鍛燒對三辛基氧化膦包覆之二氧化鈦奈米晶粒物化特性影響研究

Abstract

三辛基氧化膦包覆之二氧化鈦奈米晶粒已成功地使用非水解性溶膠凝膠法製備出來。為了解熱處理對於三辛基氧化膦包覆之二氧化鈦奈米晶粒微結構、電子結構以及表面特性的影響，高解析度穿透式電子顯微鏡、X射線繞射儀、傅立葉紅外光光譜儀、X光光電子能譜儀、熱重分析儀以及紫外光可見光光譜儀都被用來鑑定鍛燒過的樣品(250~950 ℃)。因為鍛燒的過程將表面氧化三辛基膦分子熱分解並形成磷酸分子之關係，使得加熱750 ℃以下之樣品表面由疏水性轉變成為親水性。然而疏水性質又在鍛燒950 ℃後產生在奈米晶粒表面上。參雜進入晶體結構內之鋯離子與磷離子增加了銳鈦礦晶體的熱穩定性，即使是加熱到了950 ℃之高溫也沒有晶相的轉變。除此之外，當鍛燒溫度小於750 ℃時，晶粒的大小維持在10.2-10.8奈米，並且在鍛燒950 ℃顯著地增加到16.1奈米。能隙之大小隨著晶粒大小的變化從3.4電子伏特減少到3.2電子伏特。鍛燒到550 ℃之樣品因為擁有低介達電位以至於較鍛燒950 ℃之樣品表面有較多的布忍斯特酸基。然而鍛燒950 ℃的樣品較初製備及鍛燒250 ℃與550 ℃的樣品有更高的表面活性。而路易士酸被認為是鍛燒950 ℃之樣品有高活性的主要原因。

Trioctylphosphine oxide (TOPO) capped Zr4+/TiO2 anatase nanocrystals were successfully prepared by a non-hydrolytic sol-gel route. To understand the effect of thermal treatment on the microstructures, electronic structures, and surface properties of the TOPO-capped Zr4+/TiO2 nanorystals, the samples calcined at elevated temperatures (250-950 °C) under air atmosphere were examined by means of HRTEM, XRD, TG-DSC, XPS, FTIR and UV-vis spectroscopy. Calcination below 750 °C converted the surface of the nano-crystals from hydrophobic to hydrophilic as a result of decomposition of the surface TOPO and formation of phosphate moiety. However, hydrophobic property was further obtained at 950 °C due to dehydroxylation. The introduced P5+ and Zr4+ enhanced the stability of the anatase form till 950 °C without any phase transformation. Moreover, the crystallite sizes of the samples were maintained at 10.2-10.8 nm at 250-750 °C and were remarkably increased to 16.1 nm as the calcination temperature rose to 950 °C. The band gaps of the samples declined from 3.4 to 3.2 eV upon the increasing crystallite sizes. Calcination at 550 °C resulted in lower zeta-potential and higher surface Bronsted acidity than those at 950 °C. However, the sample calcined at 950 °C showed the highest surface activity than the as-prepared nanocrytals and the samples calcined at 250 or 550 °C. Lewis acidity is considered to be responsible for the high photoactivity at 950 °C.