Electrospun polyethersulfone@MOF composite membranes for air cleaning and oil-water separation

Abstract

Filtration and separation materials have gradually become a research hotspot on account of the increasing attention paid to the global environmental pollution problem. However, most filtration and separation materials can not balance the contradiction between high filtration & separation efficiency and its reusability. In this work, we report the successful fabrication of polyethersulfone@MOF (PESU@MOF) membranes using electrospinning with 1.22 ± 0.55 µm diameter, owning excellent mechanical property and high filtration efficiency (>99 %). For heat, acid and alkalic condition treatment, the stress of PESU@MOF-0.1 membrane slightly decreases to 0.50 ± 0.01 MPa under heating 12 h at 200 ℃. At the same time, the stress of PESU@MOF-0.1 membrane declines dramatically after treated by 1.0 mol/L HCl and NaOH, respectively, for 4 h. Moreover, compared with PESU membranes, quality factor (QF) value (0.12 Pa−1) of PESU@MOF-0.075 membrane increases by nearly 134.1 %, exhibiting excellent filtration efficiency. The oil-water separation time of PESU@MOF membrane increases from 44 s to 86 s with the increase of MOF contents. At 20 cyclic filtration process, the separation time is a slight decrease from 29 s to 40 s. The nature of PESU based materials, the effective filtration and separation property, and its reusability suggest the herein engineered membranes have great potential for practical applications in air filtration and oil-water separation fields.

Graphical Abstract

Introduction

For the past few years, with the development of industrialization and urbanization, pollutions including air and water etc. have become the biggest environmental problem threatens human health [1], [2]. Take air pollution, particular matter with complex chemical compositions, emitting from industrial processing, etc., has been one of the most serious issues among various air pollutants [3]. How to effectively remove particular matter in the air. At present, an increasing numbers of research works have been focused on the development of electrospun membranes for air filtration and oil-water separation. Many polymer materials, such as polyurethane (PU) [4], [5], polymide-66 (PA-66) [6], polyimide (PI) [7], and polyethersulfone (PES) [8] etc., have been successfully electrospun into nanofibrous membranes and applied in the field of filtration and separation [9], [10].

The morphology and structure of nanofibers membranes play vital roles in filtration and separation field. It is necessary to control the fabrication of nanofibers membranes through different methods containing electrospinning [11], [12], blow-spinning [13], [14], freeze-drying [15], [16] etc. Electrospinning is a simple, quick and pliable method for producing and regulating nanofibers morphology [17]. Nanofibers are prepared with less than 1000 nm diameter and have a high surface area to the volume ratio [18]. PES nanofibers membranes are largely used in membrane technology for water treatment due to its insolubility in water as well as its excellent mechanical and thermal properties. At the same time, PES is also cost effective and using in separation industry [19]. Ming et al. designs a unique hierarchically structured composite nanofiber membrane, consisting of a zeolitic imidazolate framework-8-embedded PES fiber layer and polysulfonamide/polyethersulfone (PSA/PES) fiber layer for air filtration and oil/water separation. The results show bi-layer membranes with a basis weight of 1.44 g/m2 achieve a high filtration efficiency of 99.986 %, a low air resistance of 15 Pa, and a good QF value of 0.592 Pa−1 [13]. Cao et al. prepares polyethersulfone/polyamide 66 (PES/PA66) filtration media for airborne particles via electrospinning technique [20]. The composite membranes show excellent filtration efficiency for PM0.3–5, and the filtration efficiency for 0.3 µm particle is 99.999 %.

Metal-organic frameworks (MOF), reported in 1995 by Yaghi and Li [21], have aroused vast interest owning excellent properties including tunable pore structure, high surface areas, and easy functionalization. Based on its excellent properties, MOF has received tremendous interest in environmental fields to eliminate pollutions acting as adsorbents, catalysts and so on [21], [22], [23], [24]. However, the crystalline powder of MOF with poor processability is a big challenge in environmental application. Therefore, the usage of many polymers matrixes improves the processing and applicability of MOF powder. Herein, we use electrospinning technique to fabricate PESU@MOF composite membranes with a high filtration efficiency, excellent mechanical performance and superior oil/water separation. Initially, we study the spinning parameters to control the morphology and structure of composite membranes. Furthermore, the morphology, mechanical properties, filtration performance and oil/water separation of the membranes are carefully examined. It is believed that this designed composite membrane has broad prospects in filtration and separation field.

Section snippets

Materials

PESU particles were supplied by BASF Co. LTD, Germany. N,N-Dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), sodium hydroxide (NaOH) were purchased from Sinopharm Chemical Reagent Co., LTD., China. Hydrochloric acid (HCl, 1.0 mol/L) was bought from Guangzhou Howei Pharmaceutical Technology Co., LTD. MOF (zeolitic imidazolate framework, ZIF-8) was provided by XFNANO Co. LTD. All chemicals were of analytical grade and used without further purification.

Fabrication of nanofiber membranes

The PESU spinning solution of 30 wt %

Fabrication of PESU@MOF membranes

PESU has been widely used for commercial micro/ultrafiltration membranes because of its high thermal and chemical resistance [25]. In our work, we use electrospinning method to fabricate PESU@MOF membranes for filtration application. Fig. 1a-e depicts the surface morphologies of PESU@MOF membranes with different MOF contents. The surface morphologies of the fabricated membranes show clear and uniform morphological features. For Fig. 1a, it shows uniform and smooth surface of PESU fibers with

Conclusion

In order to develop functional membranes with the function of air filtration and oil water separation, we report the successful fabrication of PESU@MOF membranes using electrospinning technology, which display steady and excellent thermal stability (<200 ℃) and acid & alkali resistance. Compared with pure PESU membranes, the resultant membranes PESU@MOF-0.075 exhibit excellent filtration efficiency, exceeding 99.3 % for PM0.225–0.4 µm particles with a corresponding pressure drop of 57 Pa for

Article Source：https://www.sciencedirect.com/science/article/abs/pii/S2213343723007832