Amino-functionalized UiO-66-doped mixed matrix membranes with high permeation performance and fouling resistance

Abstract

For the reduction of bovine serum proteins from wastewater, a novel mixed matrix membrane was prepared by functionalizing the substrate material polyaryletherketone (PAEK), followed by carboxyl groups (C-SPAEKS), and then adding amino-functionalized UiO-66-NH2 (Am-UiO-66-NH2). Amino-functionalization of UiO-66 was accomplished by melamine, followed by an amidation reaction to immobilize Am-UiO-66-NH2, which was immobilized on the surface of the membrane as well as in the pore channels, which enhanced the hydrophilicity of the membrane surface while increasing the negative potential of the membrane surface. This nanoparticle-loaded ultrafiltration membrane has good permeation performance, with a pure water flux of up to 482.3 L·m−2·h−1 for C-SPAEKS/Am-UiO-66-NH2 and a retention rate of up to 98.7% for bovine serum albumin (BSA)-contaminated solutions. Meanwhile, after several hydrophilic modifications, the flux recovery of BSA contaminants by this series of membranes increased from 56.2% to 80.55% of pure membranes. The results of ultrafiltration flux time tests performed at room temperature showed that the series of ultrafiltration membranes remained relatively stable over a test time of 300 min. Thus, the newly developed mixed matrix membrane showed potential for high efficiency and stability in wastewater treatment containing bovine serum proteins.

1. Introduction

Carbon reduction policies and energy-saving targets have become the consensus of most countries [1], and how to obtain clean, fresh water by using energy-saving methods has become one of the challenges faced by most countries in the world [2]. Traditional water treatment methods include coagulation, adsorption, biological treatment, and filtration, but none of them can meet the requirements of people living and drinking. The ultrafiltration direction in membrane separation technology is considered one of the potential approaches to solve this problem [3e5]. Whether in general wastewater purification [6], seawater desalination, or in new fields such as drug purification and nanoparticle separation, ultrafiltration membrane technology is gradually replacing other outdated separation technologies. The characteristic pore sizes of ultrafiltration membranes are 2e100 nm. Under the effect of osmotic pressure, macromolecules such as viruses, proteins, bacteria, and colloids are blocked on the surface of the membrane, enabling the separation and treatment of wastewater.

Common substrate materials for ultrafiltration membranes are polyetherketone (PEK) [7,8], poly sulfone (PSF) [9,10], and poly vinylidene fluoride (PVDF) [11]. In comparison to other substrates, polyaryletherketone (PAEK) is an amorphous, high-temperature-resistant resin with superior mechanical properties. The benzene rings on the main chain of the polyaryletherketone molecule provide the molecular chain with rigidity, which gives PAEK good mechanical strength. Besides, the large number of ether bonds makes the molecular chain flexible, which in turn gives PAEK good toughness. Currently, PAEK faces problems of low permeability and serious membrane contamination in practical applications of ultrafiltration membranes because of their hydrophobic properties [12]. To overcome these limitations, researchers have gradually started to use polymer membranes as matrix materials and organic/inorganic fillers to control the separation effect, thus creating improved mixed matrix membranes (MMMs) [13e15]. MMMs are using doped nanoparticles to improve the hydrophobicity, contamination resistance, surface charge or pore size, and porosity of ultrafiltration membranes. This is considered one of the most promising directions for ultrafiltration membranes because of their simplicity of operation and significantly improved performance. However, the modification of matrix materials has been faced with a trade-off between performance and stability. The introduction of nanoparticles [16] (e.g., carb...