitable. Amberlite XAD-4 resin (surface area = 745 m2/g, pore diameter = 5 nm and bead size = 20-60 mesh) was obtained from Serve (Heidelberg, New York).
Synthesis of chelating resin
Amberlite XAD-4 beads (5 g) were treated with 10 mL of concentrated HNO3 and 25 mL of concentrated H2SO4 and the mixture was stirred at 60°C for 1 hour on an oil bath. Then, the reaction mixture was poured into an ice water mixture. The nitrated resin was filtered, washed repeatedly with water until free from acid and then treated with a reducing mixture of 40 g of SnCl2, 45 mL of concentrated HCl and 50 mL of ethanol. The mixture was refluxed for 12 hours at 90°C. The solid precipitate was filtered and washed with water and 2 mol/L NaOH which released amino resin (R-NH2) from (RNH3)2 SnCl6 (R = resin matrix). The amino resin was first washed with 2 mol/L HCl and finally with distilled water to remove the excess HCl. It was suspended in an ice-water mixture (350 mL) and treated with 1 mol/L HCl and 1 mol/L NaNO2 (added in small aliquots of 1 mL) until the reaction mixture showed a permanent dark blue color with starch-iodide paper. The diazotized resin was filtered, washed with ice-cold water and reacted with alizarin red-s 0.03 mol in 30 mL 2 mol/L HCl, respectively. The reaction mixture was stirred at 0-3°C for 24 hours. Then, the resulting colored beads were filtered, washed with water and dried in air.
A sample solution (50 mL) containing (0.3 μg/mL) of Rh (III) was taken in a glass stopped bottle, after adjusting its pH to the optimum value. The 0.05 g of alizarin red S-Amberlite XAD-4 was added to the bottle and the mixture was shaken for optimum time. The resin was filtered and sobbed metal ion was eluted with 1.5 M HCl (10 mL). The concentration of metal ion in the elute solution was determined by ICP-AES. The wavelength of 343 nm was used for Rh determination.
Isotherm studies of Rh (III) adsorption
Where C0 and Ce(mg/L) are initial and equilibrium concentrations of Rh(III), respectively; V (L) is the volume of the solution and m (g) is the mass of the adsorbent used.
Metal sorption as a function of pH
The degree of metal sorption at different pH values was determined by batch equilibration technique. A set of solutions (volume of each = 100 mL) containing 0.3 μg/mL of Rh(III) was taken. pH was adjusted in the range of 3-9 with 0.01 M acetate and/or phosphate buffer solutions. 0.1 g of alizarin red S-Amberlite XAD-4 was added to each solution and the mixture was shaken for 4 hours. The optimum pH for quantitative uptake of metal ions was ascertained by measuring Rh (III) content (by ICP-AES) in supernatant liquid and in the elute obtained by desorbing the metal ion from resin with 1.5 M hydrochloric acid (10 mL).
0.05 g of poly(AGE/IDA-co-DMAA)-grafted silica gel was stirred for 4 h. with 50 mL solution containing10-50 μg/mL of Rh(III) at optimum pH and 20°C. The metal ion concentration in the supernatant liquid was estimated by ICP-AES. The sorption capacity of the sorbent for the metal ion was ascertained from the difference between the metal ion concentration in the solution before and after the sorption.
Optimization of sorption time of rhodium ions
Alizarin red-s-amberliteXAD-4 (0.1 g) was shaken with 50 mL of solution containing 300 μg/mL of Rh (III) for different times (20, 60, 90, 120, 150 and 180 min) under optimum pH. After taking out the sorbent, concentration of rhodium ions in the solution was determined with ICP-AES using recommended batch method.
Isotherm parameters obtained by using non-linear method
Langmuir isotherm model
Freundlich isotherm model
Temkin isotherm model
Redlich–Peterson isotherm model
Table 1 shows that the value of RL (0.5764)is in the range of 0-1 at optimum pH which confirms the favorable uptake of the Rh(III).
Therefore, a plot of ln(qe) versus ln(Ce) (Figure 1B) enables the constant KF and exponent 1/n to be determined. The Freundlich equation predicts that the Rh(III) concentration on the adsorbent will increase as long as there is an increase in Rh(III) concentration in the liquid.
The Temkin equation suggests a linear decrease of sorption energy as the degree of completion of the optional centers of an adsorbent is increased.
Where B = RT/b and b is the Temkin constant related to heat of sorption (J/mol). A is the Temkin isotherm constant (L/g), R is the gas constant (8.314 J/mol K) and T is the absolute temperature (K). Therefore plotting qe versus ln(Ce) (Figure 1C) enables one to determine the constants A and B. Temkin parameters calculated from Equations (7 and 8) are listed in Table 1.
It has three isotherm constants, namely, A, B, and g (0 < g < 1), which characterize the isotherm. The limiting behavior can be summarized as follows:
i.e. the Langmuir form results.
i.e. the Freundlich form results.
i.e. the Henry’s Law form results.
Three isotherm constants, A, B, and g can be evaluated from the linear plot represented by Eq. (13) using a trial and error procedure. It was developed to determine the isotherm parameters by optimization routine to maximize the coefficient of determination, R2, for a series of values of A for the linear regression of ln(Ce) on ln[A(Ce/qe) − 1] and to obtain the best value of A which yields a maximum ‘optimized’ value of R 2 using the solver add-in with Microsoft’s spreadsheet, Microsoft Excel(Figure 1D).
Scat chard analysis was employed to further analyze the binding isotherms, which is an approximate model commonly used in SPE (Solid Phase Extraction) characterization. The Scat chard equation can be expressed as, Q/C = (Qmax–Q)/Kd, where C (μmol/mL) is the equilibrium concentration of rhodium; Q (μmol/g) is the equilibrium adsorption amount at each concentration Qmax (μmol/g) is the maximum adsorption amount; and Kd (μmol/mL) is the equilibrium dissociation constant at binding sites.
TGA of the resins shows two step weight losses up to 510°C. The weight loss up to 130°C was due to the water molecules in the polymer. The major weight loss after 290°C is due to the dissociation of chemically immobilized moiety and the polymeric matrix.
Stability and reusability of the adsorbent resin
Rh(III) was absorbed and desorbed on 1 g of the resin several times. It was found that sorption capacity of resin after 10 cycles of its equilibration with Rh(III), changes less than 5%. Therefore, repeated use of the resin is feasible. The resin cartridge after loading it with samples can be readily regenerated with 1.5 M HCl. The sorption capacity of the resin stored for more than 6 months under ambient conditions has been found to be practically unchanged.
Optimization of desorption time of rhodium ions
The Redlich–Peterson isotherm constants, A, B, and g as well as the coefficient of determination, R2, for the sorption of Rh(III) onto Alizarin red S-Amberlite XAD-4 using the linear regression is shown in Table 1. It can be seen that the values of (g) were close to unity, which means that the isotherms are approaching the Langmuir form and not the Freundlich isotherm. The result shows that the Langmuir isotherm best-fit the equilibrium data for adsorption of Rh(III) on Alizarin red S-Amberlite XAD-4.
Scat chard analysis
Application of method
Results obtained for Rh(III)measurement in tap water (I) and spring water (II)
Found (without spiking of Rh(III))
Added Rh(III) (μg/mL)
Found Rh(III), after preconcentration (μg/mL)
Relative standard deviation (%) a
The experimental FT-IR spectrum and thermal analysis (TGA) show this resin was satisfactory for adsorption of rhodium ion. In pH = 6.5, the results indicated 88% recovery and at 15 min (Figure 5) the adsorption of resin was about 50%. The equilibrium data and parameters of Rh(III) adsorption on modified resin were analyzed by Langmuir, Freundlich, Temkin and Redlich–Peterson models. The experimental adsorption isotherm was in good concordance with Langmuir and Freundlich models (R2 > 0.998) and based on the Langmuir isotherm the maximum amount of adsorption (qmax) was 4.842 mg/g.
The results about application of this work in real sample and environmental studies, also demonstrated the applicability of the procedure for rhodium determination in real samples with high recovery (>80%).
The authors gratefully acknowledge the support of this work by Faculty of Sciences, Tarbiat Modares University.
- Marshall MA, Mottola HA: Synthesis of silica-immobilized 8-quinolinol with (aminophenyl)trimethoxysilane. Anal Chem. 1983, 55: 2089-2093. 10.1021/ac00263a019.View ArticleGoogle Scholar
- Roldan PS, Alcantara IL, Castro GR, Rocha SC, Padilha CCF, Padilha PM: Determination of Cu, Ni, and Zn in fuel ethanol by FAAS after enrichment in column packed with 2-aminothiazole-modified silica gel. Anal Bioanal Chem. 2003, 375: 574-577.Google Scholar
- Gurnani V, Singh AK, Venkataramani B: Cellulose based macromolecular chelator having pyrocatechol as an anchored ligand: synthesis and applications as metal extractant prior to their determination by flame atomic absorption spectrometry. Talanta. 2003, 61 (15): 889-903.View ArticleGoogle Scholar
- Gurnani V, Singh AK, Venkataramani B: Cellulose functionalized with 8-hydroxyquinoline: new method of synthesis and applications as a solid phase extractant in the determination of metal. Anal Chim Acta. 2003, 485: 221-232. 10.1016/S0003-2670(03)00416-1.View ArticleGoogle Scholar
- Dmitrienko SG, Sviridova OA, Pyatkova LN, Senyavin VM: On the new approach to the theory of preferential wetting of heterogeneous solid surfaces. Anal Bioanal Chem. 2002, 374: 361-368. 10.1007/s00216-002-1513-6.View ArticleGoogle Scholar
- Gal PK, Patel S, Mshra BK: Chemical modification of silica surface by immobilization of functional groups for extractive concentration of metal ions. Talanta. 2004, 62: 1005-1028. 10.1016/j.talanta.2003.10.028.View ArticleGoogle Scholar
- Valkenberg MH, Holderich WF: Preparation and use of hybrid organic inorganic catalyst. Cat Rev. 2002, 44: 321-374. 10.1081/CR-120003497.View ArticleGoogle Scholar
- Price PM, Clark JH, Macquarrie DJ: Modified Silicas for Clean Technology. J Chem Soc Dalton Trans. 2000, 1: 101-View ArticleGoogle Scholar
- Solid Phase Extraction, Principles, Techniques and Applications. Edited by: Simpson NJK. 2000, New York: Marcel DekkerGoogle Scholar
- Camel V: Solid phase extraction of trace elements. Spectrochim Acta part B. 2003, 58: 1177-1233. 10.1016/S0584-8547(03)00072-7.View ArticleGoogle Scholar
- Gaur N, Dhankhar R: equilibrium modelling and spectroscopic studies for the biosorption of zn+2 ions from aqueous solution using immobilized spirulinaplatensis. Iran J Environ Health Sci Eng. 2009, 6: 1-6.Google Scholar
- Ghadiri SK, Nabizadeh R, Mahvi AH, Nasseri S, Kazemian H, Mesdaghinia AR, Nazmara S: methyltert-butyl ether adsorption on surfactant modified natural zeolites. Iran J Environ Health Sci Eng. 2010, 7: 241-252.Google Scholar
- Ehrampoush MH, Ghanizadeh G, Ghaneian MT: equilibrium and kinetics study of reactive red 123 dyeremoval from aqueous solution by adsorption on eggshell. Iran J Environ Health Sci Eng. 2011, 8: 101-108.Google Scholar
- Tewari PK, Singh AK: Amberlite XAD-2 functionalized with chromotropic acid: synthesis of a new polymer matrix and its applications in metal ion enrichment for their determination by flame atomic absorption spectrometry. Analyst. 1999, 120: 1847-1851.View ArticleGoogle Scholar
- Lemos VA, Baliza PX, Santos JS: Synthesis of α-Nitroso-β-Naphthol Modified Amberlite XAD-2 Resin and its Application in On-Line Solid Phase Extraction System for Cobalt Preconcentration. Sep Sci Technol. 2004, 39: 3317-3330. 10.1081/SS-200027351.View ArticleGoogle Scholar
- Saxena R, Singh AK, Rathore DPS: Salicylic Acid Functionalised Polystyrene sorbent Amberlite XAD-2: Synthesis and Applications as a preconcentrator in the Determination of Zinc(II) and Lead(II) by Atomic Absorption Spectrophotometry. Analyst. 1995, 120: 403-405. 10.1039/an9952000403.View ArticleGoogle Scholar
- Tewari PK, Singh AK: Synthesis, characterization and applications of pyrocatechol modified amberlite XAD-2 resin for preconcentration and determination of metal ions in water samples by flame atomic absorption spectrometry (FAAS). Talanta. 2001, 53: 823-833. 10.1016/S0039-9140(00)00572-5.View ArticleGoogle Scholar
- Narin I, Soylak M, Kayakirilmaz K, Elci L, Dogan M: Preparation of a Chelating Resin by Immobilizing 1-(2-Pyridylazo) 2-Naphtol on Amberlite XAD-16 and its Application of Solid Phase Extraction of Ni(II), Cd(II), Co(II), Cu(II), Pb(II) and Cr(III) in Natural Water Samples. Anal Lett. 2003, 36: 641-658. 10.1081/AL-120018254.View ArticleGoogle Scholar
- Çekiç SD, Filik H, Apak R: Use of o-aminobenzoic acid functionalized XAD-4 copolymer resin for the separation and preconcentration of heavy metal (II) ions. Anal Chim Acta. 2004, 505: 15-24. 10.1016/S0003-2670(03)00211-3.View ArticleGoogle Scholar
- Guo Y, Din B, Liu Y, Chang X, Meng S, Tian M: Preconcentration of trace metals with 2-(methylthio) aniline-functionalized XAD-2 and their determination by flame atomic absorption spectrometry. Anal Chim Acta. 2004, 504: 319-324. 10.1016/j.aca.2003.10.059.View ArticleGoogle Scholar
- Lemos VA, Baliza PX, Yamaki RT, Rocha ME, Alves APO: Synthesis and application of a functionalized resinin on-line system for copper preconcentration and determination infoods by flame atomic absorption spectrometry. Talanta. 2003, 61: 675-682. 10.1016/S0039-9140(03)00328-X.View ArticleGoogle Scholar
- Lemos VA, Baliza PX: Amberlite XAD-2 Functionalized with 2-Ami- nothiophenol as a New Sorbent for On-line Preconcentration of Cad- mium and Copper. Talanta. 2005, 67: 564-570. 10.1016/j.talanta.2005.03.012.View ArticleGoogle Scholar
- Metilda P, Sanghamitra K, Mary Gladis J, Naidu GRK, PrasadaRao T: Succinic acid functionalized Amberlite XAD-4 sorbent for the solid phase extractive preconcentration and separation of uranium (VI). Talanta. 2005, 65: 192-200.Google Scholar
- Tewari PK, Singh AK: Preconcentration of lead with Amberlite XAD-2 and Amberlite XAD-7based chelating resins for its determination by flame atomic absorption spectrometry. Talanta. 2002, 56: 735-744. 10.1016/S0039-9140(01)00606-3.View ArticleGoogle Scholar
- Saxena R, Singh AK, Sambi SS: Synthesis of a chelating polymer metrix by immobilizing alizarin red –S Amberlite XAD-2 and its application to the preconcentration of Lead (II), cadmium (II), zink(II) and nickel (II). Anal Chim Acta. 1994, 295: 199-204. 10.1016/0003-2670(94)80351-X.View ArticleGoogle Scholar
- Lemos VA, Baliza PX, Santos JS, Nunes LS, Sesus AA, Rocha ME: A new functionalized resin and its application in preconcentration system with multivariate optimization for nickel determination in food samples. Talanta. 2005, 66: 174-180. 10.1016/j.talanta.2004.11.004.View ArticleGoogle Scholar
- Dev K, Pathak R, Rao GN: Sorption behaviour of lanthanum (III), neodymium (III), therbium (III), thorium (III) and uranium (VI) on Amberlite XAD-4 resin funcionazed with bicines ligands. Talanta. 1999, 48: 579-584. 10.1016/S0039-9140(98)00274-4.View ArticleGoogle Scholar
- Prabhakaran D, Subramanian MS: A new chelating sorbent for metal ion extraction under high saline conditions. Talanta. 2003, 59: 1227-1236. 10.1016/S0039-9140(03)00030-4.View ArticleGoogle Scholar
- Brajter K, OlbrychSleszynska E, Staskiewicz M: Preconcentration and Separation of Metal Ions by Means of Amberlite XAD-2 Loaded with Pyrocatechol Violet. Talanta. 1988, 35: 65-67. 10.1016/0039-9140(88)80015-8.View ArticleGoogle Scholar
- Abollino O, Mentasti E, Porta V, Sarzanini C: Immobilized 8-oxine units on different solid sorbents for the uptake of metal traces. Anal Chem. 1990, 62: 21-26. 10.1021/ac00200a005.View ArticleGoogle Scholar
- Blain S, Appriou P, Handel H: Column Preconcentration of Trace Metals from Sea-Water with Macroporous Resins Impregnated with Lipophilic TetraazaMacrocycles. Analyst. 1991, 116: 815-820. 10.1039/an9911600815.View ArticleGoogle Scholar
- Saxena R, Singh AK: Pyrocatechol Violet immobilized Amberlite XAD-2: synthesis and metal-ion uptake properties suitable for analytical applications. Anal Chim Acta. 1997, 340: 285-290. 10.1016/S0003-2670(96)00515-6.View ArticleGoogle Scholar
- Jain VK, Sait SS, Shrivastav P, Agrawal YK: Application of chelate forming resin Amberlite XAD-2-o-vanillinthiosemicarbazone to the separation and preconcentration of copper(II), zinc(II) and lead(II). Talanta. 1997, 51: 397-404.View ArticleGoogle Scholar
- Abollino O, Aceto M, Bruzzoniti MC, Mentasti E, Sarzanini C: Determination of metals in highly saline matrices by solid-phase extraction and slurry-sampling inductively coupled plasma-atomic emission spectrometry. Anal Chim Acta. 1998, 375: 293-298. 10.1016/S0003-2670(98)00299-2.View ArticleGoogle Scholar
- Kumar M, Rathore DPS, Singh AK: Amberlite XAD-2 Functionlized with o-Aminophenol: Synthesis and Applications as Extractant for Copper(II), Cobalt(II), Cadmium(II), Nickel(II), Zinc(II) and Lead(II). Talanta. 2000, 51: 1187-1196. 10.1016/S0039-9140(00)00295-2.View ArticleGoogle Scholar
- Kumar M, Rathore DPS, Singh AK: Metal Ion Enrichment on Amberlite XAD-2 Functionalized with Tiron: Analytical Applications. Analyst. 2000, 125: 1221-1226. 10.1039/b000858n.View ArticleGoogle Scholar
- Tewari PK, Singh AK: Thiosalicylic acid-immobilized Amberlite XAD-2: metal sorption behaviour and applications in estimation of metal ions by flame atomic absorption spectrometry. Analyst. 2000, 125: 2350-2355. 10.1039/b006788l.View ArticleGoogle Scholar
- Hall KR, Eagleton LC, Acrivos A, Vermeulen T: Pore-and solid-diffusion kinetics in fixed-bed adsorption under constant-pattern condition. Ind Eng Chem Fundam. 1966, 5 (2): 212-223. 10.1021/i160018a011.View ArticleGoogle Scholar
- Ho YS, Ofomaja AE: Biosorption thermodynamics of cadmium on coconut copra meal as biosorbent. Biochem Eng J. 2006, 30: 117-123. 10.1016/j.bej.2006.02.012.View ArticleGoogle Scholar
- Gomathi Devi L, Rajashekhar KE, AnanthaRaju KS, Girish Kumar S: Kinetic modeling based on the non-linear regression analysis for the degradation of Alizarin Red S by advanced photo Fenton process using zero valent metallic iron as the catalyst Journal of Molecular Catalysis A. Chemical. 2009, 314: 88-94.Google Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.