Observation of proton diffusion in porous media using pH-imaging technology

We propose the application of pH-imaging technology to the observation of proton transport in porous media. A flat pH-imaging sensor based on the electrochemical-semiconductor principle was employed for imaging. Porous media were formed by packing particles with a few hundred-micrometer diameter such as silica sands, glass-beads and ion- exchange resins. These particles were packed on the pH-imaging sensor, respectively, followed by the addition of an acid solution from the top surface of the layer. The pH distribution formed on the interface between the sensor and the layer was repeatedly imaged with a 3 min time resolution. The dependence of proton transport on the particle type and size was clearly imaged and quantitatively evaluated. The proposed method was confirmed to be useful for understanding mass transport in porous media, thus enabling contribution to fundamental research involving the transport of chemicals in soil/aquifer/reservoir, such as bioremediation and microbial-enhanced oil recovery (Microbial EOR).