Hollow polydopamine colloidal composite particles: Structure tuning, functionalization and applications.

Engineering hollow particles with high complexity in their morphology or composition is highly desirable for both fundamental studies and practical applications. Here, we combine mussel-inspired polydopamine (PDA) chemistry with template-assisted and hydrothermal approaches to explore a general approach for engineering hollow PDA colloidal composite particles with tunable complexities in terms of particle geometry, shell architecture and chemical composition. PDA coating and hydrothermal treatment are carried out sequentially in the same environment, which not only simplifies the experimental procedure but also avoids the use of hazardous core-removers. This approach is generally applicable to a wide variety of colloidal templates irrespective of their shape, material and structure, allowing the void structure and geometry (spherical void, yolk-shell, multi-shells and non-spherical cavity) to be controlled. The surface of the PDA shell provides a versatile platform for a number of secondary reactions (e.g., electroless metallization, superhydrophobic modification, Michael addition and nanoparticle decoration). Consequently, tuning the exterior or interior of the hollow PDA shell with various functional materials offers a range of potential uses in superhydrophobic surfaces, catalysis, photocatalysis and surface-enhanced Raman spectrum sensing.