CYSTEINE-MEDIATED SYNTHESIS OF CDS BIONANOCRYSTALLITES

The synthesis of CdS bionanocrystallites has been studied by reacting Cd(II)-cysteine complexes with inorganic sulfide. Cysteine-mediated sy nthesis of CdS bionanocrystallites proceeded slightly faster at 45 deg rees C than at room temperature. The sizes of these CdS bionanocrystal lites, as determined by optical spectroscopy, increased with increasin g initial sulfide/Cd(II) ratios. Analyses of size-distribution showed significant heterogeneity in sizes only at sulfide/Cd(II) ratios of 0. 25. An ethanol precipitation procedure was developed to remove unreact ed Cd(II)-cysteine complexes. This procedure also resulted in the isol ation of CdS bionanocrystallites (bioNCs) that appeared uniform in siz e and chemical composition. Cysteine behaved like glutathione insofar as the size-range of CdS particles was concerned. However, cysteine-me diated synthesis of CdS bioNCs resulted in uniformly sized-particles a s has been observed previously with phytochelatins. Cysteine-capped Cd S particles exhibited pH-dependent changes in their properties. pH-ind uced changes were more pronounced in emission than in absorption spect ra. Photocatalytic activities of these bioNCs were indicated by reduct ion of three dyes. Irradiation of methylviologen, basic fuchsin and na phthol blue black at 366 nm in the presence of cysteine-capped CdS bio NCs caused reduction of these dyes. Samples exhibiting higher luminesc ence were also more active in the photocatalysis experiments. (C) 1998 Elsevier Science Ltd. All rights reserved.