Centrifuge‐Free Separation of Solution‐Exfoliated 2D Nanosheets via Cross‐Flow Filtration

Abstract

Solution‐processed graphene is a promising material for numerous high‐volume applications including structural composites, batteries, sensors, and printed electronics. However, the polydisperse nature of graphene dispersions following liquid‐phase exfoliation poses major manufacturing challenges, as incompletely exfoliated graphite flakes must be removed to achieve optimal properties and downstream performance. Incumbent separation schemes rely on centrifugation, which is highly energy‐intensive and limits scalable manufacturing. Here, cross‐flow filtration (CFF) is introduced as a centrifuge‐free processing method that improves the throughput of graphene separation by two orders of magnitude. By tuning membrane pore sizes between microfiltration and ultrafiltration length scales, CFF can also be used for efficient recovery of solvents and stabilizing polymers. In this manner, life cycle assessment and techno‐economic analysis reveal that CFF reduces greenhouse gas emissions, fossil energy usage, water consumption, and specific production costs of graphene manufacturing by 57%, 56%, 63%, and 72%, respectively. To confirm that CFF produces electronic‐grade graphene, CFF‐processed graphene nanosheets are formulated into printable inks, leading to state‐of‐the‐art thin‐film conductivities exceeding 104 S m−1. This CFF methodology can likely be generalized to other van der Waals layered solids, thus enabling sustainable manufacturing of the diverse set of applications currently being pursued for 2D materials.

Tailoring Electrical Properties in Carbon Nanomaterial Patterns with Multimaterial Aerosol Jet Printing

“…Graphene powders coated with ethyl cellulose, in which graphene comprises 30 wt % of the total powder, were prepared via liquid-phase exfoliation in a pilot-scale shear mixer in the presence of ethyl cellulose. This results in an average flake thickness of ∼2 nm, as described in previous work. , Bioderived CNO powders were synthesized from softwood organosolv lignin (OL) by precarbonization followed by Joule heating. Specifically, the OL was purified by washing with deionized water for 4 h at 90 °C and then precarbonized at 700 °C under N 2 .…”

“…This results in an average flake thickness of ∼2 nm, as described in previous work. 28,29 Bioderived CNO powders were synthesized from softwood organosolv lignin (OL) by precarbonization followed by Joule heating. Specifically, the OL was purified by washing with deionized water for 4 h at 90 °C and then precarbonized at 700 °C under N 2 .…”

Solution-Processable and Printable Two-Dimensional Transition Metal Dichalcogenide Inks

“…110 In addition to various centrifugation-based methods, Downing et al developed a cross-flow filtration (CFF) method with higher separation efficiency for graphene. 233 A hollow fiber cross-flow microfiltration module (CF-MF) containing bundles of hollow fiber membranes of hydrophobic polysulfone was used for the CFF process. Well-exfoliated graphene nanosheets traverse the porous membrane and are pumped out through the permeate port, while the poorly exfoliated graphite particles with thick and large sizes remain in the retentate.…”

“…In addition to various centrifugation-based methods, Downing et al. developed a cross-flow filtration (CFF) method with higher separation efficiency for graphene . A hollow fiber cross-flow microfiltration module (CF-MF) containing bundles of hollow fiber membranes of hydrophobic polysulfone was used for the CFF process.…”

Computational Fluid Dynamics Modeling of the Filtration of 2D Materials Using Hollow Fiber Membranes

“…For example, membrane technologies have been recently used for the treatment of wastewater effluent in the food industry [16]; the recovery of the bio-sourced precursor (succinic acid) of biomolecules [17]; the recovery of the lignin, which is the among the most essential bio-fuel compounds [18]; and so forth. Recently, Downing et al [19] extended the applications of microfiltration membranes to the isolation of 2D materials (graphene) through cross-flow filtration (CFF) for the formulation of printable graphene-based inks. The filtration process yielded monodisperse graphene dispersion, which is required to formulate printable inks and led to the printing of highly conductive thin films.…”