本文選題：第一性原理 + 密度泛函理論�。� 參考：《南京師范大學》2017年碩士論文

【摘要】：近年來,氫氣作為可再生能源引起了極大的關注。由于它具有豐富的含量、較高的能量密度、以及高清潔度等特點,有望成為未來的重要能量來源之一。同時,它也具有重要的工業(yè)應用價值,尤其在石化、冶金、食品加工、精密電子工業(yè)合成等領域已經得到了廣泛應用。然而,在實際應用中,氫氣的高效分離、氫氣的存儲等問題還面臨著巨大的挑戰(zhàn)。最近,石墨烯納米片C_(222)被成功合成,該納米片一經合成便引起科學家們強烈的興趣。已有的研究發(fā)現石墨片上的孔狀缺陷對其光學和電學性質都有很大影響。因此本文通過第一性原理研究了三種不同形狀的缺陷對C_(222)石墨烯納米片的電、光學性質的影響。研究結果表明中心挖去一個苯環(huán)的C_(216)相比C_(222)能隙增加了0.39 eV,使其半導體特性明顯。相反(C221和(C220分別是由(C_(222)中心挖去一個和兩個碳原子形成的單空位缺陷和雙空位缺陷結構,這兩個缺陷的存在降低了 C_(222)的能隙,使其導體特性明顯。同時能隙大小的改變也使得UV-vis吸收光譜中的最大吸收峰發(fā)生了藍移(C_(216))或紅移(C221, C220)。另外,計算結果顯示隨著缺陷密度的增加,HOMO-LUMO能隙也增加,最高至4.28 eV。吸收光譜也從400-800 nm波段移至300-500 nm波段。由于石墨烯納米片C_(216)是孔狀材料,符合分離膜材料的幾何特征,因此我們計算了它對于常見氣體(H2, O2, N2, NO, NO2,H2O, CO和C02)的選擇性和過渡能壘,研究發(fā)現它對于氫氣的擴散能壘明顯低于其它氣體,在室溫下該石墨片對氫氣相對于其他氣體的選擇率高達1048,明顯優(yōu)于多孔石墨烯、石墨炔以及傳統(tǒng)氫氣分離膜,有望成為一種理想的氫氣分離膜材料。同時,本文設計了一種Li摻雜的多孔石墨片C180,并研究了該材料作為作為儲氫材料的可能。計算結果表明Li原子在該石墨片表面不容易形成團簇。而且氫氣在Li摻雜的多孔石墨片上的平均吸附能為-0.17 eV,其絕對值明顯高于純多孔石墨片或Li摻雜的石墨烯。該吸附能的大小說明Li摻雜的多孔石墨片能夠實現在溫和條件下對氫氣的自由吸附和解離。當增加Li原子的吸附濃度時,該多孔石墨片的質量儲氫密度高達4.76 wt%,明顯優(yōu)于Li原子摻雜的石墨烯和碳納米管等材料。因此多孔石墨片C180有望成為高效的儲氫材料。
[Abstract]:In recent years, hydrogen as a renewable energy has attracted great attention. Because of its rich content, high energy density and high cleanliness, it is expected to be one of the important energy sources in the future. At the same time, it also has important industrial application value, especially in petrochemical, metallurgy, food processing, precision electronic industrial synthesis and other fields have been widely used. However, in practical application, the high efficiency separation of hydrogen and the storage of hydrogen are still facing great challenges. Recently, graphene nanochip C _ s _ 2 _ 2) was successfully synthesized, and once synthesized, it has aroused great interest from scientists. It has been found that the porous defects on the graphite sheet have great influence on the optical and electrical properties. Therefore, the effects of three different defects on the electrical and optical properties of C _ S _ (222) graphene nanocrystals have been investigated by first-principles. The results show that the gap of C _ S _ (216) with a benzene ring is increased by 0.39 EV compared with that of C _ S _ (222), which makes the semiconductor characteristic obvious. On the contrary, C221 and C220 are the structures of single vacancy defect and double vacancy defect formed by one and two carbon atoms, respectively. The existence of these two defects reduces the energy gap of CStue 222) and makes its conductor characteristic obvious. At the same time, the change of energy gap also makes the maximum absorption peak in UV-vis absorption spectrum blue shift C216C) or red shift C221, C220. In addition, the calculated results show that the HOMO-LUMO gap also increases with the increase of defect density, reaching to 4.28 EV. The absorption spectra were also shifted from 400-800 nm to 300-500 nm. Because the graphene nanochip Che 216) is a porous material which conforms to the geometric characteristics of the membrane material, we have calculated its selectivity and transition energy barrier for the common gases (H _ 2, O _ 2, N _ 2, no _ 2, O _ 2H _ 2O, CO and C _ 02). It is found that the diffusion barrier for hydrogen is obviously lower than that for other gases, and the selectivity of the graphite sheet to hydrogen relative to other gases is as high as 1048 at room temperature, which is obviously superior to that of porous graphene, graphite acetylene and traditional hydrogen separation membranes. It is expected to be an ideal membrane material for hydrogen separation. At the same time, a Li-doped porous graphite sheet C180 has been designed, and the possibility of using this material as hydrogen storage material has been studied. The results show that the Li atoms are not easy to form clusters on the surface of the graphite sheet. The average adsorption energy of hydrogen on Li-doped porous graphite is -0.17 EV, which is obviously higher than that of pure porous graphite or Li doped graphene. The adsorption energy shows that Li doped porous graphite can achieve the free adsorption and dissociation of hydrogen under mild conditions. When the adsorption concentration of Li atom is increased, the mass hydrogen storage density of the porous graphite wafer is up to 4.76 wt, which is obviously superior to that of graphene doped with Li atom and carbon nanotubes and so on. Therefore, porous graphite sheet C 180 is expected to be an efficient hydrogen storage material.
【學位授予單位】：南京師范大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ127.11;TB383.4

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