Facile Synthesis of Silver Bromide-Based Nanomaterials and Their

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Facile synthesis of silver bromide-based nanomaterials and their efficient and rapid selective adsorption mechanisms towards anionic dyes Liang Tang, Jia-jun Wang, Liang Wang, Cheng-tao Jia, Geng-xin Lv, Ning Liu, and Ming-hong Wu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.6b00743 • Publication Date (Web): 18 Jul 2016 Downloaded from http://pubs.acs.org on July 18, 2016

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ACS Sustainable Chemistry & Engineering

Facile synthesis of silver bromide-based nanomaterials and their efficient and rapid selective adsorption mechanisms towards anionic dyes Liang Tang,† Jia-jun Wang,† Liang Wang,*,‡ Cheng-tao Jia,† Geng-xin Lv,†,§ Ning Liu, ⊥

†

and Ming-hong Wu*,† Shanghai Institute of Applied Radiation, Shanghai University, 333 Nanchen Rd.,

Shanghai 200444, P. R. China ‡

Institute of Nanochemistry and Nanobiology, Shanghai University, 99 Shangda Rd.,

Shanghai 200444, P. R. China §

Division of Interfacial Water and Key Laboratory of Interfacial Physics and

Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, 2019 Jialuo Rd., Shanghai 201800, P. R. China ⊥

School of Environment and Architecture, University of Shanghai for Science and

Technology, 516 Jungong Rd., Shanghai 200093, P. R. China Author information * Corresponding Authors. Tel: +86-66135276, e-mail: [email protected] (L. Wang). Tel: +86-66137801, e-mail: [email protected] (M. H. Wu). The authors declare no competing financial interest. Hightlights:

Facile preparation and characterization of silver bromide-based nanomaterials.

Efficient and rapid selective adsorption properties of the novel nanomaterials were observed towards anionic dyes.

Adsorption equilibrium, kinetics, recyclability and mechanisms of the adsorbents for anionic dyes were well investigated.

New materials combining nanoparticle cores and surfactant cover may provide a feasible way to environment remediation.

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ACS Paragon Plus Environment


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ABSTRACT A novel adsorbent of AgBr-AgBr/CTAB nanomaterials, which was synthesized via Tollen’s reagent with the aid of hexadecyltrimethy ammonium bromide (CTAB), showed an excellent high affinity to anions and was used for removal of organic dyes in aqueous solutions.

The synthesized AgBr-AgBr/CTAB

was thoroughly

characterized by XRD, SEM, TEM, XPS, FTIR, TGA, DLS as well as zeta potential measurements. The adsorption property and capacity of AgBr-AgBr/CTAB for organic dyes were evaluated using Methylene blue (MB), Rhodamine B (RhB), Acid Red 18 (AR-18), Orange G (OG), Indigo Carmine (IC) and Methyl Orange (MO) as models. The adsorption capacity of AgBr-AgBr/CTAB complex towards four anionic dyes OG, AR-18, IC and MO solutions was 87.43 ± 2.03 mg g-1, 205.89 ± 2.12 mg g-1, 140.42 ± 2.13 mg g-1 and 104.6 ± 1.59 mg g-1, respectively. On the other hand, this adsorbent exhibited little adsorption ability towards two cationic dyes, MB (2.99 ± 0.40 mg g-1) and RhB (2.96 ± 0.60 mg g-1). Interestingly, AgBr-AgBr/CTAB could be applied to efficiently adsorb anionic dyes from binary cationic-anionic dye systems with a high separation factor, and such adsorbent could be reused at least 5 times with adsorption capacities above 95%. The removal of anionic dyes followed pseudo-first-order kinetics and Langmuir isotherm model, indicating that anionic dyes were monolayerly adsorbed on our as-prepared materials. To further elucidate the adsorption mechanism, the theoretical calculation based on first-principles was also provided. The results suggested R-SO3− groups were the active sites and electrostatic attraction was the dominating contribution for the adsorption of anionic dyes.

2


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INTRODUCTION Water crises caused by water pollution have become serious environmental issues and received more and more worldwide attentions.1,2 Due to the ecological and environmental concerns, efficient and rapid disposal strategy for water pollution is becoming a hot research topic. Among the troublesome contaminants in water, synthetic dyes are considered an important pollutant source due to their wide applications, casual and uncontrolled release, as well as their potential toxic, mutagenic and carcinogenic activities.3-5 Untreated wastewaters containing synthetic dyes can lead to serious aquatic ecological risks, exacerbate water crises and even harm human beings. Up to now, scientific research communities have developed a variety of technologies to deal with dye contaminants in wastewaters, such as adsorption,6 membrane filtration, catalytic degradation, flocculation, and advanced oxidation processes (AOPs).7,8 Among these approaches, adsorption is regarded as a promising strategy due to its high efficiency, economic feasibility and simplicity of operation.9 Up to now, a large number of adsorbent materials have been reported such as carbon-based nanomaterials,10-12 polymer resins,13,14 inorganic materials,15 natural mineral16 and some novel adsorbents.17-24 Nanoparticles exhibit large active site and unique adsorption properties because of the small sizes, large specific surface characteristics. Unfortunately, the aggregative trend severely limits its application as an adsorbent material in aqueous solution.25 Thus, development of a controlled morphology, stable nano adsorbent has become increasingly important. Silver bromide (AgBr) is an important compound that usually used as photographic material, electrochemistry and photoelectrochemistry, photocatalyst and so on.26-30 The most important property of AgBr is the enhanced band gap emission in the nano range,31 so that AgBr nanoparticles are considered as a significant photocatalyst. However, prior to photocatalytic decomposition, the first and important step for target contaminants is efficiently adsorbed on the surface of photocatalysts.32 Therefore, the adsorption behavior of toxic and deleterious substances on the materials is an important research field for researchers.33 However, AgBr, a highly

3



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efficient light-active substance, is not stable and easy to reunite dispersed in reaction mediums; thus, its application is severely limited.34 Based on this, facile synthesis of stable AgBr aroused great interest of scientists. Recently, a large number of stabilizing agents were applied to the synthesis of nanoparticles.35 The stabilization is usually performed by covering the particles with suitable surface passivating agents, which could form a covalent linkage to nanoparticles and endow the particles with increased stability.36 As is known to all, sorbents with mixed functional ligands may have enhanced adsorption ability towards the targets with different functional groups.37,38 For example, hexadecyltrimethy ammonium bromide (CTAB), a novel cationic surfactant, could be used as coating agents providing the target material with chemical and mechanical inertness.39,40 Until now, most of the researches for synthesis of AgBr mainly concerned about the topics like the effects of reactant ratio, synthesis temperature and so on.40,41 However, so little attention has been paid to the selection of silver sources. Herein, for the first time, two different silver sources, silver nitrate (AgNO3) and Tollen’s reagent, were selected to synthesize AgBr with the aid of CTAB and applied for efficient selective adsorption of anionic dyes. Four anionic dyes and two cationic dyes (Table S1) were utilized as model contaminants to evaluate the adsorption properties of our novel as-prepared absorbent. The selective adsorption capability, kinetics, isotherms and the recyclability of the adsorption process were discussed. Furthermore, the mechanisms of dyes on our as-prepared adsorbents were also investigated in details.

EXPERIMENTAL SECTION Materials and Reagents. Methylene blue (MB), Rhodamine B (RhB), Indigo Carmine (IC), Acid Red 18 (AR-18), Orange G (OG) and Methyl Orange (MO) were purchased from Sigma-Aldrich (USA). AgNO3, cetyltrimethyl ammonium bromide (CTBA), ammonium hydroxide (28 wt%), anhydrous ethanol and hydrochloric acid (HCl) were obtained from Sinopharm Chemical Reagent Co., Ltd. (China). Deionized water used in the study was produced through a Milli-Q-Plus ultra-pure water system 4


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(resistance > 18.2 MΩ cm) from Milipore (Sartorius 611, Germany). All the reagents and solvents were used as received without further treatment. Synthesis of AgBr-based Materials. AgBr nanoparticles were synthesized using a liquid-phase deposition procedure. In order to prevent the generation of elemental silver, Tollen’s reagent was formulated firstly. Specifically, 1.7 g AgNO3 was dissolved in 60 mL of deionized water, then approximately 5 mL ammonium hydroxide (28 wt%) aqueous solution was added dropwise under vigorous stirring at room temperature until the solution was clear. Meanwhile, 4.3 g CTAB was added into 300 mL deionized water under stirring and ultrasound until completely dissolved, and then the solution was wrapped with aluminum foil in the dark. Then, the above Tollen’s reagent was added dropwise into CTAB solution under vigorous stirring at room temperature. After that, the mixed solution was ultrasound 30 min, and stirred for 12 hours. The solid fractions were washed with deionized water and ethanol for several times, and then dried under vacuum at 60 °C. Powder product named AgBr-2 was finally obtained. In order to investigate the effect of different source of silver on product performance, AgNO3 was used to synthesize AgBr under the same condition, named AgBr-1. Structural Characterization. X-ray diffraction (XRD) patterns were obtained on a D/MAX-RBX-ray diffractometer (Rigaku, Japan). TEM observations were performed on a JEOL JEM-2010F electron microscope operating at 200 kV. Fourier transform infrared spectroscopy (FTIR) spectra were performed on Thermo Nicolet Avatar 370 FT-IR. XPS spectra were collected using a Kratos Axis Ultra DLD X-ray photoelectron spectrometer. Zeta potential and size of nanoparticles were determined by dynamic light scattering method using a dynamic light scattering spectrometer Nano ZS 90 (Malvern, UK). A He−Ne laser of 632.8 nm wavelength was used and the data were recorded at a scattering angle of 90°. Samples were filtered through a 22 nm microporous membrane. Thermogravimetry (TG)–differential thermal analysis

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(DTA) was performed on Pyris Diamond (Perkin–Elmer). The analysis was conducted in nitrogen atmosphere (100 mL min-1) between 25 and 800 °C. Sample of 10 mg was put in a Pt cell and heated ata constant rate of 10 °C min-1. Adsorption and Renewable Experiments. Four anionic dyes, i.e. OG, IC, AR-18, MO, and two cationic dyes, i.e. RhB, MB were chosen as the model targets for the test of adsorption performance, whose chemical properties were summarized in Table S1. For dye adsorption experiments, 10 mg synthetized adsorbents were added into 50 mL certain concentration of dye solution with stirring continuously. Samples were took at a certain interval time and centrifuged. The absorbance of supernatant was measured using UNICO 2100 visible spectrophotometer at the corresponding maximum absorption wavelength. The leaching tests of Ag from the as-prepared adsorbents were conducted by using Model PS 7800 ICP (Hitachi High-Tech Science Co., Tokyo, Japan). For regeneration measurements, AgBr-AgBr/CTAB absorbent was collected by centrifuging after dye adsorption. Subsequently, 10 mL of ethanol was used to desorb dye from absorbent. The absorbent was collected by centrifuging and washed with ethanol and deionized water for several times until the solution was colorless, and then dried under vacuum at 60 °C. The regenerated absorbent was then used for next cycle of dye removal study. In order to study the recyclability of AgBr-AgBr/CTAB complex, the abovementioned adsorption–desorption cycles were carried out for 5 cycles.

RESULTS AND DISCUSSION Characterizations of Materials. Characteristic X-ray diffraction patterns of AgBr-1 and AgBr-2 were shown in Fig. 1. The diffraction patterns of both AgBr-1 and AgBr-2 revealed that the products were in good agreement with the phase of AgBr (JCPDS No. 06-0438). The diffraction peaks at 2θ of 26.764°, 31.019°, 44.399°, 52.578°, 55.083°, 64.556° and 73.260° could be assigned to (111), (200), (220), (311), (222), (400), and (420) reflections of the face-centered cubic (fcc) 6


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structure of AgBr crystal, respectively. The sharp peaks suggested that AgBr nanoparticles were highly crystalline. For AgBr-2, however, the diffraction lines were a little intenser as compared with AgBr-1. It is noticeable that, with the existence of ammonia during synthesis process, the intensity of diffraction peaks of products keeps rising. Furthermore, a series of peaks appeared at small degree on AgBr-2, which may be attributed to a complex AgBr/CTAB containing AgBr and CTAB.40 Representative SEM and TEM images of AgBr-1 and AgBr-2 were shown in Fig. 2. Particle morphology was found to be strongly dependent on the differences of precursors. It could be observed from Fig. 2a and 2b that the AgBr particles clearly present various spherical crystals. In the case of unavoidable agglomeration of nanoparticles, AgBr nanoparticles remained uniformly dispersed with the aid of CTAB. On the other hand, Fig. 2c and 2d not only showed the formation of spherical AgBr nanoparticles but also a small amount of the flake particles. According to the flake morphology, it was believed that a complex was formed, which was consistent with the observation of Liu et al.40 That was to say, when the molar ratio of CTAB to AgNO3 was lower than 1.5:1, the product would become the color of light yellow which was consistent with the characteristic of AgBr crystal. In our experimental conditions, the molar ratio of CTAB to AgNO3 was approximately 1.1:1, so AgBr-1 could be considered as pure AgBr nanoparticles, which was also proved by the results of XRD. When ammonia was introduced, a magic Tollen’s reagent formed, which could sustainably release Ag+ in aqueous solutions as Eq. (1). When Tollen’s reagent was added dropwise under vigorous stirring, the molar ratio of CTAB to Ag(I) was a little excessive. Therefore, it was prone to generate a complex in solution. However, the total molar ratio was 1.1:1, AgBr did not be completely coated be CTAB. As a consequence, AgBr-2 synthesized with Tollen’s reagent might be AgBr-AgBr/CTAB composite. Moreover, the particle size of AgBr-2 was significantly smaller than that of AgBr-1 from Fig. 2e and 2f. To further illustrate the stability of AgBr-2, dynamic light scattering (DLS) was studied as Fig. S1. Although the Z-Average of AgBr-2 was 107.24 nm and 114.35 nm before and after adsorption experiments, both their size distribution were in the range from 50 to 180 nm. This indicated good stability of the 7



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material before and after the reaction. (1) The structure and chemical state information of AgBr-1 and AgBr-2 were obtained by the XP spectra as well. As illustrated in Fig. 3, the expected peaks from Ag 3d and Br 3d were clearly detected in XP spectra. Ag 3d3/2 and Ag 3d5/2 peaks are identified at 372.68 and 366.68 eV, respectively. Meanwhile, Br 3d5/2 and Br 3d3/2 were identified at 67.58 and 68.58 eV. The N1s almost could not be detected in AgBr-1; nevertheless, N 1s (401.4 eV) peak was obviously verified in AgBr-2 which was attributed to N+. The phenomenon implied Ag+ might be weakly ionized by Tollen’s reagent during the synthesis process of AgBr-2, thus AgBr particles could be perfectly capped by CTAB. Consequently, the particle size of AgBr-2 was significantly smaller than that of AgBr-1. Furthermore, slightly excess CTAB capping AgBr might form a stable complex structure, which made the content of N increasing. To further establish the formation of AgBr/CTAB complex in AgBr-2, FTIR spectral measurements and TG-DTA curves were both carried out. The representative results were shown in Fig. 3d, 3e and 3f. As shown in Fig. 3d, the symmetric and asymmetric −(CH2)− vibrations of pure CTAB appeared at 2850 and 2918 cm−1, respectively. The observed peaks at 1470，1468 and 1431 cm−1 for pure CTAB were due to the asymmetric and symmetric −C−H vibration of the quarternary ammonium moiety. However, no significant peak was appeared on AgBr-1, indicating pure AgBr nanoparticles were formed, which is consistent with the result of XRD. It's worth noting that the peak at 1432 cm−1 was not present and the peak at 1469 cm−1 on AgBr-2 was slightly shifted to 1470 cm−1, suggesting that AgBr clusters might influence the (CH3)3N+ vibration.42 The TG curve of AgBr-1 has almost no mass loss, which confirmed a pure AgBr formation (Fig. 3e). Whereas, the TG and DTA curve of AgBr-2 has approximately 7 % mass loss and an endothermic peak at 276 °C (Fig. 3e and 3f), which was corresponding to CTAB molecules endothermic peaks.43 As expected, characteristic peaks of CTAB are also showed on IR and XPS characterizations of the AgBr-2. Thus,

8


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as-prepared AgBr-2 may be the capping CTAB around AgBr, which could be explained by the weak ionization of Ag+ by Tollen’s reagent. However, the total molar ratio of CTAB to AgNO3 was 1.1:1 in our experimental conditions, AgBr did not be completely coated be CTAB, resulting in the generation of AgBr-AgBr/CTAB complex. It is very interesting that the complex was hardly eluted under deionized water and ethanol several times compared to AgBr-1, which indicates the formation of the complex rather than the residual CTAB. Based on the above characteristics and the nature of the materials, AgBr-1 and AgBr-2 were named AgBr and AgBr-AgBr/CTAB complex in the following study. Adsorption performance. Six typical dyes, namely, Methylene blue (MB), Orange G (OG), Acid Red 18 (AR-18), Rhodamine B (RhB), Indigo Carmine (IC) and Methyl Orange (MO) were chosen for the adsorption tests and the results are depicted in Fig. 4a. As shown in the figure, it was clear that all the six dyes were hard to be adsorbed by AgBr particles after shaking solutions for 2 h. On the other side, the adsorption capacity of AgBr-AgBr/CTAB complex aiming to four anionic dyes OG, AR-18, IC and MO solutions was 87.43 ± 2.03 mg g-1, 205.89 ± 2.12 mg g-1, 140.42 ± 2.13 mg g-1 and 104.6 ± 1.59 mg g-1, respectively, suggesting such adsorbent exhibited great adsorption capacity towards the selected anionic dyes. Otherwise, little adsorption ability towards the cationic dyes was exhibited by AgBr-AgBr/CTAB complex. The maximum capacity of AgBr-AgBr/CTAB for AR-18 was compared with those reported in other studies (Table S2). The results display that AgBr-AgBr/CTAB prepared in this study is an efficient and rapid adsorbent towards anionic dyes. The selective and recyclable adsorption properties of the AgBr-AgBr/CTAB complex toward anionic dyes make them promising candidates for the removal of anionic dyes from dye mixtures. In order to exhibit the favorable ability, binary adsorption tests were carried out. Three binary dye solutions, IC/RhB, OG/MB and OG/RhB, in a 4:1 mass ratio were prepared. Then, a certain amount of AgBr-AgBr/CTAB complex was added into the solutions for a certain time with 9



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stirring. The results showed that the colors of anionic dyes were disappeared in mixtures, and the colors of solutions turned into the corresponding colors of cationic dyes (Fig. S2), implying the anionic dyes (IC in Mixture-1 and OG in Mixture-2 and 3) were selectively adsorbed. To confirm this view, the UV-Vis spectra of mixed dye solutions before and after adsorption reaction were carried out. For instance, the spectra of Mixture-2 are illustrated in Fig. S3. Obviously, the absorption of MB (664 nm) was almost no change in the resultant solution , whereas the peak of OG (478 nm) almost disappeared, indicating that OG has been selectively removed from the OG/MB binary mixture even though the amount of OG is four times as that of MB. Moreover, the recyclability of AgBr-AgBr/CTAB complex was investigated by performing the adsorption–desorption cycles for dye compounds. Fig. 4b showed that AgBr-AgBr/CTAB could be recycled at least 5 times with an excellent adsorption of more than 95%. The good recyclability thus makes the AgBr-AgBr/CTAB potentially suitable for high-efficiency and low-cost water pollution treatment. In order to study whether to leach Ag from AgBr-AgBr/CTAB complex, the dye solution was sampled at adsorption time of 5, 10, 20 and 40 min for ICP determination. Results showed that the leaching ratios of Ag in solution were lower than 0.01 %, and the concentration of Ag in solution did not increase with the adsorption time enhancement. It demonstrated that Ag in the composites was well protected by CTAB cover. Adsorption kinetics. The effect of the contact time on the adsorption of OG, IC, MO and AR-18 by AgBr-AgBr/CTAB adsorbents was presented in Fig. 5. As can be seen from Fig. 5, almost all of the adsorption processes reached equilibrium in 40 min. The descending order of the Qe values was AR-18 (206.4 mg g−1) > IC (139.8 mg g−1) > MO (104.6 mg g−1) > OG (87.4 mg g−1). To well-study the adsorption kinetics, the pseudo-first-order and pseudo-second order kinetic models were both examined according to Eqs. (1) and (3), respectively. ln (Qe – Qt) = ln(Qe) – k1t t/Qt = 1/k2Qe2 + t/Qe 10


(2) (3)

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where, Qe and Qt (mg g-1) are the amount of organic dyes absorbed per gram of adsorbents at adsorption equilibrium and each time t (min), respectively. k1 (min-1) and k2 (g mg-1 min-1) represent pseudo-first-order and pseudo-second-order rate constant, respectively. As shown in the inset of Fig. 5 and Table 1, the fitting situation with the pseudo-second order kinetic model was better than that of the pseudo-first-order kinetic model; the former exhibited good linearity with R2 higher than 0.99. Note that the adsorption capacities calculated (qe,cal) by the pseudo-second-order model were much closer to those determined by experiments (qe,exp), the adsorption processes of anionic dyes on AgBr-AgBr/CTAB followed the pseudo-second-order kinetic model. Adsorption isotherms. The equilibrium adsorption isotherm is of equal significance,

since

it

could

not

only

describe

the

interaction

between

AgBr-AgBr/CTAB and organic dyes but also design and operate the adsorption system.44 Fig. 6 showed the adsorption isotherm for the adsorption of OG and IC on AgBr-AgBr/CTAB. To well study how the adsorbents interact with adsorbates, Langmuir and Freundlich equations were employed to evaluate adsorption isotherm according to Eqs. (4) and (5): Ce 1 Ce = Q + Q Qe 0 0 kL 1 ln Qe = ln kF + n lnCe

(4) (5)

where, Qe (mg g-1) and Ce (mg L-1) are the equilibrium adsorption capacity and concentration, respectively; Q0 (mg g-1) is the maximum adsorption capacity and kL (L mg-1) is the Langmuir equilibrium adsorption constant. kF and n are Freundlich constants indicating the sorption capacity and intensity, respectively. The isothermal constants, and the linear regression coefficients extracted from the experimental data were presented in Fig. 6 and Table 2. From Table 2, the correlation coefficients R2 for the Langmuir model were higher than those for Freundlich model. Moreover, the fitting curves of the Langmuir isotherm model exhibited good linearity as shown in Fig. 6. The calculated values of Qmax obtained 11



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from Langmuir plots were 91.41 mg g-1 and 139.28 mg g-1, which was consistent with those experimentally obtained. Hence, this study suggested that Langmuir model could better represent the anionic dyes (OG and IC) adsorption processes onto AgBr-AgBr/CTAB. That is to say, the adsorption of anionic dyes occurred on the homogeneous surface of absorbents by monolayer adsorption without interaction between the materials, and all sites are equivalent.45 Adsorption mechanisms. The excellent selective adsorption capacity of the AgBr-AgBr/CTAB might be mainly attributed to the surface charges of adsorbents. To confirm such view, the surface charges of AgBr-AgBr/CTAB were determined by zeta potential measurements. As illustrated in Fig. 7a, a series of experiments were conducted to determine the changes in zeta potential as a function of pH, and zeta potentials of AgBr-AgBr/CTAB were found to be positive over the pH range from 2 to 12. It is noteworthy that the whole zeta potentials were greater than 30 mV, indicating AgBr-AgBr/CTAB showed extremely excellent stability both in acid and alkaline environments. The effects of pH on the adsorption capacities of AgBr-AgBr/CTAB toward AR-18 and MB were studied as well; interestingly, an opposite result was observed (Fig. 7b). The adsorption capacity towards AR-18 decreased moderately with pH increase; while this trend was opposite from that towards MB. This phenomenon could be explained by the reinforced protonation of AgBr-AgBr/CTAB at a lower pH value,

which

could

be

confirmed

by

the

increased

zeta

potentials

of

AgBr-AgBr/CTAB under a lower pH value (Fig. 7a). In acidic condition, the charge density would be enhanced, and thus the electrostatic interaction between the adsorbents and anionic dye molecules would be strengthened, resulting in the improved adsorption capacity toward AR-18. In order to understand the active site and interaction between our novel adsorbents and anionic dyes, the theoretical calculation based on first-principles was provided. Herein, we used AR-18 as an example. As we known, AR-18 molecules display two structures at the equilibrium state in aqueous solutions, where the ionization of the equilibrium state is dominant formation that has negative R-SO3− 12


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groups.46 As shown in Fig. 8, S 2p appeared in the XPS after adsorption which suggested that -SO3− groups might be reactive sites. As shown in Fig. S4, based on LUMO (Fig. S4b and S4f) and HOMO (Fig. S4c, S4d and S4e) of AR-18 molecules, -SO3− was supposed to one of most important reactive sites. To pure AgBr nanoparticles, the lone pair electron of O atoms in the R-SO3− groups can transfer into 4d orbital of the Ag to form a coordination bond, which may contribute to a little adsorption for the anionic dyes. To our novel AgBr-AgBr/CTAB complex, electrostatic interaction not only enhanced the adsorption capacity for anionic dyes, but also inhibited the absorption of cationic dyes. A model was proposed based on the characterization above and a previous research,41 that is to say, AgBr-AgBr/CTAB were constituted of pure AgBr and CTA+ capped AgBr in aqueous solutions. As a consequence, AgBr-AgBr/CTAB not only form Ag-O coordination bonds to adsorb a little anionic dyes，but also can combine with anionic groups, such as -SO3− groups, forming stable adsorption systems.

Conclusion In this work, AgBr-AgBr/CTAB composite were successfully synthesized through Tollen’s reagent with the presence of CTAB in aqueous solution. Comparing to pure AgBr nanoparticles synthesized by AgNO3, AgBr-AgBr/CTAB exhibited better dispersion and smaller particle size. Six typical dyes including MB, OG, AR-18, RhB, IC and MO were adopted for the adsorption tests. When adsorption equilibrium was reached, the adsorption capacity of AgBr-AgBr/CTAB complex towards four anionic dyes OG, AR-18, IC and MO was determined as 87.43 ± 2.03 mg g-1, 205.89 ± 2.12 mg g-1, 140.42 ± 2.13 mg g-1 and 104.6 ± 1.59 mg g-1, respectively, which demonstrated that such adsorbents possessed comparatively powerful adsorption capacity towards anionic dyes. Contrarily, AgBr-AgBr/CTAB complex had little adsorption ability towards two anionic dyes, MB (2.99 ± 0.40 mg g-1) and RhB (2.96 ± 0.60 mg g-1). Futhermore, binary adsorption tests were conducted. The results showed AgBr-AgBr/CTAB could efficiently and selectively remove anionic dye from mixed anionic-cationic dyes in two minutes. The adsorption 13



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process for anionic dyes followed pseudo-second order reaction kinetics and Langmuir isotherm, indicating the adsorption process of anionic dyes on AgBr-AgBr/CTAB was monolayer. In order to understand the adsorption mechanism, determination for zeta potential of AgBr-AgBr/CTAB under various pH conditions and the theoretical calculation based on first-principles were both carried out. Zeta potential results showed AgBr-AgBr/CTAB presented positive charge, and theoretical calculation suggested negative groups on anionic dye, such as R-SO3− groups were the active sites, thus the electrostatic attraction was the dominating contribution to the adsorption

for

anionic

dyes.

From

the

view

of

environmental

impact,

AgBr-AgBr/CTAB could be used for the removal of anionic dyes in wastewater under convenient condition, as well as preconcentration of anionic dyes in dye recovery procedure and environmental remediation. More importantly, materials constructed with nanoparticle cores and surfactant cover may provide a new way to environmental applications. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the … List of the molecular structures of the target four anionic dyes and two cationic dyes, comparison results of adsorption capacity towards to AR-18 among various nanoadsorbents, size distribution of AgBr-AgBr/CTAB nanomaterials before and after adsorption, digital photographs of the smart and fast selective adsorption towards binary dyes solution, UV-Vis spectra of OG/MB mixture before and after adsorption, Molecular modeling pictures, LUMO and HOMO of AR-18 molecules. ACKNOWLEDGEMENTS The authors would like to acknowledge the financial support from the National Natural Science Foundation of China (Nos. 41573096, 11305099, 91233102, 41373098 and 41430644), Sail Plan of Shanghai for Youth (No. 16YF1404400) and Program for Innovative Research Team in University (No. IRT13078).

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REFERENCES (1) Hoekstra, A. Y. Water scarcity challenges to business. Nature climate change 2014, 4, 318-320. (2) Lu, Y.; Song, S.; Wang, R.; Liu, Z.; Meng, J.; Sweetman, A. J.; Jenkins, A.; Ferrier, R. C.; Li, H.; Luo, W. Impacts of soil and water pollution on food safety and health risks in China. Environment international 2015, 77, 5-15. (3) Chowdhury, S.; Balasubramanian, R. Graphene/semiconductor nanocomposites (GSNs) for heterogeneous photocatalytic decolorization of wastewaters contaminated with synthetic dyes: A review. Appl Catal B-Environ 2014, 160, 307-324. (4) Vijwani, H.; Nadagouda, M. N.; Namboodiri, V.; Mukhopadhyay, S. M. Hierarchical hybrid carbon nano-structures as robust and reusable adsorbents: Kinetic studies with model dye compound. Chem Eng J 2015, 268, 197-207. (5) Shah, I.; Adnan, R.; Ngah, W. S. W.; Mohamed, N.; Taufiq-Yap, Y. H. A new insight to the physical interpretation of activated carbon and iron doped carbon material: Sorption affinity towards organic dye. Bioresource Technol 2014, 160, 52-56. (6) Das, S. K.; Shome, I.; Guha, A. K. Biotechnological potential of soil isolate, Flavobacterium mizutaii for removal of azo dyes: kinetics, isotherm, and microscopic study. Separation Science and Technology 2012, 47, 1913-1925. (7) Liu, X. Y.; An, S.; Wang, Y. J.; Yang, Q.; Zhang, L. Rapid selective separation and recovery of a specific target dye from mixture consisted of different dyes by magnetic Ca-ferrites nanoparticles. Chem Eng J 2015, 262, 517-526. (8) Asghar, A.; Raman, A. A. A.; Daud, W. M. A. W. Advanced oxidation processes for in-situ production of hydrogen peroxide/hydroxyl radical for textile wastewater treatment: a review. J Clean Prod 2015, 87, 826-838. (9) Masoomi, M. Y.; Morsali, A.; Junk, P. C. Rapid mechanochemical synthesis of two new Cd(II)-based metal-organic frameworks with high removal efficiency of Congo red. Crystengcomm 2015, 17, 686-692. (10) Luan, J.; Hou, P.-X.; Liu, C.; Shi, C.; Li, G.-X.; Cheng, H.-M. Efficient adsorption of organic dyes on a flexible single-wall carbon nanotube film. J. Mater. Chem. A 2016, 4, 1191-1194. (11) Wang, Y.; Ma, J.; Zhu, J.; Ye, N.; Zhang, X.; Huang, H. Multi-walled carbon nanotubes with selected properties for dynamic filtration of pharmaceuticals and personal care products. Water research 2016, 92, 104-112. (12) Alatalo, S.-M.; Mäkilä, E.; Repo, E.; Heinonen, M.; Salonen, J.; Kukk, E.; Sillanpää, M.; Titirici, M.-M. Meso-and microporous soft templated hydrothermal carbons for dye removal from water. Green Chemistry 2016. (13) Alsbaiee, A.; Smith, B. J.; Xiao, L.; Ling, Y.; Helbling, D. E.; Dichtel, W. R. Rapid removal of organic micropollutants from water by a porous beta-cyclodextrin polymer. Nature 2015. (14) Lofrano, G.; Carotenuto, M.; Libralato, G.; Domingos, R. F.; Markus, A.; Dini, L.; Gautam, R. K.; Baldantoni, D.; Rossi, M.; Sharma, S. K.; Chattopadhyaya, M. C.; Giugni, M.; Meric, S. Polymer functionalized nanocomposites for metals removal from water and wastewater: An overview. Water research 2016, 92, 22-37. (15) Lee, K.; Park, S. W.; Ko, M. J.; Kim, K.; Park, N. G. Selective positioning of organic dyes in a mesoporous inorganic oxide film. Nat. Mater. 2009, 8, 665-671. (16) Alkaram, U. F.; Mukhlis, A. A.; Al-Dujaili, A. H. The removal of phenol from aqueous 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 31

solutions by adsorption using surfactant-modified bentonite and kaolinite. Journal of hazardous materials 2009, 169, 324-332. (17) Bootharaju, M.; Pradeep, T. Facile and rapid synthesis of a dithiol-protected Ag7 quantum cluster for selective adsorption of cationic dyes. Langmuir 2013, 29, 8125-8132. (18) Das, S. K.; Khan, M. M. R.; Parandhaman, T.; Laffir, F.; Guha, A. K.; Sekaran, G.; Mandal, A. B. Nano-silica fabricated with silver nanoparticles: antifouling adsorbent for efficient dye removal, effective water disinfection and biofouling control. Nanoscale 2013, 5, 5549-5560. (19) Ramalingam, B.; Khan, M. M. R.; Mondal, B.; Mandal, A. B.; Das, S. K. Facile Synthesis of Silver Nanoparticles Decorated Magnetic-Chitosan Microsphere for Efficient Removal of Dyes and Microbial Contaminants. ACS Sustainable Chemistry & Engineering 2015, 3, 2291-2302. (20) Patra, A. S.; Ghorai, S.; Ghosh, S.; Mandal, B.; Pal, S. Selective removal of toxic anionic dyes using a novel nanocomposite derived from cationically modified guar gum and silica nanoparticles. Journal of hazardous materials 2016, 301, 127-136. (21) Lu, L.; Li, J.; Yu, J.; Song, P.; Ng, D. H. L. A hierarchically porous MgFe2O4/gamma-Fe2O3 magnetic microspheres for efficient removals of dye and pharmaceutical from water. Chemical Engineering Journal 2016, 283, 524-534. (22) He, Y.-C.; Yang, J.; Kan, W.-Q.; Zhang, H.-M.; Liu, Y.-Y.; Ma, J.-F. A new microporous anionic metal–organic framework as a platform for highly selective adsorption and separation of organic dyes. J. Mater. Chem. A 2015, 3, 1675-1681. (23) Wang, Z.; Guo, J.; Ma, J.; Shao, L. Highly regenerable alkali-resistant magnetic nanoparticles inspired by mussels for rapid selective dye removal offer high-efficiency environmental remediation. J. Mater. Chem. A 2015, 3, 19960-19968. (24) Altmann, J.; Rehfeld, D.; Trader, K.; Sperlich, A.; Jekel, M. Combination of granular activated carbon adsorption and deep-bed filtration as a single advanced wastewater treatment step for organic micropollutant and phosphorus removal. Water research 2016, 92, 131-139. (25) Giersig, M.; Pastoriza-Santos, I.; Liz-Marz�n, L. M. Evidence of an aggregative mechanism during the formation of silver nanowires in N,N-dimethylformamide. J Mater Chem 2004, 14, 607. (26) Ji, K. M.; Dai, H. X.; Deng, J. G.; Zang, H. J.; Arandiyan, H.; Xie, S. H.; Yang, H. G. 3DOM BiVO4 supported

silver

bromide

and

noble

metals:

High-performance

photocatalysts

for

the

visible-light-driven degradation of 4-chlorophenol. Applied Catalysis B-Environmental 2015, 168, 274-282. (27) Wang, P.; Huang, B.; Zhang, X.; Qin, X.; Jin, H.; Dai, Y.; Wang, Z.; Wei, J.; Zhan, J.; Wang, S.; Wang, J.; Whangbo, M.-H. Highly Efficient Visible-Light Plasmonic Photocatalyst Ag@AgBr. Chemistry-a European Journal 2009, 15, 1821-1824. (28) Li, G.; Wong, K. H.; Zhang, X.; Hu, C.; Yu, J. C.; Chan, R. C. Y.; Wong, P. K. Degradation of Acid Orange 7 using magnetic AgBr under visible light: The roles of oxidizing species. Chemosphere 2009, 76, 1185-1191. (29) Kuai, L.; Geng, B.; Chen, X.; Zhao, Y.; Luo, Y. Facile Subsequently Light-Induced Route to Highly Efficient and Stable Sunlight-Driven Ag-AgBr Plasmonic Photocatalyst. Langmuir : the ACS journal of surfaces and colloids 2010, 26, 18723-18727. (30) Rubtsov, I. V.; Ebina, K.; Satou, F.; Oh, J. W.; Kumazaki, S.; Suzumoto, T.; Tani, T.; Yoshihara, K. Spectral sensitization and supersensitization of AgBr nanocrystals studied by ultrafast fluorescence spectroscopy. Journal of Physical Chemistry A 2002, 106, 2795-2802. (31) Pietro Calandra, A. L., Vito Marciano , Vincenzo Turco Liveri. Physicochemical Investigation

16


Page 17 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of Lightfast AgCl and AgBr Nanoparticles Synthesized by a Novel Solid-Solid Reaction. Journal of Physical Chemistry B 2003, 107, 6724-6729. (32) Jing, H.-Y.; Wen, T.; Fan, C.-M.; Gao, G.-Q.; Zhong, S.-L.; Xu, A.-W. Efficient adsorption/photodegradation of organic pollutants from aqueous systems using Cu2O nanocrystals as a novel integrated photocatalytic adsorbent. J Mater Chem A 2014, 2, 14563. (33) Zhang, L.; Cao, X. F.; Chen, X. T.; Xue, Z. L. BiOBr hierarchical microspheres: Microwave-assisted solvothermal synthesis, strong adsorption and excellent photocatalytic properties. Journal of colloid and interface science 2011, 354, 630-636. (34) Zhu, M. S.; Chen, P. L.; Liu, M. H. Ag/AgBr/Graphene Oxide Nanocomposite Synthesized via Oil/Water and Water/Oil Microemulsions: A Comparison of Sunlight Energized Plasmonic Photocatalytic Activity. Langmuir : the ACS journal of surfaces and colloids 2012, 28, 3385-3390. (35) Liu, M. Z.; Guyot-Sionnest, P. Mechanism of silver(I)-assisted growth of gold nanorods and bipyramids. Journal of Physical Chemistry B 2005, 109, 22192-22200. (36) Perez-Juste, J.; Liz-Marzan, L. M.; Carnie, S.; Chan, D. Y. C.; Mulvaney, P. Electric-field-directed growth of gold nanorods in aqueous surfactant solutions. Advanced Functional Materials 2004, 14, 571-579. (37) Dong, Z.; Wang, D.; Liu, X.; Pei, X.; Chen, L.; Jin, J. Bio-inspired surface-functionalization of graphene oxide for the adsorption of organic dyes and heavy metal ions with a superhigh capacity. J Mater Chem A 2014, 2, 5034. (38) Zhao, J.; Luque, R.; Qi, W.; Lai, J.; Gao, W.; Hasan Shah Gilani, M. R.; Xu, G. Facile surfactant-free synthesis and characterization of Fe3O4@3-aminophenol–formaldehyde core–shell magnetic microspheres. J. Mater. Chem. A 2015, 3, 519-524. (39) Li, Y.-H.; Tan, P.; Liu, X.-Q.; Zu, D.-D.; Huang, C.-L.; Sun, L.-B. Facile Fabrication of AgCl Nanoparticles and Their Application in Adsorptive Desulfurization. Journal of Nanoscience and Nanotechnology 2015, 15, 4373-4379. (40) Liu, X. H.; Luo, X. H.; Lu, S. X.; Zhang, J. C.; Cao, W. L. A novel cetyltrimethyl ammonium silver bromide complex and silver bromide nanoparticles obtained by the surfactant counterion. Journal of colloid and interface science 2007, 307, 94-100. (41) Chakraborty, M.; Hsiao, F. W.; Naskar, B.; Chang, C. H.; Panda, A. K. Surfactant-assisted synthesis and characterization of stable silver bromide nanoparticles in aqueous media. Langmuir : the ACS journal of surfaces and colloids 2012, 28, 7282-7290. (42) Xu, X.-M.; Zhong, H.-P.; Zhang, H.-M.; Mo, Y.-R.; Xie, Z.-X.; Long, L.-S.; Zheng, L.-S.; Mao, B.-W. Ordered silver adlayer formation by surface-induced dissociation of a coordination complex precursor on Au(111) and Au(100) surfaces. Chem Phys Lett 2004, 386, 254-258. (43) Wu, S. H.; Chen, D. H. Synthesis of high-concentration Cu nanoparticles in aqueous CTAB solutions. Journal of colloid and interface science 2004, 273, 165-169. (44) Fu, J.; Xin, Q.; Wu, X.; Chen, Z.; Yan, Y.; Liu, S.; Wang, M.; Xu, Q. Selective adsorption and separation of organic dyes from aqueous solution on polydopamine microspheres. Journal of colloid and interface science 2016, 461, 292-304. (45) Huang, H.; Yu, J.; Liu, W.; Jiang, X. Amino-Functionalized Multi-Walled Carbon Nanotubes as Novel Adsorbents for Selective Adsorption of Anionic Dyes in Aqueous Solution. Nano 2015, 10, 1550065. (46) Dong, H.; Chen, G.; Sun, J.; Li, C.; Yu, Y.; Chen, D. A novel high-efficiency visible-light sensitive Ag2CO3 photocatalyst with universal photodegradation performances: Simple synthesis,

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reaction mechanism and first-principles study. Applied Catalysis B: Environmental 2013, 134-135, 46-54.

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Table captions: Table 1. Kinetic parameters for the adsorption of OG, IC, MO and AR-18 onto AgBr-AgBr/CTAB nanoparticles Table 2. Isotherm parameters for OG and IC adsorption on AgBr-AgBr/CTAB nanoparticles at 298 K

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Table 1. Kinetic parameters for the adsorption of OG, IC, MO and AR-18 onto AgBr-AgBr/CTAB nanoparticles Pseudo-first-order Dye

Pseudo-second-order

Qe,exp (mg g-1)

k1 (min-1)

qe,cal (mg g-1)

R2

k2 (g mg min-1)

OG

87.43

0.0836

50.97

0.9347

4.86×10-3

89.29

0.9989

IC

139.77

0.0774

106.23

0.9879

1.99×10-3

144.93

0.9984

MO

104.63

0.112

63.40

0.9531

7.46×10-3

105.26

0.9994

AR-18

206.35

0.133

316.11

0.9450

1.42×10-3

212.76

0.9988

-1

20


qe,cal (mg g-1)

R2

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Table 2. Isotherm parameters for OG and IC adsorption on AgBr-AgBr/CTAB nanoparticles at 298 K R2

Dye

Model

Parameters

OG

Langmuir

Q0= 91.41 mg g-1 kL=3.47 L mg-1

0.9996

Freundlich

kF =50.20 n =5.15

0.7622

Langmuir

Q0= 139.28 mg g-1 kL=12.60 L mg-1

0.9999

Freundlich

kF =82.93 n =5.62

0.6843

IC

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Figure captions: Figure 1. XRD patterns of sample AgBr-1 and AgBr-2 synthesized by different precursors. Figure 2. SEM images of AgBr-1 with scale bars of (a) 10 µm and (b) 3 µm; SEM images of AgBr-2 with scale bars of (c) 20 µm and (b) 5 µm; TEM images of (e) AgBr-1 and (f) AgBr-2. Figure 3. XPS patterns of AgBr-1and AgBr-2 in (a) Ag 3d, (b) Br 3d, and (c) N 1s spectral regions; (d) FTIR spectra of pure CTAB, AgBr-1 and AgBr-2 nanoparticles; (e) TG curves for CTAB, AgBr-1 and AgBr-2, and (f) DTA curves for CTAB and AgBr-2. Figure 4. (a) The adsorption capacity of various cationic and anionic dyes on the as-prepared AgBr and AgBr-AgBr/CTAB nanoparticles; (b) Recyclability of the AgBr-AgBr/CTAB nanoparticles for the adsorption of AR-18. (Error in the evaluation of adsorption efficiency is less than 1 %.) Figure 5. Adsorption kinetics data of OG, IC, MO and AR-18 on AgBr nanoparticles. Insert: fitting curves for pseudo-second order kinetics. (Error in the evaluation of adsorption efficiency is less than 1 %.) Figure 6. Adsorption isotherms for the adsorption of OG and IC on AgBr-AgBr/CTAB nanoparticles. Insert: Langmuir isotherm model for the adsorption of OG and IC on AgBr-AgBr/CTAB nanoparticles. (Error in the evaluation of adsorption efficiency is less than 1%.) Figure 7. (a) Zeta potential at various pH for AgBr-AgBr/CTAB. (b) The effect of pH on the adsorption capacity of AgBr-AgBr/CTAB toward AR-18 and MB. Figure 8. XPS patterns of anionic dye AR-18 before and after adsorption on AgBr-AgBr/CTAB nanoparticles.

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Figure 1. XRD patterns of sample AgBr-1 and AgBr-2 synthesized by different precursors.

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Figure 2. SEM images of AgBr-1 with scale bars of (a) 10 µm and (b) 3 µm; SEM images of AgBr-2 with scale bars of (c) 20 µm and (b) 5 µm; TEM images of (e) AgBr-1 and (f) AgBr-2.

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Figure 3. XPS patterns of AgBr-1and AgBr-2 in (a) Ag 3d, (b) Br 3d, and (c) N 1s spectral regions; (d) FTIR spectra of pure CTAB, AgBr-1 and AgBr-2 nanoparticles; (e) TG curves for CTAB, AgBr-1 and AgBr-2, and (f) DTA curves for CTAB and AgBr-2.

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Figure 4. (a) The adsorption capacity of various cationic and anionic dyes on the as-prepared AgBr and AgBr-AgBr/CTAB nanoparticles; (b) Recyclability of the AgBr-AgBr/CTAB nanoparticles for the adsorption of AR-18. (Error in the evaluation of adsorption efficiency is less than 1 %.)

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Figure 5. Adsorption kinetics data of OG, IC, MO and AR-18 on AgBr nanoparticles. Insert: fitting curves for pseudo-second order kinetics. (Error in the evaluation of adsorption efficiency is less than 1 %.)

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Figure 6. Adsorption isotherms for the adsorption of OG and IC on AgBr-AgBr/CTAB nanoparticles. Insert: Langmuir isotherm model for the adsorption of OG and IC on AgBr-AgBr/CTAB nanoparticles. (Error in the evaluation of adsorption efficiency is less than 1 %.)

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Figure 7. (a) Zeta potential at various pH for AgBr-AgBr/CTAB. (b) The effect of pH on the adsorption capacity of AgBr-AgBr/CTAB toward AR-18 and MB.

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Figure 8. XPS patterns of anionic dye AR-18 before and after adsorption on AgBr-AgBr/CTAB nanoparticles.

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Facile synthesis of silver bromide-based nanomaterials and their efficient and rapid selective adsorption mechanisms towards anionic dyes Liang Tang,† Jia-jun Wang,† Liang Wang,*,‡ Cheng-tao Jia,† Geng-xin Lv,†,§ Ning Liu, ⊥

and Ming-hong Wu*,†

For Table of Contents Use Only

The as-prepared novel adsorbents exhibited efficient and rapid selected adsorption capacity towards anionic dyes via electrostatic attraction, which supplied proper ways for dye recovery and environmental remediation.

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Facile Synthesis of Silver Bromide-Based Nanomaterials and Their

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