As the demand for drinking water increases globally so does the need for distributed purification systems. The dissociation of carbon dioxide (CO2) in water to hydrogen (H+) and bicarbonate (HCO3-) ions has the potential to transform water purification by acting as an on-demand initiator for diffusiophoresis. Due to the faster diffusion of H+ in water compared to HCO3-, 9.33 × 10-9 vs 1.18 × 10-9 m2 s-1 respectively, an ion gradient develops when CO2 is fed through water. This ion gradient is capable of moving and concentrating charged colloids. Bench scale experiments using a custom concentric tubular diffusiophoretic separator were conducted to optimize particle separation. The strength of the ion gradient, was dependent on the partial pressure of CO2 applied through a Teflon AF 2400 semipermeable tube. A two-log reduction of 0.5 µm polystyrene spheres from lab grade water was achieved operating at a CO2 pressure of 250 kPa. A computational fluid mechanics model was developed to understand the formation of the necessary ion gradients required for diffusiophoresis.
