Highly salt resistant composite based protonated g-C3N4@rGO/biochar for photocatalytic degradation of organic dyes through simultaneous solar steam-electricity generation

Solar steam generation (SSG) is a promising solar energy harvesting technique for addressing global freshwater scarcity. However, the high materials cost, salt accumulation, and concentration of pollutants in the brine after SSG hindered their practical applications. Herein, the recycled sawdust waste was used as a cost-effective evaporator and decorated with protonated carbon nitride and reduced graphene oxide (rGO) which was termed as P-g-C3N4 @ rGO/DB. The g-C3N4 was protonated with sulfuric acid giving P-g-C3N4, which has high salt resistance via the Donnan exclusion mechanism. Besides, P-g-C3N4 as a metal-free semiconductor with a mild band gap (2.7 eV) was utilized for the photocatalytic degradation of the organic dyes under solar illumination to prevent the concentration of pollutants in water after desalination. Coupling rGO as electron acceptors inhibits the e−/h+ pairs recombination and traps the organic dyes on the surface of the evaporator increasing the photocatalytic degradation efficiency. The composite exhibited an excellent evaporation rate of 1.98 kg m−2 h−1 with 97.2 % solar to steam conversion efficiency as well as superior photocatalytic degradation of RhB dye under 1 sun illumination. Finally, the evaporator was coupled with a thermoelectric module achieving the maximum electricity cogeneration of 13.69 mW/m2.