The long-term viability of nanofluids: Overcoming stability, performance degradation, and risks to human health and...

Nanofluids (NFs) offer significant potential to enhance the efficiency and performance of energy systems, from solar collectors to advanced thermal storage. However, their industrial application is limited by long-term performance degradation, sedimentation, increased thermal resistance, pressure drops, clogging, and corrosion at higher nanoparticle concentrations. Additionally, the environmental and human health impacts of NFs, along with safe disposal and recycling strategies, remain largely unexplored. In this study, thermal and energy systems are first categorized, and the progression of research from 1994 to 2025 on NFs, including their discovery, properties, performance, challenges in various thermal and energy applications, and associated health and environmental assessments, is examined. In the next stage, stabilization techniques, limitations of commonly used stability characterization methods, long-term performance challenges across different systems, toxicity and environmental impacts, and approaches for sustainable disposal and recycling are discussed. Based on this analysis, future research should prioritize enhancing long-term stability, optimizing surfactant selection and nanoparticle surface modification, implementing reliable stability monitoring, minimizing toxicity, and establishing sustainable disposal and recycling practices. Addressing these challenges is essential for unlocking the practical benefits of NFs and facilitating their safe, efficient, and environmentally responsible implementation in targeted energy applications, although significant hurdles in long-term stability, toxicity mitigation, and sustainable disposal remain.