Inorg Chem. 2019 Dec 2;58(23):15710-15719. doi: 10.1021/acs.inorgchem.9b00905. Epub 2019 Nov 13.
Layered double hydroxide (LDH) has emerged as promising candidates for removing harmful oxoanions (i.e., SO, HPO, and NO ions) from wastewater because of their intrinsic ability to accommodate anionic species in the interlayer space. Highly crystalline [NiCo(OH)]Cl·0.53HO (Ni-Co LDH) particles with an exceptionally high anion-exchange capacity of 58.8 mg g and a distribution coefficient () of 2396 mL g for NO ions were successfully prepared by the flux method and a topochemical strategy. Layered NaNiCoO (NNCO) was prepared using a high-temperature flux and used as a starting material for topotactic transformation consisting of oxidative hydrolysis with KOH and NaClO and subsequent reduction with HO and NaCl. During the transformation from NNCO to Ni-Co LDH, a drastic change in the valences of the Ni and Co belonging to the host layer and in the cationic and anionic species occurs in interlayer space; the valences of the Ni and Co in NNCO were increased from Ni and Co to Ni and Co by an oxidative hydrolysis reaction with simultaneous intercalation of K ions and deintercalation of Na ions, and subsequently decreased from Ni and Co to Ni and Co by a reduction reaction with simultaneous intercalation of anionic species such as CO and Cl ions and deintercalation of Na and K ions. Through synchrotron powder X-ray diffraction analysis and Rietveld refinement, the resultant Ni-Co LDH was clearly shown to exhibit high crystallinity with less compositional deviation even after topochemical transformation in comparison with the one prepared by traditional coprecipitation and solid-state methods. Furthermore, the adsorption isotherm for NO ions elucidated that homogeneous adsorption sites are consistently constructed in the crystal structure, which could be found from the fitting to a Langmuir curve, with the value being 0.98. This work opens up a new route for the fabrication of excellent not only ion-exchangeable but also ion-conductive inorganic materials for direct utilization in environmental and energy-storage processes.
层状双氢氧化物 (LDH) 因其内在的阴离子容纳能力而成为从废水中去除有害含氧阴离子（即 SO、HPO 和 NO 离子）的有前途的候选物。通过通量法和拓扑化学策略，成功制备了具有极高阴离子交换容量（58.8mg/g）和对 NO 离子的分配系数（2396mL/g）的高结晶度 [NiCo(OH)]Cl·0.53HO (Ni-Co LDH) 颗粒。使用高温通量制备层状 NaNiCoO (NNCO)，并将其用作包括 KOH 和 NaClO 氧化水解以及随后用 HO 和 NaCl 还原的拓扑转化的起始材料。在从 NNCO 到 Ni-Co LDH 的转化过程中，主体层中 Ni 和 Co 的价态以及层间空间中阳离子和阴离子物种发生剧烈变化；NNCO 中 Ni 和 Co 的价态通过与同时插层 K 离子和脱钠离子的氧化水解反应从 Ni 和 Co 增加到 Ni 和 Co，随后通过与同时插层阴离子物种（如 CO 和 Cl 离子）和脱钠和 K 离子的还原反应从 Ni 和 Co 降低到 Ni 和 Co。通过同步辐射粉末 X 射线衍射分析和 Rietveld 精修，与传统共沉淀和固态方法制备的 Ni-Co LDH 相比，即使在拓扑转化后，所得 Ni-Co LDH 仍表现出较高的结晶度和较少的组成偏差。此外，NO 离子的吸附等温线表明，在晶体结构中始终构建了均匀的吸附位，这可以从对 Langmuir 曲线的拟合中找到， 值为 0.98。这项工作为制造不仅可离子交换而且可离子传导的无机材料开辟了一条新途径，可直接用于环境和储能过程。
