Carbon nanotube-enhanced photothermal conversion thermosensitive hydrogel for solar water evaporation: Preparation and performance

Abstract

Harnessing solar photothermal conversion for water evaporation presents an effective approach to addressing freshwater scarcity while minimizing environmental impact. This study employed carbon nanotubes as photothermal conversion materials to design and fabricate a composite thermosensitive hydrogel exhibiting high swelling capacity, excellent salt resistance, and efficient photothermal conversion for solar-driven water evaporation. Furthermore, the effects of carboxylated carbon nanotubes (CNT-COOH) and hydroxylated carbon nanotubes (CNT-OH) on the hydrogel's properties were systematically investigated. Results demonstrate that the composite hydrogel utilizing CNT-COOH as the photothermal conversion material delivered optimal overall performance, exhibiting superior mechanical properties and optimal photothermal conversion capability. It achieved swelling ratios of 385.2 g/g in pure water and 58.3 g/g in saline water, rapidly attaining swelling equilibrium within approximately 200 min. Combined with its thermosensitive property, the material reduces the enthalpy of water evaporation from 2441.5 J/g to 1687.3 J/g. Under 1 kW/m² solar irradiation, the hydrogel achieved evaporation rates of 2.35 kg m⁻² h⁻¹ in pure water and 1.71 kg m⁻² h⁻¹ in saline water, both exceeding the theoretical limit of solar water evaporation (1.46 kg m⁻² h⁻¹), demonstrating its exceptional evaporation performance. Additionally, the material demonstrated outstanding stability, self-cleaning properties, and salt tolerance during cyclic evaporation testing. This work provides a robust theoretical foundation and technical basis for developing hydrogel evaporators with high salt resistance, high swellability, and long-term durability.