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 A and 6.4–6.5 A, 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.