摻入過渡金屬氧化物以提升 g-C3N4 的光學特性;Controlling the Optical Properties of Graphitic Carbon Nitride via the Integration of Transition Metal Oxides

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Title:	摻入過渡金屬氧化物以提升 g-C3N4 的光學特性;Controlling the Optical Properties of Graphitic Carbon Nitride via the Integration of Transition Metal Oxides
Authors:	陳玟伶;Chen, Wen-Ling
Contributors:	化學工程與材料工程學系
Keywords:	石墨相氮化碳;光觸媒;密度泛函理論;g-C3N4;Photocatalysis;Density Functional Theory (DFT)
Date:	2025-07-22
Issue Date:	2025-10-17 11:25:38 (UTC+8)
Publisher:	國立中央大學
Abstract:	石墨相氮化碳（g-C3N4）因具有 2.7 eV 的間接能隙以及在二氧化碳還原與水分解等應用上的潛力，而在光催化領域中引起了廣泛的關注。然而，其光催化效率仍舊受到限制，其主要原因是無法在可見光的範圍中有所吸收，以及光生電子和電洞對間有著過快的複合速率，這會進而縮短載子的壽命。為了解決這些問題，已被提出多種改質策略，像是元素摻雜、缺陷工程，以及異質接面結構的設計。其中，金屬摻雜，特別是以 Pd、Pt 和 Au 等貴金屬作為助催化劑，被認為是最有效的手段之一。然而，這些貴金屬的高成本限制了其在大規模實際應用上的可行性。因此，使用過渡金屬作為替代已成為一種具潛力且經濟的替代方法。本研究中，過渡金屬（Mo、Ru、W）氧化物團簇被引入 g-C3N4 中並與最外圍的氮原子連接，以提升其光學性質，並同時考慮了AA與AB兩種堆疊的結構。態密度（DOS）、能帶結構、有效質量與 Bader 電荷等電子性質的計算都是透過VASP軟體執行並且基於第一性原理密度泛函理論（DFT）。此外，GW 近似和 Bethe-Salpeter 方程（GW-BSE）的結合是用在計算介電常數與吸收光譜等光學特性。經過過渡金屬的引入後，g-C3N4的能隙顯著縮小。值得注意的是，在 AA堆疊中的 Ru 以及 AB堆疊中的 Mo 均使 g-C3N4 發生了由半導體轉變為金屬性的變化，而其餘配置則仍保有間接能隙的半導體特性。此外，在 AA堆疊中引入 W 氧化物，以及在 AB堆疊中引入 Ru 氧化物，皆能最有效的擴展可見光吸收範圍並增強吸收強度。其中，W 氧化物於 AA堆疊中的修飾更導致電子與電洞間出現最高的有效質量比，顯示其能有效降低複合率，進而提升光生載子參與表面氧化還原反應的可用性，有助於緩解原始 g-C3N4 中常見的高複合速率問題。綜上所述，W 氧化物修飾的 AA 堆疊 g-C3N4 結構被認為具備極高潛力的光催化候選材料。此研究結果強調了透過整合過渡金屬氧化物簇以提升 g-C3N4 光學性質的可行性與應用潛力。;Graphitic carbon nitride has garnered considerable attention in the field of photocatalysis due to its indirect band gap of 2.7 eV and its promising applications in water splitting and CO2 reduction. Nevertheless, its photocatalytic efficiency is limited by the ability to absorb visible light and the rapid recombination rate of photogenerated electron and hole pairs, which shortens carrier lifetimes. Several modification strategies, including element doping, defect engineering, and the design of heterojunction structures, have been used to overcome these challenges. Metal doping, especially with noble-metal co-catalysts like Pd, Pt, and Au, is considered one of the most effective strategies. However, their high cost limits large-scale practical applications. Consequently, replacing these noble metals with transition metals has become a promising and economical alternative. In this study, we incorporated transition metal (Mo, Ru, W) oxide clusters into g-C3N4 to enhance its optical properties, with both AA- and AB-stacked configurations considered. The electronic properties, including the density of states (DOS), band structure, effective mass, and Bader charge were investigated using density functional theory (DFT) calculations, carried out using the Vienna Ab-initio Simulation Package (VASP). The GW approximation, coupled with the Bethe-Salpeter equation (GW-BSE) was employed to compute the dielectric constant and absorption spectra. After the integration of transition metals, the band gap significantly decreased. Notably, Ru in AA-stacking and Mo in AB-stacking induced a semiconductor-to-metal transition in g-C3N4, while all other configurations retained an indirect semiconducting nature. Additionally, the incorporation of W oxide in AA-stacking and Ru oxide in AB-stacking effectively broadened the visible-light absorption range and enhanced absorption intensity. Among these, W oxide in AA-stacking also resulted in the highest effective mass ratio between electrons and holes, indicating a lower recombination rate. This enhances the availability of charge carriers for surface redox reactions and helps mitigate the fast recombination behavior observed in pristine g-C3N4. Overall, we suggest that W oxide cluster with g-C3N4 in AA-stacking is well-suited for use in photocatalytic applications. The results highlight the promise of improving the optical properties of g-C3N4 through the integration of transition metal oxide clusters.
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