Sodium functionalised carbon nanofibers draw solution for a solar-thermal forward osmosis water desalination system

Abstract

Desalination offers the potential to bridge the demand-supply gap in the increasing global freshwater scarcity, with the forward osmosis (FO) technique appearing as an attractive solution amongst the various desalination technologies. However, the significant energy demand encountered during the draw-solute recovery process in FO desalination is considered the major anathema amongst other contending factors for which the allure of FO as a desalination technology becomes questioned. Consequently, a potentially innovative draw solution (DS) regeneration strategy, enabling the circumvention of the energy requirements associated with the recovery stage in FO desalination, is evaluated. The direct solar thermal FO (DSTFO) desalination concept is predicated on engineering and applying solar absorptive DS to directly leverage solar energy for solute recovery without recourse to electric power. In advancing the DSTFO concept, this study fabricated and evaluated a novel and highly osmotic sodium functionalised carbon nanofibres (Na/CNF) DS having a high osmotic pressure (93.9 bar), a low reverse solute flux (RSF) of 0.24 gMH, and a photothermal conversion efficiency of 63.49%, resulting in an evaporation rate of 1.85 kg/m2/hr under 2 suns of solar radiation. The DSTFO strategy offers a low-cost solution for enhancing water recovery and decreasing energy use in FO desalination systems.