Tea stain-inspired solar energy harvesting polyphenolic nanocoatings with tunable absorption spectra

Discovery and development of new sustainable photothermal materials with tunable light absorption spectra play a key role in solar energy harvesting and conversion. One possible solution to this quest is to check nature as a source of matters or inspiration. Inspired by the formation of tea stains, a unique class of dark stain materials generated by the interfacial reaction between tea polyphenols and metal substance, we reported the facile preparation and screening of a series of photothermal nanocoating layers via the metal ion (i.e. Cu(II),Fe(III), Ni(II), Zn(II)) promoted in situ polymerization of typical phenolic moieties of tea polyphenols (i.e., catechol and pyrogallol). It was found that those resulting metal-polyphenolic nanocoatings showed various promising features, such as high blackness and strong adhesion, excellent and tunable light absorption properties, good hydrophilicity and long-term stability. We further fabricated the photothermal composite devices by in situ formation of metal-polyphenolic nanocoatings on pristine silks for solar desalination, which demonstrated promising durable evaporation behaviors with excellent evaporation rates and steam generation efficiencies. We believe that this work could provide more opportunities towards new types of bio-inspired and sustainable photothermal nanomaterials for solar energy harvesting applications such as water desalination.