Facile bio-inspired synthesis of zinc sulfide nanoparticles using Chlamydomonas reinhardtii cell free extract: optimization, characterization and optical properties

Abstract

Abstract This study describes an eco-friendly, economical method to synthesize semiconductor zinc sulfide (ZnS) nanoparticles using the cell free extract of Chlamydomonas reinhardtii. Physicochemical parameters like pH, temperature and cell free extract concentration were optimized. Spherical particles measuring 8–12 nm were observed under high-resolution transmission electron microscopy (HRTEM). Elemental analysis proved that the nanoparticles were composed of zinc and sulfur, while powder X-ray diffraction (XRD) demonstrated the pure FCC crystal structure. Examination of the functional groups by Fourier transform infrared (FTIR) spectroscopy showed that algal proteins were involved in the synthesis of the nanoparticles. These nanoparticles demonstrated unique optical properties that were probed with UV-visible and photoluminescence (PL) spectroscopy. A peak at 310 nm was detected that was significantly blue-shifted from the bulk counterpart. Broad emission peaks at 410 nm and 430 nm were seen. The former was due to radiative recombination while the latter was attributed to defect states. In an effort to understand the molecular mechanism, the proteins bound to the nanoparticle surface were studied using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) and numerous proteins that are part of the cells’ oxidoreductive machinery were identified. These cellular proteins probably play a pivotal role in the synthesis and stabilization of ZnS nanoparticles.