The study, published in the Journal of Materials Science: Polymers, details a surface engineering strategy that uses phytic acid to mediate the polymerization of polyaniline and enhance the anchoring of copper ions. By leveraging the chelating properties of phytic acid, the team created a membrane surface that binds copper more effectively than standard polyaniline modifications, resulting in a material with superior antifouling performance and antibacterial activity against Escherichia coli.
The primary motivation for this work addresses the persistent challenge of biofouling in pressure-driven ultrafiltration processes. Biofouling, caused by the accumulation of pollutants and microorganisms, significantly limits membrane efficiency and lifespan by blocking pores and forming cake layers. While polysulfone membranes are widely used due to their mechanical strength and chemical resistance, their inherent hydrophobicity makes them susceptible to microbial fouling. Previous modification strategies often improved hydrophilicity but failed to adequately address the dual need for high flux and robust antibacterial properties.
The research team, led by Uttam Kumar Mandal, utilized a two-step in-situ polymerization process to modify the polysulfone flat-sheet membranes. In the first step, aniline was polymerized in the presence of copper(II) chloride as an oxidant to form a polyaniline layer on the membrane surface. In the second step, phytic acid was incorporated as a dopant. The study compared three modified membrane variants: PSF-PANI, PSF-PANI-PA1, and PSF-PANI-PA2, where PA1 and PA2 represent membranes doped with 2% and 5% phytic acid relative to the monomer concentration, respectively.
Comprehensive structural characterization confirmed the successful integration of phytic acid and copper into the membrane matrix. Attenuated Total Reflectance-Fourier Transformed Infrared spectroscopy identified characteristic vibrational bands for polyaniline and phytic acid, including peaks associated with P-O and P=O stretching vibrations. X-ray photoelectron spectroscopy provided critical evidence of the phytic acid’s role as a chelator. The survey spectra revealed a phosphorus peak at 134.09 eV in the phytic acid-doped membranes, confirming the presence of the dopant. More importantly, the copper 2p spectra showed a drastically enhanced intensity in the PSF-PANI-PA1 membrane compared to the PSF-PANI membrane, indicating that phytic acid significantly increased the adsorption capacity of copper ions within the polyaniline matrix.
Elemental mapping and Energy Dispersive X-ray Spectroscopy further illustrated the distribution of copper on the modified surfaces. The phytic acid-doped membranes displayed a denser copper distribution than the standard polyaniline-modified membrane. This enhanced copper loading was attributed to the multi-phosphonate structure of phytic acid, which acts as a high-capacity chelating platform. The study notes that this architectural modification allows for the localized immobilization of antibacterial copper ions, a key factor in the membrane’s subsequent biological performance.
Filtration experiments revealed a complex trade-off between permeability and fouling resistance. The pristine polysulfone membrane had a pure water flux of 112.7 L/m²·h. Modification with polyaniline alone increased this flux to 454.2 L/m²·h, a 302.7% increase, reflecting improved hydrophilicity. However, the addition of phytic acid led to a sharp decline in permeability. The PSF-PANI-PA2 membrane, for instance, saw its flux drop to 41.5 L/m²·h. This reduction was linked to the formation of agglomerated polyaniline fibers that partially blocked the membrane pores, as confirmed by Field Emission Scanning Electron Microscopy and Atomic Force Microscopy images.
Despite the lower water flux, the phytic acid-doped membranes demonstrated exceptional antifouling performance. Dead-end filtration experiments using bovine serum albumin as a model foulant showed that the PSF-PANI-PA2 membrane achieved a flux recovery ratio of approximately 95%. This high recovery ratio, coupled with minimal irreversible fouling, indicates that the membrane resists the adhesion of protein molecules. The study suggests that the hydrophilic and negatively charged surface of the modified membrane repels protein fouling agents, maintaining consistent transport behavior even when water flux is reduced by structural densification.
The antibacterial efficacy of the membranes was evaluated using an inhibition zone assay against Escherichia coli. The bare polysulfone membrane exhibited no detectable antibacterial effect, with uninterrupted bacterial growth adjacent to the membrane disc. In contrast, the modified membranes displayed distinct biocidal properties. The PSF-PANI membrane showed initial activity, but the phytic acid-doped membranes with higher copper loading displayed highly pronounced inhibition zones where no bacterial colonies were present. This superior antibacterial activity is directly attributed to the higher density of anchored copper ions facilitated by the phytic acid chelation.
The mechanism of antibacterial action involves a synergistic interaction between the polyaniline network and the copper ions. The study explains that polaronic charge carriers within the polyaniline accelerate the oxidation of copper and the release of Cu2+ ions. This process generates reactive oxygen species, including hydroxyl radicals, superoxide, and hydrogen peroxide. These reactive species induce oxidative stress, leading to cell membrane depolarization, lipid peroxidation, and DNA damage in the bacteria. The enhanced copper loading on the phytic acid-modified membrane ensures a sustained release of these antibacterial agents, providing a robust defense against microbial colonization.
The findings highlight the importance of balancing selectivity and fouling resistance in membrane design. While the PSF-PANI membrane offered the highest water flux, it suffered from poor fouling resistance and lower antibacterial efficacy. The PSF-PANI-PA2 membrane, although less permeable, provided superior protein rejection, minimal fouling, and enhanced antibacterial stability. The authors suggest that this trade-off aligns with the Robeson upper bound concept in membrane science, where increased selectivity often comes at the cost of reduced permeability. The phytic acid-mediated strategy offers a framework for developing self-cleaning membranes suitable for water treatment applications where long-term stability and biofouling resistance are critical.
The study acknowledges that ensuring long-term antibacterial efficacy remains a challenge, particularly regarding the leaching of copper ions over extended periods. While the phytic acid chelation helps maintain copper loading, the authors recommend future continuous cross-flow evaluations to monitor copper leaching against drinking water standards. Nevertheless, the work demonstrates that phytic acid can serve as a critical chelating agent to optimize the performance of polyaniline-copper modified membranes.
This research contributes to the broader field of membrane science by introducing a novel surface engineering approach that leverages natural biocompatible compounds. By using phytic acid not just as a dopant but as a structural anchor for copper, the team has created a membrane with dual functionality. The ability to simultaneously enhance antifouling properties and antibacterial activity addresses two of the most significant limitations in current ultrafiltration technology. The study provides a detailed characterization of the molecular interactions involved, offering insights that can be applied to the design of advanced separation membranes for diverse industrial and environmental applications.
The study utilized a flat-sheet polysulfone ultrafiltration membrane with a nominal molecular weight cutoff of 100 kDa, sourced from Alfa Laval Private Limited in India. The modification process involved dissolving copper(II) chloride dihydrate in methanol and adjusting the solution pH to 3 using 1 M hydrochloric acid before adding aniline. The polymerization reaction proceeded for 24 hours under constant orbital shaking, during which the solution color shifted from fluorescent green to reddish brown and finally to brownish green, indicating the formation of the polyaniline layer. For the phytic acid-doped variants, specific amounts of phytic acid were added to the reaction system alongside the aniline, with the remaining procedural steps remaining identical to the standard polyaniline modification protocol.
Characterization of the membrane surfaces revealed distinct morphological differences between the variants. Field Emission Scanning Electron Microscopy images showed that the standard polyaniline-modified membrane possessed a comparatively uniform porous layer, whereas the phytic acid-doped membranes exhibited agglomerated fibrous structures on their surfaces. Atomic Force Microscopy measurements confirmed that the phytic acid-doped membranes had higher values for average surface roughness, root-mean square roughness, and peak-to-peak distance compared to the unmodified and standard polyaniline membranes. These structural irregularities were attributed to the higher copper content, which promoted the agglomeration of polyaniline fibers and partially blocked the membrane pores, thereby increasing the hydraulic resistance of the material.
The antibacterial testing protocol involved sterilizing the membrane samples by autoclaving for 30 minutes before placing them on agar plates inoculated with Escherichia coli at a concentration of 10^8 colony-forming units per milliliter. The plates were incubated at 37 degrees Celsius for 24 hours, after which the diameter of the inhibition zone surrounding each sample was measured. The bare polysulfone membrane showed no detectable antibacterial effect, with bacterial growth continuing directly adjacent to the disc. In contrast, the modified membranes displayed clear inhibition zones, with the phytic acid-doped variants showing the most pronounced areas devoid of bacterial colonies, consistent with the higher density of anchored copper ions identified in the spectroscopic analyses.
The filtration experiments were conducted using a dead-end filtration unit with a 500 ml cylindrical feed chamber equipped with a stirrer for uniform mixing. The transmembrane pressure was maintained at 20 psi using nitrogen gas, and the effective membrane area was specified as 33 m² in the experimental description. The membranes were soaked overnight and compacted with double distilled water prior to testing. Performance metrics, including pure water flux, protein flux, rejection percentage, flux recovery ratio, irreversible fouling ratio, and relative flux reduction, were calculated using standard equations to quantify the separation efficiency and fouling resistance of the modified surfaces.
The study notes that the presence of copper ions can halt bacterial multiplication by damaging basic DNA or RNA structures. The synergistic mechanism involves the polyaniline network facilitating the redox cycling between copper ions, which generates reactive oxygen species such as hydroxyl radicals, superoxide, and hydrogen peroxide. These species contribute to the antibacterial efficacy by inducing oxidative stress in the bacterial cells. The authors emphasize that the phytic acid serves not only as a green dopant but as a high-capacity chelating platform that intensifies the localized immobilization of copper ions, thereby enhancing the membrane’s ability to resist biofouling and maintain operational stability over time.
Subject of Research: Surface engineering of polysulfone ultrafiltration membranes using phytic acid and polyaniline for enhanced antifouling and antibacterial performance.
Article Title: Phytic acid-mediated polyaniline-Cu modified polysulfone membrane: antifouling and antibacterial properties
Article References: Goel, V., Bhardwaj, P., & Mandal, U. K. (2026). Phytic acid-mediated polyaniline-Cu modified polysulfone membrane: antifouling and antibacterial properties. Journal of Materials Science: Polymers, 1(1), Article 28. https://doi.org/10.1007/s44493-026-00029-y
Image Credits: AI Generated
DOI: 10.1007/s44493-026-00029-y
Keywords: polysulfone membrane, polyaniline, phytic acid, ultrafiltration, antifouling, antibacterial, copper ions, water treatment, membrane science, biofouling, Phytic, acid-mediated
