Enhancing permeability and antifouling behavior of polyvinyl chloride ultrafiltration membrane embedded with cucr NLDH/graphene oxide

Abstract

Purification technologies are imperative to overcome water pollution as a worldwide concern, which contains various contaminants. The major pollutants of water sources are related to the organic solvents, oil spillage, and dyes discharged by various industries. Membrane separation processes are preferable among other conventional separation methods because of advantageous performance, lesser capital cost, facile scale-up, and cost-efficient in energy use. Some eminent membrane-based separation processes can be attributed to reverse osmosis (RO), microfiltration (MF), nanofiltration (NF), ultrafiltration (UF), and pervaporation (PV). Among these processes, ultrafiltration membranes are extensively used in wastewater treatment and the food industry, which are able to retain solutes with a diameter of 1–100 nm. Based on the constituent materials, membranes are classified into organic (polymeric) and inorganic membranes. Some advantages such as high adaptability, pore size adjustment, and properties tuning by fabrication parameters propel the researchers to polymeric membranes fabrication. In this context, inorganic membranes are utilized in a small part of commercial ultrafiltration membranes, while polymeric membranes have a prominent role. Due to the simplicity and versatility of non-solvent induced phase separation (NIPS), it has received great attention among the various techniques developed for the fabrication of polymeric membrane compared to other methods like electrospinning, thermal-induced phase separation, vapor-induced phase separation, and evaporation-induced phase separation. In summary, the fabrication mechanism of NIPS can be clarified in liquid−liquid demixing attained by the formation of two phases through the immersion of solvent/polymer solution into a coagulation bath and subsequent solvent exchange from the polymer solution through a non-solvent from a precipitation bath. A wide range of polymers, including polysulfone (PSf), polyvinylidene fluoride (PVDF), polyethersulfone (PES), polyacrylonitrile (PAN), cellulose acetate (CA), polyvinyl chloride (PVC), and polyether imide (PEI) have been used for the fabrication of membranes. However, PVC seems to be a convenient choice thanks to its low price, decent chemical and mechanical properties, solubility in diverse industrial solvents like N-methyl pyrrolidone (NMP), dimethyl acetamide (DMAc), tetrahydrofuran (THF), and dimethyl formamide (DMF) and also operation possibility for NIPS method. One of the primary limitations of membranes is attributed to the fouling phenomenon, in which the pores and membranes' surface are accumulated by unwanted soluble and particulate materials. It is derived from the hydrophobic nature of polymer materials that facilitate the fouling of hydrophobic microorganisms and proteins. Therefore, membrane performance deterioration, flux alleviation, and lifetime shortening are the sequences of fouling. Several strategies have been proposed to overcome the membranes' fouling. Fabrication of membranes via blending two polymer materials that possess various hydrophilicity levels is one of the useful methods for fouling reduction. On the other hand, the preparation of mixed-matrix membranes (MMMs) by incorporation of various nanomaterials in the casting solution was found to be a suitable method to enhance surface hydrophilicity and antifouling properties. To exemplify the extensive investigation of nanomaterials, it would be noteworthy to mention the utilization of some well-known nanomaterials such as zinc oxide (ZnO), titanium dioxide (TiO2), graphene oxide (GO), carbon nanotubes (CNTs), alumina (Al2O3), silica (SiO2), zirconium dioxide (ZrO2), and tungsten trioxide (WO3). Layered double hydroxides (LDHs) with the general formula of [M2+1-x M3+ (OH)2]x+[An-]x/n.yH2O, are another class of two-dimensional (2D) compounds that have been attractively investigated thanks to the various properties, including, high surface area, high anion exchange capacity, and adjustable composition interlayer galleries. The terms M3+ and M2+ are attributed to the trivalent and divalent metal cations, while An- indicates the charge compensating anions between LDHs' layers. Electrostatic interaction and hydrogen bonding with size to charge ration of cations and anions contribute to the stability of LDHs. Besides the extensive applications of LDHs in fuel cells, drug delivery, catalysis, flame retardants, electrochemical sensing, optical sensors, supercapacitors, biosensors, and biomedical applications, they have been studied in membrane technologies. Preparation of PES membrane by incorporating Mg-Al-Fe LDH for adsorptive removal of fluoride and phosphate can be an interesting study to exemplify their utilization in membrane modification. Moreover, the removal of Cu2+ and methylene blue (MB) by LDH/GO/PVDF composite membrane was reported. In this work, different amounts of CuCr LDH-GO were incorporated into PVC membranes. The main purpose of the study can be attributed to the improving antifouling properties and rejection performance of membranes. Within this aim, after synthesizing the CuCr LDH-GO by co-precipitation method, composite membranes were fabricated via the NIPS method through the incorporation of nanomaterials in polymeric solution before casting. Alongside the membrane characterization, the antifouling and rejection performance of membranes was assessed by separating different dyes and bovine serum albumin (BSA) protein. In addition, the photocatalytic property of CuCr LDH-GO-modified membranes were evaluated. The mean pore size and the porosity of the PVC membranes were affected in the presence of different concentrations of nanomaterials. Additionally, by increasing the concentration of the CuCr NLDH-GO in the matrix of the PVC membrane, the average surface roughness and the hydrophilicity of the PVC membranes were improved. Introduction of the CuCr NLDH-GO into the matrix of the PVC membrane was found to be effective in improving the improvement of mechanical properties of membranes based on the results of young modulus and elongation. Almost twofold enhancement of water flux was observed in 1 wt% membrane with 161.3 L/m2h compared to the bare membrane with 71.1 L/m2h. Moreover, the antifouling performance of modified membranes was assessed, and 20% improvement of FRR from 54.3% of the bare membrane to approximately 65% for