MOF-Derived Cu-TiO₂/Alginate Micromotors for Buoyancy-Regulated 3D Motion

Micro- and nanomotors (MNMs) promise impact in the areas of environmental remediation and biomedicine, but reliable three-dimensional (3D) control remains challenging. Conventional bubble-propelled MNMs can move in 3D, yet their trajectories are stochastic and energy-inefficient. Here we introduce a buoyancy-regulated strategy inspired by cyanobacteria-like microvesicles. We engineer sodium-alginate (SA)hydrogel magnetic micromotors (SA/Cu-TiO₂/Fe₃O₄), in which Cu-TiO₂ is derived from the Ti-based metal-organic framework MIL-125(Ti_v), yielding a porous and defect-rich photocatalyst with uniformly distributed Cu sites for enhanced H₂O₂ decomposition and photocatalytic activity compared with pristine TiO₂. Upon illumination, Cu-TiO₂ catalyzes H₂O₂ decomposition to generate O₂ pockets that are retained within the elastic, semipermeable alginate matrix, enabling programmable flotation and precise control of vertical (Z-axis) position as part of full 3D navigation. We analyze the energetics and cross-scale mass-transport mechanisms governing this buoyancy control, and we demonstrate guided 3D motion through a maze via magnetic steering. In model turbid water, the micromotors achieve high removal performance across diverse organic contaminants. This bioinspired platform provides a prototype and motion-control paradigm for 3D-motile MNMs, advancing practical remediation in aquatic environments.