Abstract

Metal-organic frameworks (MOFs) are high-performance adsorbents for atmospheric water harvesting but have poor water-desorption ability, requiring excess energy input to release the trapped water. Addressing this issue, a Janus-structured adsorbent with functional asymmetry is presented. The material exhibits contrasting functionalities on either face - a hygroscopic face interfaced with a photothermal face. Hygroscopic aluminum fumarate MOF and photothermal Cux S layers are in-situ grown on opposite sides of a Cu/Al bimetallic substrate, resulting in a Cux S-Cu/Al-MOF Janus hygro-photothermal hybrid. The two faces serve as independent "factories" for photothermal conversion and water adsorption-desorption respectively, while the interfacing bimetallic layer serves as a "heat conveyor belt" between them. Due to the high porosity and hydrophilicity of the MOF, the hybrid exhibits a water-adsorption capacity of 0.161g g-1 and a fast adsorption rate (saturation within 52min) at 30% relative humidity. Thanks to the photothermal Cux S, the hybrid can reach 71.5 °C under 1 Sun in 20min and desorb 97% adsorbed water in 40min, exhibiting a high photothermal conversion efficiency of over 90%. Cux S-Cu/Al-MOF exhibits minimal fluctuations after 200 cycles, and its water-generation capacity is 3.21 times that of powdery MOF in 3 h in a self-designed prototype in one cycle.

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