在化学中,光催化是在催化剂存在下光反应的加速。在催化光解中,光被吸附的底物吸收。在光生催化中,光催化活性(PCA)取决于催化剂产生电子-空穴对的能力,电子-空穴对产生能够进行二次反应的自由基(例如羟基自由基: •OH)。二氧化钛(TiO2)电解水的发现使其实际应用成为可能。
光催化最早被提及可追溯到1911年,当时德国化学家Alexander Eibner博士在他关于氧化锌(ZnO)对深蓝色颜料普鲁士蓝漂白的研究中整合了这一概念。[1][2] 大约在这个时候,Bruner和 Kozak发表了一篇讨论光照下铀酰盐存在下草酸变质的文章,[2][3] 而在1913年,Landau发表了一篇解释光催化现象的文章。他们的贡献导致了辐射测量的发展,这些测量为确定光化学反应中的光子通量提供了基础。[2][4]在光催化研究短暂缺乏之后,1921年,Baly等人使用氢氧化铁和胶体铀盐作为催化剂,在可见光谱范围的光下产生了甲醛。[2][5] 然而,直到1938年,Doodeve和Kitchener才发现二氧化钛,一种高度稳定且无毒的氧化物,在氧气的存在下,可以作为漂白染料的光敏剂,因为二氧化钛吸收的紫外光导致其表面产生活性氧,从而通过光氧化作用吸收有机化学物质。这实际上标志着首次观察到多相光催化的基本特征。[2][6]
由于缺乏兴趣和缺乏实际应用价值,光催化的研究停滞了25年多。然而,在1964年,V. N. Filimonov研究了氧化锌和二氧化钛的异丙醇光氧化;[2][7] 大约在同一时间,Kato和Mashio、Doerffler和Hauffe以及Ikekawa等人(1965)探索了氧化锌辐射中二氧化碳和有机溶剂的氧化/光氧化。[2][8][9][10] 几年后,在1970年,Formenti等人和Tanaka和Blyholde分别观察到各种烯烃的氧化和一氧化二氮(N2O)的光催化衰减。[2][11][12]
然而,光催化研究的突破发生在1972年,当时Akira Fujishima和 Kenichi Honda发现水在连接的二氧化钛和铂电极之间发生电化学光解,其中紫外光被前一电极吸收,电子从铂电极(阳极,氧化反应位点)传输到到二氧化钛电极(阴极,还原反应位点)阴极产生氢气。这是第一个氢气生产可以来自清洁和经济高效的来源的例子之一,因为当时和今天的大部分氢气生产来自天然气重整和气化。[2][13] Fujishima和 Honda的发现导致了光催化领域的其他进展;1977年,Nozik发现,在电化学光解过程中加入贵金属,如铂和金等,可以提高光催化活性,而且不需要外加电势。[2][14] Wagner和Somorjai (1980年)以及Sakata和Kawai (1981年)在他们进行的前沿研究中分别描述了钛酸锶(SrTiO3)表面通过光生产氢,以及钛酸锶和PtO2在乙醇中光照产生氢气和甲烷。[2][15][16]
光催化的研究和开发,特别是水的电化学光解,今天仍在继续。但迄今为止,还没有任何商业用途的开发。2017年,朱棣文等人评估了水的电化学光解的前景,讨论了开发一种低成本、高能效的光电化学(PEC)串联电池存在的主要挑战,这种电池将“模拟自然光合作用”。[2][17]
在均相光催化反应中,反应物和光催化剂存在于同一相中。最常用的均相光催化剂包括臭氧和光-芬顿体系(Fe+ 和Fe+/H2O2)。活性物质是被用于不同目的的•OH。臭氧产生羟基自由基的机理可以遵循两条途径。[18]
多相催化的催化剂与反应物处于不同的相。多相光催化是一门包含多种反应的学科:轻度或完全氧化、脱氢、氢转移、18O2–16O2和氘-烷烃同位素交换、金属沉积、水解毒、气体污染物去除等。
最常见的多相光催化剂是过渡金属氧化物和半导体,它们具有独特的性质。与具有连续电子态的金属不同,半导体具有空穴能量区,在该区域没有能级可用于促进固体中光活化产生的电子和空穴的复合。从填充价带的顶部延伸到空导带底部的空位区域被称为带隙。[20] 当能量大于或等于材料带隙的光子被半导体吸收时,电子从价带激发到导带,在价带中产生带正电的空穴。这种光生电子空穴对被称为激子。被激发的电子和空穴可以重新复合,并以热的形式释放从电子激发中获得的能量。激子复合是不希望发生的,较高的复合量会导致光催化剂的效率降低。因此,开发功能性光催化剂的努力通常强调延长激子寿命,使用多种方法促进电子-空穴分离,这些方法通常依赖于结构特征,例如晶相异质结(例如锐钛矿-金红石界面)、贵金属纳米颗粒、硅纳米线和取代阳离子掺杂。[21] 光催化剂设计的最终目标是促进受激电子与氧化剂之间的反应以产生还原产物,以及产生的空穴与还原剂之间的反应以产生氧化产物。由于空穴和电子的产生,氧化还原反应发生在半导体表面。在氧化反应中,空穴与表面上的水分子反应,产生羟基自由基。
这里MO代表金属氧化物:
UV + MO → MO (h + e−)
光催化效应引起的氧化反应:
h+ + H2O → H+ + •OH
2 h+ + 2 H2O → 2 H+ + H2O2
H2O2→ 2 •OH
光催化效应引起的还原反应:
e− + O2 → •O2−
•O2− + HO•2 + H+ → H2O2 + O2
HOOH → HO• + •OH
最终,两种反应都会产生羟基自由基。这些羟基自由基本质上具有很强的普适的氧化性,氧化还原电位为(E0 = +3.06 V)[22]
^Eibner, Alexander (1911). "Action of Light on Pigments I". Chem-Ztg. 35: 753–755..
^Coronado, Juan M.; Fresno, Fernando; Hernández-Alonso, María D.; Portela, Racquel (2013). Design of Advanced Photocatalytic Materials for Energy and Environmental Applications (PDF). London: Springer. pp. 1–5. ISBN 978-1-4471-5061-9..
^Bruner, L.; Kozak, J. (1911). "Information on the Photocatalysis I The Light Reaction in Uranium Salt Plus Oxalic Acid Mixtures". Elktrochem Agnew P. 17: 354–360..
^Landau, M. (1913). "Le Phénomène de la Photocatalyse". Compt Rend. 156: 1894–1896..
^Baly, E.C.C.; Helilbron, I.M.; Barker, W.F. (1921). "Photocatalysis. Part I. The Synthesis of Formaldehyde and Carbohydrates from Carbon Dioxide and Water". J Chem Soc. 119: 1025–1035..
^Goodeve, C.F.; Kitchener, J.A. (1938). "The Mechanism of Photosensitization by Solids". Faraday Soc. 34: 902–912..
^Filimonov, V.N. (1964). "Photocatalytic Oxidation of Gaseous Isopropanol on ZnO + TiO2". Dokl Akad Nauk SSSR. 154(4): 922–925..
^Ikekawa, A.; Kamiya, M.; Fujita, Y.; Kwan, T. (1965). "Competition of Homogeneous and Heterogeneous Chain Terminations in Heterogeneous Photooxidation Catalysis by ZnO". Bull Chem Soc Jpn. 38: 32–36..
^Doerffler, W.; Hauffe, K. (1964). "Heterogeneous Photocatalysis I. Influence of Oxidizing and Reducing Gases on the Electrical Conductivity of Dark and Illuminated Zinc Oxide Surfaces". J Catal. 3: 156–170..
^Kato, S.; Mashio, F. (1964). "Titanium Dioxide-Photocatalyzed Oxidation. I. Titanium Dioxide Photocatalyzed Liquid Phase Oxidation of Tetralin". Kogyo Kagaku Zasshi. 67: 1136–1140..
^Formenti, M.; Julliet F., F.; Teichner SJ, S.J. (1970). "Controlled Photooxidation of Paraffins and Olefins over Anatase at Room Temperature". C R Seances Acad, Sci Ser C. 270C: 138–141..
^Tanaka, K.I.; Blyholde, G. (1970). "Photocatalytic and Thermal Catalytic Decomposition of Nitrous Oxide on Zinc Oxide". J. Chem. Soc. D. 18: 1130..
^Fujishima, A.; Honda, K. (1972). "Electrochemical Photolysis of Water at a Semiconductor Electrode". Nature. 238: 37–38..
^Nozik, A.J. (1977). "Photochemical Diodes". Appl Phys Lett. 30 (11): 567–570..
^Wagner, F.T.; Somorjai, G.A. (1980). "Photocatalytic and Photoelectrochemical Hydrogen Production on Strontium Titanate Single Crystals". J Am Chem Soc. 102: 5494–5502..
^Sakata, T.; Kawai, T. (1981). "Heterogeneous Photocatalytic Production of Hydrogen and Methane from Ethanol and Water". Chem Phys Lett. 80: 341–344..
^Chu, S.; Li, W.; Yan, Y.; Hamann, T.; Shih, I.; Wang, D.; Mi, Z. (2017). "Roadmap on Solar Water Splitting: Current Status and Future Prospects". Nano Futures. IOP Publishing Ltd. 1 (2)..
^Wu, CH; Chang, CL (2006). "Decolorization of Reactive Red 2 by advanced oxidation processes: Comparative studies of homogeneous and heterogeneous systems". Journal of hazardous materials. 128 (2–3): 265–72. doi:10.1016/j.jhazmat.2005.08.013. PMID 16182444..
^Peternel, IT; Koprivanac, N; Bozić, AM; Kusić, HM (2007). "Comparative study of UV/TiO2, UV/ZnO and photo-Fenton processes for the organic reactive dye degradation in aqueous solution". Journal of hazardous materials. 148 (1–2): 477–84. doi:10.1016/j.jhazmat.2007.02.072. PMID 17400374..
^Linsebigler, Amy L.; Lu, Guangquan.; Yates, John T. (1995). "Photocatalysis on TiO2 Surfaces: Principles, Mechanisms, and Selected Results". Chemical Reviews. 95 (3): 735–758. doi:10.1021/cr00035a013..
^Karvinen, S.;Hirva, P;Pakkanen, T.A. (2003). "Ab initio quantum chemical studies of cluster models for doped anatase and rutile TiO2". Journal of molecular structure THEOCHEM. 626: 271–277.CS1 maint: Multiple names: authors list (link).
^Daneshvar, N; Salari, D; Khataee, A.R (2004). "Photocatalytic degradation of azo dye acid red 14 in water on ZnO as an alternative catalyst to TiO2". Journal of Photochemistry and Photobiology A: Chemistry. 162 (2–3): 317–322. doi:10.1016/S1010-6030(03)00378-2..
^Kudo, Akihiko; Kato, Hideki; Tsuji, Issei (2004). "Strategies for the Development of Visible-light-driven Photocatalysts for Water Splitting". Chemistry Letters. 33 (12): 1534. doi:10.1002/chin.200513248..
^"Snapcat Photo Catalytic Oxidation with Titanium Dioxide (2005)". CaluTech UV Air. Retrieved 2006-12-05..
^Kondrakov AO, Ignatev AN, Lunin VV, Frimmel FH, Braese S, Horn H (2016). "Roles of water and dissolved oxygen in photocatalytic generation of free OH radicals in aqueous TiO2 suspensions: An isotope labeling study". Applied Catalysis B: Environmental. 182: 424–430. doi:10.1016/j.apcatb.2015.09.038..
^"Photocatalysis Applications of Titanium Dioxide TiO2". Titanium Information. titaniumart.com..
^Kondrakov AO, Ignatev AN, Frimmel FH, Braese S, Horn H, Revelsky AI (2014). "Formation of genotoxic quinones during bisphenol A degradation by TiO2 photocatalysis and UV photolysis: A comparative study". Applied Catalysis B: Environmental. 160: 106–114. doi:10.1016/j.apcatb.2014.05.007..
^McCullagh C, Robertson JM, Bahnemann DW, Robertson PK (2007). "The application of TiO2 photocatalysis for disinfection of water contaminated with pathogenic micro-organisms: a review". Research on Chemical Intermediates. 33 (3–5): 359–375. doi:10.1163/156856707779238775..
^Hanaor, Dorian A. H.; Sorrell, Charles C. (2014). "Sand Supported Mixed-Phase TiO2 Photocatalysts for Water Decontamination Applications". Advanced Engineering Materials. 16 (2): 248–254. arXiv:1404.2652. doi:10.1002/adem.201300259..
^Cushnie TP, Robertson PK, Officer S, Pollard PM, Prabhu R, McCullagh C, Robertson JM (2010). "Photobactericidal effects of TiO2 thin films at low temperature". Journal of Photochemistry and Photobiology A: Chemistry. 216 (2–3): 290–294. doi:10.1016/j.jphotochem.2010.06.027..
^Kostedt IV, William L.; Jack Drwiega; David W. Mazyck; Seung-Woo Lee; Wolfgang Sigmund; Chang-Yu Wu; Paul Chadik (2005). "Magnetically agitated photocatalytic reactor for photocatalytic oxidation of aqueous phase organic pollutants". Environmental Science & Technology. American Chemical Society. 39 (20): 8052–8056. Bibcode:2005EnST...39.8052K. doi:10.1021/es0508121..
^Tan, S. S.; L. Zou; E. Hu (2006). "Photocatalytic reduction of carbon dioxide into gaseous hydrocarbon using TiO2 pellets". Catalysis Today. 115: 269–273. doi:10.1016/j.cattod.2006.02.057..
^Yao, Y. Yao; G. Li; S. Ciston; R. M. Lueptow; K. Gray (2008). "Photoreactive TiO2/Carbon Nanotube Composites: Synthesis and Reactivity". Environmental Science & Technology. American Chemical Society. 42 (13): 4952–4957. Bibcode:2008EnST...42.4952Y. doi:10.1021/es800191n..
^Linsebigler, A. L.; G. Lu; J.T. Yates (1995). "Photocatalysis on TiO2 Surfaces: Principles, Mechanisms, and Selected Results". Chemical Reviews. 95 (3): 735–758. doi:10.1021/cr00035a013..
^Science News.
^Mathiesen, D. (2012). "Final Report Summary - LIGHT2CAT (Visible LIGHT Active PhotoCATalytic Concretes for Air pollution Treatment)". European Commission..
^Light2CAT (2015). "Light2CAT Visible Light Active PhotoCATalytic Concretes for Air Pollution Treatment [YouTube Video]". YouTube..
^ISO 22197-1:2007.
^Unique Gas Analyser Helps to Characterize Photoactive Pigments.
^Nuño, Manuel (2014). "Study of solid/gas phase photocatalytic reactions by electron ionization mass spectrometry". Journal of Mass Spectrometry. 49: 716–726. Bibcode:2014JMSp...49..716N. doi:10.1002/jms.3396..
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