Side structural regulation strategy of 3D gear evaporators for enhanced solar water evaporation and salt harvesting

Interfacial water evaporation driven by solar energy is believed to be one of the most effective methods to reduce water pollution and scarcity globally. However, lower evaporation and salt accumulation still limit its practical application towards zero-liquid discharge. Here, a side structural regulation approach of 3D gear evaporators is sequentially designed by adhering low-cost activated carbon onto a gear-shaped hepa filter, aided by a centralized water supply through the cotton pith. These 3D gear evaporators harvest multiple energy sources with their sawtooth structure to maintain the cooling evaporation surface property, linearly escalating the evaporation rate from 3.79 kg m⁻² h⁻¹ to 8.35 kg m⁻² h⁻¹ by increasing the light incidence angle (75°). This unprecedented enhancement is due to a higher evaporation area index (EAI) which is higher than many cylindrical 3D evaporators. More importantly, concentration gradient allows salt crystallization at the edges and endows a salt harvesting rate of 72.8 g m⁻² h⁻¹ with highly saline brine (20 wt%) and zero liquid discharge in brine management. The evaporator acquired excellent purifying efficiency for simulated saltwater, dye wastewater, and real oily wastewater, generating over 4 kg m⁻² of fresh water daily during a five-day outdoor trial—sufficient to satisfy the daily drinking requirements of 2–3 people.