Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution

JES-00188; No of Pages 10 J O U RN A L OF E N V I RO N ME N TA L S CI EN CE S X X (2 0 1 4 ) XX X–XXX

Available online at www.sciencedirect.com

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Q24Q1 5

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3

Di Lei, Qianwen Zheng, Yili Wang, Hongjie Wang⁎

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Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution

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1

College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, China

6

AR TIC LE I NFO

ABSTR ACT

10

Article history:

A novel material, aminopropyl-functionalized manganese-loaded SBA-15 (NH2-Mn-SBA- 15

11

Received 15 April 2014

15), was synthesized by bonding 3-aminopropyl trimethoxysilane (APTMS) onto manganese- 16

12

Revised 16 June 2014

loaded SBA-15 (Mn-SBA-15) and used as a Cu2+ adsorbent in aqueous solution. Fourier 17

13

Accepted 28 June 2014

transform infrared spectroscopy (FT-IR), X-ray diffraction spectra (XRD), N2 adsorption/ 18

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P

98

14

desorption isotherms, high resolution field emission scanning electron microscopy (FESEM) 19 and X-ray photoelectron spectroscopy (XPS) were used to characterize the NH2-Mn-SBA-15. 20 Keywords:

The ordered mesoporous structure of SBA-15 was remained after modification. The manganese 21

35

Copper

oxides were mainly loaded on the internal surface of the pore channels while the aminopropyl 22

36

SBA-15

groups were mainly anchored on the external surface of SBA-15. The adsorption of Cu2+ on 23

37

Manganese oxides

NH2-Mn-SBA-15 was fitted well by the Langmuir equation and the maximum adsorption 24

38

Aminopropyl groups

capacity of NH2-Mn-SBA-15 for Cu2+ was over two times higher than that of Mn-SBA-15 under 25

39

Adsorption

the same conditions. The Elovich equation gave a good fit for the adsorption process of Cu2+ 26

E

C

T

34

40

R

by NH2-Mn-SBA-15 and Mn-SBA-15. Both the loaded manganese oxides and the anchored 27 aminopropyl groups were found to contribute to the uptake of Cu2+. The NH2-Mn-SBA-15 28

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showed high selectivity for copper ions. Consecutive adsorption–desorption experiments 29 showed that the NH2-Mn-SBA-15 could be regenerated by acid treatment without altering its 30 31

42 43 41 44

N C O

properties.

© 2014 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. 32

Introduction

47 48 49 50 51 52 53 54 55 56

Copper is an essential element for human life and health, but it will cause serious environmental and public health problems in cases of excessive discharge (Malkoc and Nuhoglu, 2005; Komárek et al., 2010). Due to its non-biodegradability and accumulation in the environment, great attention has been paid to studying removal processes for copper ions (Kurniawan et al., 2006; Dabrowski et al., 2004; Mohammadi et al., 2004; Sud et al., 2008; Mohsen-Nia et al., 2007). Among the established processes, the adsorption method is gaining prominence for its simplicity of operation, recovery of the heavy metals, high efficiency, lower sludge

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Published by Elsevier B.V. 33

production volume and ability to meet strict discharge specifications (Swami and Buddhi, 2006; Ngah Wan and Hanafiah, 2008). Great numbers of natural (Gündoğan et al., 2004; Basci et al., 2004) or artificial (Chen et al., 2003, 2011) materials have been developed to eliminate metal ions from aqueous solution. Recently a series of ordered mesoporous silica materials, such as MCM-41, MCM-48, and SBA-15 (Benhamou et al., 2009; Perez-Quintanilla et al., 2006) have been developed for metal ion elimination because of their high surface area and pore volume, good accessibility to active sites, rapid mass transport inside the nanostructures, good hydrothermal stability and ease of surface modification. To further enhance the efficiency and selectivity of the ordered mesoporous materials, great effort has been made to

⁎ Corresponding author. E-mail: [email protected] (Hongjie Wang)

http://dx.doi.org/10.1016/j.jes.2014.06.045 1001-0742/© 2014 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

Please cite this article as: Lei, D., et al., Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution, J. Environ. Sci. (2014), http://dx.doi.org/10.1016/j.jes.2014.06.045

57 58 Q3 59 Q4 60 61 62 63 64 65 66 67 68 69

2

1. Materials and methods

95

1.1. Chemicals

96

102

Tetraethyl orthosilicate (TEOS, 98%) and 3-aminopropyltrimethoxysilane (APTMS) were purchased from Alfa. Pluronic P123 (PEO20PPO70PEO20, Mav = 5800) was purchased from Aldrich. KMnO4, H2O2 (30%), Cu(NO3)2·5H2O, NaNO3, NaOH and HNO3 obtained from Beijing Chemical Agents Company were analytical grade and were used as received without further purification.

103

1.2. Synthesis of NH2-Mn-SBA-15

104

Preparation of SBA-15 containing the triblock copolymer Pluronic P123 (P123-SBA-15) sample was performed following a previously reported method (Zhao et al., 1998). Pluronic P123 (Aldrich) (4 g) was dissolved in 120 g of 2 mol/L HCl solution at 40°C and 8.5 g TEOS was then added. The solution was kept under stirring for 24 hr and was subsequently transferred to a Teflon-lined autoclave, where it was heated at 100°C for 48 hr. The final solid product was obtained by filtration, washed with distilled water, and then dried at 70°C overnight. The Mn-SBA-15 was synthesized according to a previous publication (Dong et al., 2005). P123-SBA-15 2 g was added into a beaker containing KMnO4 aqueous solution (400 mL, 0.1 mol/L), then stirred at room temperature for 3 hr. After being filtered off and washed thoroughly with deionized water, the resulting solid product Mn-SBA-15 was dried at 70°C. NH2-Mn-SBA-15 was prepared via a post-grafting method. The typical procedure was as follows: 1.0 g of so-obtained materials was dispersed in 100 mL of water-free toluene and refluxed with continuously stirring at 110°C. After the formation of a homogenous suspension, 0.4 mL of APTMS was added dropwise under the protection of nitrogen flow and the mixture was stirred and refluxed for 24 hr. The solid product was recovered by filtration, and later washed with toluene,

106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126

131

FT-IR spectra (Nicolet 5700, USA) measurements were recorded on anhydrous KBr pellets in the frequency range of 4000– 400 cm−1 (spectral resolution: 4 cm−1, number of scans: 32). The X-ray powder patterns were investigated by an XRD diffractometer (X'Pert PRO MPD) using Cu Kα radiation at 40 kV and 30 mA. The data were collected from 0.5°–5° for low-angle and 5°–80° for high-angle measurements. N2 adsorption/desorption experiments were conducted at 77 K using an ASAP 2020 surface analyzer (Micromeritics Co., USA). Samples were degassed at 105°C and 105 Pa under vacuum for at least 6 hr. Surface area was calculated by using the BET equation and the pore size distribution was obtained from the adsorption branch of isotherms using the BJH model. The pore volume was obtained by the t-plot method. High resolution field emission scanning electron microscopy (FESEM) was performed on a Hitachi SU-8020 scanning electron microscope. The XPS measurements were carried out with an imaging photoelectron spectrometer (Kratos AXIS Ultra, UK), using an aluminum anode X-ray source with a monochromator (Al Kα, hν = 1486.71 eV) or a dual anode (Al/Mg target). The wide scan spectra were conducted from 0 to 1100 eV with pass energy of 160 eV. The high resolution scans were conducted according to the peak being examined with pass energy of 40 eV. The binding energies were calibrated internally by the carbon deposit C 1s binding energy at 284.6 eV. The software of Vision (PR2.1.3) and Casa XPS (2.3.12Dev7) were used to fit the XPS results which were collected in binding energy forms. Surface zeta potentials were measured using a Zeta Potential Analyzer (Zeta PALS, Brookhaven Instruments Co.).

132 Q8

1.4. Batch adsorption experiments

161

Adsorption kinetics experiments were performed at initial Cu2+ concentration of 0.1 mmol/L. Typically, 0.1 g of NH2-MnSBA-15, Mn-SBA-15 was added into a 500-mL flask containing 500 mL of 0.1 mmol/L Cu2+ solution with an ionic strength of 0.01 mol/L NaNO3 and pH 5.5, which was strongly stirred at 25°C. During the kinetics experiments, aliquots of samples were withdrawn by stopping agitation at fixed intervals, selected from 1 min to 48 hr. The filtrate was passed through a 0.45 μm membrane and the extracted samples were collected. The ionic strengths of 0.01, 0.05 and 0.1 mol/L NaNO3 were used as background electrolyte. The desired solution pH was adjusted with 0.1 mol/L HNO3 or 0.1 mol/L NaOH, such that the equilibrium solutions had pH values ranging from 3.0 to 7.0. The reaction mixture consisted of 100 mL solution with initial Cu2+ concentration of 0.1 mmol/L and 100 mg/L adsorbent. After reacting for 48 hr at 25°C with a shaking speed of 140 r/min, the suspension was filtered with a 0.45 μm membrane. The adsorption isotherm experiments were conducted at pH 5.5 and at room temperature with initial Cu2+ concentrations in the range of 0.01 to 0.18 mmol/L. 10 mg of Mn-SBA-15,

162

R O

O

F

1.3. Adsorbent characterization

T

C

E

R R

105

O

101

C

100 Q7

N

99 Q6

U

98

127

D

94 93

97 Q5

acetone and ethanol successively. The final product was dried at 70°C and used for further characterization and evaluation. The synthesis route of the NH2-Mn-SBA-15 material is shown in Scheme 1.

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develop metal hybrid silica (Dragoi et al., 2009) and/or organic– inorganic hybrid mesoporous silica (Xue and Li, 2008; Jeong et al., 2011) materials. In view of its large surface area, microporous structure, high stability and large amount hydroxy groups capable of reacting with metal ions, manganese oxides are commonly introduced to the hybrid materials to enhance the efficiency and high selectivity for metal ions (Calderon Rosas et al., 2010). On the other hand, aminopropyl groups anchored on the surface of the adsorbents are reported to improve the adsorption efficiency via the formation of metal–nitrogen coordination bonds (Zhao et al., 2011). To the best of our knowledge, the most used approach is to modify mesoporous silica surfaces using aminopropyl groups to increase their adsorption of metal ions (Aguado et al., 2009), however, adsorption of aqueous Cu2+ on metal–organic–inorganic hybrid mesoporous silica has not been reported in the literature so far. The objectives of the work are: (1) to develop a novel hybrid material that has the high metal ion uptake capacity of the manganese oxides and high selectivity of aminopropylfunctionalized SBA-15; (2) to characterize the structure of the materials; and (3) to evaluate the adsorption behavior of the materials for copper ions in aqueous solution and investigate the adsorption mechanism preliminarily.

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70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92

J O U RN A L OF E N V I RO N ME N TA L S CIE N CE S X X (2 0 1 4 ) XXX –XXX

Please cite this article as: Lei, D., et al., Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution, J. Environ. Sci. (2014), http://dx.doi.org/10.1016/j.jes.2014.06.045

128 129 130

133 134 135 136 Q9 137 138 139 140 Q10 141 142 143 144 145 146 147 148 149 Q11 150 151 152 153 154 155 156 157 158 159 160 Q12

163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182

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J O U RN A L OF E N V I RO N ME N TA L S CI EN CE S X X (2 0 1 4 ) XX X–XXX

(P123-SBA-15)

P123

Pluronic P123 + TEOS + HCl

OH

OH OH

OH

KMnO4

OH

OH

(APTMS)

(NH2-Mn-SBA-15) NH2

O

Si

CH3O

NH2

Si

O

O

Toluene reflux, 24 hr, N2

F

CH3O CH3OH

Mn

(Mn-SBA-15)

R O

O

Scheme 1 – The schematic synthesis route of NH2-Mn-SBA-15. NH2-Mn-SBA-15 adsorbent was added into each 100 mL Cu2+ 184 solution with an ionic strength of 0.01 mol/L NaNO3. After 185 reacting for 48 hr at 25°C with a shaking speed of 140 r/min, 186 the suspension was passed through a 0.45 μm membrane and 187 the extracted samples were collected. 188 Four mixed solutions with other metals were prepared to 189 observe the effect of the adsorptive competing cations on 190 the Cu2+ adsorption by NH2-Mn-SBA-15: the Cu2+ and Pb2+ 191 solution, the Cu2+ and Cd2+ solution, the Cu2+ and Zn2+ 192 solution, and the Cu2+, Pb2+, Cd2+ and Zn2+ solution, the 193 concentration of each heavy metal is 0.1 mmol/L. 10 mg of 194 NH2-Mn-SBA-15 adsorbent was added into each 100 mL mixed 195 solution with an ionic strength of 0.01 mol/L NaNO3 and 196 pH 5.5. After reacting for 48 hr at 25°C with a shaking speed 197 of 140 r/min, the suspension was passed through a 0.45 μm 198 membrane and the concentration of heavy metals was 199 analyzed. 200 The concentration of heavy metals was analyzed by using 201 an atomic absorption spectrophotometer (AAS, AA-6300 202 Q13 Shimadzu Co.). The adsorption capacity of heavy metal ions 203 adsorbed per gram adsorbent (mg/g) was calculated using the 204 following equation (Eq. (1)):

D

E

T

C

E

R

R

V ðC 0 −C t Þ W

ð1Þ

U

Transmittance (%)

c

N C O

qt ¼

where, qt is the equilibrium adsorption amount, C0 (mg/L) and Ct (mg/L) are the initial and equilibrium concentrations, V (L) is the volume of the solution and W (g) is the mass of the adsorbent. In this study, the pseudo first-order equation (Eq. (2)) (Lagergren, 1898), pseudo second-order equation (Eq. (3)) (Ho and McKay, 1998) and Elovich equation (Eq. (4)) (Chien and Clayton, 1980) were used to evaluate the kinetics of the adsorption process.

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183

  qt ¼ qe 1−e−k1 t

qt ¼ β ln ðαβÞ þ β ln t

ð4Þ

where, qe (mg/g) and qt (mg/g) are the adsorption capacity of Cu2+ on the adsorbents at equilibrium and at time t (min), k1 (L/min) is the rate constant of the pseudo first-order equation and k2 (g/(mg·min −1)) is the rate constant of the second-order equation, α (mg/(g·min −1)) is the initial Cu2+ adsorption rate and β (g/mg) is the desorption constant during any one experiment. The Langmuir adsorption isotherm model (Langmuir, 1916) and Freundlich adsorption isotherm model (Freundlich, 1906) were used to determine the equilibrium experimental data. The non-linear models are represented as Eqs. (5) and (6).

C-H

a

4000

C-H

C-O-C

qmax K L C e 1 þ KL Ce

3000

2500 2000 1500 Wavenumber (cm-1)

1000

500

Fig. 1 – FT-IR images of P123-SBA-15 (line a), Mn-SBA-15 (line b) and NH2-Mn-SBA-15 (line c).

209 210 211 212 213 214

218 217 220 219 221 222 223 Q14 224 Q15 225 226 227 228 229 230

ð5Þ 232 231

Si-OH

qe ¼ K F C e 1=n

3500

208

216 215

ð3Þ

qe ¼

207

ð2Þ

q2e k2 t qt ¼ 1 þ qe k2 t

b

206 205

ð6Þ

where, qe (mg/g) is the equilibrium adsorption capacity of the adsorbent, Ce (mg/L) is the equilibrium solution concentrations of Cu2+, qmax (mg/g) is the maximum adsorption capacity, KL (L/mg) is the Langmuir equilibrium constant, KF ((mg/g)(L/mg)1/n) is the Freundlich constant, and n is the Freundlich exponent.

Please cite this article as: Lei, D., et al., Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution, J. Environ. Sci. (2014), http://dx.doi.org/10.1016/j.jes.2014.06.045

234 233 235 236 237 238 239

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J O U RN A L OF E N V I RO N ME N TA L S CIE N CE S X X (2 0 1 4 ) XXX –XXX

A

B

(110) (200) 1.5

Internsity (a.u.)

a

a 2.0

2.5 3.0 2θ (degree)

3.5

4.0

4.5

0

5.0

10

20

30

40 50 2θ (degree)

60

F

1.0

b

70

80

O

0.5

c

b

(100)

Intensity (a.u.)

c

ki ¼

K d Cu2þ

ð7Þ

K d Me2þ

244 243

Kd ¼

103 Q Ce

ð8Þ

250

1.5. Regeneration and reusability experiments

251

The regeneration and reusability of the NH2-Mn-SBA-15 were examined by acid treatment. 0.2 g copper-loaded NH2-MnSBA-15 was stirred in 100 mL of 0.1 mol/L HNO3 solution for 12 h at room temperature to strip copper ions. The final Cu2+ concentration in the aqueous phase was determined. The adsorbent was then washed with deionized water several

256

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2. Results and discussion

261 260 262

2.1. Material characterization

E

R

R

500

A

2.1.1. FT-IR

263

FT-IR spectra of the P123-SBA-15, Mn-SBA-15 and NH2-MnSBA-15 are illustrated in Fig. 1. The peaks in the range of 2850– 3000 cm−1 and at 1460 cm− 1 are attributed to C–H stretching and bending vibrations of P123 and the peak at 1350 cm−1 is corresponded to C–O–C stretching modes of P123 (Fig. 1a) (Vo et al., 2013), while the intensity of the peaks in the corresponding regions clearly weakens after the treatment by KMnO4 (Fig. 1 line b). The redox reaction between KMnO4 and P123 located in the channels of SBA-15 is thus demonstrated (Zhu et al., 2006). The shrinkage of the peak at about 960 cm−1 ascribed to the bending vibration of Si–OH was also detected, which indicates the possible reaction between the formed manganese oxides and the silanol groups of SBA-15. After aminopropyl functionalization, the

264

a

400

4.5

b

4.0

a

B

3.5 dV/dD (cm3/g.nm)

255

O

254

C

253

N

252

U

248

Volume adsorbed (cm3/g, STP)

247

C

249

where, Kd (mL/g) is the distribution ratio of the metal ion, ki represents the selectivity coefficients toward Cu2+, Q (mg/g) is the amount of the metal ion on the adsorbents, and Ce (mg/L) is the equilibrium metal ion concentration.

246 245

D

242

times. Then the resulting cleaned adsorbent was dried at 70°C 257 and subjected again to adsorption–desorption process for four 258 cycles. 259

E

241

The selectivity coefficients (ki) of the Cu2+ in the presence of the other metal Me2+ ions (Me2+ = Pb2+, Cd2+ and Zn2+) were calculated according to the following equations (Eqs. (7) and (8)):

T

240

R O

Fig. 2 – XRD patterns of samples at low angles (A) and high angles (B). line a: P123-SBA-15; line b: Mn-SBA-15; line c: NH2-Mn-SBA-15.

b

300

200

c

3.0 2.5 c

2.0 1.5 1.0

100

0.5

0

-0.5

0.0 0.0

0.2

0.4 0.6 0.8 Relative pressure (P/P0)

1.0

0

10

20

30

40 50 60 70 Pore diameter (nm)

80

90

Fig. 3 – N2 adsorption-desorption isotherms (A) and pore size distribution (B) of P123-SBA-15 (line a), Mn-SBA-15 (line b) and NH2-Mn-SBA-15 (line c). Please cite this article as: Lei, D., et al., Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution, J. Environ. Sci. (2014), http://dx.doi.org/10.1016/j.jes.2014.06.045

265 266 267 268 269 270 271 272 273 274 275 276

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Surface area Pore volume Pore diameter (m2/g) (cm3/g) (nm) 0.67 0.51 0.29

6.82 4.68 5.03

284

2.1.2. XRD

285

306

To investigate the surface structure of the absorbents, the XRD patterns were measured. The low angle XRD patterns in Fig. 2A show that P123-SBA-15 exhibits three characteristic resolved diffraction peaks, which were indexed as the (1 0 0), (1 1 0) and (2 0 0) reflections, associated with the ordered hexagonal mesoporous silica framework. The introduction of manganese oxides and aminopropyl groups caused a marked intensity decrease. However, the basal (1 0 0) diffraction peaks can be distinctly observed, which indicates that the hexagonal patterns of the SBA-15 were well maintained after the functionalization (Chen et al., 2010). The peaks of (1 1 0) and (2 0 0) become unobservable, indicating the irregular organization of the mesoporous structure at long range. The XRD patterns at high diffraction angles (Fig. 2B) show that the introduction of manganese oxides and aminopropyl groups leads to an obvious reduction of the crystallinity of the samples. There is no distinct reflection of manganese oxide crystalline phase observed outside of the pore channels of Mn-SBA-15 and NH2-Mn-SBA-15. This suggests that the formed manganese oxides are highly dispersed in the pore channels or that the diameters of the formed small clusters are below the detection limit of XRD (Tang et al., 2010).

307

2.1.3. N2 adsorption/desorption isotherms

308

As shown in Fig. 3, all of the curves of the N2 adsorption– desorption isotherms of the samples exhibit the type IV isotherms with H1 hysteresis loop type, with capillary condensation at P/P0 from 0.4 to 0.8 as defined by IUPAC,

287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305

309 310 311

C

286

E

282

R

281

R

280

N C O

279

U

278

T

283

intensity of the peaks at 2850–3000 cm−1 corresponding to C–H stretching vibrations strengthens again. Meanwhile, the band associated with the bending vibration of Si–OH bonds at about 960 cm−1 almost disappears (Fig. 1 line c). It is reasonable to suggest the partial elimination of the silanols and the successful anchoring of the aminopropyl groups onto the surface of Mn-SBA-15 (Xu et al., 2011).

277

2.1.4. FESEM

333

High resolution field emission scanning electron microscope (FESEM) images of the samples in Fig. 4 permit the observation of channel-like structures running parallel to the longer direction, and the channels correspond well to the 2D hexagonal structure typical of SBA-15 (Lombardo et al., 2012). The above results indicate that the process of loading of manganese oxides and the grafting of aminopropyl groups have little effect on the morphology of the materials and the textural order of the framework of the materials is well preserved.

334

2.1.5. XPS

344

Wide scan XPS spectra of NH2-Mn-SBA-15 before and after Cu2+ adsorption over a wide binding energy range from 0 to 1100 eV are displayed in Fig. 5A. Clear N 1 s peaks are shown in the spectrum of NH2-Mn-SBA-15, which suggests the successful grafting of aminopropyl groups onto the SBA-15 surface. The appearance of the Cu 2p binding energy peak after adsorption directly confirms the uptake of copper species by NH2-Mn-SBA-15. The computer deconvolution of the XPS spectrum of Cu2+ in Fig. 5B shows two peaks at 934.53 and 953.92 eV along with weak satellite peaks around 943.84 and 962.36 eV respectively, which provides evidence for the presence of Cu2+ species on NH2-Mn-SBA-15 after adsorption

345

F

394.7 431.9 229.5

O

P123-SBA-15 Mn-SBA-15 NH2-Mn-SBA-15

R O

t1:5 t1:6 t1:7

Sample

312

P

t1:4

which is the typical characteristic of a mesoporous structure (Haber et al., 1994). After loading of manganese oxides, the inflection point shifts clearly to lower partial pressure, corresponding to the decrease of the pore diameter of the mesoporous materials, while no clear shift of the inflection point is detected after aminopropyl functionalization. The sharpness of the hysteresis loops indicates that all of the samples have a narrow pore size distribution. The textural properties of the materials are summarized in Table 1. After treatment by KMnO4, a small decrease of the pore volume and pore size and clear increase of the BET surface area of P123-SBA-15 are detected, and this ascribed to the redox reaction between KMnO4 and the templating agent. It further indicates that most of the formed manganese oxides mainly load on the internal surfaces of the pore channels of SBA-15. Meanwhile, an inconspicuous increase of the pore diameter and a pronounced decrease of the BET surface area and the pore volume occur after the functionalization by aminopropyl groups onto Mn-SBA-15. The above phenomena indicate that aminopropyl groups are mainly anchored on the external surface of Mn-SBA-15 (Xu et al., 2011).

D

t1:3

Table 1 – Textural properties of P123-SBA-15, Mn-SBA-15 and NH2-Mn-SBA-15.

E

t1:1 t1:2

Fig. 4 – FESEM images of P123-SBA-15 (A), Mn-SBA-15 (B) and NH2-Mn-SBA-15 (C). Please cite this article as: Lei, D., et al., Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution, J. Environ. Sci. (2014), http://dx.doi.org/10.1016/j.jes.2014.06.045

313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332

335 336 337 338 339 340 341 342 343

346 347 348 349 350 351 352 353 354 355 356

6

400

Si 2p

Intensity

Si 2s Si 2s

C 1s

200

0

980

970

960

Banding engery (eV)

950

940

930

Binding engery (eV)

C

Before

O

N 1s

600

Cu 2p

Before

532.55 eV

399.62 eV

920

F

O 1s

Mn 2p Mn 2p

O KLL Cu 2p

800

943.84 eV

b

After

934.53 eV

953.92 eV

Si 2p

N 1s

C 1s

962.36 eV

Intensity 1000

B

A

Before

Mn 2p Mn 2p

O KLL

O 1s

J O U RN A L OF E N V I RO N ME N TA L S CIE N CE S X X (2 0 1 4 ) XXX –XXX

D

R O

Intensity

Intensity

530.88 eV 529.71 eV

After

532.71 eV

N 1s

P

400.13 eV

O 1s 400 395 Binding engery (eV)

390

545

540

D

405

530.78 eV 529.79 eV

535 535 525 Binding engery (eV)

520

E

410

After

363 364 365 366 367

E

R

R

362

O

361

C

360

N

359

30 25 20

U

358

(Kannamba et al., 2010). The significant N 1s binding energy shift from 399.62 to 400.13 eV in Fig. 5C for the aminopropyl groups of NH2-Mn-SBA-15 is attributed to the involvement of the lone pair of electrons on nitrogen on NH2-Mn-SBA-15 in bond formation with Cu2+ ions (Sun and Wang, 2006; Liu et al., 2006). On the other hand, the O 1s peaks in Fig. 5D centered at 529.71 and 529.79 eV assigned to Mn–O, 532.55 and 532.71 eV assigned to Si–O, and another at 530.88 and 530.78 eV could be attributed to surface hydroxyl groups. A clear increase in the content of surface hydroxyl groups is observed after Cu2+ adsorption, which implies that the surface hydroxyl groups

Adsorption capacity (mg/g)

357

C

T

Fig. 5 – (A) XPS wide scan spectra of NH2-Mn-SBA-15 before and after Cu(II) adsorption, (B) Cu 2p, (C) N 1s and (D) O 1s XPS spectra of NH2-Mn-SBA-15 before and after Cu(II) adsorption.

15 10

NH2-Mn-SBA-15 Mn-SBA-15 Pseudo first-order model Pseudo second-order model Elovich model

5 0 0

500

1000

1500

2000

2500

3000

Time (min) Fig. 6 – Adsorption kinetics of Cu(II) by Mn-SBA-15 and NH2-Mn-SBA-15. Ionic strength: 0.01 mol/L NaNO3, dosage: 100 mg/L, pH: 5.5, T: 25°C.

are also involved in the uptake of Cu2+ and different Cu2+ 368 species exist on the surface of NH2-Mn-SBA-15. 369

2.2. Copper adsorption experiments

370

2.2.1. Adsorption kinetics

371

The influence of contact time on the uptake of Cu2+ onto Mn-SBA-15 and NH2-Mn-SBA-15 is shown in Fig. 6 and the adsorption kinetics data are described by pseudo first-order, pseudo second-order and Elovich kinetic models, respectively. In this study, the removal efficiency of Cu2+ on Mn-SBA-15 and NH2-Mn-SBA-15 increases sharply during the first 60 min, then continues with a slower rate and finally tends to reach equilibrium. The model parameters listed in Table 2 distinctly show that the adsorption process follows the Elovich model more closely than the pseudo first-order and pseudo second-order models, which indicates that the predominantly chemical adsorption on the highly heterogeneous surface of the Mn-SBA-15 and NH2-Mn-SBA-15 dominates the uptake of Cu2+ (Lasheen et al., 2012; Pérez-Marín et al., 2007).

372

2.2.2. pH and ionic strength studies

386

As shown in Fig. 7, the adsorption of Cu2+ on NH2-Mn-SBA-15 is strongly dependent on the pH of the solution. The uptake of Cu2+ increases steadily in the pH range from 3 to 5.5, and the maximum removal efficiency (62%) is achieved at pH 5.5. At pH below 5, the ionic strength of the solution has a clear negative effect on the uptake of Cu2+, while there is no clear effect on the adsorption at pH 5.5 with increasing ionic

387

Please cite this article as: Lei, D., et al., Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution, J. Environ. Sci. (2014), http://dx.doi.org/10.1016/j.jes.2014.06.045

373 374 375 376 377 378 379 380 381 382 383 384 385

388 389 390 391 392 393

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Table 2 – Kinetics parameters and Isotherm parameters of adsorption of Cu2+ by Mn-SBA-15 and NH2-Mn-SBA-15.

394

Pseudo second-order

Elovich

Isotherm parameters

Langmuir

Freundlich

NH2-Mn-SBA15

K1 (L/min) qe (mg/g) R2 K2 (g/mg·min−1) qe (mg/g) R2 α (mg/(g·min−1)) β (g/mg) R2 KL (L/mg) qmax (mg/g) R2 KF (mg/g)(L/mg)1/n n R2

20.36 12.17 0.731 0.025 12.65 0.823 5.331 1.200 0.990 7.518 19.88 0.968 14.75 0.161 0.909

40.30 24.79 0.708 0.006 26.02 0.818 9.088 2.632 0.980 16.77 40.67 0.997 32.24 0.165 0.815

408

2.2.3. Adsorption isotherm

409

Under similar conditions, the maximum adsorption capacity of NH2-Mn-SBA-15 (40.67 mg/g) for Cu2+ is over two times higher than that of Mn-SBA-15 (19.88 mg/g), which indicates the crucial role of the aminopropyl group in Cu2+ adsorption. At

404 405 406

410 411 412

C

403

E

402

R

401

R

400

the same time, in comparison with the low adsorption quantity of Cu2+ onto SBA-15 (Lombardo et al., 2012), both manganese oxides and aminopropyl group produce significant effects on the removal of Cu2 + by adsorption. Meanwhile, NH2-Mn-SBA-15 also has a higher Cu2 + adsorption capacity than that of amino-group-functionalized silica as reported in other studies: 28 mg/g (Liu et al., 2000), 19.9 mg/g (Wang et al., 2009), as well as that of other Cu2 + adsorbents such as mercaptopropyl-functionalized porous silica: 13 mg/g (Lee et al., 2001), EDTA-modified SBA-15: 13.2 mg/g (Jiang et al., 2007), natural bentonite: 14.1 mg/g (Kubilay et al., 2007), and so on. The nonlinear Langmuir and Freundlich isotherms for the adsorption of Cu2+ onto Mn-SBA-15 and NH2-Mn-SBA-15 are displayed in Fig. 8 and the corresponding parameters are given in Table 2. The experimental equilibrium adsorption data are well described by the Langmuir model, which implies a monolayer adsorption of Cu2+ onto the adsorbents. This is presumably attributed to the homogeneous distribution of manganese oxides and aminopropyl groups on the surface of NH2-Mn-SBA-15 (Tao et al., 2010).

100 20

90 80 70 60 50

Zeta potential/mV

399

Removal efficiency (%)

398

N C O

397

U

396

T

407

strength from 0.01 to 0.1 mol/L NaNO3. The strong effect of the ionic strength on adsorption at pH below 5 indicates that ion exchange or outer sphere complexation contributes to Cu2+ adsorption. As the pH of the solution is increased from 3 to 5.5, the extent of the protonated form of the amino group NH+3 decreases and the inner sphere complexes of NH2⋯Cu2+ gradually form on the surface of NH2-Mn-SBA-15 (Han et al., 2006). The weak effect of the ionic strength on the Cu2+ adsorption at pH 5.5 suggests that inner-sphere complexation/chemical adsorption is the main adsorption mechanism of Cu2+ onto NH2-Mn-SBA-15 (Sparks, 1995). To avoid Cu2+ precipitation, the experiments in this study were conducted at pH 5.5, which is consistent with the zeta-potential result (5.3) of NH2-Mn-SBA-15.

395

F

Pseudo first-order

Mn-SBA-15

O

Kinetics parameters

Parameters

R O

t2:5 t2:6 t2:7 t2:8 t2:9 t2:10 t2:11 t2:12 t2:13 t2:14 t2:15 t2:16 t2:17 t2:18 t2:19

Model

P

t2:4

D

t2:3 t2:2

E

t2:1

10 0 2

3

4

5 pH

6

7

8

-10 -20

40 30 20

0.01 mol/L NaNO3 0.05 mol/L NaNO3 0.1 mol/L NaNO3

10 0 -10 3

4

5

6

7

pH Fig. 7 – Removal efficiency of Cu(II) at different initial pH and ionic strength on NH2-Mn-SBA-15. Initial Cu(II) concentration: 0.1 mmol/L, dosage: 100 mg/L, T: 25°C. Please cite this article as: Lei, D., et al., Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution, J. Environ. Sci. (2014), http://dx.doi.org/10.1016/j.jes.2014.06.045

413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432

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15 Mn-SBA-15 Langmuir model

10

NH2-Mn-SBA-15 Freundlich model

5 0

2

4

6

8

10

Equilibrium concentration (mg/L)

Fig. 8 – Adsorption isotherms of Cu(II) by NH2-Mn-SBA-15 and Mn-SBA-15. Ionic strength: 0.01 mol/L NaNO3, dosage: 100 mg/L, pH: 5.5, T: 25°C.

2.2.4. Competitive adsorption studies

434

443

The competitive adsorption of different heavy metals on the Cu2+ adsorption is summarized in Table 3. The Cu2+ adsorption capacity of NH2-Mn-SBA-15 from a multi-metallic solution is still higher. It shows the high selectivity of NH2-Mn-SBA-15 toward the Cu2+ ions. The selectivity coefficients of Cu2+ in the presence of other metal cations metal ions show the following order: ki Cd2+ ≫ ki Zn2+ > ki Pb2+. Meanwhile, all of the ki values are greater than 6, this suggest that the adsorptive competing ions in the aqueous solution have little effect on the adsorption of Cu2+ on NH2-Mn-SBA-15.

444

2.3. Regeneration and reusability studies

445

Taking into account the practical application, good desorption performance of an adsorbent is important. After four cycles, desorption efficiencies are found to be 99.1%, 98.5%, 97.8% and 97.2%, respectively. Most importantly, the adsorption capacity of the regenerated NH2-Mn-SBA-15, with value of 39.59, 39.05, 38.19 and 37.61 mg/g, respectively, is almost unaffected. These data indicate good regeneration and reusability of the NH2-Mn-SBA-15.

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R

437

O

436

C

435

3. Conclusions

455

An ordered mesoporous aminopropyl-functionalized manganese-loaded SBA-15 (NH2-Mn-SBA-15) was successfully synthesized by a post-grafting method and the adsorption behavior of Cu2+ onto the adsorbent was investigated. The

458

t3:1 t3:2 t3:3

U

457

N

454 453

456

4. Uncited reference Zhang et al., 2013

T

433

F

20

O

25

R O

30

P

35

successful anchoring of manganese oxides and aminopropyl groups on the framework of SBA-15 is evidenced by FT-IR results. The hexagonal structure of the samples is retained after functionalization. The textural properties of NH2-Mn-SBA-15 imply that the formed manganese oxides are mainly loaded on the internal surface of the pore channels while the aminopropyl groups are mainly anchored on the external surface of SBA-15. The removal of the Cu2+ is favored with increasing pH, however, it slightly decreases with increasing solution ionic strength at pH 5.5. The Langmuir model fits the experimental data well and the Cu2+ adsorption capacity of NH2-Mn-SBA-15 is 40.67 mg/g, which is over two times higher than that of Mn-SBA-15. Chemisorption is the dominant mechanism for the uptake of Cu2+ onto the highly heterogeneous surface of NH2-Mn-SBA-15. NH2-Mn-SBA-15 can be used as an effective adsorptive material for the removal of Cu2 + ions from aqueous solutions by utilizing the manganese hydroxyl groups as well as interaction between surface aminopropyl groups and Cu2 +. In the mixed metal ion solutions, NH2-Mn-SBA-15 shows higher adsorption selectivity for Cu2 + compared to other cations. NH2-Mn-SBA-15 exhibits good regeneration and reusability under experimental conditions.

D

40

E

Adsorption capacity (mg/g)

45

Table 3 – Cu2+ adsorption on NH2-Mn-SBA-15 in the presence of other metal ions.

t3:4

Solution

Q (mg/g)

Kd (mL/g)

ki

t3:5 t3:6 t3:7 t3:8

Cu2+ and Pb2+ Cu2+ and Cd2+ Cu2+ and Zn2+ Cu2+, Pb2+, Cd2+ and Zn2+

34.78 39.48 40.75 35.39

13,948 22,720 27,849 11,983

6 85 12 /

t3:9 t3:10 t3:11

Conditions: initial concentration of heavy metals: 0.1 mmol/L, temperature 25°C, pH 5.5.

459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480

482 Q16 481

483

Acknowledgments

485 484

This work was supported by the Fundamental Research Funds for the Central Universities (No. TD2010-5), the National Natural Science Research Fund (No. 51278051) and the Beijing Forestry University Young Scientist Fund (No. BLX2009018).

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REFERENCES

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Aguado, J., Arsuaga, J.M., Arencibia, A., Lindo, M., Gascón, V., 2009. Aqueous heavy metals removal by adsorption on amine-functionalized mesoporous silica. J. Hazard. Mater. 163 (1), 213–221. Basci, N., Kocadagistan, E., Kocadagistan, B., 2004. Biosorption of copper (II) from aqueous solutions by wheat shell. Desalination 164 (2), 135–140. Benhamou, A., Baudu, M., Derriche, Z., Basly, J.P., 2009. Aqueous heavy metals removal on amine-functionalized Si-MCM-41 and Si-MCM-48. J. Hazard. Mater. 171 (1–3), 1001–1008. Calderon Rosas, C.A., Franzreb, M., Valenzuela, F., Höll, W.H., 2010. Magnetic manganese dioxide as an amphoteric adsorbent for removal of harmful inorganic contaminants from water. React. Funct. Polym. 70 (8), 516–520. Chen, J.P., Wu, S.N., Chong, K.H., 2003. Surface modification of a granular activated carbon by citric acid for enhancement of copper adsorption. Carbon 41 (10), 1979–1986. Chen, G.C., Zhang, X.H., Guo, C.Y., Yuan, G.Q., 2010. Manganese-promoted Rh supported on a modified SBA-15 molecular sieve for ethanol synthesis from syngas. Effect of manganese loading. Effect of manganese loading. C. R. Chim. 13 (11), 1384–1390.

491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513

Please cite this article as: Lei, D., et al., Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution, J. Environ. Sci. (2014), http://dx.doi.org/10.1016/j.jes.2014.06.045

487 488 489

9

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N C O

R

R

E

C

D

P

R O

O

F

Liu, A.M., Hidajat, K., Kawi, S., Zhao, D.Y., 2000. A new class of hybrid mesoporous materials with functionalized organic monolayers for selective adsorption of heavy metal ions. Chem. Commun. 13, 1145–1146. Liu, C.K., Bai, R.B., Hong, L., 2006. Diethylenetriamine-grafted poly (glycidyl methacrylate) adsorbent for effective copper ion adsorption. J. Colloid Interface Sci. 303 (1), 99–108. Lombardo, M.V., Videla, M., Calvo, A., Requejo, F.G., Soler-Illia, G.J.A.A., 2012. Aminopropyl-modified mesoporous silica SBA-15 as recovery agents of Cu (II)-sulfate solutions: adsorption efficiency, functional stability and reusability aspects. J. Hazard. Mater. 223, 53–62. Malkoc, E., Nuhoglu, Y., 2005. Investigations of nickel(II) removal from aqueous solutions using tea factory waste. J. Hazard. Mater. 127 (1–3), 120–128. Mohammadi, T., Moheb, A., Sadrzadeh, M., Razmi, A., 2004. Separation of copper ions by electrodialysis using Taguchi experimental design. Desalination 169 (1), 21–31. Mohsen-Nia, M., Montazeri, P., Modarress, H., 2007. Removal of Cu2+ and Ni2+ from wastewater with a chelating agent and reverse osmosis processes. Desalination 217 (1–3), 276–281. Ngah Wan, W.S., Hanafiah, M.A.K.M., 2008. Removal of heavy metal ions from wastewater by chemically modified plant wastes as adsorbents: a review. Bioresour. Technol. 99 (10), 3935–3948. Pérez-Marín, A.B., Zapata, V.M., Ortuno, J.F., Aguilar, M., Sáez, J., Lloréns, M., 2007. Removal of cadmium from aqueous solutions by adsorption onto orange waste. J. Hazard. Mater. 139 (1), 122–131. Perez-Quintanilla, D., Hierro, I.D., Fajardo, M., Sierra, I., 2006. 2-Mercaptothiazoline modified mesoporous silica for mercury removal from aqueous media. J. Hazard. Mater. 134 (1–3), 245–256. Sparks, D.L., 1995. Environmental Soil Chemistry. Academic Press, San Diego, USA. Sud, D., Mahajan, G., Kaur, M.P., 2008. Agricultural waste material as potential adsorbent for sequestering heavy metal ions from aqueous solutions—a review. Bioresour. Technol. 99 (14), 6017–6027. Sun, S., Wang, A., 2006. Adsorption properties of carboxymethyl-chitosan and cross-linked carboxymethyl-chitosan resin with Cu (II) as template. Sep. Purif. Technol. 49 (3), 197–204. Swami, D., Buddhi, D., 2006. Removal of contaminants from industrial wastewater through various non-conventional technologies: a review. Int. J. Environ. Pollut. 27 (4), 324–346. Tang, Q.H., Hu, S.Q., Chen, Y.T., Guo, Z., Hu, Y., Chen, Y., et al., 2010. Highly dispersed manganese oxide catalysts grafted on SBA-15: synthesis, characterization and catalytic application in trans-stilbene epoxidation. Microporous Mesoporous Mater. 132 (3), 501–509. Tao, Q., Xu, Z.Y., Wang, J.H., Liu, F.L., Wan, H.Q., Zheng, S.R., 2010. Adsorption of humic acid to aminopropyl functionalized SBA-15. Microporous Mesoporous Mater. 131 (1–3), 177–185. Vo, V., Kim, H.J., Kim, H.Y., Kim, Y., Kim, S.J., 2013. Synthesis of poly (methacrylic acid)-functionalized SBA-15 and its adsorption of phenol in aqueous media. Bull. Korean Chem. Soc. 34 (12), 3570–3576. Wang, H.J., Kang, J., Liu, H.J., Qu, J.H., 2009. Preparation of organically functionalized silica gel as adsorbent for copper ion adsorption. J. Environ. Sci. 21 (11), 1473–1479. Xu, Y.Q., Zhou, G.W., Wu, C.C., Li, T.D., Song, H.B., 2011. Improving adsorption and activation of the lipase immobilized in amino-functionalized ordered mesoporous SBA-15. Solid State Sci. 13 (5), 867–874. Xue, X.M., Li, F.T., 2008. Removal of Cu (II) from aqueous solution by adsorption onto functionalized SBA-16 mesoporous silica. Microporous Mesoporous Mater. 116 (1–3), 116–122.

E

T

Chen, J.H., Liu, Q.L., Hu, S.R., Ni, J.C., He, Y.S., 2011. Adsorption mechanism of Cu (II) ions from aqueous solution by glutaraldehyde crosslinked humic acid-immobilized sodium alginate porous membrane adsorbent. Chem. Eng. J. 173 (2), 511–519. Chien, S.H., Clayton, W.R., 1980. Application of Elovich equation to the kinetics of phosphate release and sorption in soils. Soil Sci. Soc. Am. J. 44 (2), 265–268. Dabrowski, A., Hubicki, Z., Podkościelny, P., Robens, E., 2004. Selective removal of the heavy metal ions from waters and industrial wastewaters by ion-exchange method. Chemosphere 56 (2), 91–106. Dong, X., Shen, W., Zhu, Y., Xiong, L., Shi, J., 2005. Facile synthesis of manganese-loaded mesoporous silica materials by direct reaction between KMnO4 and an in-situ surfactant template. Adv. Funct. Mater. 15 (6), 955–960. Dragoi, B., Dumitriu, E., Guimon, C., Auroux, A., 2009. Acidic and adsorptive properties of SBA-15 modified by aluminum incorporation. Microporous Mesoporous Mater. 121 (1–3), 7–17. Freundlich, H.M.F., 1906. Over the adsorption in solution. J. Phys. Chem. 57, 385–470. Gündoğan, R., Acemioğlu, B., Alma, M.H., 2004. Copper (II) adsorption from aqueous solution by herbaceous peat. J. Colloid Interface Sci. 269 (2), 303–309. Haber, J., Baiker, A., Nobbenhuis, M., Kiwi, J., Thampi, R., Gratzel, M., 1994. Surface-area and porosity. Catal. Today 20 (1), 11–16. Han, R.P., Zou, W.H., Zhang, Z.P., Shi, J., Yang, J.J., 2006. Removal of copper (II) and lead (II) from aqueous solution by manganese oxide coated sand: I. Characterization and kinetic study. J. Hazard. Mater. 137 (1), 384–395. Ho, Y.S., McKay, G., 1998. Kinetic model for lead (II) sorption onto peat. Adsorpt. Sci. Technol. 16 (4), 243–255. Jeong, E.Y., Ansari, M.B., Mo, Y.H., Park, S.E., 2011. Removal of Cu (II) from water by tetrakis (4-carboxyphenyl) porphyrin-functionalized mesoporous silica. J. Hazard. Mater. 185 (2–3), 1311–1317. Jiang, Y.J., Gao, Q.M., Yu, H.G., Chen, Y.R., Deng, F., 2007. Intensively competitive adsorption for heavy metal ions by PAMAM-SBA-15 and EDTA-PAMAM-SBA-15 inorganic–organic hybrid materials. Microporous Mesoporous Mater. 103 (1–3), 316–324. Kannamba, B., Reddy, K.L., AppaRao, B.V., 2010. Removal of Cu (II) from aqueous solutions using chemically modified chitosan. J. Hazard. Mater. 175 (1–3), 939–948. Komárek, M., Čadková, E., Chrastný, V., Bordas, F., Bollinger, J.C., 2010. Contamination of vineyard soils with fungicides: a review of environmental and toxicological aspects. Environ. Int. 36 (1), 138–151. Kubilay, S., Gürkan, R., Savran, A., Sahan, T., 2007. Removal of Cu(II), Zn(II) and Co(II) ions from aqueous solutions by adsorption onto natural bentonite. Adsorption 13 (1), 41–51. Kurniawan, T.A., Chan, G., Lo, W.H., Babel, S., 2006. Physico-chemical treatment techniques for wastewater laden with heavy metals. Chem. Eng. J. 118 (1–2), 83–98. Lagergren, S., 1898. About the theory of so-called adsorption of soluble substances. K. Sven. Vetenskapsakad. Handl. 24 (4), 1–39. Langmuir, I., 1916. The constitution and fundamental properties of solids and liquids. Part I. Solids. J. Am. Chem. Soc. 38 (11), 2221–2295. Lasheen, M.R., Ammar, N.S., Ibrahim, H.S., 2012. Adsorption/desorption of Cd (II), Cu (II) and Pb (II) using chemically modified orange peel: Equilibrium and kinetic studies. Solid State Sci. 14 (2), 202–210. Lee, B., Kim, Y., Lee, H., Yi, J., 2001. Synthesis of functionalized porous silicas via templating method as heavy metal ion adsorbents: the introduction of surface hydrophilicity onto the surface of adsorbents. Microporous Mesoporous Mater. 50 (1), 77–90.

U

514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582

Please cite this article as: Lei, D., et al., Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution, J. Environ. Sci. (2014), http://dx.doi.org/10.1016/j.jes.2014.06.045

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Zhang, H., Xu, M., Wang, H.J., Lei, D., Qu, D., Zhai, Y.J., 2013. Adsorption of copper by aminopropyl functionalized mesoporous delta manganese dioxide from aqueous solution. Colloids Surf. A 435, 78–84. Zhao, D.Y., Feng, J.L., Huo, Q.S., Melosh, N., Fredrickson, G.H., Chmelka, B.F., et al., 1998. Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores. Science 279, 548–552.

Zhao, Y.L., Gao, Q., Tang, T., Xu, Y., Wu, D., 2011. Effective NH2-grafting on mesoporous SBA-15 surface for adsorption of heavy metal ions. Mater. Lett. 65 (6), 1045–1047. Zhu, S.M., Zhou, Z.Y., Zhang, D., Wang, H.H., 2006. Synthesis of mesoporous amorphous MnO2 from SBA-15 via surface modification and ultrasonic waves. Microporous Mesoporous Mater. 95 (1–3), 257–264.

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Please cite this article as: Lei, D., et al., Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution, J. Environ. Sci. (2014), http://dx.doi.org/10.1016/j.jes.2014.06.045