GaOOH-Au奈米異質結構之界面載子動力學

Abstract

由半導體與金屬所組成之奈米異質結構，因具有光誘發電子電洞對分離的特性，能被廣泛地應用於各種光電轉換用途，包含太陽能電池、光催化反應與水分解產氫等。本研究以簡便之濕式化學沈積法成功地製備具高均勻度的GaOOH奈米棒，發現反應溶液的pH值與MgSO4的添加對於所成長的GaOOH形貌有相當大的影響。為了進一步提升GaOOH之載子分離效率，使用化學還原法將Au奈米顆粒沈積於GaOOH奈米棒表面，以形成GaOOH-Au奈米異質結構，藉由調整HAuCl4的濃度，可有效控制所沈積於GaOOH奈米棒表面Au顆粒的數量。由於GaOOH與Au相對能帶結構的關係，光激發電子會由GaOOH端轉移至Au端，並留下大量電洞於GaOOH內，以達成電子電洞對的分離。 由穩定態螢光光譜(steady-state photoluminescence)的量測結果確認Au顆粒的沈積確實能提升GaOOH奈米棒的載子分離特性，其中以Au數量為1.0 mol%之GaOOH-Au樣品具有最佳的載子分離效果，利用時間解析螢光光譜(time-resolved photoluminescence)技術，則可量化光激發電子由GaOOH轉移至Au端的速率常數。與相關商用品例如P-25 TiO2 與Ga2O3粉末比較，GaOOH-Au樣品展現出較優異的光催化甲醇氧化效能，此乃因為GaOOH-Au具有顯著的載子分離特性所致。由此研究所製備出的具Au顆粒接枝的GaOOH奈米棒，預期可在光催化水分解與光激發電子儲存等用途發揮相當高的效能。

Due to the photo-induced charge separation property, semiconductor-metal nanoheterostructures have been extensively applied in many photoelectric conversion processes including photovoltaics, photocatalysis and water splitting. In this work, a facile wet-chemistry chemical precipitation approach was deveopled to prepare GaOOH nanorods (NRs) with considerable uniformity in size. It was found that the pH value of reaction solution as well as the addition of MgSO4 greatly influenced the morphology of the resultant GaOOH. To further the charge separation efficiency of GaOOH, Au nanoparticles were deposited on the surface of GaOOH NRs with a chemical reduction method. By modulating the concentration of HAuCl4 employed, the amount of Au nanoparticles decorated on GaOOH NRs can be readiy controlled. Owing to the difference in band structure between GaOOH and Au, the photoexcited electrons of GaOOH would preferentially transfer to Au, leaving photogenerated holes in GaOOH to achieve charge carrier separation. The result of steady-state photoluminescence analysis IV confirms the enhancement in charge separation efficiency for GaOOH NRs upon the deposition of Au nanoparticles. Among the different samples, GaOOH-Au with 1.0 mol% of Au was found to show the most significant charge separation efficiency. Time-resolved photoluminescence spectra were measured to quantitatively analyze the electron transfer event between GaOOH and Au. As compared to the relevant commercial products like P-25 TiO2 and Ga2O3 powders, the as-synthesized GaOOH-Au sample exhibited superior photocatalytic performance toward methanol oxidation, attributable to the effective charge separation that took place at the interface of GaOOH-Au. The current GaOOH-Au sample may find potential applications in relevant photocatalytic reactions such as water splitting and photoexcited electron storage.