以改良式水熱法成功製備BiFeO¬3奈米柱陣列於ITO基板，於水熱法前先利用旋轉塗布沉積晶種層。水熱法中使用PEG-10K和PEG-200當作複合劑，且PH值、時間和溫度等條件關鍵地影響BFO一維奈米柱的成長和其陣列。最佳的實驗條件如下: 前驅物的原子比為1.5:1.5、pH值為10到11、水熱法的溫度為200°C和6小時。在本研究中，以BiFeO¬3的壓電性質進一步提升其光催化效能。

本研究透過XRD分析來進行相鑑定其為純相的BiFeO¬3，並利用SEM分析來進行形貌鑑定，其結果顯示BiFeO¬3的奈米柱陣列受複合劑和水熱法的參數所影響。

本研究以降解亞甲基藍來探討BiFeO¬3的光催化效能，在可見光照射下其光催化效率常數為11.7 x 10-3/min，且在壓光電提升下的光催化常數提高至15.3 x 10-3/min，最後再以離子去除劑來探討光催化中主要的反應離子，另外利用I-V特徵圖探討其壓電相關性質。

Pure aligned BiFeO¬3 (BFO) was successfully synthesized on ITO/glass substrates using a modified hydrothermal method. Spin coating was used to deposit the seed layer before the hydrothermal treatment. The addition of PEG-10k and PEG-200 as complex agents in the hydrothermal synthesis and the hydrothermal conditions such as pH values, time, and temperature were observed to crucially influence the growth and alignment of one-dimensional BFO nanorods. The optimal condition was ascertained to be 1.5:1.5 atomic ratio of precursors, pH of 10 to 11, hydrothermal temperature of 200°C, and hydrothermal time of 6 hours. This research emphasized the photocatalytic and piezoelectric properties of BFO/FTO/glass as well as enhanced photodegradation via piezotronics/piezophototronics.

XRD and SEM were used to characterize the nanostructured BFO. Pure phase BFO was synthesized indicated by the XRD results. . SEM analysis showed the morphology evolution of BFO upon addition of various complex agents and varying hydrothermal parameters.

Photocatalytic abilities of aligned BFO nanorods were investigated using photodegradation of Methylene Blue (MB). Significant degradation of the dye was observed (reaction rate constant (k) ≈ 11.7 x 10-3/min) after 90 min of visible light exposure.. The piezophotocatalytic response of the BFO was investigated by applying fixed pressure and ultrasonic wave simultaneously. Enhanced dye degradation (k ≈ 15.3 x 10-3/min) was observed. cation of strain due to the waves and fixed pressure This piezoelectricity enhanced photocatalysis can be justified that induced electric charges on the surface of the material triggered strong redox reaction. From the scavenger experiments, hydroxyl (OH) and superoxide radicals (-O2) were ascertained to be crucial, however, -O2was more predominant for the photocatalytic process of MB. Piezotronic properties of the films were measured using I-V characteristics. Enhanced I-V data were observed for the aligned BFO nanorods as compared with the agglomerated films.

[1] H. Wang, L. Zhang, Z. Chen, J. Hu, S. Li, Z. Wang, J. Liu, and X. Wang, "Semiconductor heterojunction photocatalysts: design, construction, and photocatalytic performances.," Chem. Soc. Rev. 43, 5234 (2014).
[2] S. Wang, K. Wang, Y. Dai, and J. Jehng, "Water effect on the surface morphology of TiO 2 thin film modified by polyethylene glycol," Appl. Surf. Sci. 264, 470 (2013).
[3] A. Kudo, and Y. Miseki, "Heterogeneous photocatalyst materials for water splitting.," Chem. Soc. Rev. 38, 253 (2009).
[4] T. Jafari, E. Moharreri, A. Amin, R. Miao, W. Song, and S. Suib, "Photocatalytic Water Splitting—The Untamed Dream: A Review of Recent Advances," Molecules 21, 900 (2016).
[5] N. Zhang, D. Chen, F. Niu, S. Wang, L. Qin, and Y. Huang, "Enhanced visible light photocatalytic activity of Gd-doped BiFeO3 nanoparticles and mechanism insight," Sci Rep 6, 26467 (2016).
[6] S. Bai, J. Jiang, Q. Zhang, and Y. Xiong, "Steering charge kinetics in photocatalysis: intersection of materials syntheses, characterization techniques and theoretical simulations," Chem. Soc. Rev. 44, 2893 (2015).
[7] R. Marschall, "Semiconductor composites: Strategies for enhancing charge carrier separation to improve photocatalytic activity," Adv. Funct. Mater. 24, 2421 (2014).
[8] W. Wu, R. Hao, F. Liu, X. Su, and Y. Hou, "Single-crystalline α-Fe2O3 nanostructures: Controlled synthesis and high-index plane-enhanced photodegradation by visible light," J. Mater. Chem. A 1, 6888 (2013).
[9] M.R. Hoffmann, S. Martin, W. Choi, and D.W. Bahnemann, "Environmental Applications of Semiconductor Photocatalysis," Chem. Rev. 95, 69 (1995).
[10] C. Chen, W. Ma, and J. Zhao, "Semiconductor-mediated photodegradation of pollutants under visible-light irradiation," 4206 (2010).
[11] J. Xu, C. Qin, S. Bi, Y. Wan, Y. Huang, Y. Wang, and H.J. Seo, "Mixed oxide semiconductor CuInAlO4 nanoparticles: synthesis, structure and photocatalytic properties," J. Phys. D. Appl. Phys. 50, 35109 (2017).
[12] M. Anpo, "Utilization of TiO 2 photocatalysts in green chemistry*," Pure Appl. Chem.Pure Appl. Chem 72, 1265 (2000).
[13] S. Adhikari, D. Sarkar, and G. Madras, "Highly efficient WO 3 –ZnO mixed oxides for photocatalysis," RSC Adv. 5, 11895 (2015).
[14] A. Fujishima, and K. Honda, "Electrochemical photolysis of water at a semiconductor electrode.," Nature 238, 37 (1972).
[15] A. Currao, "Photoelectrochemical Water Splitting," Chim. Int. J. Chem. 61, 815 (2007).
[16] M. Ji, J. Cai, Y. Ma, and L. Qi, "Controlled Growth of Ferrihydrite Branched Nanosheet Arrays and Their Transformation to Hematite Nanosheet Arrays for Photoelectrochemical Water Splitting," ACS Appl. Mater. Interfaces 8, 3651 (2016).
[17] Z. Chen, H.N. Dinh, and E. Miller, Photoelectrochemical Water Splitting: Standards, Experimental Methods, and Protocols (2013).
[18] K. Sivula, F. Le Formal, and M. Gratzel, "Solar water splitting: Progress using hematite (⍺-Fe 2O3) photoelectrodes," ChemSusChem 4, 432 (2011).
[19] K.M. Rajesh, "Studies on Photocatalysis by Nano Titania Modified with Non-Metals," Stud. Photocatal. by Nano Titania Modif. with Non-Metals 2002, 151 (2011).
[20] S.T. Kochuveedu, "Photocatalytic and Photoelectrochemical Water Splitting on TiO 2 via Photosensitization," 2016, (2016).
[21] B. Tom, R. Jan, V.H. Jan, H. Sophia, and M. Johan, "Design of Compact Photoelectrochemical Cells for Water Splitting," 70, (2015).
[22] P.S. Bassi, S.Y. Chiam, J. Barber, and L.H. Wong, "Hydrothermal Grown Nanoporous Iron Based Titanate, Fe 2 TiO 5 for Light Driven Water Splitting," 3 (2014).
[23] D. a. Wheeler, G. Wang, Y. Ling, Y. Li, and J.Z. Zhang, "Nanostructured hematite: synthesis, characterization, charge carrier dynamics, and photoelectrochemical properties," Energy Environ. Sci. 5, 6682 (2012).
[24] T. Hisatomi, J. Kubota, and K. Domen, "Recent advances in semiconductors for photocatalytic and photoelectrochemical water splitting," Chem. Soc. Rev. 43, 7520 (2014).
[25] J. Zhu, and M. Zäch, "Nanostructured materials for photocatalytic hydrogen production," Curr. Opin. Colloid Interface Sci. 14, 260 (2009).
[26] S.P. Meshram, P. V. Adhyapak, U.P. Mulik, and D.P. Amalnerkar, "Facile synthesis of CuO nanomorphs and their morphology dependent sunlight driven photocatalytic properties," Chem. Eng. J. 204–205, 158 (2012).
[27] Y. Zhang, B. Deng, T. Zhang, D. Gao, and A. Xu, "Shape Effects of Cu 2 O Polyhedral Microcrystals on Photocatalytic Activity," 5073 (2010).
[28] G. Wang, Y. Ling, H. Wang, L. Xihong, and Y. Li, "Chemically modified nanostructures for photoelectrochemical water splitting," J. Photochem. Photobiol. C Photochem. Rev. 18, 35 (2014).
[29] B. Modak, and S.K. Ghosh, "An Efficient Strategy for Controlled Band Gap Engineering of KTaO 3," J. Phys. Chem. C acs. jpcc.5b11777 (2016).
[30] Z. Zhang, Z. Luo, Z. Yang, S. Zhang, Y. Zhang, Y. Zhou, X. Wang, and X. Fu, "Band-gap tuning of N-doped TiO2 photocatalysts for visible-light-driven selective oxidation of alcohols to aldehydes in water," RSC Adv. 3, 7215 (2013).
[31] A.M. Smith, and S. Nie, "Semiconductor Nanocrystals: Structure, Properties, and Band Gap Engineering," Acc. Chem. Res. 43, 190 (2009).
[32] F.E. Osterloh, "Inorganic nanostructures for photoelectrochemical and photocatalytic water splitting.," Chem. Soc. Rev. 42, 2294 (2013).
[33] J.S. Jang, H.G. Kim, and J.S. Lee, "Heterojunction semiconductors: A strategy to develop efficient photocatalytic materials for visible light water splitting," Catal. Today 185, 270 (2012).
[34] C.J. Chen, C.H. Liao, K.C. Hsu, Y.T. Wu, and J.C.S. Wu, "P-N junction mechanism on improved NiO/TiO2 photocatalyst," Catal. Commun. 12, 1307 (2011).
[35] O. Mehraj, B.M. Pirzada, N.A. Mir, M.Z. Khan, and S. Sabir, "A highly efficient visible-light-driven novel p-n junction Fe2O3/BiOI photocatalyst: Surface decoration of BiOI nanosheets with Fe2O3 nanoparticles," Appl. Surf. Sci. 387, 642 (2016).
[36] S. Kumar, S. Khanchandani, M. Thirumal, and A.K. Ganguli, "Achieving Enhanced Visible-Light-Driven Photocatalysis Using Type- II NaNbO 3 /CdS Core/Shell Heterostructures," (2014).
[37] X. Gu, C. Li, S. Yuan, M. Ma, Y. Qiang, and J. Zhu, "ZnO based heterojunctions and their application in environmental photocatalysis.," Nanotechnology 27, 402001 (2016).
[38] R. Long, "Electronic Structure of Semiconducting and Metallic Tubes in TiO2/Carbon Nanotube Heterojunctions: Density Functional Theory Calculations," J. Phys. Chem. Lett. 4, 1340 (2013).
[39] M.B. Starr, and X. Wang, "Coupling of piezoelectric effect with electrochemical processes," Nano Energy 14, 296 (2015).
[40] P. Dineva, D. Gross, R. Müller, and T. Rangelov, "Dynamic Fracture of Piezoelectric Materials," Solid Mech. Its Appl. 212, (2014).
[41] C.R. Bowen, H. a. Kim, P.M. Weaver, and S. Dunn, "Piezoelectric and ferroelectric materials and structures for energy harvesting applications," Energy Environ. Sci. 7, 25 (2014).
[42] D.L. Alge, "“Ferroelectricity” in a metal," Nat. Mater. News Views 12, 3 (2013).
[43] Y. Liu, Y. Zhang, Q. Yang, S. Niu, and Z.L. Wang, "Fundamental theories of piezotronics and piezo-phototronics," Nano Energy 14, 257 (2014).
[44] X. Wang, J. Zhou, and Z.L. Wang, "Nanopiezotronics and nanogenerators," Microsystems Nanotechnol. 9783642182, 115 (2012).
[45] Z.L. Wang, "Nanopiezotronics," Adv. Mater. 19, 889 (2007).
[46] Z.L. Wang, "From nanogenerators to piezotronics—A decade-long study of ZnO nanostructures," MRS Bull. 37, 814 (2012).
[47] J. Chang, and L. Lin, Piezoelectric Energy Harvesting Nanofibers (2015).
[48] W. Wu, C. Pan, Y. Zhang, X. Wen, and Z.L. Wang, "Piezotronics and piezo-phototronics - From single nanodevices to array of devices and then to integrated functional system," Nano Today 8, 619 (2013).
[49] Z.L. Wang, "Piezotronics and Piezo-Phototronics (Microtechnology and MEMS)," (2013).
[50] M. Que, R. Zhou, X. Wang, Z. Yuan, G. Hu, and C. Pan, "Progress in piezo-phototronic effect modulated photovoltaics," J. Phys. Condens. Matter 28, 433001 (2016).
[51] Y. Zhang, Y. Yang, and Z.L. Wang, "Piezo-phototronics effect on nano/microwire solar cells," Energy Environ. Sci. 5, 6850 (2012).
[52] P. Functionalities, C.F. Tan, and T. a N.E.T. Al, "Self-Biased Hybrid Piezoelectric- Photoelectrochemical Cell with," 7661 (2015).
[53] J. Wang, J.B. Neaton, H. Zheng, V. Nagarajan, S.B. Ogale, B. Liu, D. Viehland, V. Vaithyanathan, D.G. Schlom, U. V Waghmare, N.A. Spaldin, K.M. Rabe, M. Wuttig, and R. Ramesh, "Epitaxial BiFeO3 multiferroic thin film heterostructures.," Science 299, 1719 (2003).
[54] S. Li, R. Nechache, I.A.V. Davalos, G. Goupil, L. Nikolova, M. Nicklaus, J. Laverdiere, A. Ruediger, and F. Rosei, "Ultrafast microwave hydrothermal synthesis of BiFeO3 NANOPLATES," J. Am. Ceram. Soc. 96, 3155 (2013).
[55] R. Safi, and H. Shokrollahi, "Physics, chemistry and synthesis methods of nanostructured bismuth ferrite (BiFeO 3) as a ferroelectro-magnetic material," Prog. Solid State Chem. 40, 6 (2012).
[56] R. Ramesh, and N.A. Spaldin, "Multiferroics: progress and prospects in thin films," Nat. Mater. 6, 21 (2007).
[57] O.G. Udalov, N.M. Chtchelkatchev, and I.S. Beloborodov, "Coupling of ferroelectricity and ferromagnetism through Coulomb blockade in composite multiferroics," Phys. Rev. B - Condens. Matter Mater. Phys. 89, 1 (2014).
[58] J.-P. Zhou, R.-J. Xiao, Y.-X. Zhang, Z. Shi, and G.-Q. Zhu, "Novel behaviors of single-crystalline BiFeO 3 nanorods hydrothermally synthesized under magnetic field," J. Mater. Chem. C 3, 6924 (2015).
[59] S. Khikhlovskyi, "The renaissance of multiferroics: bismuth ferrite (BiFeO3) – a candidate multiferroic material in nanoscience," 14083 (2010).
[60] G. Catalan, and J.F. Scott, "Physics and applications of bismuth ferrite," Adv. Mater. 21, 2463 (2009).
[61] X.Z. Chen, Z.C. Qiu, J.P. Zhou, G. Zhu, X.B. Bian, and P. Liu, "Large-scale growth and shape evolution of bismuth ferrite particles with a hydrothermal method," Mater. Chem. Phys. 126, 560 (2011).
[62] G.D. Achenbach, and W.J. James, "Single-Phase Polycrystalline BiFeO3," 39, 49696 (1967).
[63] L.W. Martin, S.P. Crane, Y.-H. Chu, M.B. Holcomb, M. Gajek, M. Huijben, C.-H. Yang, N. Balke, and R. Ramesh, "Multiferroics and magnetoelectrics: thin films and nanostructures," J. Phys. Condens. Matter 20, 434220 (2008).
[64] J.-C. Yang, Q. He, P. Yu, and Y.-H. Chu, "BiFeO 3 Thin Films: A Playground for Exploring Electric-Field Control of Multifunctionalities," Annu. Rev. Mater. Res. 45, 150203175635006 (2014).
[65] C. Michel, J.-M. Moreau, G.D. Achenbach, R. Gerson, and W.J. James, "The atomic structure of BiFeO3," Solid State Commun. 7, 701 (1969).
[66] D. Lebeugle, D. Colson, A. Forget, M. Viret, A.M. Bataille, and A. Gukasov, "Electric-field-induced spin flop in BiFeO3 single crystals at room temperature," Phys. Rev. Lett. 100, 1 (2008).
[67] F. Huang, Z. Wang, X. Lu, J. Zhang, K. Min, W. Lin, R. Ti, T. Xu, J. He, C. Yue, and J. Zhu, "Peculiar magnetism of BiFeO3 nanoparticles with size approaching the period of the spiral spin structure," 1 (2013).
[68] M.Y. Shami, M.S. Awan, and M. Anis-Ur-Rehman, "Phase pure synthesis of BiFeO3 nanopowders using diverse precursor via co-precipitation method," J. Alloys Compd. 509, 10139 (2011).
[69] M. Valant, A. Axelsson, N. Alford, andP. Bifeo, "Peculiarities of a Solid-State Synthesis of Multiferroic Polycrystalline BiFeO Peculiarities of a Solid-State Synthesis of Multiferroic," Society 19, 5431 (2007).
[70] X. Zhang, H. Liu, B. Zheng, Y. Lin, D. Liu, and C.W. Nan, "Photocatalytic and magnetic behaviors observed in BiFeO3 nanofibers by electrospinning," J. Nanomater. 2013, (2013).
[71] S. Li, Y.H. Lin, B.P. Zhang, Y. Wang, and C.W. Nan, "Controlled fabrication of BiFeO3 uniform microcrystals and their magnetic and photocatalytic behaviors," J. Phys. Chem. C 114, 2903 (2010).
[72] K.R.S.P. Meher, C. Martin, V. Caignaert, F. Damay, and A. Maignan, "Multiferroics and magnetoelectrics: A comparison between some chromites and cobaltites," Chem. Mater. 26, 830 (2014).
[73] J.R. Teague, R. Gerson, and W.J. James, "Dielectric hysteresis in single crystal BiFeO3," Solid State Commun. 8, 1073 (1970).
[74] J.L. Zhao, H.X. Lu, J.R. Sun, and B.G. Shen, "Thickness dependence of piezoelectric property of ultrathin BiFeO 3 films," 407, 2258 (2012).
[75] H.J. Lee, S.S. Lee, J.H. Kwak, Y. Kim, H.Y. Jeong, A.Y. Borisevich, S.Y. Lee, D.Y. Noh, O. Kwon, and Y. Kim, "Depth resolved lattice-charge coupling in epitaxial BiFeO 3 thin film," Nat. Publ. Gr. 4 (2016).
[76] L.L. Hench, and J.K. West, "The sol-gel process," Chem. Rev. 90, 33 (1990).
[77] C. Anthony Raj, M. Muneeswaran, P. Jegatheesan, N. V. Giridharan, V. Sivakumar, and G. Senguttuvan, "Effect of annealing time in the low-temperature growth of BFO thin films spin coated on glass substrates," J. Mater. Sci. Mater. Electron. 24, 4148 (2013).
[78] H. Liu, Z. Liu, Q. Liu, and K. Yao, "Ferroelectric properties of BiFeO3 films grown by sol-gel process," Thin Solid Films 500, 105 (2006).
[79] A.Z. Simes, E.C. Aguiar, A.H.M. Gonzalez, J. Andŕs, E. Longo, and J.A. Varela, "Strain behavior of lanthanum modified BiFeO3 thin films prepared via soft chemical method," J. Appl. Phys. 104, (2008).
[80] A. Baji, Y.-W. Mai, Q. Li, S.-C. Wong, Y. Liu, and Q.W. Yao, "One-dimensional multiferroic bismuth ferrite fibers obtained by electrospinning techniques.," Nanotechnology 22, 235702 (2011).
[81] L.Č. Xiaomeng, X. Jimin, S. Yuanzhi, and L. Jiamin, "Surfactant-assisted hydrothermal preparation of submicrometer-sized two-dimensional BiFeO3 plates and their photocatalytic activity," J. Mater. Sci. 42, 6824 (2007). [82] C.C. Wu, "BiFeO3/ITO Fabrication Using Hydrothermal Synthesis and Its Piezophotocatalytic and Photoelectrochemical Applications,", 2016.
[83] M. Kobayashi, N. Kumada, A. Miura, T. Takei, I. Fujii, and S. Wada, "Hydrothermal Synthesis of BiFeO 3 Fine Particles," 55, 53 (2013).
[84] B.J. Han, Y. Huang, X. Wu, C. Wu, W. Wei, B. Peng, W. Huang, and J.B. Goodenough, "Tunable Synthesis of Bismuth Ferrites with Various Morphologies **," 2145 (2006).
[85] T. Tong, W. Cao, H. Zhang, J. Chen, D. Jin, and J. Cheng, "Controllable phase evolution of bismuth ferrite oxides by an organic additive modified hydrothermal method," Ceram. Int. 41, S106 (2015).
[86] J. Chen, X. Xing, and A. Watson, "Rapid Synthesis of Multiferroic BiFeO 3 Single-Crystalline Nanostructures," 3598 (2007).
[87] F. Gao, Y. Yuan, K.F. Wang, X.Y. Chen, F. Chen, J.M. Liu, and Z.F. Ren, "Preparation and photoabsorption characterization BiFeO 3 nanowires," Appl. Phys. Lett. 89, 3 (2006).
[88] Y. Zhao, J. Miao, X. Zhang, Y. Chen, X.G. Xu, and Y. Jiang, "Ultra-thin BiFeO3 nanowires prepared by a sol-gel combustion method: an investigation of its multiferroic and optical properties," J. Mater. Sci. Mater. Electron. 1 (2011).