Reduced Graphene Oxide Conjugated Cu₂O Nanowire Mesocrystals for High-Performance NO₂ Gas Sensor

作者: Suzi Deng, Verawati Tjoa, Hai Ming fan*, Hui Ru Tan, Dean C. Sayle, Malini Olivo, Subodh Mhaisalkar, Jun Wei, Chorng Haur Sow *
期刊：J. Am. Chem. Soc.2012, 134, 4905-4917

摘 要:Reduced graphene oxide (rGO)-conjugated Cu₂O nanowire mesocrystals were formed by nonclassical crystallization in the presence of GO and o-anisidine under hydrothermal conditions. The resultant mesocrystals are comprised of highly anisotropic nanowires as building blocks and possess a distinct octahedral morphology with eight {111} equivalent crystal faces. The mechanisms underlying the sequential formation of the mesocrystals are as follows: first, GO-promoted agglomeration of amorphous spherical Cu₂O nanoparticles at the initial stage, leading to the transition of growth mechanism from conventional ion-by-ion growth to particle-mediated crystallization; second, the evolution of the amorphous microspheres into hierarchical structure, and finally to nanowire mesocrystals through mesoscale transformation, where Ostwald ripening is responsible for the growth of the nanowire building blocks; third, large-scale self-organization of the mesocrystals and the reduction of GO (at high GO concentration) occur simultaneously, resulting in an integrated hybrid architecture where porous three-dimensional (3D) framework structures interspersed among two-dimensional (2D) rGO sheets. Interestingly, “super-mesocrystals” formed by 3D oriented attachment of mesocrystals are also formed judging from the voided Sierpinski polyhedrons observed. Furthermore, the interior nanowire architecture of these mesocrystals can be kinetically controlled by careful variation of growth conditions. Owing to high specific surface area and improved conductivity, the rGO-Cu₂O mesocrystals achieved a higher sensitivity toward NO₂ at room temperature, surpassing the performance of standalone systems of Cu₂O nanowires networks and rGO sheets. The unique characteristics of rGO-Cu₂O mesocrystal point to its promising applications in ultrasensitive environmental sensors.

简评：介观晶体(Mesocrystal)是一种胶体晶体 (colliod crystal),最早来源于胶体化学领域。它是晶体生长过程的一个中间态，由非球形的纳米基本单元按照材料本身晶体结构有序的组织起来的一种超结构(superstructure). 由于介观晶体是通过和生物矿化过程类似的一种非经典结晶方式，即通过纳米颗粒为前驱生长出来(nanoparticle mediate crystallization)，具备丰富的形貌近年吸引了很多注意力.目前大多数研究集中在了解其3维结构的生长机制。如果换个角度来看，人们或许可以利用这种生长方式由底至上的自组织生长有序的纳米颗粒构成的超结构。而这些超结构具备多种优良特性可以很容易的用于制备技术上有用的纳米器件。本文介绍了一种新的纳米线介观晶体，通过使用双亲的氧化石墨烯作为表面活性剂，成功的将生长过程由传统的离子前驱生长转变成了纳米颗粒为前驱的生长方式，即先形成了非晶的纳米颗粒，这些纳米颗粒在聚合物和GO的作用下团聚成微米尺寸的胶体球；这些球状聚集体经过介观尺度结构变形(mesoscale transformation)，最终形成了由相互贯穿的高个向异性纳米线组成的介观晶体。这个结构和我们在日常生活中所见的建筑工地的脚手架非常类似。在生成介观晶体的同时，氧化石墨烯在水热条件下还原成“还原氧化石墨烯”（想请教一下，rGO怎么翻译比较合适?),在高氧化石墨烯含量的时候和介观晶体杂化形成网络体系。这个杂化网络体系被制作成气体传感器，在室温下，对NO2气体有很好的检测性能，最低检测浓度为64ppb. 这个工作提供了一种新的介观晶体体系，其GO辅助的生长方式和原位杂化，可广泛用于合成其他类似的介观晶体体系。同时，介观晶体所具备的多种多样的自组装纳米结构可提供许多独特的物理化学性质，因此有望在光学，传感器，催化的多个领域有重要的应用。




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