原位光導技術量測二硫化鉬極致薄膜材料於二氧化碳光催化還原反應的應用

In-situ Photoconductivity Measurements of MoS2 Ultra-thin Film for Photocatalytic CO2 Reduction Application

柯尚緯(Ke Shawn-Wei)

指導教授 ： 陳貴賢 ； 林麗瓊

國立臺灣師範大學/理學院/化學系/碩士(2021年)

https://doi.org/10.6345/NTNU202100932

摘要

本篇論文主要探討使用熱蒸鍍與化學氣相成沉積法合成的三奈米半導體薄膜材料二硫化鉬(MoS2)在光催化二氧化碳還原的反應機制，而我們也藉由薄膜材料對環境感測優異的特性，製作光感測裝置並且使用四極式半導體探針體測量儀去觀測光電導在光催化反應中變化，來幫助我們更深入反應中電子傳遞機制。
在我們所測量光導數據主要所做的差異化實驗有環境變因和波長變因去設計實驗，而在光催化方面我們是採用氣體氣相層析去量測與計算產量，再使用長時間光導測量去比較在不同氣體環境下的數據差異，可以得知在二氧化碳和水氣得環境下確實能使光電流下降，即代表載子被氣體分子吸收還原為可循環利用的有機分子燃料。
而在波長上主要是紫外光有最佳的光響應，甚至造成了特殊的巨大持久性光導（GPPC） 性質，藉由上述兩者的數據結合，我們能推導出光激發載子與反應氣體間的電子傳遞機制。
為了解釋電子傳遞的行為，從能帶彎曲的兩種模式表面電子聚集（SEA）和表面電子消耗(SED)，並且參考了光電導的載子活期和光電流大小等特性，推論出表面電子聚集為本薄膜材料提出一個合理和完善的解釋。
本研究為了解電子傳遞效應如何影響材料的催化效率，主要的方法即是生成凡德瓦二維異質材料，藉由生長三奈米二硫化鉬薄膜於單層石墨烯來達到材料之間優異的原子級接觸和特殊傳遞特性，更藉此影響和增進光催化二氧化碳還原產率。

關鍵字

光催化 ； 二氧化碳還原反應 ； 二維奈米材料 ； 二硫化鉬薄膜 ； 石墨烯 ； 電子傳遞模型 ； 光電導 ； 凡德瓦異質結構 ； 二維-二維異質結構

並列摘要

In this thesis ,We successfully fabricate 3nm molybdenum disulfide ultra thin films on silicon dioxide and sapphire substrate by using the two steps synthesis ,thermal evaporation and chemical vapor deposition process. In addition, we focus on the photocatalytic CO2 reduction reaction process of MoS2 thin films because it has excellent photo-sensitivity on the different environment. The photoconductivity measurement is the important way to help us understand charge transfer in the reaction.
The photoconductivity measurement can be divided into three parts. First, we compare the results of product yield and long time-scale photoconductivity (PC) measurement from photocatalytic CO2 reduction reaction(CO2RR). This comparison illustrated that when the CO2 RR happened on the 3nm MoS2 thin films ,it can effectively decrease photocurrent. It proved the carrier able to react with CO2 and Water vapor and become the valuable gas product. Second, the wavelength-dependent PC measurement show that UV light source contribute the most part of photo-response in AM1.5G sunlight source and cause special great persistent photoconductivity (GPPC). Last but not least, the environment-dependent PC measurement demonstrate carrier life time is decreasing from vacuum to CO2 and H2O environment.
We consider two surface band bending model, surface electron accumulation (SEA) and surface electron depletion (SED), to explain charge transfer model of CO2RR. We compare photocurrent and carrier life time from PC measurement. The SEA model can get more suitable and perfect explanation on photocatalytic CO2RR of MoS2 thin films
Additionally, we want to realize how charge transfer affect the production of photocatalytic CO2 reduction, so we apply the Van der Waals 2D heterostructure growth way to our material. By the special charge transfer and atomic contact between 3nm MoS2 and monolayer graphene, it can affect and even improve the production of photocatalytic CO2 reduction in this thesis.

並列關鍵字

Photocatalyst ； CO2 reduction reaction ； 2D nanomaterial ； MoS2 thin films ； charge transfer model ； Photoconductivity

參考文獻

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