Influence of nickel manganese cobalt oxide nanoparticle composition on toxicity toward Shewanella oneidensis MR-1: redesigning for reduced biological impact
Lithium nickel manganese cobalt oxide (LixNiyMnzCo1−y−zO2, 0 < x, y, z < 1, also known as NMC) is a class of cathode materials used in lithium ion batteries. Despite the increasing use of NMC in nanoparticle form for next-generation energy storage applications, the potential environmental impact of released nanoscale NMC is not well characterized. Previously, we showed that the released nickel and cobalt ions from nanoscale Li1/3Ni1/3Mn1/3Co1/3O2 were largely responsible for impacting the growth and survival of the Gram-negative bacterium Shewanella oneidensis MR-1 (M. N. Hang et al., Chem. Mater., 2016, 28, 1092). Here, we show the first steps toward material redesign of NMC to mitigate its biological impact and to determine how the chemical composition of NMC can significantly alter the biological impact on S. oneidensis. We first synthesized NMC with various stoichiometries, with an aim to reduce the Ni and Co content: Li0.68Ni0.31Mn0.39Co0.30O2, Li0.61Ni0.23Mn0.55Co0.22O2, and Li0.52Ni0.14Mn0.72Co0.14O2. Then, S. oneidensis were exposed to 5 mg L−1 of these NMC formulations, and the impact on bacterial oxygen consumption was analyzed. Measurements of the NMC composition, by X-ray photoelectron spectroscopy, and composition of the nanoparticle suspension aqueous phase, by inductively coupled plasma-optical emission spectroscopy, showed the release of Li, Ni, Mn, and Co ions. Bacterial inhibition due to redesigned NMC exposure can be ascribed largely to the impact of ionic metal species released from the NMC, most notably Ni and Co. Tuning the NMC stoichiometry to have increased Mn at the expense of Ni and Co showed lowered, but not completely mitigated, biological impact. This study reveals that the chemical composition of NMC nanomaterials is an important parameter to consider in sustainable material design and usage.