Nanotube Alignment and Surface Chemistry in Altering Water and Salt Permeabilities for Imogolite-Polyamide Membranes

TL;DR

This paper explores how aligning and chemically modifying nanotubes can improve water filtration membranes while maintaining salt rejection.

Contribution

The study introduces a novel method to control nanotube orientation and surface chemistry to enhance membrane performance.

Findings

Membrane water permeance increased significantly with nanotube integration.

Salt permeability remained low when nanotube interiors were made hydrophobic.

Tailoring nanotube chemistry allows for improved water permeability without compromising salt rejection.

Abstract

Reducing the specific energy consumption of reverse osmosis (RO) processes motivates the development of new membrane materials that have enhanced water permeability while maintaining low salt permeability (high rejection). Nanocomposite membranes have shown great promise in achieving these goals, particularly those using nanotubes as fillers. Here, we report on the relationships between the orientations and surface functionalities of imogolite nanotubes (INTs) with water and salt permeabilities for polyamide nanocomposite membranes. An external electric field was used to manipulate the INT orientation within the polyamide active layer. The INT interior and exterior chemistries, respectively, were made hydrophobic using methyl triethoxysilane as a precursor during INT synthesis and post-synthesis modification with alkali-phosphate groups. Irrespective of nanotube orientation or surface chemistry, membrane permeance increased from 0.3 to ≥1.0 L m−2 h−1 bar−1. A salt permeability comparable to the conventional polyamide membrane was maintained by making the INT pore throat hydrophobic. These findings indicated that salt rejection could be tailored by manipulating the INT interior surface chemistry without sacrificing water permeability.

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