Dual-functional GO composite aerogels for water purification and desalination via heavy metal adsorption and solar evaporation

Freshwater scarcity and heavy metal (HM) contamination are significant global challenges. Herein, a graphene oxide/tannic acid/polyethyleneimine mixed aerogel was developed (GTPA) with dual functions of efficient adsorption of HM and solar-powered desalination. The adsorption of Cr(VI) and Pb(II) follows Langmuir isotherms and pseudo-second-order kinetics, indicating monolayer chemisorption. Thermodynamic experiments confirmed that adsorption can occur spontaneously. The maximum adsorption capacities of Cr(VI) and Pb(II) by GTPA were 434.78 mg·g⁻¹ and 304.88 mg·g⁻¹, respectively, and the equilibrium time was 90 min, and it showed excellent adsorption performance in coexisting ions and natural wastewater solutions. Experimental and DFT analyses showed that the adsorption mechanism mainly involved hydrogen bonding, chelation, electrostatic interactions, and synergistic effects. After 5 cycles, the adsorption efficiencies of Cr(VI) and Pb(II) by GTPA were 78.21 % and 73.18 % respectively. In solar desalination applications, the abundant hydrophilic groups in GTPA effectively break the hydrogen bond between water molecules and reduce the enthalpy of evaporation; Its high porosity and hierarchical pore structure extends the light path through multiple reflections and scattering, which improves the photon absorption efficiency. Under one-sun irradiation, GTPA achieved a water evaporation rate of 2.38·kg m⁻²·h⁻¹ and a photothermal conversion efficiency of 88.23 %. The porous structure and high adsorption capacity effectively inhibit salt crystallization and promote rapid water transport, maintaining efficient desalination even under high salt concentration conditions. The evaporated seawater was found to meet WHO and EPA standards for drinking water. GTPA effectively prevented impurities such as metal ions from entering the condensate by adsorbing contaminants. The results demonstrate that GTPA offers a novel strategy for designing aerogels with enhanced adsorption capacity and superior photothermal desalination performance.