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.


Supporting Figures
Supporting Tables Table S1.Values of the properties for each layer in the multilayer structure used for simulating temperature profiles via the finite element method.

Layer
(kg m -3 ) Figure S1.Photographic images of (a) the PVDF substrate, (b) the Teflon holder used to fix the

Figure S2 .
Figure S2.(a) Illustration of the membrane masking method for measuring the water evaporation

Figure S3 .
Figure S3.Photographic images of (a) the membrane chamber of the device for harvesting liquid

Figure S4 .
Figure S4.Geometry and mesh setup of various models for simulating temperature profiles using

Figure S10 .
Figure S10.UV-vis spectra of multilayer composition of the MOF-303 membranes.The shaded

Figure S12 .
Figure S12.Water evaporation flux from (a) various bare substrates and (b) membranes with

Figure S15 .
Figure S15.Comparison of device performance for solar steam generation among (a) devices

Figure S16 .
Figure S16.Photograph of the coastline in Keelung, Taiwan, where the seawater for the