TiO2 Composite Using

Article pubs.acs.org/jced

Facile Modification of a Polythiophene/TiO2 Composite Using Surfactants in an Aqueous Medium for an Enhanced Pb(II) Adsorption and Mechanism Investigation Jie Chen,† Ning Wang,† Hongyu Ma,† Jinwei Zhu,†,‡ Jiangtao Feng,*,† and Wei Yan*,† †

Department of Environmental Science and Engineering, State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, P. R. China ‡ Shaanxi Electrical Equipment Institute, Xi’an 710025, P. R. China S Supporting Information *

ABSTRACT: Surfactants are considered to have a strong affinity to metal ions. Thus, it is a novel design by employing sodium dodecylbenzenesulfonate (NaDBS) and hexadecyltrimethylammonium bromide (CTAB) surfactants to functionalize polythiophene/TiO2 composite via a facile and green method to improve the Pb2+ removal efficiency from the aqueous solution. Techniques such as Fourier transform infrared spectroscopy, zeta potential analysis, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and N2 isotherm analysis revealed changes in surface properties after modification, and adsorption active sites were also extensively detected. Batch adsorption investigations were carried out to study their adsorption behaviors for lead(II), and the diffusion process was carefully investigated and described via kinetic models including the Weber−Morris and pseudo-second-order model. The results indicated that modification with NaDBS or CTAB significantly changed the adsorption behavior and increased the monolayer adsorption capacity of polythiophene/TiO2 composite for Pb2+, from 151.52 mg/g to 198.41 or 213.22 mg/g. The entire adsorption process results comprehensively confirmed that the diffusion rate of Pb2+ ions was controlled by the film and intraparticle diffusion, and the combination rate of Pb2+ with active sites was limited by chemisorption. Pb2+ ions were also detected to interact with adsorption active sites including sulfur atoms, hydroxyl groups, and surfactants.

1. INTRODUCTION The liquid−solid adsorption mechanism investigation prominently focuses on the adsorption ability and adsorption kinetic of adsorbents during the liquid−solid adsorption process.1 On one hand, when it refers to the adsorption ability, isotherm equations such as Langmuir,2 Frendlich,3 and Sips4 equations are extensively. On the other hand, in terms of adsorption kinetic investigation, the Weber−Morris model,5 pseudo-first-order model,6 and pseudo-second-order model7 are widely applied to reveal the adsorption process.8 It is generally accepted that the mechanism elucidation on the metal ion adsorption is critical to get insight into the adsorption process and improve the adsorbent adsorption efficiency.9 Therefore, to obtain a full understanding of the adsorption process, one or more kinetic models should be used. Wang et al.10 used the fiber chelated with PET to adsorb Cd2+ and Ni2+, from which results of isotherms, kinetic, and thermodynamic studies showed that the adsorption rate was limited by the chemisorption. Hsu11 studied the adsorption of Cu2+ and Ni2+ by the oyster shell powder and pointed out that the groups such as CO on CaCO3 were identified as the active sites in the adsorption process. However, the mechanism discussions were still incomprehensive. © XXXX American Chemical Society

Consequently, to give out a full insight into the adsorption mechanism, the adsorption investigation coupled with spectroscopic technique characterizations needs to be discussed. Over the last few decades, surfactants have received much attention in many fields such as detergent industry, lubrication, catalysis, and so forth due to their low toxicity and relatively favorable biodegradability.12 It was found that surfactants had a strong affinity with metal ions. Thus, many reports have focused on the interaction between surfactants and metal ions in the aqueous medium, which revealed that surfactants are effective in interacting with metal ions through ion exchange or precipitation.13 Pereira et al.13 pointed out that the interaction between the long chain sodium carboxylates and the sodium dodecyl sulfate and Pb2+ ions in the aqueous solutions was alkyl chain length dependence. Ding et al.14 observed that the fluorescent sensor assembled with the anionic surfactant, sodium dodecyl sulfate (SDS), exhibited a high sensitivity toward both Cu2+ and Co2+ in the aqueous solution with a detection limit lower than 100 nM. Received: April 7, 2017 Accepted: May 31, 2017

A

DOI: 10.1021/acs.jced.7b00329 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Scheme 1. Schematic Illustration of the Synthesis Process for the Modification of PTh/TiO2 Particle Composite in an Aqueous Medium

purchased from Sinopharm Chemical Reagent Co. Ltd. were of analytical grade. The deionized water was gained from a superpure water preparation system (EPED-40TF, China). 2.2. Synthesis of the Surfactant Modified PTh/TiO2 Composite. Portions of 0.05 mol (3.6 mL) of thiophene and 0.01 mol of surfactant (3.485 g of NaDBS or 3.644 g of CTAB) were dissolved in 100 mL of deionized water. 0.8 mL of HNO3 was added into 300 mL of deionized water at 60 °C in a 500 mL of three-jacketed flask with a mechanical stirrer, and 20 mL of titanium(IV) isopropoxide was dissolved in the solution afterward. After being stirred for 60 min, the solution was cooled to the room temperature. Then the thiophene monomer/ surfactant mixture was added in the flask and stirred at room temperature for another 60 min. After that, 0.1 mol (22.82 g) of (NH4)2S2O8 was directly added into and heated to 50 °C with a stirring. Then the mixed solution was stirred for another 24 h at 50 °C. Finally, the samples were filtrated and washed with deionized water and dried at 50 °C for 24 h. The schematic illustration for the synthesis process of the modification of PTh/TiO2 particle composite in the aqueous medium was depicted in Scheme 1. The process was conducted in the water bath with a temperature control heater. 2.3. Instruments. FT-IR spectra of surfactant/PTh/TiO2 composites were recorded by the KBr pellet method on a Bruker Tensor 37 FT-IR spectrometer in the region between 400 and 4000 cm−1. XRD patterns of samples were obtained with an X’Pert Pro MRD diffractometer using Cu−Kα radiation. The thermogravimetric (TG) analysis was performed on Setaram Labsys Evo at the heating rate of 10 °C/min under the N2 atmosphere. The morphology and elemental information were obtained on a scanning electron microscope (SEM, JSM-6700F, Japan). TEM images were obtained on a JEM model 2100 electron microscope. Specifically, the samples were mixed with ethanol and being ultrasonic vibrated for 1 min, then drop-casted 1 to 2 drops onto the carbon-coated copper grids and dried in air. A Malvern Zetasizer Nano ZS90 was used to acquire zeta potentials of composites. Specifically, the samples were pretreated by adding 5 mg of sample into 10 mL of solutions with various pH values (pH = 1−13, adjusted by 0.1 M HNO3 or 0.1 M NaOH solution) and ultrasonically vibrated for 30 min. The BET specific surface area was performed on a Builder SSA-4200 (Beijing, China) at 77K. The pore distributions and the pore volume were calculated based on the Barrett−Joyner− Halenda (BJH) method using the desorption branch of N2 isotherms. The interaction between a metallic element ions and the functional groups of the samples was determined using XPS on Kratos Axis Ultra DLD with an Al monochromatic X-ray source (1486.71 eV), and all binding energies (BEs) were referenced to the C 1s hydrocarbon peak at 284.6 eV. The concentrations of Pb2+ were determined by an inductively coupled plasma emission spectrometer (ICPE-9000, Japan).

However, the study on the modification of adsorbents with surfactants to improve their adsorption capacity for heavy metals is rarely carried out. Thus, it is novel to functionalize adsorbents with surfactants to improve the metal ion removing efficiency from the aqueous solution. Among the surfactants, dodecylbenzenesulfonate (NaDBS, anionic surfactants) and hexadecyltrimethylammonium bromide (CTAB, cationic surfactants), which were commonly used in many investigations due to their low toxicity and relatively favorable biodegradability, were selected as modifying agents to functionalize PTh/TiO2 composite to investigate their different influences on adsorption. To meet the strict regulations established about water around the world in recent years, we had successfully synthesized the polythiophene/TiO2 (PTh/TiO2) composite in the nontoxic aqueous medium by a new and facile way, and a high adsorption capacity for Pb2+(151.52 mg/g) was obtained.15 Herein, to further improve the adsorption capacity, the PTh/TiO2 composite modified by surfactants was synthesized in a facile and green way we proposed. The influence of modification on physicochemical properties and adsorption behavior for lead were also fully studied. Moreover, a clear insight into adsorption process and mechanism for lead onto the surfactant modified PTh/TiO2 composites were conducted and carefully analyzed. Various techniques, such as Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermogravimetry (TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer−Emmett−Teller analysis (BET), X-ray photoelectron spectroscopy (XPS) analysis, and zeta potential, were employed for characterizations or mechanism investigations. Batch adsorption experiments including the effect of dosage, pH, agitation speed, and ionic strength as well as the adsorption isotherm studies were carefully investigated to reveal the effect of the surfactant modification on the adsorption of PTh/TiO2 composite (part of investigations was shown in the Supporting Information). The kinetic data as well as the entire adsorption process were interpreted using combination of Weber−Morris and pseudo-second-order models. At last, the clear adsorption mechanism was fully discussed and summarized using the comprehensive results acquired.

2. MATERIALS AND EXPERIMENTS 2.1. Materials. Thiophene gained from Zhejiang Qingquan Pharmaceutical & Chemical Ltd. was distilled twice and refrigerated in the dark at 273 K. Pb(NO3)2 was acquired from Tianjin Dengfeng Chemical Reagent Factory for the Pb2+ solution preparation. Sodium dodecylbenzenesulfonate (NaDBS, Tianjin Bodi Chemical Reagent Factory) and hexadecyltrimethylammonium bromide (CTAB, Tianjin Fuchen Chemical Reagent Factory) were used as modified agents. HNO3 (65−68%) obtained from Beijing Chemical Reagent Co. and NaNO3, NaOH, (NH4)2S2O8, and titanium(IV) isopropoxide B



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2.4. Batch Adsorption Studies. Various optimal adsorption conditions for Pb2+ were applied in this research (shown in the Supporting Information). 2.4.1. Study of Adsorption Isotherms. Isotherm experiments were conducted with various initial concentrations of Pb2+ solutions ranging from 100 to 1000 mg/L at 25, 35, and 45 °C, respectively. In this study, the optimal adsorption condition was applied. A portion of 0.04 g of adsorbents were mixed with 20 mL of Pb2+ solution at pH 6 with 200 rpm of agitation speed for 24 h. Then the mixture was centrifuged for 6 min. The supernatant was analyzed to determine the Pb2+ concentration. Langmuir and Freundlich models were applied to describe isotherms. The linear forms of Langmuir2 model and Freundlich3 model can be described as the following equations: Ce 1 1 = + Ce qe qmKL qm

(1)

log qe = log KF + n log Ce

(2)

The Weber−Morris model used for describing the metallic element ion diffusion process onto the composite can be expressed as follows:

qt = I + kit 1/2

where ki (mg/(min ·g)) is the diffusion rate constant; I (mg/g) is the intercept related to the thickness of the boundary layer. When I equals to zero, the adsorption rate in this stage was totally controlled by intraparticle diffusion. Otherwise the adsorption process would be controlled simultaneously by intraparticle and liquid film diffusion.17 2.4.3. Effect of pH. A sample of 0.04 g of composites was suspended in 20 mL of 100 mg/L of Pb2+ solution with different pH values ranging from 1 to 6 (adjusted using HNO3 and NaOH), and the mixture was stirred at the agitation speed of 200 rpm for 24 h at 25 °C. Then the mixture was centrifuged at 4000 rpm for 6 min. 2.4.4. Desorption Experiments. A sample of 0.04 g of adsorbents and 20 mL of 300 mg/L of Pb2+ solution was used. Then 20 mL of 1 mol/L of HNO3 or 0.1 mol/L of EDTA-2Na was applied as elution agents, and the composites were treated for 60 min; then 0.1 mol/L of NaOH was used as an active agent and treated the composites for another 60 min. Then the Pb2+ concentration of the supernatants was measured and calculated after 5 min of centrifugation. The regeneration efficiency (%) was obtained according to the following equation: q Regeneration efficiency = d × 100% qa (9)

where qe (mg/g) is the adsorption capacity at equilibrium state, qm (mg/g) is the maximum adsorption capacity, Ce (mg/L) is the equilibrium concentration of adsorbate, KL (L/mg) is an equilibrium constant of Langmuir related to the adsorption affinity, KF (mg1−n·Ln/g) is the constant of Freundlich representing the adsorption capacity when the equilibrium metal ion concentration equals to 1, and n states the degree for the dependence of the adsorption on the equilibrium concentration.16 The supernatant was analyzed to determine the concentration of Pb2+. The adsorption capacity (mg/g) and removal amount (%) were calculated according to the equations as follows: qe =

(C0 − Ce)V m

removal amount =

where qd (mg/g) is the desorbed amount of Pb2+ in the elution agents and qa (mg/g) is the adsorbed amount of Pb2+ on the composites. 2.4.5. Study of Thermodynamics. A sample of 0.04 g of adsorbents and 500 mg/L of Pb2+ solution at pH 6 was employed at different temperatures (25, 35, 40, 45 °C). The thermodynamic parameters such as Gibbs free energy [ΔG0/(kJ/mol)], entropy [ΔS0/(J/K·mol)], and enthalpy [ΔH0/(kJ/mol)] were obtained from the following equations:

(3)

C0 − Ce × 100% C0

(4)

2+

where C0 (mg/L) is the initial Pb concentrations. m (g) is the weight of adsorbent applied, and V (L) is the solution volume. 2.4.2. Study of Adsorption Kinetics. A sample of 0.04 g of adsorbents was suspended with 20 mL of three initial concentrations of Pb2+ solutions (100, 500, and 1000 mg/L) at pH 6 with the agitation speed of 200 rpm in various contact times (0−180 min). Then the mixture was centrifuged and analyzed to determine the concentration of Pb2+. The linear forms of the pseudo-first-order model6 and pseudo-second-order model7 were applied extensively to analyze the kinetic data.

ΔS° ΔH ° − R RT

(11) (12)

where KT is the distribution coefficient equaling (C0 − Ce)/Ce, and C0 and Ce (mg/L) are the Pb2+ concentrations at initial and equilibrium state, respectively. R (J/(mol·K) is the gas constant.

3. RESULTS AND DISCUSSION 3.1. Structure and Property of Surfactants/PTh/TiO2. FT-IR spectra and their assignments of composites shown in Figure S1 and Table 1 were applied to characterize the composites. For comparison, the spectra of PTh/TiO2 composite and TiO2 as-prepared were listed together.18 Results showed that surfactants/PTh/TiO2 composites were synthesized successfully. The intensities and positions of the bands related to the α-position linkage PTh had many changes after the modification owing to the interaction between surfactants and PTh during the modification. It was remarkable that new peaks situated at 2916 and 2858 cm−1 due to the symmetrical stretching vibration of C−H were observed in the spectrum of NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 composites, indicating that NaDBS and

(5)

(6)

where qe (mg/g) and qt (mg/g) are the adsorption capacity at equilibrium state and at time t (min), respectively; k1 (min−1) and k2 (g/(mg·min)) are the rate constant of the pseudo-firstorder and pseudo-second-order model, respectively. Additionally, k2 can be used to estimate the initial adsorption rate h (mg/(g·min)) as follows: h = k 2qe 2(t → 0)

(10)

ΔG° = −RT ln KT

Pseudo-second-order model: t 1 1 = + t qt qe k 2qe2

ΔG° = ΔH ° − T ΔS°

ln KT =

Pseudo-first-order model: ln(qe − qt ) = ln qe − k1t

(8) 0.5

(7) C



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Table 1. FT-IR Adsorption in the Region between 400 and 4000 cm−1 and Their Assignments wavenumbers (cm−1) NaDBS/ PTh/TiO2

CTAB/ PTh/TiO2

1645

3400 2981, 2890 1627

3359 2916, 2858 1664

1471, 1443 1203 1124, 1047, 998 774

1487, 1423 1199 1139, 1043, 987 781

1481, 1421 1190 1134, 1049, 986 765

659

663

661

603

596

588

400−700

400−700

400−700

PTh/TiO2 3000−3500

assignments O−H stretching vibration40 C−H stretching vibration41 CC in-plane bending vibration40 CC stretching vibration42 sulfate anion20 C−H aromatic bending vibration of PTh43,44 C−H out-plane bending vibration43,44 ring deformation of the C−S−C of PTh43 ring deformation of the C−S of PTh43 O−Ti−O20

Figure 1. TG analyses of the PTh/TiO2, NaDBS/PTh/TiO2, and CTAB/PTh/TiO2 composites.

CTAB were introduced successfully. Actually, the FT-IR spectrum of polythiophene/TiO2 composite after the NaDBS modification could be similar to that of unmodified one because the additional bonds from NaDBS including C−C, CC, C−S, and SO have existed in the PTh rings (see Scheme S1). In addition, the dose of NaDBS was low. Therefore, some of the peaks ascribed to NaDBS could be overlapped by PTh/TiO2. In the EDS analysis, Table 2 records the information about elements on the surface of NaDBS/PTh/TiO2 and CTAB/PTh/ TiO2 composites. The amount of C element in two composites both increased obviously after modification and that of S increase in the EDS result of NaDBS/PTh/TiO2 composite, which further confirmed that the NaDBS was introduced successfully. Thermogravimetric analysis, which gives useful information on the thermal stability of the organic functional moieties on the composites, is shown in Figure 1. For comparison, the TG data of the original PTh/TiO2 composite15 were also illustrated. The thermal degradation of two samples was mainly a three-stage process. The first weight losses of 9.7 and 6.7 wt % below 150 °C for NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 composites were ascribed to the loss of saturated water.19 The second weight losses between 150 and 450 °C, which was mainly due to the thermal decomposition of PTh and surfactants on composites, were about 15.1 and 28.3 wt %, respectively. The final weight loss above 450 °C was possibly due to the thermal decomposition of sulfate anions adsorbed chemically on the TiO2.20 The thermogravimetric results also suggested the success of the surfactant modification due to the increase for the organic content of the PTh/TiO2 composite.16 XRD patterns of TiO2, PTh/TiO2, NaDBS/PTh/TiO2, and CTAB/PTh/TiO2 were illustrated in Figure 2,15 which showed that both composites are pure anatase because the diffraction peaks at 25.3, 37.8, and 48.1 correspond well to the (101), (004), and (200) planes of anatase TiO2, respectively.20 Peaks in XRD patterns showed no significant differences between TiO2 and

Figure 2. XRD patterns of the TiO2, NaDBS/PTh/TiO2, and CTAB/ PTh/TiO2 composites.

surfactant/PTh/TiO2, suggesting surfactants only modified the surface of TiO2 rather than incorporating into TiO2 layers. Besides, the intensities decreased after modification, but the patterns had no differences after modification, confirming that the PTh as well as surfactants were mainly amorphous with low degree of crystallinity.21 The N2 adsorption−desorption study is commonly used in the surface property characterization to determine the specific surface area (SBET), pore volume (V), pore radius (R), and pore shapes. Figure 3 showed N2 adsorption−desorption isotherms, and their textural properties were listed in Table 3. For a clear comparison, the N2 adsorption−desorption isotherm of the PTh/TiO2 was also depicted in Figure S2a. It was interesting to find that the modification with different surfactants greatly changed the textual such as the pore diameter, specific surface area, and morphology of PTh/TiO2 composite. According to the shape for the adsorption branch of two composites, the adsorption−desorption isotherm of NaDBS/PTh/TiO2 composites can be classified as the Type II and the H4 hysteresis loop, indicating the presence of large mesopores embedded in a matrix with pores of much smaller size. While those of CTAB/PTh/TiO2 composites was Type III and H3 hysteresis loop, confirming the composite was comprised of aggregates (loose assemblages) of plate-like particles and

Table 2. EDS Analysis Results of the TiO2, PTh/TiO2, NaDBS/PTh/TiO2, and CTAB/PTh/TiO2 Composites C

O

S

N

element

atom/%

error/%

atom/%

error/%

atom/%

error/%

PTh/TiO2 NaDBS/PTh/TiO2 CTAB/PTh/TiO2

12.50 26.70 51.61

0.20 0.17 0.14

61.28 52.25 33.65

0.15 0.99 0.71

3.48 4.40 2.76

0.34 0.32 0.23

D

atom/%

1.01

Ti error/%

atom/%

error/%

ref.

0.52

22.73 16.65 10.96

0.99 0.93 0.69

15 this work this work



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Figure 3. Nitrogen gas adsorption−desorption isotherms and pore size distribution (insets) of the NaDBS/PTh/TiO2 (a) and CTAB/PTh/TiO2 composites (b).

of composites after modification depicted in Figure 4c−d also proved the core−shell structure of the composites. 3.2. Adsorption Research. 3.2.1. Influence of Surfactant Modification on the Adsorption Isotherm. The influence of the initial concentration on adsorption capacities of composites was illustrated in Figure 5, and the equilibrium data shown in Table 4 were fitted with the Langmuir and Freundlich models. The adsorption isotherm parameters were also obtained and are listed in Table 5. The data of NaDBS/PTh/TiO2 composite were fitted better with the Langmuir model (R2 > 0.99), indicating the homogeneous distribution of adsorption sites on the surface of NaDBS/PTh/TiO2 composite. Meanwhile the adsorption data acquired from CTAB/PTh/TiO2 composite showed a better fit to the Freundlich isotherm model (R2 > 0.99), indicating the existence of heterogeneous surface on the CTAB/PTh/TiO2 composite, which was quite different from that of PTh/TiO2 composite. Moreover, it can be observed that there was a decrease in the adsorption capacity of both composites with temperature increase over the experimental range, which was totally different from that of PTh/TiO2 composite (Table S1). It can be explained by the fact that physical process may be involved in the adsorption mechanism, and an elevation in temperature increased the escaping tendency of Pb2+ from the interface.7

Table 3. Textural Properties of the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 Composites sample

SBET (m2/g)

V (cm3/g)

R (nm)

PTh/TiO2 NaDBS/PTh/TiO2 CTAB/PTh/TiO2

229.66 97.87 6.95

0.096 0.077 0.028

1.94 2.22 2.73

slit-like pores.22 Moreover, the BET specific surface area reduced after modification, which may be owning to the block of surfactants on pores.22 The different morphology resulted from different surfactants may have a great impact on their adsorption behaviors for lead(II). SEM images of composites after modification in Figure 4a−b exhibited less aggregate morphology in NaDBS/PTh/TiO2 composite and a plate-like shape in CTAB/PTh/TiO2 composite, which was consistent with the results of N2 adsorption− desorption study (The SEM images of unmodified was shown in Figure S2b for comparison). They may be due to the enhanced dispersion of surfactants, and the morphology would be propitious to the interaction between composite and Pb2+.23 Thus, it is of great value that the ragged and less aggregate morphology would be more favorable for the Pb2+ adsorption.24 TEM images

Figure 4. Scanning electron micrographs and transmission electron microscope micrographs of the NaDBS/PTh/TiO2 (a, c) and CTAB/PTh/TiO2 composites (b, d). E



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Figure 5. Isotherms of the NaDBS/PTh/TiO2 (a) and CTAB/PTh/TiO2 composites (b) for Pb2+.

Table 4. Adsorption Isotherm Data of the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 Composites at Three Temperatures sample

temperature (°C)

C0 (mg/L)

Ce (mg/L)

Qe (mg/g)

sample

temperature (°C)

C0 (mg/L)

Ce (mg/L)

Qe (mg/g)

NaDBS/PTh/TiO2

25

100 200 300 400 600 800 1000 100 200 300 400 600 800 1000 100 200 300 400 600 800 1000

0.744 1.88 38.36 116.4 253.6 435 600 0.992 2.032 64.4 132.8 296 454.5 628.5 5.18 10.72 74.4 143.6 300.8 468 643.5

49.628 99.06 130.82 141.8 173.2 182.5 200 49.504 98.984 117.8 133.6 152 172.75 185.75 47.41 94.64 112.8 128.2 149.6 166 178.25

CTAB/PTh/TiO2

25

100 200 300 400 600 800 1000 100 200 300 400 600 800 1000 100 200 300 400 600 800 1000

0.862 17.76 89.2 149.2 265.6 421.5 592.5 4.76 34.76 98.4 159.6 286.4 435 613.5 4.62 38.76 102 159.2 293.6 448.5 621.75

49.569 91.12 105.4 125.4 167.2 189.25 203.75 47.62 82.62 100.8 120.2 156.8 182.5 193.25 47.69 80.62 99 120.4 153.2 175.75 189.125

35

45

35

45

Table 5. Adsorption Equilibrium Parameters Acquired from the Langmuir and Freundlich Models in the Adsorption of Pb2+ onto the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 Composites Langmuir sample NaDBS/PTh/TiO2

CTAB/PTh/TiO2

25 °C 35 °C 45 °C 25 °C 35 °C 45 °C

Freundlich

qm (mg/g)

KL (L/mg)

R2

n

KF (mg1−n·Ln/g)

R2

198.41 185.19 181.16 213.22 209.21 203.67

0.050 0.037 0.029 0.019 0.014 0.014

0.99 0.99 0.99 0.97 0.97 0.98

0.13 0.13 0.12 0.30 0.29 0.29

80.26 74.75 41.52 29.35 29.25 29.11

0.79 0.66 0.86 0.99 0.99 0.98

chain length dependence.13 CTAB has a longer alkyl chain, which is more likely to introduce the multiadsorption mechanism for the Pb2+ adsorption, thus resulting in the heterogeneous adsorption of CTAB/PTh/TiO2 for Pb2+. Calculated from the Langmuir model, maximum adsorption capacities of NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 composites at different temperatures were 198.41 (25 °C), 185.19 (35 °C), 181.16 mg/g (45 °C) and 213.22 (25 °C), 209.21 (35 °C), 203.67 mg/g (45 °C), respectively. The values were much larger than that of PTh/TiO2 composite (151.52 mg/g),15 confirming the effective promotion of the

However, it was shown that adsorption capacities were not indirect correlated with the textural properties such as specific surface area or pore diameter, implying that the physical sorption failed to be the main adsorption mechanism in the adsorption systems.25 Overall, these interesting changes and results can be explained as follows. The surfactant modification influenced surface properties as well as the adsorption energy and distribution of active adsorption sites on the surface of PTh/TiO2 composite, further influencing the adsorption behavior. Meanwhile, it has been confirmed that the affinity of surfactants with lead ions was alkyl F



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surfactants to Pb2+ adsorption. It can be noted interestingly that the adsorption capacities of the NaDBS/PTh/TiO2 were higher than those of CTAB/PTh/TiO2 in low Pb2+ initial concentrations, highlighting the different affinities between composites and Pb2+ at different Pb2+ initial concentrations. Adsorption capacities of surfactants/PTh/TiO2 composites were compared with various adsorbents reported to justify the validity as an adsorbent of Pb2+ and listed in Table 6. Overall, the easier synthesis and high adsorption capacity of the surfactants/ PTh/TiO2 composites make themselves more attractive and considerable.

the rate controlling step during the diffusion. From the results we found in Table 7, all fitting curves failed to pass through the origin, indicating that the intraparticle diffusion was involved but failed to control the rate of whole process,26 namely, the diffusion rate was controlled by the film and intraparticle diffusion. Many investigators reported that the curve could be separated into three portions, where the first portion indicated a film diffusion, and the second portion suggested an intraparticle diffusion, and another portion denoted the equilibrium.26,27 Multilinearities were clearly observed in the whole range in Figure S3. The first part of the plot owned steeper slope, and the external film diffusion controlled the rate of this process. The second linear portion owned a lower slope, whose rate was limited by the intraparticle diffusion, while the third portion highlighted the adsorption equilibrium. Diffusion rates in each stage were summarized in Table 8. After Pb2+ reaching the active sites, they begin to be attracted by adsorption sites. The pseudo-first-order model and pseudosecond-order model mentioned above were applied to describe the rate controlling step of this stage. The fitted parameters were listed in Table 7. By analyzing the regression coefficients (R2), and comparing the adsorption capacities (qe) with that acquired from the adsorption experiment (qexp), the data were described better by the pseudo-second-order model, and results obtained from the pseudo-second-order model were more reasonable.7 It strongly supported that the chemical adsorption may be the rate-limiting step in this process.8,28 Moreover, the initial concentration of Pb2+ had a great impact on the equilibrium constant and initial sorption rate. The equilibrium rate constant and initial sorption rate also decreased with the increase of the initial concentration. 3.2.3. Illumination of Adsorption Thermodynamics. The estimated thermodynamic parameters were calculated and listed in Table 9. The negative values of Gibbs free energy suggested that all adsorption processes were spontaneous, and the spontaneity increased with temperature. Meanwhile, the values of enthalpy are negative, confirming that whole adsorption is exothermic, while the negative values of entropy stated a decrease in disorder at the solid−liquid interface. The parameters are completely different from those of unmodified one, revealing the great influence of modification on the Pb2+ adsorption. In addition, the absolute value of Gibbs free energy and entropy of NaDBS/PTh/TiO2 composite is higher than that of CTAB/ PTh/TiO2 composite, indicating that Pb2+ adsorption on the NaDBS/PTh/TiO2 composite is easier than on the CTAB/PTh/ TiO2, even though the CTAB/PTh/TiO2 composite exhibits a larger adsorption capacity.

Table 6. Comparison for Sorption Capacities of Various Sorbents for Pb2+ adsorbents AC granular AC powder AC fibers kaolinite mesoporous silica activated alumina carbon nanotube chitosan−alginate beads chitosan cross-linked with epichlorohydrintriphosphate Fe3O4@APS@AA-co-CA MNPS Na-birnessite PTh/TiO2 NaDBS/PTh/TiO2 CTAB/PTh/TiO2

adsorption capacity (mg/g)

experimental conditions (pH, temperature, dose)

16.58 26.94 30.46 12.10 38.02 83.32 118.26 60.27 166.94

5.0, 30 °C, 1.0 g/L 5.0, 30 °C, 1.0 g/L 5.0, 20 °C, 2.0 g/L 5.5, 30 °C, 1.0 g/L 6.0, 25 °C, 2.0 g/L 5.0, 30 °C, 7.5 g/L 7.0, 25 °C, 2.0 g/L 4.5, 25 °C, 1.0 g/L 5.0, 25 °C, 0.75 g/L

45 45 46 47 48 49 50 51 52

166.12

5.5, 25 °C, 1.0 g/L

53

173.10 151.52 198.41 213.22

5.0, 30 °C, 0.5 g/L 6.0, 25 °C, 2.0 g/L 6.0, 25 °C, 2.0 g/L 6.0, 25 °C, 2.0 g/L

54 15 this work this work

ref

3.2.2. Insight of Pb2+ Diffusion Process. For a clear view of the Pb2+ diffusion process onto the modified composite, kinetic studies were conducted and discussed. Adsorption capacities of composites on Pb2+ as a function of the contact time were illustrated in Figure 6. The adsorption of Pb2+ in the first stage was a fast process due to ample highly efficient adsorption sites and the high concentration gradient of Pb2+. Also, 60 min was sufficient for the equilibrium, revealing the uniqueness of the composites prepared. The Weber−Morris model was used to describe the diffusion process of Pb2+ from the bulk to active sites on the adsorbates and

Figure 6. Contact time versus the adsorption behavior of Pb2+ onto the NaDBS/PTh/TiO2 (a) and CTAB/PTh/TiO2 composites at various initial concentrations (b). G



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Table 7. Kinetic Parameters Obtained from the Pseudo-First-Order, Pseudo-Second-Order, and Weber−Morris Models of Pb2+ Adsorption onto the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 Composites at Various Initial Concentrations pseudo-first-order model samples NaDBS/PTh/ TiO2 CT AB/PTh/ TiO2

C0 (mg/L)

qexp (mg/g)

100 500 1000 100 500 1000

49.97 162.50 192.80 49.25 147.00 203.00

k1(min−1)

qe (mg/g)

R2

0.0074 0.0092 0.0088 0.082 0.011 0.0082

0.38 2.57 3.42 0.88 3.90 4.81

0.48 0.86 0.75 0.44 0.78 0.89

pseudo-second-order model k2 (g/(mg·min))

qe (mg/g)

h (mg/(g·min)

0.82 0.011 0.0052 0.94 0.042 0.021

49.98 162.60 193.80 49.31 147.06 204.92

2053.60 282.46 196.08 2293.58 902.53 888.10

Weber−Morris model R2

ki (mg/min0.5/g)

I (mg/g)

R2

1.00 0.99 0.99 1.00 0.99 0.99

0.032 0.99 2.52 0.31 2.52 4.33

49.65 151.46 166.74 46.31 119.13 155.86

0.432 0.563 0.699 0.411 0.783 0.833

Table 8. Kinetic Parameters Obtained from the Multilinearity Weber−Morris Model of Pb2+ Adsorption onto the NaDBS/PTh/ TiO2 and CTAB/PTh/TiO2 Composites at Various Initial Concentrations sample

C0 (mg/L)

ki1 (mg/(min0.5·g))

I1 (mg/g)

R2

ki2 (mg/g·min0.5)

I2 (mg/g)

R2

NaDBS/PTh/TiO2

100 500 1000 100 500 1000

0.27 8.23 9.61 2.89 5.71 12.04

48.97 132.53 144.14 39.72 107.82 131.41

0.94 0.99 0.98 0.99 0.98 0.99

0.04 0.77 2.53 0.87 1.48 6.17

49.73 154.59 171.49 45.19 131.67 150.78

0.94 0.99 0.96 0.99 0.92 0.99

CTAB/PTh/TiO2

Table 9. Thermodynamic Parameters of Pb2+ Adsorption onto the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 Composites ΔS0 (J/K·mol)

ΔH0 (kJ/mol)

T (K)

ΔG0 (kJ/mol)

NaDBS/PTh/ TiO2

−33.13

−12.01

CTAB/PTh/ TiO2

−9.70

−4.18

298 308 313 318 298 308 313 318

−2.18 −1.85 −1.69 −1.52 −1.29 −1.19 −1.15 −1.10

Adsorption capacities of both composites increased fast with a pH value in the range 1.0−3.0, and then their growth slowed down. The highest capacities for Pb2+ at pH 6 are somewhat noticed. These results suggested that there were some highly electronegative atoms, such as oxygen in the −OH group or sulfur atoms in the polythiophene matrix on the adsorbents, where the competition was expected between H+ and Pb2+.30 The zeta potential, which reflects the properties of functional groups as well as the polarization degree on the surface of adsorbent, is vital to adsorbents used for heavy mental adsorption.8 Figure 7b showed the influence of the modification on the zeta potential of surfactant/PTh/TiO2 composites. The point of zero point charge (pHpzpc) is 3.91 and 11.42 for the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 composites, respectively. The result exhibited the change on the surface charge of PTh/TiO2 composite (4.17) for the modification. Specifically, modification may adjust the ionization degree of the composite through functional groups. NaDBS is an anionic surfactant with sulfonic acid, which may make the surface of the composite more negative, while the cationic CTAB would carry a more positive charge on the surface of the composite. It can be noted that the composites could still adsorb Pb2+ at pH< pHpzpc (3.91 or 11.42),

R2 0.99

0.99

3.3. Investigation of Adsorption Mechanism. 3.3.1. Effect of the pH Value of the Aqueous Solution. The pH value of the aqueous solution affects the surface charge and the ionization degree of composites in the solution,29 while the modification would influence the attraction of the composite from metallic element ions. The effect of solution pH values on Pb2+ adsorption capacities of two adsorbents was illustrated in Figure 7a. The entire experimental pH range was fixed from 1.0 to 6.0 to eliminate the effect of lead precipitation on the adsorption.

Figure 7. Effects of pH on the adsorption capacity of Pb2+ onto the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 composites (a) and zeta potentials of the PTh/TiO2, NaDBS/PTh/TiO2, and CTAB/PTh/TiO2 composites (b). H



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Figure 8. Recycle adsorption performance of the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 composites (a, b) and the stability performance of the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 composites (c, d).

and there was no difference in the pH adsorption edge curve even though they had different pHpzpc, indicating that the electrostatic attraction would be a secondary cause in these adsorption systems.31 3.3.2. Regeneration Study. The regeneration study was conducted for further mechanism investigation. HNO3 and EDTA-Na had been applied as elution agents in many laboratorial and large-scale investigations, which had been recognized as effective ways for the adsorbent recycle.52−55 Based on the fact that adsorption capacities of composites were strongly pH dependent, 1 mol/L of HNO3 was employed as a desorption agent, and 0.1 mol/L of NaOH was used to activate adsorbents. Results were depicted in Figure 8a−b. It was observed that adsorption capacities could be recycled, but they reduced gradually to those of the PTh/TiO2 composite over three adsorption−desorption cycles, and the adsorbents could not be reactivate by repretreated with surfactants. To further get inside of the desorption investigation, the recycle experiment was arranged into two steps, which was convenient and feasible from the practical point of view: the discarded adsorbents was immersed into 1 mol/L of HNO3 for 30 min, followed by being immersed into 0.1 mol/L of EDTA-Na for another 30 min after centrifugal separation. By this method, there was little loss of adsorption capacity after reusing for five times (shown in Figure 8c−d), confirming that adsorption mechanisms involved in this system were integrated, and some interactions caused by surfactant such as precipitation were pH independent.32 Meanwhile, this is not observed in the adsorption of Pb2+ on the PTh/TiO2 composite, showing the additional precipitation of surfactants for Pb2+ adsorption. Nevertheless, there was little loss of the adsorption capacities after being reused for five times using this method, and the stabilities of the composites were still superior to other adsorbents using other recycle methods (Table 10).

Table 10. Comparison of the Desorption Efficiency of Various Sorbents for Pb2+ Using Different Desorption Methods sample PAN-monolith spinel iron oxide 0.5 M Mg−Al LDH/ pRGO AMPS-hazelnut shell powder PTh/TiO2 NaDBS/PTh/TiO2 CTAB/PTh/TiO2

desorption method

desorption efficiency

ref

1 M HCl 0.01 M HNO3 0.1 M HCl

∼90% to ∼70% 55 ∼95% to ∼80% 52 89.09% 53

0.01 M EDTA 0.5 M HCl

45.35% ∼90%

54

1 M HNO3 1 M HNO3+0.1 M EDTA-2Na 1 M HNO3+0.1 M EDTA-2Na

99% to 92% 99% to 95%

15 this work

99% to 94%

this work

Therefore, the mechanism on the increase of the adsorption capacity by surfactants can be concluded as follows according to results obtained above. Surfactants may modify the composite from hydrophilic to hydrophobic and increase the affinity between composites and Pb2+ owning to the enhanced solubilizing effect and restricted aggregation.27 Authenticated by the regeneration study, the surfactants which could aggregate into micelles also had a great tendency to form a large metal−surfactant structure or precipitation with Pb2+.33 Hence, the modification of surfactant on the composite was effective and feasible on enhancing the adsorption capacity of Pb2+. It can be noted the adsorption capacity of PTh/TiO2 composite is promoted more significantly by CTAB than NaDBS, because the longer the alkyl chains were, the stronger the interactions would be, further resulting in a larger adsorption capacity.13 3.3.3. Active Adsorption Site Investigation. XRD patterns of composites before and after adsorption were depicted in Figure 9. I



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Figure 9. XRD patterns before and after adsorption of the NaDBS/PTh/TiO2 (a) and CTAB/PTh/TiO2 composites (b).

Figure 10. FT-IR spectra before and after adsorption of the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 composites.

indicating the formation of Pb−S appears in the two spectra after adsorption,38 further confirming the contribution of sulfur atoms in the polythiophene matrix during the adsorption process. Moreover, the adsorbed Pb2+ on composites can be readily identified by the Pb 4f XPS spectra of composites shown in Figure 11i−j. The adsorbed samples had two peaks at 136.9 and 137.7 eV that can be assigned to Pb−O and Pb−S,39 respectively, which was congruous with conclusions obtained from the FT-IR investigation that hydroxyl groups, and the sulfur atoms on polythiophene matrix were the major adsorption sites. 3.2.4. Plausible Mechanism. First, adsorption active sites on surfactants/PTh/TiO2 composites were investigated to be surfactants, hydroxyl groups, and sulfur atoms situated in the PTh matrix. The adsorption mechanisms involved the physisorption such as precipitation, electrostatic attraction and weak chemisorption such as chelation, or ion exchange. The adsorption may happen through these reactions as follows.

The results showed no additional peaks or significant differences after adsorption, presenting the Pb2+ was adsorbed on the surface of composites instead of incorporating into the layers of TiO2. However, the intensity of the peaks decreased in all cases, suggesting that a part of active sites located mainly on the surface of composites.21 Various differences in peak shift, intensity, and total or partial disappearance of peaks were observed in FITR spectra of the original and Pb2+ adsorbed composites, as shown in Figure 10. The peaks of the CC vibrations shifted from 1641 to 1620 cm−1 or from 1664 to 1625 cm−1, respectively.34 Meanwhile, the vibration strength of the thiophene ring located at 1138−1039 cm−1 deceases, and the C−S vibration peaks located at about 740−580 cm−1 are overlapped after adsorption,34 which strongly support that the carbonyl groups as well as the sulfur atoms located on polythiophene ring may be primary adsorption sites for Pb2+ adsorption. XPS spectra were widely used in identifying the interaction between metallic element ions and functional groups because the creation of chemical bonds between ions and atoms on the functional groups changes the distribution of the electrons around the atoms. Figure 11a−d shows the O 1s XPS spectra of composites before and after adsorption. The peaks at 528.6, 530.3, and 531.9 eV attributed to the oxygen in the C−O,35 Ti−O,36 and OH groups,37 respectively. After adsorption of lead, a new peak at BE of 530.9 eV assigned to Pb−O appears in both cases, indicating that hydroxyl groups on the TiO2 were involved in the formation of complex with Pb2+.34 The S 2p XPS spectra of composites depicted in Figure 11e−h show that the sulfur atom also contributed to the lead ion adsorption. The peaks situated at about 162.6 and 163.7 eV may be assigned to the sulfur atom in the polythiophene matrix, respectively, while the peaks positioned at about 167.6 and 168.8 eV can be attributed to those of SO32− and SO42− groups, respectively. A new peak at 160.3 eV

2 Composite − OH + Pb2 + → Composite − (O)2 Pb + 2H+ (ion exchange)

Composite2n − + nPb2 + → nComposite − Pb (electrostatic attraction) PTh − S + Pb2 + → (PTh − S − Pb)2 + (chelation)

Composite − Surfactant + Pb2 + → (Composite − Surfactant − Pb)2 + (s) (precipitation) J



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Figure 11. XPS O 1s spectra for the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 composites before and after adsorption of Pb2+ (a, b, c, d), XPS S 1s spectra for the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 composites before and after adsorption of Pb2+ (e, f, g, h), and XPS Pb 4f7/2 spectra for the NaDBS/PTh/TiO2 and CTAB/PTh/TiO2 composites after adsorption of Pb2+ (i, j).

Second, the adsorption behavior and mechanism for Pb2+ onto composites was summarized as follows. After composites added in the wastewater, Pb2+ ions were attracted and moved to the surface gradually. Then they diffused through the film surrounding the composites and moved into the internal particle

of composites. The adsorption rate of this procedure was controlled by the film and intraparticle diffusion. After that, Pb2+ ions were interacted with the adsorption active sites including sulfur atoms situated in the PTh matrix (through chelation), hydroxyl groups, located on the surface of composites (through K



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Scheme 2. Possible Mechanism for the Adsorption of Pb2+ from Aqueous Solution

electrostatic attraction or ion exchange), the surfactants modified on the composites (through precipitation), etc. Pb2+ ions were also adsorbed into the intraparticle of composites through physisorption. In this process, weak chemisorption such as chelation controlled the adsorption rate of this procedure. The plausible adsorption mechanism of composites for Pb2+ was also depicted in Scheme 2.

■

4. CONCLUSIONS Various changes including the textural, surface properties, and adsorption behavior were found after modification, and the modification of PTh/TiO2 composite with two kinds of surfactants significantly enhances the adsorption capacity for Pb2+ from 151.52 mg/g to 198.41 or 213.22 mg/g, due to the surface property change of PTh/TiO2 composite by surfactants and the good affinity between the composites and Pb2+. The diffusion rate was controlled by the film and intraparticle diffusion, while the adsorption rate was controlled by chemisorption. The active adsorption sites were found to be sulfur atoms situated in the PTh matrix (by chelation), hydroxyl groups located on the surface of composites (by electrostatic attraction or ionic exchange), and the surfactants modified on the composites (by precipitation). Overall, the modification using surfactants on adsorbents for metallic element ion adsorption is an effective method in industrial application.

■

parameters acquired from different models in the adsorption of Pb2+ onto PTh/TiO2 composite at 25 °C. Additional scheme: Surfactants used and their formulas. Additional experiments and discussion: Effect of the adsorbent dose; effect of the agitation speed, effect of the ionic strength; feasibility investigation for the composites adsorbing other divalent heavy metals (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (J.F.). Tel.: +86-13032912105; fax: +86-029-82664731. *E-mail: [email protected] (W.Y.). ORCID

Wei Yan: 0000-0003-0724-6911 Funding

The authors gratefully acknowledge the financial supports from the National Natural Science Foundation of China (Grant No. 21307098), and the Shaanxi Science and Technology Coordination Innovation Project, China (2015KTZDSF01-02). Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Hui, C. W.; Chen, B. N.; McKay, G. Pore-surface diffusion model for batch adsorption processes. Langmuir 2003, 19, 4188−4196. (2) Langmuir, I. The adsorption of gases on plane surfaces of glass, mica and platinum. J. Am. Chem. Soc. 1918, 40, 1361−1403. (3) Freundlich, H. Concerning adsorption in solutions. Zeitschrift Fur Physikalische Chemie–Stochiometrie Und Verwandtschaftslehre 1906, 57, 385−470. (4) Sips, R. On the structure of a catalyst surface. J. Chem. Phys. 1948, 16, 490−495. (5) Weber, W. J.; Morris, J. C. Kinetics of Adsorption on Carbon From Solution. Asce Sanit. Eng. Div. J. 1963, 1, 1−2. (6) Lagergren, S. About the theory of so called adsorption of soluble substances. Kung Sven Vetensk Adam Handl. 1898, 24, 1−39. (7) Ho, Y. S.; McKay, G. Sorption of dye from aqueous solution by peat. Chem. Eng. J. 1998, 70, 115−124.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b00329. Additional figures: FT-IR spectra of the TiO2, PTh/TiO2, NaDBS/PTh/TiO2, and CTAB/PTh/TiO2 composites; nitrogen gas adsorption−desorption isotherms and pore size distribution of the PTh/TiO2 composite and SEM image of the PTh/TiO2 composite; multifit of the adsorption kinetic data of NaDBS/PTh/TiO 2 and CTAB/PTh/TiO2 composites for Pb2+ to the Weber− Morris model. Additional table: Adsorption equilibrium L



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(8) Chen, J.; Shu, C.; Wang, N.; Feng, J. T.; Ma, H. Y.; Yan, W. Adsorbent synthesis of polypyrrole/TiO2 for effective fluoride removal from aqueous solution for drinking water purification: Adsorbent characterization and adsorption mechanism. J. Colloid Interface Sci. 2017, 495, 44−52. (9) Vasconcelos, M.; Leal, M. F. C. Adsorption and uptake of Cu by Emiliania huxleyi in natural seawater. Environ. Sci. Technol. 2001, 35, 508−515. (10) Wang, J.; Xu, L.; Cheng, C.; Meng, Y.; Li, A. Preparation of new chelating fiber with waste PET as adsorbent for fast removal of Cu2+ and Ni2+ from water: Kinetic and equilibrium adsorption studies. Chem. Eng. J. 2012, 193−194, 31−38. (11) Hsu, T. C. Experimental assessment of adsorption of Cu2+ and Ni2+ from aqueous solution by oyster shell powder. J. Hazard. Mater. 2009, 171, 995−1000. (12) Deshpande, S.; Shiau, B. J.; Wade, D.; Sabatini, D. A.; Harwell, J. H. Surfactant selection for enhancing ex-situ soil washing. Water Res. 1999, 33, 351−360. (13) Pereira, R. F.; Valente, A. J.; Burrows, H. D. The interaction of long chain sodium carboxylates and sodium dodecylsulfate with lead(II) ions in aqueous solutions. J. Colloid Interface Sci. 2014, 414, 66−72. (14) Ding, L.; Wang, S.; Liu, Y.; Cao, J.; Fang, Y. Bispyrene/surfactant assemblies as fluorescent sensor platform: detection and identification of Cu2+ and Co2+ in aqueous solution. J. Mater. Chem. A 2013, 1, 8866− 8875. (15) Chen, J.; Feng, J. T.; Yan, W. Facile synthesis of a polythiophene/ TiO2 particle composite in aqueous medium and its adsorption performance for Pb(II). RSC Adv. 2015, 5, 86945−86953. (16) Chen, J.; Feng, J. T.; Yan, W. Influence of metal oxides on the adsorption characteristics of PPy/metal oxides for Methylene Blue. J. Colloid Interface Sci. 2016, 475, 26−35. (17) Svilovic, S.; Rusic, D.; Basic, A. Investigations of different kinetic models of copper ions sorption on zeolite 13X. Desalination 2010, 259, 71−75. (18) Li, X. G.; Li, J.; Huang, M. R. Facile Optimal Synthesis of Inherently Electroconductive Polythiophene Nanoparticles. Chem. Eur. J. 2009, 15, 6446−6455. (19) Xu, J.; Yao, P.; Li, X.; He, F. Synthesis and characterization of water-soluble and conducting sulfonated polyaniline/para-phenylenediamine-functionalized multi-walled carbon nanotubes nano-composite. Mater. Sci. Eng., B 2008, 151, 210−219. (20) Li, J. J.; Zhang, Q.; Feng, J.; Yan, W. Synthesis of PPy-modified TiO2 composite in H2SO4 solution and its novel adsorption characteristics for organic dyes. Chem. Eng. J. 2013, 225, 766−775. (21) Jin, X.; Jiang, M.; Du, J.; Chen, Z. Removal of Cr(VI) from aqueous solution by surfactant-modified kaolinite. J. Ind. Eng. Chem. 2014, 20, 3025−3032. (22) Kruk, M.; Jaroniec, M. Gas adsorption characterization of ordered organic-inorganic nanocomposite materials. Chem. Mater. 2001, 13, 3169−3183. (23) Xu, Y.; Zhou, Y.; Ma, W.; Wang, S.; Li, S. Functionalized magnetic core−shell Fe3O4@SiO2 nanoparticles for sensitive detection and removal of Hg2+. J. Nanopart. Res. 2013, 15, 1−9. (24) Du, J. H.; Morris, G.; Pushkarova, R. A.; Smart, R. S. Effect of surface structure of kaolinite on aggregation, settling rate, and bed density. Langmuir 2010, 26, 13227−13235. (25) Vuković, G. D.; Marinković, A. D.; Škapin, S. D.; Ristić, M. Đ.; Aleksić, R.; Perić-Grujić, A. A.; Uskoković, P. S. Removal of lead from water by amino modified multi-walled carbon nanotubes. Chem. Eng. J. 2011, 173, 855−865. (26) Li, T.; Liu, Y.; Peng, Q.; Hu, X.; Liao, T.; Wang, H.; Lu, M. Removal of lead(II) from aqueous solution with ethylenediaminemodified yeast biomass coated with magnetic chitosan microparticles: Kinetic and equilibrium modeling. Chem. Eng. J. 2013, 214, 189−197. (27) Sarkar, M.; Majumdar, P. Application of response surface methodology for optimization of heavy metal biosorption using surfactant modified chitosan bead. Chem. Eng. J. 2011, 175, 376−387. (28) Ho, Y. S. Review of second-order models for adsorption systems. J. Hazard. Mater. 2006, 136, 681−689.

(29) El-Toni, A. M.; Habila, M. A.; Ibrahim, M. A.; Labis, J. P.; Alothman, Z. A. Simple and facile synthesis of amino functionalized hollow core−mesoporous shell silica spheres using anionic surfactant for Pb(II), Cd(II), and Zn(II) adsorption and recovery. Chem. Eng. J. 2014, 251, 441−451. (30) Sakkayawong, N.; Thiravetyan, P.; Nakbanpote, W. Adsorption mechanism of synthetic reactive dye wastewater by chitosan. J. Colloid Interface Sci. 2005, 286, 36−42. (31) Li, J. J.; Feng, J. T.; Yan, W. Excellent adsorption and desorption characteristics of polypyrrole/TiO2 composite for Methylene Blue. Appl. Surf. Sci. 2013, 279, 400−408. (32) Li, J.; Chen, S.; Sheng, G.; Hu, J.; Tan, X.; Wang, X. Effect of surfactants on Pb(II) adsorption from aqueous solutions using oxidized multiwall carbon nanotubes. Chem. Eng. J. 2011, 166, 551−558. (33) Fu, F.; Wang, Q. Removal of heavy metal ions from wastewaters: a review. J. Environ. Manage. 2011, 92, 407−418. (34) Deng, S. B.; Chen, J. P. Aminated polyacrylonitrile fibers for lead and copper removal. Langmuir 2003, 19, 5058−5064. (35) Estrade-Szwarckopf, H.; Rousseau, B.; Herold, C.; Lagrange, P. Sodium-oxygen graphite intercalation compound: XPS, UPS and STM study. Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A 1998, 310, 231−236. (36) Hopfengartner, G.; Borgmann, D.; Rademacher, I.; Wedler, G.; Hums, E.; Spitznagel, G. W. XPS studies of oxidic model catalysts internal standards and oxidation numbers. J. Electron Spectrosc. Relat. Phenom. 1993, 63, 91−116. (37) Lim, A. S.; Atrens, A. ESCA studies of nitrogen-containing stainless-steels. Appl. Phys. A: Solids Surf. 1990, 51, 411−418. (38) Wang, L.; Yan, B.; Wang, X.; Liu, C.; Liu, J. Research on effect of different heavy metal ions on C-S-H gel and its stability. J. Build. Mater. 2014, 17, 790−796. (39) Kanai, H.; Yoshiki, M.; Hayashi, M.; Kuwae, R.; Yamashita, Y. Grain-boundary-phase identification of a lead-based relaxor by X-ray photoelectron-spectroscopy. J. Am. Ceram. Soc. 1994, 77, 2229−2231. (40) Li, J. J.; Feng, J. T.; Yan, W. Synthesis of polypyrrole-modified TiO2 composite adsorbent and its adsorption performance on acid Red G. J. Appl. Polym. Sci. 2013, 128, 3231−3239. (41) Hao, S.; Zhong, Y.; Pepe, F.; Zhu, W. Adsorption of Pb2+ and Cu2+ on anionic surfactant-templated amino-functionalized mesoporous silicas. Chem. Eng. J. 2012, 189−190, 160−167. (42) Gök, A.; Omastová, M.; Yavuz, A. G. Synthesis and characterization of polythiophenes prepared in the presence of surfactants. Synth. Met. 2007, 157, 23−29. (43) Uygun, A.; Yavuz, A. G.; Sen, S.; Omastová, M. Polythiophene/ SiO2 nanocomposites prepared in the presence of surfactants and their application to glucose biosensing. Synth. Met. 2009, 159, 2022−2028. (44) Lu, Q.; Zhou, Y. Synthesis of mesoporous polythiophene/MnO2 nanocomposite and its enhanced pseudocapacitive properties. J. Power Sources 2011, 196, 4088−4094. (45) An, H. K.; Park, B. Y.; Kim, D. S. Crab shell for the removal of heavy metals from aqueous solution. Water Res. 2001, 35, 3551−3556. (46) Kadirvelu, K.; Faur-Brasquet, C.; Le Cloirec, P. Removal of Cu(II), Pb(II), and Ni(II) by adsorption onto activated carbon cloths. Langmuir 2000, 16, 8404−8409. (47) Sen Gupta, S.; Bhattacharyya, K. G. Immobilization of Pb(II), Cd(II) and Ni(II) ions on kaolinite and montmorillonite surfaces from aqueous medium. J. Environ. Manage. 2008, 87, 46−58. (48) Liu, Y.; Liu, Z. C.; Gao, J.; Dai, J. D.; Han, J. A.; Wang, Y.; Xie, J. M.; Yan, Y. S. Selective adsorption behavior of Pb(II) by mesoporous silica SBA-15-supported Pb(II)-imprinted polymer based on surface molecularly imprinting technique. J. Hazard. Mater. 2011, 186, 197− 205. (49) Naiya, T. K.; Bhattacharya, A. K.; Das, S. K. Adsorption of Cd(II) and Pb(II) from aqueous solutions on activated alumina. J. Colloid Interface Sci. 2009, 333, 14−26. (50) Tofighy, M. A.; Mohammadi, T. Adsorption of divalent heavy metal ions from water using carbon nanotube sheets. J. Hazard. Mater. 2011, 185, 140−147. M



Article

(51) Ngah, W. S. W.; Fatinathan, S. Pb(II) biosorption using chitosan and chitosan derivatives beads: Equilibrium, ion exchange and mechanism studies. J. Environ. Sci. 2010, 22, 338−346. (52) Laus, R.; Costa, T. G.; Szpoganicz, B.; Favere, V. T. Adsorption and desorption of Cu(II), Cd(II) and Pb(II) ions using chitosan crosslinked with epichlorohydrin-triphosphate as the adsorbent. J. Hazard. Mater. 2010, 183, 233−241. (53) Ge, F.; Li, M. M.; Ye, H.; Zhao, B. X. Effective removal of heavy metal ions Cd2+, Zn2+, Pb2+, Cu2+ from aqueous solution by polymermodified magnetic nanoparticles. J. Hazard. Mater. 2012, 211−212, 366−372. (54) Lee, C. Y.; Kim, T.; Komarneni, S.; Han, S.-K.; Cho, Y. Sorption characteristics of lead cations on microporous organo-birnessite. Appl. Clay Sci. 2013, 83−84, 263−269. (55) Wang, G.; Wang, J. R.; Zhang, H.; Zhan, F.; Wu, T. T.; Ren, Q. D.; Qiu, J. E. S. Functional PAN-based monoliths with hierarchical structure for heavy metal removal. Chem. Eng. J. 2017, 313, 1607−1614.

N


TiO2 Composite Using

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