Nanoparticle dispersions in carrageenan films

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Conference Proceeding

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Motivated by the widespread interest in Q-sized semiconductor particles (e.g., CdS, TiO2) and the relatively abundant seaweed resource of the Philippines, we initiated studies of dispersed semiconductor nanoparticles in seaweed biopolymers, particularly, κ-carrageenan and ι-carrageenan. Iota- and κ-carrageenan are sulfated galactans with an average of single and double sulfation groups per repeat unit, respectively. Cadmium sulfide was grown in situ on adsorbed, ultrathin films of the polysaccharide by treatment with aqueous CdCl2 followed by exposure to H2S gas. The resulting nanoparticles were studied by following the UV-Vis spectra of the films during exposure to H2S gas. The absorption band edge of the CdS-carrageenan composite was observed to vary from 2.8 eV to 2.6 eV. Based on absorption band edge theory for semiconductor particles, these results are indicative of nano-sized CdS particles raging from 40 angstrom to 60 angstrom diameter. The particle size and film morphology were additionally studied by atomic force microscopy (AFM). AFM images showed various particulate morphologies: from small particles to rod-like of dimensions in the order of 50-100 nm. These images reveal what appear to be templated crystallization of CdS in the biopolymer matrix.