g-C₃N₄ 光催化劑之開發及其在水環境中有機污染物降解之應用

Abstract

隨著抗生素、鹵代酚類及多種新興污染物於水體中的濃度不斷升高，開發具高效率、可持續性且可在可見光驅動下運作的無金屬光觸媒已成為迫切需求。其中，聚合型氮化碳（polymeric carbon nitride, g-C₃N₄, CN）因其低成本、環境友善及可調控之電子結構而備受關注；然而，CN之實際應用仍受限於載流子快速復合、可見光吸收不足及氧化還原能力有限等問題。本論文旨在透過原生摻雜策略與異質結構界面工程，調控CN之能帶結構與電荷傳輸行為，以突破其固有性能瓶頸並提升其對環境污染物之光催化降解效能。 本研究的第一部分聚焦於建構 TiO₂/CN 異質接面、Cl-CN 複合材料以及 S-TiO₂/Cl-CN 雙摻雜光觸媒，用以降解磺胺類抗生素與鹵代苯酚等污染物。透過系統性的材料鑑定（X光繞射分析、傅立葉轉換紅外光譜、穿透式電子顯微鏡、X光光電子能譜、紫外－可見光分光光譜、光致發光光譜）、動力學模型及活性氧物種（reactive oxygen species, ROS）分析，本研究證明了界面電荷轉移模式，包含 type-II、Z-scheme 與電子循環機制，可顯著提升光催化效率。此外，本研究採用反應曲面法優化合成與反應條件，成功實現對磺胺甲噁唑、4-溴苯酚與四溴雙酚A之高效降解。 本研究的第二部分提出一套完全無金屬之原生摻雜策略，分別於 CN 晶格中導入碳、氮與氧摻雜（CCN、NCN、OCN）。摻雜後材料之電子結構經由密度泛函理論的能帶結構、投影態密度及HOMO–LUMO 前線軌域分析得到全面揭示。研究顯示，碳摻雜（CCN）可促使前線軌域產生顯著空間分離並形成高度離域化之 LUMO，從而有效抑制載流子復合並提升電荷遷移能力。電化學分析（電化學阻抗譜、光電流、循環伏安）亦證實 CCN 具最低界面電荷傳輸電阻與最強之光響應。電子順磁共振實驗顯示不同摻雜樣品之 ROS 生成途徑迥異，且光催化效率主要取決於表面之電荷有效利用率，而非活性氧物種之絕對濃度。 綜合本論文之研究成果可知，原生摻雜能有效調控碳氮化物之內部電子構造，賦予材料新的反應性，從而顯著提升其在純水及複雜水體中對難降解污染物之光催化降解效能。相關之機制解析與實驗－計算整合策略提供一套可延展至未來多類環境應用之無金屬光觸媒設計藍圖，對綠色環境修復技術之發展具有重要意義。

The increasing presence of pharmaceuticals, halogenated phenols, and emerging contaminants in aquatic systems necessitates the development of efficient, sustainable, and metal-free photocatalysts capable of operating under visible light. Polymeric carbon nitride (g-C3N4), CN, is an attractive candidate due to its low cost, environmental compatibility, and tunable electronic structure; however, its practical performance is limited by rapid charge recombination, insufficient visible light harvesting, and limited redox potential. This dissertation investigates rational strategies to overcome these shortcomings by engineering indigenous dopants and heterostructure systems that modulate the band structure and charge-transfer properties of CN-based photocatalysts. The first part of this work addresses the construction of TiO2/CN heterojunctions, Cl-CN composites, S-TiO2/Cl-CN hybrid structures, and 3D/2D Cs2Ag0.95Na0.05BiBr6/CN heterostructure for the degradation of sulfonamide antibiotics and phenolic pollutants. Through systematic characterization (XRD, FT-IR, TEM, XPS, UV-Vis, PL), kinetic modeling, and reactive oxygen species analysis, we demonstrate that interfacial chain charge-transfer pathways, such as type-II, Z-scheme, electron-cycling, and S-scheme mechanisms, significantly enhance photocatalytic efficiency. Response Surface Methodology (RSM) was applied to optimize synthesis and reaction parameters, achieving high removal efficiencies for pollutants such as SMX. The second part introduces a metal-free, indigenous-doping strategy in which carbon, nitrogen, and oxygen dopants are intrinsically incorporated into the CN framework (CCN, NCN, and OCN). These dopants fundamentally change the electronic properties of CN, as confirmed by DFT band structures, partial density of states (PDOS), and HOMO-LUMO analyses. The CCN exhibits promising orbital separation, enhanced band dispersion, and a highly delocalized LUMO, resulting in suppressed electron-hole recombination and significantly improved charge mobility. Electrochemical studies (EIS, photocurrent, CV) further validate that CCN possesses the lowest charge-transfer resistance and strongest photo-response. EPR measurements reveal distinct reactive-oxygen-species pathways among the doped catalysts, showing that photocatalytic performance is not only supported by the magnitude of ROS formation but by efficient charge utilization at the catalyst surface. The system showed outstanding photocatalytic performance in actual water environment, indicating the superb ability of indigenous element doping strategy toward improving the efficiency of CN-based photocatalysts. This study indicated versatile abilities of the carbon nitride-based photocatalysts for organic pollutant degradation, especially in real wastewater matrices, by improving visible light-harvesting ability, electrochemical properties, orbital tuning, and novel approaches to the charge carrier transfer mechanisms through the photocatalyst systems.