酸鹼值與沉澱劑對共沉法生成氧化鋅錫的影響

Influence of pH value and precipitant with Zn2SnO4 formation by co-precipitation method

呂昆達(Kun-Ta Lu)

指導教授 ： 李源弘

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.01436

摘要

氧化鋅錫(Zn2SnO4，ZTO)在光觸媒、透明導電氧化物以及氣體檢測器等方面具有應用的潛力，而奈米顆粒大小及形狀會影響其在光觸媒的性質。本研究藉由共沉法來製備ZTO，選用的起始材料為二氯化鋅(ZnCl2)以及四氯化錫(SnCl4)，沉澱劑採用氫氧化鈉(NaOH)及碳酸鈉(Na2CO3)，選擇三種pH值(pH6、pH8和pH10) 作為滴定終點，起始粉末水溶液產生氫氧化鋅錫(ZnSn(OH)6)沉澱，並煅燒1000oC 1小時與5小時，比較各種不同條件下反應合成的ZTO粉末。
結果顯示在二種沉澱劑下形成的前驅體粉末，煅燒1000oC 1小時仍未反應完全，仍有Zn/Sn相的存在；煅燒5小時則Zn/Sn相消失，使ZTO反應完全。煅燒1小時NaOH與Na2CO3沉澱劑下之SnO2相強度並無顯著不同，但煅燒5小時下，使用NaOH沉澱劑得到的粉末比Na2CO3下具有較明顯的SnO2相。pH值的變化對於ZTO組成無太大的影響。由TEM可觀察顆粒大小形態，煅燒5小時的粉末顆粒比同樣條件下煅燒1小時的粉末大。同樣pH值下Na2CO3沉澱劑可以得到較小的粉末，但是團聚情形嚴重，其中pH6粒徑最小，pH10粒徑次之，pH8粒徑最大。
製備的ZTO粉末以亞甲基藍水溶液進行光觸媒降解反應，反應速率與顆粒表面積大小有關。煅燒5小時的顆粒比1小時大，且聚集現象較嚴重，因此5小時顆粒光觸媒性質較差。沉澱劑NaOH在pH6得到的顆粒最小、並且是棒狀顆粒；沉澱劑Na2CO3也在pH6時有最小顆粒，但由Na2CO3作為沉澱劑得到的顆粒具有聚集現象，會使比表面積降低，因而使得光觸媒性質降低。以NaOH作為沉澱劑、煅燒1小時、滴定終點為pH6所得到的粉末，此條件下生成的顆粒較小，無團聚現象，呈現棒狀的奈米顆粒；經由BET測試，的確有提升ZTO的比表面積，而具有最佳的光觸媒活性。

關鍵字

共沉法 ； 氧化鋅錫 ； 光觸媒 ； 奈米顆粒

並列摘要

ZTO (Zn2SnO4) has potential applications such as photocatalyst, transparent conductors and gas sensor. The sizes and the shapes of nanostructures influence the photocatalytic properties. In this research, ZTO are successfully synthesized by co-precipitation method. ZnCl2 and SnCl4•5H2O are used as raw materials. NaOH and Na2CO3 are adopted as precipitant to make precursor precipitate. The titration endpoint at pH6、pH8 and pH10 is fixed to adjust solution precipitant quantity, and the originate solution will form precipitate ZnSn(OH)6. The precipitates are calcined at 1000oC by modifying the calcination time ( 1 hour and 5 hours) and then analysed to compare.
The results show that powders calcined for 1 hour do not totally react, in which Zn/Sn phase still exists, and that the Zn/Sn phase will disappear for 5 hours calcination due to compelete calcination of ZTO. Under calcined for 1 hour, there is no significant difference between precipitant NaOH and Na2CO3. Under calcined for 5 hours, powders obtained by precipitant NaOH have more obvious SnO2 phase than those by Na2CO3. At the same calcination time, it can be seen that pH value has a slight influence on composition. TEM is used to observe the size and shape of synthesized particles. Powders in same condition calcined for 5 hours are larger than those calcined for 1 hour. Precipitant Na2CO3 can lead to finer particles, but the particles agglomerate seriously. At various pH values, the ZTO powders with treatment of pH6 possessed the smallest particles; instead, coprecipitation followed by pH10 and pH8 will result in the largest particles.
Powders obtained are used for photocatalytic degradation reaction with methylene blue solution. As a result, the degradation rate is affected by particle surface area. Powders obtained by calcined for 5 hours have worse photocatalytic activity than that calcined for 1 hour due to its larger particle size. The smallest particles can be obtained by precipitant NaOH in pH6, accompanying with some nano-rod particles. Similarly, precipitant Na2CO3 can be also used to obtain smallest particles in pH6, but particles agglomerate with each other, reducing their specific surface area. Hence, the former shows better photocatalytic activity than the latter. Consequently, powders titrated to pH6 by precipitant NaOH and calcined for 1 hour will form partly nano-rod particles with slight agglomeration. From BET test the powders have larger specific surface area than other ZTO powders and bringing about the best photocatalytic characteristics.

並列關鍵字

co-precipitation ； Zn2SnO4 ； photocatalyst ； nanoparticle

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