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Solvothermal synthesis of visible-light-active N-modified ZrO2 nanoparticles
Materials Letters 130 (2014) 139–142
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Solvothermal synthesis of visible-light-active N-modified ZrO2 nanoparticles Yanyan Zhao a, Yongcai Zhang a,n, Jing Li b, Xihua Du b a b
School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, China School of Chemistry and Chemical Engineering, Xuzhou Institute of Technology, Xuzhou 221111, China
art ic l e i nf o
a b s t r a c t
Article history: Received 31 March 2014 Accepted 4 May 2014 Available online 22 May 2014
This work reports the synthesis and evaluation of visible-light-active N-modified ZrO2 nanoparticles for photocatalytic reduction of aqueous Cr(VI). Using ZrCl4, absolute ethanol and concentrated (65–68 mass%) nitric acid as the starting materials, a simple low temperature (180 1C) solvothermal method was proposed for the synthesis of N-modified ZrO2 nanoparticles (which were abbreviated as ZrO2–HNO3). The composition, structure, BET specific surface area and optical property of ZrO2–HNO3 were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, N2 adsorption and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of ZrO2–HNO3 was tested in the reduction of aqueous Cr(VI) under visible-light (λ 4420 nm) irradiation, and compared with that of ZrO2– NH3 (which denoted the product synthesized when 65–68 mass% HNO3 was replaced by 25–28 mass% NH3 H2O). It was observed that ZrO2–HNO3 exhibited remarkable visible-light-absorbing ability and high photocatalytic activity, whereas ZrO2–NH3 exhibited little absorption of visible-light and no photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ 4420 nm) irradiation. This work suggests that ZrO2–HNO3 is a new promising visible-light-activated photocatalyst. & 2014 Elsevier B.V. All rights reserved.
Keywords: Semiconductors Nanoparticles Powder technology Functional
1. Introduction Recently, nonmetals-modified wide bandgap oxide semiconductors have received considerable attention, due to their intriguing visible-light-absorbing ability and promising applications as efficient photocatalysts [1–7] ,photovoltaic materials [8], etc. ZrO2 is an inexpensive, stable, non-toxic, wide bandgap oxide semiconductor (Eg E5.0 eV [9]), and has appropriate flat-band potentials (e.g., its conduction band and valence band potentials are 1.0 and þ4.0 V (vs. NHE at pH 0) [9], respectively) for photocatalytic purposes. However, so far, the research on nonmetalsmodified ZrO2 is still scarce. Therefore, it has great scientific and practical significance to research on nonmetals-modified ZrO2. The solvothermal method can not only synthesize the products with small crystallite size and large surface area, but also achieve the desirable doping of the products at relatively low temperatures [1–3]. Herein, a simple low temperature (180 1C) solvothermal method was proposed for the synthesis of N-modified ZrO2 nanoparticles (ZrO2–HNO3) from ZrCl4, absolute ethanol and concentrated (65–68 mass%) nitric acid. Besides, the photocatalytic activity of ZrO2–HNO3 was tested in the reduction of aqueous Cr
n
Corresponding author. Tel.: þ 86 18952568061. E-mail address: [email protected] (Y. Zhang).
http://dx.doi.org/10.1016/j.matlet.2014.05.093 0167-577X/& 2014 Elsevier B.V. All rights reserved.
(VI) under visible-light (λ 4 420 nm) irradiation, and compared with that of ZrO2–NH3. 2. Experimental Synthesis: 3 mmol ZrCl4 was placed into a 50 ml Teflon jar, and 27 ml of absolute ethanol was added and stirred until the dissolution of ZrCl4. Then, 3 ml of HNO3 (65–68 mass% or 14.36– 15.16 mol/L) or NH3 H2O (25–28 mass% or 13.32–14.44 mol/L) was added to the above solution, and stirred for 20 min. The Teflon jars were sealed into stainless steel autoclaves and heated in an electric oven at 180 1C for 12 h. After the autoclaves cooled down to room temperature naturally, the resultant precipitates were centrifuged, washed with absolute ethanol and deionized water, and dried in vacuum at 100 1C for 4 h. Characterization: The compositions, structures, BET specific surface areas and optical properties of the products were characterized by X-ray diffraction (XRD, German Bruker AXS D8 ADVANCE X-ray diffractometer), X-ray photoelectron spectroscopy (XPS, American Thermo-VG Scientific ESCALAB 250 XPS system, Al Kα radiation and adventitious C 1s peak (284.6 eV) calibration), transmission electron microscopy (TEM, American FEI Tecnai G2 F30 S-TWIN field-emission transmission electron microscopy), N2 adsorption (American Micromeritics Instrument Corporation TriStar II 3020 surface area and
140
Y. Zhao et al. / Materials Letters 130 (2014) 139–142
porosity analyzer) and UV–vis diffuse reflectance spectra (American Varian Cary 5000 UV–vis–NIR spectrophotometer). Photocatalytic activities of the products (the dosage of each product was 300 mg) were tested in the reduction of Cr(VI) in 300 ml of 50 mg/L K2Cr2O7 aqueous solution under visible-light (λ 4420 nm) irradiation [10]. The quantification method for Cr(VI) was the standard diphenylcarbazide colorimetric spectrophotometry [10].
3. Results and discussion
220
(a)
400
311 222
200
Intensity (a. u.)
111
Fig. 1(a) and (b) shows the XRD patterns of ZrO2–HNO3 and ZrO2–NH3, respectively. The main XRD peaks of both products can be indexed to cubic phase ZrO2, according to the Joint Committee on Powder Diffraction Standards card number 89-9069.
(b) 10
20
30
40 50 2θ (deg.)
60
70
80
Fig. 1. XRD patterns of (a) ZrO2–HNO3 and (b) ZrO2–NH3.
Zr 3d5/2
Zr 3d
Zr 3d3/2
ZrO2-NH3 ZrO2-HNO3
NO C-O
C=O
534 532 530 528 Binding energy (eV)
526
N 1s
C-O
Intensity (a. u.)
Intensity (a. u.)
Zr-NO/ON Zr-OH C=O Zr-O
536
C-C/C-H
C 1s
ZrO2-NH3 Zr-ON NO
Zr-NO
ZrO2-HNO3
ZrO2-HNO3
292
C-O
ZrO2-NH3
ZrO2-HNO3
192 190 188 186 184 182 180 178 176 Binding energy (eV)
ZrO2-NH3
Zr-OH Zr-O C=O
O 1s
Intensity (a. u.)
Intensity (a. u.)
The surface elemental compositions and chemical states of ZrO2–HNO3 and ZrO2–NH3 were determined by XPS. The survey XPS spectra (not shown here) reveal that ZrO2–HNO3 is composed of Zr, O, N and C, whereas ZrO2–NH3 comprises Zr, O and C. The high resolution XPS spectra of Zr 3d reveal that the binding energies of Zr 3d5/2 of ZrO2–HNO3 and ZrO2–NH3 are 182.5 and 182.1 eV (Fig. 2), respectively, which can be assigned to Zr4 þ in ZrO2 [11–13]. The O 1s XPS spectrum of ZrO2–HNO3 can be deconvoluted into three peaks at (i) 530.1, (ii) 531.6, and (iii) 532.8 eV (Fig. 2), which can be attributed to (i) lattice oxygen of ZrO2, (ii) Zr–OH, C¼O, Zr–NO and Zr–ON, and (iii) C–O and NO [11], respectively; whereas the O 1s XPS spectrum of ZrO2–NH3 can be deconvoluted into three peaks at (i) 529.7, (ii) 531.2, and (iii) 532.5 eV (Fig. 2), which can be attributed to (i) lattice oxygen of ZrO2, (ii) Zr–OH and C¼O, and (iii) C–O [11], respectively. The C 1s XPS spectra of ZrO2–HNO3 and ZrO2–NH3 can be deconvoluted into three peaks at around (i) 284.6 and 284.6 eV, (ii) 286.2 and 286.2 eV, and (iii) 288.6 and 288.9 eV (Fig. 2), which can be assigned to (i) C–C or C–H, (ii) C–O, and (iii) C¼O [11], respectively. The N 1s XPS spectrum of ZrO2–HNO3 can be deconvoluted into three peaks at (i) 398.4, (ii) 400.0, and (iii) 401.6 eV (Fig. 2), which can be assigned to (i) Zr–NO, (ii) Zr–ON, and (iii) adsorbed NO species [11], respectively; whereas the N 1s XPS spectrum of ZrO2–NH3 indicates that the N content in ZrO2–NH3 is negligible (Fig. 2). In the current solvothermal synthesis, the formation of ZrO2 in the presence of HNO3 (65–68 mass%) or NH3 H2O (25–28 mass%) was both likely via two steps: first, hydrolysis of ZrCl4 to form Zr (OH)4; second, dehydration of Zr(OH)4 to produce ZrO2. However, the hydrolysis rate of ZrCl4 in the presence of HNO3 or NH3 H2O was quite different. The highly acidic HNO3 (65–68 mass%) can inhibit the hydrolysis of ZrCl4, whereas the alkaline NH3 H2O (25– 28 mass%) can promote the hydrolysis of ZrCl4. This can be inferred from the facts that the addition of 3 ml of HNO3 (65–68 mass%) to
290 288 286 284 Binding energy (eV)
282
280
408 406 404 402 400 398 396 394 392 390 Binding energy (eV)
Fig. 2. XPS spectra of ZrO2–HNO3 and ZrO2–NH3.
Y. Zhao et al. / Materials Letters 130 (2014) 139–142
141
1.0 ZrO2-NH3 ZrO2-HNO3
Ct/C0
0.8 0.6 0.4 0.2 0.0 0
60 120 180 240 Irradiation time (min)
300
Fig. 5. Photocatalytic reduction of aqueous Cr(VI) in the presence of ZrO2–HNO3 or ZrO2–NH3 under visible-light (λ 4420 nm) irradiation. Note: C0 and Ct are the Cr (VI) concentrations at the irradiation times of 0 (i.e., just after the dark adsorption) and t min, respectively.
Fig. 3. TEM images of (a) ZrO2–HNO3 and (b) ZrO2–NH3.
1.0
Absorbance
0.8 0.6
ZrO2-HNO3
decompose itself under the solvothermal condition to generate NO species. The NO species can be adsorbed on the surface or incorporated into the crystal lattices of ZrO2 nanoparticles, forming N-modified ZrO2. The TEM images of ZrO2–HNO3 and ZrO2–NH3 are shown in Fig. 3(a) and (b), respectively. It can be seen from Fig. 3(a) and (b) that ZrO2–HNO3 and ZrO2–NH3 comprise nanocrystals with the size of about 6–14 and 5–10 nm, respectively. The BET specific surface areas of ZrO2–HNO3 and ZrO2–NH3 were determined to be 180.7 and 296.1 m2/g, respectively by N2 adsorption. Fig. 4 shows the UV–vis diffuse reflectance spectra of ZrO2–HNO3 and ZrO2–NH3. ZrO2–NH3 displays little absorption of visible-light, whereas ZrO2–HNO3 displays remarkable photoabsorption in the whole visible region (λ E400–700 nm). The strong and broad visible-light-response of ZrO2–HNO3 suggests that ZrO2–HNO3 has the potential to be an efficient visible-light-activated photocatalyst. Fig. 5 shows the photocatalytic reduction of aqueous Cr(VI) in the presence of ZrO2–HNO3 or ZrO2–NH3 under visible-light (λ 4420 nm) irradiation. ZrO2–NH3 exhibits no photocatalytic activity, because it cannot absorb the incident visible-light (λ 4420 nm) (Fig. 4). In contrast, ZrO2–HNO3 exhibits high photocatalytic activity in the reduction of aqueous Cr(VI) under visiblelight (λ 4420 nm) irradiation, for example, it can catalyze almost the complete reduction of Cr(VI) under visible-light (λ 4 420 nm) irradiation for 300 min. The high visible-light-driven photocatalytic activity of ZrO2–HNO3 can be mainly attributed to its remarkable visible-light-absorbing ability (Fig. 4).
0.4
4. Conclusions
0.2 ZrO2-NH3
0.0 300
400 500 600 Wavelength (nm)
700
800
Fig. 4. UV–vis diffuse reflectance spectra of ZrO2–HNO3 and ZrO2–NH3 in the absorbance mode.
the ZrCl4 ethanol solution only produced a homogeneous solution, whereas the addition of 3 ml of NH3 H2O (25–28 mass%) to the ZrCl4 ethanol solution immediately produced a colloidal suspension. The inhibited or slower hydrolysis of ZrCl4 in the presence of HNO3 (65–68 mass%) can facilitate the doping processes. Furthermore, the concentrated HNO3 (65–68 mass%) can be reduced by ethanol or
N-modified ZrO2 nanoparticles (ZrO2–HNO3) were synthesized via the solvothermal reactions of ZrCl4 in the mixed solution of absolute ethanol and concentrated (65–68 mass%) nitric acid at 180 1C for 12 h. ZrO2–HNO3 exhibited remarkable visible-light-absorbing ability and high photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ 4420 nm) irradiation, thus it can serve as a new promising visible-light-activated photocatalyst.
Acknowledgments This work is funded by Jiangsu Key Laboratory of Environ mental Material and Environmental Engineering, the Science & Technology Innovation Fund of Yangzhou University (2013CXJ017),
142
Y. Zhao et al. / Materials Letters 130 (2014) 139–142
and the Priority Academic Program Development of Jiangsu Higher Education Institutions. References [1] Dolat D, Quici N, Kusiak-Nejman E. Appl Catal B 2012;115 116:81–9. [2] He Z, Que W, Chen J, Yin X, He Y. ACS Appl Mater Interfaces 2012;4:6816–26. [3] Zhang YC, Yang M, Zhang G, Dionysiou DD. Appl Catal B 2013;142 143: 249–58. [4] Pathakoti K, Morrow S, Han C, Pelaez M, Dionysiou DD. Environ Sci Technol 2013;47:9988–96.
[5] Zhang G, Zhang YC, Nadagouda M, Han C, Dionysiou DD. Appl Catal B 2014;144:614–21. [6] Hu Z, Xu L, Chen J. Mater Lett 2013;106:421–4. [7] Si PZ, Jiang W, Wang HX, Li ZF, Liu JJ, Lee JG. Mater Lett 2012;68:161–3. [8] Li Y, Jia L, Wu C, Han S, Gong Y, Chi B. J Alloy Compd 2012;512:23–6. [9] Botta SG, Navío JA, Hidalgo MC, Litter MI. J Photochem Photobiol A 1999;129:89–99. [10] Zhang YC, Yao L, Zhang G, Dionysiou DD. Appl Catal B 2014;144:730–8. [11] Moulder JF, Stickle WF, Sobol PE, Bomben KD. In: Chastain J, editor. Handbook of x-ray photoelectron spectroscopy. Eden Prairie: Perkin-Elmer Corp; 1992. [12] Banerjee M, Srinivasan NB, Zhu H, Kim SJ. Cryst Growth Des 2012;12:5079–89. [13] Zhang B, Ding G, Zheng H, Zhu Y. Appl Catal B 2014;152 153:226–32.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Solvothermal synthesis of visible-light-active N-modified ZrO2 nanoparticles Yanyan Zhao a, Yongcai Zhang a,n, Jing Li b, Xihua Du b a b
School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, China School of Chemistry and Chemical Engineering, Xuzhou Institute of Technology, Xuzhou 221111, China
art ic l e i nf o
a b s t r a c t
Article history: Received 31 March 2014 Accepted 4 May 2014 Available online 22 May 2014
This work reports the synthesis and evaluation of visible-light-active N-modified ZrO2 nanoparticles for photocatalytic reduction of aqueous Cr(VI). Using ZrCl4, absolute ethanol and concentrated (65–68 mass%) nitric acid as the starting materials, a simple low temperature (180 1C) solvothermal method was proposed for the synthesis of N-modified ZrO2 nanoparticles (which were abbreviated as ZrO2–HNO3). The composition, structure, BET specific surface area and optical property of ZrO2–HNO3 were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, N2 adsorption and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of ZrO2–HNO3 was tested in the reduction of aqueous Cr(VI) under visible-light (λ 4420 nm) irradiation, and compared with that of ZrO2– NH3 (which denoted the product synthesized when 65–68 mass% HNO3 was replaced by 25–28 mass% NH3 H2O). It was observed that ZrO2–HNO3 exhibited remarkable visible-light-absorbing ability and high photocatalytic activity, whereas ZrO2–NH3 exhibited little absorption of visible-light and no photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ 4420 nm) irradiation. This work suggests that ZrO2–HNO3 is a new promising visible-light-activated photocatalyst. & 2014 Elsevier B.V. All rights reserved.
Keywords: Semiconductors Nanoparticles Powder technology Functional
1. Introduction Recently, nonmetals-modified wide bandgap oxide semiconductors have received considerable attention, due to their intriguing visible-light-absorbing ability and promising applications as efficient photocatalysts [1–7] ,photovoltaic materials [8], etc. ZrO2 is an inexpensive, stable, non-toxic, wide bandgap oxide semiconductor (Eg E5.0 eV [9]), and has appropriate flat-band potentials (e.g., its conduction band and valence band potentials are 1.0 and þ4.0 V (vs. NHE at pH 0) [9], respectively) for photocatalytic purposes. However, so far, the research on nonmetalsmodified ZrO2 is still scarce. Therefore, it has great scientific and practical significance to research on nonmetals-modified ZrO2. The solvothermal method can not only synthesize the products with small crystallite size and large surface area, but also achieve the desirable doping of the products at relatively low temperatures [1–3]. Herein, a simple low temperature (180 1C) solvothermal method was proposed for the synthesis of N-modified ZrO2 nanoparticles (ZrO2–HNO3) from ZrCl4, absolute ethanol and concentrated (65–68 mass%) nitric acid. Besides, the photocatalytic activity of ZrO2–HNO3 was tested in the reduction of aqueous Cr
n
Corresponding author. Tel.: þ 86 18952568061. E-mail address: [email protected] (Y. Zhang).
http://dx.doi.org/10.1016/j.matlet.2014.05.093 0167-577X/& 2014 Elsevier B.V. All rights reserved.
(VI) under visible-light (λ 4 420 nm) irradiation, and compared with that of ZrO2–NH3. 2. Experimental Synthesis: 3 mmol ZrCl4 was placed into a 50 ml Teflon jar, and 27 ml of absolute ethanol was added and stirred until the dissolution of ZrCl4. Then, 3 ml of HNO3 (65–68 mass% or 14.36– 15.16 mol/L) or NH3 H2O (25–28 mass% or 13.32–14.44 mol/L) was added to the above solution, and stirred for 20 min. The Teflon jars were sealed into stainless steel autoclaves and heated in an electric oven at 180 1C for 12 h. After the autoclaves cooled down to room temperature naturally, the resultant precipitates were centrifuged, washed with absolute ethanol and deionized water, and dried in vacuum at 100 1C for 4 h. Characterization: The compositions, structures, BET specific surface areas and optical properties of the products were characterized by X-ray diffraction (XRD, German Bruker AXS D8 ADVANCE X-ray diffractometer), X-ray photoelectron spectroscopy (XPS, American Thermo-VG Scientific ESCALAB 250 XPS system, Al Kα radiation and adventitious C 1s peak (284.6 eV) calibration), transmission electron microscopy (TEM, American FEI Tecnai G2 F30 S-TWIN field-emission transmission electron microscopy), N2 adsorption (American Micromeritics Instrument Corporation TriStar II 3020 surface area and
140
Y. Zhao et al. / Materials Letters 130 (2014) 139–142
porosity analyzer) and UV–vis diffuse reflectance spectra (American Varian Cary 5000 UV–vis–NIR spectrophotometer). Photocatalytic activities of the products (the dosage of each product was 300 mg) were tested in the reduction of Cr(VI) in 300 ml of 50 mg/L K2Cr2O7 aqueous solution under visible-light (λ 4420 nm) irradiation [10]. The quantification method for Cr(VI) was the standard diphenylcarbazide colorimetric spectrophotometry [10].
3. Results and discussion
220
(a)
400
311 222
200
Intensity (a. u.)
111
Fig. 1(a) and (b) shows the XRD patterns of ZrO2–HNO3 and ZrO2–NH3, respectively. The main XRD peaks of both products can be indexed to cubic phase ZrO2, according to the Joint Committee on Powder Diffraction Standards card number 89-9069.
(b) 10
20
30
40 50 2θ (deg.)
60
70
80
Fig. 1. XRD patterns of (a) ZrO2–HNO3 and (b) ZrO2–NH3.
Zr 3d5/2
Zr 3d
Zr 3d3/2
ZrO2-NH3 ZrO2-HNO3
NO C-O
C=O
534 532 530 528 Binding energy (eV)
526
N 1s
C-O
Intensity (a. u.)
Intensity (a. u.)
Zr-NO/ON Zr-OH C=O Zr-O
536
C-C/C-H
C 1s
ZrO2-NH3 Zr-ON NO
Zr-NO
ZrO2-HNO3
ZrO2-HNO3
292
C-O
ZrO2-NH3
ZrO2-HNO3
192 190 188 186 184 182 180 178 176 Binding energy (eV)
ZrO2-NH3
Zr-OH Zr-O C=O
O 1s
Intensity (a. u.)
Intensity (a. u.)
The surface elemental compositions and chemical states of ZrO2–HNO3 and ZrO2–NH3 were determined by XPS. The survey XPS spectra (not shown here) reveal that ZrO2–HNO3 is composed of Zr, O, N and C, whereas ZrO2–NH3 comprises Zr, O and C. The high resolution XPS spectra of Zr 3d reveal that the binding energies of Zr 3d5/2 of ZrO2–HNO3 and ZrO2–NH3 are 182.5 and 182.1 eV (Fig. 2), respectively, which can be assigned to Zr4 þ in ZrO2 [11–13]. The O 1s XPS spectrum of ZrO2–HNO3 can be deconvoluted into three peaks at (i) 530.1, (ii) 531.6, and (iii) 532.8 eV (Fig. 2), which can be attributed to (i) lattice oxygen of ZrO2, (ii) Zr–OH, C¼O, Zr–NO and Zr–ON, and (iii) C–O and NO [11], respectively; whereas the O 1s XPS spectrum of ZrO2–NH3 can be deconvoluted into three peaks at (i) 529.7, (ii) 531.2, and (iii) 532.5 eV (Fig. 2), which can be attributed to (i) lattice oxygen of ZrO2, (ii) Zr–OH and C¼O, and (iii) C–O [11], respectively. The C 1s XPS spectra of ZrO2–HNO3 and ZrO2–NH3 can be deconvoluted into three peaks at around (i) 284.6 and 284.6 eV, (ii) 286.2 and 286.2 eV, and (iii) 288.6 and 288.9 eV (Fig. 2), which can be assigned to (i) C–C or C–H, (ii) C–O, and (iii) C¼O [11], respectively. The N 1s XPS spectrum of ZrO2–HNO3 can be deconvoluted into three peaks at (i) 398.4, (ii) 400.0, and (iii) 401.6 eV (Fig. 2), which can be assigned to (i) Zr–NO, (ii) Zr–ON, and (iii) adsorbed NO species [11], respectively; whereas the N 1s XPS spectrum of ZrO2–NH3 indicates that the N content in ZrO2–NH3 is negligible (Fig. 2). In the current solvothermal synthesis, the formation of ZrO2 in the presence of HNO3 (65–68 mass%) or NH3 H2O (25–28 mass%) was both likely via two steps: first, hydrolysis of ZrCl4 to form Zr (OH)4; second, dehydration of Zr(OH)4 to produce ZrO2. However, the hydrolysis rate of ZrCl4 in the presence of HNO3 or NH3 H2O was quite different. The highly acidic HNO3 (65–68 mass%) can inhibit the hydrolysis of ZrCl4, whereas the alkaline NH3 H2O (25– 28 mass%) can promote the hydrolysis of ZrCl4. This can be inferred from the facts that the addition of 3 ml of HNO3 (65–68 mass%) to
290 288 286 284 Binding energy (eV)
282
280
408 406 404 402 400 398 396 394 392 390 Binding energy (eV)
Fig. 2. XPS spectra of ZrO2–HNO3 and ZrO2–NH3.
Y. Zhao et al. / Materials Letters 130 (2014) 139–142
141
1.0 ZrO2-NH3 ZrO2-HNO3
Ct/C0
0.8 0.6 0.4 0.2 0.0 0
60 120 180 240 Irradiation time (min)
300
Fig. 5. Photocatalytic reduction of aqueous Cr(VI) in the presence of ZrO2–HNO3 or ZrO2–NH3 under visible-light (λ 4420 nm) irradiation. Note: C0 and Ct are the Cr (VI) concentrations at the irradiation times of 0 (i.e., just after the dark adsorption) and t min, respectively.
Fig. 3. TEM images of (a) ZrO2–HNO3 and (b) ZrO2–NH3.
1.0
Absorbance
0.8 0.6
ZrO2-HNO3
decompose itself under the solvothermal condition to generate NO species. The NO species can be adsorbed on the surface or incorporated into the crystal lattices of ZrO2 nanoparticles, forming N-modified ZrO2. The TEM images of ZrO2–HNO3 and ZrO2–NH3 are shown in Fig. 3(a) and (b), respectively. It can be seen from Fig. 3(a) and (b) that ZrO2–HNO3 and ZrO2–NH3 comprise nanocrystals with the size of about 6–14 and 5–10 nm, respectively. The BET specific surface areas of ZrO2–HNO3 and ZrO2–NH3 were determined to be 180.7 and 296.1 m2/g, respectively by N2 adsorption. Fig. 4 shows the UV–vis diffuse reflectance spectra of ZrO2–HNO3 and ZrO2–NH3. ZrO2–NH3 displays little absorption of visible-light, whereas ZrO2–HNO3 displays remarkable photoabsorption in the whole visible region (λ E400–700 nm). The strong and broad visible-light-response of ZrO2–HNO3 suggests that ZrO2–HNO3 has the potential to be an efficient visible-light-activated photocatalyst. Fig. 5 shows the photocatalytic reduction of aqueous Cr(VI) in the presence of ZrO2–HNO3 or ZrO2–NH3 under visible-light (λ 4420 nm) irradiation. ZrO2–NH3 exhibits no photocatalytic activity, because it cannot absorb the incident visible-light (λ 4420 nm) (Fig. 4). In contrast, ZrO2–HNO3 exhibits high photocatalytic activity in the reduction of aqueous Cr(VI) under visiblelight (λ 4420 nm) irradiation, for example, it can catalyze almost the complete reduction of Cr(VI) under visible-light (λ 4 420 nm) irradiation for 300 min. The high visible-light-driven photocatalytic activity of ZrO2–HNO3 can be mainly attributed to its remarkable visible-light-absorbing ability (Fig. 4).
0.4
4. Conclusions
0.2 ZrO2-NH3
0.0 300
400 500 600 Wavelength (nm)
700
800
Fig. 4. UV–vis diffuse reflectance spectra of ZrO2–HNO3 and ZrO2–NH3 in the absorbance mode.
the ZrCl4 ethanol solution only produced a homogeneous solution, whereas the addition of 3 ml of NH3 H2O (25–28 mass%) to the ZrCl4 ethanol solution immediately produced a colloidal suspension. The inhibited or slower hydrolysis of ZrCl4 in the presence of HNO3 (65–68 mass%) can facilitate the doping processes. Furthermore, the concentrated HNO3 (65–68 mass%) can be reduced by ethanol or
N-modified ZrO2 nanoparticles (ZrO2–HNO3) were synthesized via the solvothermal reactions of ZrCl4 in the mixed solution of absolute ethanol and concentrated (65–68 mass%) nitric acid at 180 1C for 12 h. ZrO2–HNO3 exhibited remarkable visible-light-absorbing ability and high photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ 4420 nm) irradiation, thus it can serve as a new promising visible-light-activated photocatalyst.
Acknowledgments This work is funded by Jiangsu Key Laboratory of Environ mental Material and Environmental Engineering, the Science & Technology Innovation Fund of Yangzhou University (2013CXJ017),
142
Y. Zhao et al. / Materials Letters 130 (2014) 139–142
and the Priority Academic Program Development of Jiangsu Higher Education Institutions. References [1] Dolat D, Quici N, Kusiak-Nejman E. Appl Catal B 2012;115 116:81–9. [2] He Z, Que W, Chen J, Yin X, He Y. ACS Appl Mater Interfaces 2012;4:6816–26. [3] Zhang YC, Yang M, Zhang G, Dionysiou DD. Appl Catal B 2013;142 143: 249–58. [4] Pathakoti K, Morrow S, Han C, Pelaez M, Dionysiou DD. Environ Sci Technol 2013;47:9988–96.
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