Photoactive and Intrinsically Fuel Sensing Metal–Organic Framework Motors for Tailoring Collective Behaviors of Active‐Passive Colloids

Abstract

Microorganisms display nonequilibrium predator–prey behaviors, such as chasing–escaping and schooling via chemotactic interactions. Even though artificial systems have revealed such biomimetic behaviors, switching between them by control over chemotactic interactions is rare. Here, a spindle‐like iron‐based metal–organic framework (MOF) colloidal motor which self‐propels in glucose and H2O2, triggered by UV light is reported. These motors display intrinsic UV light‐triggered fuel‐dependent chemotactic interactions, which are used to tailor the collective dynamics of active‐passive colloidal mixtures. In particular, the mixtures of active MOF motors with passive colloids exhibit distinctive “chasing–escaping” or “schooling” behaviors, depending on glucose or hydrogen peroxide being used as the fuel. The transition in the collective behaviors is attributed to an alteration in the sign of ionic diffusiophoretic interactions, resulting from a change in the ionic clouds produced. This study offers a new strategy on tuning the communication between active and passive colloids, which holds substantial potentials for fundamental research in active matter and practical applications in cargo delivery, chemical sensing, and particle segregation.

Bimetallic Photo-Activated and Steerable Janus Micromotors as Active Microcleaners for Wastewater

“…The motion of the BMT-micromotors in the presence of different molar solutions of NaCl is shown in Figure S6. It can be observed that the speed of the micromotor slows down with the concentration of the NaCl solution in the presence of 1.0 wt % H 2 O 2 , which is consistent with the ionic self-diffusiophoresis mechanism of the reported work. , As shown in the first image of Figure c and Video S1e, in the absence of UV light, the micromotor exhibits Brownian motion even in 0.5 wt % H 2 O 2 for the first two seconds, while it shows active self-propulsion with the speed of ≈28 μm/s when the light is turned on. We observed that micromotors are highly active toward H 2 O 2 fuel, and it can actively give response even when the fuel concentration decreases to only 0.01 wt %.…”

“…As a result, the Si−O−M (M = Co/Zn) linkage could generate, and TPM nucleates and grows on the surface of the particles. 40,41 Finally, the nucleated TPM was thermally polymerized with the aid of an AIBN initiator. The Janus morphology of the as-prepared materials contained a smooth passive TPM part and an active rough part of the Co/Zn-NC particle (Figures 1d and S1c,d).…”

“…In this process, the hydrolyzed TPM oil was dropwise added to the Co/Zn-NC suspension containing ammonia solution, which triggers the polycondensation reaction of the TPM oil on the surface of the seed particles. As a result, the Si–O–M (M = Co/Zn) linkage could generate, and TPM nucleates and grows on the surface of the particles. , Finally, the nucleated TPM was thermally polymerized with the aid of an AIBN initiator. The Janus morphology of the as-prepared materials contained a smooth passive TPM part and an active rough part of the Co/Zn-NC particle (Figures d and S1c,d).…”

“…For comparative adsorption studies of self-propelled micromotors with a static adsorbent, 1.0 wt % of H 2 O 2 was added under UV light irradiation with external magnetic field. The suspension was sampled for different time intervals (10,20,30,40,50, 60 min) and filtered by a 0.22 μm Millipore filter by a 2 mL syringe. Then, dilution was done with ultrapure water to meet the concentration limit of the tested instrument (ICP-MS) (Table S1).…”

Morphology-Tailored Dynamic State Transition in Active-Passive Colloidal Assemblies

“…Another important class of synthetic active materials are mixtures of active self-propelled colloids and passive ones [ 15 ]. Chemically propelled active colloids may attract one or multiple passive colloids via electrostatic [ 16 ], hydrophobic [ 17 ], and phoretic [ 18 – 21 ] interactions, self-assembling into translating clusters that hold applications in cargo loading and transportation, or exhibiting predator–prey type biomimetic functions [ 22 , 23 ]. Active colloids have also been observed to orbit around passive spheres [ 24 ] or fixed posts [ 25 ].…”