製備以石墨相氮化碳為基材之奈米複合材料應用於水體淨化研究

石墨碳氮化合物（g-C3N4）是一種在光催化應用非常有前景的材料，它的用途包括通過二氧化碳還原與水分解以生產太陽能燃料，以及透過降解有機污染物以實現環境修復。這些優點反映了g-C3N4奈米結構的有利光物理性質，特別是高表面積，量子效率，界面電荷分離和傳輸，以及透過複合物形成或結合所需的表面官能度而容易修飾的材料表面。對於非均相催化過程，有機化合物和金屬衍生物可以通過表面錨定位點結合或嵌入g-C3N4基質中以提高催化反應速率，因而拓寬g-C3N4在有機汙染物分解中的催化應用。 g-C3N4的獨特結構以及金奈米粒子的出色催化特性，是利用g-C3N4作為支持以推動金奈米粒子形成高活性和環保的非均相催化劑。因此，本論文研究重點在使用TiO2 / ZnFe2O4修飾的g-C3N4為基底的奈米金屬材料修飾電極，可以進一步提高光電催化去除有機污染物的效率。 1wt％的ZnFe2O4-TiO2奈米複合材料表現出優異的循環和可重複使用之性質，並且在可見光照射下對雙酚A（BPA）光降解的穩定性保持至少10個循環(反應速率常數為0.191-0.218min-1)。ZnFe2O4-TiO2對BPA的光降解速率（高度依賴水的化學性質，包括pH值、陰離子和腐殖酸）是商業合成TiO2光催化劑的20.8-21.4倍。由於擁有更有效的光吸收與電子電荷分離的效率，ZnFe2O4 / TiO2 / g-C3N4光陰極顯著增強了可見光驅動的四環素（TE）的降解效率。透過採用光電催化（PEC）之過程，TE的降解反應常數與光催化（PC）和電催化（EC）相比之下分別提高了48倍和24倍。實驗結果清楚地表明g-C3N4為基底的光催化劑對有機污染物降解具有優越的可見光驅動的光催化活性，在光催化、水分解等領域皆具有廣泛的應用潛力，可以為將來的工業應用開拓新的途徑。此外，實驗中開發了使用熱剝離技術(thermal exfoliation process)的光化學合成奈米金與碳氮化物（g-C3N4）之奈米複合材料，能夠高度回收且可重複使用，可用於NaBH4催化還原硝基苯酚。 Au@g-C3N4（2wt％）還原4-硝基苯酚的速率常數是在pH=5的7mM NaBH4存在下是純奈米金的26.4倍。另外，實驗當中也證明了以簡單和容易的合成方法，製備具有各種金載量的金與內消旋碳氮化物（meso-CN）所合成的奈米複合材料，可還原硝基酚並可高度回收再利用。在Au@meso-CN複合材料中，高比表面積，規則孔洞、內消旋碳氮化物的石墨性質以及高度分散和空間嵌入的奈米金之一體化，使得它們作為4-硝基苯酚的催化還原的具有非常優異的表現。在NaBH4存在下，2wt％ Au@meso-CN奈米催化劑還原4-硝基酚的反應速率可以達到3.558 min-1。在使用石墨碳氮化物負載的金奈米複合物進行硝基酚還原的兩種情況下，通過EPR檢測氫自由基表明金奈米粒子吸附BH4-離子並形成Au-H的物質，並隨後將電子從Au-H轉移到硝基酚。結果清楚地表明，奈米金與碳氮化物之奈米複合材料是具有巨大應用潛力的環保催化劑，可用於硝基芳族化合物的還原，提供金奈米材料一個嶄新的方向，並為廢水處理中各種各樣的非均相催化反應提供新的處理機制。

關鍵字

水體淨化研究

並列摘要

Graphitic carbon nitride (g-C3N4) is a promising material for photocatalytic applications such as solar fuels production through CO2 reduction and water splitting, and environmental treatment through the degradation of organic pollutants. This promise reflects the advantageous photophysical properties of g-C3N4 nanostructures, notably high surface area, quantum efficiency, interfacial charge separation and transport, and ease of modification through either composite formation or the incorporation of desirable surface functionalities. For heterogeneous catalytic processes, organic compounds and metal derivatives could bind or intercalate into the matrix of g-C3N4 through the surface anchoring sites to improve the catalytic reaction rate, and thus broaden the catalytic application of g-C3N4 toward organic decomposition. The unique architecture of g-C3N4 and the outstanding catalytic performance of Au nanoparticles provide a great impetus to use g-C3N4 as a promising support to judiciously decorate Au NPs for the formation of highly active and green heterogeneous catalyst. Therefore, this thesis focuses on developing novel g-C3N4-based-nanomaterirals modifying with TiO2/ZnFe2O4, which can offer further performance enhancements in photo-electrocatalytic activity for organic pollutant removal. The 1 wt% ZnFe2O4-TiO2 nanocomposites exhibit the excellent recycling and reusable ability and can retain the stable photocatalytic activity toward Bisphenol A (BPA) photodegradation for at least 10 cycles of reaction with rate constants of 0.191 – 0.218 min-1 under visible light irradiation. The photodegradation rate of BPA by ZnFe2O4-TiO2 (which was highly dependent on the water chemistry including pH, anions, and humic acid) was 20.8−21.4 times higher than that of commercial TiO2 photocatalysts. The visible-light-driven degradation of tetracycline (TE) is enhanced remarkably by the ZnFe2O4/TiO2/g-C3N4 photocathode due to the more efficient light absorption and photogenerated charge separation. By applying photoelectrocatalytic (PEC) process, the degradation rate constant of TE is increased by 48 and 24 times as much as that of photocatalytic (PC) and electrocatalytic (EC), respectively. Results clearly demonstrate the superior visible-light-driven photoactivity of g-C3N4-based-photocatalysts toward organic pollutants degradation and can open an avenue to industrial application in the future with a wide variety of potential application in the fields of photocatalysis, water splitting and energy conversion. Moreover, a photochemical green synthesis using thermal exfoliation process is developed to fabricate Au@graphitic carbon nitride (g-C3N4) nanocomposite, highly recyclable and reusable, for the catalytic reduction of nitrophenols by NaBH4. The rate constant of 4-nitrophenol reduction over Au@g-C3N4 (2 wt%) is 26.4 times that of pure Au NP in the presence of 7 mM of NaBH4 at pH 5. Besides, I have demonstrated a simple and facile synthesis method for the fabrication of Au@meso-carbon nitride (meso-CN) nanocomposite with various Au loadings for highly recyclable reduction of nitrophenols. The integration of high surface area, regular mesopores, graphitic nature of the meso-CN support as well as highly dispersed and spatially imbedded Au NPs on the Au@meso-CN composites make them excellent as catalytic reduction of 4-nitrophenol. The kobs for 4-nitrophenol reduction over 2 wt% Au@ meso-CN nanocatalysts can be up to 3.558 min-1 in the presence of NaBH4. In both cases of using graphitic carbon nitride supported Au nanocomposites for nitrophenol reduction, The detection of H radical adducts by EPR indicates that Au NPs adsorbs BH4- ions and forms Au-H species and subsequent electron transferfrom the Au-H species to nitrophenols. Results clearly demonstrate that Au@carbon-nitride nanocomposites are promising green catalysts of great application potential for nitroaromatic reduction, which can provide a new venue for tailoring Au-based nanomaterials in elucidation of a wide variety of heterogeneous catalytic reactions in water and wastewater treatment