Autonomous extraction and separation for rare-earth metals using self-propelled droplets with a pH-responsive function

我们已经开发了自推进液滴，其具有检测化学梯度、向特定金属离子的较高浓度移动并提取该金属离子的能力。这种能力依赖于DEHPA对pH的高表面活性以及DEHPA对镝离子的亲和力。我们使用两种外部刺激作为化学信号来控制液滴运动：pH信号诱导运动，金属离子诱导方向感测。负载DEHPA的油滴自发地四处移动超过pH阈值，即使在均匀的pH场。在含有金属离子的凝胶块的存在下，液滴显示定向感测，并且它们的运动偏向于更高的浓度。金属离子的方向感测顺序为Dy>>Nd>Y>Gd。此外，通过原子吸收分光光度计的组分分析表明，金属离子可以被提取到液滴的内部。

We have developed self-propelled droplets having the abilities to detect a chemical gradient, to move toward a higher concentration of a specific metal ion, and to extract it. Such abilities rely on the high surface activity of DEHPA in response to pH and the affinity of DEHPA for the dysprosium ion. We used two external stimuli as chemical signals to control droplet motion: a pH signal to induce motility, and metal ions to induce directional sensing. The oil droplets loaded with DEHPA spontaneously move around beyond the threshold of pH even in a homogeneous pH field. In the presence of a gel block containing metal ions, the droplets show directional sensing and their motility is biased toward higher concentrations. The metal ions can be arranged in decreasing order of directional sensing as Dy>>Nd>Y>Gd. Furthermore, the analysis of component by an atomic absorption spectrophotometer reveals that the metal ions can be extracted to the interiors of the droplets.