A new strategy for fuel desulfurization by molecular inclusion with

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A new strategy for fuel desulfurization by molecular inclusion with copper(II)-#-cyclodextrin@SiO2@Fe3O4 for removing thiophenic sulfides Zunbin Duan, Xuechun Ding, Yan Wang, Lijun Zhu, and Daohong Xia Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02886 • Publication Date (Web): 28 Sep 2018 Downloaded from http://pubs.acs.org on September 29, 2018

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Energy & Fuels

A new strategy for fuel desulfurization by molecular inclusion with copper(II)-β-cyclodextrin@SiO2@Fe3O4 for removing thiophenic sulfides Zunbin Duan a,b, Xuechun Ding b, Yan Wang a,b, Lijun Zhu a and Daohong Xia* a,b a

State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, People’s

Republic of China. b

College of Chemical Engineering, China University of Petroleum, Qingdao 266580, People’s Republic of

China. *Corresponding author. Tel.: +8653286981869; fax: +8653286981787. E-mail address: [email protected].

Abstract：：Developing a new and environment-friendly desulfurization strategy for removing thiophenic sulfides from fuel is necessary nowadays. Fuel desulfurization by molecular inclusion

with

a

novel

cyclodextrin-based

copper(II)-β-cyclodextrin@silica@ferroferric

oxide

magnetic

nanomaterial

(Cu(II)-β-CD@SiO2@Fe3O4)

was

proposed for the efficient removal of thiophene (T), benzothiophene (BT) and dibenzothiophene (DBT) in fuel. Cu(II)-β-CD@SiO2@Fe3O4 was successfully prepared by the

reaction

between

3-aminopropyltrimethoxysilane

mono-6-O-toluenesulfonyl-Cu(II)-β-CD functionalized

SiO2@Fe3O4,

and

the

and structural

characterization illustrated that the active desulfurization component Cu(II)-β-CD was evenly immobilized on the surface of SiO2@Fe3O4. Furthermore, Cu(II)-β-CD@SiO2@Fe3O4 showed an outstanding desulfurization performance for thiophenic sulfides in the order of BT > DBT > T on account of the different molecular inclusion ability of Cu(II)-β-CD for the three types of thiophenic sulfides. The optimum immobilized load of Cu(II)-β-CD in Cu(II)-β-CD@SiO2@Fe3O4 was 5m%, and room temperature was favor for the desulfurization process. Cu(II)-β-CD@SiO2@Fe3O4 has a good regeneration performance. The inclusion interaction between Cu(II)-β-CD and sulfides plays a more dominant role than the coordination interaction of Cu(II) with sulfide and the physical absorption during the desulfurization process. The thiophenic sulfides mainly entered the hydrophobic cavity of Cu(II)-β-CD rather than be adsorbed on the surface of Cu(II)-β-CD@SiO2@Fe3O4. The

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results lay the foundation of desulfurization with supramolecular magnetic materials, which is significant for environmental protection and resource saving.

Key words: Copper(II)-β-cyclodextrin magnetic nanomaterial; molecular inclusion; desulfurization; benzothiophene


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1. Introduction Organic sulfur compounds in fuel can cause environmental pollution and threaten human's health. The main forms of organic sulfur in fuel

1

are mercaptan, sulfide, disulfide and

thiophene. Among organic sulfides in fuel, thiophenic sulfide accounts for about 60% ~ 70% 2, which is difficult to remove by the traditional methods including adsorption 12-14

3-11

, oxidation

and extraction 15, 16, even by the hydrogenation method without affecting the property of

fuel. The traditional nonhydrogenation methods typically have moderate operating conditions and low cost. But there are some insurmountable drawbacks for the nonhydrogenation methods. Adsorption desulfurization 8 has low selectivity for the similar polarity of molecules with and without sulfur, and the adsorbents easily adsorb olefin and aromatics (high-octane components) in fuel. Oxidation and extraction methods

13

are usually used together for fuel

desulfurization, and the organic acids generated in the desulfurization process are partially dissolved in fuel, which affects the production of fuel. In addition, hydrodesulfurization

9

is

difficult to achieve deep desulfurization without reducing the octane number of fuel. Therefore, it is necessary to seek a new and environment-friendly desulfurization method 17-19 for removing the thiophenic sulfides from fuel and producing clean fuel. Recently, a new desulfurization method based the molecular inclusion of cyclodextrin (CD) has been came forward by our group polymers (CDPs)

21

20, 21

. β-CD aqueous solution

20

and cyclodextrin

were used into the desulfurization process of fuel for the first time.

However, the performance of β-CD aqueous solution was unsatisfactory with low desulfurization efficiency. CDPs had a good desulfurization performance for thiophenic sulfides. But the separation of CDPs was difficult to handle during the desulfurization process because of the similar density of CDPs and fuel. To overcome the disadvantages of separation in the desulfurization process, magnetic separation as a rapid and effective method great

attention

in

recent

22

years.

heteropolyacid-functionalized SiO2@Fe3O4

by using magnetic materials

Magnetic

composite

28

23-27

has been paid

materials,

such

as

29

and

, AgNO3-functionalized SiO2@Fe3O4

ionic liquid-functionalized SiO2@Fe3O4 25, have been widely used to enhance the separation


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efficiency. But until now, cyclodextrin-functionalized SiO2@Fe3O4 has not been reported for the desulfurization of fuel through molecular inclusion yet. Cu(II)-β-CD, a dinuclear cyclodextrin metal complex

30, 31

, consists of β-CD with

molecular inclusion cavity and copper(II) species with coordination metal center. It is expected that Cu(II)-β-CD has higher desulfurization performance for thiophenic sulfides. In this paper, three types of functionalized magnetic composite desulfurizers, including Cu(II)-β-CD@SiO2@Fe3O4,

β-CD@SiO2@Fe3O4

and

Cu(II)@SiO2@Fe3O4,

were

synthesized to comparatively study the removal efficiency of thiophenic sulfides in the desulfurization process. The desulfurization conditions, selectivity and regeneration of Cu(II)@SiO2@Fe3O4

were

studied.

The

desulfurization

mechanism

of

Cu(II)-β-CD@SiO2@Fe3O4 was proposed based on the desulfurization and characterization results in the end.

2. Experimental section 2.1. Materials and Characterizations β-Cyclodextrin (β-CD, > 98%), NaOH (99%), CuSO4·5H2O (> 98%), FeCl3·6H2O (> 99%), FeCl2·4H2O (> 99%), ethanol (> 99%), ammonia (25 ~ 28 m%, > 99%), tetraethoxysilane (TEOS, 99%), 3-aminopropyltrimethoxysilane (APTMS, 99%), toluene (> 99%), p-toluene sulfonyl chloride (>99%), KI (99%), N-methyl pyrrolidone (NMP, > 99%), n-heptane (> 99%) and activated carbon powder (labelled as 1#AC, about 200 mesh) were purchased from Sinopharm Chemical Reagent Co. Ltd.. Thiophene (T, 99%), benzothiophene (BT, 99%), dibenzothiophene (DBT, 99%) and n-octylthiol (> 98%) were purchased from Sigma-Aldrich Inc.. Two granular activated carbons (KC-16A，6 ~12 mesh，labelled as 2#AC；GAC， 6 ~12 mesh，labelled as 3#AC) were purchased from Beijing Guang-Hua wood factory and Hainan Shuang-xin Long industrial and trade Co. Ltd., respectively. β-CD was recrystallized three times with deionized water (>18.25 MΩ·cm) before use, while other reagents were used without further purification. Characterization of the functionalized magnetic desulfurizers was carried out by using


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Fourier transform infrared spectroscopy(FT-IR, Nicolet 6700 Fourier transform infrared spectrophotometer), X-ray diffraction(XRD, Panalytical X’Pert Pro MPD diffractometer), thermogravimetric (TG, Linseis STA PT1600 analyzer) analysis, BET surface area (NOVA 2200e absorption analyzer), vibratiing sample magnetometry (VSM, Lake Shore 7410 vibrating sample magnetometer), scanning electron microscopy (SEM, Hitachi S-4800 scanning electron microscope), transmission electron microscopy (TEM, JEM-2100UHR transmission electron microscope), inductively coupled plasma-atomic emission spectroscopy (ICP-AES, ICAP-6300 analyzer), and X-ray photoelectron spectroscopy (XPS, PHI 5000 Versa Probe spectrometer).

Figure 1. (A) Preparation process of Cu(II)-β-CD@SiO2@Fe3O4; (B) molecular structures and sizes of Cu(II)-β-CD (structural formula 32, analytical structure) and thiophenic sulfides.

2.2.

Synthesis

of

Cu(II)-β-CD@SiO2@Fe3O4,

β-CD@SiO2@Fe3O4

and

Cu(II)@SiO2@Fe3O4 2.2.1. Synthesis of Cu(II)-β-CD@SiO2@Fe3O4 The synthetic route of Cu(II)-β-CD@SiO2@Fe3O4 was shown in Figure 1(A). Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) were prepared by chemical co-precipitation


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method 30, 33. Typically, FeCl3·6H2O (4.40 g, 16.3 mmol) and FeCl2·4H2O (1.60 g, 8.0 mmol) were dissolved in deionized water (100 mL) under N2 (10 mL·min-1) by vigorous mechanical stirring (1000 rpm) at 80 oC. The pH of the solution was adjusted to 9 with conc. NH3·H2O (25 ~ 28 m%, 7 mL), and there was a black solid formation immediately. After continuous stirring for 4 h, the formed black solid was collected with a magnet when the reaction liquid cooled to room temperature and centrifugal washed (3500 rpm, 10 min) by anaerobic water (100 mL × 3), anhydrous ethanol (20 mL × 4) in order. Finally, the black solid was dried for 12 h at 50 oC in a vacuum oven to give Fe3O4 MNPs (1.76 g, 95% yield). To prepare silica-coated Fe3O4 nanoparticles, Fe3O4 (0.80 g) was ultrasonically dispersed (40 KHz, 500 W) for 30 min in ethanol (100 mL), and then conc. NH3·H2O (3.00 mL) and TEOS (1.00 mL) were immediately added. After vigorous stirring with a rate of 1000 rpm at 30 oC for 24 h, the brownish black nanoparticles (SiO2@Fe3O4) were collected with a permanent magnet, centrifugal washed (3500 rpm, 10 min) by using ethanol (20 mL × 4) and dried to constant weight. SiO2@Fe3O4 (1.12 g) was obtained as a brownish black powder. Amino-functionalized SiO2@Fe3O4 was prepared by the surface functionalization of SiO2@Fe3O4 by using APTMS as the silane coupling agent. SiO2@Fe3O4 (0.80 g) was mixed with toluene (80 mL) by ultrasonic dispersion for 30 min, and then APTMS (3.46 mL, 15 mmol) was added dropwise over 5 min. This reaction system was kept at 90 oC for 12 h under N2 (10 mL·min-1) with vigorous stirring of 1000rpm. The light-brown amino functionalized SiO2@Fe3O4 (APTMS-SiO2@Fe3O4) was obtained by magnetic separation, then washed with ethanol (20 mL × 3) and acetonitrile (20 mL × 4) in turn. Finally, the light-brown solid was dried for 12 h at room temperature under vacuum to give APTMS-SiO2@Fe3O4 (2.65 g). The synthesis of active desulfurization component Cu(II)-β-CD was as follows. 0.5 mol·L-1 NaOH aqueous solution (50 mL, 25 mmol) and β-CD (1.1350 g, 1 mmol) was placed in a 250 mL flask, stirred to dissolve β-CD. 0.04 mol·L-1 CuSO4 aqueous solution (75 mL, 3 mmol) was then immediately added. The reaction liquid immediately became dark-blue, and a blue precipitation was emerged simultaneously. After stirring (500 rpm) at 30 oC for 6 h, the solution was filtered to remove the blue precipitation. Whereafter, ethanol (400 mL) was


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added into the blue filtrate, then a light-blue suspension was formed, which was filtered. The residue was washed with ethanol and dried at 35 oC in a vacuum oven to give Cu(II)-β-CD (1.16 g, 92% yield) as a light-blue power. MS (MALDI-TOF, Bruker MALDI TOF mass spectrometer; Figure S1(A)), m/z：Calc. 1256.198; Found 1256.408 [M]+. 1H NMR (400 MHz, DMSO; Bruker AVANCE III 400 MHz spectrometer; Figure S1(B)) (δ: ppm): 5.97 – 5.48 (d, 10 H, OH-2,3), 5.00 – 4.70 (s, 7 H, H-1), 4.54 – 4.27 (s, 7 H, OH-6), 3.72 – 3.50 (d, 14 H, H-3,6), 3.50 – 3.40 (m, 7 H, H-5), 3.39 – 3.02 (s, 52 H(overlaps with HOD), H-2,4). Mono-6-O-toluenesulfonyl-copper(II)-β-cyclodextrin

(m-6-TsO-Cu(II)-β-CD)

was

prepared as follows. Cu(II)-β-CD (6.9450 g, 5 mmol) was dissolved in 1 m% NaOH aqueous solution (50 mL), and the color of the solution changed to light-blue immediately. A solution of p-toluene sulfonyl chloride (0.9527 g, 5 mmol) in ethanol (2 mL) was added into the above solution dropwise over 10 min, causing the formation of a light blue precipitation. After stirring (500 rpm) at 30 oC for 2 h, the liquid was refrigerated for 24 h under 4 ± 1 oC. The light-blue precipitate was obtained through suction filtration and recrystallized three times with hot water. Finally, the solid was dried at 40

o

C under vacuum to give

m-6-TsO-Cu(II)-β-CD (2.85 g, 37% yield) as a light-blue power. MS (MALDI-TOF), m/z： Calc. 1410.214; Found 1410.289 [M]+. 1H NMR (400 MHz, DMSO) (δ: ppm): 7.52(d, J= 7.9 Hz, 2 H, ArH), 7.16(d, J= 7.9 Hz, 2 H, ArH), 5.94 – 5.51 (d, 10 H, OH-2,3), 4.98 – 4.74 (s, 7 H, H-1), 4.52 – 4.27 (s, 6 H, OH-6), 3.72 – 3.41 (m, 21 H, H-3,5,6), 3.39 – 3.00 (s, 70 H(overlaps with HOD), H-2,4), 2.30(s, 3 H, CH3). MALDI-TOF MS and 1H NMR spectrum of m-6-TsO-Cu(II)-β-CD were shown in Figure S2. Magnetic desulfurization supramolecular nanomaterial Cu(II)-β-CD@SiO2@Fe3O4 with different immobilized load of Cu(II)-β-CD (1, 3, 5 and 10 m%, labeled as Cu(II)-β-CD@SiO2@Fe3O4-1, Cu(II)-β-CD@SiO2@Fe3O4-3, Cu(II)-β-CD@SiO2@Fe3O4-5 and Cu(II)-β-CD@SiO2@Fe3O4-10, respectively) was synthesized. The typical preparation route, for example, when the immobilized loading content of Cu(II)-β-CD is 5 m%, is as follows. The synthesized APTMS-SiO2@Fe3O4 (0.95 g), m-6-TsO-Cu(II)-β-CD (0.06 g) and KI (0.01 g) were placed in NMP (50 mL), and the reaction system was ultrasonically


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dispersed for 30 min under N2 (10 mL·min-1). And then, the suspension was heated to 70 oC with vigorous stirring (1000 rpm) for 6 h under N2 (10 mL·min-1). After cooling to room temperature, the brown substance (Cu(II)-β-CD@SiO2@Fe3O4) was acquired by magnetic separation, washed with ethanol (25 mL × 3) and dried at 40 oC under vacuum. The Cu content of Cu(II)-β-CD@SiO2@Fe3O4 was measured by the ICAP-6300 analyzer in a HCl solution. 2.2.2 Synthesis of β-CD@SiO2@Fe3O4 M-6-TsO-β-CD (21% yield) as a white power was synthesized by reacting β-CD with p-toluene sulfonyl chloride according to the synthetic procedure of m-6-TsO-Cu(II)-β-CD. MS (MALDI-TOF; Figure S3(A)), m/z：Calc. 1288.394; Found 1288.298 [M]+, 1311.209 [M+ Na]+. 1H NMR (400 MHz, DMSO; Figure S3(B)) (δ: ppm): 7.56(d, J= 7.2 Hz, 2 H, ArH), 7.17(d, J= 7.2 Hz, 2 H, ArH), 5.77 – 5.65 (d, J= 3.6 Hz, 14 H, OH-2,3), 4.83 (d, J= 3.6 Hz, 7 H, H-1), 4.46 (t, J= 5.6 Hz, 6 H, OH-6), 3.63(pd, J= 12.1, 6.1 Hz, 21 H, H-3,5,6), 3.60 – 3.51 (m, 7 H, H-2), 3.40 – 3.25 (m, 7 H, H-4), 2.32(s, 3 H, CH3). Depending on the synthetic procedure of Cu(II)-β-CD@SiO2@Fe3O4-5 in the Part of 2.2.1, β-CD@SiO2@Fe3O4 as a brownness power was prepared by using m-6-TsO-β-CD and APTMS-SiO2@Fe3O4. The FT-IR spectrum and XRD pattern of β-CD@SiO2@Fe3O4 were shown in Figure S4. 2.2.3. Synthesis of Cu(II)@SiO2@Fe3O4 APTMS-SiO2@Fe3O4 (0.95 g) and CuSO4·5H2O (0.20 g) were mixed in isopropanol (50 mL) and vigorously stirred (1000 rpm) at 30 oC for 12 h. The color of the solution (blue) was gradually disappeared in the reaction process, which showed that Cu(II) was successfully loaded on the surface of APTMS-SiO2@Fe3O4. The solid was obtained through magnetic separation, washed with ethanol and dried under 50 oC under vacuum. Cu(II)@SiO2@Fe3O4 (0.99 g) was obtained as a brownness power. The structural characterization of Cu(II)@SiO2@Fe3O4 were offered in Figure S5 of the Supporting Information. Without special instructions, the loading content of active component Cu(II)-β-CD, β-CD and

Cu(II)

is

5

m%

on

Cu(II)-β-CD@SiO2@Fe3O4,

Cu(II)@SiO2@Fe3O4, respectively.


β-CD@SiO2@Fe3O4

and

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2.3. Desulfurization experiments Typically, the simulated oil containing 100 µg·g-1 sulfur was prepared by mixing different sulfide (T, BT or DBT) with n-heptane. The desulfurizer was dried at 80 °C for 2 h before the desulfurization experiment. The typical process of desulfurization was as follows. The desulfurizer was stirred with a stirring rate of 500 rpm in simulated oil at 30 oC with the mass ratio of desulfurizer to oil controlled as 1:20 (desulfurizer, 0.50 g). The sulfur concentration of the simulated oil at different time was measured by the ANTEK 9000 NS analyzer (ultraviolet fluorescence method; linear response range, 1 ~ 100 µg·mL-1; auto-injection volume, 10 µL; sufur modular, P/N 95822, 95820; oxidative furrance temperature, 1050 oC), and the removal percentage was calculated by the following equation, Removal percentage (%) = [ (S0 - St) / S0 ]×100

(1)

where S0 (µg·g-1) is the initial sulfur concentration in simulated oil, and St (µg·g-1) is the remaining sulfur concentration in simulated oil at time t. For evaluating the regeneration performance of Cu(II)-β-CD@SiO2@Fe3O4, the used Cu(II)-β-CD@SiO2@Fe3O4 was rapidly separated by magnetic separation, mixed with fresh petroleum ether (60 ~ 90 oC; m: m = 1: 50) under mechanical stirring of 500 rpm at 90 oC for 30 min, and repeated three times. And then the regenerated Cu(II)-β-CD@SiO2@Fe3O4 was reused in the desulfurization experiments for removing BT from the simulated oil.

3. Results and discussion 3.1. Material Characterizations FT-IR analysis

34

was carried out to verify the binding of Cu(II)-β-CD on the surface of

SiO2@Fe3O4 MNPs in the synthetic process. As shown in Figure 2(A), the absorption band at about 586 cm-1 is assigned to the magnetite Fe-O bond in Fe3O4. From the FT-IR spectra of SiO2@Fe3O4 and APTMS-SiO2@Fe3O4, the bending vibration peaks of SiO2

35, 36

at 1220,

1094, 804 and 471 cm-1 reveal that SiO2 was successfully achieved immobilization on the


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surface of Fe3O4. At the same time, the relative intensity of the absorption peaks at around 1500 and 750 cm-1 in APTMS-SiO2@Fe3O4 significantly enhances as a result of the introduction of -NH2, and the appearance of the characteristic peaks of -CH2 stretching vibration at 2800 ~ 3000 cm-1 show that APTMS was successfully grafted on the surface of SiO2@Fe3O4. It provides the possibility of the immobilization of active component Cu(II)-β-CD on the surface of SiO2@Fe3O4. The FT-IR spectrum of Cu(II)-β-CD is consistent with the standard spectrogram

37

, indicating the correctness of the structure of Cu(II)-β-CD.

Due to the low immobilized load of Cu(II)-β-CD, the spectrum of Cu(II)-β-CD@SiO2@Fe3O4 is roughly as same as that of APTMS-SiO2@Fe3O4. However, the spectrum of Cu(II)-β-CD@SiO2@Fe3O4 has a significant strength enhancement at about 1000 cm-1 due to the introduction of Cu(II)-β-CD, which demonstrates that Cu(II)-β-CD was covalently linked to the surface of amino-functionalized SiO2@Fe3O4 MNPs successfully. Figure 2(B1) presents the XRD patterns of the prepared Fe3O4, SiO2@Fe3O4, Cu(II)-β-CD and Cu(II)-β-CD@SiO2@Fe3O4. The XRD patterns of the prepared Fe3O4, SiO2@Fe3O4 and Cu(II)-β-CD@SiO2@Fe3O4 have six broad peaks at 30.11°, 35.73°, 43.33°, 53.80°, 57.11° and 62.90°, corresponding to (220), (311), (400), (422), (511) and (400) of Fe3O4 (JCPDS No. 85-1436)

38

, respectively. The characteristic diffraction peaks at 21.22° and 33.15°

corresponding to α-FeOOH and α-Fe2O3

39

respectively were not observed, which explains

that the prepared Fe3O4 only contains high purity and single-phase Fe3O4 composition. Meanwhile, no characteristic diffraction peaks of SiO2 (JCPDS No. 45-0111)

3, 35, 36

were

found, which means that the surface modification of Fe3O4 did not result in the change of the phase structure. No characteristic diffraction peaks of Cu(II)-β-CD were observed in the XRD pattern of Cu(II)-β-CD@SiO2@Fe3O4, implying that Cu(II)-β-CD was well immobilized on the surface of SiO2@Fe3O4. According to the Debye-Scherrer equation

40

, the calculated

average grain sizes of Fe3O4, SiO2@Fe3O4 and Cu(II)-β-CD@SiO2@Fe3O4 are 14.8, 19.8 and 21.0 nm from the (311) diffraction peak, respectively. With the increase of the immobilized load of Cu(II)-β-CD, the crystallization of Cu(II)-β-CD@SiO2@Fe3O4 gradually decreased (Figure 2(B2)).


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Figure 2. (A) FT-IR spectra of Fe3O4, SiO2@Fe3O4, APTMS-SiO2@Fe3O4, Cu(II)-β-CD and Cu(II)-β-CD@SiO2@Fe3O4;

XRD

patterns

of

(B1)

Fe3O4,

SiO2@Fe3O4,

Cu(II)-β-CD

and

Cu(II)-β-CD@SiO2@Fe3O4; (B2) Cu(II)-β-CD@SiO2@Fe3O4 with the different immobilized load of Cu(II)-β-CD.

Using the thermogravimetric analysis, the loading content of Cu(II)-β-CD on the surface of SiO2@Fe3O4

was

analyzed.

The

thermal

curves

of

Fe3O4,

SiO2@Fe3O4,

Cu(II)-β-CD@SiO2@Fe3O4 and Cu(II)-β-CD under N2 were presented in Figure S6. The synthesized substances had different degrees of weightlessness before 200 oC, mainly because


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of the evaporation of absorbed water on the material. The apparent weight loss of Cu(II)-β-CD was mainly associated with the thermal decomposition of β-CD when the temperature rose from 200 oC to 300 oC, and the slow weight loss over 300 oC may be due to the phase transformation of Cu ion. No apparent weightlessness of Fe3O4 and SiO2@Fe3O4 was observed between 200 oC and 400 oC, and the weight loss over 400 oC was as a result of the release of the skeleton water. The weight loss of Cu(II)-β-CD@SiO2@Fe3O4 was about 3.82 m% at a broad temperature range from 200 oC to 400 oC, and it is ascribed to the decomposition of β-CD, which was close to the theoretical quantity (4.09 m%) of β-CD in Cu(II)-β-CD@SiO2@Fe3O4-5. In order to investigate the surface area of the synthesized desulfurizers, the surface areas of Cu(II)-β-CD,

Fe3O4,

SiO2@Fe3O4

Cu(II)@SiO2@Fe3O4,

β-CD@SiO2@Fe3O4

and

Cu(II)-β-CD@SiO2@Fe3O4 were determined by using nitrogen adsorption-desorption method. As shown in Figure S7, the surface area of Fe3O4 MNPs (68.20 m2·g-1) was higher than that of the synthetic active desulfurization component Cu(II)-β-CD (14.04 m2·g-1). The surface area of SiO2@Fe3O4 was significantly improved mainly attributed to the decrease of density after the surface modification. Compared with SiO2@Fe3O4, the surface area of Cu(II)@SiO2@Fe3O4, β-CD@SiO2@Fe3O4 and Cu(II)-β-CD@SiO2@Fe3O4 changed slightly. The adsorption isotherms of the four materials are the type IV adsorption isotherm, and the hysteresis loops belong to H4 hysteresis loop 41. The magnetization properties of Fe3O4 and Cu(II)-β-CD@SiO2@Fe3O4 were investigated by vibration sample magnetometer (VSM). At the same field, the saturation magnetization value (Ms) of Fe3O4 was 68 emu·g-1, while that of Cu(II)-β-CD@SiO2@Fe3O4 was 42 emu·g-1 (shown in Figure 3(A1)). Although the intensity of saturation magnetization of Cu(II)-β-CD@SiO2@Fe3O4 has obvious decrease, Cu(II)-β-CD@SiO2@Fe3O4 in n-heptane solution with ultrasonic dispersion for 5 min could only take a few seconds to realize magnetic separation with an adjacent magnet (Figure 3(A2)), which is enough to ensure the rapid separation of Cu(II)-β-CD@SiO2@Fe3O4 from solution during the desulfurization process.


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Energy & Fuels

Figure 3. (A1) Hysteresis loops of Fe3O4 and Cu(II)-β-CD@SiO2@Fe3O4; (A2) magnetic separation of Cu(II)-β-CD@SiO2@Fe3O4

from

n-heptane;

TEM

images

of

(B1)

Fe3O4

and

(B2)

Cu(II)-β-CD@SiO2@Fe3O4; SEM images of (C1) Cu(II)-β-CD, (C2) Cu(II)-β-CD@SiO2@Fe3O4-5 and (C3) Cu(II)-β-CD@SiO2@Fe3O4-10.

The shape and size of synthesized Fe3O4 and Cu(II)-β-CD@SiO2@Fe3O4 were deduced from the TEM images. A typical TEM image presented in Figure 3(B1) appears a neat uniform spherical morphology of Fe3O4 MNPs. Fe3O4 MNPs indicates a certain degree of aggregation due to the synthetic method without surfactant, which is consistent with other literature results 35, 38, 39. The morphology of Cu(II)-β-CD@SiO2@Fe3O4 nanoparticles is also presented sphere, while the shape is regular and the particle size is homogeneous. It means that the surface functionalization of Fe3O4 through SiO2 and APTMS not only weakened the degree of aggregation of Fe3O4 MNPs but also be conducive to the dispersion of active component, which is beneficial to the performance of desulfurization. As can also be seen from Figure 3(B), the particle sizes of Fe3O4 and Cu(II)-β-CD@SiO2@Fe3O4 MNPs are 20 and 25 nm with a narrow size distribution, respectively, which are slightly larger than those measured from XRD. The apparent morphology of Cu(II)-β-CD and Cu(II)-β-CD@SiO2@Fe3O4 was analyzed by SEM. SEM image of Cu(II)-β-CD reveals that the particles are unstructured and serious caking (Figure 3(C1)), resulting in a small surface area and less crystallization, which is


Energy & Fuels 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

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consistent with the results of the surface area and XRD. Cu(II)-β-CD@SiO2@Fe3O4 is basically spherical morphology with a diameter of about 100 nm, and the measured size is obviously larger than that determined by XRD and TEM. The spherical nanoparticle of Cu(II)-β-CD@SiO2@Fe3O4 is obviously agglomerated when the immobilized load of Cu(II)-β-CD increases to 10 m% (shown in Figure 3(C2, C3)). It implies that the suitable immobilized load of Cu(II)-β-CD on the surface of SiO2@Fe3O4 can prevent aggregation, which may be favourable for the performance of desulfurization. 3.2. Desulfurization performance of Cu(II)-β-CD@SiO2@Fe3O4 Figure 4 displays the desulfurization performance of Cu(II)-β-CD@SiO2@Fe3O4, Cu(II)-β-CD, β-CD@SiO2@Fe3O4, Cu(II)@SiO2@Fe3O4, SiO2@Fe3O4 and Fe3O4 for removing the three thiophenic sulfides (T, BT and DBT). The six types of desulfurization materials

showed

different

desulfurization

performance,

among

which

Cu(II)-β-CD@SiO2@Fe3O4 is the best one. Furthermore, the sulfur removal performance of Cu(II)-β-CD@SiO2@Fe3O4 for different thiophenic sulfides is in the order of BT > DBT > T. The highest desulfurization percentage can reach 70.68% (BT), 65.87% (DBT), 60.89% (T), respectively. From Figure 4, we can see that with the extension of desulfurization time, the desulfurization efficiency of Cu(II)-β-CD and β-CD@SiO2@Fe3O4 first increases slowly and then decreases slightly, but that of Cu(II)-β-CD@SiO2@Fe3O4 increases sharply at first and then keeps almost unchanged. This means that the introduction of Cu(II) in β-CD may enhance the inclusion interaction between β-CD and thiophenic sulfide, and the carrier SiO2@Fe3O4 could improve the dispersion of Cu(II)-β-CD. The desulfurization performance of Cu(II)-β-CD@SiO2@Fe3O4 may be the result of the cooperative effects of the inclusion interaction of β-CD, the coordination interaction of copper ion and the physical adsorption with sulfide. According to the comparison of the desulfurization performance of different desulfurizers, the inclusion interaction between Cu(II)-β-CD and thiophenic sulfides plays a dominant role in the desulfurization process of Cu(II)-β-CD@SiO2@Fe3O4. Among the three thiophenic sulfides, BT has the strongest inclusion interaction with Cu(II)-β-CD may due to BT has a good size matching with the cavity of cyclodextrin (Figure 1(B)).


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Energy & Fuels

Figure 4. Desulfurization performance of Fe3O4, SiO2@Fe3O4, Cu(II)-β-CD, β-CD@SiO2@Fe3O4, Cu(II)@SiO2@Fe3O4 and Cu(II)-β-CD@SiO2@Fe3O4 for (A) T, (B) BT and (C) DBT in n-heptane. Desulfurization conditions: the mass ratio of desulfurizer to oil, 1:20; temperature, 30 oC. Error bars: standard deviation of three experiments.

Further, Effect of the immobilized load of Cu(II)-β-CD on the removal of BT with Cu(II)-β-CD@SiO2@Fe3O4 was studied. It can be seen from Figure 5(A) that, with the increase of immobilized load of Cu(II)-β-CD, the removal percentage increases at first and then decreases gradually, and the optimum immobilized load of Cu(II)-β-CD is 5 m%. It may be the reason that active component Cu(II)-β-CD with a low immobilized load has a favourably immobilized dispersion, can play well in the inclusion and coordination interaction of Cu(II)-β-CD@SiO2@Fe3O4 with BT. But when the immobilized load of Cu(II)-β-CD


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Page 16 of 28

enlarged (> 5 m%), the active component on the surface of SiO2@Fe3O4 showed a serious trend of aggregation (from the result of SEM), resulting in the intermolecular interference and the decrease of desulfurization efficiency.

Figure 5. Effect of (A) the immobilized load of Cu(II)-β-CD (BT; temperature, 30 oC; time, 75 min; the mass ratio of desulfurizer to oil, 1:20), (B) temperature (5 m% Cu(II)-β-CD; time, 75 min; the mass ratio of desulfurizer to oil, 1:20; mix sulfides, T: BT : DBT = 1: 1: 1), (C) the mass ratio of Cu(II)-β-CD@SiO2@Fe3O4 to oil (5 m% Cu(II)-β-CD; BT; time, 75 min; temperature, 30 oC) and (D) the initial sulfur concentration of BT (5 m% Cu(II)-β-CD; temperature, 30 oC ; time, 75 min; the mass ratio of desulfurizer

to

oil,

1:20)

on

the

removal

of

thiophenic

sulfides

from

n-heptane

by

Cu(II)-β-CD@SiO2@Fe3O4. Error bars: standard deviation of three experiments.

The desulfurization conditions (temperature, the mass ratio of desulfurizer to oil and initial sulfur concentration) of Cu(II)-β-CD@SiO2@Fe3O4 were investigated in detail. With rising the desulfurization temperature from 25

o

C to 50

o

C, the removal efficiency of

Cu(II)-β-CD@SiO2@Fe3O4 for thiophenic sulfides has a various degree decrease (shown in Figure 5(B)). High temperature does not favor for the desulfurization process. Therefore, the desulfurization process should be carried out at low temperature or room temperature. It can be

seen

from

Figure

5(C,

D)

that

the

desulfurization


performance

of

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Energy & Fuels

Cu(II)-β-CD@SiO2@Fe3O4 gradually increased with the increase of the mass ratio of desulfurizer to oil and the decrease of initial sulfur concentration. The deep desulfurization performance of Cu(II)-β-CD@SiO2@Fe3O4 was also investigated. Figure 6(A) implies that when the initial sulfur concentration of BT was below 40 µg·g-1, the remaining sulfur concentration in fuel was below 10 µg·g-1 after treatment with Cu(II)-β-CD@SiO2@Fe3O4, meaning that the novel magnetic supramolecular desulfurizer has an outstanding deep desulfurization performance for the production of clean fuel.

Figure 6. (A) Deep desulfurization performance (BT in n-heptane), (B) desulfurization selectivity (BT and n-octylthiol in n-heptane) of Cu(II)-β-CD@SiO2@Fe3O4; effect of (C) aromatic hydrocarbon and (D) hydrocarbon composition on the removal of BT by Cu(II)-β-CD@SiO2@Fe3O4 (temperature, 30 oC; time, 75 min; the mass ratio of desulfurizer to oil, 1:20). Error bars: standard deviation of three experiments.

Through the aforementioned analysis, we can figure that Cu(II)-β-CD@SiO2@Fe3O4 has an excellent desulfurization performance for the removal of T, BT and DBT, especially for BT. Moreover, the desulfurization selectivity was studied by using BT and n-octylthiol both of which contains same carbon numbers (total sulfur concentration, 100 µg·g-1; the sulfur concentration of n-octylthiol was titrimetrically determined with AgNO3 2) in n-heptane and


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the obtained result was shown in Figure 6(B). It can be clearly seen that Cu(II)-β-CD@SiO2@Fe3O4 has an excellent selectivity to BT in mixed sulfur solution. Even if the BT initial sulfur concentration was 20 µg·g-1 in simulated oil, 15.24 µg·g-1 BT sulfur was removed by Cu(II)-β-CD@SiO2@Fe3O4. The result suggests that the cavity of active component Cu(II)-β-CD has an appropriate size for BT rather than n-octylthiol. Besides containing alkanes, actual oil also contains a certain amount of aromatic hydrocarbons and olefins. First, the blended simulated oil containing toluene and n-heptane was used to identify the influence of aromatic hydrocarbon on the removal of BT with Cu(II)-β-CD@SiO2@Fe3O4. As mentioned in Figure 6(C), the desulfurization performance of Cu(II)-β-CD@SiO2@Fe3O4 for removing BT gradually decreased with the increase of toluene content. The removal percentage of BT in pure n-heptane and toluene solution was 70.79% and 50.24%, respectively. It is generally recognized that cyclodextrin and cyclodextrin derivative have a good inclusion selectivity to molecule containing aromatic ring, but have a poor selectivity to molecule with a similar structure 42. Toluene simultaneously competes with benzothiophene to enter the cavity of Cu(II)-β-CD, causing the decrease of desulfurization efficiency. Furthermore, according to the investigation about the desulfurization performance of Cu(II)-β-CD@SiO2@Fe3O4 for actual oil, the sulfur removal efficiency was 50.38% in reformed gasoline and 55.36% in chemical naphtha (Figure 6(D)). The main constituent of chemical naphtha is alkanes, while that of reformed gasoline is aromatic hydrocarbons (list in Table S1). Aromatic hydrocarbon has a larger effect on the molecular inclusion of BT than alkane, which leads to a lower desulfurization efficiency of Cu(II)-β-CD@SiO2@Fe3O4 in reformed gasoline. Meanwhile, the effect of olefin on desulfurization performance of Cu(II)-β-CD@SiO2@Fe3O4 was studied. The removal percentage of BT in 1-octene was 68.91%, which is very close to that in n-heptane (70.79%). It means that olefin has little effect on desulfurization performance of Cu(II)-β-CD@SiO2@Fe3O4 for the thiophenic sulfides.


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Figure 7. (A) Desulfurization performance of Cu(II)-β-CD@SiO2@Fe3O4 and activated carbons (temperature, 30 oC; the mass ratio of desulfurizer to oil, 1:20); (B) regenerative performance of Cu(II)-β-CD@SiO2@Fe3O4 for the removal of BT in n-heptane (temperature, 30 oC; time, 75 min; the mass ratio of desulfurizer to oil, 1:20). Error bars: standard deviation of three experiments.

Different activated carbons (powder and granular in shape) were chosen to compare the desulfurization performance with Cu(II)-β-CD@SiO2@Fe3O4. Figure 7(A) exhibits the desulfurization performance of Cu(II)-β-CD@SiO2@Fe3O4 and three activated carbons. 1#AC and 2#AC quickly reached the adsorption equilibrium than 3#AC because of their different pore diameters and volume pores (Figure 7(A) and Table S2). Although the pore diameters and volume pores of Cu(II)-β-CD@SiO2@Fe3O4 and 3#AC are very similar, the BET surface area of 3#AC (785.8 m2·g-1) is significantly greater than that of Cu(II)-β-CD@SiO2@Fe3O4

(96.5

Cu(II)-β-CD@SiO2@Fe3O4

was

m2·g-1). far

The

beyond

that

desulfurization of

3#AC,

performance

which

means

of that

Cu(II)-β-CD@SiO2@Fe3O4 has a better desulfurization ability mainly depended on the inclusion interaction between Cu(II)-β-CD and BT. The kinetic and thermodynamic parameters of BT sulfur removal process by Cu(II)-β-CD@SiO2@Fe3O4 were also analyzed. The kinetic desulfurization data (calculated through Eq. S1-S3) were fitted by pseudo-first-order and pseudo-second-order kinetic models. Simultaneously, the correlation coefficient (R2) values and calculated constants of the two kinetic equations were list in Table S3. The R2 values of pseudo-first-order and pseudo-second-order kinetic model equations were 0.9020 and 0.9877, respectively, indicating that the BT sulfur removal process was consistent with the pseudo-second-order


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kinetic model. Then, the thermodynamic parameters were analyzed using Langmuir, Freundlich and Temkin isotherm models (Eq. S4 - S6), and the R2 values of the three isotherm equations were presented in Table S4. It shows that the desulfurization process matches best with the Freundlich isotherm model with the maximum value of R2 (0.9988). According to Clapeyron-Clausius equation (Eq. S7; Figure S8), the enthalpy change (∆H) of the BT sulfur removal process was obtained from the slope of linear fitting equation. And then the Gibbs free energy (∆G) and entropy change (∆S) of the desulfurization process were calculated using Eq. S8 - S9. It is found that ∆G298.15K, ∆H and ∆S298.15K are -2.928 kJ·mol-1, -20.55 kJ·mol-1 and -78.76 J·mol-1·K-1, respectively, which means that the desulfurization process was spontaneous, exothermic and controlled by enthalpy. With mixing the used Cu(II)-β-CD@SiO2@Fe3O4 and hot petroleum ether, the regeneration of Cu(II)-β-CD@SiO2@Fe3O4 can be easily and quickly realized by magnetic separation. After being regenerated 5 recycle times, Cu(II)-β-CD@SiO2@Fe3O4 also has a relatively good function for removing BT in the simulated oil (shown in Figure 7(B)).

Figure 8. (A) FT-IR spectra, (B)XRD patterns, (C) hysteresis loops and (D) N2 adsorption-desorption isotherms and BET surface area of the fresh and used Cu(II)-β-CD@SiO2@Fe3O4 after removing BT.


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Energy & Fuels

The difference in structure between the fresh and used Cu(II)-β-CD@SiO2@Fe3O4 (after 5 recycle times for removing BT) were analyzed by FT-IR, XRD, VSM and the surface area. As shown in Figure 8, the minute differences in FT-IR spectra approximately at 1450 ~ 1315 and 785 cm-1 between fresh and used Cu(II)-β-CD@SiO2@Fe3O4 were found due to the loss of a small amount of Cu(II)-β-CD during the desulfurization process. XRD pattern and BET surface area of the used Cu(II)-β-CD@SiO2@Fe3O4 were generally consistent with those of the fresh desulfurizer, which indicates that Cu(II)-β-CD@SiO2@Fe3O4 was in good shape in the desulfurization process. Although the magnetic saturation magnetization intensity of the used Cu(II)-β-CD@SiO2@Fe3O4 had a little decreased, the fast separation of desulfurizer from n-heptane was not affected. Based on the aforementioned analysis, it could be concluded that sulfide mainly entered into the cavity of Cu(II)-β-CD rather than be adsorbed on the surface of Cu(II)-β-CD@SiO2@Fe3O4. 3.3. Desulfurization mechanism of Cu(II)-β-CD@SiO2@Fe3O4 It has been illustrated that Cu(II)-β-CD@SiO2@Fe3O4 has different performance for removing T, BT and DBT from fuel. The reason may be that the inclusion interaction between the active component Cu(II)-β-CD and thiophenic sulfides was different. For studying the desulfurization mechanism, the inclusion interaction between Cu(II)-β-CD and three sulfides (T, BT and DBT) in aqueous solution (phosphate buffered solution) was analysed by ultraviolet spectroscopy. The maximum absorption peak of T (BT and DBT) in phosphate buffered solution did not move after adding Cu(II)-β-CD, but the absorption intensity gradually increased with the increase of Cu(II)-β-CD (Figure S9(A)). The possible reason is that Cu(II)-β-CD forms inclusion complex with sulfide to induce the change of the electron cloud density of sulfide. It shows a good linear relation (R2= 0.9958, 0.9910 and 0.9948 for T, BT and DBT, respectively) between 1/∆A and 1/[Cu(II)-β-CD]0 on the basis of the equation of Benisi-Hildebrand

43

(Figure S9(B) and Eq. S10), which means that the

inclusion ratio of the inclusion complex between β-CD and sulfide is 1:1. The thermal inclusion equilibrium constant (Ka) of the Cu(II)-β-CD inclusion complexes with T, BT and DBT was obtained as 367.4, 878.6 and 740.8 L·mol-1 based on the slope and intercept of the


Energy & Fuels 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 22 of 28

linear equation. It means that the thermal stability of the Cu(II)-β-CD inclusion complexes with T, BT and DBT is in the order of BT> DBT> T, which is consistent with the desulfurization performance of Cu(II)-β-CD@SiO2@Fe3O4 for removing T, BT and DBT. This well explains why Cu(II)-β-CD@SiO2@Fe3O4 shows an efficient removal performance and selectivity for BT. Furthermore, X-ray photoelectron spectroscopy (XPS) was used to characterize Cu chemical state. The shift of Cu(II)-β-CD@SiO2@Fe3O4 in binding energy after removing BT provides an evidence of the interaction between Cu(II) and thiophenic sulfur species. The Cu2p3/2 XPS spectra of the fresh and used Cu(II)-β-CD@SiO2@Fe3O4 were fitted by the XPS peak software (Figure S10). The maximum peak of Cu2p3/2 shifted from 935.8 eV to 935.1 eV after desulfurization for BT, which implies that the π electron cloud or S atom in BT is donating

electrons

to

Cu

species,

demonstrating

the

interaction

between

Cu(II)-β-CD@SiO2@Fe3O4 and BT. However, the binding energy of S2p was not found in the XPS spectrum of the used Cu(II)-β-CD@SiO2@Fe3O4 because of the low concentration of sulfur on the surface of desulfurizer (Figure S11), which further confirms that most of BT entered into the cavity of Cu(II)-β-CD and was not adsorbed on the surface of desulfurizer.

Figure 9. Schematic diagram of Cu(II)-β-CD@SiO2@Fe3O4 for the removal of thiophenic sulfides.

Finally, a reasonable desulfurization mechanism of Cu(II)-β-CD@SiO2@Fe3O4 (Figure 9) was proposed as follows, (1) the inclusion interaction between Cu(II)-β-CD and thiophenic sulfide; (2) the coordination interaction of Cu(II); (3) the physical absorption for sulfide. The inclusion interaction plays a more dominant role than the other two interactions during the


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Energy & Fuels

desulfurization process. The different inclusion interactions between Cu(II)-β-CD and the three thiophenic sulfides are the reason for the different desulfurization performance and selectivity of Cu(II)-β-CD@SiO2@Fe3O4. The process of removing thiophenic sulfides by Cu(II)-β-CD@SiO2@Fe3O4 is mainly achieved by Cu(II)-β-CD with inclusion and coordination interactions, and secondly by physical adsorption. 4. Conclusions Cu(II)-β-CD@SiO2@Fe3O4 has been prepared for the first time to remove thiophenic sulfides from fuel through molecular inclusion. Cu(II)-β-CD@SiO2@Fe3O4 has the best desulfurization performance for removing BT among the three types of thiophenic sulfides (T, BT and DBT) under the same condition. The structural characterization of the used Cu(II)-β-CD@SiO2@Fe3O4 illustrates that most of BT enters the inside cavity of Cu(II)-β-CD and a few of BT is adsorbed on the surface of Cu(II)-β-CD@SiO2@Fe3O4. During the removal of BT by using Cu(II)-β-CD@SiO2@Fe3O4, the inclusion interaction between Cu(II)-β-CD and BT plays a dominant role. The present study lays the foundation of the removal of thiophenic sulfides from fuel through molecular inclusion with supramolecular magnetic materials. Acknowledgment This work was supported by the National Natural Science Foundation of China (Grant No. 21376265, U1662115) and the Fundamental Research Funds for the Central Universities (Grant No. 17CX06023, 18CX02118A).

References 1. Soleimani, M.; Bassi, A.; Margaritis, A., Biodesulfurization of refractory organic sulfur compounds in fossil fuels. Biotechnol. Adv. 2007, 25, (6), 570-596. 2. Yin, C. L.; Xia, D. H., A study of the distribution of sulfur compounds in gasoline produced in China. Part 1. A method for the determination of the distribution of sulfur compounds in light petroleum fractions and


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gasoline. Fuel 2001, 80, (4), 607-610. 3. Song, C. S., An overview of new approaches to deep desulfurization for ultra-clean gasoline, diesel fuel and jet fuel. Catal. Today 2003, 86, (1-4), 211-263. 4. Tian, W.; Sun, L.; Song, X.; Liu, X.; Yin, Y.; He, G., Adsorptive desulfurization by copper species within confined space. Langmuir 2010, 26, (22), 17398-17404. 5. Zhao, G.; Liu, Q.; Tian, N.; Yu, L.; Dai, W., Highly efficient benzothiophene capture with a metal-modified copper-1,3,5-benzenetricarboxylic acid adsorbent. Energ. Fuel 2018, 32, (6), 6763-6769. 6. Peralta, D.; Chaplais, G.; Simon-Masseron, A.; Barthelet, K.; Pirngruber, G. D., Metal-organic framework materials for desulfurization by adsorption. Energ. Fuel 2012, 26, (8), 4953-4960. 7. Dai, W.; Tian, N.; Liu, C.; Yu, L.; Liu, Q.; Ma, N.; Zhao, Y., (Zn, Ni, Cu)-BTC functionalized with phosphotungstic acid for adsorptivedesulfurization in the presence of benzene and ketone. Energ. Fuel 2017, 31, (12), 13502-13508. 8. Saleh, T. A., Simultaneous adsorptive desulfurization of diesel fuel over bimetallic nanoparticles loaded on activated carbon. J. Clean Prod. 2018, 172, 2123-2132. 9. AL-Hammadi, S. A.; Al-Amer, A. M.; Saleh, T. A., Alumina-carbon nanofiber composite as a support for MoCo catalysts in hydrodesulfurization reactions. Chem. Eng. J. 2018, 345, 242-251. 10. Saleh, T. A.; Sulaiman, K. O.; AL-Hammadi, S. A.; Dafalla, H.; Danmaliki, G. I., Adsorptive desulfurization of thiophene, benzothiophene and dibenzothiophene over activated carbon manganese oxide nanocomposite: with column system evaluation. J. Clean Prod. 2017, 154, 401-412. 11. Saleh, T. A.; Alhooshani, K. R.; Abdelbassit, M. S. A., Evaluation of AC/ZnO composite for sorption of dichloromethane, trichloromethane and carbon tetrachloride: kinetics and isotherms. J. Taiwan. Inst. Chem. E.


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Energy & Fuels

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A new strategy for fuel desulfurization by molecular inclusion with

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