TiN, ZrN, and HfN Nanoparticles on Nanoporous Aluminum Oxide Membranes for Solar-Driven Water Evaporation and Desalination

Water desalination via thermal evaporation using plasmonic nanostructures which harness and convert solar irradiation to provide the requisite heat input is gaining interest as a scalable and sustainable method to address global freshwater scarcity. To meet growing freshwater demand in such a manner, new, inexpensive plasmonic nanomaterials that exhibit high solar-to-vapor-conversion efficiencies are being sought. Here, plasmonic metal nitride interfaces consisting of TiN, ZrN, and HfN nanoparticles (NPs) with sizes ranging between 10 and 20 nm drop-cast onto nanoporous anodic aluminum oxide (AAO) membranes were analyzed for water evaporation and desalination. Evaporation rates of 1.10 ± 0.05, 1.27 ± 0.04, and 1.36 ± 0.03 kg m^–2 h^–1 and solar-to-vapor efficiencies of 78, 88, and 95% were observed for TiN, ZrN, and HfN, respectively, under 1 sun illumination. Computational analysis of the solar absorption cross-section of the nitride NPs was consistent with this trend. The HfN–AAO interface was further explored for desalination purposes using Atlantic Ocean saltwater as a source and showed evaporation rates of 1.2 ± 0.2 and 6.1 ± 0.4 kg m^–2 h^–1 and solar-to-vapor efficiencies of 87 and 99% under 1 and 4 suns, respectively. Inductively coupled plasma mass spectrometry (ICP-MS) measurements showed effective removal of the major metal ions (Na⁺, K⁺, Mg²⁺, and Ca²⁺) following the desalination process using the HfN–AAO interface.