Preparation of an adsorptive membrane of polyvinylidene fluoride incorporated functionalized boron nitride nanosheets for arsenic removal

Abstract

Incorporating nanomaterials into membranes will enhance wastewater treatment efficiency with their unique characteristics, such as higher permeability, thermal stability, surface roughness, hydrophilicity, and fouling control. In this study, the surface-modified boron nitride with phosphoric acid 2-hydroxyethyl methacrylate ester (PA/BN) was grafted with polyethylene glycol (PEG) via conventional grafting. The PEG grafted PA/BN (PEG-g-PA/BN) melt blended with polyvinylidene fluoride (PVDF) resin by using an internal mixer at different mass percentages (100% PVDF (PVDF), 3% PEG-g-PA/BN + 97% PVDF (97:3 BN), 5% PEG-g-PA/BN + 95% PVDF (95:5 BN), 7% PEG-g-PA/BN + 93% PVDF (93:7 BN), and 7% PEG-g-PA/BNNS + 93% PVDF (93:7 BNNS). Phase inversion technique was used to cast the blended mixture into a thin membrane. The prepared membranes were analyzed with different characterization techniques to determine chemical composition, crystallinity, morphology, and thermal properties. The prepared composite membrane was evaluated in terms of water permeability, anti-fouling resistance, and solute rejection efficiency with deionized water, bovine serum albumin, and arsenic solution as well. PVDF membranes show high water flux and porosity. The water flux and porosity of the blends decrease as the percentage of PEG-g-PA/BN increases. However, the highest removal capacity for arsenic was observed at 93:7 BN. The adsorption of arsenic ions takes place via complexation with PA/BN in the PVDF matrix. This was confirmed with field emission scanning electron microscopy-energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy analyses.

1. Introduction

Membrane separation is widely used in industrial processes due to its simplicity, high performance, and sustainability. In recent years, membrane technology has drastically improved the efficiency of removing and filtering a wide range of pollutants, including organic matter and heavy metals [1]. Multiple membrane technologies including microfiltration, ultrafiltration, nanofiltration, and reverse osmosis are explicitly employed to remove heavy metals from aqueous solutions that exhibit different separation capabilities. Increasing numbers of studies have been reported on the efficiency of metal removal by preparation of adsorptive membrane via incorporation of adsorbents onto the membrane matrix [2,3]. The development of adsorptive membranes has received significant attention due to their low operating pressure, reusability, regeneration capability, high removal capacity, and flux [4].

An adsorption membrane combines both adsorption and filtration in a single step, which appears very promising. An adsorptive membrane performs both adsorption and filtration functions. In general, the membrane relies on an adsorption process that involves mass transfer by interacting with solid surfaces chemically and physically [5]. In essence, adsorption membrane has a greater affinity for ions and molecules which captures them via chelating or complexation. Typically, adsorptive membranes have pore sizes ranging from nanofiltration to microfiltration [6]. Polymer membranes are ideal for microfiltration, ultrafiltration, and nanofiltration due to their cost efficiency and simplicity. Unfortunately, polymer membranes exhibit poor affinity for metal ions and other organic pollutants. In order to achieve efficient adsorptive membranes, inorganic and organic adsorbent materials are purposefully incorporated into polymeric membranes [7]. However, inorganic materials are highly favorable as adsorbent materials due to its fast kinetic, high adsorptive capacity, and impressive physical properties. Therefore, incorporation of nanomaterials in adsorptive membranes has garnered enormous attention in recent years [8,9].