Lee Won Jun, Bernasek Steven L, Han Chong Soo
Department of Chemistry, Chonnam National University, Gwangju 61186, Korea.
Nano Bio Research Institute, Jeonnam Bioindustry Foundation, Jangseong 57248, Jeollanamdo, Korea.
ACS Omega. 2018 Sep 30;3(9):11544-11549. doi: 10.1021/acsomega.8b01453. Epub 2018 Sep 20.
The rice plant produces an amorphous silica layer in the husk covering the brown rice grain as a part of a protective respiration system. The layer shows high permeation molecular flow while the Brunauer-Emmett-Teller isotherm indicates the existence of nanometer-sized pores. Here, we interpret the inner structure of the layer as a porous network consisting of void spheres with a degree of 2-5 and tunnels with a length of 2-7 nm based on the transmission electron microscopy images. In the network, the gas molecules travel through the tunnels and move in random directions after collisions with the walls of the spheres. A tree network was introduced to understand the permeance of the layer and the reflection of the molecule of the root or parent sphere was estimated for a specific case. The tree becomes a graph with cycles in a finite space such as the silica layer and the reflection of the root sphere in the graph converses to that of the tree. On the basis of the properties of the network, the high permeance of the silica layer in the rice husk can be explained. It is suggested that the specific system restricts the movements of the gas molecules and can be applied to reduce the size of gas phase separation and chemical reactor systems providing a new view to understand nanoscaled porous materials.
水稻植株在覆盖糙米的稻壳中产生一层无定形二氧化硅层，作为其保护性呼吸系统的一部分。该层显示出高渗透分子流，而布鲁诺尔-埃米特-泰勒等温线表明存在纳米级孔隙。在此，基于透射电子显微镜图像，我们将该层的内部结构解释为由二维至五维的空球和长度为2至7纳米的通道组成的多孔网络。在该网络中，气体分子穿过通道，并在与球壁碰撞后向随机方向移动。引入树形网络以理解该层的渗透率，并针对特定情况估计根球或母球分子的反射率。树形网络在诸如二氧化硅层这样的有限空间中成为具有循环的图，并且图中根球的反射率与树形网络的反射率相同。基于该网络的特性，可以解释稻壳中二氧化硅层的高渗透率。研究表明，该特定系统限制了气体分子的运动，可应用于减小气相分离和化学反应器系统的尺寸，为理解纳米级多孔材料提供了新视角。
