Micro-/Macroscopically Synergetic Control of Switchable 2D/3D Photothermal Water Purification Enabled by Robust, Portable, and Cost-Effective Cellulose Papers.

Solar energy, as a renewable and sustainable resource, is considered to be a promising candidate for solving the water shortage through an interfacial solar-to-thermal conversion. Despite tremendous advances are achieved, it is still challenging for limited size, high-cost, and complicated fabrication protocols. More importantly, a favorable 2D/3D structure transformation to adapt to diverse conditions is considered to be very important. Inspired by the transformers with changeable geometries, herein, a large-area polypyrrole chemically functionalized cellulose paper (PPyP) with tunable microstructures and macroscopic geometries is developed via an in situ controlled oxypolymerization reaction. The resulted PPyP enables tunable 2D interfacial solar vaporization and even adapt itself to realization of 3D structures transformation for high-efficient water evaporation of up to 2.99 kg m-2 h-1 under 1 sun via an alternative kirigami/origami approach. Significantly, the PPyP can realize a switchable transformation between 2D and 3D structures to adapt diverse environments, demonstrating significant potentials in environmentally adaptable water purification.