Membrane capacity and fouling mechanisms for ultrathin nanomembranes in dead-end filtration

Ultrathin membrane technologies hold promise for improvements in membrane-based separation, however much remains to be learned about the ability of these membranes to support practical filtration processes. Here we examine the performance of new nanoporous silicon nitride (NPN) membranes in dead-end filtration using different methods for generating transmembrane pressure while varying nanoparticle types, sizes and concentrations. We infer membrane fouling by the amount of filtrate generated after a minute of dead-end filtration and show that each of these parameters has a strong influence on the rate of NPN fouling. Inverted centrifugation, which pulls large particles and aggregates away from the membrane as solvent passes through, increases filtrate volumes compared to forward centrifugation. Fitting filtration results to classic fouling models indicate that particles larger than the pores appear to foul membranes via cake formation at all concentrations, while filtration with particles much smaller than pores are impacted by pore obstruction before cake build up. Using direct comparisons in centrifuge devices, we show that NPN membranes have a comparable capacity to process suspensions of small colloids by dead end filtration at similar solvent speeds to thicker polycarbonate track-etched membranes, even with permeabilities more than two orders of magnitude higher.