Bacteria mediated Biosynthesis of FeO Nanoparticles for Desalination of

Sea Water Using Thin Film Nanocomposite Membrane

Nishant Srivastava1 and Mausumi Mukhopadhyay1,*

1Department of Chemical Engineering, Sardar Vallabhbhai National Institute of Technology, Surat-395007, Gujarat, India

ABSTRACT

The biosynthesis of nanoparticles was emerged as economical, environment friendly, non toxic and easy to handle alternative to chemical processes. In the present study, a facile, green, economical synthesis of Iron oxide (FeO) nanoparticles using three Gram negative bacteria Ralstonia eutropha, Zooglea ramigera and Erwinia herbicola was reported. All the three bacterial strains showed potential for the extracellular synthesis of FeO nanoparticles. The nanoparticles were characterized with Transmission Electron Microscope (TEM), Scanning Electron Microscope with energy dispersive X-ray (SEM-EDX), Dynamic Light Scattering (DLS) and Fourier Transform Infra Red spectroscopy (FT-IR) techniques. The TEM analysis revealed that the biosynthesized FeO nanoparticles from Ralstonia eutropha, Zooglea ramigera and Erwinia herbicola were in the size range of 20-40 nm. Morphologically FeO nanoparticles were spherical in shape. The SEM analysis was in agreement with TEM results. The EDX spectrum of biosynthesized FeO nanoparticles was indicated the presence of strong peaks of Fe at 6.5 and 7.2 KeV and of oxygen at 0.5 KeV respectively which confirmed the presence of pure FeO. The weak signals of carbon, phoshphorus and nitrogen generated during the EDX analysis were perhaps associated with enzymes or proteins from a bacterium either capped or present near the biologically synthesized FeO nanoparticles. The signal of copper was associated with the glass underlay. The DLS analysis of FeO nanoparticles was also observed. DLS analysis revealed that the Ralstonia eutropha mediated biosynthesized particles were in the size range of 43 nm to 72
nm. The Zooglea ramigera mediated nanoparticles were in the range of 43 to 91 nm. Similarly, FeO nanoparticles biologically synthesized using Erwinia herbicola showed average size of 32 nm. The size obtained by DLS was bigger compared to the TEM observations, as DLS analysis measured the hydrodynamic diameter of nanoparticles. The FT-IR spectrum from R. eutropha revealed the functional groups present and responsible for
stabilizing and dispersion of FeO nanoparticles. In the spectral data the peak at 3269 cm-1
showed the presence of a primary amine whereas, peak at 16382 cm-1 referred to the carbonyl stretch vibrations in the amide bond of protein. The FT-IR spectrum revealed a peak at 2926 cm-1 stretching vibration of C-H bonds. The peaks at 1273 and 1183 cm-1 related to C-N bonds stretching. C-O stretching vibration peaks at 1047 cm-1 were also observed. The FT-IR spectrum supports the hypothesis of the presence of protein on the FeO nanoparticle surface. These protein molecules were responsible for reduction of ferrous ions into the FeO nanoparticles and their stability. The proteins present on the FeO nanoparticles surface was acted as capping agent. Similar observation was found for Z. ramigera and E. herbicola.
The biosynthesized FeO nanoparticles were utilized for the fabrication of the thin film nanocomposite (TFN) membrane. FeO nanoparticles were pre-assembled on a polyethylsulfone (PES) ultrafiltration support which served as seeds for polyamide nanocomposite membrane fabrication. The thin film nanocomposite-FeO (TFN) membrane was further used for desalination of salt water using membrane setup.
The TFN-FeO membrane was effective for the desalination of natural and artificial sea water. The desalination of sea water was monitored by measuring the concentration of sodium, magnesium, calcium and potassium by ICP-AES. The change in pH, conductivity, hardness and chloride concentration was also measured. About 37% Na, 40% K and 34% Ca removal was obtained with biogenic FeO-TFN membrane process. The conductivity, hardness and chloride concentration was decreased by 35%, 31% and 33% respectively. Approximately
35% desalination was achieved with FeO-TFN membrane. With artificial salt water the percentage removal of Na: 15%, K: 56% and Ca: 40% was observed. The conductivity decreased by 40%, hardness reduced by 31% and chloride concentration decreased by 30% respectively.

Figure 1: TEM (Scale-200 nm), SEM (100 nm) and EDX images of biosynthesized FeO nanoparticles using bacteria Ralstonia eutropha (a), (b), (g); Zooglea ramigera (c), (d), (h) and Erwinia herbicola (e), (f), (i).

Figure 2: SEM image of (a) PES membrane; (b) and (c) FeO-TFN membrane and (d) FeO- TFN membrane after desalination process.