Weizheng Wang,Yumeng Zhang,Wenhui Wu,Xiaoyu Liu,Xuanxuan Ma,Guixiang Qian,Jiyang Fan
The organic–inorganic hybrid metal halide perovskites with different dimensions and diverse architectures are highly attractive materials for optoelectronic applications. However, people know little about the dynamics of their formation processes. Here, we study both experimentally and theoretically the self-assembly formation dynamics of the luminescent colloidal CH3NH3PbBr3 nanocrystals. We have observed their successive transformations from original spherical quantum dots to periodically stacked nanoplatelets when the primitive colloidal nanocrystals with a high concentration were maintained in liquid for a prolonged period of time. A theoretical dynamic collision model by taking into account the popular van der Waals force, the polarization force that is unique for the perovskites, and the electrostatic forces between particle surfaces in the presence of the surface ligands is proposed to explain the self-assembly process of the colloidal CH3NH3PbBr3 nanocrystals. The result reveals that the rather easy self-assembly of the organic–inorganic hybrid perovskites with different morphologies in the absence of enough surface ligands is closely related to their intrinsic polarization force, whereas the presence of the surface ligands could hamper the self-assembly process. The proposed theoretical model is general and can be used to analyze the self-assembly dynamics of various types of colloidal nanostructures.
Hui Zhang,Qiang Fu,Hongyun Qin,Xia Chen,Qicheng Zhang,Zixu Dong,Haoyuan Li,Shoudong Wang,Ming Wang
Hydrogen recovery from ammonia purge gas is a desirable method to relieve the pressure of increasing demand for hydrogen. Metal-organic frameworks (MOFs) are promising adsorbents for the separation of the H 2 –N 2 mixture. However, the separation of the H 2 –N 2 mixture using MOFs remains challenging due to the lack of adsorptive mechanism. Herein, the adsorption mechanism of the H 2 –N 2 mixture in SIFSIX-2-Cu-i has been systematically investigated with the method of a combination of excess adsorption experiments, molecular simulations , and DFT calculations. In the Grand Canonical Monte Carlo (GCMC) simulations, the polarizable force field was first applied to the adsorption of pure H 2 or N 2 and H 2 –N 2 mixture in SIFSIX-2-Cu-i. Ab Initio Molecular Dynamics (AIMD) was performed to investigate the distribution of the guest molecules in the pores of SIFSIX-2-Cu-i. Finally, Density functional theory (DFT) calculations were performed to predict the transfer of charge between MOF and guest molecules. Results revealed two binding sites of H 2 or N 2 in SIFSIX-2-Cu-i. A relatively high thermodynamic adsorption selectivity for N 2 over H 2 has been observed in SIFSIX-2-Cu-i. Furthermore, SIFSIX-2-Cu-i also exhibits a greater affinity with N 2 than with H 2 , which is probably because of the stronger induction interactions between F2 atoms and N 2 molecules. These findings are of significance to guide the design of the new highly selective adsorbents for the separation of H 2 /N 2 .
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