發(fā)布時間：2018-04-15 17:09

  本文選題：碳化硅 + 分解水　； 參考：《北京科技大學(xué)》2016年博士論文

【摘要】：在半導(dǎo)體催化劑的作用下,利用太陽能分解水制備清潔能源氫能被認為是解決化石能源短缺和環(huán)境問題的有效途徑之一。碳化硅(SiC)作為重要的非金屬材料半導(dǎo)體,具有化學(xué)性質(zhì)穩(wěn)定、高電子遷移率等優(yōu)良性質(zhì)。其導(dǎo)帶、價帶的位置完全滿足光分解水的要求,是理想的可見光響應(yīng)分解水的催化劑。本工作以SiC為主體催化劑,圍繞兩個問題,一是SiC的光生電子和空穴在催化劑內(nèi)部的分離、轉(zhuǎn)移、復(fù)合是如何進行的,二是如何能更好延長SiC光生電子和空穴的存在時間,促進其光生電荷的分離,抑制其復(fù)合。通過BiVO4及其量子點、還原石墨烯以及金屬助劑的定向負載對SiC進行表面修飾,探究上述兩個問題在這些催化劑中的作用行為,從而深入地了解SiC自身在光催化分解水反應(yīng)過程中的催化反應(yīng)機理。具體研究結(jié)果如下：(1)采用化學(xué)沉淀法利用BiVO4對SiC進行修飾,復(fù)合物中異質(zhì)結(jié)的構(gòu)建促進了其光生電子和空穴的分離,增加了復(fù)合物中光生電子的壽命,催化性能最佳的樣品SiC/BiVO4(1:1)的光生電子壽命達到4.34 ns,相比SiC光生電子壽命3.56 ns,提高了21%。通過Pt分子探針實驗檢測,復(fù)合物中的光生電子按照Z型電子轉(zhuǎn)移體系進行傳輸。在FeCl3為犧牲劑,可見光(L420nm)下反應(yīng)4h,SiC/BiVO4(1:1)催化劑的產(chǎn)氧量為131.7 μmol,產(chǎn)氧速率為658.8μmol·h-1·g-1,其在420nm處的量子效率達到了1.04%。(2)將GO引入SiC/BiVO4復(fù)合物催化劑中。此催化劑中,光生電子仍以Z型傳導(dǎo)路徑進行傳輸。GO的引入,進一步增加了光生電子壽命,催化性能最佳的樣品SiC/GO-1%/BiVO4的達到4.67 ns,相比SiC,提高了31.2%。引入的GO,在反應(yīng)過程中被部分還原為RGO,其優(yōu)異的導(dǎo)電性能,提高了光生電子在此復(fù)合物中的轉(zhuǎn)移速率。相同反應(yīng)條件下,SiC/GO-1%/BiVO4的產(chǎn)氧量為195.7 μmol,產(chǎn)氧速率為988.2 pmol·h·g-1,在420 nm處的量子效率達到了1.56%。(3)采用水熱法將量子點QD-BiVO4定向沉積于SiC的C面上。這種定向沉積進一步增加了復(fù)合物中光生電子的壽命,催化性能最佳的樣品SiC/BiVO4(1:0.1)的光生電子壽命達到4.96 ns,相比SiC提高了39.5%。在復(fù)合物催化劑中,光生電子仍然按照Z型電子轉(zhuǎn)移體系進行傳輸。QD-BiVO4定向沉積在SiC的C面上,縮短了Z型電子傳導(dǎo)路徑的距離,傳輸效率更高。相同反應(yīng)條件下,SiC/QD-BiVO4(1:0.1)催化劑的分解水產(chǎn)氧量為413.8 μmol,產(chǎn)氧速率為2069μmol·h-1·g-1,其在420nm處的量子效率達到了3.1%。(4)采用光沉積法利用Pt修飾了SiC, Pt在SiC表面是定向分布的,呈正價態(tài)Ptδ+。其在SiC的表面與Si相互作用形成Pt-Si鍵。Pt-Si鍵的形成構(gòu)建了一個電子轉(zhuǎn)移的通道,促進了光生電子由SiC表面加速、定向轉(zhuǎn)移到Pt的表面參與光還原產(chǎn)氫反應(yīng),從而有效地抑制了光生電荷的復(fù)合。在Na2S和Na2SO3作為犧牲劑,可見光(λ420 nm)下反應(yīng)3h, Pt/SiC (PD)催化劑的分解水氫氣的最大產(chǎn)量為41.3μL,產(chǎn)氫速率為1376 μL·h-1·9-1,在420 nm處的量子效率為1.81%。(5)通過第一性原理計算和實驗結(jié)果,SiC的Si面是光生電子的富積面,C面是光生空穴的富積面。利用Pt、MnO2(Pt作為還原反應(yīng)助劑,MnO2作為氧化反應(yīng)助劑)作為目標(biāo)物進行了驗證。Pt定向沉積在SiC的Si面上,充當(dāng)光生電子的捕獲中心和光還原反應(yīng)的活性中心,MnO2定向沉積在SiC的C面上,充當(dāng)光生空穴的捕獲中心和光氧化反應(yīng)的活性中心。Pt和MnO2在SiC的表面上實現(xiàn)了空間分離,有利于地促進了SiC表面光生電子和空穴的分離。在犧牲劑的存在下,光催化產(chǎn)氫反應(yīng),Pt/SiC/MnO2,3 h的反應(yīng)中,氫氣的最大產(chǎn)量為396μL,產(chǎn)氫速率為2640 μL·h-1·g-1。光催化產(chǎn)氧反應(yīng),Pt/SiC/MnO2樣品3h的反應(yīng)中,氧氣的最大產(chǎn)量為36.8μL,產(chǎn)氧速率為245.7 μL·h-1·g-1。(6)將Z型光催化體系引入SiC中,以Pt/SiC為產(chǎn)氫催化劑,WO3為產(chǎn)氧催化劑,I-/IO3-為氧化還原離子對,構(gòu)建了Z型光催化全解水的反應(yīng)體系。負載的Pt的最佳含量為0.5%(wt),反應(yīng)溶液的最佳pH值為3。在整個Z型光催化體系反應(yīng)過程中,還原H+產(chǎn)氫反應(yīng)步驟是整個催化反應(yīng)過程的決速步。此Z型光催化反應(yīng)體系在4h的光照反應(yīng)中,其催化分解水產(chǎn)生氫氣的最大產(chǎn)量為25.1μL,氧氣的產(chǎn)量為12.4μL,在420nm處的量子效率為0.021%。氫氣和氧氣按照體積比為2:1的計量比產(chǎn)出,實現(xiàn)了以SiC為基的可見光下的全解水。
[Abstract]:In the semiconductor catalyst, using solar energy water decomposition preparation of hydrogen energy is considered to be one of the effective ways to solve the shortage of fossil energy and environmental issues. Silicon carbide (SiC) as an important semiconductor non metallic materials, has stable chemical properties, excellent properties of high electron mobility. The conduction band and the valence band fully meet photodecomposition water requirement is the ideal response to visible light catalyst. The decomposition of water using SiC as the main catalyst, about two issues, one is the separation of SiC, the photogenerated electrons and holes in the catalyst transfer inside the composite, is how the two is how to extend the SiC light time better the electron and hole, promote the separation of photogenerated charges, inhibition of the composite. Through the BiVO4 and quantum dots, reduced graphene and directed metal additives load on the SiC surface modification, the inquiry Two problems in the behavior of these catalysts, and in-depth understanding of SiC itself in the catalytic reaction mechanism of water in the reaction process of photocatalytic decomposition. The main results are as follows: (1) precipitation of SiC was modified by BiVO4 using the chemical construction, promote the separation of photogenerated electrons and holes heterojunction in the compound, increases the lifetime of photogenerated electrons in the compound, the best catalytic performance of sample SiC/BiVO4 (1:1) of the photogenerated electron lifetime reached 4.34 ns, compared to the SiC electron lifetime of 3.56 ns, increased by 21%. through experimental inspection of Pt molecular probe, complexes of photoinduced electron transfer in Z type of electron transfer system. As the sacrificial agent in FeCl3, visible light (L420nm) under the reaction of 4h, SiC/BiVO4 (1:1) catalysts for oxygen production is 131.7 mol, oxygen production rate of 658.8 mol - H-1 - g-1, the 420nm in the quantum efficiency of 1.04%. (2) GO The introduction of SiC/BiVO4 composite catalyst. This catalyst, the photogenerated electrons to the conduction path of Z type transmission.GO, further increase of the electron lifetime, sample SiC/GO-1%/BiVO4 best catalytic performance of up to 4.67 ns, compared to SiC, 31.2%. increased the introduction of GO, in the reaction process was partially reduced to RGO and its excellent conductive properties, improve the photoinduced electron transfer rate in this complex. Under the same reaction conditions, SiC/GO-1%/BiVO4 oxygen production is 195.7 mol, oxygen production rate was 988.2 pmol - H - g-1, the quantum effect at 420 nm rate of 1.56%. (3) by hydrothermal method quantum dots QD-BiVO4 directional deposition in SiC C surface. The directional deposition further increases the life of the photogenerated electron compound, sample SiC/BiVO4 best catalytic performance (1:0.1) of the photogenerated electron lifetime reached 4.96 ns, compared to SiC increased 39.5%. in Composite catalyst, the photogenerated electrons are still in accordance with the Z type electron transfer system for transmission directional.QD-BiVO4 deposited on SiC C face, shorten the Z electronic conduction path distance, higher transmission efficiency. Under the same conditions, SiC/QD-BiVO4 (1:0.1) decomposition of aquatic oxygen catalyst is 413.8 mol, the rate of oxygen production 2069 mol - H-1 - g-1, the 420nm in the quantum efficiency of 3.1%. (4) by using Pt modified by SiC light deposition method, Pt is a directional distribution on the surface of SiC positive valence Pt 8. The SiC with Si on the surface of the interaction between the formation of Pt-Si bond formation of.Pt-Si bond construction an electron transfer channel, promotes photogenerated electrons by SiC surface acceleration, directional transfer to the surface of Pt in light hydrogen reaction, so as to effectively suppress the recombination of photogenerated charge. As a sacrificial agent in Na2S and Na2SO3, visible light (a 420 nm) under the reaction of 3H, Pt/Si C (PD) catalyst for decomposition of hydrogen water maximum output is 41.3 L, the hydrogen production rate of 1376 L - H-1 - 9-1, the quantum efficiency at 420 nm 1.81%. (5) by first principle calculation and experimental results, Si SiC is the accumulation of surface electron, C surface is photohole rich area. By using Pt, MnO2 (Pt as a reaction agent, MnO2 as oxidation additives) as the object is verified.Pt directional deposition on SiC Si surface, acting as electron capture center and photoreduction activity center, MnO2 SiC C in directional deposition on the surface, a photohole capture center and photooxidation of the active center of.Pt and MnO2 in SiC on the surface to realize spatial separation, is conducive to promote the separation of SiC surface photoinduced electrons and holes. In the presence of a sacrificial agent, photocatalytic reaction, Pt/SiC/MnO2,3 h reaction. The maximum hydrogen production 閲忎負396渭L,浜ф阿閫熺巼涓，

本文編號：1755023