Recyclable Multifunctional Magnetic Mesoporous Silica

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Recyclable Multifunctional Magnetic Mesoporous Silica Nanocomposite for Ratiometric Detection, Rapid Adsorption and Efficient Removal of Hg(II) Yanyan Wang, Meiyao Tang, He Shen, Guangbo Che, Yu Qiao, and Bo Liu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b03040 • Publication Date (Web): 15 Dec 2017 Downloaded from http://pubs.acs.org on December 18, 2017

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ACS Sustainable Chemistry & Engineering

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Recyclable

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Nanocomposite for Ratiometric Detection, Rapid Adsorption

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and Efficient Removal of Hg(II)

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Yanyan Wang,[a,b] Meiyao Tang[a,b], He Shen[c,d], Guangbo Che,*[a,c] Yu

5

Qiao[a,b], and Bo Liu[a,b]

6

[a]

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Friendly Materials, Chinese Ministry of Education, Jilin Normal

8

University, Changchun 130103, P. R. China

9

[b]

Multifunctional

Magnetic

Mesoporous

Silica

Key Laboratory of Preparation and Application of Environmental

College of Chemistry, Jilin Normal University, Siping 136000, P. R.

10

China

11

[c]

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Chinese Ministry of Education, Jilin Normal University, Changchun

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130103, PR China

14

[d]

Key Laboratory of Functional Materials Physics and Chemistry,

College of Physics, Jilin Normal University, Siping 136000, P. R. China

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*Corresponding author. Guangbo Che, E-mail address: [email protected]

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ACS Paragon Plus Environment

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Abstract:

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In this paper, multifunctional inorganic–organic nanocomposites were fabricated

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through encapsulating CdTe quantum dots and Rhodamine 6G-deprived receptor into

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the nonporous and mesoporous shell of the magnetic mesoporous silica

5

nanocomposites. The resultant nanomaterials display an obvious core-shell structure,

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superparamagnetic property, ordered mesoporous characteristics, and highly selective,

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sensitive, and regenerative ratiometric fluorescent sensing performance for

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determination of Hg2+. A good linearity is obtained between IRh6G/IQDs and Hg2+

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concentration (0.7 to 90×10−8 mol•L−1), exhibiting a detection limit as low as 2.5×10-9

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mol•L-1. Moreover, the multifunctional nanocomposites possess acceptable Hg2+

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adsorption capacity and can be simply separated by magnet. Real water sample assays

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further verified its good mercury ion analysis and removal ability. Our results reveal

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that high sensitivity, selectivity, rapid adsorption, efficient removal ability, and good

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reusability as well as better accuracy can be simultaneously achieved by combining

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magnetic mesoporous silica nanocomposite with ratiometric fluorescence sensing

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properties than the traditional intensity-based fluorescence methods. This recyclable

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multifunctional hybrid nanostructure may have great potential for Hg2+ detection and

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removal in environmental, biological, and toxicological areas.

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Key words: Multifunctional, Ratiometric Fluorescence Sensor; Renewable

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Adsorbents; Mercury

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1 2

Introduction As one of the most hazardous and widespread pollutants, mercury arises from

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diverse natural factors and human activities.1,

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capacity for thiol groups in enzymes and proteins, which will result in the dysfunction

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of cells, thus causing health problems in many organs such as kidney, brain, and

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central nervous system.3 Both elemental and ionic mercury, even at very low

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concentration, still can pose severe risks for human health and natural ecosystems.4, 5

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Therefore, exploring of selective, sensitive, reusable, and low cost functional

9

materials to detect and remove Hg2+ is urgently needed for environmental, biological

10

2

Mercury exhibits strong binding

and industrial areas.

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Fluorescent sensors based on small molecule probes are a good choice for the

12

determination of mercury ions because of their high sensitivity and selectivity,

13

low-cost, easy operation, and real-time sensing with fast response time.6 However,

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there are some inevitable limitations for their practical applications, such as poor

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solubility in aqueous solution, easy photobleaching, and difficult to be separated and

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recovered, as well as removal of mercury ion from the sample. In recent years,

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multifunctional hybrid nanocomposites, prepared by the integration of fluorescent

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probes into nanostructured supports, have attracted tremendous interest and emerged

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as promising materials for simultaneously selective detection and efficient removal of

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specific analytes.7 Incorporation of advanced nanomaterials and nanostructures into

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optical Hg2+ probes leads to significant improvement in the performance of sensors in

22

terms

of

sensitivity,

sensitivity,

limit

of

detection,

3


reproducibility,

and


1

multifunctionality.8-10

2

As an important class of advanced nanomaterials, magnetic mesoporous silica

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nanocomposites have received special research interests from variety applications

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such as multimodal imaging, drug delivery, water treatment, and catalysis, 11-14 owing

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to their well-defined magnetic property, large surface area, tailored mesoporous

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characteristics, and tunable pore size and volume. There are some significant

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advantages for grafting organic probes onto magnetic mesoporous silica

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nanocomposites as a sensor and adsorbent.15,16,21 Serving as nanoreactors,

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multifunctional hybrid nanocomposites can accelerate the access and diffusion of

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specific analytes, form an enhanced local concentration nearby probes, and supply the

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amplified target−receptor interface for sensing and adsorption. Furthermore, it is easy

12

to realize low cost and rapid collection, targeting separation, and convenient recycling

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by the magnetic property of multifunctional nanomaterials. In addition, low toxicity

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and favorable biocompatibility make receptor-immobilized magnetic mesoporous

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silica nanocomposites ideal for real sample assays.

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There have been some reports of multifunctional hybrid nanomaterials based on

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magnetic mesoporous silica nanocomposite for fast mercury ions detection and

18

efficient removal, 17-21 and a single intensity-based fluorescence probe was selected by

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most of them as sensing signals. However, only one emission feature sometimes may

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be problematic for precise fluorometric analyses and quantification, which could be

21

also affected by excitation source fluctuation, light scattering of sample matrix,

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microenvironment around the probe, and many other analyte-independent 4


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interferences. Ratiometric fluorescence sensing, which rely on a self-calibration of

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different emission bands through simultaneously measuring two or more sensing

3

signals and calculation of their intensity ratio, is proposed to improve signal-to-noise

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ratio and avoid above unfavorable influences.22,23 Recently, ratiometric sensing with

5

simple structure design has been achieved by arranging two different fluorophores,

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one as the inert reference and the other as sensitive report units, in individual

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positions of a nanomaterial such as silica nanoparticles, MOF, QDs, and polymers.24-27

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Up to now, rare works emphasized in magnetic mesoporous silica nanocomposite with

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ratiometric fluorescence sensing properties. It is expected that combining the merits of

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ratiometric fluorescence detection and magnetic mesoporous silica nanocomposites

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would be very important and promising for solving mercury pollution in practical

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environment.

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Herein, we prepare a rationally-designed multifunctional hybrid nanomaterial by

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immobilizing CdTe quantum dots and Rhodamine 6G-deprived receptor into inner

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and outer shell of the magnetic mesoporous silica nanocomposite for reliable and

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convenient determination, rapid adsorption, and efficient removal of Hg2+. In this

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work, water soluble CdTe QDs and spirolactam Rhodamine 6G derivatives are chosen

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as the reference and Hg2+ receptor for ratiometric sensing. QDs is preferable due to

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the advantages of size-tunable emission, high quantum yield, remarkable Stokes’ shift,

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and insensitive to photobleaching, which could effectively reduce the interference of

21

light source.28 The spirolactam of rhodamine derivatives changed to ring-opening

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state was a well-known process for the selective mercury ion analysis.29 This 5



1

multifunctional hybrid nanocomposite was fully characterized, and its selectivity,

2

sensitivity, reproducibility and absorbability towards Hg2+ were also carefully

3

investigated. The feasibility of the multifunctional hybrid nanocomposites for Hg2+

4

determination and removal in real water samples were further studied. Our results

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reveal that high sensitivity, selectivity, rapid adsorption, efficient removal ability, and

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good reusability as well as better accuracy can be simultaneously achieved by this

7

strategy.

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Experimental Details

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Materials

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Iron chloride hexahydrate, tetraethyl orthosilicate (TEOS), anhydrous sodium acetate,

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(3-Aminopropyl) triethoxysilane (APTES), sodium citrate, hexadecyl trimethyl

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ammonium bromide (CTAB), ethylene glycol, Rhodamine 6G (Rh6G) and all used

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analytical grade solvents were purchased from Aladdin Reagent Co. Ltd. (Shanghai,

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China). Water soluble MPA-capped CdTe-QDs were prepared and purified as depicted

15

in the literature.30 N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride

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(EDC), N-Hydroxysuccinimide (NHS), and phosphate buffer solution (PBS, pH 7.4)

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were purchased from Alfa Aesar. Ammonia solution (28 wt%), concentrated HCl (37

18

wt%), mercury perchlorate trihydrate, and the other metal perchlorate salts were

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purchased from China National Pharmaceutical Group Corporation (Beijing, China).

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The tetrahydrofuran and toluene were treated with desiccant before using. Deionized

21

water was employed in all the aqueous experiment.

22

Synthesis of Magnetite Particles (Fe3O4) 6


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A modified solvothermal reaction was utilized to synthesize the Fe3O4 nanoparticles.31

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FeCl3•6H2O (1.35 g, 5 mmol), NaAc (3.6 g, 44 mmol), sodium citrate (0.40 g, 1 mmol)

3

and ethylene glycol (40 mL) were mixed and vigorously stirred until forming a

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homogeneous solution (deep yellow). Then they were transferred into the autoclave

5

(50 mL), and kept reaction for 16 h at 200 °C. After naturally cooled to ambient

6

temperature, the obtained product was treated by centrifugation, repeated washing

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with deionized water and ethanol, and vacuum drying at 60 °C.

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Synthesis of Magnetic Mesoporous Silica Nanocomposites Encapsulated with

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CdTe QDs (QDs-MMS)

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The QDs-MMS was synthesized as the following procedures: Fe3O4 nanoparticles (50

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mg) were first dissolved in a mixture of deionized water (10 mL), ethanol (40 mL),

12

and ammonia solution (500 µL) under ultrasonication for 30 min. Then add 30 µL

13

TEOS drop wise into the above solution followed by a 6 h reaction at ambient

14

temperature. Subsequently, APTES (200 µL) was put in dropwise, and reacted

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continuously for 24 h. After that, the reaction mixture was centrifuged, and dispersed

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in 2 mL pure water and 20 mL PBS buffer. Then, 2 mL as-prepared CdTe QDs were

17

introduced in the presence of EDC/NHS (5 mL, 1mg•mL-1), and stirred in dark for 8 h.

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The resulting mixture were centrifuged, washed with distilled water, and re-dispered

19

in a solution of deionized water (10 mL), ethanol (40 mL) and ammonia solution (500

20

µL). An outer protective SiO2 layer was formed after 30 µL TEOS was added

21

dropwise into the above solution for a 6 h reaction. Finally, the mesoporous SiO2 layer

22

was coated by dispersing the resulting product in a mixture of ammonia solution (600 7



1

µL), deionized water (40 mL), ethanol (30 mL) and CTAB (0.15 g). After stirring for

2

0.5 h, a dropwise addition of 400 µL TEOS was carried out, and maintained reaction

3

for 6 h. This mesoporous coating repeated twice. An acid extraction process was

4

employed to remove the templating agents CTAB as previous reported procedure. 32

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The final product was centrifuged, washed repeatedly with distilled water and ethanol,

6

and dried in vacuum at 80 °C.

7

Synthesis of Rhodamine 6G-Functionalized Magnetic Mesoporous Silica

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Nanocomposites Encapsulated with CdTe QDs (QDs-MMS-Rh6G).

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Rhodamine 6G (0.5 g) in 50 mL anhydrous THF was mixed with 2.0 mL APTES,

10

refluxed for 6 h. After evaporating the solvent, the obtained solid denoted Rh6G-Si

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was dispered in 50 mL anhydrous toluene together with QDs-MMS (0.5 g), and

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refluxed for 48 h under N2 atmosphere. Then, the suspension was treated by

13

centrifugation and repeated washing with THF and toluene for several times to

14

produce the final product QDs-MMS-Rh6G (in 0.25 g yield).

15

Characterization

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Scanning electronic microscopy (SEM) and transmission electron microscopy (TEM)

17

images of the resultant products were taken by JSM-7800F and JEM2100HR,

18

respectively. X-ray diffraction (XRD) was analyzed on the Rigaku D/max-2500

19

diffractometer with Cu Ka radiation. Frontier Spectrometer was utilized to record

20

Fourier-transform infrared (FT-IR) spectra. Nitrogen adsorption-desorption isotherms

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were performed at 77 K on Autosorb-IQ-C; the calculation model of surface areas and

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pore size distributions and volume was Brunauer–Emmett–Teller (BET) and 8


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Barrett–Joyner–Halenda (BJH). Magnetization measurements data were collected at

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300 K from MPMS3 superconduting quantum interference device. The ratiometric

3

sensing performance of QDs-MMS-Rh6G was measured with a Hitachi F-4600

4

fluorescence spectrophotometer. Typically, multifunctional nanocomposites was

5

dispersed in PBS solution with different Hg2+ concentration, transferred into a quartz

6

cell, and tested at least three times. The adsorption experiments were implemented

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with a suspension of 5 mg QDs-MMS-Rh6G into 10 mL Hg2+ aqueous solution with

8

an initial concentration of 13 to 60 mg•L-1 at room temperature; the adsorption

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equilibrium and efficiency (removal ability) were detected through residual Hg2+ by

10

induced couple plasma atomic emission spectroscopy (ICP), and no additional buffer

11

solution was used during this process.

12

Results and Discussion

13

Synthesis and Characterization of QDs-MMS-Rh6G

14

The fabrication strategy of the functionalized nanomaterial QDs-MMS-Rh6G is

15

represented in Scheme 1. As observed from TEM images, the Fe3O4 nanoparticles had

16

a nearly spherical shape with rough surface and the mean diameter of them was about

17

200 nm (Fig. 1a) Through a modified Stober process, a thin SiO2 layer with amino

18

groups ( ~12 nm) were coated on the surface of Fe3O4 nanoparticles (Fig. 1b), which

19

not only serves as the spacer to provide functional groups for subsequent CdTe

20

coating, but also isolate the decorated QDs from Fe3O4 core to prevent the

21

luminescence quenching.33,34 The coated CdTe nanoparticles have formed a

22

continuous and uniform layer on the surface of the SiO2, and the average thickness is 9



1

about 27 nm (Fig. 1c). Then a thin protective SiO2 layer (∼12 nm in thickness) was

2

coated again in order to increase the structural stability (Fig. 1d).35, 36 Subsequently,

3

we selected CTAB and TEOS as the organic template and silica source to form the

4

mesoporous shell. The well-defined sandwich structure of QDs-MMS can be seen in

5

Fig. 1e, containing a Fe3O4 core, a middle nonporous silica layer encapsulated with

6

CdTe, and an outer mesoporous silica phase. Moreover, the highly open mesopores

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are perpendicular to the surface of nanopheres (Fig. 1f), favorable for the

8

functionalization of Rh6G probes as well as the Hg2+ diffusion and absorption. As

9

revealed by SEM images, QDs-MMS-Rh6G (Fig. 1h) and QDs-MMS (Fig. 1g) has

10

much similar morphological character, indicating that the spherical morphology did

11

not influence by the immobilization of Rh6G probes.

12

As shown in Fig. 2, the wide-angle XRD pattern of prepared Fe3O4 nanoparticles can

13

be identified to a face-centered cubic phase magnetite (JCPDS card No. 01-075-0449)

14

marked as M. QDs-MMS exhibit other two distinct diffraction peaks assigning to the

15

featured crystallographic planes of cubic CdTe (JCPDS card No.15-0770), marked as

16

Q, indicating good crystallinity of CdTe shell. The final QDs-MMS-Rh6G possesses

17

similar diffraction characteristics as the parent Fe3O4 and CdTe nanoparticles,

18

demonstrating that the magnitite and CdTe are well-retained in silica matrix.

19

Incorporation of Rh6G-derived receptors into the synthesized QDs-MMS was proved

20

by FT-IR and fluorescent spectroscopy (see Supporting Information, Fig. S1 and S2).

21

The multifunctional microspheres exhibit characteristic absorptions of methylene and

22

Si−O−Si framework, which originated from Rh6G-Si and the covalent junction with 10


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1

Si-O network.37,38 Compare to QDs-MMS, the multifunctional microspheres depict an

2

obvious fluorescent increase at 545 nm when introducing Hg2+. These results indicate

3

that we have successfully grafted Rh6G-derived probes onto the QDs-MMS.

4

Moreover, we treated QDs-MMS-Rh6G solution by centrifugation on different days,

5

and monitored the fluorescence intensity of the corresponding supernatant. The

6

supernatant exhibited no fluorescence emission, suggesting that no obvious dye and

7

QD leakage occurred because they were grafted covalently onto the silica layer.

8

2D ordered hexagonal mesoporous structure could be confirmed by three resolved

9

diffraction peaks of 100, 110, and 200 in QDs-MMS-Rh6G’s low-angle XRD pattern

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(Fig. 3A). Based on the IUPAC classification39, the QDs-MMS-Rh6G’s N2

11

adsorption-desorption isotherms is found to be type-IV curves (Figure 3B), further

12

proving the existence of mesopores with a narrow size distribution at approximate 2.3

13

nm (inset of Fig. 3B). The pore volume and BET surface area of QDs-MMS-Rh6G

14

are 0.26 cm3•g-1 and 462 m2•g-1. These tailored mesoporous nanostructures do great

15

favor for Hg2+ detection and adsorption.

16

The magnetization measurements for pure Fe3O4 and QDs-MMS-Rh6G powder were

17

carried out at room temperature. As presented in Fig. 4, neither of the Fe3O4 and

18

QDs-MMS-Rh6G display obvious hysteresis, indicating their superparamagnetic

19

features. The saturation magnetization for Fe3O4 and QDs-MMS-Rh6G were found to

20

be 70.5 and 23.5 emu•g-1, respectively. Our multifunctional nanocomposites can give

21

a fast response to external magnetic field, direct towards specific locations, and

22

rapidly achieve homogeneous dispersion through a slight shake (Fig. 4 inset), which 11



1

enables QDs-MMS-Rh6G suitable for quick and easy separation.

2

Ratiometric Sensing Performance of QDs-MMS-Rh6G towards Hg2+

3

The ratiometric sensing performance of prepared multifunctional nanocomposites

4

were evaluated by measuring their fluorescence as function of different Hg2+

5

concentration, as shown in Fig. 5A. The emission spectrum of QDs-MMS-Rh6G

6

without Hg2+ only exhibits the luminescence of CdTe QDs at around 625 nm (λex =

7

365 nm). After the addition of Hg2+, a distinct Rh6G emission peak at 545 nm

8

appeared and dramatically enhanced with the increasing Hg2+ concentration. The

9

fluorescence quenching of rhodamine moiety in the free state could be ascribed to a

10

spirolactam structure; upon complexation with Hg2+, the spirolactam of Rh6G-derived

11

receptor conversed into a ring-opening structure, causing the recovery of

12

fluorescence30, 40. During the sensing process, the luminescence intensity of CdTe

13

QDs hardly changes, which means that nonporous silica shell can give good protect

14

for the encapsulated QDs, and make their luminescence stable enough to be reference

15

signal. Thus, we can take use of these two fluorescence signals’ ratio as detection

16

index to effectively minimize those analyte-independent interferences. Based on this

17

strategy, a working curve has been established between I545/I625 and Hg2+

18

concentration ranging from 0.7 to 90×10-8 mol•L-1, showing a good linearity with the

19

linearly dependent coefficient R2 of 0.9986 (Fig. 5B). Under optimized conditions, the

20

detection limit of QDs-MMS-Rh6G for Hg2+ is as low as 2.5×10-9 mol•L-1, adequate

21

for high-sensitivity Hg2+ determination.41

22

The selectivity of QDs-MMS-Rh6G toward Hg2+ is highly-demand for practical 12


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1

determination, so selectivity experiments were expanded for variety competing ionic

2

species, such as other heavy metal ions (Pb2+, Ag+ and Cu2+) often quenching the

3

QDs’ luminescence 42,43 some transition metal ions (Ni2+, Zn2+, Cr2+, Mn2+ and Co2+),

4

and some abundant cellular cations (K+, Mg2+, Na+, and Ca2+). It can be observed

5

from Fig. 6 that only the addition of Hg2+ will induce a significant increase in

6

fluorescence ratio comparing to the blank counterpart, whereas very slight or even no

7

changes happened to the other metal ions, as represented by red bars. Moreover, the

8

ratiometric sensing process of QDs-MMS-Rh6G for Hg2+does not be interfered when

9

coexistence with the chosen competing ionic species, as represented by green bars.

10

These results indicate that the multifunctional nanocomposites can realize highly

11

selective Hg2+ ratiometric detection and be avoiding interferences from some common

12

quenchers for QDs.

13

The operational pH range was also investigated for Hg2+ detection procedures.

14

Fluorescence ratios I545/I625 of QDs-MMS-Rh6G without and with addition of Hg2+

15

versus pH values are presented in Supporting Information, Fig. S3. The appropriate

16

pH scope for Hg2+ determination is found to be between pH 5.0 and 9.0. In this region,

17

a prominent increment in intensity ratio of fluorescence could be induced by Hg2+,

18

and it remained fairly stable, suggesting that QDs-MMS-Rh6G can be applied in

19

physiological and environmental situations.

20

Regeneration Ability of QDs-MMS-Rh6G

21

The recyclability of QDs-MMS-Rh6G after determination of Hg2+ (10µM) is

22

estimated by repeated detection/reuse cycles, and the operating protocol is shown in 13



Page 14 of 39

1

Scheme 1. We recorded the changes of fluorescence ratio I545/I625 after each step, and

2

the corresponding results are in Fig. 7. After being dispersed in Hg2+ solution, the

3

fluorescence emission of QDs-MMS-Rh6G at 545 nm could be fully recovered

4

through eluting with 100 equiv of KI, which could be attributing to the stronger

5

Hg2+-binding capability of the iodide anion, thus leading to the spirolactam structure

6

of Rh6G-derived receptor close again, and fluorescence disappeared. 44 When treated

7

QDs-MMS-Rh6G was re-dispersed to the solution, Hg2+ reacted with the spirolactam

8

causing the ring-open state take place again, and fluorescence reproduced. This

9

phenomenon is reproducible, and sensitivity of QDs-MMS-Rh6G for Hg2+ still keeps

10

high level after 8-time recycling. More importantly, such recovery response can be

11

completed within a few seconds. These results prove that QDs-MMS-Rh6G has

12

excellent regeneration ability.

13

Adsorptive Capacity of QDs-MMS-Rh6G

14

We have also investigated the adsorptive capability of QDs-MMS-Rh6G to access

15

their practicability as an Hg2+ absorbent. First, the calculation of adsorption capacity

16

were executed on the basis of equation (1) by researching the mass balance of

17

Hg2+,45-47 where Ce and C0 stand for the equilibrium and initial Hg2+ concentrations

18

(mg•L-1), V represents for the solution volume (L), M corresponds to the mass of

19

QDs-MMS-Rh6G (g), and qe means the QDs-MMS-Rh6G ‘s equilibrium adsorption

20

capacity (mg•g-1).

21

(1)

14


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1

The sorption dynamic curve of QDs-MMS-Rh6G with initial Hg2+ concentration at 60

2

mg•L-1 is presented in Fig. 8A. The adsorption of Hg2+ by QDs-MMS-Rh6G is found

3

to be a rapid process, attributing to the tailored mesoporous structure and the high

4

Hg2+-binding ability of Rh6G-derived probe, and their maximum Hg2+ adsorption

5

capacity is 17.7 mg•g-1. Furthermore, the adsorption equilibrium data acquired by

6

calculation at different initial concentrations of Hg2+ can be well fitted and interpreted

7

by the Langmuir sorption isotherm equation (2),48-50 with a correlation coefficient

8

value R of 0.9996, as shown in Fig. 8B, where qe, Ce, b and qm are representive of the

9

equilibrium adsorption capacity (mg•g-1), equilibrium concentration of Hg2+ (mg•L-1),

10

adsorption equilibrium constant (L•mg-1), and maximum adsorption capacity (mg•g-1),

11

respectively. （2）

12 13

The calculation results of qm and b are 17.72 mg•g-1 and 4.91 L•mg-1. The acceptable

14

adsorption capacity indicates that QDs-MMS-Rh6G can be used as a good adsorbent

15

for Hg2+.

16

Application on Real Sample Analysis

17

To demonstrate the practicability of QDs-MMS-Rh6G, the detection performance of

18

Hg2+ was evaluated in real water samples. The corresponding optical response

19

(I545/I625) was compared with the standard working plot, and the results were

20

summarized in Table1. The concentration of Hg2+ in real water sample can be simply

21

and accurately detected by our proposing strategy. It was found that the detected Hg2+ 15



Page 16 of 39

1

concentration obtained from working plot was in good agreement with those standard

2

addition concentrations, and the quantitative recoveries of Hg2+ are ranged from

3

97.6 % to 102.3 %, indicating that the accuracy of QDs-MMS-Rh6G is satisfactory.

4

The removal ability of QDs-MMS-Rh6G is also estimated to further assess its

5

feasibility. We treated a certain amount of Hg2+ solution (3×10−5 M, 50 mL) with a

6

certain mass of QDs-MMS-Rh6G (~30 mg) for a moment. Then the solution was

7

centrifuged by a magnet, and the residual Hg2+ in the supernatant was analyzed by ICP.

8

After treatment, there was no detectable concentration of Hg2+ in the supernatant,

9

revealing the effective Hg2+ removal ability of our well-designed QDs-MMS-Rh6G

10

Conclusion

11

In summary, we rationally design and fabricate multifunctional hybrid nanomaterial

12

by integrating reference unit CdTe QDs and report unit Rh6G with core-shell

13

magnetic mesoporous silica nanocomposites. The well-designed nanocomposites can

14

recognize Hg2+ through a highly selective and sensitive ratiometric fluorescence

15

sensing process, and their detection limit are found to be 2.5×10-9 mol•L-1. The

16

ratiometric fluorescence response is reversible and steady in a wide pH scope. The

17

obtained nanocomposites possess strong superparamagnetic features, showing facile

18

separability and excellent reusability. Furthermore, QDs-MMS-Rh6G has an

19

acceptable adsorption capacity for rapid and effective Hg2+ removal. This hybrid

20

nanomaterial was also applicable for real water sample assays. Thus, our recyclable

21

multifunctional

22

chemosensor and absorbent for environmental restoration.

nanostructure

offers

great

promising

16


as

high-performance

Page 17 of 39 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


1

Supporting Information Available:

2

FT-IR spectra of Rh6G-Si and QDs-MMS-Rh6G. The fluorescent spectroscopy of

3

QDs-MMS and QDs-MMS-Rh6G with and without Hg2+. The pH effect on the

4

fluorescence ratio for QDs-MMS-Rh6G with and without Hg2+. Comparison of

5

different methods for Hg2+ detection and removal.

6

Acknowledgments.

7

This work is supported by the National Natural Science Foundation (No. 21576112,

8

61705078 and 61704065) and Natural Science Foundation Project of Jilin Province

9

(No. 20150623024TC-19 and 20150520006JH).

17



1

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3 4

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1

Figure Captions

2

Scheme 1. Fabrication Strategy of the functionalized material QDs-MMS-Rh6G and

3

Treatment and reuse for mercury ion solution

4

Figure

5

Fe3O4@SiO2@CdTe, (d) Fe3O4@SiO2@CdTe@SiO2, (e) QDs-MMS and (f) its

6

magnified view; SEM images of (g) QDs-MMS and (h) QDs-MMS-Rh6G.

7

Figure 2. The wide-angle XRD patterns of (a) Fe3O4 nanoparticles, (b) QDs-MMS,

8

and (c) QDs-MMS-Rh6G.

9

Figure 3. (A) The low-angle XRD pattern of QDs-MMS-Rh6G, and (B) The nitrogen

10

adsorption-desorption isotherms of QDs-MMS-Rh6G and its pore size distribution

11

(inset).

12

Figure 4. The magnetic hysteresis loops of Fe3O4 (black line),and QDs-MMS-Rh6G

13

(red line), and the separation-recovery process of QDs-MMS-Rh6G (inset).

14

Figure 5. (A) Fluorescence spectra of QDs-MMS-Rh6G (20 mg•L-1) upon addition of

15

various amounts of Hg2+, and (B) Fluorescence ratio (I545/I625) of QDs-MMS-Rh6G as

16

a function of the Hg2+ concentration in the range of 0.7 to 90×10-8 mol•L-1. Excitation

17

at 365 nm.

18

Figure 6. Variations of QDs-MMS-Rh6G’s fluorescence ratio to various interfering

19

ions. The red bars represent the fluorescence ratio of QDs-MMS-Rh6G in the absence

20

(Blank) and presence of various interfering ions (all at 10-3 M). The green bars

21

represent the change of fluorescence ratio that occurs upon the subsequent addition of

22

10-6 M of Hg2+ to the above solution. Excitation at 365 nm.

1.

TEM

images

of

(a)

Fe3O4 particles,

27


(b)

Fe3O4@SiO2,

(c)


1

Figure 7. Fluorescence ratio changes of QDs-MMS-Rh6G (20 mg•L-1) by alternately

2

dispersing in 10 µM Hg2+ solution, and eluting with 100 equiv of KI. The cyclic index

3

is the number of alternating dispersing/eluting cycles.

4

Figure 8. (A) The adsorption kinetic curve of QDs-MMS-Rh6G for Hg2+, and (B)

5

Langmuir adsorption isotherm for Hg2+ by QDs-MMS-Rh6G.

6

Table 1. Determination of Hg2+ in real water sample.

7 8

28


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1

Scheme 1. Fabrication strategy of the functionalized material QDs-MMS-Rh6G and

2

treatment and reuse for mercury ion solution.

3 4 5

29



Page 30 of 39

1

Figure

2

Fe3O4@SiO2@CdTe, (d) Fe3O4@SiO2@CdTe@SiO2, (e) QDs-MMS and (f) its

3

magnified view; SEM images of (g) QDs-MMS and (h) QDs-MMS-Rh6G.

1.

TEM

images

of

(a)

Fe3O4 particles,

4 5 6 7 8

30


(b)

Fe3O4@SiO2,

(c)

Page 31 of 39 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


1 2

Figure 2. The wide-angle XRD patterns of (a) Fe3O4 nanoparticles, (b) QDs-MMS,

3

and (c) QDs-MMS-Rh6G.

4 5 6

31



1 2

Figure 3. (A) The low-angle XRD pattern of QDs-MMS-Rh6G, and (B) The nitrogen

3

adsorption-desorption isotherms of QDs-MMS-Rh6G and its pore size distribution

4

(inset). 5

(A) 6

7 8 9

(B)

32


Page 32 of 39

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1

Figure 4. The magnetic hysteresis loops of Fe3O4 (black line), and QDs-MMS-Rh6G

2

(red line), and the separation-recovery process of QDs-MMS-Rh6G (inset).

3 4

33



1 2

Figure 5. (A) Fluorescence spectra of QDs-MMS-Rh6G (20 mg•L-1) upon addition of

3

various amounts of Hg2+, and (B) Fluorescence ratio (I545/I625) of QDs-MMS-Rh6G as

4

a function of the Hg2+ concentration in the range of 0.7 to 90×10-8 mol•L-1. Excitation

5

at 365 nm. 6

(A) 7

8 9

(B)

34


Page 34 of 39

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1

Figure 6. Variations of QDs-MMS-Rh6G’s fluorescence ratio to various interfering

2

ions. The red bars represent the fluorescence ratio of QDs-MMS-Rh6G in the absence

3

(Blank) and presence of various interfering ions (all at 10-3 M). The green bars

4

represent the change of fluorescence ratio that occurs upon the subsequent addition of

5

10-6 M of Hg2+ to the above solution. Excitation at 365 nm.

6

7 8

35



1

Figure 7. Fluorescence ratio changes of QDs-MMS-Rh6G (20 mg•L-1) by alternately

2

dispersing in 10 µM Hg2+ solution, and eluting with 100 equiv of KI. The cyclic index

3

is the number of alternating dispersing/eluting cycles.

4

5 6 7 8

36


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1

Figure 8. (A) The adsorption kinetic curve of QDs-MMS-Rh6G for Hg2+, and (B)

2

Langmuir adsorption isotherm for Hg2+ by QDs-MMS-Rh6G. 3

(A)4 5 6

(B)

37



Page 38 of 39

1 2

Table 1. Determination of Hg2+ in real water sample. initial ± SD

Added

Found ± SD *

Relative Recovery

RSD

（10-7 mol•L-1）

（10-7 mol•L-1）

（10-7 mol•L-1）

（%））

（%））

0

2

2.03±0.033

101.5

1.6

0

5

4.88±0.134

97.6

2.7

0

8

8.06±0.145

100.7

1.8

0

2

1.98±0.073

99.0

3.8

0

5

5.02±0.057

100.4

1.1

0

8

8.19±0.189

102.3

2.3

Samples

Deionized water

Tap water

* Relative standard deviations were calculated with n=5.

3 4

38


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1

For Table of Contents Use Only

2 3 4 5 6

Well-designed recyclable QDs-MMS-Rh6G can simultaneously achieve ratiometric

7

detection, rapid adsorption and efficient removal of Hg(II), in favor for environmental

8

sustainability.

9

39


Recyclable Multifunctional Magnetic Mesoporous Silica

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