Exposure to NaCl enhances Cd2＋ biosorption potential of Sesuvium portulacastrum (L.)

Abstract

Cadmium (Cd2＋) is a major heavy metal pollutant and it causes many serious effects on the environment. The established Cd2＋ removal methods are expensive and produce secondary waste, while biosorption is a potential alternative. In view of this, Sesuvium portulacastrum (L.) is explored, which is a facultative halophyte and is known to survive under both salt and heavy metal stress conditions. Using the dried powder of Sesuvium biomass, two independent biosorbents were prepared including ConB (grown under control condition) and NaClB (grown under 200 mM NaCl) and their Fourier-transform infrared spectroscopy (FTIR) indicated significant alteration in peak position of various functional groups. The Cd2＋ biosorption capacity in NaClB (306 mg g−1) was found higher than ConB (203 mg g−1). The kinetic and equilibrium studies revealed the contribution of intraparticle diffusion in the biosorption process of both the biosorbents. Further, the higher intraparticle diffusion rate constant indicated the faster biosorption process in NaClB. The experimental data correlated better with Freundlich equilibrium isotherm (r2=0.96 for ConB and r2=0.99 for NaClB) than Langmuir, indicating multilayer biosorption and heterogeneity within the biosorbents. Scanning electron microscope (SEM) imaging indicated that the rough surface of ConB changed to smooth after Cd2＋ biosorption, with lesser number of pores. In case of NaClB, Cd2＋ biosorption narrowed the vertical channels. EDX (Energy Dispersive X-ray) spectrum validated the Cd2＋ binding in both ConB and NaClB. Taken together, the study highlighted NaCl-treated Sesuvium as an eco-friendly green biosorbent for Cd2＋ removal from aqueous solutions.