Frequency-dependent stability of CNT Joule heaters in ionizable media and desalination processes

Abstract

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.

The relative insignificance of advanced materials in enhancing the energy efficiency of desalination technologies

“…Surface heating intuitively offers the advantage of reducing the required energy since less water is heated, while also eliminating temperature polarization and its detrimental effects. 69,70 With surface-heating DCMD gaining considerable momentum, recent studies have proposed the use of solar energy by developing MD membranes with photothermal surface coatings (e.g., plasmonic nanoparticles or carbon nanotubes), effectively introducing a novel STD system which obviates the need for external solar collectors. 50,51 While the benefits of surface heating are apparent for single-pass DCMD operation-common in small laboratory-scale systemsour recent process modeling importantly reveals that conventionally heated DCMD is in fact considerably more energy efficient under practical operation involving recirculation of the feed stream (see ESI † for details).…”

Electric‐Field‐Induced Ionic Sieving at Planar Graphene Oxide Heterojunctions for Miniaturized Water Desalination

“…[ 1 ] Nanomaterial‐based technologies, capable of effectively and affordably extracting potable water from unconventional water sources (such as, salt water, industrial waste water, and rain water), make critical contribution for sustainable water use. [ 2–5 ] Particularly, 2D‐material‐based nanofluidic membranes are considered as promising materials for next‐generation water desalination and purification. [ 6 ] For example, monolayer graphene with sub‐nanometer pores exhibits nearly 100% salt rejection and high water permeability, [ 7,8 ] with orders of magnitude greater than commercial reverse osmosis (RO) membranes (≈2 Lm −2 h −1 bar −1 ).…”

Dual‐Function Electrocatalytic and Macroporous Hollow‐Fiber Cathode for Converting Waste Streams to Valuable Resources Using Microbial Electrochemical Systems

“…CNTs could also be deposited onto the ceramic membrane surface via spray coating [55] or vacuum-filtration. [56] CNT-Polyvinyl alcohol (CNT-PVA) layers with excellent conductivity and stability were spray coated on flat ceramic membranes, which served as Joule heaters in membrane distillation.…”

“…[56] CNT-Polyvinyl alcohol (CNT-PVA) layers with excellent conductivity and stability were spray coated on flat ceramic membranes, which served as Joule heaters in membrane distillation. [55] Fan et al [56] mixed CNTs with polyacrylonitrile (PAN) to cast CNT layers onto a porous ceramic hollow fiber substrate via a vacuum-filtration process. After pyrolysis in a hydrogen atmosphere, the conductive hollow fiber membrane exhibited effective membrane fouling mitigation in an electric field.…”