Comparative Cradle-to-Gate Life Cycle Assessment of Hydrothermal Zinc Oxide Nanowire Synthesis Methods

Abstract

Zinc oxide nanowires (ZnO NWs) are promising materials for applications in sensors, transistors, and energy harvesting devices, owing to their unique structural and electronic properties. Despite advances in synthesis techniques, their environmental impacts remain an important consideration for sustainable nanomaterial development. In this study, we introduce a novel hydrothermal synthesis route inspired by Fehling's reaction, enabling the growth of ZnO NWs at low temperature and atmospheric pressure using bio-based and low-cost reagents such as glucose. To assess the environmental footprint of this method, a comparative life cycle assessment (LCA) methodology was employed using the OpenLCA software. The new route was benchmarked against a conventional solgel/hydrothermal synthesis under similar growth conditions. Results show that the Fehling-inspired method significantly reduces environmental impacts-by one to two orders of magnitude-across key categories such as climate change, ozone depletion, and human toxicity. In both methods, the silicon wafer substrate and electricity use emerged as the dominant contributors to overall impacts while chemical inputs had relatively minor effects, reinforcing the green chemistry potential of the proposed process. Sensitivity analyses explored several strategies for further impact reduction, including testing the influence of substrate materials, energy optimization, and regionalization. This work underscores the value of LCA as a tool for early-stage process evaluation and highlights practical opportunities for improving the sustainability of nanomaterial synthesis.