Polydopamine-Mediated CdS Crystal Growth Behavior and the Synergistic Photocatalytic–Adsorption Mechanisms in Removing Rhodamine B

Polydopamine (PDA) is an excellent polymer with abundant chemical properties, such as broadband light absorption, surface redox activities, hydrophilic surface, chemical coupling, and adsorption capacities toward cation molecules/ions. Herein, we synthesized the PDA/CdS hybrid material by employing PDA nanoparticles as the substrate via hydrothermal reactions at various temperatures. Results indicate that the chelation between Cd2+ ions and the PDA substrate can facilitate the heterogeneous nucleation of CdS nanoparticles to obtain the uniform dispersion status on the PDA surface. PDA/CdS was then employed to study the photocatalytic–adsorption activities in removing rhodamine B (RhB), where CdS and PDA primary served as the photocatalyst and adsorption matrix, respectively, under xenon lamp irradiation. The capacity of PDA nanoparticles toward RhB adsorption is reduced along with the increased hydrothermal temperature because of an elevated carbonization degree, while the photocatalytic activity and resistance to photocorrosion of CdS nanoparticles are improved. The synergistic effect between photocatalysis and adsorption is significant for RhB removal. Finally, we demonstrate that the extremely complex surface chemical properties of PDA can infer the photocatalytic–adsorption behavior of PDA/CdS greatly by the experiments with sacrificial agents and the pre-illumination process.