(749e) Life Cycle Assessment (LCA) of Iron Oxide Nanoparticles () Synthesis By Co-Precipitation: Traditional and Novel Microfluidic Methods

Iron oxide nanoparticles (IONPs) have found application in a wide variety of fields including, remediation of contaminated soil and water, drug delivery, medical diagnostics, memory data storage, and targeted cancer therapies [1][2]. In addition, IONPs can be used as a support to other functional materials, and they can be easily separated by the application of magnetic fields, thereby facilitating their recovery from the reaction medium.

Shape, size distribution, and surface chemistry of the IONPs are largely dependent on the synthesis method [2]. Additionally, it also determines to a great extent the distribution and type of structural defects or impurities in the obtained materials, and ultimately all the factors might impact the magnetic response. IONPs can be produced through different processes based on physical, chemical and biological methods with differing mechanisms, inputs, yields, and reaction conditions [3][4]. In this regard, some of the simplest and most common methods to produce IONPs include sol-gel and chemical coprecipitation of iron chlorides [5]. Alternatively, less popular methods due to high associated costs and complexity include those based on sonochemistry and thermal decomposition [6][7][8]. Most recently, synthesis enabled by microfluidic devices have gained significant attention because they provide a powerful platform for preparing, functionalizing, and manipulating nano/micro materials [9], in addition to a remarkable ability to provide effective mixing and create a uniform environment for material preparation [10][11]. One main drawback of microfluidics is the need of sophisticated cleanroom manufacturing techniques to precisely control the features of the devices [12]. We have overcome this major issue by introducing a low-cost manufacturing method for the devices that relies on widely available and inexpensive laser cutting techniques [13][14].

To evaluate whether the synthesis methods induce potential environmental impacts, it is possible to apply a number of methodologies including, Environmental Impact Assessment (EIA), Strategic Environmental Assessment (SEA), and Life Cycle Assessment (LCA). This approach has been successful in estimating environmental impacts, respect to a baseline, within a geographical framework for a number of processes, including solid waste management [15], biogas production [16], and nanomaterials [17]. LCA can be conducted either by considering all involved activities during the life of a product in the so-called “cradle to grave” approach or alternatively by only looking at the unit operations of the production process itself in the so-called “cradle to gate” approach [18][19]. In the former, the analysis will include activities from extraction of raw materials to manufacturing to recycling and disposal at the end-of-life stage. In contrast, the latter will only require details of the manufacturing process. According to a recent study by Feijoo et al. [20], when assessing the outcomes from the LCA, they observed that the manufacturing of nanoproducts is mainly dominated by the environmental impacts associated with energy and chemical use. Moreover, this work highlighted the lack of comparable reports and insufficient data availability as the two main challenges currently encountered with the application of LCA to nanoproducts. These two limitations directly increase the uncertainty level associated with the estimation of the environmental impact indexes for the production of nanoparticles [20]. As a result, studies on the environmental impact of nanoproduct production are rather scarce and report contradictory results [17][20]. This is problematic as the number of processes enabled by nanotechnology has dramatically increased during the past decade.

This study was therefore aimed at evaluating the possible environmental impacts associated with two coprecipitation methods for the synthesis of IONPs, i.e., the traditional one and that enabled by microfluidic devices. Here, we explored the implementation of the "cradle to gate" descriptive approach to laboratory-scale processes. In this case, we needed to consider different aspects such as required energy reagents and the generated waste. The functional unit to conduct the analysis for both synthesis methods was defined as 0.5 g of the NPs produced per batch. However, this functional unit is only valid for this work, because the selection of a weight based functional unit makes sense when comparing production processes to produce an equivalent amount of nanomaterial. For our first approach, we defined the system boundaries starting with use of raw materials and ending with the production of the IONPs. While the water and energy consumption was taken into account, emissions and wastewater treatment assessment were disregarded.

To create the inventory report for the LCA, real-time data of both processes was collected and processed. It included consumption’s data of water and energy, the exact weight of each reagent, and waste generated. Missing data such as environmental impacts associated to iron (II) chloride tetrahydrate, and tetramethylammonium hydroxide (TMAH) were estimated from reports, handbooks, and protocols. The LCA was carried out with the aid of the Ecoinvent 3.6 database of Simapro®. Additionally, characterization factors were from the International Reference Life Cycle Data System (ILCD). The eight impact categories considered in this study were human toxicity, ecotoxicity, climate change, resource depletion, acidification, and human health photochemical ozone formation.

Regarding the results, impact assessment shows that microfluidic method presented higher environmental impacts than the traditional co-precipitation method. The microfluidic method required more energy and materials and, consequently, it had the largest impacts in all categories compared to the traditional co-precipitation method. Additionally, a new impact category was considered, which contemplated the reuse of the microfluidic device to synthesize additional amounts of IONPs . However, results show that for the new category the overall importance with respect to the other analyzed categories was almost negligible. These results can be explained by our omission of the energy and materials used during the manufacture stage where significant impacts to the environment and human health might be considerable.

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