發(fā)布時(shí)間：2018-03-31 02:19

  本文選題：超臨界CO_2　切入點(diǎn)：TiO_2/WO_3·H_2O　出處：《鄭州大學(xué)》2017年碩士論文

【摘要】：氧化鎢材料作為一種典型的n型半導(dǎo)體,可廣泛應(yīng)用于光催化、電催化及電致變色智能窗等方面,已成為環(huán)境與能源領(lǐng)域的研究熱點(diǎn)之一。氧化鎢材料價(jià)格低廉,來(lái)源豐富,具有良好的化學(xué)穩(wěn)定性和耐光腐蝕性,是一種可用于大規(guī)模生產(chǎn)的能源材料。氧化鎢材料種類(lèi)繁多,既有化學(xué)計(jì)量的WO_3,又有含有氧缺陷的亞化學(xué)計(jì)量WO_(3-x),另外還有含結(jié)晶水的水合氧化鎢(WO_3·nH_2O)。在實(shí)際應(yīng)用中,形貌、維度和結(jié)構(gòu)等因素都會(huì)極大地影響到氧化鎢材料的性能。與塊體材料相比,低維度納米材料具有更大的比表面積和載流子傳輸性能;而結(jié)構(gòu)的不同,同樣能反映出性能的差異,與WO_3相比,亞化學(xué)計(jì)量的WO_(3-x)結(jié)構(gòu)中氧空位充當(dāng)淺層供體,可以提高導(dǎo)電性和供體密度,從而增強(qiáng)表面物種(例如CO_2,H_2,NO_2等)的吸附。此外,單純的氧化鎢材料在應(yīng)用于光催化劑時(shí),受光催化機(jī)理的限制,會(huì)發(fā)生光生電子和空穴的復(fù)合,影響光催化的效率。而通過(guò)與其他半導(dǎo)體(如TiO_2)構(gòu)筑半導(dǎo)體/半導(dǎo)體復(fù)合異質(zhì)結(jié)構(gòu)則能很好的促進(jìn)光生電子和空穴的有效分離,避免光生電子-空穴對(duì)的復(fù)合�；谝陨线@些因素,本文主要進(jìn)行了以下研究:(1)我們利用超臨界CO_2輔助剝離得到具有少層結(jié)構(gòu)的WO_3·H_2O納米片。與塊體材料相比,維度調(diào)控得到的該超薄納米片具有大的比表面積,可以暴露出更多的活性位點(diǎn)。之后我們運(yùn)用一種簡(jiǎn)單且新穎的方法,即在超臨界CO_2環(huán)境中將該超薄納米片與本組之前工作制得的TiO_2納米片復(fù)合構(gòu)筑得到類(lèi)范德華異質(zhì)結(jié)-TiO_2/WO_3·H_2O異質(zhì)結(jié)。兩者的納米片層結(jié)構(gòu)使得其發(fā)生充分堆疊。在用作光催化劑時(shí),相較于單純Ti O_2和WO_3·H_2O納米片,該異質(zhì)結(jié)表現(xiàn)良好的光電流響應(yīng)和對(duì)甲基橙高效的降解效率。經(jīng)分析發(fā)現(xiàn),在光照下,TiO_2的光生電子會(huì)轉(zhuǎn)移到WO_3·H_2O中,而WO_3·H_2O的空穴則會(huì)轉(zhuǎn)移到TiO_2中,這樣便避免了光生電子-空穴對(duì)的復(fù)合,促進(jìn)了兩者的分離,進(jìn)而提高了光催化活性。(2)出于安全考慮,我們用NaBH4代替常用的H_2對(duì)商用WO_3在高溫下進(jìn)行氫化反應(yīng),通過(guò)這一簡(jiǎn)單的方法制備得到含有氧缺陷的亞化學(xué)計(jì)量WO_(3-x)。結(jié)果表明,在對(duì)WO_3進(jìn)行高溫氫化后,邊緣形成無(wú)序區(qū)域,說(shuō)明了氧空位的生成,并且隨著氫化溫度的提高(400℃),邊緣無(wú)序區(qū)域擴(kuò)大,表明氧空位含量增大。根據(jù)紫外-可見(jiàn)光-近紅外測(cè)試發(fā)現(xiàn),氫化之后,WO_(3-x)在近紅外區(qū)域1050 nm處出現(xiàn)一個(gè)明顯的特征峰,表現(xiàn)出明顯的表面等離子共振效應(yīng)。之后對(duì)樣品進(jìn)行電催化析氫性能測(cè)試,結(jié)果表明400℃下氫化的WO_(3-x)樣品析氫效率明顯提高,Tafel斜率為66 mV dec-1,遠(yuǎn)低于本體WO_3(113 mV dec-1)。并且在與文獻(xiàn)報(bào)道的氧化鎢基材料的Tafel斜率比較發(fā)現(xiàn)該樣品仍具有很大的優(yōu)勢(shì)。
[Abstract]:Tungsten oxide, as a typical n-type semiconductor, can be widely used in photocatalysis, electrocatalysis and electrochromic smart windows, and has become one of the research hotspots in the field of environment and energy. With good chemical stability and photo-corrosion resistance, tungsten oxide is a kind of energy material which can be used in mass production. There are not only stoichiometric WO3s, but also sub-stoichiometric WOs with oxygen defects, as well as tungsten oxide hydrated with crystalline water, WO _ 3nH _ 2O. In practical applications, the morphology, Factors such as dimension and structure can greatly affect the properties of tungsten oxide. Compared with bulk materials, low-dimensional nanomaterials have greater specific surface area and carrier transport properties, while different structures can also reflect the differences in performance. Compared with WO_3, the oxygen vacancy in the substoichiometric WOSP 3-x structure acts as a shallow donor, which increases the conductivity and donor density, thus enhancing the adsorption of surface species (e.g., CO2T / H2S / NO2, etc.). In addition, simple tungsten oxide materials are used in photocatalysts. Due to the limitation of photocatalytic mechanism, the combination of photogenerated electrons and holes will occur. By constructing semiconductor / semiconductor composite heterostructures with other semiconductors (such as TiO-2), the effective separation of photogenerated electrons and holes can be promoted. To avoid photogenerated electron-hole pair compounding. Based on the above factors, the following studies have been carried out in this paper: 1) We use supercritical CO_2 assisted stripping to obtain WO_3 H2O nanocrystals with low layer structure. Compared with bulk materials, The dimensionally regulated nanocrystals have a large specific surface area to expose more active sites. Then we use a simple and novel approach. In the supercritical CO_2 environment, the ultrathin nanocrystals were combined with the previously worked TiO_2 nanostructures to obtain the van der Waals heterojunction-TiO-2 / WO / 3H _ 2O heterostructures. The nanostructures of the two nanostructures made them stack sufficiently. When used as photocatalysts, Compared with simple TiO-2 and WO_3 H2O nanochips, the heterojunction exhibits good photocurrent response and high degradation efficiency to methyl orange. It is found that the photogenerated electrons of tio _ 2 are transferred to WO_3 H _ 2O under light, while the holes of WO_3 H _ 2O are transferred to TiO_2. In this way, the combination of photogenerated electron-hole pairs is avoided, the separation of the two is promoted, and the photocatalytic activity is improved. (2) for safety reasons, we use NaBH4 to hydrogenate commercial WO_3 at high temperature instead of the commonly used H-2. By this simple method, sub-stoichiometric WOCs with oxygen defects were prepared. The results showed that after hydrogenation of WO_3 at high temperature, disordered regions formed at the edges, indicating the formation of oxygen vacancies. With the increase of hydrogenation temperature, the edge disordered region expands, which indicates that the oxygen vacancy content increases. According to the UV-Vis and NIR measurements, there is a characteristic peak at 1050 nm in the near infrared region after hydrogenation. It showed obvious surface plasmon resonance effect. Then the electrocatalytic hydrogen evolution performance of the sample was tested. The results showed that the hydrogen evolution efficiency of the hydrogenated WO _ 2 _ (3-x) sample was significantly increased by 66mV dec-1, which was far lower than that of the bulk WO_3(113 _ (MV) _ (dec-1). Compared with the reported Tafel slope of the tungsten oxide based material in the literature, it was found that the sample still had a great advantage.
【學(xué)位授予單位】：鄭州大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TQ136.13

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