In Situ Growth of\nWell-Aligned MOF Nanoneedle Arrays\ninto Composite Photothermal Membranes for Solar Desalination

The solar-driven interfacial evaporation (SDIE) technology\nserves\nas a clean and facile approach combining seawater desalination to\naddress water shortage and energy crisis. Recently, porous organic\nframework materials have aroused great attention, and the development\nof MOF-based composites with significant performance in photothermal\nconversion and water activation has become one of the important focuses\nin this field. In this work, an MOF-based composite photothermal membrane\n(PON@MOF) was prepared via the in situ growth of metal–organic\nframework (MOF) nanoneedle arrays induced by a pyridine-based organic\npolymer nanowire network (PON). The PON@MOF membrane possessed an\nMOF array layer, a PON-induced layer, and a porous support layer.\nThe PON is rich in coordinated nitrogen atoms for anchoring the metal-ion\nsource, and the main role of the PON layer is to provide favorable\nnucleation sites and orient in situ growth of well-aligned MOF nanoneedle\narrays. With the highly conjugated framework of PON@MOF and the light\ntrapping of the nanoarrays strengthening the photothermal conversion\nas well as the hydrophilic chemical structure facilitating the decrease\nof the water evaporation enthalpy, the PON@MOF membrane realizes highly\nefficient thermal vapor conversion. Under solar irradiation (1.0 kW\nm<sup>–2</sup>), PON@MOF demonstrated an evaporation rate of\n2.14 kg m<sup>–2</sup> h<sup>–1</sup> and a solar-to-vapor\nconversion efficiency of 98.5%. Meanwhile, the PON@MOF membrane has\nexcellent salt resistance and stability, highlighting its potential\napplication in desalination. Overall, this work provides a special\nidea for the structural design of photothermal composites for solar\ndesalination and freshwater production.