An integrated highly hydrated cellulose network with a synergistic photothermal effect for efficient solar-driven water evaporation and salt resistance

Abstract

Solar-driven water evaporation is an effective approach for using solar energy to purify seawater and wastewater. However, the high energy requirements of bulk water evaporation fundamentally restrict the practicality of solar freshwater production. Herein, we demonstrate an efficient hierarchical solar evaporator by combining polydopamine (PDA) and Ti₃C₂T_x MXene (MX) with a cellulose network skeleton of delignified wood (DW). By integrating activated water in a hydrated cellulose network and the synergistic photothermal effect between PDA and MX, the obtained PDMX@DW evaporator achieved a high evaporation rate of 2.08 kg m⁻² h⁻¹ and energy efficiency of 93.6% under 1 sun illumination. Differential scanning calorimetry and dark evaporation experiments indicated that the water in PDMX@DW exhibited a lower vaporization enthalpy (1915 J g⁻¹) than bulk water (2440 J g⁻¹). Raman spectral analysis and density functional theory calculations were used to investigate the structure of water molecules in the cellulose network, and it turns out that high contents of weakly hydrogen-bonded intermediate water were the most likely origin of the reduced vaporization enthalpy. More importantly, due to the interactive cellulose network structure and increased water supply rate, PDMX@DW exhibited excellent salt resistance and long-term stability in high-concentration brine. This work provides an effective method for breaking the evaporation limitation of the traditional wood-based evaporator and improving its salt resistance.