Environmental Sustainability Evaluation of Iron Oxide Nanoparticles Synthesized via Green Synthesis and the Coprecipitation Method: A Comparative Life Cycle Assessment Study.

Green synthesis, based on green chemistry, is replacing the traditional methods, aiming to contribute with an enhanced environmental sustainability, which can be achieved using nontoxic compounds from biological resources, such as natural extracts from plants. In this study, the life cycle assessment (LCA) of iron oxide nanoparticles prepared through the green synthesis and the coprecipitation method is reported by following a cradle-to-gate approach. The LCA allowed quantifying and normalized the environmental impacts produced by the green synthesis (1.0 × 10-9), which used a Cymbopogon citratus (C. citratus) extract and sodium carbonate (Na2CO3). The impacts were also determined for the coprecipitation method (1.4 × 10-8) using the iron(II) salt precursor and sodium hydroxide (NaOH). The contribution of C. citratus extract and Na2CO3 as the precursor and pH-stabilizing agents, respectively, was compared regarding the iron(II) and NaOH compounds. Environmental sustainability was evaluated in human toxicity, ecosystem quality, and resource depletion. The major environmental contribution was found in the marine aquatic ecotoxicity (7.6 × 10-10 and 1.22 × 10-8 for green synthesis and the coprecipitation method) due to the highest values for ethanol (3.5 × 10-10) and electricity (1.4 × 10-8) usage since fossil fuels and wastewater are involved in their production. The C. citratus extract (2.5 × 10-12) presented a better environmental performance, whereas Na2CO3 (4.3 × 10-11) showed a slight increase contribution compared to NaOH (4.1 × 10-11). This is related to their fabrication, involving toxic compounds, land occupation, and excessive water usage. In general, the total environmental impacts are lower for the green synthesis, suggesting the implementation of environmentally friendlier compounds based on natural sources for the production of nanomaterials.