A swarm of liquid metal microdroplets for recyclable catalysis with high spatial-temporal precision

Nanocatalysts have aroused broad interest due to their long-lasting water-remediation capability. However, conventional nanocatalysts based on noble-metal nanoparticles rely on passive solute diffusion. Therefore, demands for improvements in yields of desired products, reductions in the use of noble metals, and improvements in nanocatalyst recyclability by magnetic separation pose significant challenges to the passive nanocatalysts. Herein, we developed a general method for liquid metal microdroplets modification with noble metal nanoparticles (e.g., Au and Ag), resulting in microdroplets with exceptional catalytic properties to decompose organic pollutants. The LM-Fe@PDA@Au and LM-Fe@PDA@Ag catalysts were dynamically well assembled, and they moved according to predesigned trajectories under magnetic-field control. The liquid metal microdroplets, on the one hand, are microscale matrices for embedding the magnetic particles; on the other hand, are microscale carriers for the fixation of noble metal nanoparticles, to maintain the uniform segregation of the nanoparticles. Due to their excellent mobility and three-dimensional convection, the catalysts could conduct an on-the-fly catalysis with high spatial-temporal precision at preassigned locations. Compared to conventional passive nanocatalysts based on noble-metal nanoparticles, the liquid metal microdroplets catalysts, which were based on the active colloidal swarms, showed temporally and spatially enhanced catalytic activity and improved catalytic rate constants. The catalysts could be easily collected using a magnet, and their inner liquid metal microdroplets could be recycled by treating the catalysts with a base. The work is of potential industrial significance to enhance the catalytic efficiency and shorten the catalytic time during water remediation, with the precious inner components recyclable.