Deterioration of anion-adsorption abilities of layered double hydroxides synthesized in agarose gel
Deterioration of anion-adsorption abilities of layered double hydroxides synthesized in agarose gel
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DOI：
10.1016/j.clay.2019.105435
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发表时间：
2020-03
影响因子：
5.6
通讯作者：
T. Hibino
中科院分区：
文献类型：
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作者：
T. Hibino
为了改善废水处理中的固液分离性能，在琼脂糖凝胶中合成了Mg-Al层状双氢氧化物（LDH），并将所得的含LDH的杂化水凝胶干燥。干燥的水凝胶的阴离子吸附能力进行了比较与LDH通过常规的恒pH值共沉淀法在低过饱和度合成。发现了一个令人惊讶的结果：干燥的杂化水凝胶的吸附能力随储存时间而降低，而通过常规方法合成的LDH的吸附能力基本保持不变。进一步的研究表明，通过快速混合Mg-Al水溶液和NaOH水溶液在高过饱和度（即，与用于制备混合水凝胶的方法类似的方法）也随时间降低。因此，只有LDH合成的共沉淀在高过饱和度显示恶化在存储时间的阴离子吸附能力。观察到的结果，伴随着恶化表明，减少是由于形成的口袋中的相互相邻的Al占据的阳离子位点的金属氢氧化物层的Mg-Al LDH作为一个结果的快速混合的起始溶液。相互邻近的Al占据位点的存在被认为是由于相互排斥而不稳定的。这种不稳定性可能导致含有相邻Al占据位点的氢氧化物部分与层间OH-和Cl−阴离子一起逐渐分解，形成氢氧化铝或碱式氯化铝，以及附近的Mg（OH）2部分从LDH结构中分离。
With the goal of improving solid–liquid separability in wastewater treatment, Mg-Al layered double hydroxides (LDH) were synthesized in agarose gel, and the resulting LDH-containing hybrid hydrogels were dried. The anion-adsorption abilities of the dried hydrogels were compared with those of LDH synthesized by means of a conventional constant-pH coprecipitation method at low supersaturation. A surprising result was found: the adsorption abilities of the dried hybrid hydrogels decreased with storage time, whereas the adsorption abilities of the LDH synthesized by the conventional method remained essentially constant. Further investigation revealed that the adsorption abilities of LDH synthesized by rapid mixing of aqueous Mg-Al and aqueous NaOH at high supersaturation (i.e., a method similar to that used to prepare the hybrid hydrogel) also decreased over time. Therefore, only LDH synthesized by coprecipitation at high supersaturation showed deterioration during storage time in anion-adsorption abilities. Observed results that accompanied the deterioration suggest that the decrease was due to the formation of pockets of mutually adjacent Al-occupied cation sites in the metal hydroxide layers of the Mg-Al LDH as a result of rapid mixing of the starting solutions. The presence of mutually adjacent Al-occupied sites is thought to be in instability due to mutual repulsion. This instability may have led to gradual decomposition of hydroxide moieties containing mutually adjacent Al-occupied sites together with interlayer anions of OH–and Cl−to form aluminum hydroxide or basic aluminum chloride, as well as to separation of nearby Mg(OH)2moieties from LDH structure.