Composite magnetite-lignin as photothermal material for clean water production

Biomass-derived photothermal materials possess a strong capacity for absorbing sunlight and converting it into thermal energy, meeting the criteria needed for localized heat in solar steam generation. Lignin, a by-product of the pulping process, is rarely used for creating high-value products. In this study, we present a method to synthesize a magnetite-lignin composite via an electrochemical process using a monopolar Fe electrode arrangement at a pH of 9 over 3 hours. We examined how varying the Na-lignin ratio in the electrolyte solution affects the synthesis. The magnetite-lignin composite, with a size of approximately 184.1 nm, displays a cubic morphology, a surface area of 354.3 m²/g, and a tap density of 0.665 g/cm³. Notably, this composite achieves excellent light absorption at 99.24%. When deposited onto a polystyrene foam substrate in a bilayer heat-localization solar steam generation (SSG) system, the photothermal material effectively absorbs sunlight, converting it to heat and vaporizing water, yielding a high solar evaporation rate of 0.661 kg/m²/h under standard sunlight. Our research introduces a low-cost, simple, and highly efficient approach for industrial-scale, sustainable photothermal applications in bilayer SSG systems for solar-driven water purification, enabling clean water production from seawater.