Effects of polyaniline nanoparticles in polyethersulfone ultrafiltration membranes: Fouling behaviours by different types of foulant

Abstract

Polyethersulfone (PES) was modified by blending it with polyaniline (PANI) nanoparticles to improve the membrane performance. Three types of membranes: PES (controlled sample), PES-PANI self-synthesised, and PES-PANI (commercial), were evaluated by direct interaction with BSA, humic acid, silica nanoparticles, Escherichia coli and Bacillus bacteria. The surface hydrophilicity of the modified PES membranes was enhanced by the addition of PANI nanoparticles and showed improved fouling resistance and a high flux recovery ratio as well as improvement in BSA and humic acid rejection even with higher pore sizes. The modified membrane also showed less attack from the bacteria, demonstrating improved biofouling activity.

Introduction

Membrane separation technology has emerged as a competitive technology for separations and purifications in many areas. Membrane technology has many advantages due to the flexibility and performance reliability of the membrane systems and the increasing demand of a technology that is cost competitiveness and environmental friendly. Ultrafiltration is an important membrane separation processes and has become a leading separation tool for various industrial applications due to its unique separation capability and low energy consumption. The ultrafiltration application areas include food and chemical processing, waste water treatment, pharmaceutical, and biotechnology [1]. Polyethersulfone (PES) is a frequently chosen polymer for the preparation of ultrafiltration membranes and displays excellent membrane-forming properties, such as good thermal resistance, chemical inertness, and strong mechanical properties [2]. Nevertheless, PES typically has a hydrophobic surface that leads to severe membrane fouling, causing the deterioration of membrane performance and decreased membrane life [3].

Due to these problems, several studies have been conducted in order to enhance PES membrane structure and performance. These studies primarily focused on hydrophilic modification of the membrane surfaces, since this method can lead to membranes with low fouling behaviour and higher flux. Some of the modifications reported were UV-initiated graft polymerisation [4], plasma graft [5], and blending with hydrophilic polymeric materials [6]. Blending with hydrophilic polymeric materials is an effective technique since the membranes formed after the modification possess a different structure and properties from the unmodified membrane. The polymeric additives in a casting solution act as pore-forming agents and could suppress macrovoid formation, with the hydrophilisation effect on the membrane clearly observable [7]. Some of the polymeric additives used by researchers are polysulphoxideamide [8], polyethylene glycol (PEG) [9], poly(vinyl butyral) (PVB) [10], and polyvinylpyrrolidone (PVP) [11].

In this study, polyaniline (PANI) nanoparticles were used as a hydrophilic polymeric material for blending with PES matrix membranes. PANI is one of the conducting polymer groups, and it has major applications in chemistry, physics, material science, and engineering [12]. PANI's special characteristics, such as its ease of synthesis, environmental stability [13], simple doping/dedoping chemistry, relatively low cost [14], and solubility in highly aprotic solvents like N-methyl-2-pyrrolidone (NMP) [15], have attracted considerable research into this conducting polymer. PANI already has some application in membrane technology, including use for gas separation [16], pervaporation [17], and semi-conductor [18]. In this present work, PANI nanoparticles were used to improve the hydrophilic properties and permeability of the substrate membrane. PANI's properties, such as high surface energy and high hydrophilicity, were used to obtain superhydrophilic membrane surfaces [19]. During membrane formation, PANI nanoparticles were blended with the PES matrix polymer in order to form a membrane with new properties. In addition, this new polymer matrix was shown to be protected against degradation because of the ability of PANI to act as a radical scavenger [20].

Our previous research indicated that PANI can exist stably in the PES polymer matrix and enhance the membrane performance without diminishing the advantageous properties of PES [21]. The optimal parameters of the blending membrane have also been determined by the response surface method (RSM) approach [22]. In this study, three types of membranes were prepared by phase inversion induced by immersion precipitation using the composition obtained from the RSM method reported previously [22]. The membranes were unmodified PES membranes (controlled) and PES membranes modified with self-synthesised PANI and commercially available PANI nanoparticles. The controlled membrane was prepared using the PES membrane material without any modification, while PES-PANI (produced) and PES-PANI (commercial) membranes were prepared by blending the PES solution with PANI solution before proceeding to the casting process. Then, these membranes were tested with four different types of foulants in order to study the membrane fouling behaviour. The purpose of this work was to investigate the fouling reduction effect of blended membranes during the filtration process. This study was mainly focused on the reduction of the fouling effect of PES/PANI-modified membranes compared to the controlled membranes, and the difference between self-synthesised PANI and commercially available PANI on membrane performance.