MOF-303 with Lowered Water Evaporation Enthalpy for Solar Steam Generation

Hydrophilic metal-organic frameworks (MOFs) are promising for solar steam generation from waste or seawater. In this study, we propose a MOF-based Janus membrane for efficient solar steam generation. We selected MOF-303 for its hydrophilic properties and 1D channels with 6.5 Å cavity diameter, making it an excellent water-absorbing layer. Characterization via Raman spectroscopy and differential scanning calorimetry indicates that the nanoconfinement within MOF-303 can reduce the water evaporation enthalpy, thereby boosting water production efficiency. When deposited on various substrates, MOF-303 aimed to optimize solar steam generation. We enhanced the membrane performance by incorporating carbon black (CB), polydopamine (PDA), and perfluoro-functionalized poly(3,4-ethylenedioxythiophene) (PEDOT-F), materials known for their solar-to-thermal energy conversion capabilities. PEDOT-F, in particular, also served as a hydrophobic layer, preventing salt recrystallization during seawater operation. Under one sun irradiation, the water evaporation flux for deionized water increased from 0.31 to 0.79 kg h^-1 m^-2 using a porous hydrophilic poly(vinylidene difluoride) substrate and further to 2.36 kg h^-1 m^-2 with the optimized MOF-303-CB/PDA-PEDOT-F membrane, achieving an energy conversion efficiency of 97%. Additionally, the desalination capability of the MOF-303 membrane effectively reduced metal ion concentrations (Na⁺, K⁺, Mg²⁺, and Ca²⁺) to meet the WHO drinking water standards. These findings demonstrate the significant potential of the MOF-303-based Janus membrane for practical applications in solar steam generation and desalination, combining high water evaporation rates with excellent energy conversion efficiency.