Chemically stable two-dimensional MXene@UIO-66-(COOH)2 composite lamellar membrane for multi-component pollutant-oil-water emulsion separation
Graphical abstract
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).
References (56)
- et al.
An environment-friendly and multi-functional absorbent from chitosan for organic pollutants and heavy metal ion
Carbohydr Polym
(2016) - et al.
TiO2-alginate composite aerogels as novel oil/water separation and wastewater remediation filters
Compos B Eng
(2019) - et al.
Green one-step synthesis of ZnO/cellulose nanocrystal hybrids with modulated morphologies and superfast absorption of cationic dyes
Int J Biol Macromol
(2019) - et al.
Gravity-driven and high flux super-hydrophobic/super-oleophilic poly(arylene ether nitrile) nanofibrous composite membranes for efficient water-in-oil emulsions separation in harsh environments
Compos B Eng
(2019) - et al.
Fabrication of robust, ultrathin and light weight, hydrophilic, PVDF-CNT membrane composite for salt rejection
Compos B Eng
(2019) - et al.
Easily enlarged and coating-free underwater superoleophobic fabric for oil/water and emulsion separation via a facile NaClO2 treatment
Separ Purif Technol
(2018) - et al.
A simple way to an ultra-robust superhydrophobic fabric with mechanical stability, UV durability, and UV shielding property
J Colloid Interface Sci
(2018) - et al.
A waterproofing textile with robust superhydrophobicity in either air or oil surroundings
J Taiwan Inst Chem Eng
(2017) - et al.
Design of durable and efficient poly(arylene ether nitrile)/bioinspired polydopamine coated graphene oxide nanofibrous composite membrane for anionic dyes separation
Chem Eng J
(2018) - et al.
Efficient transformation of trichloroethylene activated through sodium percarbonate using heterogeneous zeolite supported nano zero valent iron-copper bimetallic composite
Chem Eng J
(2017)