Biodesulfurization of dibenzothiophene by microbial cells coated with magnetite nanoparticles

Abstract

Microbial cells of Pseudomonas delafieldii were coated with magnetic Fe3O4 nanoparticles and then immobilized by external application of a magnetic field. Magnetic Fe3O4 nanoparticles were synthesized by a coprecipitation method followed by modification with ammonium oleate. The surface-modified Fe3O4 nanoparticles were monodispersed in an aqueous solution and did not precipitate in over 18 months. Using transmission electron microscopy (TEM), the average size of the magnetic particles was found to be in the range from 10 to 15 nm. TEM cross section analysis of the cells showed further that the Fe3O4 nanoparticles were for the most part strongly absorbed by the surfaces of the cells and coated the cells. The coated cells had distinct superparamagnetic properties. The magnetization (delta(s)) was 8.39 emu.g(-1). The coated cells not only had the same desulfurizing activity as free cells but could also be reused more than five times. Compared to cells immobilized on Celite, the cells coated with Fe3O4 nanoparticles had greater desulfurizing activity and operational stability.

FIG. 1.

TEM images of magnetite nanoparticles.

FIG. 2.

TEM images of ultrathin cross sections of cells coated with magnetite nanoparticles.

FIG. 3.

Magnetization curves for the coated cells as determined with a vibrating sample magnetometer. σ_s, saturation magnetization; emu, electromagnetic unit; Oe, Oersted.

FIG. 4.

Photographs of P. delafieldii cell suspensions in columns under three different conditions. (A) Cells coated with magnetite nanoparticles; (B) free cells; (C) coated cells concentrated and collected by an external magnet.

FIG. 5.

SEM image of P. delafieldii R-8 immobilized by Celite.

FIG. 6.

Time course of desulfurization of dibenzothiophene by different cell preparations. □, residual DBT concentration after consumption by free cells; ▴, 2-HBP concentration produced by free cells; ▾, residual DBT concentration after consumption by magnetic nanoparticle-coated cells; ⋄, 2-HBP concentration produced by magnetic nanoparticle-coated cells; ▵, residual DBT concentration after consumption by Celite-immobilized cells; ▿, 2-HBP concentration produced by Celite-immobilized cells.

FIG. 7.

Repeated biodesulfurization by coated cells.