Growth of CdS nanorods in nonionic amphiphilic triblock copolymer systems

Size-tunable CdS nanorods have been synthesized via the reaction at low temperature (25-65 degreesC) of air-insensitive inorganic precursors cadmium acetate and sodium sulfide in an aqueous phase with surfactant. Nonionic pluronic amphiphilic triblock copolymers, (EO)(x)(PO)(y)(EO)(x), were employed as structure-directing agents. The effects of the (EO)/(PO) ratio, surfactant size, and mole ratio between surfactant and precursors in controlling the diameter and the morphology of the final product were investigated. Transmission electron microscopy (TEM) images show that the diameter of the CdS nanorods synthesized by this method can be controlled by varying the surfactant species, the mole ratio between the inorganic precursors and triblock copolymer, and the reaction temperature. However, if the reaction is refluxed in organic solvent (ethylene glycol and glyme) without surfactant, the morphology of the product will change to microrods with flat ends, dumbbell-shaped microrods, and cotton-ball-like microparticles. The hydrophilic poly(ethylene oxide) fraction, (EO),, of the triblock copolymers plays a decisive role in controlling the morphology of the final product, and the hydrophobic poly(isopropylene oxide) fraction, (PO)y, affects the diameter of the nanocrystallites. The typical size of CdS nanorods synthesized using (EO)20(PO)70(EO)20 is about 5.0-7.0 nm in diameter and 30-90 nm in length. The X-ray powder diffraction pattern is consistent with the hexagonal wurtzite crystal structure. This low-temperature aqueous synthesis route can be considered as an environmentally friendly and inexpensive method of producing nearly monodisperse CdS particles and arrays (sigma < 10%).