Membraneless water filtration using CO2

Abstract

Water purification technologies such as microfiltration/ultrafiltration and reverse osmosis utilize porous membranes to remove suspended particles and solutes. These membranes, however, cause many drawbacks such as a high pumping cost and a need for periodic replacement due to fouling. Here we show an alternative membraneless method for separating suspended particles by exposing the colloidal suspension to CO2. Dissolution of CO2 into the suspension creates solute gradients that drive phoretic motion of particles. Due to the large diffusion potential generated by the dissociation of carbonic acid, colloidal particles move either away from or towards the gas–liquid interface depending on their surface charge. Using the directed motion of particles induced by exposure to CO2, we demonstrate a scalable, continuous flow, membraneless particle filtration process that exhibits low energy consumption, three orders of magnitude lower than conventional microfiltration/ultrafiltration processes, and is essentially free from fouling.

Cleaning by Surfactant Gradients: Particulate Removal from Porous Materials and the Significance of Rinsing in Laundry Detergency

“…Because the diffusiophoretic velocity u dp ∝ ∇ln c, reducing the overall solute concentration does not necessarily reduce u dp [11,13]. For example, in the case of an SDS integrating u dp , while neglecting Brownian motion [14]. (e, f) Particle number density normalized by the value at t = 0 s (n/n0) over time for different solutes (red: NaCl; blue: SDS).…”

“…Similar principles have been applied to design 'salt traps' [11] and 'soluto-inertial beacons' [12]. Diffusiophoresis has been proposed as an inexpensive way to measure zeta potentials [13]; it can be induced by gas dissociation and exploited as a continuous separation process [14]; and in the presence of an opposing flow can lead to rapid pore blocking [15].…”

Accumulation of Colloidal Particles in Flow Junctions Induced by Fluid Flow and Diffusiophoresis

“…Diffusiophoresis, which has received recent interest because of experimental and theoretical advances [7][8][9][10][11][12][13][14][15][16][17], refers to the motion of colloidal particles induced by the solute gradients. The local solute gradient gives rise to the particle motion due to the osmotic pressure gradient developed along the particle surface (chemiphoresis) and the liquid junction potential generated by the diffusion of ions with different diffusivities (electrophoresis).…”

Interfacially driven transport theory: a way to unify Marangoni and osmotic flows

“…The theoretical model developed here can help to solve this kind of complex interplay. A better understanding of diffusio-phoresis could also lead to design processes using diffusio-phoresis mechanisms [40][41] . The simulation could also be more realistic by integrating a dependence of the viscosity on the concentration and a non-ideality of the osmotic pressure to account for colloid-colloid interactions.…”