Zhao Bing, Guo Min, Qian Zhiqiang, Li Jun, Wu Zhijian, Liu Zhong
Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China.
Dalton Trans. 2020 Oct 20;49(40):14180-14190. doi: 10.1039/d0dt02960b.
The ion-exchange process is usually influenced by the surface properties of the adsorbents. In particular, the prophase adsorption/desorption process is confined by different crystal facets. In this research, spinel Li4Ti5O12 nanosheets with an exposed (1-14) high-index facet were prepared by a hydrothermal method followed by calcination treatment. Then, a H4Ti5O12 adsorbent was obtained, covered with the same (1-14) facets, after treatment with 0.2 M HCl. This special facet-exposed H4Ti5O12 has high cycling ability, with the adsorption uptake remaining at 96.84% after four cycles, a fast adsorption equilibrium time (equilibrium time < 60 min), excellent ion adsorption selectivity for Li+ uptake (separation factor: Li+ > K+ > Ca2+ > Na+ > Mg2+), and good adsorption capacity for Li+ uptake (21.57 mg g-1 ). With the help of X-ray photoelectron spectroscopy analyses, the Li+ adsorption process on the H4Ti5O12 nanosheets is shown to be an ion-exchange process. In addition, the coordination relationship between lithium and oxygen ions was investigated, illustrating that the four-coordinated structure is more stable than other complexes. These results indicate that hydrogen ions are exchanged for lithium ions at tetrahedral 8a sites, leading to the H4Ti5O12 structure with high stability in the adsorption-desorption cycling process.
离子交换过程通常受吸附剂表面性质的影响。特别是，前期的吸附/解吸过程受不同晶面的限制。在本研究中，通过水热法并经过煅烧处理制备了具有暴露的（1-14）高指数晶面的尖晶石Li4Ti5O12纳米片。然后，用0.2 M HCl处理后获得了覆盖有相同（1-14）晶面的H4Ti5O12吸附剂。这种特殊的暴露晶面的H4Ti5O12具有高循环能力，四个循环后吸附量保持在96.84%，吸附平衡时间快（平衡时间<60分钟），对Li+吸收具有优异的离子吸附选择性（分离因子：Li+>K+>Ca2+>Na+>Mg2+），对Li+吸收具有良好的吸附容量（21.57 mg g-1）。借助X射线光电子能谱分析，表明H4Ti5O12纳米片上的Li+吸附过程是一个离子交换过程。此外，研究了锂和氧离子之间的配位关系，表明四配位结构比其他配合物更稳定。这些结果表明，氢离子在四面体8a位点与锂离子交换，导致H4Ti5O12结构在吸附-解吸循环过程中具有高稳定性。
