Extracellular polymeric substances of a marine bacterium mediated synthesis of CdS nanoparticles for removal of cadmium from aqueous solution

Abstract

Hypothesis: Microbial extracellular polymeric substances (EPS) are natural metal adsorbent and effective bio-reductant. In the biosynthesis of CdS NPs, functional groups of EPS act as capping and stabilizing agents. The NPs enriched EPS have enhanced adsorption capacity of cadmium ions, which may be due to increased adsorptive sites.

Experiment: The current study demonstrates, an efficient biosynthesis method to prepare CdS NPs using EPS extracted from a marine bacterium Pseudomonas aeruginosa JP-11 and its comparison with chemical method using D-glucose. The synthesized NPs were characterised by Ultraviolet-visible spectroscopy, ATR-FTIR spectrometry, X-ray diffraction, Field emission scanning electron microscopy and Transmission electron microscopy. Atomic absorption spectroscope (AAS) was used to study adsorption capacity of pristine EPS, functionalized EPS and NPs incorporated functionalized EPS.

Findings: Spherical CdS NPs of 20-40nm diameter were synthesized with high crystallinity confirmed by XRD, FESEM and TEM analysis. The ATR-FTIR peaks within 2300-2600cm(-1) range showed a prominent shift in sulphydryl group (SH). The cadmium removal efficiency by CdS NPs incorporated functionalized EPS (88.66%) was higher than functionalized EPS (80.81%) and pristine EPS (61.88%) after 48h of incubation. The experimental data of adsorption thermodynamics and kinetics of Cd by NPs incorporated functionalized EPS was fitted in Langmuir isotherm model.

Keywords: Cadmium sulphide; Extracellular polymeric substances; Functionalization; Marine bacteria; Nanoparticles.