缺陷可調控的氧化鋅之研究： 合成、性質與應用

An Investigation of ZnO with Tailored Defects: Synthesis, Properties and Applications

陳婷婷(Ting-Ting Chen)

指導教授 ： 李紫原

國立清華大學/工學院/材料科學工程學系/博士(2014年)

https://doi.org/10.6843/NTHU.2014.00106

摘要

在光觸媒及物理性紫光線防曬劑的應用上，氧化鋅的光催化活性扮演非常重要的角色。本研究的主要目的為研發新的合成方法，增加氧化鋅中的本質缺陷，藉此控制其載子再復合的性質，並同時滿足相關應用上對於光催化活性的要求。在本研究中，將使用兩種不同的方法來製備具有本質缺陷的氧化鋅作為光觸媒及物理性紫光線防曬劑的材料。
第一，在熱溶劑法的合成中，添加微量的氧化石墨烯，其產物為同時具有順磁性的氧空缺及鋅空缺的氧化鋅。在順磁性缺陷的生成反應，氧化的石墨烯不僅中具有催化作用的特性，並且會改變缺陷生成的方式。 同時具備順磁性的氧空缺及鋅空缺的氧化鋅展現出優異的光催化活性，能快速地分解甲基橙。根據電子順磁共振的能與犧牲試劑的測試，在光催化的過程中，由於順磁性的氧空缺及鋅空在氧化鋅的能隙中增加了額外的能階，進而加速電子電洞對的分離，降低了電子電洞對的再復合的機率，並且在氧化鋅的表面會產生高活性的電洞及氫氧自由基，進而提升光催化的表現。
第二部分為以熱分解非晶/層狀鋅鹽的微米球，來製備具有缺陷的氧化鋅微米球以作為新一代的物理性紫外光防曬材料。其中，先以回流法合成均勻的非晶/層狀鋅鹽微米球。此反應中，以檸檬酸鈉為螯合劑，捕捉溶液中的鋅離子，以防生成氧化鋅。 藉由調整檸檬酸根與氫氧根離子的濃度，進而控制非晶/層狀鋅鹽的微米球的尺寸及均勻性。同時，本文將針對溶液中鋅離子、檸檬酸根離子與氫氧根離子的濃度關係對於產物的形貌及結構影響進行探討。 熱分解非晶/層狀鋅鹽的微米球後所得到的氧化鋅微米球具有高濃度的氧空缺，因此造成吸收可見光的特性並且有效地抑制光催化活性。除此之外，更具有米式散射的特性，使得均勻的氧化鋅微米球具有成為物理性紫光線防曬劑材料之潛力。

關鍵字

氧化鋅 ； 缺陷 ； 光催化 ； 米式散射

並列摘要

Defects play a very important role in photoactivity of ZnO for the applications of photocatalysis and cosmetic physical UV blocker. In this study, there are two strategies to synthesize the defect-tailored ZnO. First, as graphene oxide (GO) is used as an additive in a solvothermal reaction, paramagnetic VO+ and VZn- defects are formed in ZnO. Whereas, in the absence of GO, only paramagnetic VO+ defects are produced through oxygen desorption. Experimental results indicate that GO not only acts as a catalyst for the ionization reaction, but also changes the dominant defect formation pathway in ZnO lattice. Both GO and reduced graphene oxide (rGO) function as catalysts for further ionization to create paramagnetic zinc and oxygen vacancies, respectively.
ZnO/rGO with many zinc and oxygen vacancies exhibits significant photocatalytic activity. Photoluminescence and electron paramagnetic resonance measurements indicate that the zinc vacancies and oxygen vacancies are generated on the ZnO surface, and are crucial to that photocatalytic behavior. The photodegradation of methylene orange is significantly reduced by the addition of scavengers with the ZnO/rGO by scavenges of h+ and •OH. Both zinc and oxygen vacancies cause effective charge separation in the photodegradation of methylene orange, which markedly inhibits the recombination of charges.
Second, thermal decompose of amorphous/layered basic zinc salts (LBZ) spheres is used to prepare highly defected ZnO with Mie scattering properties as a cosmetic physical UV blocker material. Amorphous/layered basic zinc salts spheres are synthesized in a reflux reaction. The trisodium citrate is employed as the chelating agent. The sphere size is controlled by the nuclei number which depends on the competition between hydroxyl ion and citrate to complex with Zn2+. The formation pathway and morphology evolution are discussed.
The wurtzite ZnO sphere obtained by thermal decomposition exhibits the visible absorption owing to the oxygen vacancies in ZnO lattice. In addition, excess oxygen vacancies in the ZnO spheres become a recombination center and reduced the radical formation during photocatalysis. The uniform microspheres exhibit Mie scattering in the visible range due to the interaction with specific incident electromagnetic radiation, and thus the full absorption spectrum is easily obtained by tuning the size of spheres. Such uniform ZnO spheres exhibit superior visible absorption and Mie scattering effects thus is expected for the material of cosmetic physical UV blocker.

並列關鍵字

zinc oxide ； defect ； photocatalyst ； Mie scattering

參考文獻

142. T.-T. Chen, I. C. Chang, M.-C. Tsai, Y.-C. Chang, M.-H. Yang, P.-C. Chen, H.-T. Chiu and C.-Y. Lee, CrystEngComm, 2014, 16, 3341-3347.

121. E. Hendry, F. Wang, J. Shan, T. F. Heinz and M. Bonn, Physical Review B, 2004, 69, 081101.

55. D. R. Dreyer, H.-P. Jia and C. W. Bielawski, Angewandte Chemie International Edition, 2010, 49, 6813-6816.

112. Z. Xia, J. Sha, Y. Fang, Y. Wan, Z. Wang and Y. Wang, Crystal Growth & Design, 2010, 10, 2759-2765.

98. G. D. Yuan, W. J. Zhang, J. S. Jie, X. Fan, J. A. Zapien, Y. H. Leung, L. B. Luo, P. F. Wang, C. S. Lee and S. T. Lee, Nano Letters, 2008, 8, 2591-2597.