Elsevier

Composites Part B: Engineering

Volume 197, 15 September 2020, 108188
Composites Part B: Engineering

Chemically stable two-dimensional MXene@UIO-66-(COOH)2 composite lamellar membrane for multi-component pollutant-oil-water emulsion separation

https://doi.org/10.1016/j.compositesb.2020.108188Get rights and content

Highlights

  • A multitasking 2D MXene@UIO-66-(COOH)2 composite lamellar membrane was designed via a facial strategy.

  • The membrane showed promising synergistic separation performance for various oil-in-water emulsions and dye.

  • The membrane possessed high antifouling resistance and excellent recyclability.

  • The membrane possessed outstanding chemical stability and corrosion resistance in harsh chemical conditions.

Abstract

Multi-component pollutant-oil-water emulsion from the fast-growing industry seriously threatens the human health and ecological environment, which poses a huge challenge to membrane technology. Recently, 2D MXene materials have shown promising and potential candidates for functional separation membranes. Herein, for the first time, a multitasking hierarchical MXene@UIO-66-(COOH)2 composite membrane supported on nylon 66 microporous substrate was designed via a facial strategy, which possessed high chemical stability and efficient multi-component pollutant-oil-water emulsion separation performance. The promising synergistic separation performance of various oil-in-water emulsions and dye, high antifouling resistance, and excellent recyclability of MXene@UIO-66-(COOH)2 composite membrane originated from the inherent hydrophilicity, low oil adhesion feature, and hierarchical intercalation structure of membrane. Furthermore, the chemically stable MXene@UIO-66-(COOH)2 composite membrane exhibited outstanding corrosion resistance under strong acid (3 M HCl), alkali (1 M NaOH) and salty (Saturated NaCl) solutions. Therefore, this work provides a powerful platform for designing stable and functional 2D membrane materials for multi-component pollutant-oil-water emulsion separation in harsh chemical environments.

Introduction

With the rapid development of modern industry, the growing consumption of oils and petrochemical products brings a large amount of oily wastewater, which is a great threat to ecological environment and human health [[1], [2], [3], [4]]. In most cases, the components of oily wastewater are very complex because they contain not only insoluble oils, but also various soluble organic pollutants and heavy metal ions [[5], [6], [7]]. Therefore, the comprehensive treatment of oily wastewater containing multiple pollutants is one of the hotspots in the field of wastewater treatment. Up to now, membrane technology has attracted tremendous interests in the area of oily wastewater treatment because of its easy operation, high efficiency, and low energy consumption [[8], [9], [10], [11]]. However, most commercial membranes are polymer-based, their intrinsic hydrophobicity usually cause serious membrane fouling [12], which limits their performance.

Recently, many studies focus on the exploitation of two-dimensional (2D) nanomaterials based membranes including graphene oxide (GO), metal organic framework nanosheets (MOFs), and zeolite nanosheets because the precise and rational control of interlayer distances endow the membranes with highly specific separation performance [[13], [14], [15]]. Although the above-mentioned 2D nanomaterials based membranes exhibit advanced separation performance in terms of selectivity and permeability, there are still some bottlenecks limiting their practical application of separation. For example, the abundant carboxyl groups on the surface of GO would become negatively charged through hydration. Consequently, the stacked GO membranes easily disintegrate in water because of electrostatic repulsion between GO nanosheets [16]. In addition, the easily exfoliated zeolites [17] or MOFs [18] are limited and their exfoliation conditions are harsh, which hinder their application in membrane separation. Therefore, the exploration of new 2D nanomaterials based membranes with superior properties is an alternative way to overcome the bottlenecks of membranes.

MXene, as a fashioned 2D transition metal carbide and/or nitride nanomaterial, has received increasing attention since it was developed by Gogotsi and Barsoum in 2011 [19]. Owing to its flexibility, excellent structural stability, and high electrical conductivity, MXene is widely applied in supercapacitors [20], lithium ion batteries [21], and hydrogen evolution reaction [22]. Recently, several reports found that Mxene with natural hydrophilic properties exhibited potential candidate as a 2D material in the field of oil/water and dyes separation [[23], [24], [25]]. For example, Ding et al. [23] fabricated the 2D lamellar membrane by using Ti3C2Tx MXene nanosheets, which showed favorable water permeance (>1000 L m−2 h−1·bar−1) and rejection rate (>90%) for rhodamine B. Li et al. [26] developed ultra-thin MXene sheet membranes (~30 nm) through vacuum-assisted filtration (Using PES substrates as supporting layer), which exhibited low oil adhesion and high oil removal efficiency (Filtrate permeance:437–540 L m−2 h−1·bar−1 and rejection rate > 99.5%). Nevertheless, there are still important topics that deserve further study in the area of MXene based separation membranes [27]. On the one hand, oily wastewater is often accompanied by soluble heavy metals and dyes in complicated conditions [28], but the current MXene based separation membranes rarely involve the comprehensive treatment of them. On the other hand, MXene based separation membranes also suffer from the problem of permeability-selective (P-S) trade-offs, similar to other two-dimensional membranes [29,30].

In order to conquer the limitations of existing concepts mentioned above, the intercalation of nanoparticles into the 2D nanomaterial sheets was developed [31,32]. In general, the intercalated nanoparticles should be stable and capable of removing contaminants and increasing the permeability of membrane. Among many nanoparticles, the metal organic frameworks (MOFs) have emerged as promising candidates due to their high density active sites, large specific surface area, and adjustable pore size [33]. However, the application of general MOF materials is greatly limited by their poor hydrothermal stability and chemical stability when considering the treatment of oily wastewater in harsh chemical environments. Hence, the UIO-66 and its derivatives (UiO-66-NH2, UiO-66-(OH)2, UiO-66-(COOH)2, etc.) as new class of zirconium-based porous MOFs are exploited, which possess high mechanical strength, high thermal stability, excellent corrosion and solvent resistance [34]. Consequently, some advances in stable UIO-66 MOFs hybrid materials for oil/water separation applications are made in the past several years [35,36]. These research works inspired us that hybridization of UIO-66 MOFs with MXene nanosheets would provide an alternative way to obtain stable 2D lamellar membrane for separation of complicated oily wastewater under harsh conditions; however, it is not reported elsewhere.

Herein, we proposed a new and chemically stable MXene@UIO-66-(COOH)2 2D hierarchical lamellar membrane via a simple vacuum assisted self-assembly process (Fig. 1). Our newly developed hierarchical composite membrane possessed excellent separation efficiency for both oil-water emulsion and methylene blue because of the synergistic effect of UIO-66-(COOH)2 nanoparticles and MXene nanosheets, thus realizing the comprehensive treatment of multi-component pollutant-oil-water emulsions. In addition, the inherent hydrophilicity and low oil adhesion feature endowed the MXene@UIO-66-(COOH)2 composite membrane with excellent antifouling resistance and recyclability. More importantly, the good environment adaptability in strong acid/alkali and salty conditions enabled the MXene@UIO-66-(COOH)2 composite membrane to cope with actual oil-water separation in the harsh chemical environments. Therefore, this work opens an alternative way to develop high-performance 2D lamellar composite membranes for multi-component pollutant-oil-water emulsion separation under harsh conditions.

Section snippets

Materials

Ti3AlC2 powders were obtained from 11 Technology Co., Ltd, China. LiF (99.9%), Pyromellitic acid and ZrCl4 were purchased from Aladdin Industrial Corporation, Shanghai, China. Hydrochloric acid, acetic acid, sodium dodecyl sulfate (SDS), hexane, isooctane, 1,3,5 trimethylbenzene, and toluene were provided by Kelong Chemical Co. Ltd., Chengdu, China. Nylon 66 microporous substrate with the thickness of 0.2 μm was supplied by Jinteng Experimental Equipment Co., Ltd., Tianjin, China.

Preparation of MXene nanosheets

Firstly, the

Results and discussion

In the current work, m-Ti3C2Tx as sub-family of MXene was prepared by acid-etching method [38], as shown in Fig. 1. Owing to the chemical stability and hydrophilicity, the 2D Ti3C2Tx nanosheets were chosen as the building blocks for constructing stable MXene composite membranes. The exfoliated Ti3C2Tx was prepared by using 3D Ti3AlC2 powder as precursor. Considering the high chemical activity of Ti–Al bond, the LiF/HCl aqueous fluoride-containing acidic solution was selected as corrosive agent

Conclusions

In summary, novel chemically stable two-dimensional MXene@UIO-66-(COOH)2 composite lamellar membrane supported on nylon 66 microporous substrate was successfully prepared through vacuum assisted self-assembly process. The hydrophilicity, low oil adhesion force, and hierarchical intercalation structure of composite membrane were perfectly suited for multi-component pollutant-oil-water emulsion separation including various oil-in-water emulsions and dye. Typically, the hydrophilic property of

Declaration of competing interest

We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Acknowledgements

This work was financially supported by National Natural Science Foundation of China (51903215), Sichuan Province Sci-Tech Supported Project (2020YJ0168), China Postdoctoral Science Foundation (2017M622999 and 2019T120823).

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