本文選題：光催化 + 表面科學(xué)　； 參考：《山東大學(xué)》2017年博士論文

【摘要】：1972年Fujishima和Honda教授發(fā)現(xiàn)光照下TiO_2電極可以把水裂解為氫氣和氧氣,之后迅速掀起了光催化領(lǐng)域的研究熱潮。光催化材料在催化分解水制氫、降解各種有機和無機污染物、太陽能電池以及光還原二氧化碳等領(lǐng)域具有重要的應(yīng)用前景。分子尺度上對光催化反應(yīng)基本過程的理解,對提高催化劑的催化效率和選擇性具有重要意義。催化劑表面是多相催化發(fā)生的直接場所,研究表面與反應(yīng)物分子的相互作用行為,對深入理解光催化機理是非常重要的。氧化鈦(TiO_2)和氧化鋅(ZnO)是目前研究和應(yīng)用最為廣泛的光催化材料,把這兩種材料表面作為模型表面來研究光催化機理具有很強的代表性。人們利用多種超高真空表面科學(xué)分析技術(shù),在單晶TiO_2與ZnO表面分子吸附與反應(yīng)過程的研究中取得了豐富成果。但是,很多分子尺度上的基礎(chǔ)問題依然存在爭議,利用更多的實驗手段從不同角度來研究表面化學(xué)過程對于澄清這些問題是非常有必要的。表面紅外反射吸收光譜(Infrared Reflection Absorption Spectroscopy,IRRAS)對吸附分子具有很強的化學(xué)分辨能力,并對分子周圍環(huán)境比較敏感,非常適合研究表面分子的吸附位置、吸附構(gòu)型、反應(yīng)路徑和分子-分子相互作用等問題,已經(jīng)成功地應(yīng)用于金屬單晶表面化學(xué)和催化反應(yīng)機理研究中。但是由于單晶氧化物表面吸附分子振動的紅外吸收信號極弱,其上表面化學(xué)過程的紅外光譜研究非常缺乏。我們設(shè)計搭建了新型的超高真空-真空紅外光譜(Ultrahigh Vacuum-Vacuum Fourier Transform Infrared Spectrometer,UHV-FTIRS)系統(tǒng),該系統(tǒng)經(jīng)過優(yōu)化的光路設(shè)計,具有極高的穩(wěn)定性與靈敏度,可以在超高真空環(huán)境中原位監(jiān)測氧化物單晶表面的分子過程。利用這套裝置,我們系統(tǒng)地研究了金紅石型單晶TiO_2(110)表面和纖鋅礦型單晶ZnO(1010)表面等典型氧化物表面的分子吸附位置與吸附構(gòu)型、分子間相互作用以及分子-表面電荷轉(zhuǎn)移等問題。主要研究內(nèi)容與結(jié)果如下:1.分別利用CO和NO分子研究了 TiO_2(110)表面氧空位(Vo)引入極化子參與的分子吸附過程。對于CO吸附,位于次表層六配位Ti位(Ti6c)的極化子轉(zhuǎn)移到CO下方的五配位Ti位(Ti5c),分子周圍靜電場環(huán)境的改變引起了分子振動頻率的微弱紅移;對于NO吸附,次表層的Ti6c極化子直接轉(zhuǎn)移到Ti:3d-NO:2p雜化軌道,引起了 N-O伸縮頻率的巨大紅移。不同的極化子參與的分子吸附圖像取決于極化子態(tài)與分子最低未占據(jù)分子軌道(Lowest Unoccupied Molecular Orbital,LUMO)的能級排布情況。2.利用偏振分辨和方向分辨的IRRAS,我們系統(tǒng)研究了 TiO_2(110)理想配比表面和還原性表面NO吸附與反應(yīng)路徑。在理想配比TiO_2(110)表面,確定了吸附于Ti5c的雙配位順式(NO)_2二聚體構(gòu)型(cis-(NO)_2/TiTi),并給出了 NO→cis-(NO)_2/TiTi → N_2O + Oa的反應(yīng)路徑。而在還原性TiO_2(110)表面,Vo的存在明顯地改變了 NO的吸附與反應(yīng)路徑。實驗發(fā)現(xiàn)三種與Vo相關(guān)的NO吸附構(gòu)型,它們都和Vo引入的極化子有著強的相互作用,引起了分子振動頻率的極大紅移。NO通入量足夠高時,所有的NO中間態(tài)最終全部轉(zhuǎn)化為N_2O分子。3.我們研究了 TiO_2(110)表面Au團簇的生長、電荷態(tài)表征及其調(diào)控。以CO為探針分子,利用其振動頻率的改變來表征Au團簇的電荷態(tài),我們發(fā)現(xiàn)TiO_2(110)表面原位生長的Au團簇以電中性形式存在。通過TiO_2(110)表面2NO →N_2O+ Oa反應(yīng),成功實現(xiàn)了對Au/TiO_2界面處Au原子從電中性到正電性的調(diào)控,反映到CO頻率上有20-26 cm-1的較大藍移。頻率藍移大小,即Au正電性強弱,取決于表面Oa原子數(shù)目及Au團簇尺寸。4.我們研究了 CO_2在TiO_2(110)表面的吸附位置、吸附構(gòu)型和分子-分子相互作用。隨著(CO_2覆蓋度的增加,90K時,CO_2依次吸附于Vo位、Vo近鄰的Ti5c位、遠離Vo的Ti5c位和橋位氧(Obr)位。紅外光沿[001]和[1(?)0]晶向入射的IRRAS譜均發(fā)現(xiàn)了(CO_2的v3(O(CO)反對稱伸縮振動分裂為兩個吸收峰,意味著近鄰CO_2之間發(fā)生了振動耦合。結(jié)合密度泛函(DFT)計算,我們提出了兩種(CO_2的耦合轉(zhuǎn)子結(jié)構(gòu)來解釋近鄰CO_2在兩個方向的吸收峰分裂。CO_2覆蓋度為1.5分子單層(monolayer,ML)時,通過方向分辨和偏振分辨的IRRAS,確定了吸附于Obr位的CO_2沿[1(?)0]方向的水平吸附構(gòu)型。5.我們發(fā)現(xiàn)了ZnO(10(?)0)表面CO_2一維分子鏈的形成并研究了其演化過程。在9OK時ZnO(10(?)0)表面CO_2的吸附過程中,隨著覆蓋度增加,IRRAS譜中出現(xiàn)了一系列CO_2吸收峰的精細結(jié)構(gòu),結(jié)合DFT計算,依次把它們歸屬為沿[0001]方向形成的CO_2單體、二聚體、三聚體以及更長的分子聚合體。這種新奇的鏈式生長過程是由于界面電荷再分布引起的增強的CO_2分子與表面三配位Zn原子(Zn3c)之間的庫倫吸引作用導(dǎo)致的。低(CO_2覆蓋度時,表面退火可以使較短的分子鏈變的更長。高覆蓋度時,退火至150K局域的(2×1)結(jié)構(gòu)會演化為一種局域的(1×1)結(jié)構(gòu)中間態(tài),進一步升高溫度最終演化為規(guī)范的(2×1)結(jié)構(gòu)。我們提出了一個動力學(xué)機制解釋了這種相演化過程。
[Abstract]:In 1972, Fujishima and Honda found that the TiO_2 electrode can break water into hydrogen and oxygen under light, and then quickly set off the research boom in the field of photocatalysis. Photocatalytic materials have important applications in the field of catalytic decomposition of water for hydrogen production, degradation of various organic and inorganic pollutants, solar cells and light and carbon dioxide. The understanding of the basic process of photocatalytic reaction on the molecular scale is of great significance for improving the catalytic efficiency and selectivity of the catalyst. The surface of the catalyst is a direct place for the occurrence of multiphase catalysis. It is very important to study the interaction between the surface and the reactant molecules. It is very important to understand the mechanism of photooxidation. Titanium oxide (TiO_2) and oxygen are very important. Zinc (ZnO) is the most widely used photocatalytic material for research and application. It is very representative to study the photocatalytic mechanism of the surface of these two materials as a model surface. A variety of ultra high vacuum surface scientific analysis techniques have been used in the study of the adsorption and reaction of TiO_2 and ZnO on the surface of single crystal. However, many basic problems on the molecular scale are still controversial. It is necessary to use more experimental methods to study the surface chemical processes from different angles to clarify these problems. The Infrared Reflection Absorption Spectroscopy (IRRAS) has a strong chemical fraction for the adsorbate molecules. It is very suitable for the study of the adsorption location of surface molecules, the adsorption configuration, the reaction path and the interaction of molecules and molecules, which have been successfully applied to the study of the surface chemistry and catalytic reaction mechanism of the single crystal. The signal is very weak, and the infrared spectrum of the upper surface chemical process is very short. We designed and built a new ultra high vacuum vacuum infrared spectroscopy (Ultrahigh Vacuum-Vacuum Fourier Transform Infrared Spectrometer, UHV-FTIRS) system. The system has been designed with optimized optical path, with high stability and sensitivity. The molecular process of in-situ monitoring of the surface of a single oxide single crystal in an ultra high vacuum environment is used. Using this set of devices, we have systematically studied the molecular adsorption position and adsorption configuration, intermolecular interaction and molecular surface charge transfer on the surface of the TiO_2 (110) and the ZnO (1010) surface of the monocrystalline monocrystalline monocrystalline rutile The main contents and results are as follows: 1. using CO and NO molecules, the molecular adsorption process of TiO_2 (110) surface oxygen vacancy (Vo) is introduced into the polaron. For CO adsorption, the polaron at the subsurface six coordination Ti bit (Ti6c) is transferred to the five coordination Ti bit (Ti5c) below CO, and the environment of the electrostatic field around the molecule is changed. The weak red shift of the molecular vibration frequency; for NO adsorption, the Ti6c Polaron in the subsurface is transferred directly to the Ti:3d-NO:2p hybrid orbit, causing a huge red shift of the N-O expansion frequency. The molecular adsorption images of different polarons are dependent on the polaron and the molecular lowest unoccupied sub orbits (Lowest Unoccupied Molecular Orbital, LUM). O's energy level arrangement.2. uses polarization resolution and directional resolution IRRAS, we systematically study the NO adsorption and reaction path of TiO_2 (110) ideal ratio surface and reductive surface. In the ideal ratio TiO_2 (110) surface, the dual coordination CIS (NO) _2 two polymer (cis- (NO) _2/TiTi) adsorbed on Ti5c is determined. The reaction path of /TiTi to N_2O + Oa, while on the reduced TiO_2 (110) surface, the existence of Vo obviously changes the adsorption and reaction path of NO. The experiment found that the NO adsorption configurations related to Vo have strong interaction with the polaron introduced by Vo, which caused the maximum red shift.NO of the molecular vibrational frequency to be high enough. Some NO intermediate states were eventually converted to N_2O molecule.3.. We studied the growth of Au clusters on the TiO_2 (110) surface, the characterization of the charge state and its regulation. CO was used as a probe molecule to characterize the charge state of the Au cluster by the change of its vibrational frequency. We found that the Au clusters of the original growth of the TiO_2 (110) surface exist in the form of electrical neutrality. Through TiO_2 (1) 10) the surface 2NO to N_2O+ Oa reaction, successfully realized the regulation of Au atom from electrical neutral to positive on the Au/TiO_2 interface, reflecting a large blue shift of 20-26 cm-1 on the frequency of CO. The frequency blue shift, that is, the magnitude of the Au positive power, depends on the number of Oa atoms on the surface and the Au cluster size.4.. With the addition of the adsorption configuration and molecular molecular interaction, with the increase of CO_2 coverage, 90K, CO_2 adsorbed on Vo bit, Vo near Ti5c bit, far away from Vo Ti5c and bridge position oxygen (Obr). In conjunction with the density functional (DFT) calculation, two kinds of coupling rotor structure (CO_2) are proposed to explain the IRRAS that is resolved and polarization resolved by the directional resolution and polarization resolution of the adjacent CO_2 in two directions with the absorption peak division.CO_2 coverage of 1.5 molecular monolayers (monolayer, ML), and the CO_2 adsorbed on the Obr bit is along [1 (?) 0. ] the horizontal adsorption configuration.5. in the direction of the ZnO (10 (?) 0) surface CO_2 one-dimensional molecular chain formation and its evolution process. In the 9OK ZnO (10 (?) 0) surface CO_2 adsorption process, with the increase of the coverage, IRRAS spectrum appears a series of CO_2 absorption peak of the fine structure, combined with DFT calculation, they belong to [0001] in turn along [0001]. The CO_2 monomer, the two polymer, the trimer, and the longer molecular polymer. This novel chain growth process is caused by the Kulun attraction between the enhanced CO_2 molecule and the surface three coordination Zn atom (Zn3c) caused by the redistribution of the interface charge. Low (CO_2 coverage, the surface annealing can make the shorter molecular chain change. " When the high coverage is high, the (2 * 1) structure annealed to the local area of 150K will evolve into a local (1 * 1) structure intermediate state, which will further increase the temperature to the standard (2 * 1) structure. We have proposed a kinetic mechanism to explain the phase evolution process.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：O644.1;O647.3
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本文編號：1907826