- Email: [email protected]
CeO2 microcomposite with visible light-driven photocatalytic activity
Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Q1 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 61 62 63 64 65 66
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis of Ag2CO3/CeO2 microcomposite with visible light-driven photocatalytic activity Changle Wu n Testing Center of Yangzhou University, Yangzhou 225009, China
art ic l e i nf o
a b s t r a c t
Article history: Received 1 February 2015 Accepted 18 March 2015
Ag2CO3/CeO2 microcomposite was synthesized via chemical precipitation from pure CeO2 microspheres, AgNO3, and NaHCO3. X-ray diffraction, inductively coupled plasma optical emission spectroscopy, field emission scanning electron microscope, and high resolution transmission electron microscopy results confirmed the forming of Ag2CO3/CeO2 microcomposite. Field emission scanning microscope and high resolution transmission electron microscopy results of the as-synthesized Ag2CO3/CeO2 microcomposite revealed that Ag2CO3 particles were uniformly deposited on the surface of CeO2 microspheres (core). UV–vis diffuse reflectance spectra of both pure CeO2 and Ag2CO3/CeO2 microcomposite displayed a band gap edge at about 360 390 nm. However, compared with pure CeO2, an additional broad tail from approximately 400 nm to 800 nm appeared in the UV–vis diffuse reflectance spectrum of Ag2CO3/CeO2 microcomposite. The photocatalytic studies indicated that the as-synthesized Ag2CO3/CeO2 microcomposite was a kind of promising photocatalyst in remediation of water polluted by some chemically stable azo dyes under visible light irradiation. & 2015 Published by Elsevier B.V.
Keywords: Microcomposites Semiconductors Electron microscope Optical materials and properties
1. Introduction Owing to high photocatalytic activity, low cost, environmentally friendly feature [1], and an alternative semiconductor material for most widely used photocatalyst-TiO2 [2,3], CeO2 has been widely used as a photocatalyst [4]. However, due to a wide band gap of 3.2 eV, poor photon absorption of CeO2 limits its application in visible light photocatalyst [5]. In order to shift the optical absorption of CeO2 into the visible region, one possible approach is to combine CeO2 photocatalyst with narrow band gap semiconductor [4]. Silver carbonate (Ag2CO3) is an important narrow band gap semiconductor and it can be used as highly visible-light-response photocatalysts with a band gap of 2.30 eV (539 nm) [6]. Although Ag2CO3 is unstable in pure crystal form, it can also be applied in photocatalytic reaction [6]. For example, Ag2CO3 could maintain its stability and photocatalytic activity after Ag2CO3 is coupled with oxides, such as Ag2O [6]. However, to the best of our knowledge, the reports on synthesis and the photocatalytic properties of Ag2CO3/CeO2 microcomposite are scarce up to now. As reported, chemical precipitation is an effective and promising approach to synthesize CeO2 nanoparticles [5,7–10] or Ag2CO3/Ag2O microcomposites [6]. Herein, we report the synthesis of Ag2CO3/CeO2 n
Tel.: þ 86 514 87979022; fax: þ86 514 87979244. E-mail address: [email protected]
microcomposite by a simple chemical precipitation route, as well as the characterization of the resultant products by inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), high resolution transmission electron microscopy (HRTEM), bet (BET) surface area measurement and UV–vis diffuse reflectance spectra. Furthermore, the photocatalytic activities of pure CeO2 and the assynthesized Ag2CO3/CeO2 microcomposite are also studied by degrading Rhodamine 6G (R6G) in water under the visible light (λ4420 nm) irradiation.
2. Materials and methods All the chemical reagents used in this work, including Ce(NO3)3 6H2O, AgNO3, ethanol, and NaHCO3, were of analytical grade purchased from Sinopharm Chemical Reagent Co., Ltd., China. Pure CeO2 microspheres were fabricated by a solvothermal route from Ce(NO3)3 6H2O in ethanol at 180 1C for 12 h. The detailed synthesis process was reported in our previous report [5]. Ag2CO3/CeO2 microcomposite was prepared by a simple chemical precipitation method. The typical procedure for preparation of Ag2CO3/CeO2 was as follows: 0.25 g (1.45 mmol) of CeO2 microspheres dispersed in 80 mL distilled water, and the suspension was sonicated for 10 min. Then, 10 mL of 0.1 mol/L NaHCO3 aqueous solution was added to the CeO2 suspension and stirred magnetically at room temperature for 10 min. Subsequently,
http://dx.doi.org/10.1016/j.matlet.2015.03.086 0167-577X/& 2015 Published by Elsevier B.V.
Please cite this article as: Wu C. Synthesis of Ag2CO3/CeO2 microcomposite with visible light-driven photocatalytic activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.03.086i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
C. Wu / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
20
25
30
40
45
50
Ag2CO3(330) Ag2CO3(-132) Ag2CO3(-161) Ag2CO3(202)
Ag2CO3(310)
55
#
60
# CeO2(331)
CeO2(322)
Ag2CO3(-231)
#
CeO2(311)
#
Ag2CO3(211) Ag2CO3(221)
Ag2CO3(111) Ag2CO3(040) Ag2CO3(200) Ag CO (121) Ag2CO3(031) 2 3 Ag2CO3(220) Ag2CO3(210) Ag2CO3(131) 35
a. Pure CeO2 b. Ag2CO3/CeO2
CeO2(220)
CeO2(111)
a
#
CeO2(200)
Ag2CO3(130)
Ag2CO3(110)
#
b
Ag2CO3(-101)
10 mL of 0.1 mol/L AgNO3 aqueous solution was added quickly into the above solution with stirring. After being stirred at room temperature for 1 h, the as-formed precipitates were filtrated, washed with distilled water and ethanol, and finally dried in air at 70 1C for 12 h. The obtained products were characterized by XRD (Bruker D8 ADVANCE diffractometer system), FESEM (Philips S-4800), HRTEM (Holland F-30), UV–vis diffuse reflectance spectra (Cary 5000 spectrophotometer, Varian), ICP-OES (optima 7300 DV, PerkinElmer), and BET surface area (Micromeritics Tristar 3000). The photocatalytic reactivity of the as-synthesized pure CeO2 and Ag2CO3/CeO2 microcomposite was evaluated using 0.03 g (300 mL of 0.1 g/L) R6G as a probe molecule under the irradiation by an 1000 W Xe lamp (λ4420 nm). The detailed photocatalytic process was as described in our earlier report [5].
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 61 62 63 64 65 66
65
70
75
80
2Theta/degree Fig. 1. XRD patterns of (a) pure CeO2 and (b) as-synthesized Ag2CO3/CeO2 microcomposite. The reflections marked by # belong to CeO2.
3. Results and discussion The value of Ag/Ce in the as-synthesized Ag2CO3/CeO2 microcomposite was determined by ICP-OES to be about 67.7 mol%, which is close to the ratio of Ag/Ce in the reactants. Fig. 1a and b shows the XRD patterns of the as-synthesized pure CeO2 and Ag2CO3/CeO2 microcomposite at room temperature. The XRD patterns in Fig. 1b indicate the formation of a mixture of monoclinic phase Ag2CO3 (JCPDS card no. 070-2184) and cubic phase CeO2, while the XRD patterns in Fig. 1a can be indexed to single fluorite cubic phase CeO2 (JCPDS card no. 043-1002). No peaks corresponding to other Ag-containing or Ce-containing phases were detected in XRD patterns of the as-synthesized products in Fig. 1b, which demonstrated that the forming of Ag2CO3/CeO2 microcomposite had been achieved by this chemical precipitation method. The bet (BET) surface area measurement revealed that the as-synthesized pure CeO2 and Ag2CO3/CeO2 microcomposite had surface areas of 19 m2/g and 21 m2/g, respectively. The morphology of pure CeO2 and Ag2CO3/CeO2 are characterized by FESEM and the results are displayed in Fig. 2a1–b2. From Fig. 2a1 and a2, it can be seen that pure CeO2 displayed regular sphere-like particles with particle size 0.8–3 μm. The surfaces of pure CeO2 microspheres were clean. For Ag2CO3/CeO2 microcomposite, it showed from Fig. 2b1 and b2 that the surface of microspheres became rough due to Ag2CO3 deposition, while the size of microspheres does not change obviously. In order to confirm that small Ag2CO3 particles were uniformly deposited on the surface of the CeO2 microspheres (core), the composition analyses of the as-synthesized Ag2CO3/CeO2 sample were characterized by an XPS etching method and HREM energydispersive X-ray spectroscopy (EDS) mapping (scanning model of HRTEM) method using a FEI F30 microscope equipped with an EDAX energy EDS. HRSTEM-EDS mapping results in Fig. 2b3–b7 of the Ag2CO3/CeO2 sample revealed that Ag2CO3 particles were uniformly deposited on the surface of the CeO2 core. Moreover, smaller-sized Ag2CO3 particles were tightly attached to the surface of large-sized
Fig. 2. (a1, a2) FESEM images of pure CeO2 microspheres; (b1, b2) FESEM images and (b3–b7) HRTEM mapping images of the as-synthesized Ag2CO3/CeO2 microcomposite.
Please cite this article as: Wu C. Synthesis of Ag2CO3/CeO2 microcomposite with visible light-driven photocatalytic activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.03.086i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
C. Wu / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
1.6
1.0
a. CeO2 b. Ag2CO3/CeO2
350 ~ 390 nm
1.4
0.9
without catalyst pure CeO2 Ag2CO3/CeO2
0.8 1.2
b
0.7
1.0
0.6
C/C0
Absorbance (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
3
0.8
0.5 0.4
0.6
0.3
0.4
0.2 0.2
0.1
a 0.0 200
0.0 250
300
350
400
450
500
550
600
650
700
750
800
0
10
20
30
40
50
60
70
80
90
100
110
120
Irradiation time (min)
Wavelength (nm) Fig. 3. UV–visible diffuse reflectance spectra of: (a) pure CeO2 and (b) Ag2CO3/ CeO2.
Fig. 4. Photodegradation of R6G using (a) pure CeO2 and (b) Ag2CO3/CeO2 microcomposite.
CeO2 microspheres, and they cannot be separated from each other even by continuous ultrasonic dispersion in ethanol for 1 h before the HRTEM test. The detailed XPS etching results of Ag2CO3/CeO2 by Ar þ are shown in Supporting information. From Fig. 3, the band gap edge at the wavelength of about 360 390 nm can be found in the UV–vis diffuse reflectance spectra of both pure CeO2 [10] and Ag2CO3/CeO2 microcomposite. Comparing with pure CeO2, an additional broad tail from approximately 400 nm to 800 nm appeared in the spectra of the Ag2CO3/CeO2 microcomposite. The result indicated that the as-synthesized Ag2CO3/CeO2 microcomposite had optical capability nearly in the whole range of visible light spectrum. The photocatalytic activities of the as-prepared pure CeO2 and Ag2CO3/CeO2 microcomposites are shown in Fig. 4. C0 and C in Fig. 4 are the initial concentration after the equilibrium adsorption and the reaction concentration of R6G, respectively. As shown in Fig. 4, R6G aqueous solution can be obviously decolorized by the Ag2CO3/CeO2 photocatalyst under visible light irradiation. By contrast, when pure CeO2 substitutes for Ag2CO3/CeO2 microcomposite as the photocatalyst, the decolorizing of R6G takes place at a much slower rate under the same conditions. For example, the decolorization ratio of R6G is nearly 90% over 0.3 g of Ag2CO3/CeO2 microcomposite, which is greatly higher than only 3.0 % over 0.3 g of pure CeO2, when irradiated by the visible light for 40 min. Furthermore, without any photocatalyst, the degradation of R6G hardly occurs when subjected to the visible light irradiation for 40 min. It is worth noting that the decolorization ratio of R6G is 80% over 0.3 g of this novel Ag2CO3/CeO2 photocatalyst under visible light irradiation only for 10 min. The superior photocatalytic performance of Ag2CO3/CeO2 microcomposite can be explained by its enhanced visible light absorption ability. For a better understanding of the photocatalytic activities of the as-synthesized pure CeO2 and Ag2CO3/CeO2 microcomposites, the kinetic analysis of R6G degradation is also discussed in terms of the Langmuir Hinshel wood model, which is shown in the Supporting information. In addition, the result of the total organic carbon (TOC) measurement and the actual UV–visible spectra of degradation of R6G, which is also shown in
Supporting information, confirmed that decolorization of R6G in our experiments was related to the process of photo-degradation of R6G.
4. Conclusions In the absence of any surfactant and template, Ag2CO3/CeO2 microcomposite was successfully obtained by a chemical precipitation process, and verified by ICP-OES, XRD, FESEM, HRTEM, and BET measurements. The proposed method was simple, mild and cost-effective, which may be suitable for industrial production of Ag2CO3/CeO2 microcomposite. UV–visible diffuse reflectance spectra indicated that the as-synthesized Ag2CO3/CeO2 microcomposite had optical capability nearly in the whole range of visible light spectrum. The photocatalytic results show that coupling of Ag2CO3 with CeO2 can greatly enhance the photocatalytic efficiency of CeO2 under visible light irradiation.
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.03.086.
References [1] Wang Y, Wang F, Chen Y, Zhang D, Li B, Kang S. Appl Catal B: Environ 2014;147:602–9. [2] Meng FM, Sun ZQ. Mater Chem Phys 2009;118:349–53. [3] Wang LN, Lu F, Meng FM. INT J Photoenergy 2012;2012:1–7. [4] Huang K, Li YH, Lin S, Liang C, Xu X, Zhou YF, et al. Mater Lett 2014;124:223–6. [5] Wu C. Mater Lett 2015;139:382–4. [6] Yu C, Li G, Kumar S, Yang K, Jin R. Adv Mater 2014;26:892–8. [7] Lu F, Meng FM, Wang LN, Lu JJ, Sang Y. Mater Lett 2012;73:154–6. [8] Bo QH, Meng FM, Wang LN. Mater Lett 2014;133:216–9. [9] Meng FM, Wang LN, Cui JB. J Alloy Compd 2013;556:102–8. [10] Wang LN, Meng FM, Li KK, Lu F. Appl Surf Sci 2013;286:269–74.
Please cite this article as: Wu C. Synthesis of Ag2CO3/CeO2 microcomposite with visible light-driven photocatalytic activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.03.086i
61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Q1 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 61 62 63 64 65 66
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis of Ag2CO3/CeO2 microcomposite with visible light-driven photocatalytic activity Changle Wu n Testing Center of Yangzhou University, Yangzhou 225009, China
art ic l e i nf o
a b s t r a c t
Article history: Received 1 February 2015 Accepted 18 March 2015
Ag2CO3/CeO2 microcomposite was synthesized via chemical precipitation from pure CeO2 microspheres, AgNO3, and NaHCO3. X-ray diffraction, inductively coupled plasma optical emission spectroscopy, field emission scanning electron microscope, and high resolution transmission electron microscopy results confirmed the forming of Ag2CO3/CeO2 microcomposite. Field emission scanning microscope and high resolution transmission electron microscopy results of the as-synthesized Ag2CO3/CeO2 microcomposite revealed that Ag2CO3 particles were uniformly deposited on the surface of CeO2 microspheres (core). UV–vis diffuse reflectance spectra of both pure CeO2 and Ag2CO3/CeO2 microcomposite displayed a band gap edge at about 360 390 nm. However, compared with pure CeO2, an additional broad tail from approximately 400 nm to 800 nm appeared in the UV–vis diffuse reflectance spectrum of Ag2CO3/CeO2 microcomposite. The photocatalytic studies indicated that the as-synthesized Ag2CO3/CeO2 microcomposite was a kind of promising photocatalyst in remediation of water polluted by some chemically stable azo dyes under visible light irradiation. & 2015 Published by Elsevier B.V.
Keywords: Microcomposites Semiconductors Electron microscope Optical materials and properties
1. Introduction Owing to high photocatalytic activity, low cost, environmentally friendly feature [1], and an alternative semiconductor material for most widely used photocatalyst-TiO2 [2,3], CeO2 has been widely used as a photocatalyst [4]. However, due to a wide band gap of 3.2 eV, poor photon absorption of CeO2 limits its application in visible light photocatalyst [5]. In order to shift the optical absorption of CeO2 into the visible region, one possible approach is to combine CeO2 photocatalyst with narrow band gap semiconductor [4]. Silver carbonate (Ag2CO3) is an important narrow band gap semiconductor and it can be used as highly visible-light-response photocatalysts with a band gap of 2.30 eV (539 nm) [6]. Although Ag2CO3 is unstable in pure crystal form, it can also be applied in photocatalytic reaction [6]. For example, Ag2CO3 could maintain its stability and photocatalytic activity after Ag2CO3 is coupled with oxides, such as Ag2O [6]. However, to the best of our knowledge, the reports on synthesis and the photocatalytic properties of Ag2CO3/CeO2 microcomposite are scarce up to now. As reported, chemical precipitation is an effective and promising approach to synthesize CeO2 nanoparticles [5,7–10] or Ag2CO3/Ag2O microcomposites [6]. Herein, we report the synthesis of Ag2CO3/CeO2 n
Tel.: þ 86 514 87979022; fax: þ86 514 87979244. E-mail address: [email protected]
microcomposite by a simple chemical precipitation route, as well as the characterization of the resultant products by inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), high resolution transmission electron microscopy (HRTEM), bet (BET) surface area measurement and UV–vis diffuse reflectance spectra. Furthermore, the photocatalytic activities of pure CeO2 and the assynthesized Ag2CO3/CeO2 microcomposite are also studied by degrading Rhodamine 6G (R6G) in water under the visible light (λ4420 nm) irradiation.
2. Materials and methods All the chemical reagents used in this work, including Ce(NO3)3 6H2O, AgNO3, ethanol, and NaHCO3, were of analytical grade purchased from Sinopharm Chemical Reagent Co., Ltd., China. Pure CeO2 microspheres were fabricated by a solvothermal route from Ce(NO3)3 6H2O in ethanol at 180 1C for 12 h. The detailed synthesis process was reported in our previous report [5]. Ag2CO3/CeO2 microcomposite was prepared by a simple chemical precipitation method. The typical procedure for preparation of Ag2CO3/CeO2 was as follows: 0.25 g (1.45 mmol) of CeO2 microspheres dispersed in 80 mL distilled water, and the suspension was sonicated for 10 min. Then, 10 mL of 0.1 mol/L NaHCO3 aqueous solution was added to the CeO2 suspension and stirred magnetically at room temperature for 10 min. Subsequently,
http://dx.doi.org/10.1016/j.matlet.2015.03.086 0167-577X/& 2015 Published by Elsevier B.V.
Please cite this article as: Wu C. Synthesis of Ag2CO3/CeO2 microcomposite with visible light-driven photocatalytic activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.03.086i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
C. Wu / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
20
25
30
40
45
50
Ag2CO3(330) Ag2CO3(-132) Ag2CO3(-161) Ag2CO3(202)
Ag2CO3(310)
55
#
60
# CeO2(331)
CeO2(322)
Ag2CO3(-231)
#
CeO2(311)
#
Ag2CO3(211) Ag2CO3(221)
Ag2CO3(111) Ag2CO3(040) Ag2CO3(200) Ag CO (121) Ag2CO3(031) 2 3 Ag2CO3(220) Ag2CO3(210) Ag2CO3(131) 35
a. Pure CeO2 b. Ag2CO3/CeO2
CeO2(220)
CeO2(111)
a
#
CeO2(200)
Ag2CO3(130)
Ag2CO3(110)
#
b
Ag2CO3(-101)
10 mL of 0.1 mol/L AgNO3 aqueous solution was added quickly into the above solution with stirring. After being stirred at room temperature for 1 h, the as-formed precipitates were filtrated, washed with distilled water and ethanol, and finally dried in air at 70 1C for 12 h. The obtained products were characterized by XRD (Bruker D8 ADVANCE diffractometer system), FESEM (Philips S-4800), HRTEM (Holland F-30), UV–vis diffuse reflectance spectra (Cary 5000 spectrophotometer, Varian), ICP-OES (optima 7300 DV, PerkinElmer), and BET surface area (Micromeritics Tristar 3000). The photocatalytic reactivity of the as-synthesized pure CeO2 and Ag2CO3/CeO2 microcomposite was evaluated using 0.03 g (300 mL of 0.1 g/L) R6G as a probe molecule under the irradiation by an 1000 W Xe lamp (λ4420 nm). The detailed photocatalytic process was as described in our earlier report [5].
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 61 62 63 64 65 66
65
70
75
80
2Theta/degree Fig. 1. XRD patterns of (a) pure CeO2 and (b) as-synthesized Ag2CO3/CeO2 microcomposite. The reflections marked by # belong to CeO2.
3. Results and discussion The value of Ag/Ce in the as-synthesized Ag2CO3/CeO2 microcomposite was determined by ICP-OES to be about 67.7 mol%, which is close to the ratio of Ag/Ce in the reactants. Fig. 1a and b shows the XRD patterns of the as-synthesized pure CeO2 and Ag2CO3/CeO2 microcomposite at room temperature. The XRD patterns in Fig. 1b indicate the formation of a mixture of monoclinic phase Ag2CO3 (JCPDS card no. 070-2184) and cubic phase CeO2, while the XRD patterns in Fig. 1a can be indexed to single fluorite cubic phase CeO2 (JCPDS card no. 043-1002). No peaks corresponding to other Ag-containing or Ce-containing phases were detected in XRD patterns of the as-synthesized products in Fig. 1b, which demonstrated that the forming of Ag2CO3/CeO2 microcomposite had been achieved by this chemical precipitation method. The bet (BET) surface area measurement revealed that the as-synthesized pure CeO2 and Ag2CO3/CeO2 microcomposite had surface areas of 19 m2/g and 21 m2/g, respectively. The morphology of pure CeO2 and Ag2CO3/CeO2 are characterized by FESEM and the results are displayed in Fig. 2a1–b2. From Fig. 2a1 and a2, it can be seen that pure CeO2 displayed regular sphere-like particles with particle size 0.8–3 μm. The surfaces of pure CeO2 microspheres were clean. For Ag2CO3/CeO2 microcomposite, it showed from Fig. 2b1 and b2 that the surface of microspheres became rough due to Ag2CO3 deposition, while the size of microspheres does not change obviously. In order to confirm that small Ag2CO3 particles were uniformly deposited on the surface of the CeO2 microspheres (core), the composition analyses of the as-synthesized Ag2CO3/CeO2 sample were characterized by an XPS etching method and HREM energydispersive X-ray spectroscopy (EDS) mapping (scanning model of HRTEM) method using a FEI F30 microscope equipped with an EDAX energy EDS. HRSTEM-EDS mapping results in Fig. 2b3–b7 of the Ag2CO3/CeO2 sample revealed that Ag2CO3 particles were uniformly deposited on the surface of the CeO2 core. Moreover, smaller-sized Ag2CO3 particles were tightly attached to the surface of large-sized
Fig. 2. (a1, a2) FESEM images of pure CeO2 microspheres; (b1, b2) FESEM images and (b3–b7) HRTEM mapping images of the as-synthesized Ag2CO3/CeO2 microcomposite.
Please cite this article as: Wu C. Synthesis of Ag2CO3/CeO2 microcomposite with visible light-driven photocatalytic activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.03.086i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
C. Wu / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
1.6
1.0
a. CeO2 b. Ag2CO3/CeO2
350 ~ 390 nm
1.4
0.9
without catalyst pure CeO2 Ag2CO3/CeO2
0.8 1.2
b
0.7
1.0
0.6
C/C0
Absorbance (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
3
0.8
0.5 0.4
0.6
0.3
0.4
0.2 0.2
0.1
a 0.0 200
0.0 250
300
350
400
450
500
550
600
650
700
750
800
0
10
20
30
40
50
60
70
80
90
100
110
120
Irradiation time (min)
Wavelength (nm) Fig. 3. UV–visible diffuse reflectance spectra of: (a) pure CeO2 and (b) Ag2CO3/ CeO2.
Fig. 4. Photodegradation of R6G using (a) pure CeO2 and (b) Ag2CO3/CeO2 microcomposite.
CeO2 microspheres, and they cannot be separated from each other even by continuous ultrasonic dispersion in ethanol for 1 h before the HRTEM test. The detailed XPS etching results of Ag2CO3/CeO2 by Ar þ are shown in Supporting information. From Fig. 3, the band gap edge at the wavelength of about 360 390 nm can be found in the UV–vis diffuse reflectance spectra of both pure CeO2 [10] and Ag2CO3/CeO2 microcomposite. Comparing with pure CeO2, an additional broad tail from approximately 400 nm to 800 nm appeared in the spectra of the Ag2CO3/CeO2 microcomposite. The result indicated that the as-synthesized Ag2CO3/CeO2 microcomposite had optical capability nearly in the whole range of visible light spectrum. The photocatalytic activities of the as-prepared pure CeO2 and Ag2CO3/CeO2 microcomposites are shown in Fig. 4. C0 and C in Fig. 4 are the initial concentration after the equilibrium adsorption and the reaction concentration of R6G, respectively. As shown in Fig. 4, R6G aqueous solution can be obviously decolorized by the Ag2CO3/CeO2 photocatalyst under visible light irradiation. By contrast, when pure CeO2 substitutes for Ag2CO3/CeO2 microcomposite as the photocatalyst, the decolorizing of R6G takes place at a much slower rate under the same conditions. For example, the decolorization ratio of R6G is nearly 90% over 0.3 g of Ag2CO3/CeO2 microcomposite, which is greatly higher than only 3.0 % over 0.3 g of pure CeO2, when irradiated by the visible light for 40 min. Furthermore, without any photocatalyst, the degradation of R6G hardly occurs when subjected to the visible light irradiation for 40 min. It is worth noting that the decolorization ratio of R6G is 80% over 0.3 g of this novel Ag2CO3/CeO2 photocatalyst under visible light irradiation only for 10 min. The superior photocatalytic performance of Ag2CO3/CeO2 microcomposite can be explained by its enhanced visible light absorption ability. For a better understanding of the photocatalytic activities of the as-synthesized pure CeO2 and Ag2CO3/CeO2 microcomposites, the kinetic analysis of R6G degradation is also discussed in terms of the Langmuir Hinshel wood model, which is shown in the Supporting information. In addition, the result of the total organic carbon (TOC) measurement and the actual UV–visible spectra of degradation of R6G, which is also shown in
Supporting information, confirmed that decolorization of R6G in our experiments was related to the process of photo-degradation of R6G.
4. Conclusions In the absence of any surfactant and template, Ag2CO3/CeO2 microcomposite was successfully obtained by a chemical precipitation process, and verified by ICP-OES, XRD, FESEM, HRTEM, and BET measurements. The proposed method was simple, mild and cost-effective, which may be suitable for industrial production of Ag2CO3/CeO2 microcomposite. UV–visible diffuse reflectance spectra indicated that the as-synthesized Ag2CO3/CeO2 microcomposite had optical capability nearly in the whole range of visible light spectrum. The photocatalytic results show that coupling of Ag2CO3 with CeO2 can greatly enhance the photocatalytic efficiency of CeO2 under visible light irradiation.
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.03.086.
References [1] Wang Y, Wang F, Chen Y, Zhang D, Li B, Kang S. Appl Catal B: Environ 2014;147:602–9. [2] Meng FM, Sun ZQ. Mater Chem Phys 2009;118:349–53. [3] Wang LN, Lu F, Meng FM. INT J Photoenergy 2012;2012:1–7. [4] Huang K, Li YH, Lin S, Liang C, Xu X, Zhou YF, et al. Mater Lett 2014;124:223–6. [5] Wu C. Mater Lett 2015;139:382–4. [6] Yu C, Li G, Kumar S, Yang K, Jin R. Adv Mater 2014;26:892–8. [7] Lu F, Meng FM, Wang LN, Lu JJ, Sang Y. Mater Lett 2012;73:154–6. [8] Bo QH, Meng FM, Wang LN. Mater Lett 2014;133:216–9. [9] Meng FM, Wang LN, Cui JB. J Alloy Compd 2013;556:102–8. [10] Wang LN, Meng FM, Li KK, Lu F. Appl Surf Sci 2013;286:269–74.
Please cite this article as: Wu C. Synthesis of Ag2CO3/CeO2 microcomposite with visible light-driven photocatalytic activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.03.086i
61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119