An efficient superhydrophilic photothermal membrane of graphene-decorated TiO2 nanotube arrays for solar desalination

Abstract

Light absorption and salt resistance are two primary factors for the performance of Interfacial Solar Driven Water Evaporation (ISDWE) technology. This paper presents a superhydrophilic photothermal membrane composed of graphene-modified titanium dioxide (GR-TiO₂) nanotubes, which was prepared on a titanium mesh surface by anodic oxidation and electrochemical methods. The superhydrophilic nanostructured GR-TiO₂ mesh, featuring a staggered tight-weaving structure, facilitates seawater transport and guides salt crystallization towards the mesh edges, preventing surface accumulation. The tubular structure with nanotube arrays on the titanium mesh and an inner cavity structure maximizes light trapping through both multiply scattering, and omnidirectionally absorbing the light. This synergy played by tubular structure and graphene generated more optical absorption, reaching 89.64 % in the entire solar spectrum. In the salt tolerance experiment, the system removed over 99 % of NaCl from the evaporated water, maintaining long-term membrane durability. At 17 wt% brine, salt crystallizes at both the edges and the centre of the GR-TiO₂ membrane after a 10-h evaporation cycle, achieving a salt recovery rate of 225.55 g m⁻² h⁻¹. This study utilizes ISDWE technology to achieve integrated production of salt and fresh water, presenting a novel approach to address the issue of salt crystallization in solar desalination.