Cost-effective seawater desalination by photothermal membranes composed of biopolymers-doped graphene oxide using direct solar steam generation strategy

Abstract

The current study detailed the impact of the qualitative and quantitative addition of biopolymers, besides the influence of the drying method on the efficacy of the prepared photothermal membranes in seawater desalination using the direct solar steam generation (DSSG) strategy. Three natural polymers (NP) (i.e., cellulose acetate (CA), gum Arabic (GA), and sodium alginate (SA)), one synthetic polymer (i.e., polyvinyl alcohol; PVA) were used in membranes' preparation at different (NP/PVA) weight ratios, while graphene oxide (GO) and silica aerogel (SG) were added as a photothermal absorber and to enhance membrane floatability, respectively. The solar-driven evaporation experiments revealed that the evaporation rates (ER) were enhanced by increasing the NP/PVA ratio. Freeze-dried photothermal membranes demonstrated higher performances (ER = 1.59–3.62 kg/m2/h) compared with the freezing-thawed membranes (ER = 1.36–2.95 kg/m2/h) under 1-sun illumination when the NP/PVA ratio increased from 1:1 to 2:1. Interestingly, among all freeze-dried membranes, SA-based membranes at (SA/PVA = 3:1) ratio reflected the highest performance (ER = 4.33 kg/m2/h) at 1-sun illumination. The recorded high ER can be interpreted by several features: increasing the hydrophilic character of the composite membranes at high NP/PVA ratios, the high microporous structure of the internal channels when applying the freeze-drying method; the high GO content which effectively converts light to thermal energy; adequate membrane thickness (∼0.5 mm); besides the presence of SG to maintain the membrane floatability inducing heat localization. Thus, the study provided low-cost freshwater production at affordable rates using biopolymers-doped graphene oxide for desalination using DSSG systems.