Composition controllable alga-mediated green synthesis of covellite CuS nanostructure: An efficient photocatalyst for degradation of toxic dye

Abstract

A facile, convenient and green method has been devised for the synthesis of a covellite phase copper sulfide nanoparticles (CuSNPs) using aqueous extract of a green alga, Chlorella ellipsoidea. The algal phytochemicals are conjectured to have served as both reducing and capping agent. The absorption features in the NIR region of the UV–visible-NIR spectrum confirmed the formation of covellite copper sulfide nanostructures. The FTIR spectrum of the as-synthesized CuSNPs indicated the involvement of functional groups of biomolecule as surface-ligands on the outer surface of the nanoparticle. The XRD reflections were indexed to hexagonal phase covellite CuS structure. The TEM study revealed a predominantly spherical morphology of particle size in the range of 9–23 nm with some agglomeration. The dark field microscope images also confirm the formation of CuS nanoparticles. EDX analysis of the synthesized nanoparticles confirms the presence of only ‘Cu’ and ‘S’ indicating formation of pure CuS nanoparticles. The as-synthesized nanoparticles exhibited excellent photocatalytic property for the degradation of a water soluble toxic methylene blue dye under scattered sunlight. The dye degradation (rate = 0.03692 min−1) was ascertained to be pseudo-first order with regression coefficient, R2 being 0.96884. The photocatalyst is readily recoverable and showed excellent stability even after four cycles.