Polyamidoamine Dendrimers and

Article pubs.acs.org/jced

Preparation of Graphene-Oxide/Polyamidoamine Dendrimers and Their Adsorption Properties toward Some Heavy Metal Ions Fan Zhang,*,†,‡ Bo Wang,† Shengfu He,† and Ruilin Man‡ †

College of Chemistry and Chemical Engineering, Jishou University, Jishou 416000, China College of Chemistry and Chemical Engineering, Central South University, Changsha, 410083, China

‡

Downloaded via TULANE UNIV on December 20, 2018 at 12:14:17 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: Graphene oxide/polyamidoamine dendrimers (GO/PAMAMs) were prepared via a “grafting to” method. The adsorption behavior of the GO/ PAMAMs for Pb(II), Cd(II), Cu(II), and Mn(II) was studied, and the effects of solution pH, adsorption time, and initial metal ion concentration on adsorption capacity of the adsorbent were also investigated. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic processes, and the results indicated that the adsorption of Pb(II), Cd(II), Cu(II), and Mn(II) followed a second-order type reaction kinetics and the adsorption of Pb(II), Cd(II), Cu(II), and Mn(II) onto GO/PAMAMs is a chemical adsorption. The adsorption capacities of GO/PAMAMs were found to be 568.18, 253.81, 68.68, and 18.29 mg/g for Pb(II), Cd(II), Cu(II), and Mn(II), respectively. The adsorption reached equilibrium within 60 min and characteristics of the adsorption process were evaluated by using the Langmuir and Freundlich isotherm models. The adsorption processes fit better with the Langmuir model for Cu(II) and Mn(II) than for Pb(II) and Cd(II); the adsorption of Cu(II) and Mn(II) on GO/PAMAMs was a typical monomolecular layer adsorption.

■

INTRODUCTION There are plenty of mineral resources in Western Hunan in China; however, a lot of wastewater and waste residue containing heavy metal ions affect sustainable exploitation and utilization of the mineral resources. Water pollution by heavy metal ions has become an urgent problem to be solved. Adsorptive removal of heavy metal ions has been widely applied using such materials as activated carbon,1−4 multiwalled carbon nanotubes, 5−8 zeolites,9−12 chitosan,13−20 metal oxide,21,22 polymer absorbents,23 and agricultural byproducts.24,25 Recently, some effective adsorbents based on graphene and graphene composites were made and applied in removing heavy metal ions.26−34 For example, the polypyrrole− reduce graphene oxide composite showed a highly selective removal capacity with a high Hg2+ adsorption capacity of 980 mg·g−1 and an extremely high desorption rate of up to 92.3 %, showing practical utility for wastewater treatment.26 Graphene oxide (GO) aerogels prepared by a unidirectional freeze-drying method were used as an effective adsorbent for Cu2+ removal from water.28 Deng et al. found that the functionalized graphene could be fabricated by a simple and fast method of electrolysis with potassium hexafluorophosphate solution as electrolyte under the static potential of 15 V; the adsorption processes reached equilibrium in just 40 min and the adsorption isotherms were described well by Langmuir and Freundlich classical isotherms models.33 Polyamidoamine dendrimers (PAMAMs) are highly reactive because of the presence of a large amount of terminal functional groups.35,36 Mamadou et al.37 found that the Cu(II) © 2014 American Chemical Society

binding capacities of the EDA core PAMAM dendrimers were much larger and more sensitive to solution pH than those of linear polymers with amino groups, and the metal ion laden dendrimers can be regenerated by decreasing the solution pH to 4.0, thus enabling the recovery of the bound Cu(II) ions and recycling of the dendrimers. Dendrimer/titania composite materials prepared by the effective immobilization of dendrimers onto titania could improve metal ion removal from industrial wastewater.38 The GO-PAMAMs were prepared via a “grafting-from” strategy by Yang Yuan et al.39 The total adsorption capacity of these heavy metal ions can reach 1.0007 mmol/g. In the present study, GO was modified by PAMAMs via a “graftingto” method. Compared to the grafting-from strategy, the GO/ PAMAMs were prepared more easily and present more efficient adsorption properties for heavy metal ions. The adsorption behavior of GO/PAMAMs for heavy metal ions in water solution was studied by changing the concentration of heavy metal ions, pH values, and temperature. To interpret the mechanisms of metal adsorption processes, the pseudo-firstorder and pseudo-second-order kinetic models were all used to describe the kinetic processes. Meanwhile, the characteristics of the adsorption process were evaluated by using the Langmuir and Freundlich isotherm models. Received: March 12, 2014 Accepted: April 8, 2014 Published: April 21, 2014 1719

dx.doi.org/10.1021/je500219e | J. Chem. Eng. Data 2014, 59, 1719−1726

Journal of Chemical & Engineering Data

■

Article

EXPERIMENTAL SECTION Materials. The suppliers and purities of the chemicals used in this work are listed in Table 1.

1.5 h, forming a thick paste. After the addition of distilled water (80 mL), the solution was stirred at 90 ± 5 °C for 0.5 h. Then distilled water (200 mL) was added, followed by slow addition of H2O2 (7 mL, 30 %), which turned the color of the solution from dark brown to yellow. The warm solution was then filtered and washed with the distilled water. High-speed centrifugation was done at 9000 r/min for 15 min. It was repeated until the solution was neatly neutral. Then the distilled water inside the solution was replaced by DMF. Finally, the graphene oxide dispersion in DMF was sonicated for 1 h with the use of an ultrasonic cleaner. Preparation of PAMAMs. Generation 2 PAMAMs (G2 PAMAMs) can be easily prepared according to the procedures described in the literature.35,36 In this paper, G2 PAMAMs were used to modify the GO (Scheme 1). Preparation of GO/PAMAM Composites. A typical example of the preparation of GO/PAMAMs is given as follows:42,43 A 5 g sample of G2-PAMAMs solved in 20 mL of absolute methanol was added into 120 mL of the DMF solution of exfoliated GO (1.0 g) with magnetic stirring in a 250 mL glass flask. After being refluxed in a water bath for 24 h at 80 °C, the warm solution was then filtered and washed with absolute ethanol (200 mL). The filter wafer was then dispersed in absolute ethanol (200 mL) by mechanical agitation. This was repeated until all excess of G2-PAMAMs was removed (4 times) from the precipitates. The colloidal sediment was transferred into a glass dish and dried under vacuum at 100 °C for 12 h. Characterization. The GO/PAMAMs were analyzed by Fourier transform infrared (FT-IR) (Nicolet iS10, Thermo Fisher Scientific) using KBr pellets in the 4000 cm−1 to 500 cm−1 region. Thermogravimetric analysis (TGA/DSC1, Mettler Toledo) measurement was performed under nitrogen atmosphere from 40 °C to 800 °C at a heating rate 10 °C/min. Raman spectra were obtained using a confocal microprobe Raman system (Renishaw, RM 2000). Scanning electron

Table 1. Chemical Suppliers and Purities chemical name N,N-dimethylformamide graphite lead nitrate cadmium nitrate tetrahydrate copper sulfate pentahydrate manganese sulfate monohydrate sodium nitrate potassium permanganate concentrated sulfuric acid hydrogen peroxide a

supplier Shanghai Reagents Pingdu Graphite Tianjin Chemical Reagent Tianjin Chemical Reagent Tianjin Chemical Reagent Tianjin Chemical Reagent Shanghai Reagents Shanghai Reagents Shanghai Reagents Shanghai Reagents

supplier weight % puritya 99.0 99.0 99.0 99.0 99.0 99.0 99.0 99.5 98.0 30.0

Used without further purification.

Graphite, lead nitrate, cadmium nitrate tetrahydrate, copper sulfate pentahydrate, manganese sulfate monohydrate, sodium nitrate, and potassium permanganate were prepared using an electronic balance with uncertainty of 0.001 g, and N,Ndimethylformamide, concentrated sulfuric acid, and hydrogen peroxide were prepared using a graduated container with uncertainty of 0.1 mL. Preparation of Dimethylformamide (DMF) Solution of GO. GO was prepared by a modified Hummers method.40,41 In a typical reaction, graphite (1.0 g), NaNO3 (1.0 g), and H2SO4 (46 mL) were stirred together in an ice bath. KMnO4 (6.0 g) was then slowly added. Once mixed, the solution was transferred to a 35 ± 5 °C water bath and stirred for about Scheme 1. Preparation of GO/PAMAM Composites

1720



Article

of carbonyl or carboxyl groups. The bands at 1385 cm−1 and 1240 cm−1 in GO/PAMAMs are attributed to the stretching of the C−N, −NH2 groups.44 It is noted that new bands also appeared at 3380 cm−1 (−NH−), 1650 cm−1 and 1521 cm−1 (−CONH−), and 1450 cm−1(−CH2−),45 which demonstrated that the PAMAMs have been grafted onto the flakes of GO. Raman spectroscopy can provide some information on the defects (D-band), in-plane vibration of sp2 carbon atoms (Gband), as well as the stacking orders (2D-band). The intensity ratio (ID/IG) of the D and G peaks is often referred to present the quantities of defects in the carbon materials.45,46 Compared to the Raman spectrum of graphite displaying a typical G peak at 1585 cm−1, the G peak of the GO band is broadened and shifted to 1595 cm−1 (see Supporting Information, Figure S1). The Raman spectrum of the GO/PAMAMs also contains both a G and D band at 1595 cm−1 and 1353 cm−1, respectively, and the ratio of ID and IG decreased from 1.04 (GO) to 1.01 (GO/ PAMAMs). The results are attributed to the creation of some structural defects such as vacancies and topological defects generated during the oxidation-modification process. The XRD pattern of graphite exhibits a single peak at 26.2° corresponding to an interlayer spacing of 0.345 nm. As for the graphene oxide, it shows a major peak at 11.1° and the interlayer spacing of 0.7964 nm due to the introduction of the oxygen functional groups; the XRD diffraction peak of GO/ PAMAMs shows a broad peak at 21.6°47 (see Supporting Information, Figure S2). The weight loss (∼3 wt %) of the GO/PAMAMs up to 100 °C could be primarily due to evaporation of solvent. From 100 °C to 200 °C, the GO/PAMAMs lost weight (∼5 wt %) suggesting that GO was reduced into graphene sheets and showed a better thermal stability48 (see Supporting Information, Figure S3). The SEM image and its magnification of GO/PAMAMs are shown in Figure 2 panels a and b, respectively. GO/PAMAMs exhibit a porous structure and are expected to have more adsorption sites for the removal of heavy metal ions. However, due to the interaction of the oxygen-containing functional groups, the surface of GO sheets is relatively smooth and compact.44 The BET specific surface area of GO/PAMAMs is 25 m2/g, which was much lower than that of previous graphene oxide sample data.43 This might be due to the incomplete exfoliation of graphene oxide and the agglomerations occurred during the preparation process. As shown in Scheme 1, the multiamino groups in GO/PAMAMs were easily reacted with the epoxy or carboxyl in another GO flake, which should result in the agglomerations of GO/PAMAMs. The multiamino and carboxyl groups of GO/PAMAMs had good chemical adsorption property to heavy metal ions.49 The adsorption performances of GO/PAMAMs for metal ions at different solution pH values are shown in Figure 3. As shown in Figure 3, the adsorption capacities for heavy metal ions varied with increasing solution pH. At pH lower than 3, the H3O+ ions of higher concentration will compete with M(II) to seize the adsorption sites.50 As a result, less adsorption capacities were observed at low pH. With an increase of pH, the protonation degree of the amino groups weakened, and the coordination and chelating ability of these amino groups toward Pb(II), Cd(II), Cu(II), and Mn(II) strengthened. But at pH higher than 4.5, the adsorption capacity for Pb(II) decreased sharply because Pb(II) might precipitate.51 Results of the zeta potential measurement for GO/PAMAMs at

microscopy (SEM) was carried out using a JSM-3400N instrument conducting at 30 keV. The N2-based Brunaer Emmett Teller (BET) surface area of GO/PAMAMs was determined by the surface area analyzer (NOVA4200e, Quantachrome). The zeta potential of the GO/PAMAMs was measured using a Zeta-sizer (Nano ZS-90, Malvern). The concentrations of metal ions were determined by an atomic absorption spectrometer (AA-6300C, Shimadzu). The pH values of metal ion solutions were measured with a PHSJ-4A pH meter (Shanghai Precision Science Equipment Co. Ltd.). Adsorption Kinetics Experiments. An 800 mL portion of the metal ions solution of 200 mg/L was placed into a roundbottomed flask, GO/PAMAMs (0.1 g) were added into the flask and stirred under a water bath at 25 °C. Then 5 mL of this solution was taken out for filtration at given time intervals; 2 mL of that filtrate was transferred to a 100 mL volumetric flask. The concentrations of metal ions were determined by using an atomic absorption spectrometer (AAS). The amount of metal ions adsorbed by GO/PAMAMs was calculated according to eq 1:

Q=

(C 0 − C )V W

(1)

where Q is the amount of metal ions adsorbed onto unit amount of the GO/PAMAMs (mmol/g), C0 and C are the initial and equilibrium concentrations of the metal ions in the aqueous phase (mmol/L), respectively. V is the volume of the aqueous phase (L), and W is the dry weight of the adsorbent (g). Isothermal Adsorption Experiments. A 100 mL portion of a metal ions solution was placed into round-bottomed flask, and GO/PAMAMs (0.1 g) were added into the solution. After ultrasonic treatment for 1 h, the flask was transferred to water bath, and the mixture was stirred for 4 h at 25 °C. After the mixture was filtered, the equilibrium concentration of the metal ions was determined by using AAS. This procedure was repeated for different concentrations of metal ions solutions. The amount of metal ions adsorbed by GO/PAMAMs was calculated according to eq 1.

■

RESULTS AND DISCUSSION As shown in Figure 1, The bands at 1620 cm−1 and 1731 cm−1 are associated with the stretching of the −OH and CO bond

Figure 1. FTIR spectra of GO and GO/PAMAMs composites. 1721



Article

Figure 2. SEM image of GO/PAMAMs (a) and its magnification (b).

increase of the adsorption capacity of GO/PAMAMs for heavy metal ions. The optimum pH values at which the maximum metal uptake was obtained were 4.5, 5.0, 4.5 and 4.0 for Pb(II), Cd(II), Cu(II) and Mn(II), respectively. These optimum pH values were used for experiments that followed. Figure 5a shows the adsorption kinetic curves of Pb(II), Cd(II), Cu(II), and Mn(II) onto GO/PAMAMs. It can be seen that the adsorption capacities of Pb(II), Cd(II), and Cu(II) (except Mn(II)) onto GO/PAMAMs increase sharply during the first 120 min and then tend toward equilibrium. To reveal the mechanism of metal adsorption processes pseudo-firstorder52 and pseudo-second-order53 equations were fitted to measured data. The pseudo-first-order kinetic model is generally expressed as the equation:

Figure 3. The influence of pH on the adsorption capacity: temperature, 25 °C; adsorption time, 4 h. GO/PAMAMs 0.1 g, Pb(II) 414 mg/L, Cd(II) 224 mg/L, Cu(II) 128 mg/L, and Mn(II) 110 mg/L; 0.1 L.

⎛ Q ⎞ −ln⎜⎜1 − t ⎟⎟ = k1t + C , Qe⎠ ⎝

different pH are shown in Figure 4. Zeta potentials of the GO/ PAMAMs decreased with increasing pH. The PZCs were

F = Q t /Q e

(2)

where Qe and Qt are the amounts of the metal ions adsorbed (mg/g) at equilibrium and at contact time t (min), respectively, k1 (1/min) is the rate constant. The plots of −ln(1 − F) versus t are depicted in Figure 5b and the rate constants (k2) are presented in Table 2. The experimental data were also fitted by the pseudo-secondorder kinetic model which was given with the equation below: ⎛ 1 ⎞ t 1 ⎜⎜ ⎟⎟t = + Qt k 2Q e 2 ⎝Qe ⎠

(3)

where k2 (g/(mg·min)) is the rate constant of pseudo-secondorder adsorption reaction. The plots of t/Qt versus t are shown in Figure 5c and the rate constants (k2) are presented in Table 2. In Table 2, the R2 values of the pseudo-first-order kinetic model for the adsorption of Pb(II), Cd(II), Cu(II) and Mn(II) onto GO/PAMAMs were 0.9883, 0.9885, 0.9668, and 0.9419, and those of pseudo-second-order kinetic model were 0.9981, 0.9963, 0.9948, and 0.9948. It indicated that the pseudosecond-order kinetic model provided a better correlation in contrast to the pseudo-first-order model for the adsorption of Pb(II), Cd(II), Cu(II), and Mn(II) onto GO/PAMAMs. It is possible to suggest that the adsorption of Pb(II), Cd(II), Cu(II), and Mn(II) followed a second-order type reaction kinetics which is based on the assumption that the ratedetermining step is a chemical adsorption.51

Figure 4. Zeta potentials of GO/PAMAMs under various pH conditions.

estimated to be ca. pH 7 for GO/PAMAMs. It was obvious that in the pH ranges, the surface of GO/PAMAMs is positively charged. With the pH increased, the adsorption capacity of GO/PAMAMs for heavy metal ions increased and the number of positive charges on GO/PAMAMs decreased. Then it might be that the electrostatic attraction between GO/PAMAMs and heavy metal ions was relatively weak, and with the repulsion between heavy metal ions and positive charge on GO/ PAMAMs weakened, the chelating ability of amino groups toward heavy metal ions strengthened, which contributes to the 1722



Article

Figure 5. (a) Kinetic adsorption curve of GO/PAMAMs for metal ions: m(GO/PAMAMs composites) = 1g; temperature, 25 °C; C0 =800 mg/L; Pb(II), pH = 4.5; Cd(II), pH = 5.0; Cu(II), pH = 4.5; Mn(II), pH = 4.0. (b) The simulated pseudo-first-order kinetics. (c) The simulated pseudo-second-order kinetics. Figure 6. (a) Adsorption isotherms of GO/PAMAMs for metal ions: adsorption time, 4 h; m(GO/PAMAMs composites) = 0.1 g; temperature, 25 °C; Pb(II), pH = 4.5; Cd(II), pH = 5.0; Cu(II), pH = 4.5; Mn(II), pH = 4.0. (b) Linear fitting curves with Langmuir model for Pb(II), Cd(II), Cu(II), and Mn(II). (c) Linear fitting curves with Freundlich model for Pb(II), Cd(II), Cu(II), and Mn(II).

The adsorption isotherms of GO/PAMAMs for different metal ions are shown in Figure 6a. When the initial concentration of the metal ions increased from 1 mmol/L to 6 mmol/L, the adsorption capacities of GO/PAMAMs at 25 °C for Pb(II), Cd(II), Cu(II), and Mn(II) increased in the range of (144.6 to 436.1, 41.0 to 151.1, 31.1 to 63.9, and 10.9 to 17.6) mg/g, respectively. Obviously, the adsorption capacities followed the order of Pb(II) > Cd(II) > Cu(II) > Mn(II). These results indicated that the GO/PAMAMs had stronger adsorption ability and higher affinity to Pb(II) than to Cd(II), Cu(II), or Mn(II).

To quantify the sorption capacity of GO/PAMAMs for Pb(II), Cd(II), Cu(II), and Mn(II), the two most commonly used isotherms, namely Langmuir and Freundlich, were adapted. The Langmuir adsorption equation54 was as follows:

Table 2. Parameters of Two Kinetic Models for Pb(II), Cd(II), Cu(II) and Mn(II) Adsorption onto GO/PAMAMs first-order rate constants

second-order rate constants

metal

Qe (mg/g)

k1(1/min)

R2

k2(g/mg·min)

Qe (mg/g)

R2

Pb(II) Cd(II) Cu(II) Mn(II)

115.6 82.2 55.2 18.2

0.013 15 0.013 61 0.014 46 0.008 58

0.9883 0.9885 0.9668 0.9419

0.000 24 0.000 26 0.000 24 0.001 39

126.7 92.4 66.2 20.1

0.9981 0.9963 0.9948 0.9948

1723



Qe = Qm

Article

bCe 1 + bCe

for the heavy metal ions were highly pH dependent. The adsorption process for the heavy metal ions for GO/PAMAMs can be explained with the pseudo-second-order type kinetic model, which is based on the assumption that the ratedetermining step is a chemical adsorption. The adsorption of GO/PAMAMs for Cu(II) or Mn(II) was a typical monomolecular layer adsorption. The maximum adsorption capacity of GO/PAMAMs for Pb(II) is found to be 568.18 mg/g, which is higher than that for Cd(II), Cu(II), or Mn(II). The adsorption reaches the equilibrium state within 60 min. All of the above results indicate that GO/PAMAMs have excellent adsorption properties for removing heavy metal ions from wastewater.

(4)

Ce C 1 = e + Qe Qm bQ m

(5)

where Qm (mg/g) is the maximum adsorption capacity of metal ions per unit weight of adsorbent; b represents the equilibrium constant of adsorption reaction (L/mg). The plots of 1/Qe versus 1/Ce are shown in Figure 6b and the values of Qm and b were presented in Table 3.

■

Table 3. Related Constants and Linear Regression Coefficients of Langmuir− Freundlich Fitting for Pb(II), Cd(II), Cu(II), and Mn(II), Adsorption onto GO/PAMAMs

S Supporting Information *

adsorbate fitting model Langmuir

Freundlich

Qm (mg/g) b (L/mg) R2 k (mg/g) n R2

Pb(II)

Cd(II)

Cu(II)

Mn(II)

568.2 0.0038 0.8585 25.32 2.3346 0.9409

253.8 0.0032 0.9070 2.71 1.5009 0.9274

68.7 0.0385 0.9904 13.82 3.5744 0.7008

18.3 0.0492 0.9904 5.22 4.5846 0.7608

Raman spectroscopy and X-ray diffraction (XRD) patterns of the graphite, GO, and GO/PAMAMs, the TGA curves of graphite, GO/PAMAMs, and GO. This material is available free of charge via the Internet at http://pubs.acs.org.

■

ln Q e = ln k +

*E-mail: [email protected]. Funding

This work was supported by Natural Science Foundation of Hunan Province (No. 11JJ3053), the Postdoctoral Science Foundation of Central South University, Key Science and Technology Financing Projects of Ministry of Education (No. 211124) of China.

(6)

1 ln Ce n

AUTHOR INFORMATION

Corresponding Author

The Freundlich adsorption equation55 and its logarithmic form were as follows: Q e = kCe1/ n

ASSOCIATED CONTENT

Notes

(7)

The authors declare no competing financial interest.

■

where k and n are the Freundlich constants, k is roughly an indicator of the adsorption capacity (mg/g), and 1/n is an empirical parameter relating the adsorption intensity. The plots of ln Qe versus ln Ce are shown in Figure 6c, and the values of k and n are presented in Table 3. As shown in Table 3, the linear correlation coefficients (R2) values of Langmuir isotherms were 0.8585, 0.9070, 0.9904, and 0.9904 for Pb(II), Cd(II), Cu(II), and Mn(II) onto GO/ PAMAMs, respectively. These results indicated that the adsorption experimental data of Cu(II) and Mn(II) onto GO/PAMAMs fit with the Langmuir model better than those of Pb(II) and Cd(II). The R2 values suggested that the adsorption of Cu(II) or Mn(II) on GO/PAMAMs was a typical monomolecular layer adsorption. In addition, it can be calculated from the fitting results that the adsorption capacity Qm of Pb(II), Cd(II), Cu(II), and Mn(II) onto GO/PAMAMs were 568.2, 253.8, 68.7, and 18.3 mg/g, respectively. As shown in Table 3, the adsorption capacity of Pb(II) onto GO/ PAMAMs was far more than that of Cd(II), Cu(II), or Mn(II). Therefore, it might be concluded that GO/PAMAMs possessed much superior adsorption ability and higher affinity for Pb(II) than Cd(II), Cu(II), or Mn(II). As can be seen from Table 3, the R2 values of Freundlich isotherms were in the range of 0.7008 to 0.9409, which suggested that the adsorption processes did not fit well with the Freundlich model.

REFERENCES

(1) Zhao, X. W.; Jia, Q.; Song, N. Z.; Zhou, W. H.; Li, Y.S. J. Adsorption of Pb(II) from an aqueous solution by titanium dioxide/ carbon nanotube nanocomposites: Kinetics, thermodynamics, and isotherms. Chem. Eng. Data. 2010, 55, 4428−4433. (2) Zaini, M. A. A.; Amano, Y.; Machida, M. Adsorption of heavy metals onto activated carbons derived from polyacrylonitrile fiber. J. Hazard. Mater. 2010, 180, 552−560. (3) Machida, M.; Fotoohi, B.; Amamo, Y.; Ohba, T.; Kanoh, H.; Mercier, L. Cadmium(II) adsorption using functional mesoporous silica and activated carbon. J. Hazard. Mater. 2012, 221−222, 220− 227. (4) Machida, M.; Fotoohi, B.; Amamo, Y.; Mercier, L. Cadmium(II) and lead(II) adsorption onto hetero-atom functional mesoporous silica and activated carbon. Appl. Surf. Sci. 2012, 258, 7389−7394. (5) Tang, W. W.; Zeng, G. M.; Gong, J. L.; Liu, Y.; Wang, X. Y.; Liu, Y. Y.; Liu, Z. F.; Chen, L.; Zhang, X. R.; Tu, D. Z. Simultaneous adsorption of atrazine and Cu (II) from wastewater by magnetic multiwalled carbon nanotube. Chem. Eng. J. 2012, 211−212, 470−478. (6) Wang, J. P.; Ma, X.; Fang, G.; Pan, M.; Ye, X.; Wang, S. Preparation of iminodiacetic acid functionalized multi-walled carbon nanotubes and its application as sorbent for separation and preconcentration of heavy metal ions. J. Hazard. Mater. 2011, 186, 1985−1992. (7) Yang, S.; Li, J.; Shao, D.; Hu, J.; Wang, X. Adsorption of Ni(II) on oxidized multi-walled carbon nanotubes: Effect of contact time, pH, foreign ions and PAA. J. Hazard. Mater. 2009, 166, 109−116. (8) Zhang, Z.; Zhang, H.; Hua, Y.; Yang, X.; Yao, S. Novel surface molecularly imprinted material modified multi-walled carbon nanotubes as solid-phase extraction sorbent for selective extraction gallium ion from fly ash. Talanta. 2010, 82, 304−311.

■

CONCLUSIONS In the presented study, GO/PAMAMs were prepared and characterized. The adsorption capacities of the GO/PAMAMs 1724



Article

(9) Ji, F.; Li, C.; Tang, B.; Xu, J.; Lu, G.; Liu, P. Preparation of cellulose acetate/zeolite composite fiber and its adsorption behavior for heavy metal ions in aqueous solution. Chem. Eng. J. 2012, 209, 325−333. (10) Lin, J.; Zhan, Y.; Zhu, Z. Adsorption characteristics of copper (II) ions from aqueous solution onto humic acid-immobilized surfactant-modified zeolite. Colloids Surf., A 2011, 384, 9−16. (11) Jovanovic, M.; Rajic, N.; Obradovic, B. Novel kinetic model of the removal of divalent heavy metal ions from aqueous solutions by natural clinoptilolite. J. Hazard. Mater. 2012, 233−234, 57−64. (12) Chiang, Y. W.; Ghyselbrecht, K.; Santos, R. M.; Martens, J. A.; Swennen, R.; Cappuyns, V.; Meesschaert, B. Adsorption of multiheavy metals onto water treatment residuals: Sorption capacities and applications. Chem. Eng. J. 2012, 200−202, 405−415. (13) Li, N.; Bai, R. Highly Enhanced Adsorption of Lead Ions on Chitosan Granules Functionalized with Poly(acrylic acid). Ind. Eng. Chem. Res. 2006, 45, 7897−7904. (14) Wen, Y.; Tang, Z.; Chen, Y.; Gu, Y. Adsorption of Cr(VI) from aqueous solutions using chitosan-coated fly ash composite as biosorbent. Chem. Eng. J. 2011, 175, 110−116. (15) Yan, H.; Dai, J.; Yang, Z.; Yang, H.; Cheng, R. Enhanced and selective adsorption of copper(II) ions on surface carboxymethylated chitosan hydrogel beads. Chem. Eng. J. 2011, 174, 586−594. (16) Zhu, Y.; Hu, J.; Wang, J. Competitive adsorption of Pb(II), Cu(II), and Zn(II) onto xanthate-modified magnetic chitosan. J. Hazard. Mater. 2012, 221−222, 155−161. (17) Lin, J.; Zhan, Y. Adsorption of humic acid from aqueous solution onto unmodified and surfactant-modified chitosan/zeolite composites. Chem. Eng. J. 2012, 200−202, 202−213. (18) Dai, J.; Yang, H.; Yan, H.; Shangguan, Y.; Zheng, Q.; Cheng, R. Phosphate adsorption from aqueous solutions by disused adsorbents: Chitosan hydrogel beads after the removal of copper(II). Chem. Eng. J. 2011, 166, 970−977. (19) Kołodýnska, D. Adsorption characteristics of chitosan modified by chelating agents of a new generation. Chem. Eng. J. 2011, 179, 33− 43. (20) Pérez-Fonseca, A. A.; Gómez, C.; Dávila, H.; González-Núñez, R.; Robledo-Ortíz, J. R.; Vázquez-Lepe, M. O.; Herrera-Gómez, A. Chitosan supported onto agave fiberPostconsumer HDPE for Cr(VI) Adsorption. Ind. Eng. Chem. Res. 2012, 51, 5939−5946. (21) Chang, Y. Y.; Lee, S. M.; Yang, J. K. Removal of As(III) and As(V) by natural and synthetic metal oxides. Colloids Surf. A Physicochem. Eng. Asp. 2009, 346, 202−207. (22) Hua, M.; Zhang, S.; Pan, B.; Zhang, W.; Lv, L.; Zhang, Q. Heavy metal removal from water/wastewater by nanosized metal oxides: A review. J. Hazard. Mater. 2012, 211−212, 317−331. (23) Liu, L.; Wu, J.; Li, X.; Ling, Y. Sonochemical degradation of alachlor in the presence of process intensifying additive. Sep. Purif. Technol. 2013, 103, 92−100. (24) Srivastava, V. C.; Mall, I. D.; Mishra, I. M. Antagonistic competitive equilibrium modeling for the adsorption of ternary metal ion mixtures from aqueous solution onto bagasse fly ash. Ind. Eng. Chem. Res. 2008, 47, 3129−3137. (25) Gardea-Torresdey, J.; Hejazi, M.; Tiemann, K.; Parsons, J. G.; Duarte-Gardea, M.; Henning, J. Use of hop (Humulus lupulus) agricultural byproducts for the reduction of aqueous lead(II) environmental health hazards. J. Hazard. Mater. B 2002, 91, 95−112. (26) Chandra, V.; Kim, K. S. Highly selective adsorption of Hg2+ by a polypyrrole-reduced graphene oxide composite. Chem. Commun. 2011, 47, 3942−3944. (27) Zhang, N.; Qiu, H.; Si, Y.; Wang, W.; Gao, J. Fabrication of highly porous biodegradable monoliths strengthened by graphene oxide and their adsorption of metal ions. Carbon 2011, 49, 827−837. (28) Mi, X.; Huang, G.; Xie, W.; Wang, W.; Liu, Y.; Gao, J. Preparation of graphene oxide aerogel and its adsorptionfor Cu2+ ions. Carbon 2012, 50, 4856−4864. (29) Machida, M.; Mochimaru, T.; Tatsumoto, H. Lead (II) adsorption onto the graphene layer of carbonaceous materials in aqueous solution. Carbon 2006, 44, 2681−2688.

(30) Sreeprasad, T. S.; Maliyekkal, S. M.; Lisha, K. P.; Pradeep, T. Reduced graphene oxide−metal/metal oxide composites: Facile synthesis and application in water purification. J. Hazard. Mater. 2011, 186, 921−931. (31) Liu, L.; Li, C.; Bao, C.; Jia, Q.; Xiao, P.; Liu, X.; Zhang, Q. Preparation and characterization of chitosan/graphene oxide for the adsorption of Au(III) and Pd(II). Talanta 2012, 93, 350−357. (32) Hao, L.; Song, H.; Zhang, L.; Wan, X.; Tang, Y.; Lv, Y. SiO2/ graphene composite for highly selective adsorption of Pb(II) ion. J. Colloid Interface Sci. 2012, 369, 381−387. (33) Deng, X.; Lü, L.; Li, H.; Luo, F. The adsorption properties of Pb(II) and Cd(II) on functionalized graphene prepared by electrolysis method. J. Hazard. Mater. 2010, 183, 923−930. (34) Li, Z.; Chen, F.; Yuan, L.; Liu, Y.; Zhao, Y.; Chai, Z.; Shi, W. Uranium(VI) adsorption on graphene oxide nanosheets from aqueous solutions. Chem.Eng. J. 2012, 210, 539−546. (35) Tomalia, D. A.; Baker, H.; Dewald, J.; Hall, M.; Kallos, G.; Martin, S.; Roeck, J.; Ryder, J.; Smith, P. A new class of polymers: Starburst-dendritic macromolecules. Polym. J. 1985, 17, 117−132. (36) Tomalia, D. A. Dendritic macromolecules: Synthesis of starburst dendrimers macromolecules. Macromolecules 1986, 19, 2466−2468. (37) Mamadou, S. D.; Simone, C.; Pirabalini, S.; James, H. J., Jr.; William, A. G., III. Dendrimer enhanced ultrafiltration. 1. Recovery of Cu(II) from aqueous solutions using PAMAM dendrimers with ethylene diamine core and terminal NH2 groups. Environ. Sci. Technol. 2005, 39, 1366−1377. (38) Barakat, M. A.; Ramadan, M. H.; Alghamdi, M. A.; Algarny, S. S.; Woodcock, H. L.; Kuhn, J. N. Remediation of Cu(II), Ni(II), and Cr(III) ions from simulated wastewater by dendrimer/titania composites. J. Environ. Manage. 2013, 117, 50−57. (39) Yuan, Y.; Zhang, G.; Li, Y.; Zhang, G.; Zhang, F.; Fan, X. Poly(amidoamine) modified graphene oxide as an efficient adsorbent for heavy metal ions. Polym. Chem. 2013, 4, 2164−2167. (40) Ou, E. C.; Zhang, X. J.; Chen, Z. M.; Zhan, Y. G.; Xiong, Y. Q.; Xu, W. J. Macroscopic, free-standing Ag-reduced, graphene oxide Janus films prepared by evaporation-induced self-assembly. Chem. Eur. J. 2011, 17, 8789−8793. (41) Cote, L. J.; Kim, F.; Huang, J. Langmuir−Blodgett assembly of graphite oxide single layers. J. Am. Chem. Soc. 2009, 131, 1043−1049. (42) Compton, O. C.; Dikin, D. A.; Putz, K. W.; Brinson, L. C.; Nguyen, S. B. T. Electrically conductive ‘‘alkylated’’ graphene paper via chemical reduction of amine-functionalized graphene oxide paper. Adv. Mater. 2010, 22, 892−896. (43) Che, J.; Shen, L.; Xiao, Y. A new approach to fabricate graphene nanosheets in organic medium: Combination of reduction and dispersion. J. Mater. Chem. 2010, 20, 1722−1727. (44) Ma, H. L.; Zhang, Y. W.; Hu, Q. H.; Yan, D.; Yu, Z. Z.; Zhai, M. L. Chemical reduction and removal of Cr(VI) from acidic queous solution by ethylenediamine-reduced graphene oxide. J. Mater. Chem. 2012, 22, 5914−5916. (45) Zeng, Y. L.; Huang, Y. F.; Jiang, J. H.; Zhang, X. B.; Tang, C. R.; Shen, G. L.; Yu, R. Q. Functionalization of multi-walled carbon nanotubes with poly(amidoamine) dendrimer for mediator-free glucose biosensor. Electrochem. Commun. 2007, 9, 185−190. (46) Graf, D.; Molitor, F.; Ensslin, K.; Stampfer, C.; Jungen, A.; Hierold, C.; Wirtz, L. Spatially resolved raman spectroscopy of singleand few-layer graphene. Nano Lett. 2007, 7, 238−242. (47) Xiong, Y.; Xie, Y.; Zhang, F.; Ou, E.; Jiang, Z.; Ke, L.; Hu, D.; Xu, W. Reduced graphene oxide/hydroxylated styrene−butadiene− styrene tri-block copolymer electroconductive composites: Preparation and properties. Mater. Sci. Eng., B 2012, 177, 1157−1163. (48) Krishnamoorthy, K.; Veerapandian, M.; Mohan, R.; Kim, S. J. Investigation of Raman and photoluminescence studies of reduced graphene oxide sheets. Appl. Phys. A: Mater. Sci. Process. 2012, 106, 501−506. (49) Gao, B. J.; Gao, Y. C.; Li, Y. B. Preparation and chelation adsorption property of composite chelating material poly(amidoxime)/SO2 towards heavy metal ions. Chem. Eng. J. 2010, 158, 542−549. 1725



Article

(50) Juang, R. S.; Shao, H. J. A simplified equilibrium model for sorption of heavy metal ions from aqueous solutions on chitosan. Water Res. 2002, 36, 2999−3008. (51) Bai, L.; Hu, H. P.; Fu, W.; Wan, J.; Cheng, X. L.; Zhuge, L.; Chen, Q. Y. Synthesis of a novel silica-supported dithiocarbamate adsorbent and its properties for the removal of heavy metal ions. J. Hazard. Mater. 2011, 195, 261−275. (52) Lagergren, S. About the theory of so-called adsorption of soluble substances. K. Sven. Vetenskapsakad. Hand. 1898, 24, 1−39. (53) Ho, Y. S.; McKay, G. Sorption of dye from aqueous solution by peat. Chem. Eng. J. 1998, 70, 115−124. (54) Langmuir, I. The adsorption of gases on plane surfaces of glass, mica and platinum. J. Am. Chem. Soc. 1918, 40, 1361−1403. (55) Freundlich, H. Z. Ü ber die adsorption in lös. Phys. Chem. 1907, 57, 385−470.

1726


Polyamidoamine Dendrimers and

Recommend Documents