Polyaniline-Coated Carbon Nanotube Ultrafiltration Membranes: Enhanced Anodic Stability for In Situ Cleaning and Electro-Oxidation Processes

Abstract

Electrically conducting membranes (ECMs) have been reported to be efficient in fouling prevention and destruction of aqueous chemical compounds. In the current study, highly conductive and anodically stable composite polyaniline-carbon nanotube (PANI-CNT) ultrafiltration (UF) ECMs were fabricated through a process of electropolymerization of aniline on a CNT substrate under acidic conditions. The resulting PANI-CNT UF ECMs were characterized by scanning electron microscopy, atomic force microscopy, a four-point conductivity probe, cyclic voltammetry, and contact angle goniometry. The utilization of the PANI-CNT material led to significant advantages, including: (1) increased electrical conductivity by nearly an order of magnitude; (2) increased surface hydrophilicity while not impacting membrane selectivity or permeability; and (3) greatly improved stability under anodic conditions. The membrane's anodic stability was evaluated in a pH-controlled aqueous environment under a wide range of anodic potentials using a three-electrode cell. Results indicate a significantly reduced degradation rate in comparison to a CNT-poly(vinyl alcohol) ECM under high anodic potentials. Fouling experiments conducted with bovine serum albumin demonstrated the capacity of the PANI-CNT ECMs for in situ oxidative cleaning, with membrane flux restored to its initial value under an applied potential of 3 V. Additionally, a model organic compound (methylene blue) was electrochemically transformed at high efficiency (90%) in a single pass through the anodically charged ECM.

Single and binary protein electroultrafiltration using poly(vinyl-alcohol)-carbon nanotube (PVA-CNT) composite membranes

“…Two-way analysis of variance (ANOVA) followed by post hoc Tukey's multiple comparisons tests were performed using Graphpad Prism version 6.01 (Graphpad Software, La Jolla, CA, USA) to assess the statistical differences among the weighted factor means at a significance level of p < 0.05. reported measurements [5,11]. With an approximate 10 µm thickness of the selective layer [5], the length fraction of the support layer, X, was determined to be 0.91.…”

“…Two-way analysis of variance (ANOVA) followed by post hoc Tukey's multiple comparisons tests were performed using Graphpad Prism version 6.01 (Graphpad Software, La Jolla, CA, USA) to assess the statistical differences among the weighted factor means at a significance level of p < 0.05. reported measurements [5,11]. With an approximate 10 µm thickness of the selective layer [5], the length fraction of the support layer, X, was determined to be 0.91. Based on image analysis of SEM images of the PVA-CNT surface using the NIH ImageJ software (minimum size of 0.007 µm 2 , circularity parameter of 0.01-1), the typical pore size of the PVA-CNT network (assuming circular pores) was determined to be 475 nm (S5 Fig). The results indicate that the pore size of the conductive network is significantly larger than that of the underlying selective layer of the polysulfone membrane.…”

“…As can be seen, unlike electroultrafiltration processes with electrodes on each side of the membrane, the external electric field terminates with the poly(vinyl-alcohol)carbon nanotube layer, which is upstream of the semipermeable, polymeric membrane. Jassby et al [5][6][7][9][10][11] developed methods of coating commercial polymeric UF membranes with a thin layer of a poly(vinyl-alcohol) (PVA) polymer cross-linked with multiwalled carbon nanotubes to form highly electrically conductive PVA-CNT composite membranes. In a study of the effect of moderate applied electric potentials (-1.5 and -3.4 V vs Ag/AgCl references) on fouling of high concentrations (3-5 g/L) of synthetic wastewater containing negatively charged alginic acid during EUF using PVA-CNT composite membranes, Dudchenko and Jassby et al observed substantial fouling inhibition and reduction of operating pressure in a constant flux system [6].…”

Preparation of flexible hollow PANI/Feixu composite fibers

“…Another advantage is that they are hollow which can combine other functional materials to form multi‐functional composite fibers. These special characteristics of the composites provide a possible way to make hollow‐fiber membrane, flexible electronic device and other flexible and conductive 1D PANI composite devices …”

Carbon Nanotube Membranes: Synthesis, Properties, and Future Filtration Applications

“…The oxidation of methylene blue has also been achieved through the application of oxidizing electrochemical potentials to polyaniline/MWNT composite membranes [120]. The latter showed a number of favourable attributes for this application, including significant levels of hydrophobicity and electrical conductivity.…”