Versatile coating with multifunctional performance for solar steam generation

In this work, a new kind of material, tannic [email protected]@Fe3+ ([email protected]@Fe3+) composite coating, with multifunctional performance has been developed for solar steam generation. The [email protected]@Fe3+ has many advantages: (a) Scalability. The fabrication process is facile and mild; it can be realized in aqueous solution at room temperature, without high pressure, toxic organic solvents, or complex equipment. (b) Cost-effectiveness. The reagents used for preparation of [email protected]@Fe3+ are low-cost and readily available. (c) Universality and good stability. [email protected]@Fe3+ firmly adheres on surfaces of various substrates with diverse shapes (cotton, filter paper, wood, polyurethane sponge, and even chemically inert and highly hydrophobic polyvinylidene fluoride membranes), and can withstand rinsing treatment (3000 r/min for 96 h), cyclic frost-thaw test (−18 °C ⇄ 30 °C, 90 times), and both high and low pH environments. Many other reported coatings, such as carbon black, fail under similar process strain. (d) Anti-crude oil-fouling property. The [email protected]@Fe3+ possesses stable superhydrophilicity and underwater superoleophobicity, which collectively endow substrates with the ability to resist fouling by oils. (e) Broad and strong light absorption. [email protected]@Fe3+ can transform various substrates with diverse shapes into black materials with broadband light absorption due to its d-d transitions and rough surface. Together, these properties of [email protected]@Fe3+ enable substrates with nearly any structural design to be easily transformed into photothermal materials for efficient solar steam generation. As a proof of concept, poplar wood is treated with [email protected]@Fe3+, achieving a water evaporation rate of ~1.8 kg m−2 h−1 (one sun), which is a record among wood-based photothermal materials.