本研究主要探討不同熱處理溫度下，還原氧化石墨烯做為光觸媒的差異性，分別比較130、150及170 oC熱處理溫度下，根據在還原程度不同，對於二氧化碳光催化還原的影響。
在低溫熱還原過程中，隨著溫度增加，官能基含量將減少，使得石墨烯層間距離縮短，出現多層結構，同時也降低了親水性質。另一方面，由O 2p軌域所產生的半導體能隙，將因官能基的減少而有縮小趨勢，螢光激發光譜訊號則在熱處理溫度大於150 oC時開始下降，而熱處理溫度在170 oC時，將開始出現導體區域。
結合親疏水性、石墨烯層數、吸光能力及螢光放光能力，得到在150 oC熱還原時，有最高的甲醇產率，可達0.31 μmole g-cat-1 hr-1，想比於未還原之氧化石墨烯高約1.7倍，更比常見之商用P25 TiO2觸媒高近8倍。由此可知，氧化石墨烯經由熱還原的方式調節能隙形成的還原氧化石墨烯，進而更適合作為光催化二氧化碳的光觸媒。

Carbon dioxide is one of the main contributors in the greenhouse gases that contributes to the problem of global warming. One of the solutions to such problem is converting this gas into useful products through photoreduction process. In this thesis, graphene oxide (GO), which has attracted a lot of scientist, is investigated as a potential CO2 photoreduction catalyst. We have used different thermal reduction level of graphene oxide and correlated these products with its corresponding CO2 photoreduction performance.
We have found out that as the reduction temperature increases, the less the functional groups are observed, resulting to a more hydrophobic nature of the reduced-GO (RGO). In addition, the reduction of functional groups also correlates to the red shift in light absorption and eventual quenching in the PL signal of RGOs. The effect of the hydrophobic nature and the reduction of band gap are obtained for the sample reduced at 150oC with yield of 0.31 μmole g-1 -cat hr-1. This is 1.7-fold higher than that of pristine GO (0.18μmole g-1 -cat hr-1).

[1] W. Fan, Q. Zhang, Y. Wang, Semiconductor-based nanocomposites for photocatalytic H2 production and CO2 conversion. Physical Chemistry Chemical Physics, 15 (2013) 2632-2649.
[2] A.D. Handoko, K. Li, J. Tang, Recent progress in artificial photosynthesis: CO2 photoreduction to valuable chemicals in a heterogeneous system. Current Opinion in Chemical Engineering, 2 (2013) 200-206.
[3] W. Tu, Y. Zhou, Z. Zou, Photocatalytic Conversion of CO2 into Renewable Hydrocarbon Fuels: State-of-the-Art Accomplishment, Challenges, and Prospects. Advanced Materials, (2014) DOI: 10.1002/adma.201400087.
[4] A. Fujishima, K. Honda, Electrochemical Photolysis of Water at a Semiconductor Electrode. Nature, 238 (1972) 37-38.
[5] M. Halmann, Photoelectrochemical reduction of aqueous carbon dioxide on p-type gallium phosphide in liquid junction solar cells. Nature, 275 (1978) 115-116.
[6] T. Inoue, A. Fujishima, S. Konishi, K. Honda, Photoelectrocatalytic reduction of carbon dioxide in aqueous suspensions of semiconductor powders. Nature, 277 (1979) 637-638.
[7] J. Mao, K. Li, T. Peng, Recent advances in the photocatalytic CO2 reduction over semiconductors. Catalysis Science & Technology, 3 (2013) 2481-2498.
[8] S. Kuwabata, H. Uchida, A. Ogawa, S. Hirao, H. Yoneyama, Selective photoreduction of carbon dioxide to methanol on titanium dioxide photocatalysts in propylene carbonate solution. Journal of the Chemical Society, Chemical Communications, (1995) 829-830.
[9] S. Kaneco, Y. Shimizu, K. Ohta, T. Mizuno, Photocatalytic reduction of high pressure carbon dioxide using TiO2 powders with a positive hole scavenger. Journal of Photochemistry and Photobiology A: Chemistry, 115 (1998) 223-226.
[10] K. Kočí, L. Obalová, L. Matějová, D. Plachá, Z. Lacný, J. Jirkovský, O. Šolcová, Effect of TiO2 particle size on the photocatalytic reduction of CO2. Applied Catalysis B: Environmental, 89 (2009) 494-502.
[11] K. Kočí, K. Matějů, L. Obalová, S. Krejčíková, Z. Lacný, D. Plachá, L. Čapek, A. Hospodková, O. Šolcová, Effect of silver doping on the TiO2 for photocatalytic reduction of CO2. Applied Catalysis B: Environmental, 96 (2010) 239-244.
[12] O. Ola, M. Maroto-Valer, D. Liu, S. Mackintosh, C.-W. Lee, J.C.S. Wu, Performance comparison of CO2 conversion in slurry and monolith photoreactors using Pd and Rh-TiO2 catalyst under ultraviolet irradiation. Applied Catalysis B: Environmental, 126 (2012) 172-179.
[13] J. Lin, Z. Pan, X. Wang, Photochemical Reduction of CO2 by Graphitic Carbon Nitride Polymers. ACS Sustainable Chemistry & Engineering, 2 (2013) 353-358.
[14] J. Mao, T. Peng, X. Zhang, K. Li, L. Ye, L. Zan, Effect of graphitic carbon nitride microstructures on the activity and selectivity of photocatalytic CO2 reduction under visible light. Catalysis Science & Technology, 3 (2013) 1253-1260.
[15] Q.-H. Zhang, W.-D. Han, Y.-J. Hong, J.-G. Yu, Photocatalytic reduction of CO2 with H2O on Pt-loaded TiO2 catalyst. Catalysis Today, 148 (2009) 335-340.
[16] L. Liu, H. Zhao, J.M. Andino, Y. Li, Photocatalytic CO2 Reduction with H2O on TiO2 Nanocrystals: Comparison of Anatase, Rutile, and Brookite Polymorphs and Exploration of Surface Chemistry. ACS Catalysis, 2 (2012) 1817-1828.
[17] P. Pathak, M.J. Meziani, Y. Li, L.T. Cureton, Y.-P. Sun, Improving photoreduction of CO2 with homogeneously dispersed nanoscale TiO2 catalysts. Chemical Communications, (2004) 1234-1235.
[18] B. Vijayan, N.M. Dimitrijevic, T. Rajh, K. Gray, Effect of Calcination Temperature on the Photocatalytic Reduction and Oxidation Processes of Hydrothermally Synthesized Titania Nanotubes. The Journal of Physical Chemistry C, 114 (2010) 12994-13002.
[19] Q. Liu, Y. Zhou, W. Tu, S. Yan, Z. Zou, Solution-Chemical Route to Generalized Synthesis of Metal Germanate Nanowires with Room-Temperature, Light-Driven Hydrogenation Activity of CO2 into Renewable Hydrocarbon Fuels. Inorganic Chemistry, 53 (2013) 359-364.
[20] X. Li, Z. Zhuang, W. Li, H. Pan, Photocatalytic reduction of CO2 over noble metal-loaded and nitrogen-doped mesoporous TiO2. Applied Catalysis A: General, 429–430 (2012) 31-38.
[21] N. Zhang, S. Ouyang, P. Li, Y. Zhang, G. Xi, T. Kako, J. Ye, Ion-exchange synthesis of a micro/mesoporous Zn2GeO4 photocatalyst at room temperature for photoreduction of CO2. Chemical Communications, 47 (2011) 2041-2043.
[22] H.-a. Park, J.H. Choi, K.M. Choi, D.K. Lee, J.K. Kang, Highly porous gallium oxide with a high CO2 affinity for the photocatalytic conversion of carbon dioxide into methane. Journal of Materials Chemistry, 22 (2012) 5304-5307.
[23] A.L. Linsebigler, G. Lu, J.T. Yates, Photocatalysis on TiO2 Surfaces: Principles, Mechanisms, and Selected Results. Chemical Reviews, 95 (1995) 735-758.
[24] G. Liu, L. Wang, H.G. Yang, H.-M. Cheng, G.Q. Lu, Titania-based photocatalysts-crystal growth, doping and heterostructuring. Journal of Materials Chemistry, 20 (2010) 831-843.
[25] I.H. Tseng, W.-C. Chang, J.C.S. Wu, Photoreduction of CO2 using sol–gel derived titania and titania-supported copper catalysts. Applied Catalysis B: Environmental, 37 (2002) 37-48.
[26] W.-N. Wang, W.-J. An, B. Ramalingam, S. Mukherjee, D.M. Niedzwiedzki, S. Gangopadhyay, P. Biswas, Size and Structure Matter: Enhanced CO2 Photoreduction Efficiency by Size-Resolved Ultrafine Pt Nanoparticles on TiO2 Single Crystals. Journal of the American Chemical Society, 134 (2012) 11276-11281.
[27] C.-W. Tsai, H.M. Chen, R.-S. Liu, K. Asakura, T.-S. Chan, Ni@NiO Core–Shell Structure-Modified Nitrogen-Doped InTaO4 for Solar-Driven Highly Efficient CO2 Reduction to Methanol. The Journal of Physical Chemistry C, 115 (2011) 10180-10186.
[28] M. Abou Asi, C. He, M. Su, D. Xia, L. Lin, H. Deng, Y. Xiong, R. Qiu, X.-z. Li, Photocatalytic reduction of CO2 to hydrocarbons using AgBr/TiO2 nanocomposites under visible light. Catalysis Today, 175 (2011) 256-263.
[29] C. Wang, R.L. Thompson, P. Ohodnicki, J. Baltrus, C. Matranga, Size-dependent photocatalytic reduction of CO2 with PbS quantum dot sensitized TiO2 heterostructured photocatalysts. Journal of Materials Chemistry, 21 (2011) 13452-13457.
[30] G. Xi, S. Ouyang, J. Ye, General Synthesis of Hybrid TiO2 Mesoporous “French Fries” Toward Improved Photocatalytic Conversion of CO2 into Hydrocarbon Fuel: A Case of TiO2/ZnO. Chemistry – A European Journal, 17 (2011) 9057-9061.
[31] S.-I. In, D.D. Vaughn, R.E. Schaak, Hybrid CuO-TiO2−xNx Hollow Nanocubes for Photocatalytic Conversion of CO2 into Methane under Solar Irradiation. Angewandte Chemie International Edition, 51 (2012) 3915-3918.
[32] S. Qin, F. Xin, Y. Liu, X. Yin, W. Ma, Photocatalytic reduction of CO2 in methanol to methyl formate over CuO–TiO2 composite catalysts. Journal of Colloid and Interface Science, 356 (2011) 257-261.
[33] M. Abou Asi, L. Zhu, C. He, V.K. Sharma, D. Shu, S. Li, J. Yang, Y. Xiong, Visible-light-harvesting reduction of CO2 to chemical fuels with plasmonic Ag@AgBr/CNT nanocomposites. Catalysis Today, 216 (2013) 268-275.
[34] M.M. Gui, S.-P. Chai, B.-Q. Xu, A.R. Mohamed, Enhanced visible light responsive MWCNT/TiO2 core–shell nanocomposites as the potential photocatalyst for reduction of CO2 into methane. Solar Energy Materials and Solar Cells, 122 (2014) 183-189.
[35] Y.T. Liang, B.K. Vijayan, K.A. Gray, M.C. Hersam, Minimizing Graphene Defects Enhances Titania Nanocomposite-Based Photocatalytic Reduction of CO2 for Improved Solar Fuel Production. Nano Letters, 11 (2011) 2865-2870.
[36] Y.T. Liang, B.K. Vijayan, O. Lyandres, K.A. Gray, M.C. Hersam, Effect of Dimensionality on the Photocatalytic Behavior of Carbon–Titania Nanosheet Composites: Charge Transfer at Nanomaterial Interfaces. The Journal of Physical Chemistry Letters, 3 (2012) 1760-1765.
[37] T.-F. Yeh, J.-M. Syu, C. Cheng, T.-H. Chang, H. Teng, Graphite Oxide as a Photocatalyst for Hydrogen Production from Water. Advanced Functional Materials, 20 (2010) 2255-2262.
[38] T.-F. Yeh, F.-F. Chan, C.-T. Hsieh, H. Teng, Graphite Oxide with Different Oxygenated Levels for Hydrogen and Oxygen Production from Water under Illumination: The Band Positions of Graphite Oxide. The Journal of Physical Chemistry C, 115 (2011) 22587-22597.
[39] H.-C. Hsu, I. Shown, H.-Y. Wei, Y.-C. Chang, H.-Y. Du, Y.-G. Lin, C.-A. Tseng, C.-H. Wang, L.-C. Chen, Y.-C. Lin, K.-H. Chen, Graphene oxide as a promising photocatalyst for CO2 to methanol conversion. Nanoscale, 5 (2013) 262-268.
[40] A.K. Geim, K.S. Novoselov, The rise of graphene. Nat Mater, 6 (2007) 183-191.
[41] C.-I. Wang, A.P. Periasamy, H.-T. Chang, Photoluminescent C-dots@RGO Probe for Sensitive and Selective Detection of Acetylcholine. Analytical Chemistry, 85 (2013) 3263-3270.
[42] L. Ye, J. Fu, Z. Xu, R. Yuan, Z. Li, Facile One-Pot Solvothermal Method to Synthesize Sheet-on-Sheet Reduced Graphene Oxide (RGO)/ZnIn2S4 Nanocomposites with Superior Photocatalytic Performance. ACS Applied Materials & Interfaces, 6 (2014) 3483-3490.
[43] X.-J. Zhang, G.-S. Wang, W.-Q. Cao, Y.-Z. Wei, J.-F. Liang, L. Guo, M.-S. Cao, Enhanced Microwave Absorption Property of Reduced Graphene Oxide (RGO)-MnFe2O4 Nanocomposites and Polyvinylidene Fluoride. ACS Applied Materials & Interfaces, 6 (2014) 7471-7478.
[44] B.C. Brodie, Sur le poids atomique du graphite. Ann. Chim. Phys., 59 (1860) 466-472.
[45] L. Staudenmaier, Verfahren zur Darstellung der Graphitsäure. Berichte der deutschen chemischen Gesellschaft, 31 (1898) 1481-1487.
[46] W.S. Hummers, R.E. Offeman, Preparation of Graphitic Oxide. Journal of the American Chemical Society, 80 (1958) 1339-1339.
[47] D.C. Marcano, D.V. Kosynkin, J.M. Berlin, A. Sinitskii, Z. Sun, A. Slesarev, L.B. Alemany, W. Lu, J.M. Tour, Improved Synthesis of Graphene Oxide. ACS Nano, 4 (2010) 4806-4814.
[48] A.L. Higginbotham, D.V. Kosynkin, A. Sinitskii, Z. Sun, J.M. Tour, Lower-Defect Graphene Oxide Nanoribbons from Multiwalled Carbon Nanotubes. ACS Nano, 4 (2010) 2059-2069.
[49] A. Lerf, H. He, T. Riedl, M. Forster, J. Klinowski, 13C and 1H MAS NMR studies of graphite oxide and its chemically modified derivatives. Solid State Ionics, 101–103, Part 2 (1997) 857-862.
[50] A. Lerf, H. He, M. Forster, J. Klinowski, Structure of Graphite Oxide Revisited‖. The Journal of Physical Chemistry B, 102 (1998) 4477-4482.
[51] L.J. Cote, J. Kim, V.C. Tung, J. Luo, F. Kim, J. Huang, Graphene oxide as surfactant sheets. Pure and Applied Chemistry, 83 (2010).
[52] B. Zhao, P. Liu, Y. Jiang, D. Pan, H. Tao, J. Song, T. Fang, W. Xu, Supercapacitor performances of thermally reduced graphene oxide. Journal of Power Sources, 198 (2012) 423-427.
[53] Y. Zhu, X. Li, Q. Cai, Z. Sun, G. Casillas, M. Jose-Yacaman, R. Verduzco, J.M. Tour, Quantitative Analysis of Structure and Bandgap Changes in Graphene Oxide Nanoribbons during Thermal Annealing. Journal of the American Chemical Society, 134 (2012) 11774-11780.
[54] X. Gao, J. Jang, S. Nagase, Hydrazine and Thermal Reduction of Graphene Oxide: Reaction Mechanisms, Product Structures, and Reaction Design. The Journal of Physical Chemistry C, 114 (2009) 832-842.
[55] M. Hirata, T. Gotou, S. Horiuchi, M. Fujiwara, M. Ohba, Thin-film particles of graphite oxide 1:: High-yield synthesis and flexibility of the particles. Carbon, 42 (2004) 2929-2937.
[56] M. Helbig, H.-H. Hörhold, Investigation of poly(arylenevinylene)s, 40. Electrochemical studies on poly(p-phenylenevinylene)s. Die Makromolekulare Chemie, 194 (1993) 1607-1618.
[57] W. Alhalasah, R. Holze, Electrochemical bandgaps of a series of poly-3-p-phenylthiophenes. J Solid State Electrochem, 11 (2007) 1605-1612.
[58] C. Botas, P. Álvarez, C. Blanco, R. Santamaría, M. Granda, M.D. Gutiérrez, F. Rodríguez-Reinoso, R. Menéndez, Critical temperatures in the synthesis of graphene-like materials by thermal exfoliation–reduction of graphite oxide. Carbon, 52 (2013) 476-485.
[59] C.D. Zangmeister, Preparation and Evaluation of Graphite Oxide Reduced at 220 °C. Chemistry of Materials, 22 (2010) 5625-5629.
[60] T. Szabó, O. Berkesi, I. Dékány, DRIFT study of deuterium-exchanged graphite oxide. Carbon, 43 (2005) 3186-3189.
[61] T. Szabó, O. Berkesi, P. Forgó, K. Josepovits, Y. Sanakis, D. Petridis, I. Dékány, Evolution of Surface Functional Groups in a Series of Progressively Oxidized Graphite Oxides. Chemistry of Materials, 18 (2006) 2740-2749.
[62] X. Li, G. Zhang, X. Bai, X. Sun, X. Wang, E. Wang, H. Dai, Highly conducting graphene sheets and Langmuir-Blodgett films. Nat Nano, 3 (2008) 538-542.
[63] T.-F. Yeh, J. Cihlář, C.-Y. Chang, C. Cheng, H. Teng, Roles of graphene oxide in photocatalytic water splitting. Materials Today, 16 (2013) 78-84.
[64] C.-T. Chien, S.-S. Li, W.-J. Lai, Y.-C. Yeh, H.-A. Chen, I.S. Chen, L.-C. Chen, K.-H. Chen, T. Nemoto, S. Isoda, M. Chen, T. Fujita, G. Eda, H. Yamaguchi, M. Chhowalla, C.-W. Chen, Tunable Photoluminescence from Graphene Oxide. Angewandte Chemie International Edition, 51 (2012) 6662-6666.
[65] G. Eda, Y.-Y. Lin, C. Mattevi, H. Yamaguchi, H.-A. Chen, I.S. Chen, C.-W. Chen, M. Chhowalla, Blue Photoluminescence from Chemically Derived Graphene Oxide. Advanced Materials, 22 (2010) 505-509.
[66] K.P. Loh, Q. Bao, G. Eda, M. Chhowalla, Graphene oxide as a chemically tunable platform for optical applications. Nat Chem, 2 (2010) 1015-1024.
[67] E.J. Park, B. Jeong, M.-G. Jeong, Y.D. Kim, Synergetic effects of hydrophilic surface modification and N-doping for visible light response on photocatalytic activity of TiO2. Current Applied Physics, 14 (2014) 300-305.