Nonradiative Photothermal Process Coupled With Hydrogen‐Bond Regulations of Water Molecules in Covalent Organic Frameworks for Efficient Solar Steam Generation

ABSTRACT Covalent organic frameworks (COFs) with porous channels and tailor‐made structures are proposed as promising photothermal materials for solar steam generation (SSG). However, their poor light absorption in the near‐infrared (NIR) regions and hydrophobicity impede the efficient photothermal conversion and the decrease of water evaporation enthalpy. Herein, we develop two novel piperazine‐linked phthalocyanine‐based COFs (CoPc‐NH‐TABQ‐iAA and CoPc‐NH‐BTM‐iAA) with unique inclined AA stacking configurations via heterogeneous solvothermal synthesis for the first time, in which the hydrophilicity of COFs are regulated by non‐conjugated 1,2,4,5‐tetramino‐benzoquinone (TABQ) with rich C═O groups and conjugated 1,2,4,5‐benzenetetramine (BTM) without C═O groups. Benefited from the narrow bandgap of 1.17 eV and hydrophilic C═O groups, the CoPc‐NH‐TABQ‐iAA COF shows broadband absorptions from visible to NIR regions, a nonradiative photothermal process, and abundant hydrogen‐bond binding sites, which facilitate efficient photothermal conversion. As a result, CoPc‐NH‐TABQ‐iAA demonstrates an excellent water evaporation rate of 2.56 kg m −2 h −1 and a long‐term durability of 100 h under 1 sun. To the best of our knowledge, the ultra‐high stability exceeds the vast majority of organic photothermal materials. Control experiments of CoPc‐NH‐BTM‐iAA without C═O groups and molecular dynamics simulations reveal that the regulation of the hydrogen‐bond microenvironment between water molecules can effectively boost the photothermal water evaporation.