多離子摻雜石墨型氮化碳之電化學分析與水凝膠之應用

Photoelectrochemical Analysis of Multi-ion Doped Graphite Carbon Nitride (g-C3N4) and Its Application on Hydrogel Formation

朱怡親(Yi-Ching Chu)

指導教授 ： 胡哲嘉

中原大學/工學院/化學工程研究所/碩士(2019年)

https://doi.org/10.6840/cycu201900447

摘要

如何有效地解決廢水問題是目前備受矚目的議題，其中利用可吸收太陽光能的光觸媒材料來處理廢水是較永續的方式。而現今常見的光觸媒皆含有金屬成分，且僅能吸收佔太陽光中5%的紫外光(λ<400 nm)，因此我們選擇了不含金屬成分且能吸收可見光(400 nm< λ<700 nm)的石墨型氮化碳(graphitic carbon nitride, g-C3N4)。
石墨型氮化碳僅含有碳及氮原子，其能隙約為2.70 eV，且具有良好的耐熱性、耐酸鹼性、耐溶劑性，然而石墨型氮化碳的表面有高密度的原子空缺，容易導致電子電洞對再結合，光觸媒性能降低。因此本實驗選擇了磷、硫、氧原子進行多摻雜，來填補或取代石墨型氮化碳(CN)之空缺，使用固相法將不同重量百分比的磷、硫離子摻雜至氧化的石墨型氮化碳(PxSyOCN, x,y=5,10,15)。從XRD檢測結果顯示，經過摻雜的石墨型氮化碳在13.1度及27.1度有出現特徵峰，代表有保持原先(100)和(002)的晶格結構，然而摻雜含量達15 wt%時，會出現過度摻雜且破壞其晶格結構的情況。透過FTIR與XPS分析，推測出磷、硫、氧原子各自填補或取代的位置，並分析其光電化學之特性，透過Mott-Schottky圖可以知道CN與PSOCN皆為n型半導體，且摻雜後的石墨型氮化碳之費米能階皆有向負電位移動，其中P10S5OCN在照射可見光後具有最強的光電流，且其在XPS元素分析中，磷、硫、氧原子的含量也是最多的。
最後因製備出的光觸媒皆為粉體，在進行有機染劑催化實驗時，粉體難以回收再利用，因此利用石墨型氮化碳為光觸媒之特性，以光聚合的方式製備高強度的N,N-二甲基丙烯酰胺(DMA)、N,N-二甲基雙(丙烯酰胺)(MBA)與石墨型氮化碳的複合水凝膠，石墨型氮化碳不僅扮演著光觸媒的角色，且在水凝膠中也扮演著交聯起始劑與結構增強劑，並能成功將光觸媒粉體固定於膠體中，達到更有效的回收粉體光觸媒及循環使用的效果。P10S5OCN除了擁有強的光電流外，其固定於水凝膠中並催化有機染劑之速率常數(k)也為最大值，因此可以得到P10S5OCN為最佳摻雜比例之石墨型氮化碳。

關鍵字

石墨型氮化碳 ； 多摻雜 ； 光電化學 ； 水凝膠 ； 甲基藍

並列摘要

Graphitic carbon nitride (g-C3N4) is a promising visible light-driven photocatalyst with a band gap energy of 2.70 eV. However, abundant surface defects and unwanted carbon or nitrogen vacancies may lead to high charge recombination that results in a decrease of photocatalytic activity. In this study, P and S were co-doped on oxygenated g-C3N4(PSOCN) using a thermal condensation method with different weight ratio of P and S (PxSyOCN, x, y =5,10,15). Photoelectrochemical properties including impedance spectroscopy, Mott-Schottky analysis, and photocurrent density, and the degradation of organic pollutants under visible light irradiation were investigated.
XRD diffraction peaks of PSOCN located at 13.1° and 27.1° were assigned to (100) and (002) crystal plane of graphite-type carbon nitride (CN). The SEM images showed that both CN and PSOCN had irregular stacked shape and plate-like morphologies, indicated that doping were not affect the surface morphologies. In the UV-vis spectra, the absorption wavelength of PSOCN exhibited a shoulder at approximately 440-500 nm, and its band gap is a little smaller than that of CN. In Mott-Schottky test, PSOCN and CN samples are n-type semiconductors, and Fermi level of PSOCN all move to negative potential, indicating electronic of PSOCN are more easily moved to conduction band. Especially, P10S5OCN had the most large photocurrent density.
In addition, PSOCN hydrogel was fabricated using photoinduced polymerization method. PSOCN hydrogel enables not only to decompose a commonly seen dye, methyl blue, but also to be recycled easily. In summary, P10S5OCN is the best weight ratio in PSOCN. Its photocurrent density is larger than others, and P10S5OCN hydrogel also has better degradation efficiency of methyl blue.

並列關鍵字

g-C3N4 ； photoelectrochemical ； n-type ； hydrogel

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