A characterization of cadmium sulfide/polymer interactions by solid state nuclear magnetic resonance.

摘要

Cadmium sulfide (CdS) nanoparticles (NP) of ∼4 nm in diameter and a moderate particle size distribution have been synthesized in the presence of 1-thioglycerol (TG) and characterized by TEM, powder XRD, absorption, photoluminescence and 113Cd, 13C and 1H solid-state NMR (SSNMR). The CdS NPs, which are coated with 1-thioglycerol (TG), were dialyzed to remove excess 1-thioglycerol and salt by-products present. The TG that is bound to the surface of the NPs remains after dialysis and SSNMR studies reveal that the molecules have restricted motion. 113Cd NMR shows that the surface sites of the NPs have a structure similar to that of the core and that TG is involved in the NP surface reconstruction. Broad photoluminescence was observed for the NPs, indicating the presence of defect sites on the surface of the NPs. Powder XRD shows that the NPs have the wurtzite crystal structure. The aqueous solubility and stability of the TG coated NPs allowed for the fabrication of polymer-NP composites.;Composites were produced by combining CdS-TG-D NPs with polyvinylpyrrolidone (PVP) and sulfonated polystyrene (PSS). 1H-113Cd SSNMR revealed broadening and an upfield shift of the 113Cd resonance suggesting a small modification to the NP surface upon interaction with the polymers. Broadening of the signal from the OH group of TG in the 1H NMR spectrum indicates an interaction between the polymer and TG. 1H-13C SSNMR was used to study the interfacial polymer material in the composites. Changes in T1rho(1H) indicate a change in the molecular dynamics of TG, consistent with a direct interaction with the polymer. The glycerol portion of TG is proposed to form hydrogen bonds with the carbonyl and amine groups of PVP and the sulfonate group of PSS. The hydrogen bond interaction also leads to a change in the dynamics of PVP, as observed from SSNMR relaxation measurements. In contrast, the interaction between TG and the sulfonate group had little influence on the dynamics of the organic portion of the polymer.;CdS nanoparticles, with diameters of 3--7 nm, were also synthesized within a poly(styrene sulfonate) matrix using ion-exchange and precipitation, and the polymer-nanoparticle composite has been cast into films. The material is characterized at both the atomic and molecular levels using high-resolution TEM (HRTEM), powder X-ray diffraction and solid-state NMR (SSNMR). The structure surrounding the Cd2+ sites in the precursor, poly(cadmium 4-styrene sulfonate), is highly disordered upon drying and becomes more ordered with hydration. The increase in order results from water migrating to the Cd 2+ sites and the polymer adopting a micellar structure. SSNMR and TEM studies shows that there is nearly quantitative conversion of the Cd 2+ to CdS, with only trace amounts of Cd(OH)2 and amorphous CdS interacting with the polymer present, and that the CdS nanoparticles are in the cubic phase, which extends to the particle surface. 113Cd SSNMR shows that the overall structural order of the NPs increases when they are synthesized in the presence of the polymer matrix. Exposure of the composite film to ambient conditions over several months results in the partial oxidation of only the first few outermost layers of the NPs.