利用密度泛函理論計算探討元素摻雜對g-C3N4光催化效率的提升;Enhancing Photocatalytic Performance of Graphitic Carbon Nitride g-C3N4 through Element Doping: Using Density Functional Theory

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Title:	利用密度泛函理論計算探討元素摻雜對g-C3N4光催化效率的提升;Enhancing Photocatalytic Performance of Graphitic Carbon Nitride g-C3N4 through Element Doping: Using Density Functional Theory
Authors:	許萬淵;Hsu, Wan-yuan
Contributors:	化學工程與材料工程學系
Keywords:	密度泛函理論;石墨氮化碳;元素參雜;光催化劑;可見光吸收;DFT;GW-BSE;element doped;g-C3N4;photocatalytic;visible light absorption
Date:	2024-08-22
Issue Date:	2024-10-09 15:30:41 (UTC+8)
Publisher:	國立中央大學
Abstract:	石墨氮化碳（g-C3N4）因其適中的帶隙（約2.7 eV）以及卓越的化學和熱穩定性，已成為環境光催化領域中的重要候選材料。然而，由於可見光吸收有限、比表面積不足、電子導電性差及光生電子-空穴對的高復合率，其應用效果仍不理想。為了克服這些缺點並提升光催化效率，對g-C3N4 進行改性變得十分必要。在眾多改性策略中，元素摻雜是一種有效且簡單的方法，可以調整其電子結構並促進光催化性能。本研究利用密度泛函理論（DFT）計算研究非金屬摻雜（B、P）、金屬摻雜（Na、K）及共摻雜（Na+B、Na+P、K+B、K+P）對g-C3N4 光學性質的影響。此外，採用了多種分析方法，包括GW-BSE 方法、態密度（DOS）分析、能帶結構分析、Bader 電荷分析、有效質量分析，以及最高佔據分子軌道（HOMO）和最低未佔據分子軌道（LUMO）分析，去探討這些參雜元素對於g-C3N4 的光學性質和電子特性的影響。由可見光吸收光譜發現，所有摻雜方法均不同程度地擴展了可見光吸收範圍，並增強了可見光吸收強度。能帶結構分析表明，摻雜元素的引入使帶隙有所縮小，其中Na+B 共摻雜使帶隙顯著下降，從2.7 eV 減少到0.15 eV，顯著增強了對可見光的吸收。此外，HOMO 和LUMO 的分析顯示，元素摻雜可以增加軌道雜化和離域化。有效質量分析結果表明，摻雜可以有效降低純g-C3N4 中較高的空穴有效質量。這些結果表明，摻雜能提高載流子的遷移率並減少光生電子-空穴對的複合率。本研究證實了各種摻雜策略在提高g-C3N4 光催化性能方面的有效性，並提供了摻雜引起的電子結構變化的深入見解。;Graphitic carbon nitride, recognized for its intermediate band gap of approximately 2.7 eV and exceptional chemical and thermal stability, has emerged as a prominent candidate in environmental photocatalysis. Nonetheless, its effectiveness remains suboptimal due to limited absorption of visible light, inadequate surface area, poor electronic conductivity, and high recombination rates of photogenerated electron-hole pairs. To address these shortcomings and enhance photocatalytic efficiency, modifying g-C3N4 is imperative. Among the various strategies for modification, element doping stands out as an efficient and straightforward method for adjustment the electronic structure and promoting photocatalytic performance. This study utilizes density functional theory (DFT) calculations to investigate how non-metal doping (B, P), metal doping (Na, K), and co-doping (Na+B, Na+P, K+B, K+P) affect the optical properties of g-C3N4. Various analysis methods were employed, including the GW plus Bethe-Salpeter equation (GW-BSE) method, density of states (DOS) analysis, bandstructure analysis, Bader charge, effective mass, as well as analysis of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Their visible light absorption spectra were obtained, revealing varying degrees of broadened visible light absorption ranges and increased visible light absorption intensities across all doping methods. The band structure indicates a reduction in band gap depending on the doping element introduced. A significant decrease was observed in the case of Na+B co-doping, at which the band gap decreased from 2.7 to 0.15 eV. This substantial reduction contributes to a notable enhancement in the visible light absorption spectrum compared to g-C3N4. Additionally, the analysis of HOMO and LUMO indicates that element doping can increase orbital hybridization and delocalization. Effective mass analysis also shows that doping can effectively reduce the high hole effective mass of pristine g-C3N4. These results suggest that elements doped is beneficial for improving carrier mobility and reducing the recombination rate. This study demonstrates the efficacy of various doping strategies, in enhancing the photocatalytic performance of g-C3N4 and provides insights into the electronic structure modifications induced by doping.
Appears in Collections:	[National Central University Department of Chemical & Materials Engineering] Electronic Thesis & Dissertation

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