Facile and Efficient Synthesis of Nitrogen-Functionalized Graphene

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Facile and efficient synthesis of nitrogen-functionalized graphene oxide as a copper adsorbent and its application Kexin Zhang, Haiyan Li, Xingjian Xu, and Hongwen Yu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b04095 • Publication Date (Web): 08 Feb 2016 Downloaded from http://pubs.acs.org on February 9, 2016

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Industrial & Engineering Chemistry Research

Facile and efficient synthesis of nitrogenfunctionalized graphene oxide as a copper adsorbent and its application Kexin Zhang, Haiyan Li, Xingjian Xu and Hongwen Yu* Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, 4888 Shengbei Rd, Changchun 130102, China.

ABSTRACT:

In this work, we report a room-temperature approach to synthesizing nitrogen-functionalized graphene oxide (GO). The chemical structure of GO- triethylenetetramine-methacrylate (GOTETA-MA) was characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and

13

C Nuclear Magnetic Resonance, respectively. The GO-TETA-MA

demonstrated extremely efficient removal of copper from wastewater. The adsorption capacity was found to be 34.4 mg/g for Cu(II) (at pH=5 and 25 °C). The final concentration of Cu(II) was lower than the quality standard for ground water, and even lower than the allowable level of copper contaminant in drinking water in China. The effects of several parameters on adsorption, including pH value, contact time, adsorption temperature, initial concentration, acid stability, and thermal stability, were investigated. Kinetic data were well described by a pseudo-first-order

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model. Both Freundlich and Langmuir isotherm models were applied to the experimental data analysis, and the former proved to be a better fit. The underlying mechanism of synergistic adsorption of heavy metal ions was considered. Then, the removal efficiency for four copper fungicides was studied and was found to reach 100%. These results suggest that GO-TETA-MA has the potential to be applied in environmental management.

KEYWORDS: Modified graphene oxide; Adsorption; Cu(II); Fungicides INTRODUCTION Environmental pollution, especially heavy metal ions in water, caused by industrial and agricultural activities, severely threaten the ecological balance and human health due to their non-biodegradable and persistent nature [1, 2]. Of all the known heavy metal ions, copper ions pose a wide environmental threat, as copper sulfate has been used as an algicide since the early 1900s in eutrophic lakes and is still widely used today [3]. Residues of Cu(II) in soil were surveyed in areas where copper fungicide has been applied over a long period, and the effects of copper on plant growth in polluted soils has been found to be harmful [4-5]. Meanwhile, Cu(II) ions in soil can “drift”, leading to polluted surface waters and groundwater [6]. In addition, excessive copper ions pose a risk to both human beings and the ecological environment; thus, it is necessary to eliminate copper ions from waste-water prior to being released into the environment [7]. Until now, the various removal methods used have included ion exchange [8], membrane filtration [9], precipitation [10], adsorption [11-12], and other processes. Among these methods, adsorption is widely used because of its simplicity, high efficiency, and low cost. Graphne oxide (GO), one of the most important derivatives of graphene, has the sufficient quantity of


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oxygenous functional groups (epoxy, hydroxyl, and carboxyl groups) and high water solubility serve GO sheets great promise as an ideal adsorbent. Therefore, GO has attracted tremendous interest. GO has abundant oxygen atoms on the surface that, can be used as anchoring sites for metal ion chelation. This makes GO a potential super adsorbent material. In recent years, GO has been functionalized to improve its adsorption efficiency. Liu et al. [13] utilized triethanolamine as a modifier to obtain a novel GO-based adsorbent, GO-TEA. Clemonne [14] reported a method to chemically functionalize graphene sheets with N-(trimethoxysilylpropyl) ethylenediamine triacetic acid via a silanization reaction. GO-EDTA was found to be an ideal adsorbent for Pb(II). An amino-functionalized magnetic graphene composite material was prepared, and showed effectiveness in removing Cr(VI), Pb(II), Hg(II), Cd(II), and Ni(II) ions from an aqueous solution [15]. However, research into copper adsorbents remains insufficient. In this work, we report on the usage of a triethylenetetramine (TETA)-grafted GO as an effective Cu(II) adsorbent. First, amine groups were introduced onto GO via a cross-linked reaction between the abundant and active oxygen groups (such as –COOH and -OH) at GO and the amino groups at TETA. Second, the functionalized GO was reacted with potassium cyanate to form composites of methacrylate (MA) with pendant urea groups. After the cross-linking reaction, the adsorption capacity of GO was increased because a number of amino groups were formed that, could chelate with metal ions effectively. The composite absorbent was used to remove Cu(II) ions in an aqueous solution, and it exhibited excellent adsorption performance. The resulting final concentration was less than 0.1 mg/L. The optimal condition of the Cu(II) ions with sorption by GO-TETA-MA was determined based on contact time, pH, initial Cu(II) concentration, and temperature. The adsorption mechanism was analyzed by applying three kinetic models to fit the experimental data, including pseudo-first-order, pseudo-second-order, and intra-particle diffusion


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models. The adsorption equilibrium was expressed by the Langmuir and Freundlich isotherms. Furthermore, the stability property of GO-TETA-MA was studied, and the removal of copper from fungicide-contaminated wastewater was quantitatively demonstrated.

EXPERIMENTAL SECTION Materials. Graphite (325 mesh, 99.99%) was obtained from Bay Carbon, Inc., Michigan, USA. Triethylenetetramine (99%), potassium cyanate(99%), 1-ethyl-3-(3-dimethyl aminoprophy) carbondiimide hydrochloride (EDC), and N-hydroxyl succinimide (NHS) were purchased from Aladdin. Copper nitrate (Cu(NO3)2, 99%), sulfuric acid (H2SO4, 99%) , and other routine chemicals were purchased from Beijing Chemical Works. All of the reactants were used without any further purification. Preparation of GO-TETA. Graphene oxide was prepared using the modified Hummers method [16]. The synthesis scheme for GO-TETA-MA is shown in the Figure 1. 1 g of the GO was dispersed by sonication in 200 ml of deionized water. Into this yellow-brown homogeneous dispersion, a solution of EDC (0.05 M) and NHS (0.05 M) was added and continuously stirred for 2 h in order to active the carboxyl groups of GO. Then, 1 ml of the coupling agent TETA was added and stirred at room temperature for 12 h [17]. The product was poured into deionized water and filtered using a 0.22 µm polycarbonate filter membrane. The product was then dried in a vacuum oven at 40 °C. Preparation of GO-TETA-MA. 1 g of GO-TETA was dispersed in the deionized water and stirred for 30 min. Subsequently, 10 ml of hydrochloric acid was added with stirring, and the mixture was stirred for 1 h at room temperature. Then, the potassium cyanate solution (1.05 g)


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was added and the system was closed and stirred for 12 h at room temperature. The recovered composite was washed well with deionized water and dried in a vacuum oven at 40 °C for 4 h. Adsorption kinetics. The metal ion uptake capacities were measured as a function of time to determine the optimum contact times for the adsorption of Cu(II) ions on GO-TETA-MA. First, 50 mg of GO-TETA-MA was placed in a 50 ml plastic tube with 30 ml of 100 mg/L Cu(II) solution. The test tubes were shaken at 200 rpm on a vortex shaker. The solution was filtered immediatly when the reaction times reached 5, 10, 25, 40, 60, 80, 100, and 120 min. The concentrations of metal ions were determined using an inductive coupled plasma emission spectrometer (ICP). The removal efficiency (E%) and adsorption capacity at equilibrium (qe) can be calculated according to the following equation: % =

=

× 100%

(1)

(2)

where C0 and Ce are the initial and equilibrium concentrations of Cu(II) (mg/L), respectively; qe is the amount of metal ion adsorbed per unit amount of adsorbents (mg/g); V is the volume of Cu(II) solution (L); and m is the dry weight of the adsorbents (g). Adsorption isotherms. To perform an adsorption isotherm analysis, a typical adsorption experiment was conducted by adding 50 mg GO-TETA-MA to a 30 ml Cu(II) solution at different concentrations (60, 80, 100, 120, and 140 mg/L). The equilibrium concentration of the Cu(II) ions was determined using ICP. Effect of pH on adsorption. Experiments were performed to determine the effect of pH on the adsorption process of Cu(II) ions on the adsorbent. First, 50 mg of GO-TETA-MA was placed in a 50 ml Erlenmeyer flask with 30 ml of 100 mg/L Cu(II) solution in a shaker. The pH value of


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the solution was varied in the range of 1.0~6.0. The pH of the solution was adjusted by adding of drops of aqueous NaOH or HCl solution (1.0 mol/L). Effect of temperature on adsorption. About 30 mL of 100 mg/L Cu(II) solution was mixed with 50 mg of the sample. This was shaken at five different temperatures (10, 20, 30, 40, and 50˚C) under the conditions determined in the previous experiments. Characterization. The pH value of the solution was measured by a PH S220-K pH meter made by Mettler Toledo Company. Fourier transform infrared spectroscopy (FTIR) spectra were recorded with a PerkinElmer spectrometer at 4000-500 cm-1 using 32 scans and 4 cm-1 of resolution. The X-ray photoelectron spectrum (XPS) measurements were performed using an ESCALAB-MKII spectrometer (VG Co., United Kingdom) with Al Kα X-ray radiation as the Xray excitation source. The

13

C Nuclear Magnetic Resonance (13C NMR) measurements were

carried out on a Bruker DRX-400 MHz NMR spectrometer. Thermogravimetric analysis (TGA) data were obtained with a thermogravimetric analyzer (PerkinElmer TG4000) in an air atmosphere with temperatures ranging from ambient to 1173 K and a rate of heating at 283 K min-1. The concentration of the metal ions was determined by an inductive coupled plasma emission spectrometer (ICP-5000, Juguang, China).

RESULTS AND DISCUSSION The functional groups on the surface of the GO and GO-TETA-MA were identified through FTIR using the extracted powder. As shown in Figure 2, GO exhibits the following characteristic FT-IR features: a broad peak at 3422 cm-1 attributable to hydroxyl stretching vibrations of the COOH, C-OH groups; the characteristic absorption peak at 1738 cm-1 corresponding to the C=O stretching vibrations of the –COOH groups; the peak at 1622 cm-1 assigned to the C=C group;


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the peak at 1228 cm-1 assigned to the stretching vibrations of C-O; and the absorption bands at 1052 cm-1 assigned to the O-H deformations of the C-OH groups. In the FT-IR spectrum of GOTETA-MA, the band observed at 3214 cm-1 is due to the stretching of -NH2, and the stretching vibrations at 1365 cm-1 and 1604 cm-1 can be assigned to O-N, O=C-N [18-19]. It can be distinctly observed that the –NH2 absorbance band shifted to the lower value, which proves that the cyanate groups reacted with the –NH groups of GO-TETA-MA and were converted to N-C (NH2) =O graft points. Consequently, the above results demonstrate that the GO was successfully modified. The chemical bonding states in GO and GO-TETA-MA were analyzed by XPS with the corresponding results shown in Figure 3. In Figure 3(a), two different peaks centered at 286 and 532 eV were detected corresponding to C 1s and O 1s, respectively. In addition to these peaks, N 1s at ~400 eV was observed for GO-TETA-MA. Figure 3(b) shows the N 1s spectrum of GOTETA-MA. The peak centered at 399.35 eV is attributed to the primary amine group, and the N 1s peak of GO-TETA-MA at 400.7 eV represents the secondary amine and tertiary amine groups [13, 20]. The qualitative XPS analysis is consistent with the FTIR results. The presence of nitrogen on the GO-TETA-MA sample confirms the successful synthesis of GO-TETA-MA. An analysis with

13

C NMR was performed on GO and GO-TETA-MA (Figure 4) to provide

an understanding of the chemical structure of these materials. From Figure 4, the

13

C NMR

spectra of the GO and GO-TETA-MA samples exhibit a similar chemical shift. The three major peaks at 60, 70, and 130 ppm are unambiguously assigned to the C-O-C, C-OH, and sp2 groups on the GO surface, the minor peaks at 167 and 187 ppm are attributed to the O-C=O and C=O, respectively [21]. After the modification of the nitrogen atoms on the GO surface, two new peaks


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were observed at 37 and 46 ppm, which could be assigned to C-NH and C-N. It can be concluded that the GO-TETA-MA composite was successfully synthesized. The surface morphology of the GO and GO-TETA-MA was investigated, and it is found in the Supporting Information. It is clear that the organic molecule covered the convoluted surface of platelets and so the surface of GO-TETA-MA are very rough, which indicated that GO could stick into the organics matrix (Figure S1a, 1b). In addtion, A representative EDX of GO-TETAMA is shown in Figure S1c, the presence of C, O, and N at GO-TETA-MA surface is confirmed by the signal of above elements, which proves that the TETA-MA chains is grafted onto the surface of the GO sheets. Figure S2 shows the maximum adsorption capacity of two adsorbents towards Cu(II). The maximum Cu(II) removal values were 0.5 and 0.76 mmol/g by the GO and GO-TETA-MA, which indicated that the GO-TETA-MA has excellent adsorption capacity for the removal of Cu(II). In order to estimate the adsorption properties, the obtained GO-TETA-MA as an adsorbent for different heavy metal ions, Pb(II), Cu(II), Cr(II) and Zn(II) were chosen to evaluate their affinity to the GO-TETA-MA (Figure S3). The adsorption capacity value of GO-TETAMA increased with the order of Zn(II)< Pb(II)< Cr(II)< Cu(II). Obviously, the adsorbent exhibited better adsorption selectively for Cu (II) than other metal ions. Adsorption is a physicochemical process that involves the mass transfer of a solute from the liquid phase to the adsorbent’s surface [22]. A kinetic study provided important information about the mechanism of metal ion uptake onto GO-TETA-MA, this information is necessary to depict the adsorption rate of the adsorbent and to control the residual time of the entire adsorption process. Batch experiments examining the adsorption kinetics for the Cu(II) ion on 50 mg GO-TETA-MA were executed using an initial concentration of 100 mg/L for Cu(II) at pH=5.


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Figure 5 shows the effect of the contact time on the adsorption of Cu(II) ions. It is seen that the adsorption capacity of Cu(II) increased as the contact time increased. The GO-TETA-MA adsorbent had excellent performance during the initial adsorption period. This result might be due to the availability of a large number of vacant sites that became saturated with contact time. The optimum contact time for the adsorption of Cu(II) appears to be 60 min. In order to investigate the mechanism of sorption, the adsorption kinetics of the Cu(II) ions onto the GO-TETA-MA was studied using the pseudo-first-order and pseudo-second-order kinetic models. The pseudo-first-order kinetic equation is expressed as follows [23-24]:

= −

(3)

Integrating this for the boundary conditions t = 0 to t = t and qt = 0 to qt = qt , it can be expressed in linear form: log − = −

."#"

$

(4)

where qe and qt are the amounts (mg/g) of Cu(II) adsorbed at time t and at equilibrium, respectively, and k1 is the rate constant of the pseudo-first-order adsorption (min-1). The value of log (qe-qt) can be calculated from the experimental results and plotted against t (min). The pseudo-second-order model kinetic model is expressed by:

= −

(5)

Integrating this for the boundary conditions t = 0 to t = t and qt = 0 to qt = qt , gives:

= + $

(6)

Eq. (6) can be rearranged to obtain a linear form:

=

& &

+ $

(7)


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where k2 is the pseudo-second-order rate constant of adsorption (mg/g). The slope and intercept of the linear plot t/qe versus t yield the values of qe and k2. From figure 6, it can be seen that the correlation coefficients of the pseudo-first-order model are higher than those of the pseudo-second-order model. This suggests that the pseudo-first-order adsorption mechanism is predominant. The adsorption kinetic data were tested to determine whether intra-particle diffusion is the rate-limiting step. The intra-particle diffusion kinetic model can be written as follow:

= ' $ #.(

(8)

where kid is the intra-particle diffusion rate constant, Its value can be obtained from the slope of the plot qt versus t0.5. The qt versus t0.5 curve suggests the applicability of intra-particle diffusion controlling the kinetics of the adsorption. It was observed from figure 7 that intraparticle diffusion is not the rate-limiting step and that the adsorption mechanism is quite complex. Adsorption isotherms can describe the interactive behavior between the solution and the adsorbent. The experimental data for Cu(II) adsorption onto GO-TETA-MA were analyzed using the Langmuir and Freundlich isotherm models, in order to simulate and understand the adsorption mechanism. From the linear form of this isotherm, the Langmuir equation is given as follows [25]:

= )

*+,

+

(9)

*+,

where qmax (mg/g) is the theoretical maximum heavy metals adsorption amounts, qe (mg/g) is the amount of metal ions adsorbed by the adsorbent at equilibrium, Ce (mg/L) is the equilibrium concentration of metal ions, and b is the equilibrium adsorption constant.


10

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The Freundlich isotherm model is expressed as follows [26]:

= - + . /

(10)

where qe (mg/g) is the amount of metal ions adsorbed by adsorbent at equilibrium, Ce (mg/L) is the equilibrium concentration of metal ions, and KF and n are Freundlich constants related to the adsorption capacity and adsorption intensity, respectively. Table 1 Parameters for the calculation of Langmuir and Freundlich models. Langmuir

Freundich

qm (mg/g)

b (L/mg)

R2

KF (mol1-n Ln/ g)

n

R2

26.7451

0.1198

0.9861

0.79

3.6747

0.9968

Parameters of Langmuir and Freundlich models calculated from the sorption isotherms are shown in Table 1. According to the value of the correlation coefficients (R2) , the Freundlich models fits the experimental data better than the Langmuir models. The maximum adsorption capacities of Cu (II) on GO-TETA-MA is 26.7451. In addtion, the value of n (calculated from the Freundlich model) is 3.6747 represents the favorable adsorption process (1 < n < 10) in the present case [27], demonstrating that the synergistic contribution of functional groups or binding sites on the surface of GO-TETA-MA significantly improves the Cu (II) adsorption process. As shown in figure 8, high values of the correlation coefficient indicate that the Freundlich model fits the experimental data better than Langmuir model. This shows that the Freundlich isotherm is an ideal model of the adsorption process. Furthermore, the heterogeneous nature of the adsorption surface on the GO-TETA-MA is demostrated. The pH of the solution affects the adsorptive process through the protonation and deprotonation of functional groups of the active sites on the adsorption surface. This is because the


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protons in the acid solution can protonate the binding sites of the chelating molecules, and the hydroxide in the basic solution may become complex and precipitate many metals [28]. Therefore, a variation in pH can affect the kinetics and equilibrium characteristics of the adsorption process. In this study, the effect of the pH value on the adsorption capacity was investigated over a range of 1.0 to 6.0. The obtained results in Figure 9 show that, as the pH value increases, the adsorption capacity of Cu(II) also gradually increases. In acid solutions, the amine groups are easily protonated, and the decrease in the adsorption may be attributed to the protonation of amino groups that hinders the complex formation according to the following reaction. However, as the pH increases, the protonation of amino groups is reduced so that the surface of the GO-TETA-MA has more amino grous to coordinate with Cu(II). With further increases in the pH, hydroxy in the solution becomes adsorbed at the surface of the amino groups, and more electrostatic adsorption replaces the coordination [15, 29]. R − NH + H 4 → R − NH"4 R − NH + Cu

4

→ R − NH Cu

4

R − NH + OH → R − NH OH R − NH OH + Cu

4

→ R − NH OH ⋯ Cu

4

This study aimed to investigate the effect of pH on adsorption in the Cu(II) ion removal process. The Cu(II) ions start to become precipitated above pH=6; consequently, pH = 5 was selected for further investigation of the metal removal in order to avoid heavy metal precipitation conditions. The influence of temperature on the adsorption capacity is shown in figure 10, which indicates that the adsorption capacity of Cu(II) increased as the temperature increased from 10 to 40 oC. This elucidates that the adsorption of Cu(II) ions in the system is an endothermic process and there is good thermal stability of GO-TETA-MA.


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A chitosan adsorbent can be dissolved in an acid solution, while a metal oxide under an acid condition is not stable. Hence, the stability of the adsorption material is an important precondition in the adsorption process. Most studies have focused on GO properties, and only a few have focused on the stability of the modified adsorbent in different systems. To determine the pH stability of GO-TETA-MA, the following experiments were performed. First, 100 mg of GO-TETA-MA was placed in a 50 ml Erlenmeyer flask with 30 ml of deionized water in a shaker. The pH value of the solution was varied in the range 1.0~7.0 by adding of drops of aqueous HCl solution. The total nitrogen content was analyzed using an automatic azotometer. From Table 2, it is seen that there was no nitrogen content in the sample solution. Table 2. The total nitrogen content in various system pH

1

2

3

4

5

6

7

Total N (%)

0.0088

0.0079

0.0066

0.0073

0.0082

0.009

0.013

Thermogravimetic measurement analysis (TGA) is a useful technique for determining the composition and thermal stability of materials. Figure 11 shows the TGA curves of the GOTETA-MA composite. The sample exhibits a few weight loss stages. The TGA curves show an initial slight weight loss at the range of 100~150°C, which is due to the decomposition of the grafted organic groups and water vapor [3]. At temperatures above 200 °C, the weight decrease in GO-TETA-MA is due to the pyrolysis of the liable oxygen-containing functional groups. As the temperature further increases, the weight decrease in GO-TETA-MA primarily comes from the thermal decomposition of the stable functional group. These results demonstrate that the physicochemical performance of GO-TETA-MA is sufficient for resisting acid, alkali, and heat.


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Each year, the world uses about 3 million tons of pesticides (composed of herbicides, insecticides, and fungicides) that are formulated from about 1600 different chemicals [30]. The pesticides have made a significant contribution to food security. However, with the growth in world population and the expansion of cultivation, the abuse of fungicides has resulted in a drastic increased in pesticide residues. Pesticides add much pollution to the environment and adversely affect human health. The copper fungicide is one kind of pesticide that can pollute surface waters and groundwater; their copper adsorbent research and application is very important. In this study, the fungicides cupric hydroxide, copper sulfate, cuprous oxide, and copper busic chloride were obtained from the DuPont Company and the removal efficiencies of these four fungicides were studied. They were diluted according to instructions. The results are provided in Figure 12. The removal in the four fungicide solutions was found to be 99.8, 77, 86, and 89%, respectively. The final concentration was lower than 0.1 mg/L. The Cu(II) ions in these samples were eliminated satisfactorily after extraction and pre-concentration procedures, which indicates that this material is reliable and practical. It is promising that the GO-TETA-MA adsorbent can be widely applied in the removal of Cu(II) from heavy-metal-contaminated water. Table 3. The removal of Cu(II) ions from fungicides solution using GO-TETA-MA. Fungicides

Initial Cu(II) conc. Equilibrium Cu(II) Removal effect (%) （PPM） conc.（PPM）

copper sulfate

86.3729

0.0889

99.8%

cupric hydroxide

85.7883

19.6866

77%

cuprous oxide

2.3935

0.3347

86%

copper chloride 0.1814 hydroxide

0.0199

89%


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CONCLUSIONS In summary, we obtained a novel GO-based adsorbent, GO-TETA-MA. This composite shows a high capacity for the adsorption for Cu(II) ions, with a removal efficiency of copper fungicide reaching up to 100%. The final ion concentration is less than 0.1 mg/L, and also less than the allowable levels of contaminant copper in drinking water in China. Meanwhile, the GO-TETAMA adsorbent is good at resisting to acid, alkali, and heat. The experimental data was found to obey the pseudo-first-order kinetic model, and the adsorption isotherms data of Cu(II) ions on the adsorbent were fit well by the Freundlich isotherm model. The GO-TETA-MA has a higher copper adsorption capability in an aqueous solution. This study suggests that the GO-TETA-MA composite can be used in the recovery of Cu(II) from wastewater.

AUTHOR INFORMATION Corresponding Author *H. Yu. E-mail: [email protected]. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (No. 21277142), “Cross-disciplinary Collaborative Teams Program for Science, Technology and Innovation” of Chinese Academy of Sciences, the “Hundred Talents Project” of the Chinese Academy of


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Science, the Important Deployment Project of Chinese Academy of Sciences (KZZD-EW-TZ16), CAS Interdisciplinary Innovation Team.

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[7] Wu, W. Q.; Yang, Y.; Zhou, H. H.; Ye, T. T.; Huang, Z. Y.; Liu, R. et al. Highly Efficient Removal of Cu(II) from Aqueous Solution by Using Graphene Oxide. Water air soil poll 2012, 1372. [8] Rao, G. P.; Lu, C.; Su, F. Sorption of divalent metal ions from aqueous solution by carbon nanotubes: a review. Sep. Purif. Technol. 2007, 58, 224. [9] Soylak, M.; Unsal, Y. E.; Kizil, N.; Aydin, A. Utilization of membrane filtration for preconcentration of Cu(II) and Pb (II) in food, water and geological samples by atomic absorption spectrometry. Food. Chem. Toxicol. 2010, 48, 517. [10] Matlok, M. M.; Howerton, B. S.; Atwood, D. A. Chemical precipitation of lead from lead battery recycling plant wastewater. Ind. Eng. Chem. Res. 2002, 41, 1579. [11] Huang, Z. H.; Zheng, X.; Lv, W.; Wang, M.; Yang, Q. H.; Kang, F. Adsorption of lead (II) ions from aqueous solution on low-temperature exfoliated graphene nanosheets. Langmuir 2011, 27, 7558. [12] Dichiara, A. B.; Webber, M. R.; Gorman, W. R.; Rogers R. E. Removal of copper ions from aqueous solutions via adsorption on carbon nanocomposites. ACS Appl. Mater. Interfaces 2015, DOI: 10.1021/acsami.5b04974. [13] Liu, G.; Gui, S.; Zhou, H.; Zeng, F.; Zhou, Y.; Ye, H. A strong adsorbent for Cu2+: graphene oxide modified with triethanolamine. Dalton Trans. 2014, 43, 6977. [14] Madadrang, C. J.; Kim, H. Y.; Gao, G.; Wang, N.; Zhu, J.; Feng, H. et al. Adsorption Behavior of EDTA-Graphene Oxide for Pb (II) Removal. ACS Appl. Mater. Interfaces 2012, 4, 1186.


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[15] Guo, X.; Du, B.; Wei, Q.; Yang, J.; Hu, L.; Yan, L. et al. Synthesis of amino functionalized magnetic graphenes composite material and its application to remove Cr(VI), Pb(II), Hg(II), Cd(II) and Ni(II) from contaminated water. J. Hazard. Mater. 2014, 278, 211. [16] Hummer Jr, W. S.; Offman, R. E. Preparation of graphitic oxide. J. Am. Chem. Soc. 1958, 80, 1339. [17] Depan, D.; Girase, B.; Shah, J. S.; Misra, R. D. Structure-process-property relationship of the polar graphene oxide-mediated cellular response and stimulated growth of osteoblasts on hybrid chitosan network structure nanocomposite scaffolds. Acta Biomater 2011, 7, 3432. [18] Fan, L.; Luo, C.; Sun, M.; Li, X.; Qiu, H. Highly selective adsorption of lead ions by water-dispersible magnetic chitosan/graphene oxide composites. Colloids Surf. B 2013, 103, 523. [19] Chen, H.; Wang, Y.; Dong, S. An Effective Hydrothermal Route for the Synthesis of Multiple PDDA-Protected Noble-Metal Nanostructures. Inorg. Chem. 2007, 46, 10587. [20] Ramanathan, T.; Fisher, F. T.; Ruoff, R. S.; Brinson, L. C. Amino-functionalized carbon nanotubes for binding to polymers and biological systems. Chem. Mater. 2005, 17, 1290. [21] Cai, W.; Piner, R. D.; Stadermann, F. J.; Park, S.; Shaibat, M. A.; Ishii, Y. et al. Synthesis and Solid-State NMR Structural Characterization of 13C-Labeled Graphite Oxide. Science 2008, 321, 1815. [22] Zhu, H. Y.; Jiang, R.; Xiao, L.; Zeng, G. M. Preparation, characterization, adsorption kinetics and thermodynamic of novel magnetic chitosan enwrapping nanosized gamma-Fe2O3 and muti-walled carbon nanotubes with enhanced adsorption properties for methyl orange. Bioresour. Technol. 2010, 101, 5063.


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[23] 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. [24] Zhang, Y.; Chen, Y.; Wang, C.; Wei, Y. Immobilization of 5-aminopyridine-2-tetrazole on cross-linked polystyrene for the preparation of a new adsorbent to remove heavy metal ions from aqueous solution. J. Hazard. Mater. 2014, 276, 129. [25] Langmuir, I. The constitution and fundamental properties of solids and liquids. J. Am. Chem. Soc. 1917, 183, 102. [26] Freundlich, H. über die adsorption in lösungen. Z. Phys. Chem., 1906, 57, 385. [27] Sheela, T.; Nayaka, Y. A. Kinetics and thermodynamics of cadmium and lead ions adsorption on NiO nanoparticles, Chem. Eng. J., 2012, 191, 123. [28] Srivastava, V. C.; Mall, I. D.; Mishra, I. M. Adsorption of toxic metal ions onto activated carbon study of sorption behavior through characterization and kinetics. Chem. Eng. Process. 2008, 47, 1269. [29] Fan, L.; Luo, C.; Sun, M.; Li, X.; Qiu, H. Highly selective adsorption of lead ions by water-dispersible magnetic chitosan/graphene oxide composites. Colloid. Surface. B 2013, 103, 523. [30] Horrigan, L.; Lawrence, R. S.; Walker, P. How Sustainable Agriculture Can Address the Environmental and Human Health Harms of Industrial Agriculture. Environ. Health Perspect. 2002, 110, 445.


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Insert Table of Contents Graphic and Synopsis Here H 2N

NH

GO-TETA HN

GO

O O OH OH O

O OH

OH

O

O

O N H

O

O O

OH OHN O

OH OH

HN

OH HO OH

OH

HO

NH

O HO

O

OH

OH

OH O HO

OH

O

OH

OH HO

O OH

OH O HN

NH

OH

NH

OH O O

OH HO

O

OH

OH O HO

OH

O

H 2N

H2 N

O

O O

O

O

HN

NH2

O

N

N

NH

O

NH

OH

O OH O

N H2 N O

O OH

OH O HO O

OH

HN

N NH2

HO O

N O

OH HN

OH HO OH

H 2N O

NH O

N

OH

OH O O

OH

O

NH2 O

O

GO-TETA-MA NH2

H2 N

O

N NH2 O

O

Cu2+

HN NH 2

N

O

O

H2N

NH2 O

O

NH

O OH OH O

N H2 N O

NH 2

O OH

NH2 OH O HO O OH

O

HN

OH HO

O

N

OH

OH O O

OH HO

N O NH

NH

OH

O

N

NH2 O NH2

OH

H 2N O

O HN

NH2

O

O

O

Figure 1 Preparation of GO- TETA-MA Composites and its interaction with heavy metal

Figure 2 The removal of Cu(II) ions from fungicides solution using GO-TETA-MA


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We report a room-temperature approach to synthesizing nitrogen-functionalized graphene oxide. The removal efficiency for four copper fungicides was studied and was found to reach 100%.


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Figure 1. Preparation of GO- TETA-MA Composites and its interaction with heavy metal 320x174mm (300 x 300 DPI)


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Figure 2. FT-IR spectra for the GO and GO-TETA-MA 252x220mm (300 x 300 DPI)



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Fig. 3. (a) XPS spectra of GO and GO-TETA-MA samples. (b) N1s spectra of GO-TETA-MA. 517x217mm (300 x 300 DPI)


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Fig. 4. 13C NMR spectra of the GO and GO-TETA-MA. 492x217mm (300 x 300 DPI)



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Figure. 5. Effect of contact time on the adsorption of Cu(II). 278x224mm (300 x 300 DPI)


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Figure. 6. Pseudo-first-order (left) and pseudo-second-order (right) kinetics models for Cu(II) ions onto the GO-TETA-MA adsorbent. 558x223mm (300 x 300 DPI)



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Figure. 7. The intra-particle diffusion model of Cu(II) ions onto the GO-TETA-MA. 274x219mm (300 x 300 DPI)


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Figure. 8. Langmuir (left) and Freundlich (right) isotherm models for adsorption of Cu(II) ions onto the GOTETA-MA. 548x220mm (300 x 300 DPI)



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Figure. 9. The influence of pH on the adsorption of Cu(II) by GO-TETA-MA. 275x224mm (300 x 300 DPI)


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Figure. 10. The influence of temperature on the adsorption of Cu(II) by GO-TETA-MA. 268x219mm (300 x 300 DPI)



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Figure. 11. The TGA curve of GO-TETA-MA. 272x217mm (300 x 300 DPI)


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Figure. 12. The removal of Cu(II) ions from a fungicide solution using GO-TETA-MA. 280x208mm (300 x 300 DPI)


Facile and Efficient Synthesis of Nitrogen-Functionalized Graphene

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