Photothermal Carbon Black Nanoparticle Coating Increases Scaling Resistance in Solar Membrane Distillation

Self-heating membranes show promise for off-grid solar membrane distillation (MD). High scaling resistance was indicated in solar MD systems when only driven by the self-heating surface due to the low bulk feedwater temperature. However, low temperatures also result in low permeate flux compared to conventionally heated MD systems. To identify the trade-off between high flux and scaling resistance, we investigated the effect of an increasing feed temperature (Tfeed) on permeate flux and scaling resistance in MD. Increasing Tfeed between 30 and 70 °C while maintaining a constant distillate temperature of 20 °C confirmed that higher Tfeed increases permeate flux but also results in an earlier flux decline caused by higher membrane scaling. Similar findings were obtained when a self-heating layer was used; however, the self-heating layer in solar MD also resulted in a lower flux decline despite the high feedwater temperature. This effect is attributed to an increase in the hydrophilicity of the heated layer compared to the pristine membrane, which is hypothesized to reduce the deposition of scaling precursors on the surface. These findings indicate benefits beyond flux improvement for self-heating MD membranes when used in challenging waters rich in inorganic scaling species.