ANEXO

PUBLICACIÓN RELACIONADA CON EL TRABAJO DE TESIS

1. M.M. Castillo-Ortega, I. Santos-Sauceda, F. Rodríguez-Félix, J.C. Encinas, D.E.

Rodríguez-Félix, T. del Castillo-Castro, J.L. Valenzuela-García, L.S. Quiroz-Castillo,

P.J. Herrera-Franco, Adsorption and desorption of a gold-iodide complex onto cellulose

acetate membrane coated with polyaniline or polypyrrole: a comparative study, Journal

of Membrane Science, enviado Noviembre 2010.

Revista: Journal of Membrane Science Adsorption and desorption of a gold-iodide complex onto cellulose acetate membrane coated with polyaniline or polypyrrole: a comparative study M.M. Castillo-Ortega1, I. Santos-Sauceda1, F. Rodriguez-Félix2, J.C. Encinas1, D.E. Rodriguez-Félix1, T. del Castillo-Castro1, J.L. Valenzuela-García3, L.S. Quiroz-Castillo3, P.J. Herrera-Franco4

1 Departamento de Investigación en Polímeros y Materiales, Universidad de Sonora, C.P. 83 000, Hermosillo, Sonora, México 2 Departamento de Investigación y Posgrado en Alimentos, Universidad de Sonora, C.P. 83 000, Hermosillo, Sonora, México. 3 Departamento de Ingeniería Química y Metalurgia, Universidad de Sonora, C.P. 83 000, Hermosillo, Sonora, México 4 Unidad de Materiales, Centro de Investigación Científica de Yucatán, calle 43 No. 130 Col. Chuburná de Hidalgo, C.P. 97200, Mérida, Yucatán, México. Abstract A comparative study of cellulose acetate membrane coated with polyaniline or polypyrrole for adsorption and subsequent desorption of a gold-iodide complex was accomplished. CA-PAA-TPP membranes coated polyaniline or polypyrrole are effective adsorbents for recovery of AuI2

- complex. The adsorption of Au on membranes was attributed to the exchange of Cl- and AuI2

- complex ions. The adsorption equilibrium data were found to obey the Langmuir isotherm model for CA-PAA-TPP-PANI, and Freundlich isotherm model for CA-PAA-TPP-PPy. Desorption of AuI2

- complex with NH4OH solution 3M reached 97% for CA-PAA-TPP-PPy membrane. This work shows a method convenient for recovery of gold through complex with iodine without use of cyanide solutions. Keywords: Membranes; conducting polymers; ion exchangers 1. Introduction A large number of publications about different materials with electroconductive polymers used to prepare membranes with a variety of applications have been reported, including chitosan-g-polyaniline with ability to separate water-isopropanol mixtures [1], polypyrrole-coated carbon nanotube can be directly used as supercapacitor electrodes without backing metal films or binders [2], polyaniline grafted polyacrylonitrile used for reversible immobilization of GOD [3], polyaniline asymmetric hollow fiber membranes for gas separation [4], polyaniline-polypropylene membrane with nanofiltration properties [5], polypyrrole doped with sulfonated calix[6]arene in the cation exchange membrane for transferring a range of metal ions [6], polypyrrole based composite membranes for transport of anions and cations across membranes [7], in a previous work, cellulose acetate-polyaniline membranes were tested as ion-exchange materials of a gold-iodide complex [8].

Films containing electroconductive polymers with ionic exchange properties have been reported: solvation effects on ion exchange of polypyrrole films [9], anion exchange of electropolymerized polyaniline films [10]. On the other hand, recovery of precious metals using different techniques and materials are reported. For example, recovery of gold, silver, palladium, platinum, etc. through biosorption [11]; recovery copper using activated carbon and ion-exchange resins [12]; using mesoporous silica matrix for the adsorptive recovery of Au3+ [13]; recovery gold by a combined method of biosorption and incineration [14], [15]; gold recovery using a combination of biosorption, biocrystallization, and pyro-crystallization techniques [16]; adsorption of different heavy metal ions using anion exchange polymer [17]; adsorption of Au(III) using various resins [18]; sorption of gold onto carbon activated [19]; selective recovery of gold by cementation or adsorption onto activated carbon or ion-exchange resins [20]; our previous work, kinetic experiments of adsorption of a gold-iodide complex onto acetate cellulose-polyaniline membranes [21]. The present work is focused on the comparative studies for the adsorption of gold from iodine-iodide aqueous solutions and subsequent desorption, using cellulose acetate membranes coated with polyaniline or polypyrrole as adsorbent material. 2. Experimental Materials The materials used in this study included cellulose acetate (CA) powder, 39.7 wt % acetyl content, average Mn = 50,000 (Aldrich); poly(acrylic acid, sodium salt) (PAA) 35wt %, w 15,000 (Aldrich); acetic acid, glacial (Sigma); hydrochloric acid (Merck); ammonium persulfate (J.T. Baker); triphenyl phosphate 99% (TPP), (Aldrich); potassium iodide, (Fermont); iodine 99.99%, (Fermont); gold powder 99.99%, (Aldrich); ferric chloride ACS (Fermont); Ammonium hydroxide, (Monterrey). Aniline 99%, (Aldrich), and pyrrole 98% (Aldrich) were distilled under vacuum in nitrogen atmosphere before use. All other reagents were used as received. 2.1 Preparation of CA membrane coated with polyaniline or polypyrrole CA membranes modified with PAA and plasticized with TPP, (CA-PAA-TPP), were prepared using a modification of the procedure described in a previous article [8]. CA (4 g) was weighed and dissolved in 50 mL of acetic acid, with constant stirring for 4 h, and subsequently, 5 mL of PAA was added under stirring for 2 h. Finally, 1 g of TPP was added to the solution, under continuous agitation for 2 h. The membranes were prepared using the phase inversion method. The solution was dispersed using an applicator (Elcometer 3600) on a glass of approximately 15 x 25 cm. The plate was then placed in a coagulation bath (ice water mixture) for 5 min. The plate with the solution was then immersed in the cold water for 30 min. Finally, the membrane was peeled off from the glass plate, washed in water, and dried at 25°C for 24 h on filter paper. For the coating of membranes with polyaniline, (CA-PAA-TPP-PANI), a solution of 0.5M of aniline in HCl was prepared dissolved in 0.02M aqueous solution. The membranes were cut into strips to facilitate their coating. The strips were immersed in the aniline solution for 5

min. Next, the strip was removed, drained, and placed in a glass vessel containing a solution of ammonium persulfate 0.5M for 5 min. Subsequently, the membranes were dried at 25°C for 24 h. For the coating of membranes with polypyrrole, (CA-PAA-TPP-PPy), a similar procedure described for the coating with polyaniline was used, 0.5M ferric chloride and 0.5M pyrrole solutions, and equal contact times as in the case of polyaniline. 2.2 SEM imaging

The morphology of the membranes was evaluated using a JEOL 5410LV Scanning Electron Microscopy (SEM), operated at 15 kV. The samples were gold-sputtered prior to the SEM examination. 2.3 The electrical conductivity

The electrical conductivity was measured by the standard two-point probe method. The measurements were done at 25°C with tungsten electrodes of 6 mm diameter and a Steren Mul-040 multimeter. 2.4 Mechanical analysis

The tensile properties of the membranes were determined using a Universal testing machine (MINIMAT) equipped with a 200 N load cell using a constant crosshead speed of 1mm/min. The evaluation was performed as described in the ASTM D882 “Test Methods for Tensile Properties of Thin Plastic Sheeting” standard. Before testing the samples were conditioned at a 60% relative humidity and room temperature, 25°C. 2.5 Test of application as ion-exchange membranes Using a modified of the procedure described in a previous article [21], the leaching solution was prepared as follows: 12 g iodine total (I2 + KI) were used, with a KI to I2 ratio of 2:1. The solution of gold-iodide complex (AuI2

-) was prepared using the leaching solution, to which a predetermined amount of gold was added to achieve the concentration of 10 ppm. Total Au concentration was verified by atomic absorption spectroscopy using a Perkin Elmer 3110 atomic absorption spectrometer. The kinetic experiments were done as follows: the membranes were cut into pieces of 1x1 cm. The pieces of membranes were introduced in a flask Erlenmeyer, and submerged in the solution of AuI2

- complex, under constant magnetic agitation (155 rpm), after which the pieces of membranes were immediately removed from solution of AuI2

- complex. The contact time of the membrane with the solution of AuI2

- complex was changed in a range of 0 to 720 min. The initial concentration of Au was 10 ppm. The experiment was carried out at 25 ° C. The membrane concentration was 10 g L-1 (solid/liquid ratio; grams of membrane/liter of solution). The concentration of Au in the solution was analyzed by atomic absorption spectroscopy. 2.6 Equilibrium experiments In the equilibrium experiments, membranes coated with polyaniline or polypyrrole were used as follows: the membranes were cut into pieces of 1x1 cm. Different amounts of mass

membranes, range of 2 to 30 g L-1, were introduced in flasks Erlenmeyer and submerged in the solution of AuI2

- complex, under constant magnetic agitation (155 rpm) for 12 h, after which the pieces of membranes were immediately removed from the solution of AuI2

- complex. The experiment was carried out at 25 ° C. The concentration of Au in the solution was analyzed by atomic absorption spectroscopy. To obtain the adsorption isotherms, solutions of different concentrations of Au were used (ranges 1 - 10 ppm). The solid/liquid ratio (grams of membrane/liter of solution) used varied from 2 to 30 g L-1. The membranes were cut into pieces of 1x1 cm and were introduced in flasks Erlenmeyer and submerged in the solution AuI2

- complex, under constant magnetic agitation (155 rpm) for 12 h, after which the pieces of membranes were immediately removed from the solution AuI2

- complex. The experiment was carried out at 25 ° C. The concentration of Au in the solution was analyzed by atomic absorption spectroscopy. 2.7 Desorption test of the complex (AuI2

-) The desorption experiment was performed using a NH4OH solution 3M, the membrane with (AuI2

-) was placed in the solution, varying the contact time in a time interval of 0 to 720 min. The concentration of Au in the solution was analyzed by atomic absorption spectroscopy. 3. Results and Discussion Figure 1 (a) shows the SEM micrographs of the surface of CA-PAA-TPP membrane, showing a fairly homogeneous pores sizes with diameter between 3-5 µm. Figure 1 (b) shows the SEM images of the cross-section of a CA-PAA-TPP membrane, where the pores of the surface and cross-section can be observed. It can be observed that the pores on one surface can follow several paths to cross to the other side of the membrane, and this is a proof that exist asymmetric structure on the membrane. With the use of the applicator, the reported method [8] was improved, having control of the thickness of the membranes obtained. When CA-PAA-TPP membranes were coated with polyaniline (PANI) or polypyrrole (PPy), an electroconductive material with potential application in ion exchange was obtained. Table I summarizes the electrical conductivity determined for each membrane coated with PANI or PPy. The electrical conductivities of the membranes ranged from <10-10 to 10-3 depending of electroconductive polymer used. The electrical conductivity of the membranes prepared with polypyrrole is one order of magnitude greater than that of the membranes coated PANI. This result agrees well with the typical maximum doping levels for PANI and PPy reported in the literature [22]. Values of tensile strength, Young´s modulus and strain at break are shown in the Table I. Membranes AC-PAA-TPP-PANI shows higher values of three parameters as compared to membranes AC-PAA-TPP-PPy. These results suggest that the membrane coated with polyaniline is a membrane with better mechanical properties than that coated with polypyrrole. The membranes coated with polyaniline or polypyrrole were used in the testing of the kinetic. The results are presented in Figure 2, where the percentage adsorption of Au was calculated according to the following expression

Percentage adsorption of Au = 0

0 100)(C

xCC − (1)

Where C0 is the initial concentration of total Au (ppm), and C is the concentration of Au (ppm) in the solution at time t. Figure 2 shows that the percentage adsorption of Au increases with time and achieves equilibrium at about 360 min for both membranes, coated with polyaniline or polypyrrole, for an initial Au concentration of 10 ppm. It shows that the adsorption of Au remained almost constant, implying equilibrium has been reached. The membranes coated with the polyaniline showed a higher gold recovery than those coated with polypyrrole. These results are attributed to the presence in polyaniline and polypyrrole, of chains doped with chloride ions, which are used to give electrostatic stability, these chloride ions may be interchanged with other anions such as the AuI2

- complex. These results are consistent with the ideal structures proposed for polypyrrole and polyaniline at the maximum level of doping, which in polyaniline is greater (0.5) than for polypyrrole (0.3), as shows Figure 3. Figure 4 shows a schematic drawing of our model of ion exchange for polypyrrole, similar for that reported for polyaniline [21]. Figure 5 shows the effect of the solid/liquid ratio; grams of membrane/liter of solution on the percentage adsorption of AuI2

- complex of membranes coated with polyaniline or polypyrrole. In both cases, the percentage of extracted amount of gold increases as the amount of adsorbent material increases. This is an expected result because the larger the amount surface of membrane, the greater capacity of adsorption is available. However, the percentage of gold adsorption is higher for the membranes coated with polyaniline, which is an expected results because of the level of doping of polyaniline and polypyrrole, as mentioned above. The equilibrium experimental data were adjusted in the linear forms of isotherms of Langmuir, Freundlich and Temkin. The best agreement was found for the Langmuir model for the coated polyaniline membrane and for Freundlich model and the coated polypyrrole membrane. The equations of these models are shown in (2) and (3), respectively.

Where Q is the amount of Au adsorbed per unit weight of membrane at equilibrium concentration (mg/g), C is the equilibrium concentration of Au (ppm) in the aqueous solution, Qm is the maximum capacity of adsorption, K is the constant of the isotherm of Langmuir; c1 and c2 are empirical constants of Freundlich. Figure 6 shows the equilibrium isotherms of Langmuir for CA-PAA-TPP-PANI. The best linear fit of experimental data was obtained for the Langmuir isotherm. These results suggest a monolayer adsorption process, without lateral interactions between the adsorbed molecules. Figure 7 shows the equilibrium isotherms of Freundlich for CA-PAA-TPP-PPy. The best linear fit of experimental data was obtained for

mm QKCQQ111 +=

(2)

Cc

cQ log1loglog2

1 += (3)

the Freundlich isotherm. These results suggest a non-monolayer adsorption process with lateral interactions between the adsorbed molecules. Figure 8 shows desorption of (AuI2

-) complex with NH4OH solution 3M at 720 min, reached 97% for CA-PAA-TPP-PPy membrane and 74% for CA-PAA-TPP-PANI membrane. At equivalent conditions of treatment with NH4OH and considering a lower maximum level of doping to polypyrrole compared to polyaniline, is achieved almost complete desorption of the complex AuI2

- of CA-PAA-TPP-PPy membrane. These results are consistent with those obtained in the adsorption of gold complex revised above. The gold complex desorption mechanism proposed for the membranes coated with polyaniline and polypyrrole, is ionic-exchange, Figure 9 shows mechanism of desorption proposed for polypyrrole.

4. Conclusions CA-PAA-TPP membranes having control of their thickness, with the use of the applicator were prepared and characterized by SEM, electrical properties and mechanical properties. The CA-PAA-TPP-PANI membranes show higher effective mechanical properties then the CA-PAA-TPP-PPy membrane. CA-PAA-TPP membranes coated with polyaniline or polypyrrole are effective adsorbents for recovery of AuI2

- complex. The adsorption of Au on these membranes was attributed to the exchange of Cl- and AuI2

- complex ions. The adsorption equilibrium data were found to obey the Langmuir isotherm model for CA-PAA-TPP-PANI, and Freundlich isotherm model for CA-PAA-TPP-PPy. Desorption of AuI2

- complex with NH4OH solution 3M reached 97% for CA-PAA-TPP-PPy membrane. This work shows a method convenient for recovery of gold through complex with iodine without use of cyanide solutions. Acknowledgements This work was supported by grant from the CONACYT (Project CB–2008–105003). The authors thank their colleague Jesus Javier Cervantes Soto for his assistance in the analysis of the aqueous samples by absorption spectroscopy, and Jose Antonio Villegas Gasca for his assistance in the analysis SEM.

References

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[21] F. Rodriguez, M.M. Castillo-Ortega, J.C. Encinas, V.M. Sanchez-Corrales, M. Perez-Tello, G.T. Munive, Adsorption of a gold-iodide complex (AuI2

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Table captions. Table I. Electrical conductivity values and mechanical properties of AC -PAA-TPP membrane without coated, and coated with PANI or PPy Figure captions. Figure 1. SEM micrographs of CA-PAA-TPP membrane (a) surface (b) cross-section Figure 2. Adsorption kinetics of AuI2

- complex onto AC -PAA-TPP membrane coated with PANI or PPy, solid/liquid ratio = 10, [Aui] = 10 ppm, T = 25 °C. Figure 3. Ideal structures proposed for (a) polyaniline and (b) polypyrrole at the maximum level of doping, 0.5 and 0.3 respectively. Figure 4. Schematic representation of the ion- exchange process of AuI2

- onto CA-PAA-TPP-PPy membranes. Figure 5. Effect of solid/liquid ratio; grams of membrane/liter of solution, on the percentage adsorption of AuI2

- complex on membranes with coated of PANI or PPy. Figure 6. Adsorption isotherm of Langmuir for AuI2

- complex on CA-PAA-TPP-PANI membranes. Figure 7. Adsorption isotherm of Freundlich for AuI2

- complex on CA-PAA-TPP-PPy membranes. Figure 8. Percentage of Au desorption against time of CA-PAA-TPP-PANI and CA-PAA-TPP-PPy membranes. Figure 9. Schematic representation of the desorption process of AuI2

- onto CA-PAA-TPP-PPy

Table I. Electrical conductivity and mechanical properties values of AC -PAA-TPP membrane without coated, and coated with PANI or PPy

Membrane Electrical conductivity

( S cm-1)

Tensile strength (MPa)

Young´s modulus

(MPa)

Strain at break (mm/mm)

AC-PAA-TPP <10-10 1.015±0.166 20.654±3.117 0.134±0.035

AC-PAA-TPP-PANI

2.02X10-4± 3.56x10-5

1.574±0.485 26.645±6.165 0.0954±0.0257

AC-PAA-TPP-PPy

2.68X10-3 ± 1.82x10-3

0.614±0.218 12.054±0.735 0.040±0.016

Figure 1. SEM micrographs of CA-PAA-TPP membrane (a) surface (b) cross-section

(b) (a)

Figure 2. Adsorption kinetics of AuI2- complex onto AC -PAA-TPP membrane coated

with PANI or PPy, solid/liquid ratio = 10, [Aui] = 10 ppm, T = 25 °C.

0

10

20

30

40

50

60

0 100 200 300 400 500 600 700 800

Perc

enta

ge o

f Au

adso

rptio

n

Time (min)

Membrane CA-PAA-TPP-PANI

Membrane CA-PAA-TPP-PPy

(a)

(b) Figure 3. Ideal structures proposed for (a) polyaniline and (b) polypyrrole at the maximum level of doping, 0.5 and 0.3 respectively.

n

H

N

H

N NH

Cl -

H

N+

Cl -

+

n Cl - +

N

NH

NH

Figure 4. Schematic representation of the ion- exchange process of AuI2- onto

CA-PAA-TPP-PPy membranes.

AuI2-

n

COO -

COO -

N

COO -

COO-

COO -

COO -

COO - H

N H

N

+

N

Cl -

H

N

+

N

H

n

COO -

COO -

N

COO -

COO-

COO -

COO -

COO -H

N H

N

+

N

AuI2-

H

N

+

N

H

+ Cl -

Figure 5. Effect of solid/liquid ratio; grams of membrane/liter of solution, on the percentage adsorption of AuI2

- complex on membranes with coated of PANI or PPy.

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30 35

Porc

enta

ge o

f Au

adso

rptio

n

Solid/liquid ratio (g/L)

Membrane CA-PAA-TPP-PANI

Membrane CA-PAA-TPP-PPy

Figure 6. Adsorption isotherm of Langmuir for AuI2- complex on

CA-PAA-TPP-PANI membranes.

r = 0.889

0

4

8

12

16

20

24

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

1/Q

(g/

mg)

1/C (L/mg)

Experimental dataLangmuir model

r = 0.956

-1.5

-1.2

-0.9

-0.6

-0.3

0

-0.5 -0.2 0.1 0.4 0.7 1

Log

Q

Log C

Experimental dataFreundlich model

Figure 7. Adsorption isotherm of Freundlich for AuI2- complex on

CA-PAA-TPP-PPy membranes.

Figure 8 Percentage of Au desorption against time of CA-PAA-TPP-PANI and CA-PAA-TPP-PPy membranes.

0

20

40

60

80

100

0 100 200 300 400 500 600 700

Perc

enta

ge o

f Au

deso

rptio

n

Time ( min)

Membrane CA-PAA-TPP-PANIMembrane CA-PAA-TPP-PPy

Figure 9. Schematic representation of the desorption process of AuI2

- onto CA-PAA-TPP-PPy

n

COO -

COO -

N

COO -

COO-

COO -

COO -

COO - H

NH

N

+

N

AuI2-

H

N

+

NH

NH4OH

H2O + + NH4AuI2

n

COO -

COO -

N

COO -

COO-

COO -

COO -

COO -H

N H

N

+

N H

N

N