以石墨烯修飾二氧化鈦粒子及奈米管進行光催化甲醇溶液產氫之研究

Abstract

自1970年代石油危機，利用光能生產氫氣作為替代能源的技術逐漸受關注。起因於1972本多藤島效應的發現，以半導體受光催化來分解水的研究，成為綠色能源的新課題。隨後，水分解的異相光催化系統(Heterogeneous photocatalytic system)有賴光催化材料的改善，和犧牲劑的投入得以逐步發展。 在眾多具備光催化活性的半導體中，以二氧化鈦 (TiO2)的歷來研究最為豐富及深入，加上便宜、無毒、以及化學、光學穩定性好，二氧化鈦是最有潛力投入工業尺度應用的材料。 近年來，石墨烯受到奈米研究領域的關注。利用氧化減薄法，可以既簡便而又大量地製備氧化石墨烯 (GO)。理論上，還原氧化石墨烯 (rGO)導電性良好，加上可以進行奈米尺度的修飾，適合用作改善二氧化鈦的光催化活性。考慮石墨烯披覆於二氧化鈦的技術各式各樣，本研究分別以水熱還原法 (HrGO)、光還原法 (PrGO)及熱還原法 (TrGO)製備TiO2/rGO，並發現TiO2/HrGO在紫外光下 (365nm)催化產氫表現最好，1%披覆比例的產氫量比純TiO2提升2.7倍。 另外，本研究對二氧化鈦進行同時改質、披覆上石墨烯及進行還原，製備出二氧化鈦奈米管/還原氧化石墨烯 (TiNT/rGO)。在改質過程中，由於晶型改變使TiNT吸收峰藍移，在0%及1%披覆比例下產氫量較TiO2差。但由於比表面積大，當披覆比例提升至2%，TiNT/rGO的產氫量比純TiO2提升了13倍。

1970s was known to be the time of oil crisis. Since then, technologies of utilizing light to produce hydrogen energy had drawn much attention. Hydrogen produced from water splitting was considered to be one of the potential candidates of alternative energy owing to the discovery of Honda-Fujishima effect. By applying sacrificial reagents and improving photocatalysts, heterogeneous photocatalytic system of water splitting became possible few years later. Among various semiconductors, TiO2 is probably the most suitable material for industrial scale photocatalysts in future. TiO2 is cheap, nontoxic and stable. Its properties had also been well studied. Recently, nanomaterial researchers had been concerned about graphene. Oxidative exfoliation allows graphene oxide (GO) to be synthesized in gram-scale through facile method. Theoretically, reduced GO (rGO) possess good conductivity. Also GO is capable to be manipulated under nanometer scale, which is suitable for composition on TiO2 powder to further enhance photocatalytic activity. Considering various existing reduction methods, here in we synthesized TiO2/rGO by hydrothermal reduction (HrGO), photo-assisted reduction (PrGO) and thermal reduction (TrGO). Under UV irradiation, TiO2/HrGO was discovered to perform best among others, with 2.7 fold hydrogen production for 1%w/w compare with mere TiO2. In addition, synthesizing TiO2 nanotube (TiNT) with simultaneous composition and reduction of GO had been achieved to produce TiNT/rGO. Crystallinity changed along with nanotube fabrication and subsequent blue shift of absorption edge was observed. As a result, TiNT of 0% and 1%w/w rGO composition possess worse photocatalytic activities than that of TiO2. For the fact that specific surface area of TiNT is much higher than TiO2, hydrogen production rate of 2% composition of rGO on TiNT increased dramatically by 13 fold compare to mere TiO2