Inorganic precipitate membranes play an important role in biomineralization, chemobrionics, and origin-of-life research. They can involve a range of catalytic materials, affect crystal habits, and show complex permeabilities. We produce such membranes in a microfluidic device at the reactive interface between laminar streams of hydroxide and Co(II) solutions. The resulting linear membranes show striking color bands that, over time, expand in the direction of the Co(II) solution. The cumulative layer thicknesses (here up to 600 μm) obey square root laws, indicating diffusion control. The effective diffusion coefficients are proportional to the hydroxide concentration, but the membrane growth slows down with increasing concentrations of Co(II). On the basis of spatially resolved Raman spectra and other techniques, we present chemical assignments of the involved materials. Electron microscopy reveals that the important constituent β-Co(OH)<sub>2</sub> crystallizes as thin hexagonal microplatelets. Under drying, the membrane curls into spirals, revealing mechanical differences between the layers. Another example is the case of iron phosphate membranes. We show that in the presence of acetyl-phosphate, the membrane causes the formation of pyrophosphate which might have served as the energy currency of early life emerging in hydrothermal vents. The latter product is identified by aqueous <sup>31</sup>P-NMR spectroscopy from samples removed from the microfluidic device. This result demonstrates the usefulness of microfluidics-based synthesis for origin-of-life studies that require the exploration of vast parameter spaces.

Self-organization of layered inorganic membranes in microfluidic devices

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.