3D photothermal hydrogels derived from spinel CoMn2O4@MXene nanocomposites for an efficient solar-driven evaporation system

Abstract

Freshwater scarcity and waterborne diseases are among the most pressing global challenges resulting from climate change and industrial expansion. Solar-driven interfacial evaporation systems (SDIEs) present a new approach that enables higher solar-to-heat and heat-to-vapor conversion efficiencies for higher evaporation rates of freshwater generation. However, sustainable evaporation also faces challenges associated with salt accumulation and heat losses to the environment and bulk water. Herein, a new class of photothermal nanocomposites (spinel CoMn₂O₄/Ti₃C₂ MXene nanosheets) is synthesized that exhibits enhanced photothermal conversion behavior. The 3D photothermal hydrogel is constructed by integrating the CoMn₂O₄@MXene nanocomposite into a polyvinyl alcohol (PVA) matrix, where a 3D porous architecture facilitates rapid water transport (hygroscopic value), localized heat confinement (39.7 °C), and salt rejection (3.5 wt%). The cross-linked hydrogel matrix prevents nanocomposite leaching during continuous evaporation (1.45 kg m⁻² h⁻¹) under one sun solar intensity. Evaporation performance under different salinities (3.5–15 wt%) confirmed the sustainability of the evaporator and reduced variability in evaporation rates, and effective desalination of seawater (salinity reduction: 99.98%) is demonstrated. This work provides a scalable, multifunctional platform for sustainable clean water generation.