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Processing of chromium oxide-pillared layered HMWO6 (M = Nb, Ta) and their catalytic performances for photodegradation of rhodamine B
Inorganica Chimica Acta 421 (2014) 307–309
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Note
Processing of chromium oxide-pillared layered HMWO6 (M = Nb, Ta) and their catalytic performances for photodegradation of rhodamine B Xian-Ji Guo a,⇑, Shuo-Feng Wang a, Shu-Min Liu a, Lei Zhao b, Tao Yu a, Wen-Feng Duan a, Xiang-Qian Xu a a b
The College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, PR China School of Chemical Engineering and Energy, Zhengzhou University, Zhengzhou 450001, PR China
a r t i c l e
i n f o
Article history: Received 23 November 2012 Received in revised form 11 June 2014 Accepted 16 June 2014 Available online 21 June 2014 Keywords: Layered niobium-tungsten acid Layered tantalum-tungsten acid Pillaring Chromium oxide Photocatalytic degradation
a b s t r a c t Chromium oxide-pillared layered HMWO6 (M = Nb, Ta) was prepared through an ion-exchange route with Cr(OAc)3 as a chromium-pillaring agent and n-propylamine as a pre-expanding agent. The pillaring process and the structure of the pillared products were investigated. Our results indicated that the concentration of Cr(OAc)3 solution affected significantly the intercalation performance of guest species containing Cr in the interlayer regions. The photodegradations of rhodamine B by using the chromium oxide-pillared layered products as catalyst were also investigated. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Due to having d(0) electron configuration, M2O5 (M = Nb, Ta) and M(V)-based perovskite-type oxides are potential photocatalysts [1–3]. As early as 1980s, the layered H4Nb6O17 was found to be photocatalytically active [4]. In recent years, scientists have extensively devoted efforts to study the compounds containing Nb or Ta [5–10]. However, the photocatalysts are not suitable for being directly used in industrial scale owing to their rather-low efficiency. Some recent publications indicate that pillaring of Nb- or Tabased layered compounds with inorganic oxide is an effective way for improving the structure and catalytic property of the layered parent [11,12]. Kim reported that CrOx-pillared layered titanate had a higher photocatalytic activity under visible light [13]. Such performance of the CrOx-pillared layered compound was mainly ascribed to excitation of the intercalated CrOx in the interlayer regions. Based on this fact, we consider that the pillaring of Nb- or Ta-based layered oxides with CrOx should be a significant work for fabricating novel photocatalysts. Besides CrOx-pillared titanate, the pillaring of some other layered metallic oxides (H4Mn14O26, HTiNbO5 and HLaNb2O7) with chromium oxide was also achieved by Suib’s group et al [14–16]. In this study, we select HNbWO6 and HTaWO6 as the layered hosts, ⇑ Corresponding author. Tel.: +86 371 67761876; fax: +86 371 67761744. E-mail address: [email protected] (X.-J. Guo). http://dx.doi.org/10.1016/j.ica.2014.06.012 0020-1693/Ó 2014 Elsevier B.V. All rights reserved.
investigating their pillaring behaviors with chromium oxide, and testing the photocatalytic performances of the corresponding pillared products. In additional, we attempt to improve the photocatalytic property of the CrOx-pillared layered products by means of nitrogen doping. 2. Experimental LiMWO6 (M = Nb or Ta) was prepared by heating a stoichiometric mixture of Li2CO3, WO3 and M2O5. Ion exchange of LiMWO6 was performed with aqueous HNO3 solution (2 mol L 1) at room temperature to afford HMWO6nH2O. The protonated layered metallic oxide was further subjected to react with n-propylamine solution(0.1 mol L 1), giving rise to n-propylamine-pre-expanded layered intermediates. The layered intermediates (denoted as C3-HMWO6) was in turn dispersed in a Cr(OAc)3 solution (0.01– 0.1 mol L 1), followed by stirring firstly at room temperature, then at 333 K and finally under refluxing for 24 h each. The as-synthesized products were washed thoroughly, then dried, and finally calcined. The calcined products were denoted as CrOx-HMWO6. The nitrogen-doped sample, denoted as N-CrOx-HMWO6, was obtained by heating the mixture of CrOx-HMWO6 and urea at 673 K for 2 h. Prior to the heat treatment, CrOx-HMWO6 and urea were thoroughly mixed and ground. Powder XRD was determined with a PANalytical X’Pert PRO diffractometer. FT-IR spectra were recorded on a Nicolet 380 spectrometer. TG/DSC analysis was performed on a NETZSCH STA
X.-J. Guo et al. / Inorganica Chimica Acta 421 (2014) 307–309
b
a 2
4
6
8
14
(002) 1.82 nm
d
(002) 4.00nm
Intensity
(006)
(004)
12
Fig. 2. XRD patterns of CrOx-HNbWO6 obtained at (a) 623 K and (b) 673 K.
(004)
d c
10
2-Theta / degree
2.32nm
Intensity
(002) 1.84 nm
(002) 2.94 nm
As shown in Fig. 1, the basal interlayer distance d002 of HNbWO61.5H2O is 1.28 nm, which corresponds with the (0 0 2) diffraction at 2h = 6.9° (Fig. 1(a)). After HNbWO61.5H2O was converted to C3-HNbWO6, the corresponding d002 was expended to 1.84 nm as suggested by the (0 0 2) diffraction at 2h = 4.8° (Fig. 1(b)). Besides the strong (0 0 2) diffraction, (0 0 4) and (006) diffractions of the amine-pre-expanded intermediate are also clearly observed, suggesting that C3-HNbWO6 should have a well-ordered layered structure. Although either LiNbWO6 or HNbWO6nH2O cannot react directly with Cr(OAc)3 solution, the C3-HNbWO6, due to its opened interlayer, facilitates the intercalation of polyhydroxyacctato-Cr3+ species derived from Cr(OAc)3. One can see that the Cr(OAc)3 concentration is a key factor that affects the intercalating behavior. When the C3-HNbWO6 powder was reacted with a relatively-low concentration Cr(OAc)3 solution (0.025 mol L 1) for 24 h under refluxing and stirring, the obtained solid exhibited no longer the (0 0 4) and (0 0 6) peaks except for a weak (0 0 2) diffraction (Fig. 1(c)). Moreover, no a significant shift was observed for the (0 0 2) peak, compared with that of C3HNbWO6. By employing 0.1 mol L 1 Cr(OAc)3 solution to conduct the experiment under the same conditions, however, the intercalation of polyhydroxyacctato-Cr3+ species in the interleaves was well achieved, leading to a new phase with a greatly-expanded d002 of 2.94 nm (2h = 3.0°, Fig. 1(d)). The presence of (0 0 4) peak (2h = 6.0°) is an indicative of well organization of the polyhydroxyacctato-Cr3+-intercalated layered intermediate. FT-IR characterization showed that there were two stronger adsorptions centered at 1456 and 1545 cm 1 on the spectrum of polyhydroxyacctato-Cr3+-intercalated intermediate. The two IR adsorptions originated in symmetrical/asymmetrical stretching vibrations of the OCO bonds in acetate groups [14]. The difference
(002) 1.77 nm
3. Results and discussion
between the two peaks was 89 cm 1, verifying that the intercalated polyhydroxyacctato-Cr3+ species contained –OCOO groups [17]. The polyhydroxyacctato-Cr3+ species can be reasonably expressed as [Crm(OH)n(OAc)x](3m–n–x)+. TG/DSC analysis indicated that there were two main mass-loss stages in the heat-treatment process of polyhydroxyacctato-Cr3+intercalated layered intermediate. The mass loss of 293–453 K is assigned to the loss of physically adsorbed water in the interlayer regions, while that from 483 to 623 K associated with an exothermal peak centered at 566 K accounts for the oxidative decomposition of the interlayered organic species. When the polyhydroxyacctato-Cr3+-intercalated intermediate underwent the oxidative decomposition, a transformation of polyhydroxyacctato-Cr3+ cations to chromium oxide-like clusters which acted as the interlayer pillars, was achieved. The resultant layered products obtained by calcining the polyhydroxyacctato-Cr3+-intercalated layered intermediates, are thus designated as CrOx-pillared layered HNbWO6 (CrOx-HNbWO6). The d002 of CrOx-HNbWO6 obtained at 623 K is 1.96 nm (2h = 4.5°, Fig. 2a). The CrOx-HNbWO6 exhibited a high thermostability. Upon calcination at 673 K, the layered
(002) 1.96 nm
409PC thermal analyzer by heating the sample at 10 K/min in air flow. Photocatalytic degradation experiments were performed in a glass container. Under stirring, the CrOx-HMWO6 or N-CrOxHMWO6 (50–200 mg) was dispersed in 150 mL of rhodamineB aqueous solution (10 mg L 1). A Uv-light lamp with a wavelength of 254 nm was used. To allow adsorption-desorption equilibrium to be established, the suspension was stirred for 30 min in a dark environment before irradiation.
Intensity
308
(002) 1.04 nm
c
b
(002) 1.28 nm
b a
a 2
4
6
8
10
12
14
16
2-Theta / degree Fig. 1. XRD patterns of HNbWO61.5H2O (a), C3-HNbWO6 (b), intermediate products obtained from the reaction between C3-HNbWO6 and Cr(OAc)3 solution of 0.025 mol L 1 (c), and 0.1 mol L 1 (d).
2
4
6
8
10
12
14
2-Theta /degree Fig. 3. XRD patterns of HTaWO60.5H2O (a), C3-HTaWO6 (b), intermediate products (c) obtained from the reaction between C3-HTaWO6 and Cr(OAc)3 solution of 0.05 mol L 1, and CrOx-HTaWO6 (673 K) (d).
X.-J. Guo et al. / Inorganica Chimica Acta 421 (2014) 307–309
1.0
found to be efficient for the photo-degradation reaction. Fig. 4 shows the result of photocatalytic experiment using CrOx-HTaWO6 (673 K) as catalyst. One can see that the CrOx-HTaWO6 exhibited a good photocatalytic performance. Upon irradiation in the presence of CrOx-HTaWO6, ca. 72% of rhodamine B was degraded after 120 min. In Fig. 5, the photocatalytic activity of N-CrOx-HNbWO6 for rhodamine B degradation is shown. One can see that the catalytic performance of CrOx-HNbWO6 was greatly improved by doping the CrOx-pillared layered sample with nitrogen. About 68% of rhodamine B was degraded over the nitrogen-doped sample after 120 min.
a
Ct / C0
0.8
0.6
0.4
309
b 4. Conclusions
0.2 0
20
40
60
80
100
120
Irradiation time (min) Fig. 4. Plots of Ct/C0 (Ct is the concentration of rhodamine B at t, C0 is the initial concentration) versus irradiation time for photodegradation of rhodamine B with (a) no catalyst and (b) 200 mg of CrOx-HTaWO6.
1.0
a
Intercalating of polyhydroxyacctato-Cr3+ cations in the interleaves of layered HMWO6 (M = Nb, Ta) can be achieved through a stepwise ions-exchange way. By calcining the polyhydroxyacctato-Cr3+-intercalated layered intermediates in air, chromium oxide-pillared layered HMWO6 can be produced. The investigation on the pillaring process indicates that the suitable concentration of Cr(OAc)3 solution should be essential for the successful pillaring. The result of photocatalytic experiment indicates that chromium oxide-pillared layered HTaWO6 has a potential to be developed as the efficient catalyst for photodegradation of some organic compounds. Acknowledgements
Ct /C 0
0.8 We thank Natural Science Foundation of Education Department of Henan Province of China (No. 2010A150022), National Natural Science Foundation of China (No. J1210060) and Foundation of Graduate School of Zhengzhou University for supporting this work.
0.6
Appendix A. Supplementary material
b
0.4
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ica.2014.06.012.
0
20
40 60 80 100 Irradiation time (min)
120
Fig. 5. Plots of Ct/C0 (Ct is the concentration of rhodamine B at t, C0 is the initial concentration) versus irradiation time for photodegradation of rhodamine B with (a) no catalyst and (b) 50 mg of N-CrOx-HNbWO6.
structure was still retained with only a slightly decreased d002 (d002 = 1.77 nm, 2h = 5.0°, Fig. 2b). We also investigated the pillaring behavior of HTaWO6 with chromium oxide, and found that the suitable concentration of Cr(OAc)3 solution for fabricating the polyhydroxyacctato-Cr3+intercalated HTaWO6 was 0.05 mol L 1. As shown in Fig 3, the basal interlayer distance d002 of C3-HTaWO6 is 1.82 nm (Fig 3(b)). After C3-HTaWO6 was reacted with Cr(OAc)3 solution of 0.05 mol L 1, the d002 was greatly expanded to 4.00 nm (Fig 3(c)). The (002) diffraction peak of the calcined pillared layered product (CrOx-HTaWO6, 673 K) shifted to about 2h 3.8°, whose intensity became very weak, corresponding to a d002 of 2.32 nm (Fig 3(d)). The photocatalytic performance of CrOx-HNbWO6 and CrOxHTaWO6 are quite different. When CrOx-HNbWO6 was employed as the photocatalyst, the degradation of rhodamine B was negligible even after 120 min of irradiation. However, CrOx-HTaWO6 was
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
Z.G. Zhou, J.H. Ye, H. Arakawa, Chem. Phys. Lett. 332 (2000) 271. Z.G. Zhou, J.H. Ye, H. Arakawa, Mater. Res. Bull. 36 (2001) 1185. T. Ohuchi, T. Miyatake, Y. Hitomi, T. Tanaka, Catal. Today 120 (2007) 233. K. Domen, A. Kudo, M. Shibata, A. Tanaka, K. Maruya, T. Onishi, J. Chem. Soc., Chem. Commun. (1986) 1706. Y. Qiu, L. Wang, C.F. Leung, G. Liu, S. Yang, T.C. Lau, Appl. Catal. A 402 (2011) 23. H.G. Kim, D.W. Hwang, J.S. Lee, J. Am. Chem. Soc. 126 (2004) 8912. J.H. Wu, Y.H. Cheng, J.M. Lin, Y.F. Huang, M.L. Huang, S.C. Hao, J. Phys. Chem. C 111 (2007) 3624. X.Y. Chen, T. Yu, X.X. Fan, H.T. Zhang, Z.S. Li, J.H. Ye, Z.G. Zhou, Appl. Surf. Sci. 253 (2007) 8500. H.J. Liu, G.G. Liu, G.H. Xie, M.L. Zhang, Z.H. Hou, Z.W. He, Appl. Surf. Sci. 257 (2011) 3728. L.M. Torres-Martinez, A. Gruz-López, I. Juárez-Ramírez, M.E.M.I. Rosa, J. Hazard. Mater. 165 (2009) 774. X.J. Guo, W.H. Hou, W.P. Ding, Y.N. Fan, Q.J. Yan, Y. Chen, Microporous Mesoporous Mater. 80 (2005) 269. B.Z. Lin, X.L. Li, B.H. Xu, Y.L. Chen, B.F. Gao, X.R. Fan, Microporous Mesoporous Mater. 155 (2012) 16. T.W. Kim, S.G. Hur, S.J. Hwang, H. Park, W. Choi, J.H. Choy, Adv. Funct. Mater. 17 (2007) 307. Y. Ma, S.L. Suib, T. Ressler, J. Wong, M. Lovallo, M. Tsapatisis, Chem. Mater. 11 (1999) 3545. Y. Chen, W. Hou, C. Guo, Q. Yan, Y. Chen, Dalton Trans. (1997) 359. X. Guo, W. Hou, G. Bao, Q. Yan, Solid State Ionics 177 (2006) 1293. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, fourth ed., Wiley, New York, 1986.
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Note
Processing of chromium oxide-pillared layered HMWO6 (M = Nb, Ta) and their catalytic performances for photodegradation of rhodamine B Xian-Ji Guo a,⇑, Shuo-Feng Wang a, Shu-Min Liu a, Lei Zhao b, Tao Yu a, Wen-Feng Duan a, Xiang-Qian Xu a a b
The College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, PR China School of Chemical Engineering and Energy, Zhengzhou University, Zhengzhou 450001, PR China
a r t i c l e
i n f o
Article history: Received 23 November 2012 Received in revised form 11 June 2014 Accepted 16 June 2014 Available online 21 June 2014 Keywords: Layered niobium-tungsten acid Layered tantalum-tungsten acid Pillaring Chromium oxide Photocatalytic degradation
a b s t r a c t Chromium oxide-pillared layered HMWO6 (M = Nb, Ta) was prepared through an ion-exchange route with Cr(OAc)3 as a chromium-pillaring agent and n-propylamine as a pre-expanding agent. The pillaring process and the structure of the pillared products were investigated. Our results indicated that the concentration of Cr(OAc)3 solution affected significantly the intercalation performance of guest species containing Cr in the interlayer regions. The photodegradations of rhodamine B by using the chromium oxide-pillared layered products as catalyst were also investigated. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Due to having d(0) electron configuration, M2O5 (M = Nb, Ta) and M(V)-based perovskite-type oxides are potential photocatalysts [1–3]. As early as 1980s, the layered H4Nb6O17 was found to be photocatalytically active [4]. In recent years, scientists have extensively devoted efforts to study the compounds containing Nb or Ta [5–10]. However, the photocatalysts are not suitable for being directly used in industrial scale owing to their rather-low efficiency. Some recent publications indicate that pillaring of Nb- or Tabased layered compounds with inorganic oxide is an effective way for improving the structure and catalytic property of the layered parent [11,12]. Kim reported that CrOx-pillared layered titanate had a higher photocatalytic activity under visible light [13]. Such performance of the CrOx-pillared layered compound was mainly ascribed to excitation of the intercalated CrOx in the interlayer regions. Based on this fact, we consider that the pillaring of Nb- or Ta-based layered oxides with CrOx should be a significant work for fabricating novel photocatalysts. Besides CrOx-pillared titanate, the pillaring of some other layered metallic oxides (H4Mn14O26, HTiNbO5 and HLaNb2O7) with chromium oxide was also achieved by Suib’s group et al [14–16]. In this study, we select HNbWO6 and HTaWO6 as the layered hosts, ⇑ Corresponding author. Tel.: +86 371 67761876; fax: +86 371 67761744. E-mail address: [email protected] (X.-J. Guo). http://dx.doi.org/10.1016/j.ica.2014.06.012 0020-1693/Ó 2014 Elsevier B.V. All rights reserved.
investigating their pillaring behaviors with chromium oxide, and testing the photocatalytic performances of the corresponding pillared products. In additional, we attempt to improve the photocatalytic property of the CrOx-pillared layered products by means of nitrogen doping. 2. Experimental LiMWO6 (M = Nb or Ta) was prepared by heating a stoichiometric mixture of Li2CO3, WO3 and M2O5. Ion exchange of LiMWO6 was performed with aqueous HNO3 solution (2 mol L 1) at room temperature to afford HMWO6nH2O. The protonated layered metallic oxide was further subjected to react with n-propylamine solution(0.1 mol L 1), giving rise to n-propylamine-pre-expanded layered intermediates. The layered intermediates (denoted as C3-HMWO6) was in turn dispersed in a Cr(OAc)3 solution (0.01– 0.1 mol L 1), followed by stirring firstly at room temperature, then at 333 K and finally under refluxing for 24 h each. The as-synthesized products were washed thoroughly, then dried, and finally calcined. The calcined products were denoted as CrOx-HMWO6. The nitrogen-doped sample, denoted as N-CrOx-HMWO6, was obtained by heating the mixture of CrOx-HMWO6 and urea at 673 K for 2 h. Prior to the heat treatment, CrOx-HMWO6 and urea were thoroughly mixed and ground. Powder XRD was determined with a PANalytical X’Pert PRO diffractometer. FT-IR spectra were recorded on a Nicolet 380 spectrometer. TG/DSC analysis was performed on a NETZSCH STA
X.-J. Guo et al. / Inorganica Chimica Acta 421 (2014) 307–309
b
a 2
4
6
8
14
(002) 1.82 nm
d
(002) 4.00nm
Intensity
(006)
(004)
12
Fig. 2. XRD patterns of CrOx-HNbWO6 obtained at (a) 623 K and (b) 673 K.
(004)
d c
10
2-Theta / degree
2.32nm
Intensity
(002) 1.84 nm
(002) 2.94 nm
As shown in Fig. 1, the basal interlayer distance d002 of HNbWO61.5H2O is 1.28 nm, which corresponds with the (0 0 2) diffraction at 2h = 6.9° (Fig. 1(a)). After HNbWO61.5H2O was converted to C3-HNbWO6, the corresponding d002 was expended to 1.84 nm as suggested by the (0 0 2) diffraction at 2h = 4.8° (Fig. 1(b)). Besides the strong (0 0 2) diffraction, (0 0 4) and (006) diffractions of the amine-pre-expanded intermediate are also clearly observed, suggesting that C3-HNbWO6 should have a well-ordered layered structure. Although either LiNbWO6 or HNbWO6nH2O cannot react directly with Cr(OAc)3 solution, the C3-HNbWO6, due to its opened interlayer, facilitates the intercalation of polyhydroxyacctato-Cr3+ species derived from Cr(OAc)3. One can see that the Cr(OAc)3 concentration is a key factor that affects the intercalating behavior. When the C3-HNbWO6 powder was reacted with a relatively-low concentration Cr(OAc)3 solution (0.025 mol L 1) for 24 h under refluxing and stirring, the obtained solid exhibited no longer the (0 0 4) and (0 0 6) peaks except for a weak (0 0 2) diffraction (Fig. 1(c)). Moreover, no a significant shift was observed for the (0 0 2) peak, compared with that of C3HNbWO6. By employing 0.1 mol L 1 Cr(OAc)3 solution to conduct the experiment under the same conditions, however, the intercalation of polyhydroxyacctato-Cr3+ species in the interleaves was well achieved, leading to a new phase with a greatly-expanded d002 of 2.94 nm (2h = 3.0°, Fig. 1(d)). The presence of (0 0 4) peak (2h = 6.0°) is an indicative of well organization of the polyhydroxyacctato-Cr3+-intercalated layered intermediate. FT-IR characterization showed that there were two stronger adsorptions centered at 1456 and 1545 cm 1 on the spectrum of polyhydroxyacctato-Cr3+-intercalated intermediate. The two IR adsorptions originated in symmetrical/asymmetrical stretching vibrations of the OCO bonds in acetate groups [14]. The difference
(002) 1.77 nm
3. Results and discussion
between the two peaks was 89 cm 1, verifying that the intercalated polyhydroxyacctato-Cr3+ species contained –OCOO groups [17]. The polyhydroxyacctato-Cr3+ species can be reasonably expressed as [Crm(OH)n(OAc)x](3m–n–x)+. TG/DSC analysis indicated that there were two main mass-loss stages in the heat-treatment process of polyhydroxyacctato-Cr3+intercalated layered intermediate. The mass loss of 293–453 K is assigned to the loss of physically adsorbed water in the interlayer regions, while that from 483 to 623 K associated with an exothermal peak centered at 566 K accounts for the oxidative decomposition of the interlayered organic species. When the polyhydroxyacctato-Cr3+-intercalated intermediate underwent the oxidative decomposition, a transformation of polyhydroxyacctato-Cr3+ cations to chromium oxide-like clusters which acted as the interlayer pillars, was achieved. The resultant layered products obtained by calcining the polyhydroxyacctato-Cr3+-intercalated layered intermediates, are thus designated as CrOx-pillared layered HNbWO6 (CrOx-HNbWO6). The d002 of CrOx-HNbWO6 obtained at 623 K is 1.96 nm (2h = 4.5°, Fig. 2a). The CrOx-HNbWO6 exhibited a high thermostability. Upon calcination at 673 K, the layered
(002) 1.96 nm
409PC thermal analyzer by heating the sample at 10 K/min in air flow. Photocatalytic degradation experiments were performed in a glass container. Under stirring, the CrOx-HMWO6 or N-CrOxHMWO6 (50–200 mg) was dispersed in 150 mL of rhodamineB aqueous solution (10 mg L 1). A Uv-light lamp with a wavelength of 254 nm was used. To allow adsorption-desorption equilibrium to be established, the suspension was stirred for 30 min in a dark environment before irradiation.
Intensity
308
(002) 1.04 nm
c
b
(002) 1.28 nm
b a
a 2
4
6
8
10
12
14
16
2-Theta / degree Fig. 1. XRD patterns of HNbWO61.5H2O (a), C3-HNbWO6 (b), intermediate products obtained from the reaction between C3-HNbWO6 and Cr(OAc)3 solution of 0.025 mol L 1 (c), and 0.1 mol L 1 (d).
2
4
6
8
10
12
14
2-Theta /degree Fig. 3. XRD patterns of HTaWO60.5H2O (a), C3-HTaWO6 (b), intermediate products (c) obtained from the reaction between C3-HTaWO6 and Cr(OAc)3 solution of 0.05 mol L 1, and CrOx-HTaWO6 (673 K) (d).
X.-J. Guo et al. / Inorganica Chimica Acta 421 (2014) 307–309
1.0
found to be efficient for the photo-degradation reaction. Fig. 4 shows the result of photocatalytic experiment using CrOx-HTaWO6 (673 K) as catalyst. One can see that the CrOx-HTaWO6 exhibited a good photocatalytic performance. Upon irradiation in the presence of CrOx-HTaWO6, ca. 72% of rhodamine B was degraded after 120 min. In Fig. 5, the photocatalytic activity of N-CrOx-HNbWO6 for rhodamine B degradation is shown. One can see that the catalytic performance of CrOx-HNbWO6 was greatly improved by doping the CrOx-pillared layered sample with nitrogen. About 68% of rhodamine B was degraded over the nitrogen-doped sample after 120 min.
a
Ct / C0
0.8
0.6
0.4
309
b 4. Conclusions
0.2 0
20
40
60
80
100
120
Irradiation time (min) Fig. 4. Plots of Ct/C0 (Ct is the concentration of rhodamine B at t, C0 is the initial concentration) versus irradiation time for photodegradation of rhodamine B with (a) no catalyst and (b) 200 mg of CrOx-HTaWO6.
1.0
a
Intercalating of polyhydroxyacctato-Cr3+ cations in the interleaves of layered HMWO6 (M = Nb, Ta) can be achieved through a stepwise ions-exchange way. By calcining the polyhydroxyacctato-Cr3+-intercalated layered intermediates in air, chromium oxide-pillared layered HMWO6 can be produced. The investigation on the pillaring process indicates that the suitable concentration of Cr(OAc)3 solution should be essential for the successful pillaring. The result of photocatalytic experiment indicates that chromium oxide-pillared layered HTaWO6 has a potential to be developed as the efficient catalyst for photodegradation of some organic compounds. Acknowledgements
Ct /C 0
0.8 We thank Natural Science Foundation of Education Department of Henan Province of China (No. 2010A150022), National Natural Science Foundation of China (No. J1210060) and Foundation of Graduate School of Zhengzhou University for supporting this work.
0.6
Appendix A. Supplementary material
b
0.4
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ica.2014.06.012.
0
20
40 60 80 100 Irradiation time (min)
120
Fig. 5. Plots of Ct/C0 (Ct is the concentration of rhodamine B at t, C0 is the initial concentration) versus irradiation time for photodegradation of rhodamine B with (a) no catalyst and (b) 50 mg of N-CrOx-HNbWO6.
structure was still retained with only a slightly decreased d002 (d002 = 1.77 nm, 2h = 5.0°, Fig. 2b). We also investigated the pillaring behavior of HTaWO6 with chromium oxide, and found that the suitable concentration of Cr(OAc)3 solution for fabricating the polyhydroxyacctato-Cr3+intercalated HTaWO6 was 0.05 mol L 1. As shown in Fig 3, the basal interlayer distance d002 of C3-HTaWO6 is 1.82 nm (Fig 3(b)). After C3-HTaWO6 was reacted with Cr(OAc)3 solution of 0.05 mol L 1, the d002 was greatly expanded to 4.00 nm (Fig 3(c)). The (002) diffraction peak of the calcined pillared layered product (CrOx-HTaWO6, 673 K) shifted to about 2h 3.8°, whose intensity became very weak, corresponding to a d002 of 2.32 nm (Fig 3(d)). The photocatalytic performance of CrOx-HNbWO6 and CrOxHTaWO6 are quite different. When CrOx-HNbWO6 was employed as the photocatalyst, the degradation of rhodamine B was negligible even after 120 min of irradiation. However, CrOx-HTaWO6 was
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