From ocean to ocean: Ulva prolifera biochar-sodium alginate hydrogel as a sustainable evaporator for efficient solar desalination and salt recovery

A marine biomass-based evaporator was made from Ulva prolifera and sodium alginate for green, low-cost solar desalination. • COMSOL simulation showed that the inverted cone structure promoted Marangoni convection for directional salt crystallization. • The evaporation and salt recovery rates reached values of 3.02 kg·m −2 ·h −1 and 3.13 kg·m −2 ·day −1 in 10 wt% NaCl solution. Solar-driven interfacial evaporation technology for saline water desalination, with advantages such as environmental friendliness and low cost, is of great significance for alleviating global water scarcity. However, salt scaling on the evaporator surface can reduce the evaporation rate and seriously threaten the system stability. Here, a sustainable inverted cone-shaped solar evaporator was fabricated using Ulva prolifera and sodium alginate as raw materials, achieving the synergy of efficient freshwater production and salt recovery. Under 1 sun irradiation, the fully marine biomass-based evaporator exhibited evaporation rates of 3.37 kg·m −2 ·h −1 and 3.02 kg·m −2 ·h −1 for 3.5 wt% and 10 wt% NaCl solutions, respectively, with no significant decay after 5 cycles. The unique 3D inverted-cone structure combined with the concentration gradient-induced Marangoni convection (verified by COMSOL simulation) promoted the saline radial transport and directional crystallization, enabling a salt collection rate of 3.13 kg·m −2 ·day −1 in 10 wt% NaCl. Furthermore, laboratory and outdoor performance tests using simulated seawater and real seawater demonstrated its application potential. This study provides a novel strategy for efficient seawater desalination and resource utilization. Download: Download high-res image (255KB) Download: Download full-size image