Synthesis and assembly of ordered nanostructures of ZnS, Zn_xCd_1−xS and CdS nanoparticles at the air/water interface

Parallel nanochains of ZnS and ZnxCd1−xS alloys, and polygonal nanoplates of CdS were prepared at the air/water interface under Langmuir monolayers of 5,10,15,20-tetra-4-oxy(2-stearic acid) phenyl porphyrin (TSPP) at room temperature and characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selective-area electron diffractometry (SAED), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and UV–vis spectroscopy. The results indicate that all the nanostructures are composed of tiny metal sulfide nanoparticles. The formed ZnS and ZnxCd1−xS alloy nanoparticles are cubic zinc blende, and CdS nanoparticles are hexagonal wurtzite nanocrystals, respectively. The formation of the nanochains should be attributed to the self-assembly and aggregation of the cubic zinc blende ZnS or ZnxCd1−xS nanoparticles under the direction of the linear porphyrin supramolecular arrays; while the formation of the nanoplates of CdS should be ascribed to oriented attachment of wurtzite CdS nanoparticles at the interfaces, indicating the large influences of crystal structures on the organization of the nanoparticles and the final nanostructures. After treatment at higher temperature, the nanochains of ZnS and ZnxCd1−xS were preserved with improved crystallinity, while hexagonal and round nanorings composed of CdS nanoparticles appeared.