Asymmetric yolk@shell structured Fe-doped polydopamine or carbon@mesoporous silica composite particles

Materials featuring integrated nanostructures and components exhibit promising multifunctional properties, making them well-suited for cutting-edge applications. Herein, we employed post- and pre-doping strategies to introduce Fe(III) ions into polydopamine (PDA) nanospheres for the construction of asymmetric yolk@shell structured Fe-doped PDA or carbon@mesoporous silica composite particles. The pre-doping strategy yielded PDA with a maximum Fe(III) content of 8.6%, far exceeding the 0.96% achieved by the post-loading approach. The variations in Fe(III) content influenced the core-to-cavity volume ratio of Fe-doped PDA@mesoporous silica composites, with higher Fe(III) levels corresponding to lower surface roughness of the shell layer. In the photothermal tests, under 808 nm near-infrared (NIR) irradiation at a power density of 1 W cm^-2, the photothermal conversion efficiencies of PDA@SiO₂, Fe(III)@PDA@SiO₂, and Fe(III)-loaded PDA@SiO₂-3 were determined to be 30.1%, 32.9%, and 51.0%, respectively. Within a specific range, higher Fe(III) content corresponded to more pronounced improvements in photothermal conversion efficiency. After high temperature treatment under a N₂ atmosphere, the yolk@shell structure remained intact, while the core exhibited significant shrinkage. The prepared composite nanomaterials, featuring an asymmetric yolk@mesoporous shell structure, should have many promising applications in environmental science and nanobiomedicine.