Article pubs.acs.org/IECR
Sorption Behavior of Thiourea-Grafted Polymeric Resin toward Silver Ion, Reduction to Silver Nanoparticles, and Their Antibacterial Properties Pradipta Kumar, Khursheed B. Ansari, Aditya C. Koli, and Vilas G. Gaikar* Department of Chemical Engineering, Institute of Chemical Technology, Nathalal Parikh Marg, Matunga, Mumbai-19, India S Supporting Information *
ABSTRACT: The present work focused on the selective sorption of silver ions from aqueous solutions by a thiourea-grafted mesoporous polystyrene resin and subsequent reduction of the Ag+ ions to silver nanoparticles (AgNPs) embedded in the polymer matrix. The effects of various parameters such as pH, contact time, concentration, temperature, and presence of competing metal ions were studied for the optimum uptake of silver ions to enhance the yield of AgNPs. The most favorable sorption of silver ions was observed in the pH range of 1.5−1.0 and at 27−30 °C. A chemical method was used for in situ reduction of the adsorbed silver ions to AgNPs on the polymer matrix. The polymer-embedded AgNPs showed a very good bactericidal activity against Escherichia coli. The AgNPs were separated from the polymer support by ultrasonication and characterized by TEM, UV−vis spectroscopy, EDX, and XRD. The particles were of cubic phase (fcc) and were monodispersed with a mean diameter of 8 nm.
■
INTRODUCTION The sorption of valuable metal ions from aqueous solutions by an appropriate adsorbent is a technique of great interest for various applications.1,2 Among the adsorbents used, functionally modified poly(styrene−divinylbenzene) (PS−DVB) resins have been extensively studied for the recovery and removal of heavy-metal ions from aqueous solutions because of their good mechanical strength and ease of chemical modification for desired separations.3−5 The selection of a metal-selective PS− DVB resin depends entirely on the functional groups present on the matrix. The loading of an ion-specific ligand on the polystyrene matrix controls the metal-ion selectivity in sorption from multi-ion solutions, as well as the sorption capacity for the selected metal ion. A judicious selection or design of the ligand helps in the selective extraction of an analyte even in the presence of larger concentration of other metal ions.6−12 Silver is a precious metal that is mostly found in the wastewaters of photographic,13,14 jewelry,15 electroplating/ electronics,16 battery,15 dental/medical products/drugs,17 and catalytic processes.18 There is a significant need to prepare silver nanoparticles (AgNPs) uniformly dispersed in a polymer matrix for several applications,19−21 as the nanoparticles in their free form undergo aggregation because of a high surface free energy. This aggregation decreases the efficacy of the nanoparticles in applications where a high surface-to-volume ratio is critical.22 For example, in healthcare applications, the AgNPs diffuse into the bacterial cell membrane, making them a powerful antibacterial agent.23 This antibacterial property of AgNPs and silver ions against a wide range of microorganisms has long been known.24,25 Even though the mechanism of antibacterial action of silver nanoparticles is similar to that of silver ions, AgNPs are considered to be more effective than bulk silver or silver ions.25,26 However, a decrease in the antibacterial activity is observed because the nanoparticles undergo aggregation during synthesis or isolation processes. This © 2013 American Chemical Society
problem can be eliminated if the nanoparticles can be synthesized in situ within a polymer support where the presence of specific functional groups on the matrix decreases the surface free energy of the nanoparticles through coordination, thereby eliminating the possibility of their aggregation. The most commonly used functional groups that can act as stabilizing agents are thiols, amines, sulfonates, phosphine oxides, and carboxylates.27 In this work, we focused on the selective uptake of Ag+ ions from aqueous solutions on thiourea-grafted poly(styrene− DVB) resins and their subsequent reduction with hydrazine hydrate to prepare AgNPs, both in free form and embedded and stabilized by the thiol groups in the polymer support.
■
EXPERIMENTAL SECTION
Materials and Methods. Thiourea, K2CO3, and hydrazine hydrate (all AR-grade) were used as received from S.D. Fine Chemicals, Mumbai, India. AR-grade AgNO3 was purchased from Merck India Ltd. (Mumbai, India). Aqueous HNO3 (0.1 mol/dm3) solutions were prepared using spectroscopic-grade HNO3 from Spectrochem Pvt. Ltd. (Mumbai, India) to adjust the pH of the solutions. Chloromethylated polystyrene (CMPS), cross-linked with 2% divinylbenzene in bead form, was obtained from Auchtel Pvt. Ltd. (Mumbai, India) and had a chlorine content of 3.5 mequiv/g. Standard solutions (ICPgrade, 1000 mg/dm3) of Ag(I), Co(II), Cu(II), Ni(II), Zn(II), Cd(II), Pb(II), La(III), Cs(I), and Sr(II) were obtained from S.D. Fine Chemicals. Escherichia coli (SCS110) strain, nutrient Received: Revised: Accepted: Published: 6438
December 24, 2012 April 8, 2013 April 20, 2013 April 20, 2013 dx.doi.org/10.1021/ie3035866 | Ind. Eng. Chem. Res. 2013, 52, 6438−6445
Industrial & Engineering Chemistry Research
Article
Scheme 1. Synthesis of Grafted Polymer (TPS−DVB)
Synthesis of Silver Nanoparticles on Polymer Support. TPS−DVB resin (1.0 g) was added to an aqueous solution of silver nitrate (150 mg/10 cm3) and stirred at 27 ± 3 °C for 24 h. The polymer beads were then filtered and washed thoroughly with water until no precipitation was observed with NaCl. The beads were then dried at 60−70 °C for 7 h. The dried silver-ion-loaded beads (Ag+−TPS−DVB) were then added to an aqueous solution of hydrazine hydrate (0.2 N, 20 cm3) at 27 ± 3 °C and held at that temperature for 5 h with occasional stirring. The beads were isolated from the solution by filtration, washed with water until neutral pH, and then dried at 60−70 °C for 7 h. To investigate the leaching of Ag0 from the polymer support, two techniques were employed. In the first method, the silverembedded beads were placed in a stoppered conical flask containing water at 50−55 °C with reciprocal shaking at 100 strokes/min on an orbital shaker for 3 days. Second, the Ag0− TPS−DVB beads were subjected to an ultrasonication process, while suspended in water, in the temperature range of 40−50 °C for up to 200 s. Samples from each technique were withdrawn at regular intervals of time and dissolved in concentrated HNO3. The silver ion concentrations in the solutions were measured by ICP−AES. Antibacterial Study of Embedded Nanosilver Particles (Ag0−TPS−DVB). Escherichia coli was selected as an indicator bacteria for the evaluation of the antibacterial activity of AgNPs loaded on the polymeric resin. E. coli was inoculated in 50 cm3 of nutrient broth medium and grown at 37 °C for 24 h. The bacterial suspension was harvested by centrifugation for 10 min at 3000g and washed twice with 50 cm3 of phosphate-buffered saline (PBS, pH 7.4) solution. The stock suspension of E. coli was prepared by resuspending the final bacterial pellets in PBS solution. The antibacterial activity of Ag0−TPS−DVB was checked by adding different quantities of resin samples (50 and 100 mg) to 10 cm3 of E. coli cell suspensions contained in PBS solution (pH 7.4). Each suspension was thoroughly mixed on an orbital shaker, and aliquots were withdrawn at regular intervals. The cell number density was examined by the spread plate method, in which the E. coli cells were spread on a nutrient agar plate and incubated at 37 °C for 24 h and then bacterial colonies were counted on a colony counter. A control experiment was conducted to evaluate the non-involvement of the TPS−DVB resin in the antibacterial activity.
broth, and agar−agar were purchased from Himedia Lab, Mumbai, India. The metal-ion concentrations were measured by inductively coupled plasma atomic emission spectroscopy (ICP−AES) (ARCOS, MS Spectro, Kleve, Germany) with an instrument detection limit (IDL) of 10 ppb for all metal ions. The samples were acidified with dilute HNO3 solution before being subjected to analysis. Under the operating conditions, a charge-coupled device (CCD) was used along with a radiofrequency (RF) generator power of 1400 W, and the frequency of the RF generator was 27.12 MHz. Argon was used as the auxiliary gas, as the nebulizer gas, and for the generation of plasma at flow rates of 1, 0.8, and 12 dm3/min, respectively. The pump speed was maintained at 30 rpm for injection of samples into the plasma. Absorption spectra of well-dispersed silver nanoparticles were recorded on a Perkin-Elmer UV−vis− 2700 double-beam spectrophotometer with an optical path length of 0.01 m. The polymer beads were analyzed by scanning electron microscopy (SEM, JEOL, JSM) for surface morphology. The beads were coated with platinum before scanning. The electric current was 15 mA, and the accelerating voltage was 20−30 kV. The elemental analysis of AgNPs in isolation and in polymer-embedded form (Ag0−TPS−DVB) was performed using energy-dispersive X-ray analysis (EDX) by SEM. Transmission electron microscopy (TEM) images were collected using a Philips CM200 microscope with an operating voltage of 200 kV. One milligram of nanosilver was added to 5 cm3 of spectroscopic-grade methanol and subjected to sonication for 15 min. A drop of the sample was deposited and dried on a grid before visualization. XRD analysis was performed using an X-ray powder diffractometer (Bruker AXS D8 Advance, Karlsruhe, Germany) equipped with PW3123/00 curved Ni-filtered Cu Kα radiation (λ = 1.54056 Å) generated at 40 kV and a current of 30 mA. Synthesis of Functional Modified Resin. Thiourea grafted on poly(styrene−DVB) resin (TPS−DVB) was synthesized and characterized according to the methods described in our previous report.11 Ion Uptake Studies. The silver ion uptake was investigated by suspending 20 mg of the resin in a stoppered conical flask containing 20 cm3 of silver nitrate solution with an initial concentration of 142 mg/dm3. The flask was kept on an orbital shaker with an agitation rate of 100 strokes/min at ambient temperature of 298 ± 2 K for 24 h to reach equilibrium. Samples were removed at regular intervals and analyzed for silver content by ICP−AES. To determine the equilibrium adsorption, the polymer beads were equilibrated with silver nitrate solutions of five different concentrations at 303, 313, and 323 K. The residual metal-ion concentrations were measured by ICP−AES. The competitive sorption of silver ions in the presence of other metal ions was performed in independent batches using binary mixtures of the metal ions with silver.
■
RESULTS AND DISCUSSION
The grafted TPS−DVB resins with a functional group loading of 2.2 mmol/g showed a specific Brunauer−Emmett−Teller (BET) macropore surface area of 31.4 m2/g and an average pore size of 353 Å, with a pore volume of 0.278 cm3/g.11 The functional modification was carried out by reacting thiourea with chloromethylated polystyrene (CMPS) to obtain the grafted polymer as shown in Scheme 1. Before the sorption study, this modified resin was tested for its oxidative stability in 6439
dx.doi.org/10.1021/ie3035866 | Ind. Eng. Chem. Res. 2013, 52, 6438−6445
Industrial & Engineering Chemistry Research
Article
Figure 1. Effect of pH on the sorption of silver ion and possible complexation with the adsorbent.
Figure 2. FTIR bands corresponding to Ag+−TPS−DVB at pH (A) 3.5 and (B) 1.0.
further confirmed the oxidative stability of TPS−DVB in the presence of silver ion. As the surface chemical properties of an adsorbent change with the pH of the solution, the sorption behavior of the resin was investigated at varying pH conditions. The pH range of 0− 7 was screened at constant values of the concentration of silver ions, amount of resin, equilibrium time, and temperature. Dilute aqueous solutions of HNO3 and NaOH, each with 0.1 mol/dm3 concentration, were used to maintain the pH of the AgNO3 solution. The amount of metal-ion uptake by the adsorbent was estimated from the initial and residual metal-ion concentrations (Co and Ce, respectively) in the aqueous solutions. The adsorption capacity per unit weight of adsorbent, Qav, was calculated from the difference in the concentrations (Co − Ce) and the weight of the solid adsorbent (Ws). Figure 1 shows the pH dependence of silver-ion sorption by the resin with possible complex formation between TPS−DVB and Ag+ over the studied pH range. A significant change in the Qav value in the pH range of 3.5−0 was observed. At pH values between 7 and 3.5, the amount of Ag+ adsorbed was nearly constant and was due to the interaction between sulfur of the thioether group and Ag+. As the pH was decreased from 3.5 to 1.0, an
the presence of silver ion. The grafted polymer is a derivative of isothiourea that is different from thiourea in its oxidative properties. Thiourea, containing the CS group, is extremely unstable toward oxidation because of the mismatch in size between the carbon and sulfur atoms, resulting in incomplete πorbital overlap.28 On the other hand, the isothiourea derivative (TPS−DVB) is stable toward oxidation because of the unavailability of an enolizable S−H bond. This was verified from the unchanged IR bands of the resin before and after sorption studies at neutral pH (Figure S1 of the Supporting Information). However, in acidic medium (pH 1.0), the FTIR spectral changes (Figure S2, Supporting Information) that occurred were not because of the oxidation but because of the shifting of the free base (TPS−DVB) to the isothiouronium salt (A) (Scheme 1). This was confirmed when a blank run was conducted in the absence of silver ion at acidic pH (1.0) containing the grafted polymeric resin (TPS−DVB). The FTIR spectral pattern obtained (from TPS−DVB to A) was found to be exactly identical to that expected for Scheme 1 (from A to TPS−DVB). This evidence supports the non-involvement of metal salt (Ag+) in the apparent FTIR spectral changes, which 6440
dx.doi.org/10.1021/ie3035866 | Ind. Eng. Chem. Res. 2013, 52, 6438−6445
Industrial & Engineering Chemistry Research
Article
increase in the Qav value was observed, which can be attributed to the greater stability of Ag+ ions in the acidic pH range and complex formation between the positive part of the imine salt with the anion part of the metal salt.29−31 This was confirmed as the value of the equilibrium pH was always less than the initial pH of the solution and the characteristic peak for the imine salt (2051 cm−1) was observed in the FTIR spectrum of the beads (Figure 2). Panels A and B of Figure 2 show the IR bands corresponding to Ag+−TPS−DVB at pH 3.5 and 1.0, respectively. At pH values below 1.0, a sharp decrease in the adsorbed amount was observed because of the leaching of the ligand from the polymer surface. This was further verified from the elemental composition of the resin measured after the adsorption run at that pH (Table S1, Supporting Information). The resin was found to be stable over a pH range of 7−1, and the maximum adsorption capacity was in the pH range between 1.0 and 1.5. The higher adsorption capacity toward Ag+ at low pH values makes this resin useful for the separation of silver ions, if present with other metal ions from different sources. The interference of other metal ions in the sorption of silver ion was studied at pH 1.0 to evaluate the selectivity of the resin. The competitive sorption of Ag+ was carried out from aqueous solutions of a binary mixtures of nitrate salts of both silver and M, where M = Co2+, Cu2+, Ni2+, Zn2+, Cd2+, Pb2+, Hg2+, Pd2+, Cs1+, Sr2+, and La3+. The separation factor (α) between each pair of metal ions is a measure of the selective sorption of Ag+ by the adsorbent. It was calculated as the ratio of the distribution coefficients of the two metal ions
α=
KdAg KdM
(1)
where Kd (dm3/g) is the distribution coefficient, which is calculated as Kd =
Co − Ce V CeWs
Figure 3. (A) Effect of contact time. (B) Lagergren’s plot. (C) Intraparticle diffusion plot.
uptake rate decreased, and it took almost 24 h to reach 97% of the equilibrium adsorption capacity. The adsorption kinetics can be explained through Lagergren’s model for the removal of heavy metals from aqueous solutions as represented by the equation33,34
(2)
Table S2 (Supporting Information) shows that, except for Hg(II), the resin exhibited an excellent selectivity for silver ions over other divalent transition metals such as Co, Ni, Cu, Zn, and Cd; alkali and alkaline earth metals such as Cs+ and Sr2+; pblock elements such as Pb2+; and trivalent lanthanum. Table S2 (Supporting Information) also compares the separation factors obtained in the current process with those reported in the literature. The α values for Ag+ with the TPS−DVB resin are quite high as compared to those with the other adsorbents. There are several cases where the selective separation of silver ion is needed from other metal ions, especially from samegroup elements such as copper. Ag/Cu separation in the field of hydrometallurgy has generated significant interest among researchers for developing a good extractant or adsorbent.6,32 The TPS−DVB resin with αAg(I)/Cu(II) = 1556 can thus be used for the efficient separation of these two elements. Hence, resin with such a high separation factor can be used for the selective separation or preconcentration of silver ions from aqueous solutions. The lack of selectivity of the resin for the separation of Ag(I)/Hg(II) mixtures could be because of the equal affinities of the thioether group toward these two ions. Figure 3A shows the time-dependent sorption of silver ion on the resin. A minimum of 24 h was required to reach equilibrium. As expected, the initial rate of adsorption was high because of the large number of available vacant sites, and 50% of the adsorption was complete within 3 h. However, the
log(qe − qt ) = log qe −
⎛ k ⎞ ⎜ ⎟t ⎝ 2.303 ⎠
(3)
where k is the rate constant for pseudo-first-order adsorption (h−1) and qe and qt are the amounts of Ag+ adsorbed on the adsorbent (mg/g) at equilibrium and at time t, respectively. The theoretical qe value and the rate constant k were calculated from the intercept and slope, respectively, of the plot of log(qe − qt) versus t (Figure 3B). Because the calculated qe value (130 mg/g) agrees with the experimental data (135 mg/g), the adsorption kinetics is well represented by Lagergren’s model. Further, the rate of adsorption of silver ions on the polymer matrix was verified for intraparticle diffusion limitations where the intraparticle diffusional characterization constant (kid, mmol g−1 min−0.5) was calculated from the slope of the plot of ln(qt) versus ln(t) (Figure 3C).29 A comparison with the value for thiourea-modified chitosan for the adsorption of Ag+ (kid =1.368)29 shows that the kid value for the adsorption of Ag+ obtained in the current process (4.78) was almost 3 times higher.29 Further, the adsorption of silver ion on TPS−DVB resin was studied at three different temperatures keeping the optimum pH (∼1.0) and equilibrium period (24 h) constant (Figure 4). 6441
dx.doi.org/10.1021/ie3035866 | Ind. Eng. Chem. Res. 2013, 52, 6438−6445
Industrial & Engineering Chemistry Research
Article
over the matrix support. The mechanism of action is shown in Figure 5.
Figure 5. Graphical representation of the adsorption−reduction of Ag+ on TPS−DVB beads.
AgNPs, with a high surface free energy, were stabilized by the functional groups present on the polymer surface. The stability of Ag0 on the support was investigated by separate leaching experiments. The rate of release of Ag0 from the polymer in a batch process was found to be 0.02% per hour at 50−55 °C. This shows the good stability of Ag0 nanoparticles over the polymer support. However, AgNPs in free form can be obtained by subjecting the Ag0−TPS−DVB resin to ultrasonication. Figure 6 shows the percent leaching of Ag0 with
Figure 4. Adsorption isotherms of silver ion on the resin at different temperatures.
The experimental batch adsorption data were further analyzed through the Langmuir model, the mathematical expression of which is given by Ce Ce 1 = + Q av Q max KLQ max
(4)
3
where Ce (mg/dm ) is the concentration of metal ions in the solution at equilibrium, Qav is the metal-ion concentration in the resin phase (mg/dm3), Qmax (mg/g) is the Langmuir constant representing the maximum monolayer adsorption capacity, and KL (dm3/mg) is the Langmuir constant related to the energy of adsorption. A good correlation between the experimentally adsorbed amount (qexp) and the value obtained from the Langmuir model (qpre) was found for the uptake of silver ions. The values of KL and Qmax at different temperatures are reported in Table S3 (Supporting Information). Because both the adsorption constant and the adsorption capacity decreased with increasing temperature, the adsorption process is accompanied by the release of energy. The magnitude of energy (enthalpy) released was calculated using the van’t Hoff equation35
Figure 6. Rate of leaching of Ag+ from the polymer support.
time in the ultrasonication process. Almost 50% of the AgNPs were released into the solution within 30 s at 50−55 °C, and the rest were released within 200 s to reach a plateau. Figure 7A,B shows a comparison of SEM images of the polymer surface before and after the ultrasonication process. Figure 7A shows the embedded nanoparticles on the surface of the polymer, whereas Figure 7B shows the bare surface. Panels C and D of Figure 7 show the elemental analyses of the beads before and after ultrasonication, respectively, confirming the complete release of the AgNPs during the ultrasonication process. The optical properties of the AgNPs were examined by UV− vis spectroscopy. AgNPs are known to display size quantization properties; thus, a change in optical properties is expected with changing particle size and shape. The AgNPs are strongly efficient for absorbing and scattering light. The strong interaction of the AgNPs with light occurs because the conduction of electrons on the surface of the metal undergoes surface plasmon resonance (SPR) when excited by light at specific wavelengths.36,37 An intense SPR band centered at 410 nm was observed when AgNPs properly dispersed in water were scanned between 200−800 nm with a resolution of 1 nm (Figure S4, Supporting Information). The symmetrical nature
−ΔH ΔS + (5) RT R where R is the gas constant (8.314 J/mol. K) and T is the absolute temperature. The enthalpy (ΔH, J/mol) and entropy (ΔS, J mol−1 K−1) obtained from the slope and intercept, respectively, of the plot of ln(KL) against 1/T are reported in Table S3 (Supporting Information). The Gibbs free energy (ΔG) of the sorption process, calculated at three different temperatures, is also included in Table S3 (Supporting Information). Quantitatively, 1.0 g of the resin was found to adsorb 135 mg of silver ion. The presence of silver ion on the polymer matrix was supported by elemental analysis. The peaks in the EDX spectrum (Figure S3, Supporting Information) at 2.31 and 2.98 keV correspond to the binding energies of SKa and AgLa, respectively. After the adsorption process, the Ag+loaded resins (Ag+−TPS−DVB) were subjected to a reduction technique in which hydrazine hydrate was used as the reducing agent (Experimental Section) to produce Ag0 nanoparticles ln KL =
6442
dx.doi.org/10.1021/ie3035866 | Ind. Eng. Chem. Res. 2013, 52, 6438−6445
Industrial & Engineering Chemistry Research
Article
Figure 7. (A,B) SEM images and (C,D) EDX spectra of the polymer surface (A,C) before and (B,D) after ultrasonication.
Figure 8. High-resolution TEM image and PSD of as-prepared AgNPs.
and (222) crystal planes suggests that the nanoparticles are mostly oriented in the (111) plane. The literature data show that the prime factor in the antibacterial properties of AgNPs is the presence of the (111) lattice plane.40,41 The interplanar spacing (dhkl) values calculated from Bragg’s law for the respective planes were 2.354, 2.038, 1.441, 1.231, and 1.181 Å, and the value of the lattice constant was 4.077 Å. These values are in good agreement with the data reported for standard silver (JCPDS PDF card 04-0783). From the XRD spectrum, the average crystalline size of the nanoparticles was obtained using the full width at half-maximum (fwhm) according to the Debye−Scherrer formula42
of the plasma band suggests a narrow particle size distribution. The TEM image (Figure 8) shows the well dispersed and spherical nature of the as-prepared AgNPs in the range of 4−12 nm. Image analysis indicating the particle size distribution with a mean diameter of 8 nm is also shown in Figure 8. The EDX analysis of AgNPs for the elemental composition shows peaks at 2.98, 3.15, and 3.41 keV corresponding to the binding energies of AgLa, AgLb, and AgLb2, respectively, indicating the presence of only silver in the sample (Figure S5, Supporting Information). The diffraction peaks of the AgNPs were recorded at Bragg angles of 38.1°, 44.3°, 64.3°, 77.43°, and 81.5°, which can be indexed to the lattice planes for (111), (200), (220), (311), and (222), respectively, of fcc crystals (Figure S6, Supporting Information).38,39 A high intensity of the (111) crystal plane compared to the (200), (220), (311),
d= 6443
Kλ β cos θ
(6)
dx.doi.org/10.1021/ie3035866 | Ind. Eng. Chem. Res. 2013, 52, 6438−6445
Industrial & Engineering Chemistry Research
Article
where K is the Scherrer constant (0.89), λ (1.54 Å) is the wavelength of the X-rays, β is the fwhm (0.0134), and θ is the Bragg angle. The d value (11 nm) calculated from this equation is comparable to that determined from the particle size distribution (PSD) data obtained from the TEM measurements. The AgNPs prepared in this work can be used in several applications either alone (catalysis, electronics, surfaceenhanced Raman spectroscopy, lubricating materials, biosensing, paints, medicine, clothing, cosmetics, sunscreens, and food products)40,43−45 or in embedded form making a hybrid organic−inorganic nanocomposite19−21 (antibacterial−antifungal agent, adsorbent for the removal of toxic metal ions from water, and catalyst).1,2 Embedded nanosilver on the polymer support (Ag0−TPS−DVB) was tested for its bactericidal activity. Figure 9 shows the antibacterial activity of Ag0−
can be useful for the selective separation of silver ions from Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Cs1+, Sr2+, Pb2+, La3+, and Pd2+. The adsorption process was controlled by Lagergren’s kinetic model and was well fitted by the Langmuir model. The chemical reduction of the adsorbed Ag+ formed silver nanoparticles capped on the polymer beads that were oriented in the fcc phase with a mean diameter of 8 nm and showed antibacterial activity against Escherichia coli.
■
ASSOCIATED CONTENT
S Supporting Information *
FTIR spectra of the resin before and after sorption study at neutral pH (Figure S1). FTIR spectral changes from free base (TPS−DVB) to the isothiouronium salt at acidic pH (1.0) (Figure S2). EDX spectrum of Ag+−TPS−DVB resin (Figure S3). Electronic spectrum, EDX spectrum, and XRD pattern of as-prepared AgNPs (Figures S4−S6, respectively). Elemental compositions of the resin at different pH values (Table S1). Competitive sorption study of Ag+ in the presence of other metal salts and comparison with literature data (Table S2). Langmuir constant at different temperatures for the adsorption of Ag+ and calculated thermodynamic parameters (Table S3). This material is available free of charge via the Internet at http://pubs.acs.org.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Tel.: +91-22-33612013. Fax: +91-22-33611020. Notes
The authors declare no competing financial interest.
■
Figure 9. Antibacterial activity of Ag0−TPS−DVB against E. coli as a function of time.
ACKNOWLEDGMENTS P.K thanks the University Grant Commission (India) for financial assistance and IITB SAIF, IITB Department of Earth Science, for analytical support.
TPS−DVB when exposed to E. coli as a function of time. The antibacterial activity of nanosilver toward E. coli is because of the interaction of metallic silver with the thiol groups of the enzymes and proteins that are important for bacterial respiration and the transport of important substances across/ within the cell membrane and the alteration of the function of bacterial cell membrane due to silver binding to the cell membrane.46 A 63% reduction in bacterial count was obtained in 0.5 h for 50 mg of resin. Further, with an increase in the resin loading to 100 mg, an increase in the antibacterial activity (100%) was observed within the same time. No bacterial count was observed after 1.0 h of contact time. Literature data show that the antibacterial effect of embedded nanosilver on various supports is strongly dependent on the release rate of silver ions and the direct contact of the AgNPs with the cells.47 In the current study, because the release rate of silver from the polymer support was negligible under the given hydrodynamic conditions, the antibacterial activity was because of the direct contact of the cell membrane with the surface of the metallic silver.
■
REFERENCES
(1) Sumesh, E.; Bootharaju, M. S.; Anshup, Pradeep, T. A Practical Silver Nanoparticle-Based Adsorbent for the Removal of Hg2+ from Water. J. Hazard. Mater. 2011, 189, 450. (2) Wei, Q.; Li, B.; Li, C.; Wang, J.; Wang, W.; Yang, X. PVP-Capped Silver Nanoparticles as Catalysts for Polymerization of Alkylsilanes to Siloxane Composite Microspheres. J. Mater. Chem. 2006, 16, 360. (3) Raju, C. S. K.; Subramanian, M. S. A Novel Solid Phase Extraction Method for Separation of Actinides and Lanthanides from High Acidic Streams. Sep. Purif. Technol. 2007, 55, 16. (4) Raju, C. S. K.; Subramanian, M. S. Sequential Separation of Lanthanides, Thorium and Uranium Using Novel Solid Phase Extraction Method from High Acidic Nuclear Wastes. J. Hazard. Mater. 2007, 145, 315. (5) Kumar, P.; Madyal, R. S.; Joshi, U. K.; Gaikar, V. G. Design and Synthesis of Polymer-Bound Penta-aza Ligand for Selective Adsorptive Separation of Cobalt(II) from Zirconium(IV). Ind. Eng. Chem. Res. 2011, 50, 8195. (6) Abd El-Ghaffar, M. A.; Abdel-Wahab, Z. H.; Elwakeel, K. Z. Extraction and Separation Studies of Silver(I) and Copper(II) from Their Aqueous Solution Using Chemically Modified Melamine Resins. Hydrometallurgy 2009, 96, 27. (7) Xu, Q.; Yin, P.; Zhao, G.; Sun, Y.; Qu, R. Adsorption Selectivity and Dynamic Adsorption Behaviors of Cu(II), Ag(I), and Au(III) on Silica Gel Encapsulated by Amino Functionalized Polystyrene. J. Appl. Polym. Sci. 2010, 117, 3645.
■
CONCLUSIONS The adsorption of silver ion on thiourea-grafted mesoporous polystyrene beads shows the optimum sorption of Ag+ at a pH of 1−1.5 with a maximum adsorption capacity of 135 mg of Ag+ per gram of resin. The resin showed high selectivity for Ag+ and 6444
dx.doi.org/10.1021/ie3035866 | Ind. Eng. Chem. Res. 2013, 52, 6438−6445
Industrial & Engineering Chemistry Research
Article
(8) Syed Moosa Hasany, S. M.; Ahmad, R. Removal of Traces of Silver Ions from Aqueous Solutions Using Coconut Husk as a Sorbent. Sep. Sci. Technol. 2004, 39, 3509. (9) Wang, X.; Zhang, L.; Ma, C.; Song, R.; Hou, H.; Li, D. Enrichment and Separation of Silver from Waste Solutions by Metal Ion Imprinted Membrane. Hydrometallurgy 2009, 100, 82. (10) Abd El-Ghaffar, M. A.; Mohamed, M. H.; Elwakeel, K. Z. Adsorption of Silver(I) on Synthetic Chelating Polymer Derived from 3-Amino-1,2,4-triazole-5-thiol and Glutaraldehyde. Chem. Eng. J. 2009, 151, 30. (11) Kumar, P.; Ansari, K. B.; Gaikar, V. G. Selective Removal of Silver Impurity from Oxaliplatin by Sorption on Functionalized Polymer. Ind. Eng. Chem. Res. 2012, 51, 14209. (12) Gherrou, A.; Kerdjoudj, H.; Molinari, R.; Drioli, E. Removal of Silver and Copper Ions from Acidic Thiourea Solutions with a Supported Liquid Membrane Containing D2EHPA as Carrier. Sep. Purif. Technol. 2002, 28, 235. (13) Huang, M.; Tso, E.; Datye, A. K. Removal of Silver in Photographic Processing Waste by TiO2-Based Photocatalysis. Environ. Sci. Technol. 1996, 30, 3084. (14) Nakiboglu, N.; Toscalı, D.; Nişli, G. A Novel Silver Recovery Method from Waste Photographic Films with NaOH Stripping. Turk. J. Chem. 2003, 27, 127. (15) Purcell, T. W.; Peters, J. J. Sources of Silver in the Environment. Environ. Toxicol. Chem. 1998, 17, 539. (16) Renner, H. Silver, Silver Compounds and Silver Alloys. In Ullmann’s Encyclopedia of Industrial Chemistry, 5th ed.; Elvers, B., Hawkins, S., Russey, W., Schulz, G., Eds.; Wiley−VCH Verlag GmbH: Weinheim, Germany, 1993; Vol. A24. (17) Scow, K.; Goyer, M.; Nelken, L. Exposure Risk Assessment for Silver; Technical Report prepared for Office of Water Regulations and Standards; U.S. Environmental Protection Agency: Washington, DC, 1981; p 228. (18) Lockhart, H. B. Silver Compounds. In Kirk−Othmer Encyclopedia of Chemical Technology, 2nd ed.; Grayson, M., Ed; John Wiley & Sons: New York, 1983; Vol. 21, pp 16−32. (19) Chibac, A.; Melinte, V.; Buruiana, T.; Balan, L.; Buruiana, E. C. One-Pot Synthesis of Photocrosslinked Sol−Gel Hybrid Composites Containing Silver Nanoparticles in Urethane−Acrylic Matrixes. Chem. Eng. J. 2012, 200−202, 577. (20) Długosz, M.; Bulwan, M.; Kania, G.; Nowakowska, M.; Zapotoczny, S. Hybrid Calcium Carbonate/Polymer Microparticles Containing Silver Nanoparticles as Antibacterial Agents. J. Nanopart. Res. 2012, 14, 1313. (21) Cheng, Y. J.; Zeiger, D. N.; Howarter, J. A.; Zhang, X.; Lin, N. J.; Antonucci, J. M.; Gibson, S. L. In situ Formation of Silver Nanoparticles in Photocrosslinking Polymers. J. Biomed. Mater. Res. B 2011, 97 (1), 124. (22) Jun, B. H.; Byun, J. W.; Jee Yeon Kim, J. Y.; Kang, H.; Park, H. J.; Jeyong Yoon, J.; Lee, Y. S. Facile Method of Preparing SilverEmbedded Polymer Beads and Their Antibacterial Effect. J. Mater. Sci. 2010, 45, 3106. (23) Mandal, A.; Meda, V.; Zhang, W. J.; Farhan, K. M.; Gnanamani, A. Synthesis, Characterization and Comparison of Antimicrobial Activity of PEG/TritonX-100 Capped Silver Nanoparticles on Collagen Scaffold. Colloids Surf. B 2012, 90, 191. (24) Ivan Sondi, I.; Salopek-Sondi, B. Silver Nanoparticles as Antimicrobial Agent: A Case Study on E. coli as a Model for GramNegative Bacteria. J. Colloid Interface Sci. 2004, 275, 177. (25) Morones, J. R.; Elechiguerra, J. L.; Camacho, A.; Holt, K.; Kouri, J. B.; Ramirez, J. T.; Yacaman, M. J. The Bactericidal Effect of Silver Nanoparticles. Nanotechnology 2005, 16, 2346. (26) Kong, H.; Jang, J. Antibacterial Properties of Novel Poly(methyl methacrylate) Nanofiber Containing Silver Nanoparticles. Langmuir 2008, 24, 2051. (27) Garcia-Barrasa, J.; Lopez-de Luzuriaga, J. M.; Miguel Monge, M. Silver Nanoparticles: Synthesis through Chemical Methods in Solution and Biomedical Applications. Cent. Eur. J. Chem. 2011, 9, 7.
(28) Sahu, S.; Sahoo, P. R.; Patel, S.; Mishra, B. K. Oxidation of Thiourea and Substituted Thioureas: A Review. J. Sulfur Chem. 2011, 32, 171. (29) Wang, L.; Xing, R.; Liu, S.; Yu, H.; Qin, Y.; Li, K.; Feng, J.; Li, R.; Li, P. Recovery of Silver(I) Using a Thiourea-Modified Chitosan Resin. J. Hazard. Mater. 2010, 180, 577. (30) Donia, A. M.; Atia, A. A.; Elwakeel, K. Z. Recovery of Gold(III) and Silver(I) on a Chemically Modified Chitosan with Magnetic Properties. Hydrometallurgy 2007, 87, 197. (31) El-Menshawy, A. M.; Kenawy, I. M.; El-Asmy, A. A. Modification of Chloromethylated Polystyrene with 2-Mercabtobenzothiazole for Application as a New Sorbent for Preconcentration and Determination of Ag+ from Different Matrices. J. Hazard. Mater. 2010, 173, 523. (32) Diehl, H.; Butler, J. P. The Separation of Silver from Copper by Electro-Deposition from Ammoniacal Solution. Analyst 1952, 77, 268. (33) Hsien, L.; Yu, K.; Jia, C. Equilibrium and Kinetics of Heavy Metal Ion Exchange. J. Chin. Inst. Chem. Eng. 2007, 38, 71. (34) Meena, A. K.; Rajagopal, C.; Mishra, G. K. Removal of Heavy Metal Ions from Aqueous Solutions Using Chemically (Na2S) Treated Granular Activated Carbon as an Adsorbent. J. Sci. Ind. Res. 2010, 69, 449. (35) Atia, A.; Donia, A. M.; El-Boraey, H. A.; Mabrouk, D. H. Adsorption of Ag(I) on Glycidyl Methacrylate/N,N-Methylene BisAcrylamide Chelating Resins with Embedded Iron oxide. Sep. Purif. Technol. 2006, 48 (3), 281. (36) Gopinath, V.; Mubarak-Ali, D.; Priyadarshini, S.; Priyadharsshini, N. M.; Thajuddin, N.; Velusamy, P. Biosynthesis of Silver Nanoparticles from Tribulus terrestris and Its Antimicrobial Activity: A Novel Biological Approach. Colloids Surf. B 2012, 96, 69. (37) Kora, A. J.; Sashidhar, R. B.; Arunachalam, J. Aqueous Extract of Gum Olibanum (Boswellia serrata): A Reductant and Stabilizer for the Biosynthesis of Antibacterial Silver Nanoparticles. Process Biochem. 2012, 47, 1516. (38) Shukla, M. K.; Singh, R. P.; Reddy, C. R. K.; Jha, B. Synthesis and Characterization of Agar-Based Silver Nanoparticles and Nanocomposite Film with Antibacterial Applications. Bioresour. Technol. 2012, 107, 295. (39) Bhatte, K. D.; Deshmukh, K. M.; Patil, Y. P.; Sawant, D. N.; Fujita, S.; Arai, M.; Bhanage, B. M. Synthesis of Powdered Silver Nanoparticles Using Hydrogen in Aqueous Medium. Particuology 2012, 10, 140. (40) Pal, S.; Tak, Y. K.; Song, J. M. Does the Antibacterial Activity of Silver Nanoparticles Depend on the Shape of the Nanoparticle? A Study of the Gram-Negative Bacterium Escherichia coli. Appl. Environ. Microbiol. 2007, 73, 1712. (41) Amin, M.; Anwar, F.; Janjua, M. R. S. A.; Iqbal, M. A.; Rashid, U. Green Synthesis of Silver Nanoparticles through Reduction with Solanum xanthocarpum L. Berry Extract: Characterization, Antimicrobial and Urease Inhibitory Activities against Helicobacter pylori. Int. J. Mol. Sci. 2012, 13, 9923. (42) Boulch, F.; Schouler, M. C.; Donnadieu, P.; Chaix, J. M.; Djurado, E. Domain Size Distribution of Y-Tzp Nano-Particles Using XRD and HRTEM. Image Anal. Stereol. 2001, 20, 157. (43) Chimentao, R. J.; Kirm, I.; Medina, F.; Rodríguez, X.; Cesteros, Y.; Salagre, P.; Sueirasa, J. E. Different Morphologies of Silver Nanoparticles as Catalysts for the Selective Oxidation of Styrene in the Gas Phase. Chem. Commun. 2004, 846. (44) Cole, J. R.; Halas, N. J. Optimized Plasmonic Nanoparticle Distributions for Solar Spectrum Harvesting. Appl. Phys. Lett. 2006, 89, 153120. (45) Savage, N.; Diallo, M. S. Nanomaterials and Water Purification: Opportunities and Challenges. J. Nanoparticle Res. 2005, 7, 331. (46) Sadeghi, B.; Jamali, M.; Kia, Sh.; Amininia, A.; Ghafari, S. Synthesis and Characterization of Silver Nanoparticles for Antibacterial Activity. Int. J. Nano Dimens. 2010, 1, 119. (47) Jun, B. H.; Byun, J. W.; Kim, J. Y.; Kang, H.; Park, H. J.; Yoon, J.; Lee, Y. C. Facile Method of Preparing Silver-Embedded Polymer Beads and Their Antibacterial Effect. J. Mater. Sci. 2010, 45, 3106. 6445
dx.doi.org/10.1021/ie3035866 | Ind. Eng. Chem. Res. 2013, 52, 6438−6445
