Cationic defect-engineered CuMn2O4photothermal membranes to leverage interfacial solar steam generation

Abstract

Herein, we report efficient and cost-effective utilization of CuMn<inf>2</inf>O<inf>4</inf> (CMO) nanostructures to generate drinkable pure water from saline and wastewater via interfacial solar steam generation (ISSG). Defect-tunable cubic crystalline CMO nanoparticles (CMO<inf>NP</inf>) and nanoflakes (CMO<inf>NF</inf>) were synthesized using the co-precipitation method by varying the Mn-concentration (CuMn<inf>x</inf>O<inf>4</inf>, where x = 1.5 and 2). These CMO nanostructures comprising mixed oxidation states of Cu+/Cu2+ and Mn3+/Mn4+ and O2− exhibited distinct morphologies and optical band offsets. The CMO<inf>NF</inf> obtained with reduced Mn content showed a high surface area (43.5 m2 g−1), lower bandgap (∼0.9 eV), and excellent hydrophilicity compared to CMO<inf>NP</inf>, enabling rapid and effective spectral absorbance. The CMO<inf>NF</inf> based photothermal membrane generated an interfacial temperature of ∼37.5 °C under 1 Sun illumination, leading to a steam generation rate of 1.61 kg m−2 h−1. Under direct sunlight, a rate of 1.21 kg m−2 h−1 was recorded with stable performance maintained up to 40 consecutive cycles. The CMO<inf>NF</inf> membrane delivered excellent purification performance for 3.5 wt% saline water and 100 ppm RhB and MB dyes, with evaporation rates of ∼1.41, 1.37, and 1.24 kg m−2 h−1, respectively. The remarkable NIR/IR absorption activity of CMO<inf>NF</inf> resulted in a maximum surface temperature of ∼49.7 °C under IR illumination, exhibiting an evaporation rate of 3.64 kg m−2 h−1, which demonstrates its strong potential for ISSG. In addition, the CMO<inf>NF</inf> membrane maintained its structural integrity and chemical composition even after multiple ISSG cycles, highlighting its durability and suitability as a cost-effective and efficient material for continuous solar-driven steam generation. This journal is © The Royal Society of Chemistry, 2026