(Ag-In-Zn)S固態溶液光催化效率提升研究

Enhancement of Photocatalytic Activity of Silver-Indium-Zinc Sulfide Solid Solutions

王蓓瑛(Pei-Ying Wang)

指導教授 ： 李元堯 ； 李岱洲

國立中正大學/工學院/化學工程學系/碩士(2012年)

摘要

能源與溫室效應為21世紀最重要的挑戰，而無污染物排放問題的氫能源則成為取代石化燃料的最佳替代能源，這也使得發展可見光光觸媒來分解水產生氫氣之研究變得相當必要。文獻報導(Ag-In-Zn)S固態溶液具有高產氫效率(7.37 µmol/cm2•h)，且可藉由調整[Zn]/[Ag]比例將其吸收波長在紫外光與可見光之間調整。
本研究進一步的改變固態溶液中的銦含量來提升光化學活性。藉由小幅度的改變[In]/[Ag]比例可以使(Ag-In-Zn)S光觸媒之產氫效率有顯著的改善，與[In]/[Ag]=1的固態溶液相比，產氫效率最高可提升3倍。從SEM圖可發現，當改變[In]/[Ag]比例時，固態溶液表面的階梯結構數量也會跟著改變，而這些階梯結構的邊緣為光觸媒的活性點，有利於電子電洞的分離進而提升光轉換效率。固態溶液中的另一成分，鋅，可用來控制能隙值，藉由調整銦與鋅的比例，我們可得到最佳的產氫效率(17.26 µmol/cm2•h)。
根據反應動力學可知，提升溫度有助於提升水解反應效率，因此在另一部分的實驗中，我們將提升溫度來進行光催化反應。調整核殼結構奈米粒子(Ag@Au)的外層奈米殼(Au)厚度可將其吸收波段從可見光移至紅外光。吸收波段落於紅外光附近的奈米粒子(>700 nm)可將太陽能轉換為熱能，在我們的可見光光觸媒系統內，此獨特的性質提供我們能一個可以更有效利用太陽光的方法。然而，此核殼結構奈米粒子的吸收波段過於寬廣，與一部分的可見光波段相重疊，因此減低了金屬硫化物光觸媒的效率，未來若能在核殼結構奈米粒子外層包覆(Ag-In-Zn)S固態溶液，其產氫效率將更進一步的提升。

關鍵字

固態溶液 ； 產氫 ； 光觸媒 ； 光化學反應

並列摘要

The energy and greenhouse effect are big challenges of 21st century. Hydrogen is the most promising replacement for fossil fuels without any pollutant emission. The development of visible-light-driven photocatalysts for water splitting is critical. The (Ag-In-Zn)S solid solution has a high activity with a hydrogen evolution rate of 7.37 µmol/cm2•h and its absorption can be tuned from UV light to visible light by adjusting [Zn]/[Ag] ratio.
In this study, we further extended the investigation, changed the amount of indium in a series of solid solutions, and increased the photochemical activity substantially. With little adjustment of the ratios of [In]/[Ag], the hydrogen production rate of the photocatalysts, (Ag-In-Zn)S, are significantly improved. The most enhancement of the activity can go up to three times, compared to the photocatalyst of [In]/[Ag]=1. SEM images show that different amount of nanosteps on the surface related to the ratios of [In]/[Ag]. These edges of nanosteps are considered as the active sites that facilitates the electron-hole separation, leading to higher solar-to-fuel conversion efficiency. The other ingredient, zinc, is used to control the band gap. With both variations in indium and zinc, the highest efficiency of this photocatalyst is 17.26 µmol/cm2•h.
According to reaction kinetics, the water splitting reaction rate increases with temperature. In a separate experiment, the photocatalystic reactions were carried out at elevated temperatures. The absorption of core-shell nanoparticles (Ag@Au) can be adjusted systematically from visible light to IR range by altering the thickness of nanoshell (Au). The nanoparticles have an absorption edge in the IR range (>700 nm), which can convert the solar energy to heat. This unique property provides us a way to further utilize solar energy in the system of our visible-light-driven photocatalysts. However, the broad absorption of core-shell also covered the visible-light region, which decrease the efficiency of the metal sulfide photocatalysts. If the core-shell nanoparticles can be covered with (Ag-In-Zn)S solid solution, the efficiency of hydrogen production will be further raised in the future.

並列關鍵字

Solid solution ； Hydrogen evolution ； Photocatalyst ； Photochemical reaction

參考文獻

2. Turner, J.A., 1999, "A Realizable Renewable Energy Future", Science, 285, No. 5428, 687.

3. Walker, G.R. and P.C. Sernia, 2004, "Cascaded DC-DC Converter Connection of Photovoltaic Modules", IEEE Transactions On Power Electronics, 19, No. 4, 1130-1139.

4. Kogan, A., 2000, "Direct Solar Thermal Splitting of Water and On-site Separation of The Products — IV. Development of Porous Ceramic Membranes for a Solar Thermal Water-splitting Reactor", Int. J. Hydrogen Energy, 25, No. 11, 1043-1050.

5. Fujishima, A. and K. Honda, 1972, "Electrochemical Photolysis of Water at a Semiconductor Electrode", Nature, 238, No. 5358, 37-8.

6. Kawai, T. and T. Sakata, 1980, "Conversion of Carbohydrate into Hydrogen Fuel by a Photocatalytic Process", Nature, 286, No. 5772, 474-476.