Influence of Structural Defects on Biomineralized ZnS Nanoparticle Dissolution: An in-Situ Electron Microscopy Study

Abstract

The dissolution of metal sulfides, such as ZnS, is an important biogeochemical process affecting fate and transport of trace metals in the environment. However, current studies of in situ dissolution of metal sulfides and the effects of structural defects on dissolution are lacking. Here we have examined the dissolution behavior of ZnS nanoparticles synthesized via several abiotic and biological pathways. Specifically, we have examined biogenic ZnS nanoparticles produced by an anaerobic, metal-reducing bacterium Thermoanaerobacter sp. X513 in a Zn-amended, thiosulfate-containing growth medium in the presence or absence of silver (Ag), and abiogenic ZnS nanoparticles were produced by mixing an aqueous Zn solution with either HS-rich gas or NaS solution. The size distribution, crystal structure, aggregation behavior, and internal defects of the synthesized ZnS nanoparticles were examined using high-resolution transmission electron microscopy (TEM) coupled with X-ray energy dispersive spectroscopy. The characterization results show that both the biogenic and abiogenic samples were dominantly composed of sphalerite. In the absence of Ag, the biogenic ZnS nanoparticles were significantly larger (i.e., ∼10 nm) than the abiogenic ones (i.e., ∼3-5 nm) and contained structural defects (e.g., twins and stacking faults). The presence of trace Ag showed a restraining effect on the particle size of the biogenic ZnS, resulting in quantum-dot-sized nanoparticles (i.e., ∼3 nm). In situ dissolution experiments for the synthesized ZnS were conducted with a liquid-cell TEM (LCTEM), and the primary factors (i.e., the presence or absence structural defects) were evaluated for their effects on the dissolution behavior using the biogenic and abiogenic ZnS nanoparticle samples with the largest average particle size. Analysis of the dissolution results (i.e., change in particle radius with time) using the Kelvin equation shows that the defect-bearing biogenic ZnS nanoparticles (γ = 0.799 J/m) have a significantly higher surface energy than the abiogenic ZnS nanoparticles (γ = 0.277 J/m). Larger defect-bearing biogenic ZnS nanoparticles were thus more reactive than the smaller quantum-dot-sized ZnS nanoparticles. These findings provide new insight into the factors that affect the dissolution of metal sulfide nanoparticles in relevant natural and engineered scenarios, and have important implications for tracking the fate and transport of sulfide nanoparticles and associated metal ions in the environment. Moreover, our study exemplified the use of an in situ method (i.e., LCTEM) to investigate nanoparticle behavior (e.g., dissolution) in aqueous solutions.

How Microbial Biofilms Control the Environmental Fate of Engineered Nanoparticles?

“…This suggests that surface interaction with surrounding compounds influences ZnS NPs structure. Eskelsen et al (2018) also observed structural defaults (twins) on the (111) face of biogenic ZnS NPs, to a lower extent because of the unfavorable particles's orientation. The authors detected carbon traces in biogenic ZnS NPs aggregates and assumed a microbial metabolite interaction with ZnS NPs.…”

“…Regarding ZnS NPs, Xu et al (2016) highlighted by electronic microscopy that biogenic ZnS NPs dissolution starts where the structural defects are observed. Also, Eskelsen et al (2018) have calculated a higher surface energy for biogenic ZnS NPs, compared with the abiotic ones, suggesting a higher reactivity. In contrast, smaller abiotic ZnS NPs have a higher available specific surface area for oxidative dissolution.…”

“…It seems that SRB-induced ZnS NPs are bigger than ZnS-NPs formed in abiotic systems at similar conditions (Peltier et al, 2011;da Costa et al, 2012;Xu et al, 2016;Eskelsen et al, 2018). It could be explained by the progressive production of sulfide by SRB leading to a lower saturation index, since a lower saturation index favors particle growth (Mersmann, 1999).…”

Cadmium-Containing Quantum Dots Used in Electronic Displays: Implications for Toxicity and Environmental Transformations

“…The fact ZnS dissolved preferably when it is shelled over CdSe than when it is the sole constituent of a nanoparticle can arise from the fact ZnS is likely to have more defects if it is grown over materials with different epitaxies (CdSe and CdS), as it has been shown by others. 42 However, the difference between CdSe and ZnS is greater than that between CdS and ZnS. Therefore, the alloyed shells may decrease dissolution.…”

Benefits at the nanoscale: a review of nanoparticle‐enabled processes favouring microbial growth and functionality

“…Shape, size, and surface coating of (nano)particles were also shown to affect binding of the particles to E. coli and Helicobacter pylori (Westmeier et al ., 2018). Reaction rates are controlled by the density of defects on the surface, which can lead to higher reaction rates for defect‐rich nanoparticles compared to defect‐poor nanoparticles (Eskelsen et al ., 2018). Lastly, it has been suggested that the binding efficiency of the same nanoparticle to microbes may differ depending on the bacterial species (discussed in Stauber et al ., 2018) and the bacterial growth state (Eymard‐Vernain et al ., 2018).…”