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Water shortages and brine waste management are increasing challenges for coastal and inland regions, with high-salinity brines presenting a particularly challenging problem. These high-salinity waters require the use of thermally driven treatment processes, such as membrane distillation, which suffer from high complexity and cost. Here, we demonstrate how controlling the frequency of an applied alternating current at high potentials (20 V) to a porous thin-film carbon nanotube (CNT)/polymer composite Joule heating element can prevent CNT degradation in ionizable environments such as high-salinity brines. By operating at sufficiently high frequencies, these porous thin-films can be directly immersed in highly ionizable environments and used as flow-through heating elements. We demonstrate that porous CNT/polymer composites can be used as self-heating membranes to directly heat high-salinity brines at the water/vapour interface of the membrane distillation element, achieving high single-pass recoveries that approach 100%, far exceeding standard membrane distillation recovery limits.

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The electrochemical prevention and removal of CaSO4 and CaCO3 mineral scales on electrically conducting carbon nanotube - polyamide reverse osmosis membrane was investigated. Different electrical potentials were applied to the membrane surface while filtering model scaling solutions with high saturation indices. Scaling progression was monitored through flux measurements. CaCO3 scale was efficiently removed from the membrane surface through the intermittent application of a 2.5 V potential to the membrane surface, when the membrane acted as an anode. Water oxidation at the anode, which led to proton formation, resulted in the dissolution of deposited CaCO3 crystals. CaSO4 scale formation was significantly retarded through the continuous application of 1.5 V DC to the membrane surface, when the membrane was operated as an anode. The continuous application of a sufficient electrical potential to the membrane surface leads to the formation of a thick layer of counter-ions along the membrane surface that pushed CaSO4 crystal formation away from the membrane surface, allowing the formed crystals to be carried away by the cross-flow. We developed a simple model, based on a modified Poisson-Boltzmann equation, which qualitatively explained our observed experimental results.

Oil/water separations have become an area of great interest, as growing oil extraction activities are increasing the generation of oily wastewaters as well as increasing the risk of oil spills. Here, we demonstrate a membrane-based and fouling-free oil/water separation method that couples carbon nanotube-poly(vinyl alcohol) underwater superoleophobic ultrafiltration membranes with magnetic Pickering emulsions. We demonstrate that this process is insensitive to low water temperatures, high ionic strength, or crude oil loading, while allowing operation at high permeate fluxes and producing high quality permeate. Furthermore, we develop a theoretical framework that analyzes the stability of Pickering emulsions under filtration mechanics, relating membrane surface properties and hydrodynamic conditions in the Pickering emulsion cake layer to membrane performance. Finally, we demonstrate the recovery and recyclability of the nanomagnetite used to form the Pickering emulsions through a magnetic separation step, resulting in an environmentally friendly, continuous process for oil/water separation.