本文選題：光催化　切入點：制氫　出處：《西安交通大學(xué)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：面對化石能源的日益枯竭及由此帶來的能源和環(huán)境危機,尋找新型可再生、無污染的替代能源已經(jīng)刻不容緩。利用太陽能光催化分解水制氫,將太陽能轉(zhuǎn)換為可存儲、高能量密度且清潔無污染的氫能,是解決這些危機的有效途徑之一。然而制約這一技術(shù)產(chǎn)業(yè)化的瓶頸在于高效可見光光催化劑的開發(fā)。隨著對半導(dǎo)體光催化過程的研究,人們發(fā)現(xiàn),光生電荷的分離及其在晶體表面發(fā)生有效氧化還原反應(yīng)是提高太陽能氫能轉(zhuǎn)化效率并最終工業(yè)化的關(guān)鍵。本文首先從提高光生電子和空穴分離出發(fā),以具有暴露{101}和{001}晶面的Cu_2WS_4單晶十面體和孿晶Cd_(1-x)Zn_x S固溶體納米球和一維納米棒為模型光催化劑,提出通過有序“結(jié)”結(jié)構(gòu)設(shè)計,實現(xiàn)光催化產(chǎn)氫反應(yīng)中的物理過程強化,并構(gòu)建了這些有序“結(jié)”與產(chǎn)氫性能的定性和定量的關(guān)系。其次,從強化界面化學(xué)反應(yīng)和揭示金屬助催化劑促進光催化反應(yīng)的作用機制的角度著手,通過對金屬助催化劑生長動力學(xué)的表面擴散和刻蝕再機理的系統(tǒng)研究,完成了不同形貌金屬助催化劑生長過程的動力學(xué)定量理論體系的構(gòu)建,為后面深入研究其作用機理打下基礎(chǔ)。概括起來,主要分為以下內(nèi)容和結(jié)論。首先,采用一步水熱方法,以Cu Cl、Na_2WO_4為前驅(qū)體,硫代乙酰胺為硫源成功合成具有{001}和{101}兩種晶面且比例可控的十面體形貌Cu_2WS_4單晶半導(dǎo)體。通過原位光還原貴金屬和創(chuàng)新的氧化刻蝕實驗發(fā)現(xiàn)這兩種晶面能有效分離光生電子和空穴,這種類似于半導(dǎo)體中“結(jié)”的結(jié)構(gòu),可被稱之為“類同質(zhì)結(jié)”。該催化劑在負載1.5 wt%Ru金屬助催化劑后,效率可以提高30倍左右,425 nm處表觀量子效率也達到11%,為國際同期報道光催化劑的較高水平�；趯υ擉w系下的光致氧化和還原反應(yīng)的動力學(xué)的定性認識(還原反應(yīng)為光反應(yīng)中的限速步驟),通過對和{101}晶面比例的控制,實現(xiàn)了對氧化還原反應(yīng)活性位面積的有效調(diào)控,并在高{001}/{001}晶面比例的Cu_2WS_4十面體上獲得了更高的產(chǎn)氫活性。這種借助有單晶晶面設(shè)計所形成的類同質(zhì)結(jié),分布有序、結(jié)構(gòu)可調(diào),可以方便地用于光催化反應(yīng)動力學(xué)的定量研究,也為獲得更高活性的光催化劑提供了新的思路。晶面類同質(zhì)結(jié)雖然有序,但其受晶面?zhèn)�數(shù)的限制而數(shù)量有限,急需找到一種既能保持有序性、還能高密度獲得的結(jié)構(gòu)�；诰婷娼Y(jié)構(gòu)差異而產(chǎn)生“結(jié)”效果的思想,很容易讓人聯(lián)想到晶體中的缺陷。缺陷處也會發(fā)晶體結(jié)構(gòu)畸變,可聯(lián)想到面心立方晶體中的平行共格孿晶面。以Cd_(1-x)Zn_x S固溶體為模型,利用水熱方法合成了包含大量貫穿整個晶體的平行共格孿晶面的閃鋅礦(Zinc blende,ZB)結(jié)構(gòu)球形Cd_(1-x)Zn_x S半導(dǎo)體。在結(jié)構(gòu)上,每一個這種共格孿晶面實際上在ZB Cd_(1-x)Zn_x S晶體中引入了一個具有3層雙原子層的纖鋅礦(Wurtzite,WZ)結(jié)構(gòu)片段。通過計算發(fā)現(xiàn),Cd_(1-x)Zn_x S晶體中ZB/WZ界面可以形成II型交錯式能帶排列結(jié)構(gòu),并能迅速發(fā)生光生電荷分離,因此也是“結(jié)”的作用方式,可稱之為“孿晶同質(zhì)結(jié)”。在電勢差的作用下,電子能夠定向移動到兩個孿晶面中間的ZB區(qū)域發(fā)生還原反應(yīng),空穴被吸收到孿晶面上發(fā)生氧化反應(yīng)。對比相同成分非孿晶固溶體,發(fā)現(xiàn)孿晶Cd_(1-x)Zn_x S固溶體納米球具有更高的產(chǎn)氫活性,其最高產(chǎn)氫活性出現(xiàn)在x=0.5處,即Cd_(0.5)Zn_(0.5)S,為1.79 mmol h~(-1),425 nm處量子效率為43%,是國際同期報道的無負載光催化劑中最高值。進一步研究發(fā)現(xiàn),這些結(jié)平行、有序地分布于晶體中,因此,如果能在孿晶面垂直方向獲得一維結(jié)構(gòu),應(yīng)該能夠更好地發(fā)揮平行孿晶同質(zhì)結(jié)的協(xié)同效應(yīng)。利用動力學(xué)控制,制備了具有長徑比約為1.9和4.0的納米孿晶棒,而基于這些光催化劑的光催化分解水產(chǎn)氫結(jié)果也證明了上述想法。具有最高長徑比的Cd_(1-x)Zn_x S納米棒,其可見光產(chǎn)氫速率達到了2.58 mmol h~(-1),其425 nm處的量子效率為62%,為目前國際報道無負載光催化劑的最高效率。研究結(jié)果直接證明了以高密度、有次序的平行共晶格孿晶面為結(jié)構(gòu)基礎(chǔ)的一維同質(zhì)結(jié)對光催化的效率的提高作用。通過單晶晶面和孿晶構(gòu)建的(類)同質(zhì)結(jié),如同異質(zhì)結(jié)光催化劑一樣可以廣泛應(yīng)用于其他半導(dǎo)體光催化劑的設(shè)計,開創(chuàng)了強化電荷分離物理過程的新方法。光催化是界面上的光化學(xué)反應(yīng),需要基于化學(xué)反應(yīng)的協(xié)同強化才能進一步提高光催化效率。金屬助催化劑在產(chǎn)氫過程中起著至關(guān)重要的作用,而其在光催化中的作用機制與其微觀結(jié)構(gòu)息息相關(guān)�；诖�,本文最后以金屬Pd為模型,使用種子生長的方法,對金屬生長過程中表面擴散、刻蝕再生長過程進行了系統(tǒng)的定量研究,實現(xiàn)了對單金屬、雙金屬(包括合金)納米立方體、納米八面體和各類高指數(shù)面納米晶體等的定量動力學(xué)控制。在含有助催化劑參與的光催化界面化學(xué)反應(yīng)過程中,助催化劑分布狀態(tài)(如大小、形貌等)的定量控制是實現(xiàn)助催化劑作用機理認識及效用最大化的有效途徑。
[Abstract]:With the increasing depletion of fossil fuels and the resulting energy and environmental crisis, looking for new renewable, non polluting alternative energy sources is urgent. The photocatalytic decomposition of water to hydrogen using solar energy and convert solar energy into storage, high energy density and clean energy, is one of the effective ways to solve the crisis. However, the bottleneck the technology industry is to develop efficient visible light catalyst. With the research of semiconductor photocatalytic process it was found that the separation of photogenerated charge and effective redox reaction is to improve the conversion efficiency of solar hydrogen and ultimately the key to industrialization on the crystal surface. This paper improve the separation of the photogenerated electrons and holes starting with the exposure of {101} and {001} surface of single crystal Cu_2WS_4 ten surface and twin Cd_ (1-x) Zn_x S solid solution nanoparticles and a rod for Wiener meters Model of photocatalyst, put forward through the orderly "knot" structure design, physical implementation process of photocatalytic hydrogen production in strengthening, and the construction of the relationship between these ordered "knot" and hydrogen production performance of qualitative and quantitative. Secondly, starting from the mechanism of enhancement of interfacial chemical reaction and reveal the metal catalytic agent to promote the photocatalytic reaction the angle of the system, through the research of surface diffusion on metal catalyst growth kinetics and etching mechanism, completes the construction of quantitative kinetic theory system with different morphologies of metal catalyst of the growth process, for the following deep to lay the foundation for the study of its mechanism. To sum up, mainly divided into the following contents and conclusions. First of all, a one-step hydrothermal method with Cu, Cl, Na_2WO_4 as precursor and thioacetamide were successfully synthesized with {001} and {101} two kinds of crystal surface and the proportion of the ten controllable shape surface Cu_2WS_4 The single crystal semiconductor etching. Oxidation reduction of noble metal and innovation by in situ light found that two kinds of crystal surface can effectively separate the photogenerated electrons and holes, the similar structure on the semiconductor in the "knot", can be called the "homojunctions." the catalyst at a load of 1.5 wt%Ru metal catalyst, efficiency can be improved by about 30 times, 425 nm apparent quantum efficiency reached 11%, as reported in the same period of photocatalyst international high level. Qualitative understanding of the oxidation and reduction reaction induced by dynamics in the system of light (based on the reduction reaction is light reaction in the limit of Su Buzhou), by controlling the crystal surface and {101} ratio the realization of the effective regulation of the redox reaction activity area, and in the high {001}/{001} surface ratio of Cu_2WS_4 ten surface was obtained on hydrogen production with higher activity. This is formed by single crystal homogeneous design Node distribution, orderly, adjustable structure, can be used for the quantitative study of photocatalytic reaction kinetics, to light the more active catalysts provide a new way of thinking. Crystal class homojunctions although orderly, but affected by the limited number of planes and a limited number of urgent need to find a can keep order, can obtain high density structure. Have a "knot" effect of crystal plane structure based on the difference of the thought, it is reminiscent of the defects in the crystal. The defects will be made of crystal structure distortion, Lenovo to F.C.C parallel coherent twin plane (1-x to Cd_. Zn_x) S solid solution as a model, a large number of runs through the whole crystal parallel coherent twin surface of sphalerite was synthesized by hydrothermal method including (Zinc blende, ZB) Cd_ (1-x) Zn_x spherical structure. The structure of S semiconductor, ZB Cd_ in each of the coherent twin surface reality (1-x) Zn_ The introduction of X S crystal in a double atomic layer has 3 layers of wurtzite structure (Wurtzite, WZ) fragment. It was found that the Cd_ (1-x) ZB/WZ interface Zn_x S crystal can be formed in a staggered type II band alignment structure, and can quickly place photoinduced charge separation, mode of action and is therefore "knot", which can be called "twin homojunctions." in the potential function, the electron can move to two ZB regional directional twin plane in the middle of the reduction reaction, the hole is absorbed into the oxidation reaction on the twin plane with the same components. Untwinned solid solution, the results show that the twins Cd_ (1-x) Zn_x S solid nanospheres with hydrogen producing high activity, the highest hydrogen production activity appeared at x=0.5, Cd_ (0.5) Zn_ (0.5) S, 1.79 mmol h~ (-1), 425 nm quantum efficiency is 43%, no photocatalyst maximum in international reporting period further study found that these Parallel, orderly distribution in the crystal, therefore, if we can get one-dimensional structure in the twin plane vertical direction, should be able to play a better parallel twin homojunctions synergy. Controlled by kinetics, were prepared with the length diameter ratio is 1.9 and 4 nano twin rods, and the photocatalytic decomposition of these catalysts hydrogen results also proved that the idea has the highest aspect ratio. Based on Cd_ (1-x) Zn_x S nanorods, the visible light hydrogen production rate of 2.58 mmol h~ (-1), the quantum efficiency at 425 nm was 62%, the highest efficiency of current international reported photocatalysts. The results directly proved to high density, increase efficiency and order of the co twin plane parallel lattice structure based on one-dimensional homogeneous photocatalysis. Constructed by single crystal and twin (class) homojunction, heterojunction photocatalysts can be the same as Widely applied to other semiconductor photocatalyst design, created a new method to enhance the charge separation process. Physical photocatalysis is a photochemical reaction on the interface, need chemical reaction and enhanced in order to further improve the photocatalytic efficiency. Based on the metal catalyst plays a crucial role in the hydrogen production process, and its photocatalytic the mechanism is closely related to its microstructure. Based on this, this paper finally using metal Pd as a model, using the method of seed growth, the metal surface diffusion growth process, etching regrowth process was studied systematically, the realization of single metal, double metal (including alloy) nanocubes, quantitative dynamics control nano eight surface and all kinds of high index surface nano crystal etc.. The photocatalytic interfacial chemical reaction with the catalyst involved in the process of the catalyst distribution (such as large The quantitative control of small, morphologies, etc. is an effective way to realize the mechanism understanding and utility maximization of cocatalyst.

【學(xué)位授予單位】：西安交通大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：O643.36;TQ116.2

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相關(guān)期刊論文 前1條

1 周磊;張勇;李建華;李英;;納米材料合成方法淺析[J];中國粉體工業(yè);2011年03期

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本文編號：1610628