利用密度泛函理論探討環氧基和羥基對氧化石墨烯光學性質的影響

The Influence of Epoxy and Hydroxyl Groups to Optical Properties of Graphene Oxides by Density Functional Theory

李郁柔(Yu-Jou Lee)

指導教授 ： 林子仁

中原大學/工學院/化學工程研究所/碩士(2020年)

https://doi.org/10.6840/cycu202000175

摘要

石墨烯和氧化石墨烯在各種光學應用中都是特別有淺力的新興材料，但對含氧官能基對氧化石墨烯光學性質的影響，目前的理解還不足夠，所以本模擬計算是利用時變密度泛函（TD-DFT）研究環氧基和羥基在石墨烯基面上對UV以及螢光光譜的影響。相較於石墨烯，含氧官能基會使氧化石墨烯的吸收波長產生紅移現象，而且含氧官能基也會使氧化石墨烯的HOMO-LUMO Gap變小。從HOMO-LUMO和NBO（national bond orbital）分析中，環氧基會在氧化石墨烯表面形成trap state，而羥基會在表面上形成trap state或分割HOMO與LUMO。含氧官能基也會使氧化石墨烯UV吸收強度下降，這是因為HOMO與LUMO的重疊區域較小所造成。而在放射光譜中，氧化石墨烯的螢光波長相較於石墨烯都有嚴重的紅位移，但其中我們發現只有環氧基才能產生不可忽略的螢光放射強度。從上述統整揭示環氧基或是羥基接在石墨烯基面上時，會破壞石墨烯表面碳原子的sp2混成軌域而形成trap state、HOMO-LUMO Gap縮小使吸收光譜和放射光譜產生紅移、改變HOMO與LUMO電子的分佈使transition dipole moment降低，且讓吸收和放射光譜的強度下降。

關鍵字

氧化石墨 ； 時變密度泛函 ； UV ； 螢光

並列摘要

Graphene and graphene oxide (GO) attract much attention because they exhibit innovative optical properties. GO exhibits good water dispersibility, biocompatibility, and high affinity for specific biomolecules, but how oxygen-containing functional groups influence its optical properties is still unclear.
Therefore, we used the time-dependent density functional theory (TD-DFT) to study how epoxy and hydroxyl groups influence the absorption and fluorescence of GO. Compared with graphene, the epoxy and hydroxyl groups cause the absorption wavelength of GO redshift and also decrease HOMO-LUMO Gap. From HOMO-LUMO and NBO, national bond orbital analysis, the epoxy groups form trap state on the GO surface, while the hydroxyl group forms trap state or split the orbital of HOMO and LUMO on the surface. Because of the small overlaps between HOMO and LUMO, the epoxy and hydroxyl groups reduce the absorption intensity of GO. GO also shows vivid redshifts of fluorescence wavelength compared to graphene. In particular, we found that only the epoxy group can cause the non-negligible oscillator strength of fluorescence. Based on the simulation, the epoxy and hydroxyl groups destroy sp2 hybrid orbital of carbon atoms to form trap state on GO surface, decrease the HOMO-LUMO Gap leading to the redshift of absorption and fluorescence spectra and changed the distribution of HOMO and LUMO resulting in the reduced transition dipole moment and intensity of absorption and fluorescence spectra.

並列關鍵字

Graphene oxide ； Time-dependent functional theory ； UV ； Fluorescence

參考文獻

參考文獻

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