NIR light-propelled bullet-shaped carbon hollow nanomotors with controllable shell thickness for the enhanced dye...

Materials with asymmetric nanostructures have attracted tremendous research attention due to their unique structural characteristics, excellent physicochemical properties, and promising prospects. However, it is still difficult to design and fabricate bullet-shaped nanostructure due to its structural complexity. Herein, for the first time, we successfully constructed NIR light-propelled bullet-shaped hollow carbon nanomotors (BHCNs) with an open mouth on the bottom of nano-bullet for the enhanced dye removal, by employing bullet-shaped silica nanoparticles (B-SiO₂ NPs) as a hard template. BHCNs were formed by the growth of polydopamine (PDA) layer on the heterogeneous surface of B-SiO₂ NPs, followed by the carbonization of PDA and subsequent selective etching of SiO₂. The shell thickness of BHCNs was able to be facilely controlled from ≈ 14 to 30 nm by tuning the added amount of dopamine. The combination of streamlined bullet-shaped nanostructure with good photothermal conversion efficiency of carbon materials facilitated the generation of asymmetric thermal gradient field around itself, thus driving the motion of BHCNs by self-thermophoresis. Noteworthily, the diffusion coefficient (De) and velocity of BCHNs with shell thickness of 15 nm (BHCNs-15) reached to 43.8 μm⋅cm^-2 and 11.4 μm⋅s^-1, respectively, under the illumination of 808 nm NIR laser with the power density of 1.5 W⋅cm^-2. The NIR laser propulsion caused BCHNs-15 to enhance the removal efficiency (53.4% vs. 25.4%) of methylene blue (MB) as a typical dye because the faster velocity could produce the higher micromixing role between carbon adsorbent and MB. Such a smart design of the streamlined nanomotors may provide a promising potential in environmental treatment, biomedical and biosensing applications.