Nanosized strongly-magnetic bacterially-produced iron sulfide materials

Using sulfate-reducing bacteria and a novel bioreactor strongly magnetic iron sulfide material has been produced. TEM studies reveal that a substantial fraction of the material consists of particles of a few nanometres in diameter. Normal X-ray diffraction showed no lines. Neutron scattering revealed some Bragg peaks and peaks in the radial distribution which may be associated with the results from the extended X-ray absorption fine structure (EXAFS). At small angles the neutron scattering revealed that a large fraction of the sample had particle diameters of the order of 2 nm. EXAFS gave results consistent with the neutron scattering. The trapped magnetisation was monitored as the temperature was slowly increased from 4.2 K. 75% of the trapped flux was lost between 4.2 and 20 K. Some particles remained blocked at 300 K showing hysteresis, but with an applied field greater than 1 T the magnetisation was linear with the field. This material is an excellent adsorbent for many metal ions, (C) 1999 Elsevier Science B.V. All rights reserved.