Carbon nanotube-nano-Fe3O4 composite graphene hydrogel with optimized 3D structure for high-performance solar evaporation

Abstract

In the face of increasingly scarce freshwater resources, harnessing sustainable solar energy for water evaporation offers an effective pathway to alleviate the water crisis. In this study, we prepared a highly efficient hydrogel solar evaporator (GHCFeP) using graphene oxide (GO), carbon nanotubes (CNTs), nano-Fe₃O₄, and polyvinyl alcohol (PVA) as raw materials. The combination of CNTs' excellent molecular thermal vibration effect and nano-Fe₃O₄'s superior light absorption and photothermal conversion mechanism endows the composite hydrogel with better photothermal conversion capabilities. Meanwhile, the introduction of PVA enhances the water transport capacity within the hydrogel. Furthermore, this work optimizes the three-dimensional (3D) structure of the hydrogel, reducing the “dead evaporation zone” on the evaporator's surface and enhancing the hydrogel's evaporation rate. Due to GHCFeP's low evaporation enthalpy (1377 kJ/kg), under 1.0 sun illumination, its evaporation rate reaches 2.133 ± 0.166 kg·m⁻²·h⁻¹ in pure water and 1.778 ± 0.181 kg·m⁻²·h⁻¹ in simulated seawater. Additionally, by shaping the evaporator into a honeycomb-like structure, the evaporation rate of GHCFeP is further improved. The honeycomb-shaped GHCFeP exhibits an evaporation rate of 2.304 ± 0.042 kg·m⁻²·h⁻¹ in pure water with a photothermal conversion efficiency of 92.4 %, and an evaporation rate of 2.045 ± 0.050 kg·m⁻²·h⁻¹ in simulated seawater. In summary, this work not only develops an efficient solar evaporator but also achieves higher photothermal conversion efficiency through optimized 3D structuring, providing new insights and strategies for related research.