Piña-Salazar Elda Zoraida, Sagisaka Kento, Hayashi Takuya, Hattori Yoshiyuki, Sakai Toshio, Ōsawa Eiji, Kaneko Katsumi
Research Initiative for Supra-Materials, Interdisciplinary Cluster for Cutting Edge Research, Shinshu University, Nagano 380-8553, Japan.
Division of Chemistry and Materials, Faculty of Textile Science and Technology, Shinshu University, Ueda 386-8567, Japan.
Nanomaterials (Basel). 2021 Oct 20;11(11):2772. doi: 10.3390/nano11112772.
Detonation nanodiamond aggregates contain water that is removed by thermal treatments in vacuo, leaving available pores for the adsorption of target molecules. A hard hydrogel of detonation nanodiamonds was thermally treated at 423 K for 2 h, 10 h, and 52 h in vacuo to determine the intensive water adsorption sites and clarify the hygroscopic nature of nanodiamonds. Nanodiamond aggregates heated for long periods in vacuo agglomerate due to the removal of structural water molecules through the shrinkage and/or collapse of the pores. The agglomerated nanodiamond structure that results from long heating periods decreases the nitrogen adsorption but increases the water adsorption by 40%. Nanodiamonds heated for long times possess ultramicropores <0.4 nm in diameter in which only water molecules can be adsorbed, and the characteristic mouth-shaped mesopores adsorb 60% more water than nitrogen. The pore mouth controls the adsorption in the mesopores. Long-term dehydration partially distorts the pore mouth, decreasing the nitrogen adsorption. Furthermore, the nitrogen adsorbed at the pore mouth suppresses additional nitrogen adsorption. Consequently, the mesopores are not fully accessible to nitrogen molecules because the pore entrances are blocked by polar groups. Thus, mildly oxidized detonation nanodiamond particles can show a unique molecular sieving behavior.
爆轰纳米金刚石聚集体含有通过真空热处理去除的水，从而留下可供吸附目标分子的孔隙。对爆轰纳米金刚石的硬水凝胶在423K下进行2小时、10小时和52小时的真空热处理，以确定密集的水吸附位点并阐明纳米金刚石的吸湿特性。由于通过孔隙的收缩和/或坍塌去除结构水分子，在真空中长时间加热的纳米金刚石聚集体会发生团聚。长时间加热导致的团聚纳米金刚石结构会降低氮吸附，但会使水吸附增加40%。长时间加热的纳米金刚石具有直径小于0.4nm的超微孔，其中只能吸附水分子，而特征性的口形中孔吸附的水比氮多60%。孔口控制着中孔内的吸附。长期脱水会使孔口部分变形，降低氮吸附。此外，吸附在孔口的氮会抑制额外的氮吸附。因此，由于孔口被极性基团堵塞，氮分子无法完全进入中孔。因此，轻度氧化的爆轰纳米金刚石颗粒可以表现出独特的分子筛分行为。
