Hydrogen assisted synthesis of branched nickel nanostructures: a combined theoretical and experimental study
Hydrogen assisted synthesis of branched nickel nanostructures: a combined theoretical and experimental study
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氢辅助合成支化镍纳米结构：理论与实验相结合的研究
DOI：
10.1039/c7cp04673a
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发表时间：
2017
影响因子：
3.3
通讯作者：
Chen Biaohua
中科院分区：
文献类型：
--
作者：
Liang Xin;Liu Ning;Qiu Huiyun;Zhang Cong;Mei Donghai;Chen Biaohua
小分子在特定晶面上的选择性吸附在形貌可控的金属纳米晶合成中起着重要作用。在本工作中，氢气是一种很好的封闭剂，可以直接合成支化镍纳米晶，即二次支化(Ni-Sb)纳米颗粒和多孔(Ni-MP)纳米颗粒。利用从头算热力学和Wulff结构原理，发现：(I)在氢气存在下(PH2=6bar)，小面结构的稳定性遵循Ni(100)>；Ni(111)>；Ni(110)的顺序，导致沿<；111>；和<；110>；方向的竞争过生长；(Ii)随着氢气压力的增加，由于Ni2+的大量还原，在晶体表面沉积镍的速率增加，沉积和表面扩散之间的竞争成为纳米晶生长过程的关键因素；(3)表面Ni原子在Ni(111)面上的扩散能垒低于在Ni(110)面上的扩散能垒，尤其是在氢覆盖的表面上，表明在PH2=14bar时，只沿<；111>；方向的动力学过度生长将占主导地位；(Iv)基于从头算的Wulff结构原理预测了不同氢压下的形状和形貌，HRTEM结果进一步证实了这一点。最后，与无氢条件下合成的镍纳米粒子(Ni-NP)相比，氢助支化镍纳米材料，尤其是Ni-MP，对苯乙酮和硝基苯的加氢反应表现出更高的催化活性。
The selective adsorption of small molecules over specific facets plays an important role in morphology controlled synthesis of metal nanocrystals. In the present work, hydrogen is found to be a good capping agent for direct synthesis of branched nickel nanocrystals, i.e., secondary branching (Ni-SB) nanoparticles and multipods (Ni-MP). Using ab initio thermodynamics and the Wulff construction principle, it has been found that: (i) in the presence of hydrogen (PH2 = 6 bar), the facet structure stability follows the order of Ni(100) > Ni(111) > Ni(110), resulting in competitive over-growth along the <111> and <110> directions; (ii) with increasing hydrogen pressure, the Ni deposition rate over the crystal surface increases as a result of more Ni2+ reduction; the competition between deposition and surface diffusion, therefore, becomes the vital factor for the nanocrystal growth process; (iii) the diffusion energy barrier of a surface Ni atom on Ni(111) is lower than that on Ni(110), especially on hydrogen covered surfaces, indicating that the kinetic over-growth only along the <111> direction producing Ni-MP will be dominant under PH2 = 14 bar; (iv) the ab initio based Wulff construction principle predicts the shapes and morphologies at different hydrogen pressures which is further confirmed with HRTEM results. Finally, compared with nickel nanoparticles (Ni-NP) synthesized in the absence of hydrogen, the hydrogen assisted branched Ni nanomaterials, especially the Ni-MP, show higher catalytic activities for hydrogenation reactions of acetophenone and nitrobenzene.