The metal sulfide nanoparticles (MSNPs) of transition metals such as copper (Cu), cobalt (Co) and nickel (Ni) are important hosts/carriers of these metals within an ecosystem, and yet their basic attributes (e.g., phase, size and shape distribution) that affect their solubilities remain poorly described owing to the difficulties in isolating these MSNPs from complex natural samples. Here, we advocate for the use of synthesis-based approaches towards a better characterization of the diversity of MSNPs that can form under conditions that mimic the chemical range of natural environments. In our study, we synthesize MSNPs in the presence of a multi-salt medium containing sulfate-reducing Desulfovibrio vulgaris in batch reactors at near-neutral pH. The biogenic metal sulfides are precipitated as 2-50 nm-sized nanoparticles, often containing defects that may enhance the nanoparticle reactivity. The dominant metal-hosting phase is found to vary as a function of the initial dissolved metal-to-Fe ratio. In Fe-poor systems, the metals are precipitated as their respective (near) stoichiometric metal sulfide phase such as CuS, Co9S8 and NiS. Comparatively, in Fe-rich systems that are more representative of natural environments, the metals are co-precipitated with Fe resulting in phases such as chalcopyrite (CuFeS2) and Co- or Ni-rich mackinawite (MexFe1-xS). The presence and metabolism of D. vulgaris are found to modify the phase selectivity, crystallinity and sizes of the metal sulfide nanoparticles relative to abiotic controls, highlighting the importance of including microbial cells in the experimental design. Comparative transmission electron microscopy analyses of synthetic and naturally-occurring MSNPs indicate that both share similar attributes, justifying our synthesis-based approaches. Nonetheless, naturally-occurring MSNPs tend to be more diverse, indicating that other factors yet to be tested in our study (e.g., pH and temperature gradient) may also be important in controlling the types of MSNPs that can form.

Synthesis-based approaches towards characterization of the diversity of metal sulfide nanoparticles that can plausibly formed in nature

2019 Spring National Meeting

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