The role of copper oxide nanomaterials in solar desalination: a systematic review of integration strategies

Abstract

Low freshwater productivity and the intermittent nature of operation remain the major limitations of conventional solar still (SS) desalination systems, restricting their large-scale and long-term applicability despite their simplicity and low environmental impact. This review comprehensively analyzes the role of copper oxide nanoparticles (CuO NPs) as an effective multifunctional enhancement agent for overcoming these limitations. CuO NPs can be used as a nanofluid in the water basin and as a nanocoating on absorber surfaces to enhance the absorption of solar radiation and, consequently, increase evaporation rates and freshwater productivity. CuO NPs can also be employed as an additive for phase change materials (PCMs) to improve heat charging and discharging characteristics and to modify melting and solidification temperatures, thereby extending SS operation for several hours after sunset. The dual application of CuO NPs as a PCM additive and as an absorber surface coating provides up to 80.20% enhancement in freshwater productivity, achieves a thermal efficiency of 63.71%, and reduces the cost per liter of distilled water by up to 75% compared to conventional SSs. CuO NPs have been applied in both passive and active SS configurations, either individually or in hybrid arrangements. This review critically examines the effects of CuO nanofluid concentration, hybrid CuO-based nanofluids with other nanomaterials, and CuO nanocomposites, highlighting the superior performance of CuO NPs compared to alternative nanoparticles in terms of yield, thermal performance, and economic feasibility. In addition to experimental investigations, relevant theoretical and numerical modeling studies are integrated to provide design-oriented insights and optimization pathways for high-performance SSs.