This feature endows that the hollow SnO2 nanoparticles have high surface area. As shown in Figure 2d, the HRTEM image confirms that the SnO2 particles consist of small SnO2 grains, and their

size is about 3 ~ 5 nm. From the insets of Figure 2d, there are two lattice fringes with lattice spacing of about 0.334 and 0.26 nm, which can be assigned to the (110) and (101) planes of tetragonal rutile-phase SnO2 nanoparticles, respectively. Figure 2 SAED patterns and TEM images at low and high magnifications. (a) TEM image at low magnification (the inset is the histogram of particle diameters). (b) SAED patterns and (c) TEM images at high magnification (the Torin 1 inset scale bar is 10 nm) of the as-prepared hollow SnO2 nanoparticles, and (d) HRTEM image of a single SnO2 nanoparticle (the inset scale bar is 2 nm). Subsequently, the morphologies of the carbon-coated hollow SnO2 nanoparticles (SnO2@C) were further studied by TEM and HRTEM. Figure 3a

shows the TEM image of the SnO2@C nanoparticles. It can be seen that the SnO2@C nanoparticles still maintained a uniform morphology. The inset histogram diameters illustrate that the average diameter of SnO2@C nanoparticles is 55.7 nm. Compared with the naked hollow SnO2 nanoparticles, the thickness of the carbon coating layer is about 2 ~ 3 nm. As shown in Figure 3b, the bright rings in the SAED pattern can be well indexed to the structure of the rutile-phase SnO2, which demonstrate Nivolumab in vivo that the structure of SnO2 is also not change by carbon coating. From the magnified TEM images (Figure 3c),

a thin carbon layer on the surface of the SnO2 nanoparticles can be observed clearly, and the thermal gravimetric analysis (Additional file 1: Figure S1) illustrates that about 37% of carbon has coated the SnO2 nanoparticles. The HRTEM image (Figure 3d) shows that the carbon layer is smooth, continuous, and has a thickness of about 2 ~ 3 nm. There are lattice BCKDHB fringes with lattice spacing of about 0.334 nm, which can be indexed to the (110) plane of tetragonal rutile-phase SnO2 nanoparticles. The above results prove that the carbon has been successfully coated on the surface of the hollow SnO2 nanoparticles, and the morphology is still maintained after the coating treatment. Figure 3 TEM images at low and high magnifications. (a) TEM image at low magnification (the inset is the histogram of the particle diameters). (b) SAED patterns and (c) TEM image at high magnification (the inset scale bar is 10 nm) of the as-prepared carbon-coated hollow SnO2 nanoparticles and (d) HRTEM image (d) of a single SnO2@C nanoparticle (the inset scale bar is 2 nm). We also investigated the potential application of the as-synthesized carbon-coated hollow SnO2 nanoparticles to be used as an adsorbent in wastewater treatment.