Precipitation Synthesis of Mesoporous Photoactive Al2O3 for

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Precipitation Synthesis of Mesoporous Photo-active Al2O3 for Constructing g-C3N4-based Heterojunctions with Enhanced Photocatalytic Activity Fa-tang Li, Ya-bin Xue, Bo Li, Ying-juan Hao, Xiaojing Wang, Rui-hong Liu, and Jun Zhao Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie5036258 • Publication Date (Web): 27 Nov 2014 Downloaded from http://pubs.acs.org on December 2, 2014

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Industrial & Engineering Chemistry Research

Precipitation Synthesis of Mesoporous Photo-active Al2O3

for

Heterojunctions

Constructing with

Enhanced

g-C3N4-based Photocatalytic

Activity Fa-tang Li,*,† Ya-bin Xue,† Bo Li,‡ Ying-juan Hao,† Xiao-jing Wang,† Rui-hong Liu,† and Jun Zhao† †

College of Science, Hebei University of Science and Technology, Shijiazhuang 050018, China.

‡

Analytical & Testing Center of Hebei Province, Hebei University of Science and Technology, Shijiazhuang, 050018, China.

ACS Paragon Plus Environment

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ABSTRACT. Mesoporous γ-Al2O3 with high surface area (159 m2/g) is prepared via precipitation method. The as-synthesized Al2O3 exhibits optical absorption ability in ultraviolet region and is used as active component to be combined with g-C3N4 to form effective heterostructured photocatalysts. This heterojunction structure is confirmed by XRD, SEM, element map, TEM, HRTEM, FT-IR, and XPS measurements. The photocatalytic performances of the composites are evaluated by the degradation of rhodamine B (RhB) and methyl orange (MO). Among them, 2g-C3N4:1Al2O3 (weight ratio) exhibits the highest photocatalytic activity, the reaction rate constant of which is 2.5 and 3.7 times that of pure g-C3N4 in degradation of RhB and MO, respectively. The enhancement in activity of heterojunctions is ascribed to their high specific surface areas, excellent adsorption abilities for dyes, and efficient transfer of photogenerated electrons from LUMO of g-C3N4 to defect sites of γ-Al2O3.

KEYWORDS. Mesoporous Al2O3; Precipitation synthesis; g-C3N4; Heterojunction; Visible-light photocatalysis.


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1. INTRODUCTION With the ever-increasing deterioration of environmental associated with economic growth, semiconductor photocatalysis technique has aroused much attention in degrading pollutants due to its potential utilization for clean, safe, and inexhaustible solar energy in the past few decades. The development of visible-light-driven photocatalysts is an essential prerequisite for practical application because visible light (390–750 nm) accounts for around 43% of the incoming solar spectrum.1 Recently, graphite carbon nitride (g-C3N4) has attacked great interest because of its inexpensive and relative narrow band gap of 2.70 eV, since Wang et al. reported its high photocatalytic ability in water splitting.2 Afterwards, the excellent performances of g-C3N4 in degradation of pollutants, catalytic oxidation of hydrocarbon, oxygen reduction reaction, CO2 activation/reduction, and esterification of alcohols have been exploited.3–5 However, similar to other narrow-band-gap semiconductors, g-C3N4 also suffers from high recombination rate of photo-induced charge carriers and low quantum yield.6 In order to enhance the photocatalytic ability of pristine g-C3N4, many strategies have been employed, such as metal or nonmetal ions doping,7-9 morphology modification,10,11 acid treatment,12,13 noble metals deposition,14,15 anchoring dye sensitization,16 conjugated polymer modification,17 and heterojunctions construction for electrons transfer6,18–33 or enhancing specific surface area.34 Among these methods, coupling g-C3N4 with other semiconductors is an effective measure based on the fact that the lowest unoccupied molecular orbital (LUMO) potential of gC3N4 (-1.13 eV)31 is much more negative than conduction band (CB) edges of the great majority of semiconductors, which makes it easy for photo-generated electrons to transfer from g-C3N4 LUMO to the CB of other components. For example, silver-compounds,6, 18,19 TiO2,20 ZnO,21,32,33 bismuthates,22–24 vanadates and rare earth element oxides,25–28 germinates,29 SnO2,30 and WO331


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have been used to form heterojunctions with bulk or mesoporous g-C3N4. However, most of the aforementioned materials are noble/rare metal oxides, or heavy metal oxides, which are either expensive or harmful to environment and human health as secondary pollutants after use, and decreases the applicability of g-C3N4 as a kind of cheap photocatalyst. Hence, searching for inexpensive and nontoxic materials to modify g-C3N4 is still a challenging and valuable task. Al2O3 is widely applied as supporter material owning to its promising features as excellent chemical inertness, low cost, and good thermal stability.35–37 As an earth-abundant and light metal oxide, Al2O3 would not take side effects to the earth and environment. In the field of photocatalysis, for a long time, Al2O3 is mainly used only as inert supporting material to modify the porous structures, surface areas, or the adsorptive performance of primary catalysts and does not have active role.38–41 Recently, Hankare et al.42 reported the active role of Al2O3, that is, the defect sites of Al2O3can accept electrons from TiO2 in ternary TiO2-Al2O3-ZnFe2O4 composite. Our group also reported that amorphous Al2O3 prepared via combustion synthesis exhibits ultraviolet-light absorption ability arising from its shorter Al-O bond length43,44 and the fabricated Al2O3/TiO2 composites can greatly improve the photocatalytic activity of pristine TiO2.45 In this research, mesoporous γ-Al2O3 with high surface area is prepared by precipitation method. Then the Al2O3/g-C3N4 heterostructured photocatalysts are constructed. Compared to pristine g-C3N4, the novel composites exhibited enhanced photocatalytic activity in degradation of RhB under visible light illumination. This work not only presents a method for preparing a photo-active Al2O3, but also provides new insight into engineering defective materials for enhancing photocatalytic activities of heterojunctions.


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2. EXPERIMENTAL 2.1. Catalysts preparation All chemicals were purchased from Aladdin (Shanghai, China) and taken as received without further purification. Polycondensation of melamine was employed to obtain g-C3N4 according to Ref. (2). Typically, 5 g of melamine was put in a semi-covered crucible and heated in a muffle furnace at 550 °C for 2 h with a heating rate of 10 °C/min. Al2O3 was prepared via precipitation route. 0.02 mol Al(NO3)3·9H2O was dissolved in 200 mL distilled water. Then 1 mol/L NaOH solution was dropped into the Al(NO3)3 solution till the formation of Al(OH)3 colloid with a pH of 8.5. After stirring the colloid for 0.5 h, the sediment was filtered, washed and dried. Subsequently, the solid particles were calcined at 600 °C for 2 h to obtain Al2O3. Al2O3/g-C3N4 composites were synthesized via facile chemisorption. In a typical procedure, 0.2 g of g-C3N4 and 0.1 g of Al2O3 were separately mixed with 100 ml of methanol and sonicated for 30 min. Then the two suspensions were merged together and continually stirred in a covered beaker for 24 h. Till the complete volatilization of methanol, Al2O3/g-C3N4 powders were achieved, which are labeled as xg-C3N4:yAl2O3, where x, y represent their weight ratio. 2.2. Characterization of catalysts The samples were characterized by powder X-ray diffraction (XRD) on a Rigaku D/MAX 2500 X-ray diffractometer. N2 adsorption/desorption analysis was carried out by Quantachrome NOVA2000. The scanning electron microscopy (SEM) and element mapping images were achieved from HITACHI S4800 instrument equipped with energy dispersive X-ray spectrometers (EDS, Bruker Quantax). Transmission electron microscopy (TEM) and highresolution electron microscopy (HREM) measurement were performed by a JEOL JEM-2010


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microscope. Fourier transform infrared (FT-IR) spectra were collected using a Shimadzu IRPrestige 21 spectrometer. X-ray photoelectron spectroscopy (XPS) measurements were recorded on a PHI 1600 ESCA XPS system. The UV-vis diffuse reflectance spectra (DRS) were obtained by Thermo Scientific Evolution 220 spectrophotometer. The photocurrent measurements were carried out in three-electrode cell with electrolyte solution of 0.2M Na2S+0.04M Na2SO3 on a Shanghai Chenhua CHI-660E electrochemical workstation. The Pt wire and Ag/AgCl electrode were employed as counter and the reference electrodes, respectively. 2.3. Photocatalytic activity test Degradation of rhodamine B (RhB) and methyl orange (MO) was employed as probe reaction to investigate the photocatalytic activity of the as-prepared samples. A 350-W Xe lamp with a 400 nm cut-off filter was used as the visible-light source, the total light intensity of which was 0.45 W/cm2 in the range of 400-1064 nm measured by a Newport 842-PE optical power/energy meter. In each experiment, 0.10 g of sample was added into 100 mL of RhB or MO aqueous solution (10 mg/L) and then the suspension was continuously stirred for 30 min to measure the adsorption efficiency of photocatalysts for dyes. Afterwards, the light was turned on to irradiate the reaction. At scheduled intervals, about 3 mL of suspension was withdrawn and centrifuged to sediment the solid particles, and the dyes concentrations in the supernatants were measured at their maximum absorbance using a Thermo Scientific Evolution 220 UV–vis spectrophotometer. The removal efficiency of pollutants was recorded as C/C0, where C is the RhB or MO reaction concentration, and C0 is the initial concentration of 10 mg/L. 3. RESULTS AND DISCUSSION 3.1. XRD patterns and SBET


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Fig. 1 shows the XRD patterns of Al2O3, g-C3N4, and various Al2O3/g-C3N4 hybrids. The diffraction peaks of the obtained Al2O3 are indexed to its cubic γ-phase (JCPDS card No. 100425). Typical peaks at 2-theta degree of 39.5°, 45.9°, and 67.0° can be observed, corresponding to (222), (400), and (440) planes of γ-Al2O3, respectively. From the inset pattern it is seen that the as-prepared γ-Al2O3 exhibits weaker diffraction peaks compared to commercial γ-Al2O3, indicating its lower crystallinity. From Al(NO3)3 to Al2O3 via the precipitation and calcination, the processes can be expressed by the following equations.46,47 Al 3+ + OH − → Al (OH ) 3

(1)

Al (OH ) 3 → γ - AlOOH + H 2 O (2) (3)

C3N4 3 C3N4: 1 Al2O3 1 C3N4: 1 Al2O3 1 C3N4: 3 Al2O3

As-prepared γ-Al2O3

Intensity(a.u.)

2γ - AlOOH → γ - Al 2 O3 + H 2 O

Intensity(a.u.)

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


Al2O3

20

40

Commericial γ-Al2O3

20

60

40

60

2-Theta(°)

80

80

100

100

2-Theta(O)

Fig. 1. XRD patterns of g-C3N4, heterojunctions, Al2O3, and comparison of commercial and asprepared γ-Al2O3 (inset). In the XRD pattern of Al2O3, both the raw material of Al(NO3)3 and the intermediate product of γ-AlOOH (JCPDS card No. 21-1307) are not observed, demonstrating the


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transformation of Al(NO3)3 to Al2O3 is complete. As for g-C3N4, the peaks at 27.4o and 13.2o, corresponding to (002) and (100) planes (JCPDS 87-1526), are due to the stacking of the conjugated aromatic system in graphite and the interlayer structural packing, respectively,48,49 which is consistent with the degrees reported in the literature.49 From the patterns of representative Al2O3/g-C3N4 composites presented in Fig. 1, all the peaks of g-C3N4 and Al2O3 can be observed, even in the 1g-C3N4:3Al2O3 sample (corresponding to 25.0 wt% C3N4 in this hybrid). This phenomenon is different from previous reports,6,23,26 where it is difficult to detect the peaks of g-C3N4 when the g-C3N4 content in composites is lower than 30wt%, even 50wt% because the high crystalline substance depresses the peaks of g-C3N4. In this work, Al2O3 with very low crystallinity cannot depress the intensity g-C3N4. It also can be seen that the peaks of gC3N4 become higher with increasing the g-C3N4 content. Fig. 2a exhibits the N2 adsorption/desorption isotherm of the as-synthesized Al2O3, which is IV Brunauerisotherm50 with a H3 hysteresis loop and thus indicates the presence of mesopores (2 nm−50 nm).51 The inset curve demonstrates Al2O3 has a narrow and uniform pore size distribution. The obtained surface area, total pore volume, and average pore diameter of Al2O3 are 159.9 m2/g, 0.26 m3/g, and 6.7 nm, respectively. The data of SBET, total pore volume, and average pore diameter of all the samples are summarized in Table 1. It can be seen that the pore volumes of hybrids are smaller than that of pristine Al2O3 because some pore canals of Al2O3 are occupied by g-C3N4.Meanwhile, the composites show decreased SBET because of the introduction of g-C3N4 with low SBET, which can be observed from the N2 adsorption/desorption isotherm of 2g-C3N4:1Al2O3as representative shown in Fig. 2b. Nevertheless, the as-obtained heterojunctions still possess higher SBET values than do lots of reported materials combining g-C3N4 with crystalline matters. For example, Liu et al.52 prepared ZnO/g-C3N4 hybrids with surface areas of


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11-17 m2/gand the SBET of GdVO4/g-C3N4 composites is in the range of 36-65 m2/g reported by He and coworkers.25 The high specific surface areas of the as-prepared hybrids benefit the adsorption of pollutants on the surface of photocatalysts and the subsequent degradation process.

100 80

1.5

140

1.0

120

0.5

100

0.0 0

20

40

60

80

Pore width (nm)

60 40 20 0 0.0

0.2

0.4

0.6

0.8

1.0

b

3/g)

160

2.0

dV/dlog(w) pore volume (cm

120

180

a

Adsorbed quantity (cm3/g)

140

dV/dlog(w) pore volume (cm

160

3/g)

180

Adsorbed quantity (cm3/g)

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


80

0.5

0.0

0

20

40

60

80

Pore width (nm)

60 40 20 0 0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure (P/P0)

Relative pressure (P/P0)

Fig. 2. N2 adsorption/desorption isotherms and pore size distribution curves (inset) of (a) theassynthesized Al2O3 and (b) 2g-C3N4:1Al2O3. Table 1. SBET, pore parameters of samples and their adsorptive performances and photocatalytic kinetic equations for removal of RhB

SBET Sample

g-C3N4

(m2/g)

15.3

Pore volume ( cm3 g-1)

0.03

Average poredia meter (nm)

7.9

Adsorption efficiency Fitted for RhB equation (%)

(min-1)

Correlation coefficient (R)

10.2

y= 0.0220x + 0.1072

0.0220

0.9891

0.0024

0.9989

0.0316

0.9911

Al2O3

159.9

0.26

6.7

31.3

y= 0.0024x + 0.3747

3g-C3N4:1Al2O3

46.8

0.17

6.5

15.7

y= 0.0316x


k

9


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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+ 0.1707

2g-C3N4:1Al2O3

1g-C3N4:1Al2O3

1g-C3N4:2Al2O3

1g-C3N4:3Al2O3

60.2

82.4

101.7

124.5

0.20

0.20

0.22

0.24

5.6

5.8

6.6

6.5

15.4

y= 0.0547x + 0.1672

0.0547

0.9982

16.8

y= 0.0362x + 0.1838

0.0362

0.9954

17.7

y= 0.0249x + 0.1942

0.0249

0.9853

19.0

y= 0.0124x + 0.2102

0.0124

0.9849

3.2. Morphology observation The as-prepared Al2O3 exhibits an irregular bulk structure because of the agglomeration of particles, as is shown in Fig. 3a. Fig. 3b exhibits the SEM image of the hybrid 2g-C3N4:1Al2O3, from which it is seen that flocculent g-C3N4 is covered or deposited on the surface of Al2O3, elucidating their good combination. EDS element maps further verify the close integration of Al2O3 and g-C3N4, as shown in Fig. 4. The TEM image of 2g-C3N4:1Al2O3 shown in Fig. 5a indicates that the black Al2O3 is deposited on the gray g-C3N4 sheet. After coupling with g-C3N4, it can be seen from Fig. 5b that there are three kinds of regions. The gray area can be ascribed to g-C3N4 and the dark “cloud-like” region is assigned to Al2O3 due to its higher atomic number. There is also a little regular striped part, which is the characteristic of crystals and the lattice


10

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fringe of 0.198 nm corresponds to the (400) plane of γ-Al2O3. It is seen clearly from Fig. 5b that the crystallinity of as-obtained Al2O3 is very weak.

Fig. 3. SEM images of (a) pristine Al2O3 and (b) 2g-C3N4:1Al2O3.


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Fig. 4. EDS element maps of sample 2g-C3N4:1Al2O3.

Fig. 5. (a) TEM and (b) HRTEM images of 2g-C3N4:1Al2O3. 3.3. FT-IR and XPS spectra analysis FT-IR measurement was carried out to further observe the samples, as shown in Fig. 6. For pure Al2O3, there is a main broad peak from 500-900 cm−1, which is a typical feature of inorganic oxides and can be assigned to the Al-O stretching vibration. There are no strong absorbance bands at 485, 626, 742, 1068, 1161 cm−1, further confirming there is no γ-AlOOH phase in the product.53 As for these composites, three peaks shift compared to pure g-C3N4. 1632.8 cm−1, attributable to the C=N stretching vibration modes30 and 1409.0, 1241.2 cm−1 originating from aromatic C–N stretching54 in pure g-C3N4 shift to 1635.7, 1416.8, and 1248.0


12

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cm−1 in hybrid 1g-C3N4:1Al2O3 as representative, respectively, revealing that there is interaction between g-C3N4 and Al2O3 after combination. As for 1g-C3N4:3Al2O3, the shifts are not obvious, which is ascribed to the less g-C3N4content and thus the weak bonding force between g-C3N4 and Al2O3. It is also seen that with the increase of the g-C3N4 ratio, the peaks of g-C3N4 also strengthen and the broad peak of Al2O3 weakens.

a Transmittance (%)

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b c

1409.0 1632.8 1241.2

d

e 1635.7

1248.0

1416.8

4000

3500

3000

2500

2000

1500

1000

500

Wavelengh (cm-1)

Fig. 6. FT-IR spectra of selected samples: a: pure g-C3N4, b: 3g-C3N4:1Al2O3, c: 1gC3N4:1Al2O3, d: 1g-C3N4:3Al2O3, and e: pure Al2O3. Fig. 7a exhibits the XPS survey spectra of Al2O3 and 2g-C3N4:1Al2O3. After introducing gC3N4, the peak of N1s emerges, the C1s signal strengthens and the peak intensities at O1s, Al2s, and Al2p of 2g-C3N4:1Al2O3 decrease compared to those of Al2O3. Fig. 7b and 7c demonstrate the XPS high resolution spectra of O1s and Al2p, respectively. The O1s peak at 531.1 eV and Al2p at 74.2 eV for pristine Al2O3 shift to 532.1 eV and 74.8 eV for 2g-C3N4:1Al2O3 heterojunction, respectively, indicating there is chemical interaction between the two components. From the N1s shown in Fig. 7d, it is seen that the N1s peak at 398.9 eV of pure gC3N4, which is derived from sp2-hybridized N atoms (C=N-C),55 is shifted to 398.1 eV for 2g-


13


C3N4:1Al2O3 hybrid. However, there is no any change in peak positions for the C1s spectra, as shown in Fig. 7e, in which the peak at 284.6 eV is attributed to the contaminated carbon and 288.2 eV is derived from sp2-bonded C atoms (N-C=N) in C3N4.56 The N1s and C1s results imply that the interaction occurs between Al2O3 and the N atoms in C3N4, which may be related to the hydrogen bond generated via the H atoms on the N element of C3N4.44 The structure diagram of C3N4 is shown in Fig. 7d.

b

531.1 eV Al2O3

O1s

a

N1s 2g-C 3N 4:1Al2O 3 C1s

Intensity (a.u.)

Intensity (a.u.)

O1s

Al2p O1s

Al2s

Al2O 3

C1s 1200

1000

800

600

400

532.1 eV 2g-C3N4:1Al2O3

Al2p Al2s

200

0

540

538

536

534

Al2p

532

530

528

526

Binding Energy (eV)

Binding energy (eV)

N1s

c

74.2 eV Al2 O3

H

Intensity (a.u.)

N

398.1 eV 2g-C 3N 4:1Al2O 3

N N

N

H N

N N N H N

N

N N

N

H

N N

N N

d

398.9 eV g-C 3N 4

H

N

N

Intensity (a.u.)

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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N N

H N

N N

N N

H N H

H

74.8 eV 2g-C 3N 4 :1Al2O 3

82

80

78

76

74

72

70

68 410

408

406

Binding energy (eV)


404

402

400

398

396

394

Binding energy (eV)

14

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Intensity (a.u.)

C1s

e

288.2 eV

pure g-C 3N4

284.6 eV

2g-C3N4:1Al2O3

Al2O3

294

292

290

288

286

284

282

280

Binding energy (eV)

Fig. 7. (a) XPS survey spectra and high resolution XPS spectra of (b) O1s, (c) Al2p, (d) N1s, and (e) C1s of various samples. 3.4. Optical absorption performance and photocatalytic activity The optical absorption of as-prepared samples was characterized by DRS, as shown in Fig. 8. The as-prepared Al2O3 shows ultraviolet light absorption ability due to the defect structure, implying its photo-active function. Pure g-C3N4 exhibits the strongest light absorption ability in the range of 300-470 nm. Compared to pristine g-C3N4, the light absorption thresholds of the hybrids show slight blue-shift and their absorption strengths decrease to various extents due to the introduction of Al2O3. 1.0 0.8

Intensity (a.u.)

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


C 3N 4 3C3N4:1Al2O3

0.6

1C3N4:1Al2O3 2C3N4:1Al2O3 1C3N4:2Al2O3

0.4

1C3N4:3Al2O3 Al2O3

0.2 0.0 200

300

400

500

600

700

800

Wavelength (nm)


15


Fig. 8.UV-vis diffuse reflectance spectra of the as-prepared samples. Fig. 9a shows the adsorption and photocatalytic degradation efficiency of RhB under visible light illumination. The adsorption efficiency for RhB is 10.2% over g-C3N4, while those over Al2O3-based hybrids vary from 15.4% to 19.0% due to the high surface area of composites. The pure Al2O3 exhibits the highest adsorption efficiency of 31.3% due to its largest surface area. The photocatalytic blank test shows that the degradation efficiency of 10 mg/L of RhB is 5.2% in 80 min in the absence of catalyst, confirming that there is very little self-photolysis for RhB and it is a relative stable dye molecular under visible light irradiation. When photocatalysts were introduced to the reaction system, photocatalytic degradation efficiency of RhB is about 93.6%, 98.9%, 96.2%, 90.1%, 70.9%, 86.5%, and 43.8% over 3g-C3N4:1Al2O3, 2g-C3N4:1Al2O3, 1gC3N4:1Al2O3, 1g-C3N4:2Al2O3, 1g-C3N4:3Al2O3, pure g-C3N4, and bare Al2O3, respectively. The removal of RhB over bare Al2O3 is ascribed to the photosensitization effect of RhB because Al2O3 can only respond to ultraviolet-light. 2g-C3N4:1Al2O3 exhibits the highest photocatalytic activity among these samples, showing the combination of g-C3N4 with the as-prepared photoactive Al2O3 is an effective route. Meanwhile, the reason responsible for the lowest activity of 1g-C3N4:3Al2O3 heterojunction is that the content of g-C3N4 in this composite is too low and thus fewer electrons can be generated to participate in the photocatalytic reaction.

1.0

Light off

Light on

a

0.8 0.6 0.4 0.2

No catalyst Al2O3 1C3N4:3Al2O3

ln(C0/C)

C/C0

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 32

C 3N4

-40

2C 3 N4 :1Al2 O 3

4.0

1C 3 N4 :1Al2 O 3

3.5

3C 3 N4 :1Al2 O 3

1C 3 N4 :3Al2 O 3 Al2O 3

2.0 1.5 1.0 0.5

2C3N4:1Al2O3

-20

C 3N 4

2.5

3C3N4:1Al2O3

b

1C 3 N4 :2Al2 O 3

3.0

1C3N4:2Al2O3 1C3N4:1Al2O3

0.0

4.5

0.0

0

20

40

60

Irradiation time (min)

80

0

20


40

60

80


16

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1.0

c

0.9 C3N4

0.8

2C3N4:1Al2O3

C/C0

0.7

0.8 0.7

2C 3N 4:1Al2O 3

0.6

0.6

lnC0/C

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


0.5

C3N 4

0.5 0.4

y= 0.0037x+0.0702

0.3 0.2 0.1

y=0.0010x+0.0094

0.0 0

0.4 -30

20

40

60

80 100 120 140 160 180 200


0

30

60

90

120

150

180


Fig. 9. Time-course variation of (a) C/C0, (b) ln(C0/C) of RhB, and (c) C/C0 and ln(C0/C) (inset) of MO solution under visible light illumination with and without catalysts. In order to quantitatively compare the photocatalytic performances of the various composites, the pseudo-first-order reaction is taken using equation as follows:45 ln C0 / C = kt + ln C0 / C1 where k is the pseudo-first-order rate constant, C0 and C1 are the concentrations at initial time and after adsorption at 30 min, respectively. C is the reaction concentration at time t. Fig. 9b illustrates the time-course variation of ln(C0/C) and the fitted rate constant k and correlation coefficient (R) are listed in Table 1. It is found that the k value (0.0547 min-1) of heterojunction 2g-C3N4:1Al2O3 is about 2.5 times that of pure g-C3N4 (0.0220 min-1). Although pristine g-C3N4 possesses the highest visible-light absorption ability and 1g-C3N4:3Al2O3 has the highest specific surface area (except for the ultraviolet-light-driven pure Al2O3), both their photocatalytic abilities are lower than that of 2g-C3N4:1Al2O3, proving that mere optical absorption performance or surface area is not the main factor determining activity of photocatalysts.


17


It is known that RhB is a kind of cationic dye. To investigate the universality of the asprepared photocatalysts, a less photosensitive anionic dye, MO, is selected as the objective pollutant. Fig. 9c shows the time-course variation of C/C0 and ln(C0/C) (inset) of MO solution over 2g-C3N4:1Al2O3 and pristine g-C3N4 under visible light irradiation. The kinetic equation of MO degradation is y=0.0037x+0.0702 and y=0.0010x+0.0094 for 2g-C3N4:1Al2O3 and g-C3N4, respectively. That is, the reaction rate constant (0.0037 min-1) of 2g-C3N4:1Al2O3 is 3.7 times as high as that (0.0010 min-1) of g-C3N4, demonstrating the high photocatalytic performances of heterojunctions. Furthermore, the 2g-C3N4:1Al2O3 hybrid exhibits better ability in degradation of MO than in degradation of RhB. The reason is that the photosensitization effect of MO is much weaker than that of RhB and hybrids have higher pure photocatalytic ability than bare g-C3N4. To investigate the stability of the photocatalyst, which is crucial for practical application, the stability test of sample 2g-C3N4:1Al2O3 was conducted repeatedly for five times, as shown in Fig. 10. The photocatalytic efficiency decreases slightly from 98.9% to 93.5% after five times recycling caused by the loss of photocatalyst particles. 1.0

first run

second run

third run

forth run

fifth run c

C/C0

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 18 of 32

0.5

0.0 0 20 40 60 800 20 40 60 800 20 40 60 800 20 40 60 80 0 20 40 60 80


Fig. 10. Time-course variation of C/C0 of RhB over 2g-C3N4:1Al2O3 in recycling experiments.


18

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3.5. Photocatalytic mechanism To observe the separation efficiency of photo-generated electrons and holes, transient photocurrent responses of pure g-C3N4 and 2g-C3N4:1Al2O3 electrodes under visible light irradiation were performed. As shown in Fig. 11, both the samples exhibit stable and reversible photocurrent curves via six on-off cycles. The photocurrent value of the 2g-C3N4:1Al2O3 hybrid electrode is about 2.7 times that of the bare g-C3N4, demonstrating the high separation efficiency of the electrons and holes in heterjunctions. Light on off

2C3N4:1Al2O3

0.00006

Current intensity (A)

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


C3N4

0.00004

0.00002

0.00000

0

40

80

120

160

200

240

Time (s)

Fig. 11. Transient photocurrent responses of pure g-C3N4 and 2g-C3N4:1Al2O3 photocatalysts electrodes with light on/off cycles under visible light irradiation (λ> 420 nm). The reactive species generated in the photocatalytic process are investigated in the presence of scavengers of KI, tert-butyl alcohol (TBA), and 1,4-benzoquinone(BQ) to capture hole (h+), •OH radical, and superoxide anion radical (•O2−), respectively.57-59 From the results shown in Fig. 12a it is obvious that 1 mM BQ quenches completely the degradation of RhB, showing •O2− has significance influence on pollutant degradation. Whereas in the presence of 10.0 mM TBA, there is almost no change for the removal of RhB, indicating •OH is not an active species


19


generated in this system. It is also seen that the addition of 2 mM KI decreases the degradation efficiency of RhB slightly, which demonstrates that h+ has certain effect for the elimination of RhB. In a word, the scavenger experiments indicate •O2− and h+ are the main and assistant reactive oxidation species responsible for the degradation of RhB, respectively.

1.8

1.0

a

0.6 0.4

BQ KI TBA No scavenger

0.2

b

1.6

Absorbance(a.u)

0.8

C/C0

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 20 of 32

1.4

1C3N4:3Al2O3

1.2

C3N4 1C3N4:2Al2O3

1.0

3C3N4:1Al2O3 1C3N4:1Al2O3

0.8

2C3N4:1Al2O3

0.6 0.4 0.2

0.0 -20

0

20

40

60


80

0.0 200

250

300

350

400

Wavelength (nm)

Fig. 12. (a) Photocatalytic degradation of RhB in the presence of scavengers; (b) UV-vis absorption spectra of NBT in various photocatalyst suspensions. To further investigate the difference of photocatalytic activities among various photocatalysts, nitroblue tetrazolium (NBT, 2.5 × 10-5 mol/L) was employed to observe the amount of •O2− because NBT has a maximum absorption peak at 259 nm while the product of •O2− and NBT does not.60 Fig. 12b shows UV-vis absorption spectra of product of •O2− and NBT over the as-prepared photocatalysts after 40 min reaction. It is seen that the order of intensity decrease is 2g-C3N4:1Al2O3>1g-C3N4:1Al2O3>3g-C3N4:1Al2O3>1g-C3N4:2Al2O3>g-C3N4>1gC3N4:3Al2O3, which is in accordance with their photocatalytic activities, further showing •O2− is the active species.


20

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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


Based on above-mentioned experimental data and measurement, the possible routes of photo-generated electron transfer and photocatalytic reaction of RhB in Al2O3/g-C3N4 heterojunctions are proposed as Scheme 1. The as-obtained mesoporosity and weak crystallinity of Al2O3 diversify the surface active sites and defects.61 Under visible-light irradiation, electrons are excited from highest occupied molecular orbital (HOMO) of g-C3N4 to its LUMO, then some of them can migrate to the defect sites of Al2O3 serving as electron acceptor, which enhances the separation efficiency of photo-generated electrons and holes, and photocatalytic activity. As a result, O2 adsorbed on the surface of photocatalysts can trap the electrons on the defective sites and LUMO to generate •O2−. Subsequently, RhB dye molecules react with •O2− and holes, then are degraded.

Scheme 1. Schematic diagram of electrons transfer and radicals generation over Al2O3/g-C3N4 heterojunctions. 4. Conclusion Mesoporous photo-active Al2O3 with high surface area was developed via simple precipitation route and efficient Al2O3/g-C3N4 heterostructured photocatalysts were constructed.


21


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 32

The as-prepared 2g-C3N4:1Al2O3 heterojunction shows the highest photocatalytic activity in degrading rhodamine B (RhB) under visible-light illumination, the reaction rate constant of which is 2.5 times that of pristine g-C3N4. In degradation of methyl orange (MO), its photocatalytic ability is 3.7 times as high as that of pure g-C3N4.The recycle tests indicate that the heterojunction is a stable and reusable photocatalyst in solution. This work not only presents a method to synthesize photo-active Al2O3 and can enlarge its application in photocatalysis, but also provides reference for the research on role of defects in transferring photo-induced electrons. AUTHOR INFORMATION Corresponding Author *Corresponding author. Tel.: +86 311 81669971; Fax: +86 311 81668528. E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (No. 21376061, 21076060), the Program for New Century Excellent Talents in University (No. NCET-12-0686), Natural

Science

Foundation

for

Distinguished

Young Scholar

of

Hebei

Province

(B2015208010), and Scientific Research Foundation for High-Level Talent in University of Hebei Province (GCC2014057).


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REFERENCES (1)

Maity, S.; Zhu, M.; Shinabery, R. S.; Zheng, N. Intermolecular [3+2] cycloaddition of

cyclopropylamines with olefins by visible-light photocatalysis. Angew. Chem. Int. Ed. 2012, 51, 222. (2)

Wang, X. C.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen,

K.;

Antonietti, M. A metal-free polymeric photocatalyst for hydrogen production from water

under visible light. Nat. Mater. 2009, 8, 76. (3)

Wang, Y.; Wang, X. C.; Antonietti, M. Polymeric graphitic carbon nitride as a

heterogeneous organocatalyst: From photochemistry to multipurpose catalysis to sustainable chemistry. Angew. Chem. Int. Ed. 2012, 51, 68. (4)

Zheng, Y.; Liu, J.; Liang, J.; Jaroniec, M.; Qiao, S. Z. Graphitic carbon nitride materials:

controllable synthesis and applications in fuel cells and photocatalysis. Energy Environ. Sci.2012, 5, 6717. (5)

Song, L. M.; Zhang, S. J.; Wu, X. Q.; Tian, H. F.; Wei, Q. W. Graphitic C3N4

photocatalyst for esterification of benzaldehyde and alcohol under visible light radiation. Ind. Eng. Chem. Res. 2012, 51, 9510. (6)

Xu, H.; Yan, J.; Xu, Y.; Song, Y.; Li, H. ; Xia, J. ; Huang, C. ; Wan, H. Novel visible-

light-driven AgX/graphite-like C3N4 (X = Br, I) hybrid materials with synergistic photocatalytic activity. Appl. Cataly. B: Environ. 2013, 129, 182.


23


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

(7)

Page 24 of 32

Chang, C.; Fu, Y.; Hu, M.; Wang, C. Y.; Shan, G. Q.; Zhu, L. Y. Photodegradation of

bisphenol A by highly stable palladium-doped mesoporous graphite carbon nitride (Pd/mpgC3N4) under simulated solar light irradiation. Appl. Cataly. B: Environ. 2013, 142–143, 553. (8)

Liu, G.; Niu, P.; Sun, C. H.; Smith, S. C.; Chen, Z. G.; Lu, G. Q.; Cheng, H. M. Unique

electronic structure induced high photoreactivity of sulfur-doped graphitic C3N4. J. Am. Chem. Soc. 2010, 132, 11642. (9)

Dong, G. H.; Zhao, K.; Zhang, L. Z.

Carbon self-doping induced high electronic

conductivity and photoreactivity of g-C3N4. Chem. Commun. 2012, 48, 6178. (10)

Schwinghammer, K.; Mesch, M. B.; Duppel, V.; Ziegler, C.; Senker, J.; Lotsch, B. V.

Crystalline carbon nitride nanosheets for improved visible-light hydrogen evolution. J. Am. Chem. Soc. 2014, 136, 1730. (11)

Dong, F; Ou, M. Y.; Jiang, Y. K.; Guo, S.; Wu, Z. B. Efficient and durable visible light

photocatalytic performance of porous carbon nitride nanosheets for air purification. Ind. Eng. Chem. Res. 2014, 53, 2318. (12)

Zhang, X. S.; Hu, J. Y.; Jiang, H. Facile modification of a graphitic carbon nitride

catalyst to improve its photoreactivity under visible light irradiation. Chem. Eng. J. 2014, 256, 230. (13)

Liu, C.; Jing, L. Q.; He, L. M.; Luan, Y. B.; Li, C. M. Phosphate-modified graphitic C3N4

as efficient photocatalyst for degrading colorless pollutants by promoting O2 adsorption. Chem. Commun. 2014, 50, 1999.


24

Page 25 of 32

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


(14)

Yang, Y. X.; Guo, Y. N.; Liu, F. Y.; Yuan, X.; Guo, Y. H.; Zhang, S. Q.; Guo, W.; Huo,

M. X. Preparation and enhanced visible-light photocatalytic activity of silver deposited graphitic carbon nitride plasmonic photocatalyst. Appl. Catal. B: Environ. 2013, 142, 828. (15)

Yu, J. G.; Wang, K.; Xiao, W.; Cheng, B. Photocatalytic reduction of CO2 into

hydrocarbon solar fuels over g-C3N4-Pt nanocomposite photocatalysts. Phys. Chem. Chem. Phys. 2014, 16, 11492. (16)

Min, S. X.; Lu,G. X. Enhanced electron transfer from the excited Eosin Y to mpg-C3N4

for highly efficient hydrogen evolution under 550 nm irradiation. J. Phys. Chem. C 2012, 116, 19644. (17)

Wang, D. S.; Sun, H. T.; Luo, Q. Z.; Yang, X. L.; Yin, R. An efficient visible-light

photocatalyst prepared from g-C3N4 and polyvinyl chloride. Appl. Catal. B: Environ. 2014, 156, 323. (18)

Katsumata, H.; Sakai, T.; Suzuki, T.; Kaneco, S. Highly efficient photocatalytic activity

of g-C3N4/Ag3PO4 hybrid photocatalysts through z-scheme photocatalytic mechanism under visible light. Ind. Eng. Chem. Res. 2014, 53, 8018. (19)

Shi, L.; Liang, L.; Ma, J.; Wang, F. X.; Sun, J. M. Enhanced photocatalytic activity over

the Ag2O–g-C3N4 composite under visible light. Catal. Sci. Technol. 2014, 4, 758. (20)

Wang, X. J.; Yang, W. Y.; Li, F. T.; Xue, Y. B.; Liu, R. H.; Hao, Y. J. In situ microwave-

assisted synthesis of porous N-TiO2/g-C3N4 heterojunctions with enhanced visible-light photocatalytic properties. Ind. Eng. Chem. Res. 2013, 52, 17140.


25


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

(21)

Page 26 of 32

Liu, W.; Wang, M. L.; Xu, C. X.; Chen, S. F. Facile synthesis of g-C3N4/ZnO composite

with enhanced visible light photooxidation and photoreduction properties. Chem. Eng. J. 2012, 209, 386. (22)

Wang, X. J.; Wang, Q.; Li, F. T.; Yang, W. Y.; Zhao, Y.; Hao, Y. J.; Liu, S. J. Novel

BiOCl–C3N4 heterojunction photocatalysts: In situ preparation via an ionic-liquid-assisted solvent-thermal route and their visible-light photocatalytic activities. Chem. Eng. J. 2013, 234, 361. (23)

Pan, C. S.; Xu, J.; Wang, Y. J.; Li, D.; Zhu, Y. F. Dramatic activity of C3N4/BiPO4

photocatalyst with core/shell structure formed by self-assembly. Adv. Funct. Mater. 2012, 22, 1518. (24)

Li, Z. S.; Yang, S. Y.; Zhou, J. M.; Li, D. H.; Zhou, X. F.; Ge, C. Y.; Fang, Y. P. Novel

mesoporous g-C3N4 and BiPO4 nanorods hybrid architectures and their enhanced visible-lightdriven photocatalytic performances. Chem. Eng. J. 2014, 241, 344. (25)

He, Y. M.; Cai, J.; Li, T. T.; Wu, Y.; Lin, H. J.; Zhao, L. H.; Luo, M. F. Efficient

degradation of RhB over GdVO4/g-C3N4 composites under visible-light irradiation. Chem. Eng. J. 2013, 215–216, 721. (26)

Li, T. T.; Zhao, L. H.; He, Y. M.; Cai, J.; Luo, M. F.; Lin, J. J. Synthesis of g-

C3N4/SmVO4 composite photocatalyst with improved visible light photocatalytic activities in RhB degradation. Appl. Catal. B: Environ. 2013, 129, 255. (27)

He, Y. M.; Cai, J.; Zhang, L. H.; Wang, X. X.; Lin, H. J.; Teng, B. T.; Zhao, L. H.;

Weng, W. Z.; Wan, H. L.; Fan, M. H. Comparing two new composite photocatalysts, t-LaVO4/g-


26

Page 27 of 32

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


C3N4 and m-LaVO4/g-C3N4, for their structures and performances. Ind. Eng. Chem. Res. 2014, 53, 5905. (28)

He, Y. M.; Cai, J.; Li, T. T.; Wu, Y.; Yi, Y. M.; Luo, M. F.; Zhao, L. H. Synthesis,

characterization, and activity evaluation of DyVO4/g-C3N4 composites under visible-light irradiation. Ind. Eng. Chem. Res. 2012, 51, 14729. (29)

Sun, L. M.; Qi, Y.; Jia, C. J.; Jin. Z.; Fan, W. L. Enhanced visible-light photocatalytic

activity of g-C3N4/Zn2GeO4 heterojunctions with effective interfaces based on band match. Nanoscale 2014, 6, 2649. (30)

Zang, Y. P.; Li, L. P.; Li, X. G.; Lin, R.; Li, G. S. Synergistic collaboration of g-

C3N4/SnO2 composites for enhanced visible-light photocatalytic activity. Chem. Eng. J. 2014, 246, 277. (31)

Zang, Y. P.; Li, L. P.; Zuo, Y.; Lin, H. F.; Li, G. S.; Guan, X. F. Facile synthesis of

composite g-C3N4/WO3: a nontoxic photocatalyst with excellent catalytic activity under visible light. RSC Adv. 2013, 3, 13646. (32)

Chen, D. M.; Wang, K. W.; Xiang, D. G.; Zong, R. L.; Yao, W. Q.; Zhu, Y. F.

Significantly enhancement of photocatalytic performances via core–shell structure of ZnO@mpg-C3N4. Appl. Catal. B: Environ. 2014, 147, 554. (33)

Chen, D. M.; Wang, K. W.; Ren, T. Z.; Ding, H.; Zhu, Y. F. Synthesis and

characterization of the ZnO/mpg-C3N4 heterojunction photocatalyst with enhanced visible light photoactivity. Dalton Trans. 2014, 43, 13105.


27


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

(34)

Page 28 of 32

Wang, X. X.; Wang, S. S.; Hu, W. D.; Cai, J.; Zhang, L. H.; Dong, L. Z.; Zhao, L. H.; He,

Y. M. Synthesis and photocatalytic activity of SiO2/g-C3N4 composite photocatalyst. Mater. Lett. 2014, 115, 53. (35)

Awadallah, A. E.; Mostafa, M. S.; Aboul-Enein, A. A.; Hanafi, S. A. Hydrogen

production via methane decomposition over Al2O3–TiO2 binary oxides supported Ni catalysts: Effect of Ti content on the catalytic efficiency. Fuel 2014, 129, 68. (36)

Saha, A.; Eyman, D. P. Surface optimization and redox behavior of vanadium oxides

supported on γ-Al2O3. Ind. Eng. Chem. Res. 2011, 50, 9027. (37)

Al-Ghamdi, S. A.; Hossain, M. M.; de Lasa, H. I. Kinetic modeling of ethane oxidative

dehydrogenation over VOx/Al2O3 catalyst in a fluidized-bed riser simulator. Ind. Eng. Chem. Res. 2013, 52, 5235. (38)

Chu, S. Z.; Inoue, S.; Wada, K.; Li, D.; Haneda, H. Highly porous TiO2/Al2O3 composite

nanostructures on glass by anodization and the sol–gel process: fabrication and photocatalytic characteristics. J. Mater. Chem. 2003, 13, 866. (39)

Anderson, C.; Bard, A. J. Improved photocatalytic activity and characterization of mixed

TiO2/SiO2 and TiO2/Al2O3 materials. J. Phys. Chem. B 1997, 101, 2611. (40)

Liu, W. J.; Zeng, F. X.; Jiang, H.; Zhang, X. S.; Li, W. W. Composite Fe2O3 and

ZrO2/Al2O3 photocatalyst: Preparation, characterization, and studies on the photocatalytic activity and chemical stability. Chem. Eng. J. 2012, 180, 9.


28

Page 29 of 32

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


(41)

Bouslama, M.; Amamra, M. C.; Jia, Z.; Amar, M. B.; Chhor, K.; Brinza, O.; Abderrabba,

M.; Vignes, J. L.; Kanaev, A. Nanoparticulate TiO2–Al2O3 photocatalytic media: Effect of particle size and polymorphism on photocatalytic activity. ACS Catal. 2012, 2, 1884. (42)

Hankare, P. P.; Patil, R. P.; Jadhav, A.; Garadkar, K. M.; Sasikala, R. Enhanced

photocatalytic degradation of methyl red and thymol blue using titania–alumina–zinc ferrite nanocomposite. Appl. Catal. B: Environ. 2011, 107, 333. (43)

Li, F. T.; Zhao, Y.; Liu, Y.; Hao, Y. J.; Liu, R. H.; Zhao, D. S. Solution combustion

synthesis and visible light-induced photocatalytic activity of mixed amorphous and crystalline MgAl2O4 nanopowders. Chem. Eng. J. 2011, 173, 750. (44)

Li, F. T.; Zhao, Y.; Wang, Q.; Wang, X. J.; Hao, Y. J.; Liu, R. H.; Zhao, D. S. Enhanced

visible-light photocatalytic activity of active Al2O3/g-C3N4 heterojunctions synthesized via surface hydroxyl modification. J. Hazard. Mater. 2015, 283, 371. (45)

Li, F. T.; Zhao, Y.; Hao, Y. J.; Wang, X. J.; Liu, R. H.; Zhao, D. S.; Chen, D. M. N-

doped P25 TiO2–amorphous Al2O3 composites: One-step solution combustion preparation and enhanced visible-light photocatalytic activity. J. Hazard. Mater. 2012, 239, 118. (46)

Wang, Z. J.; Tian, Y.; Fan, H. S.; Gong, J. H.; Yang, S. G.; Ma, J. H.; Xu, J. Facile seed-

assisted hydrothermal fabrication of γ-AlOOH nanoflake films with superhydrophobicity. New J. Chem. 2014, 38, 1321. (47)

Kong, J.; Chao, B. X.; Wang, T.; Yan, Y. L. Preparation of ultrafine spherical AlOOH

and Al2O3 powders by aqueous precipitation method with mixed surfactants. Powder Technol. 2012, 229, 7.


29


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

(48)

Page 30 of 32

Wu, G. S.; Thind, S. S.; Wen, J. L.; Yan, K.; Chen, A. C. A novel nanoporous-C3N4

photocatalyst with superior high visible light activity. Appl. Catal. B: Environ. 2013, 142–143, 590. (49)

Sun, J. X.; Yuan, Y. P.; Qiu, L. G.; Jiang, X.; Xie, A. J.; Shen, Y. H.; Zhu, J. F.

Fabrication of composite photocatalyst g-C3N4–ZnO and enhancement of photocatalytic activity under visible light. Dalton Trans. 2012, 41, 6756. (50)

Brunauer, S.; Emmet, P.H.; Teller, E. On a theory of the van der Waals adsorption of

gases. J. Am. Chem. Soc. 1940, 62, 1723. (51)

Yu, H. G.; Liu, R.; Wang, X. F.; Wang, P.; Yu, J. G. Enhanced visible-light

photocatalytic activity of Bi2WO6 nanoparticles by Ag2O cocatalyst. Appl. Catal. B: Environ. 2012, 111–112, 326. (52)

Liu, W.; Wang, M. L.; Xu, C. X.; Chen, S. F.; Fu, X. L. Significantly enhanced visible-

light photocatalytic activity of g-C3N4 via ZnO modification and the mechanism study. J. Mol. Catal. A: Chem. 2013, 368–369, 9. (53)

Wang, Z. J.; Du, H.; Gong, J. H.; Yang, S. G.; Ma, J. H.; Xu, J. Facile synthesis of

hierarchical flower-like γ-AlOOH films via hydrothermal route on quartz surface. Colloid. Surface. A 2014, 450, 76. (54)

Liu, L.; Ma, D.; Zheng, H.; Li, X. J.; Cheng, M. J.; Bao, X. H. Synthesis and

characterization of microporous carbon nitride. Micropor. Mesopor. Mater. 2008, 110, 216. (55)

Xiang, Q. J.; Yu, J. G.; Jaroniec, M. Preparation and enhanced visible-light photocatalytic

H2-production activity of graphene/C3N4 composites. J. Phys. Chem. C 2011, 115, 7355.


30

Page 31 of 32

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


(56)

Yang, N.; Li, G. Q.; Wang, W. L.; Yang, X. L.; Zhang, W. F. Photophysical and enhanced

daylight photocatalytic properties of N-doped TiO2/g-C3N4 composites. J. Phys. Chem. Solids 2011, 72, 1319. (57)

Palominos, R.; Freer, J.; Mondaca, M. A.; Mansilla, H. D. Evidence for hole participation

during the photocatalyticoxidation of the antibiotic flumequine. J. Photoch. Photobio. A 2008, 193, 139. (58)

Li, X. C.; Jiang, G. L.; He, G. H.; Zheng, W. J.; Tan, Y.; Xiao, W. Preparation of porous

PPy-TiO2 composites: Improved visible light photoactivity and the mechanism. Chem. Eng. J. 2014, 236, 480. (59)

Zhao, C.; Pelaez, M.; Duan, X. D.; Deng, H. P.; O'Shea, K.; Fatta-Kassinos, D.;

Dionysiou, D. D. Role of pH on photolytic and photocatalytic degradation of antibiotic oxytetracycline in aqueous solution under visible/solar light: Kinetics and mechanism studies. Appl. Catal. B: Environ. 2013, 134–135, 83. (60)

Xu, X. L.; Duan, X.; Yi, Z. G.; Zhou, Z. W.; Fan, X. M.; Wang, Y. Photocatalytic

production of superoxide ion in the aqueous suspensions of two kinds of ZnO under simulated solar light. Catal. Commun. 2010, 12, 169. (61)

Lee, S. W.; Paraguay-Delgado F.; Arizabalo R. D.; Gómez R.; Rodríguez-González V.

Understanding the photophysical and surface properties of TiO2–Al2O3 nanocomposites. Mater. Lett. 2013, 107, 10.


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Precipitation Synthesis of Mesoporous Photoactive Al2O3 for

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