Alameda Lucas T, Moradifar Parivash, Metzger Zachary P, Alem Nasim, Schaak Raymond E
J Am Chem Soc. 2018 Jul 18;140(28):8833-8840. doi: 10.1021/jacs.8b04705. Epub 2018 Jul 6.
The synthesis of refractory materials usually relies on high-temperature conditions to drive diffusion-limited solid-state reactions. These reactions result in thermodynamically stable products that are rarely amenable to low-temperature topochemical transformations that postsynthetically modify subtle structural features. Here, we show that topochemical deintercalation of Al from MoAlB single crystals, achieved by room-temperature reaction with NaOH, occurs in a stepwise manner to produce several metastable Mo-Al-B intergrowth phases and a two-dimensional MoB (MBene) monolayer, which is a boride analogue to graphene-like MXene carbides and nitrides. A high-resolution microscopic investigation reveals that stacking faults form in MoAlB as Al is deintercalated and that the stacking fault density increases as more Al is removed. Within nanoscale regions containing high densities of stacking faults, four previously unreported Mo-Al-B (MAB) intergrowth phases were identified, including MoAlB, MoAlB, MoAlB, and MoAlB. One of these deintercalation products, MoAlB, is identified as the likely MAB-phase precursor that is needed to achieve a high-yield synthesis of two-dimensional MoB, a highly targeted two-dimensional MBene. Microscopic evidence of an isolated MoB monolayer is shown, demonstrating the feasibility of using room-temperature metastable-phase engineering and deintercalation to access two-dimensional MBenes.
耐火材料的合成通常依赖高温条件来驱动扩散受限的固态反应。这些反应会生成热力学稳定的产物，而这些产物很少能进行低温拓扑化学转变，从而对细微的结构特征进行合成后修饰。在此，我们表明，通过与氢氧化钠在室温下反应实现的从MoAlB单晶中进行Al的拓扑化学脱嵌，是以逐步方式发生的，产生了几种亚稳的Mo-Al-B共生相和二维MoB（MBene）单层，它是类似于石墨烯状MXene碳化物和氮化物的硼化物。高分辨率显微镜研究表明，随着Al被脱嵌，MoAlB中会形成堆垛层错，并且随着更多Al被去除，堆垛层错密度增加。在包含高密度堆垛层错的纳米尺度区域内，鉴定出了四个以前未报道的Mo-Al-B（MAB）共生相，包括MoAlB、MoAlB、MoAlB和MoAlB。这些脱嵌产物之一MoAlB被确定为可能是高产率合成二维MoB（一种高度靶向的二维MBene）所需的MAB相前驱体。展示了孤立的MoB单层的微观证据，证明了使用室温亚稳相工程和脱嵌来获得二维MBene的可行性。
