Reduction and transformation of nanomagnetite and nanomaghemite by a sulfate-reducing bacterium

Changes in Magnetic Properties of Magnetite Nanoparticles Upon Microbial Iron Reduction

“…Our study showed that microbial iron reduction can influence both the crystallographic and magnetic properties of the magnetite NPs even without changing their mineral types, and particle size and concentration (Byrne et al., 2015; Zhou et al., 2019). Therefore, the bioreduction of magnetite NPs deserves attention when the magnetic signals are used in paleoenvironment reconstruction (Byrne et al., 2015; Maher, 2009; Mewafy et al., 2011; Zhou et al., 2019).…”

“…Natural magnetite nanoparticles (NPs) are important iron oxides in the surficial Earth system, and widely used as a paleoenvironmental indicator (e.g., Chang et al., 2016; Faivre & Schuler, 2008; J. H. Li et al., 2009; J. H. Li, Benzerara, et al., 2013; Liu et al., 2012; Maher, 2011; Zhu et al., 2012). The natural magnetite NPs have multiple origins, including volcano eruption, magmatic crystallization, rock weathering and pedogenesis, and biologically controlled or biologically induced mineralization (Byrne et al., 2015; J. H. Li et al., 2020, 2021; Liu et al., 2012; Zhou et al., 2019). Various magnetic properties that reveal the concentration, domain state, and crystallinity of magnetite NPs are closely associated with the past environmental changes (Liu et al., 2012).…”

“…Therefore, the magnetic properties of magnetite NPs might be altered during the reduction or oxidation processes that commonly occur during deposition (Liu et al., 2012; Y. L. Li, et al., 2013; Zhou et al., 2019). For example, oxidized magnetite NPs with a Fe 2+ /Total Fe (Fe 2+ /Fe T ) ratio lower than 33% exhibit smaller lattice parameters, lower magnetic susceptibility, and higher coercivity than the perfect stoichiometric magnetite NPs (i.e., Fe 2+ /Fe T = 33%; Byrne et al., 2015, 2016; Gorski & Scherer, 2010; Y. L. Li et al., 2009; Radon et al., 2020; Zhou et al., 2019). By employing a low‐temperature magnetic analysis, Özdemir and Dunlop (2010) further reported a broader Verwey transition region and lower remanence loss in partially oxidized magnetite NPs.…”

“…Noticeably, iron oxides often undergo 100–300 times of Fe(II)‐Fe(III) transition before burial (Canfield et al., 1993). Therefore, the magnetic properties of magnetite NPs might be altered during the reduction or oxidation processes that commonly occur during deposition (Liu et al., 2012; Y. L. Li, et al., 2013; Zhou et al., 2019). For example, oxidized magnetite NPs with a Fe 2+ /Total Fe (Fe 2+ /Fe T ) ratio lower than 33% exhibit smaller lattice parameters, lower magnetic susceptibility, and higher coercivity than the perfect stoichiometric magnetite NPs (i.e., Fe 2+ /Fe T = 33%; Byrne et al., 2015, 2016; Gorski & Scherer, 2010; Y. L. Li et al., 2009; Radon et al., 2020; Zhou et al., 2019).…”

“…Besides modern ecosystems, it has been thought that microbial iron reduction is likely one of the earliest forms of microbial respiration due to the lack of other electron acceptors such as oxygen, nitrate, and sulphate (Vargas et al., 1998; Walker, 1987; Walker & Brimblecombe, 1985; Wiechert, 2002). In this reduction process, magnetite NPs could carry excess Fe 2+ (i.e., Fe 2+ /Fe T > 33%; Byrne et al., 2015, 2016; Dong et al., 2000; Gorski & Scherer, 2010; Kukkadapu et al., 2005; Y. L. Li et al., 2009; Zhou et al., 2019). However, the changes in mineralogical and magnetic properties of magnetite NPs during microbial iron reduction are not well understood.…”