Abstract

Biogenic iron oxides could find application in catalysis but their structure and composition should be well characterized. The content of organic rests due to their origin should also be controlled. Samples of natural biomass and biomass obtained after cultivation in Adler's medium of the Sphaerotilus- Leptothrix group of bacteria were treated by different techniques to reduce or totally remove the organic residues. The aim of the study was to find procedures, which prevent changes in the oxidation state of the iron and of the type of iron-containing compound(s) during treatment. Mossbauer spectroscopy, IRS, DTA, and SEM were used in the study. Chemical treatment with H2O2 or NaOH at room temperature did not significantly change the samples. Thermal treatment in oxidative flow mixture conducted up to 250 °C resulted in a transformation of the iron-containing phases only. The organic matter, which is included in the structure of the particles, cannot easily be affected. DTA revealed that removal of organic rests occurred in the interval of 250-600 °C. However, the transformation of the initial compounds could not be prevented using such a treatment.

Highlights

  • At the present time iron-containing materials obtained by bacteria, fungi, yeasts and viruses give rise to certain interest since no energy consumption is necessary for their synthesis.[1,2,3,4] Bacteria from the Sphaerotilus-Leptothrix group participate in biogeochemical rotation of the iron that occurs in the lithosphere

  • The following parameters of hyperfine interactions of the Mössbauer spectral components were determined by computer fitting: isomer shift (IS), quadrupole splitting (QS), hyperfine effective field (Heff) as well as line width (FWHM) and component relative weight (G)

  • The spectrum of the Natural biomass sample in the far-IR region is characterized by poorly resolved bands at about 370 and 415 cm–1 and a shoulder at about 460 cm–1 (Figure 1b, spectrum 1)

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Summary

Introduction

At the present time iron-containing materials obtained by bacteria, fungi, yeasts and viruses give rise to certain interest since no (or at least minimum) energy consumption is necessary for their synthesis.[1,2,3,4] Bacteria from the Sphaerotilus-Leptothrix group participate in biogeochemical rotation of the iron that occurs in the lithosphere. The deposition of ferric ions is extracellulary in the form of sheaths and it is not related to energy supply.[6,7,8] Interest to the biosynthesis of iron-containing compounds is dictated from the fact that there are methods to produce nanosized iron oxide compounds (hematite, magnetite, goethite, etc.) but they are relatively expensive or use harmful chemical materials, the yields being not high enough.[9,10] Biogenic iron materials have application to electrical devices and electrochemical sources,[3,11,12] purification of waters, soil and air,[13,14,15,16,17] and catalysis. Biogenic iron oxides have been applied as catalysts in reactions of oxidation[10,18,19,20] or as an (immobilising) support for catalysts of very high activity.[2,21,22,23] Investigations in this field are still scarce and concentrated only on a small number of reactions

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