物理化学学报 >> 2019, Vol. 35 >> Issue (6): 644-650.doi: 10.3866/PKU.WHXB201805068

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ZnO纳米棒阵列到纳米管结构的自转化机制及其在相变封装材料中的应用

冯英杰1,王进平2,刘丽丽1,王习东1,*()   

  1. 1 北京大学工学院,北京 100871
    2 中国石化北京化工研究院,北京 100013
  • 收稿日期:2018-05-24 录用日期:2018-07-04 发布日期:2018-07-09
  • 通讯作者: 王习东 E-mail:xidong@pku.edu.cn
  • 基金资助:
    51472006(北京市公共发展基金及国家自然科学基金)

Self-Conversion from ZnO Nanorod Arrays to Tubular Structures and Their Applications in Nanoencapsulated Phase-Change Materials

Yingjie FENG1,Jinping WANG2,Lili LIU1,Xidong WANG1,*()   

  1. 1 College of Engineering, Peking University, Beijing 100871, P. R. China
    2 Beijing Research Institute of Chemical Industry, SINOPEC, Beijing 100013, P. R. China
  • Received:2018-05-24 Accepted:2018-07-04 Published:2018-07-09
  • Contact: Xidong WANG E-mail:xidong@pku.edu.cn
  • Supported by:
    The project was supported by the Common Development Fund of Beijing, China and the National Natural Science Foundation of China(北京市公共发展基金及国家自然科学基金)

摘要:

基于极性晶体的晶面能理论,不添加任何辅助添加剂,本论文仅通过调节水热结晶条件实现了对ZnO纳米管阵列结构的可控合成。通过晶体表面能计算表明,具有Zn终端的[0001]面由于具有较高的表面能,属于不稳定晶面。因此,随着生长结晶过程的进行,为了最终达到系统的低能量稳定状态,ZnO纳米棒的顶面[0001]面会逐渐优先溶解,并最终形成管状结构。其中,与晶面能紧密相关的溶解结晶平衡浓度是影响管状结构形成的重要因素。本论文通过确定水热生长条件下,ZnO纳米棒向纳米管结构转变的临界浓度,成功验证了由棒状结构向管状结构的自转化机理并缩短了管状结构的转化时间。由于ZnO纳米管阵列优秀的传导性能和可填充性,以及对基底材料的广泛适用性等特点,本研究进一步将其应用在相变材料的封装领域。实验结果表明,ZnO纳米管阵列薄膜封装相变材料表现出更好的热传导性能和储放热性能,在恒温器件领域展现出良好的应用潜力。

关键词: ZnO纳米管, 表面能, 溶解结晶平衡, 自转化, 相变封装材料

Abstract:

In the emerging field of nanoscience, tubular structures have been attracting remarkable interest due to their well-defined geometry, high specific area, and exceptional physical and chemical properties. Among them, oriented ZnO tubular arrays are regarded as promising candidates for various applications such as optoelectronics, solar cells, sensors, field emission, piezoelectrics, and catalysis. Although template-directed and selective dissolution synthesizing strategies are commonly used to prepare ZnO nanotubes, repeatability and large scale preparation are still challenging. In this study, ZnO nanotube arrays were controllably prepared by tuning the hydrothermal parameters, without the use of any additives. The mechanism underlying the self-conversion of ZnO nanorods to nanotubes was comprehensively studied based on the surface energy theory. It has been proved that the metastable top surface of the ZnO nanorods dissolves preferentially to reach a stable state during the hydrothermal growth. The specific surface energy of different crystal faces of ZnO nanorods was calculated using molecular dynamics simulation. The top surface of the ZnO nanorod, the Zn-terminated [0001] face, demonstrated much higher surface free energy than did the lateral faces, which indicated that the self-dissolution of top face (002) is energetically favorable. The self-conversion behavior of ZnO nanorod arrays with different diameters was specifically investigated by adjusting the initial precursor concentration, density of the crystal seed layers, and growth time. The dissolution-crystallization equilibrium concentration, determined by crystal surface energy, was found to be a key factor for the formation of the tubular structure. Notably, the critical equilibrium conditions for the self-conversion of ZnO nanorods to nanotubes, including zinc ion concentration and pH, have been identified by studying parameters corresponding to the dissolution-crystallization equilibrium for the metastable top surface of the ZnO nanorods. The preparation of the ZnO nanotube arrays was successfully accelerated and simplified via two-step procedure: (1) preparation of ZnO nanorod arrays and (2) self-conversion of ZnO nanorods to nanotubes. The preparation method based on the self-conversion mechanism from rods to tubes for polar oxides is simpler and more easily controllable as compared to the reported methods involving variety of additives. Because of the advantages of adaptability to a wide range of substrates, excellent conducting properties, and filling ability, the prepared ZnO nanotube array films were used in encapsulating phase-change materials. The encapsulated phase-change material exhibited excellent heat storage/release properties and heat conductivities. This indicates the potential application of precision devices for temperature control.

Key words: ZnO nanotubes, Crystal surface energy, Dissolution-crystallization equilibrium, Self-conversion, Encapsulated phase-change materials

MSC2000: 

  • O647