本次研究成功利用三階段合成成功製備出CeO2@TiO2@CeO2三明治中空核殼結構。TEM結果顯示，在CeO2核與TiO2奈米顆粒之間形成一層連續界面，然而在TiO2與外層CeO2之間形成的界面為兩相混和的帶狀結構，並未形成一連續界面，其形成原因為TiO2為一較鬆散的殼層結構，使得外層CeO2奈米顆粒可形成在縫隙之中，因此進一步提升CeO2與TiO2界面面積。從吸收光譜得知當形成三明治結構後，整體結構缺陷含量上升，同時紫外光-可見光光譜及螢光光譜顯示吸收範圍成功提升至可見光區，也延長了光激發電子電洞對的壽命。在紫外光及可見光底下以10-5M之亞甲基藍溶液當作待降解物進行光觸媒研究，結果顯示速率常數k可分別達0.11及0.032 min-1，此數值較TiO2@CeO2核殼結構有顯著提升。
關鍵字：三明治結構、界面、光催化

In this study, microscale CeO2@TiO2@CeO2 sandwich-structured hollow spheres were successfully synthesized by a three-step method. First, CeO2 hollow spheres were prepared by spray pyrolysis. Next, TiO2 nanoparticles were deposited on the surface of the annealed CeO2 hollow spheres. Finally, CeO2 nanoparticles were modified on the TiO2@CeO2 core-shell structure to form a sandwich structure.
The TEM results indicated that an obvious thin-layer interface structure was formed between the CeO2 core and the TiO2 interlayer. However, between the TiO2 interlayer and the surface CeO2, the thin-layered interfacial structure is replaced by a wide and mixed band-like region. The reason for the formation of such a region is that the interlayer of TiO2 has a loose structure, so that CeO2 nanoparticles are also deposited in the gap, which further increases the interface area between CeO2 and TiO2. XAS analysis showed that the overall defect concentration increased further after the sandwich structure was formed. UV-vis and PL spectra show that this sandwich structure effectively extends the absorption range to the visible region and prolongs the lifetime of photon-induced electron-hole pairs. Using 10-5M methylene blue as the target dye, the photocatalyst performance under ultraviolet light and visible light is significantly improved, and the rate constant k can reach 0.11 and 0.032 min-1, respectively. This value is more than two times higher than that of the TiO2@CeO2 core-shell structure sample.

[1] Akira, Fujishima, and Honda Kenichi. "Electrochemical photolysis of water at a semiconductor electrode." Nature 238.5358 (1972): 37-38.
[2] Chen, Y. C., Chang, Y. C., Gloter, A., Hsu, P. K., Song, J. M., & Chen, S. Y. "Synergetic effect of interface and surface on photocatalytic performance of TiO2@ hollow CeO2 core–shell nanostructures." Applied Surface Science 566 (2021): 150602.
[3] Wang, J., Tafen, D. N., Lewis, J. P., Hong, Z., Manivannan, A., Zhi, M., ... & Wu, N. "Origin of photocatalytic activity of nitrogen-doped TiO2 nanobelts." Journal of the American Chemical Society 131.34 (2009): 12290-12297.
[4] Sood, S., Umar, A., Mehta, S. K., & Kansal, S. K. "Highly effective Fe-doped TiO2 nanoparticles photocatalysts for visible-light driven photocatalytic degradation of toxic organic compounds." Journal of colloid and interface science 450 (2015): 213-223.
[5] Borgarello, E., Kiwi, J., Graetzel, M., Pelizzetti, E., & Visca, M. "Visible light induced water cleavage in colloidal solutions of chromium-doped titanium dioxide particles." Journal of the American chemical society 104.11 (1982): 2996-3002.
[6] Tian, G., Fu, H., Jing, L., Xin, B., & Pan, K."Preparation and characterization of stable biphase TiO2 photocatalyst with high crystallinity, large surface area, and enhanced photoactivity." The Journal of Physical Chemistry C 112.8 (2008): 3083-3089.
[7] Yang, M. H., Chen, P. C., Tsai, M. C., Chen, T. T., Chang, I. C., Chiu, H. T., & Lee, C. Y. "Alkali metal ion assisted synthesis of faceted anatase TiO 2." CrystEngComm 15.15 (2013): 2966-2971.
[8] Di, L., Xu, Z., Wang, K., & Zhang, X. "A facile method for preparing Pt/TiO2 photocatalyst with enhanced activity using dielectric barrier discharge." Catalysis Today 211 (2013): 109-113.
[9] Cheng, C., Amini, A., Zhu, C., Xu, Z., Song, H., & Wang, N. "Enhanced photocatalytic performance of TiO2-ZnO hybrid nanostructures." Scientific reports 4.1 (2014): 1-5.
[10] Vieira, G. B., José, H. J., Peterson, M., Baldissarelli, V. Z., Alvarez, P., & Moreira, R. D. F. P. M. "CeO2/TiO2 nanostructures enhance adsorption and photocatalytic degradation of organic compounds in aqueous suspension." Journal of Photochemistry and Photobiology A: Chemistry 353 (2018): 325-336.
[11] Linsebigler, Amy L. Guangquan Lu, and John T. Yates Jr. "Photocatalysis on TiO2 surfaces: principles, mechanisms, and selected results." Chemical reviews 95.3 (1995): 735-758.
[12] Borgarello, E., Kiwi, J., Graetzel, M., Pelizzetti, E., & Visca, M. "Visible light induced water cleavage in colloidal solutions of chromium-doped titanium dioxide particles." Journal of the American chemical society 104.11 (1982): 2996-3002.
[13] Klosek, S., & Raftery, D. "Visible light driven V-doped TiO2 photocatalyst and its photooxidation of ethanol." The Journal of Physical Chemistry B 105.14 (2001): 2815-2819.
[14] Choi, Wonyong, Andreas Termin, and Michael R. Hoffmann. "The role of metal ion dopants in quantum-sized TiO2: correlation between photoreactivity and charge carrier recombination dynamics." The Journal of Physical Chemistry 98.51 (2002): 13669-13679.
[15] Koao, L. F., Dejene, F. B., Swart, H. C., & Botha, J. R. "The effect of Ce3+ on structure, morphology and optical properties of flower-like ZnO synthesized using the chemical bath method." Journal of luminescence 143 (2013): 463-468.
[16] Liu, Y., Fang, P., Cheng, Y., Gao, Y., Chen, F., Liu, Z., & Dai, Y. "Study on enhanced photocatalytic performance of cerium doped TiO2-based nanosheets." Chemical engineering journal 219 (2013): 478-485.
[17] Hsu, P. K. Surface-sensitive magnetism of mesoscopic hollow CeO2 spheres.(2021) 274, 115481.
[18] Zhao, J., Zou, X. X., Su, J., Wang, P. P., Zhou, L. J., & Li, G. D."Synthesis and photocatalytic activity of porous anatase TiO2 microspheres composed of {010}-faceted nanobelts." Dalton Transactions 42.13 (2013): 4365-4368.
[19] Mikhailova, M. P., & Titkov, A. N. "Type II heterojunctions in the GaInAsSb/GaSb system." Semiconductor science and technology 9.7 (1994): 1279.
[20] Wei, H., Wang, L., Li, Z., Ni, S., & Zhao, Q. "Synthesis and photocatalytic activity of one-dimensional CdS@TiO2 core-shell heterostructures." Nano-Micro Letters 3.1 (2011): 6-11.
[21] Montini, T., Melchionna, M., Monai, M., & Fornasiero, P. "Fundamentals and catalytic applications of CeO2-based materials." Chemical reviews 116.10 (2016): 5987-6041.
[22] H. Yahiro, Y. Eguchi, K. Eguchi, H.J.J.o.a.e. Arai, Oxygen ion conductivity of the ceria-samarium oxide system with fluorite structure, 18(4) (1988) 527-531
[23] Tseng, C. H. T., Paul, B. K., Chang, C. H., & Engelhard, M. H. "Continuous precipitation of ceria nanoparticles from a continuous flow micromixer." The International Journal of Advanced Manufacturing Technology 64.1 (2013): 579-586.
[24] Xue, Y., Wu, Z., He, X., Yang, X., Chen, X., & Gao, Z. Constructing a Z-scheme Heterojunction of Egg-Like Core@shell CdS@TiO2 Photocatalyst via a Facile Reflux Method for Enhanced Photocatalytic Performance
[25] Kusmierek, Elzbieta. "A CeO2 semiconductor as a photocatalytic and photoelectrocatalytic material for the remediation of pollutants in industrial wastewater: a review." Catalysts 10.12 (2020): 1435.
[26] Y. Liu, Z. Lockman, A. Aziz, J.J.J.o.P.C.M. MacManus-Driscoll, Size dependent ferromagnetism in cerium oxide (CeO2) nanostructures independent of oxygen vacancies, 20(16) (2008) 165201.
[27] Chikazumi, S., & Graham, C. D. Physics of Ferromagnetism 2e, Oxford University Press on Demand2009.
[28] Torres, P, Thermal Conductivity of Rutile and Anatase TiO2 from First-Principles. (2019) 123(51), 30851-30855.
[29] Hanaor, D. A., & Sorrell, C. C. Sorrell, Review of the anatase to rutile phase transformation, 46(4) (2011) 855-874.
[30] Nowotny, M. K., Sheppard, L. R., Bak, T., & Nowotny, J. Nowotny, Defect chemistry of titanium dioxide. Application of defect engineering in processing of TiO2-based photocatalysts, 112(14) (2008) 5275-5300
[31] Chen, Fujung, et al. "Synergistic effect of CeO2 modified TiO2 photocatalyst on the enhancement of visible light photocatalytic performance." Journal of Alloys and Compounds 714 (2017): 560-566.
[32] M.K. Nowotny, L.R. Sheppard, T. Bak, J.J.T.J.o.P.C.C. Nowotny, Defect chemistry of titanium dioxide. Application of defect engineering in processing of TiO2-based
[33] Sposito, Ricarda, et al. "Evaluation of zeta potential of calcined clays and time-dependent flowability of blended cements with customized polycarboxylate-based superplasticizers." Construction and Building Materials 308 (2021): 125061.
[34] Shah, Aarif Hussain, and Mushtaq Ahmad Rather. "Effect of calcination temperature on the crystallite size, particle size and zeta potential of TiO2 nanoparticles synthesized via polyol-mediated method." Materials Today: Proceedings 44 (2021): 482-488.
[35] Tian, J., Sang, Y., Zhao, Z., Zhou, W., Wang, D., Kang, X., ... & Huang, H. (2013). Enhanced photocatalytic performances of CeO2/TiO2 nanobelt heterostructures. small, 9(22), 3864-3872.
[36] Vieira, G. B., José, H. J., Peterson, M., Baldissarelli, V. Z., Alvarez, P., & Moreira, R. D. F. P. M. (2018). CeO2/TiO2 nanostructures enhance adsorption and photocatalytic degradation of organic compounds in aqueous suspension. Journal of Photochemistry and Photobiology A: Chemistry, 353, 325-336.
[37]J. Tian, Y. Sang, Z. Zhao, W. Zhou, D. Wang, X. Kang, H. Liu, J. Wang, S. Chen, H.J.S. Cai, Enhanced photocatalytic performances of CeO2/TiO2 nanobelt
[38] A.O. Ibhadon, P.J.C. Fitzpatrick, Heterogeneous photocatalysis: recent advances and applications, 3(1) (2013) 189-218.
[39] E.A. Kozlova, T.P. Korobkina, A.V.J.i.j.o.h.e. Vorontsov, Overall water splitting over Pt/TiO2 catalyst with Ce3+/Ce4+ shuttle charge transfer system, 34(1) (2009) 138- 146.
[40] Yuan, B., Long, Y., Wu, L., Liang, K., Wen, H., Luo, S., ... & Ma, J. (2016). TiO2@ h-CeO2: a composite yolk–shell microsphere with enhanced photodegradation activity. Catalysis Science & Technology, 6(16), 6396-6405.
[41] 鄭信民,林麗娟工業材料雜誌,X 光繞射應用簡介,(2002).
[42] B.K. Teo, Extended X-ray Absorption Fine Structure (EXAFS) Spectroscopy, EXAFS: Basic Principles and Data Analysis, Springer1986, pp. 21-33.
[43] Luca V, Djajanti S, Howe RF. Structural and Electronic Properties of Sol−Gel Titanium Oxides Studied by X-ray Absorption Spectroscopy. The Journal of Physical Chemistry B. 1998;102(52):10650-7.
[44] Ma, R., Zhang, S., Wen, T., Gu, P., Li, L., Zhao, G., ... & Wang, X. "A critical review on visible-light-response CeO2-based photocatalysts with enhanced photooxidation of organic pollutants." Catalysis today 335 (2019): 20-30.
[45] Nachimuthu, P., Shih, W. C., Liu, R. S., Jang, L. Y., & Chen, J. M. "The study of nanocrystalline cerium oxide by X-ray absorption spectroscopy." Journal of Solid State Chemistry 149.2 (2000): 408-413.
[46] Liu, Y., Fang, P., Cheng, Y., Gao, Y., Chen, F., Liu, Z., & Dai, Y. "Study on enhanced photocatalytic performance of cerium doped TiO2-based nanosheets." Chemical engineering journal 219 (2013): 478-485.
[47] Koao, L. F., Dejene, F. B., Swart, H. C., & Botha, J. R. "The effect of Ce3+ on structure, morphology and optical properties of flower-like ZnO synthesized using the chemical bath method." Journal of luminescence 143 (2013): 463-468.
[48] Cheng, H., Wang, J., Zhao, Y., & Han, X. "Effect of phase composition, morphology, and specific surface area on the photocatalytic activity of TiO 2 nanomaterials." Rsc Advances 4.87 (2014): 47031-47038.
[49] Klosek, Sarah, and Daniel Raftery. "Visible light driven V-doped TiO2 photocatalyst and its photooxidation of ethanol." The Journal of Physical Chemistry B 105.14 (2001): 2815-2819.
[50] Qin, S., Xin, F., Liu, Y., Yin, X., & Ma, W. Photocatalytic reduction of CO2 in methanol to methyl formate over CuO–TiO2 composite catalysts
[51] Song, Y., Waterhouse, G. I., Han, F., Li, Y., & Ai, S. "CeO2@ N/C@ TiO2 Core‐shell Nanosphere Catalyst for the Aerobic Oxidation of 5‐Hydroxymethylfurfural to 5‐Hydroxymethyl‐2‐Furancarboxylic Acid." ChemCatChem 13.12 (2021): 2931-2941.
[52] Zhang, Q., Cheah, P., Han, F., Dai, Q., Yan, Y. "Effects of calcination temperature on crystal structure and photocatalytic activity of CaIn2O4/In2O3 composites." Ceramics International 45.17 (2019): 21851-21857.
[53] Zhang, L., Zhang, J., Jiu, H., Zhang, X., & Xu, M. "Preparation of hollow core/shell CeO2@ TiO2 with enhanced photocatalytic performance." Journal of Materials Science 50.15 (2015): 5228-5237.
[54] Chen, Pei‐Lin, and I‐Wei Chen. "Reactive cerium (IV) oxide powders by the homogeneous precipitation method." Journal of the American Ceramic Society 76.6 (1993): 1577-1583.
[55] Channei, D., Inceesungvorn, B., Wetchakun, N., & Phanichphant, S. "Synthesis of Fe3O4/SiO2/CeO2 core–shell magnetic and their application as photocatalyst." Journal of nanoscience and nanotechnology 14.10 (2014): 7756-7762.
[56] Shin, D., Shin, J., Yeo, T., Hwang, H., Park, S., & Choi, W.. "Scalable synthesis of triple‐core–shell nanostructures of TiO2@ MnO2@ C for high performance supercapacitors using structure‐guided combustion waves." Small 14.11 (2018): 1703755.
[57] Chaisuk, C., Wehatoranawee, A., Preampiyawat, S., Netiphat, S., Shotipruk, A., & Mekasuwandumrong, O. "Preparation and characterization of CeO2/TiO2 nanoparticles by flame spray pyrolysis." Ceramics International 37.5 (2011): 1459-1463.
[58] Fan, Z., Meng, F., Gong, J., Li, H., Hu, Y., & Liu, D. "Enhanced photocatalytic activity of hierarchical flower-like CeO2/TiO2 heterostructures." Materials Letters 175 (2016): 36-39.
[59] Choudhury, B., Borah, B., & Choudhury, A. Extending photocatalytic activity of TiO2 nanoparticles to visible region of illumination by doping of cerium, 88(2) (2012) 257-264.
[60] Tripathi, A. K., Singh, M. K., Mathpal, M. C., Mishra, S. K., & Agarwal, A. , Study of structural transformation in TiO2 nanoparticles and its optical properties, 549 (2013) 114-120.