Characterization and size control of cadmium sulfide/cadmium disulfide nanoparticles within random ionomer solutions

Abstract

A solution method was used to synthesize cadmium sulfide/cadmium disulfide (CdS₍₂₎) semiconductor nanoparticles which were imbedded within the core of ionic aggregates of poly(styrene-co-cadmium methacrylate) (P(S-co-CdMA)) random ionomers. This polymer serves as an effective stabilizer for CdS₍₂₎ nanoparticles. The formation process of the nanoparticles was characterized by Fourier-transform infrared spectroscopy, UV-vis spectroscopy, transmission electron microscopy and energy dispersive spectroscopy. The crystal structure of the nanoparticles was determined to be cubic CdS and cubic CdS₂, whose lattice constants are 5.83 Å and 6.4–6.5 Å, respectively. Cubic phase CdS₂ nanoparticles are reported for the first time to form in solution at room temperature. The size control of CdS₍₂₎ quantum dots in the range of 2–5 nm was accomplished by varying the neutralization level (NL), copolymer composition (MAA), initial solution concentration of P(S-co-CdMA), and ratio of sulfur to cadmium (S∶Cd) during the nanoparticle formation process. A 2² × 3² full factorial design was used to systematically analyze the influences of these main factors and their interactions on the diameter of as-prepared nanoparticles. It was found that the diameter of the nanoparticles increased with increases in NL and S∶Cd ratio, with the latter as the most important factor. An empirical relationship was obtained relating the diameter of initially formed nanoparticles to NL, S∶Cd and the interaction between S∶Cd and ionomer concentration. The stability of CdS₍₂₎ nanoparticles was also investigated, which can be improved by increasing the sulfur to cadmium ratio.