Interfacially Super‐Assembled Asymmetric and H₂O₂ Sensitive Multilayer‐Sandwich Magnetic Mesoporous Silica Nanomotors for Detecting and Removing Heavy Metal Ions

Abstract

Asymmetric hollow and magnetic mesoporous silica nanocomposites have great potential applications due to their unique structural-functional properties. Here, asymmetric multilayer-sandwich magnetic mesoporous silica nanobottles (MMSNBs) are presented through an interfacial super-assembly strategy. Asymmetric hollow silica nanobottles (SNBs) are first prepared, and Fe 3 O 4 nanoparticles monolayers and mesoporous silica layers are uniformly super-assembled on the surfaces of SNBs, respectively. The high Fe 3 O 4 nanoparticles loading endows MMSNBs with a high magnetization (8.5 emu g −1 ), while the mesoporous silica layers exhibit high surface area (613.4 m 2 g −1 ) and large pore size (3.6 nm). MMSNBs can be employed as a novel type of enzyme-powered nanomotors by integrating catalase (Cat-MMSNBs), which show an average speed of 7.59 µm s −1 (≈25 body lengths s −1 ) at 1.5 wt% H 2 O 2 . Accordingly, the water quality can be monitored by evaluating the movement speed of Cat-MMSNBs. Moreover, MMSNBs act as a good adsorbent for removing more than 90% of the heavy metal ions with the advantage of the mesoporous structure. In addition, the good magnetic response enables the MMSNBs with precise directional control and is conducive to recycling for repeated operation. This bottom-up interfacial super-assembly construction strategy allows for a new understanding of the rational design and synthesis of multi-functional nanomotors.

A Practical Guide to Analyzing and Reporting the Movement of Nanoscale Swimmers

“…These concerns are not hypothetical but are already widespread in the nanoswimmer literature. By surveying 40+ recent literature reports of nanoswimmers, we see reoccurring inconsistencies that include blurry, drifting trajectories captured by optical microscopes, 58,60,61,65,68,73,79,88,92 inappropriate speed calculations and fitting of mean square displacement, 57,61,68,[71][72][73][74][75]77,79,82,83,89 and lack of proper and complete control experiments. 68,70,72,89 These inconsistencies are often accompanied by other issues, such as an incomplete reporting of experimental details, a casual discussion of the propulsion mechanism of a nanoswimmer, and sometimes even a lack of supporting videos to confirm selfpropulsion.…”

“…Although a parabolic MSD for a large microswimmer makes the extraction of V straightforward, seeing a parabola on the MSD plot of a nanoswimmer is alarming and not expected, because, as we have mentioned a few times, their small size and small τr dictate that their MSD contains only the linear regime unless a camera of a high frame rate was used. The most likely source for seeing such an anomaly with a nanoswimmer is the presence of convective drift, 58,60,61,65,68,73,79,88,92 which could arise from a number of possible sources: an uneven stage, leaks in containment, growth and collapse of bubbles, and/or disturbance to the fluid from adding solutes or solvents, to name a few. Difficult to eliminate completely, drift collectively moves all nanoswimmers in the field of view in the same direction and, as a result, superimposes a directional force on a diffusive nanoswimmer, rendering its entire MSD plot parabolic, even for ∆t>>τr.…”

“…Both refer to the transport of colloidal particles in a self-generated chemical gradient, 31,45,172 with major differences being whether the chemically active particle is a combination of source and sink of chemicals (self-electrophoresis) or just a source (self-diffusiophoresis). The particular case of self-diffusiophoresis, which is the most commonly invoked mechanism for a chemical nanoswimmer, [59][60][61][62]66,79 can be further divided into ionic and neutral types, depending on the nature of the released chemicals. Ionic self-diffusiophoresis occurs when the released ions have different diffusivities or different interactions with the particle, and it weakens as the solution ionic strength increases.…”

Superassembled Hierarchical Asymmetric Magnetic Mesoporous Nanorobots Driven by Smart Confined Catalytic Degradation

“…Micro‐ and nanoscale robots are artificial, smart, active materials that can propel themselves in diverse fluids; they have attracted significant attention in medical imaging, [1] intelligent sensing, [2] drug delivery, [3] and other important applications [4] . Asymmetric, hollow, open, bottlelike micro‐/nanomotors (MNMs) are particularly attractive because their large cavity with a delicate opening has a stronger confinement effect than solid spheres; this is beneficial to the formation of highly asymmetric fields around the particle for directional self‐propulsion.…”

“…Up to now, various propulsion mechanisms have been explored to power MNMs, such as magnetic propulsion, selfelectrophoresis, [9] self-diffusiophoresis, [2,10] bubble propulsion, [11] and so on. Among these, catalytic MNMs based on noble metals are attractive because the catalyst is not easily consumed; this ensures sustainable movement of the motor.…”