(146b) Enhanced Diffusiophoretic Mobility and Removal of Colloidal Water Contaminants By Tunable CO2 Flux

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.