本文選題：氧化鐵 + 光解水　； 參考：《蘇州大學(xué)》2015年碩士論文

【摘要】：光催化分解水制備氫氣是將太陽(yáng)能轉(zhuǎn)化為氫能的一項(xiàng)具有挑戰(zhàn)且意義重大的課題。在眾多半導(dǎo)體材料催化劑中,我們選擇研究氧化鐵體系,主要是氧化鐵具有很多獨(dú)特的優(yōu)勢(shì),如容易獲得、溶液中性能穩(wěn)定、能帶寬度合適等。盡管氧化鐵理論計(jì)算得到的光解水效率很高,但目前的實(shí)際效率較低,主要原因包括氧化鐵本身的光生電子-空穴復(fù)合速度快,不利于形成光電流的電荷遷移,空穴傳輸距離短,不足2 nm,差的導(dǎo)電性等。此外,一個(gè)限制氧化鐵效率的重要因素是其能帶位置不合適,需要施加一個(gè)偏壓讓氫氣還原,從而使整個(gè)反應(yīng)進(jìn)行。氧化鐵光解水催化過(guò)程中的各種其它因素也會(huì)導(dǎo)致偏壓的產(chǎn)生,降低效率。降低氧化鐵光解水過(guò)程中的偏壓是目前相關(guān)領(lǐng)域一個(gè)重要的研究方向。在本論文中我們發(fā)展了多種方法來(lái)提高氧化鐵光解水的性能,主要通過(guò)控制氧化鐵表面還原處理的深度來(lái)降低偏壓,取得了很好的效果。以下是本論文的具體內(nèi)容:我們首先對(duì)氧化鐵的水熱合成方法進(jìn)行了改進(jìn),進(jìn)一步控制其形貌和重復(fù)性(第二章)。性能良好的未進(jìn)行摻雜或其他修飾處理的空白氧化鐵樣品是進(jìn)一步處理手段取得良好效果的前提,是一項(xiàng)基礎(chǔ)但非常重要的工作。水熱法目前在制備空白氧化鐵樣品上具有獨(dú)特的優(yōu)勢(shì),通常用簡(jiǎn)單的方法可以得到目前報(bào)道中性能較高的產(chǎn)物,因此得到了廣泛應(yīng)用。我們?cè)趯?shí)驗(yàn)過(guò)程中發(fā)現(xiàn),目前的方法需要比較嚴(yán)格的條件,溫度、壓力以及濃度等變化的時(shí)候往往不能得到重復(fù)性好的高性能空白氧化鐵樣品。我們通過(guò)研究水熱法前驅(qū)溶液中反應(yīng)物NaNO3和FeCl3.6H2O濃度的影響,去除了以往方法中必須添加的HCl,并減小兩種反應(yīng)物濃度,在不改變其它條件的情況,合成出厚度合適、分布均勻的顆粒狀氧化鐵,值得一提的是,這種方法得到的空白樣品具有良好的性能而且重復(fù)性非常高。在改進(jìn)空白樣品的制備條件之后,我們基于課題組前期氧空穴摻雜的實(shí)驗(yàn)研究,發(fā)展了氨硼烷水溶液熱分解產(chǎn)氫來(lái)對(duì)氧化鐵進(jìn)行還原處理。這種處理方法同樣可以形成表面氧空穴摻雜來(lái)提高效率。對(duì)比以前的方法,這種在氧化鐵表面滴加氨硼烷溶液直接加熱還原的方法操作簡(jiǎn)單,最佳條件下處理的氧化鐵光電流比空白樣提高近兩倍,改善效果明顯。更有意義的是,在加熱過(guò)程中我們發(fā)現(xiàn)樣品覆蓋坩堝后進(jìn)行還原處理得到的樣品光解水效果更好,且起始電壓(偏壓)有明顯改善。深入的研究證明這不是濃度增加的效果,而是加熱過(guò)程中坩堝覆蓋引起壓力增大導(dǎo)致的深層處理的效果。通過(guò)增加壓力,氧化鐵表面還原深度也會(huì)增加,達(dá)到近表面的層次,實(shí)驗(yàn)證實(shí)近表面層次的還原處理能夠有效增加光解水效果,同時(shí)也是偏壓降低的重要原因。氧化鐵還原程度太大的時(shí)候,會(huì)產(chǎn)生光催化活性低的Fe3O4,從而影響氧化鐵的催化性,因此在表面處理中增加過(guò)大的濃度會(huì)降低效率,但壓力增加的情況下繼續(xù)向近表面層處理則可以提高效率。我們的實(shí)驗(yàn)還比較了利用缺氧氣氛來(lái)產(chǎn)生氧空穴的方法,這種方法實(shí)現(xiàn)了體相摻氧空穴(近似體相還原),但效果比表面處理更差。因此合適的還原處理的深度(或氧空穴的分布深度)既不是在表面層,也不是在體相,而是近表面層比較合適。只有產(chǎn)生合適深度的氧空穴,才能有最佳催化活性。該結(jié)果可能對(duì)其他偏壓降低的過(guò)程有一定的借鑒意義,同時(shí)提出了氧化鐵修飾過(guò)程中深度處理的重要性。在本論文的第四章我們還進(jìn)行了用不同方法將鎳元素?fù)诫s進(jìn)氧化鐵的研究。我們使用sputtering技術(shù)在樣品表面電鍍鎳元素,之后退火處理。然而結(jié)果表明,這種處理方法并不是有效的,甚至阻礙了其本身的光催化性�？赡苁请婂冞^(guò)程破壞了氧化鐵自身的納米結(jié)構(gòu)。我們將在未來(lái)的工作中深入研究其具體原因。
[Abstract]:The preparation of hydrogen by photocatalytic decomposition of water is a challenging and significant subject to convert solar energy into hydrogen energy. In a large number of semiconductor materials, we choose to study iron oxide system, mainly the iron oxide has a lot of unique advantages, such as easy to obtain, solution neutrality stability, and the suitable band width. The efficiency of the photolysis water is very high, but the current efficiency is low, the main reason is that the photoelectron electron hole compound speed is fast, it is not good for the charge migration of the photocurrent, short hole transmission distance, less than 2 nm, and the conductivity of difference. In addition, an important factor limiting the efficiency of iron oxide is its energy band. The position is not suitable, a partial pressure is required to reduce the hydrogen to make the whole reaction proceed. Other factors in the catalytic process of ferric oxide photolysis will also lead to the generation of bias, reducing the efficiency. Reducing the bias in the photolysis of iron oxide is an important research direction in the related field. In this paper, we develop A variety of methods to improve the performance of ferric oxide photolysis water, mainly by controlling the depth of the iron oxide surface reduction to reduce the bias voltage, has achieved good results. The following is the specific content of this paper: we first improved the hydrothermal synthesis method of iron oxide, control its morphology and repeatability (second chapters). Good performance. The blank iron oxide samples without doping or other modification are the prerequisite for further treatment. It is a basic but very important work. The hydrothermal method has a unique advantage in the preparation of blank iron oxide samples. In the course of the experiment, we found that the current method needs more stringent conditions, and the temperature, pressure and concentration often do not get good reproducible high performance blank iron oxide samples. We have studied the effects of the concentration of NaNO3 and FeCl3.6H2O on the reactant in the hydrothermal solution. The HCl, which must be added in the previous method, is removed and the concentration of two reactants is reduced. The granular iron oxide with suitable thickness and uniform distribution is synthesized without changing other conditions. It is worth mentioning that the blank samples obtained by this method have good performance and high repeatability. The preparation conditions of blank samples are improved. Then, based on the experimental study of the initial oxygen vacancy doping in the project group, we developed the reduction of hydrogen from the aqueous solution of the amborane water solution to the iron oxide reduction treatment. This method can also form the surface oxygen vacancy doping to improve the efficiency. Compared with the previous method, the solution is directly heated and reduced by the solution of the borane on the surface of the iron oxide. The method of operation is simple, the photoelectric current of iron oxide treated under the best condition is nearly two times higher than that of blank sample, and the improvement effect is obvious. It is more meaningful that in the heating process we found that the sample covered crucible after the reduction treatment was better, and the initial voltage (bias voltage) was obviously improved. It is not the effect of increasing concentration, but the effect of deep treatment caused by increasing the pressure of crucible during the heating process. By increasing the pressure, the reduction depth of the iron oxide surface will also increase to reach the near surface level. It is proved that the reduction treatment in the near surface layer can increase the effect of photodissociation water, and also the bias is reduced. Important reasons. When the iron oxide reduction is too large, the Fe3O4 of low photocatalytic activity will be produced, which will affect the catalytic activity of iron oxide, so increasing the concentration in the surface treatment will reduce the efficiency, but the high efficiency can be carried out to the near surface treatment under the condition of increasing pressure. Our experiment also compares the use of oxygen deficiency. The method of producing oxygen vacancies, this method realizes the oxygen vacancy of the body phase (the reduction of the approximate body phase), but the effect is worse than the surface treatment. Therefore, the appropriate depth of the reduction treatment (or the depth of the distribution of oxygen vacancies) is neither in the surface layer nor in the body phase, but in the near surface layer. Only the oxygen vacancies at the right depth are produced, only It may have the best catalytic activity. This result may be of reference to the process of other partial pressure reduction and the importance of depth treatment in the process of modification of iron oxide. In the fourth chapter of this paper, we also carried out the research on the doping of nickel in the iron oxide by different methods. We use the sputtering technology on the sample surface. Electroplating nickel and then annealing treatment. However, the results show that this treatment is not effective or even hinders its photocatalytic activity. It may be that the electroplating process destroys the nanostructure of iron oxide itself. We will study the specific reasons in future work.

【學(xué)位授予單位】：蘇州大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TQ116.2;O643.36

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