Abstract 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)2 moieties from LDH structure.

中文翻译：

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琼脂糖凝胶合成层状双氢氧化物阴离子吸附能力下降

摘要 为了提高废水处理中的固液分离性，在琼脂糖凝胶中合成了镁铝层状双氢氧化物（LDH），并干燥所得的含LDH的杂化水凝胶。将干燥的水凝胶的阴离子吸附能力与通过常规恒定 pH 共沉淀法在低过饱和度下合成的 LDH 的阴离子吸附能力进行了比较。发现了一个令人惊讶的结果：干燥的混合水凝胶的吸附能力随着储存时间的延长而降低，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，通过在高过饱和度下快速混合 Mg-Al 水溶液和 NaOH 水溶液合成 LDH 的吸附能力（即 一种类似于用于制备混合水凝胶的方法）也随着时间的推移而减少。因此，只有在高过饱和度下通过共沉淀合成的 LDH 在阴离子吸附能力的储存期间表现出恶化。伴随恶化的观察结果表明，由于起始溶液的快速混合，在 Mg-Al LDH 的金属氢氧化物层中形成了相互相邻的铝占据阳离子位点的口袋。由于相互排斥，相互相邻的铝占据位点的存在被认为是不稳定的。这种不稳定性可能导致包含相互相邻的 Al 占据位点的氢氧化物部分与 OH- 和 Cl- 的层间阴离子逐渐分解，形成氢氧化铝或碱性氯化铝，