Selective Molecular Separation on Ti3C2TxâGraphene Oxide

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Selective Molecular Separation on TiCT-Graphene Oxide Membranes during Pressure-Driven Filtration: Comparison with Graphene Oxide and MXenes Kyoung Min Kang, Dae Woo Kim, Chang E. Ren, Kyeong Min Cho, Seon Joon Kim, Junghoon Choi, Yoon Tae Nam, Yury Gogotsi, and Hee-Tae Jung ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b10932 • Publication Date (Web): 03 Nov 2017 Downloaded from http://pubs.acs.org on November 3, 2017

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ACS Applied Materials & Interfaces

Selective

Molecular

Separation

on

Ti3C2Tx-

Graphene Oxide Membranes during Pressure-Driven Filtration: Comparison with Graphene Oxide and MXenes Kyoung Min Kang†,⊥, Dae Woo Kim†,⊥, Chang E. Ren ‡,⊥, Kyeong Min Cho†, Seon Joon Kim†, Jung Hoon Choi†, Yoon Tae Nam†, Yury Gogotsi ‡,* and Hee-Tae Jung†,* †

Department of Chemical and Biomolecular Engineering (BK-21 plus) & KAIST Institute for

Nanocentury, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea ‡

Department of Materials Science and Engineering, and A. J. Drexel Nanomaterials Institute,

Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, USA K. M. Kang, D. W. Kim, and C. E. Ren contributed equally to this work. Corresponding authors : Y. Gogotsi ([email protected]) and H.-T. Jung ([email protected]) KEYWORDS: Nanofiltration, MXene, graphene oxide, membrane, two dimensional materials.

ACS Paragon Plus Environment

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ABSTRACT In this work, we prepared 90-nm-thick Ti3C2Tx-graphene oxide (GO) membranes laminated on a porous support by mixing GO with Ti3C2Tx. This process was chosen to prevent the penetration of target molecules through inter-edge defects or voids with poor packing. The lattice period of the prepared membrane was 14.28 Å, as being swelled with water, resulting in an effective interlayer spacing of around 5 Å, which corresponds to two layers of water molecules. The composite membranes effectively rejected dye molecules with hydrated radii above 5 Å, as well as positively charged dye molecules, during pressure-driven filtration at 5 bar. Rejection rates were 68% for methyl red, 99.5% for methylene blue, 93.5% for rose Bengal, and 100% for brilliant blue (hydrated radii of 4.87, 5.04, 5.88, and 7.98 Å, respectively). Additionally, the rejections of composite membrane were compared with GO membrane and Ti3C2Tx membrane.


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INTRODUCTION MXenes, which have a general formula of Mn+1XnTx (M is an early-transition metal, X is C and/or N, and Tx denotes surface termination such as OH, O, and F; n = 1, 2, or 3), are a large family of two-dimensional (2D) transition-metal carbides and nitrides. They have attracted much attention because of their various applications in energy storage,1-5 separation membranes,6 and electromagnetic interference shielding,7 to name a few. MXenes were usually prepared by selectively etching A-group elements (mostly from IIIA and IVA) from a layered hexagonal MAX (Mn+1AXn) phase.2 Because of the termination of etched metal surface with oxygen functional groups such as O and OH or F, Ti3C2Tx MXenes typically have hydrophilic and negatively charged surfaces, as well as high electrical conductivities (2400–6500 S cm−1).7-9 Because of their sheet-like 2D morphology, they can be stacked into rigid thin films on an appropriate support. These stacks have a variable effective interlayer spacing of 2.9 Å, due to a layer of water molecules, between dried slits and 6.4 Å (three layers of water molecules), when swelled with water.6 2D materials such as graphene, graphene oxide (GO), and transition-metal chalcogenides separate target molecules by mechanical sieving through the stacked layers and by electrostatic interaction between target molecules and charged surfaces.10-12 Especially, because narrow interlayer spacing of water-intercalated MXenes around 6.4 Å can be effective to reject small ions,6 MXenes hold promise in membrane applications. However, there are only few reports on the use of Ti3C2Tx membranes in molecular separation. Monovalent ions (K+, Na+, Li+) diffuse through Ti3C2Tx films with thickness of several micrometers faster than multivalent ions (Mg2+ and Al3+) during concentration gradient-driven diffusion.6 Recently, Li et al. reported MXene membranes containing pores with sizes about 2 nanometers13 and enhanced water flux (up to


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1000 L m−2 h−1 bar–1) during pressure-driven filtration. However, the membrane was selective toward dye molecules with sizes larger than 2.5 nm; it exhibited ~90% rejection rate for Evans blue molecules, with the rejection rate decreasing with hydraulic pressure. Despite the ideal effective interlayer spacing of MXene, the use of MXene membranes in separating small molecules and ions in pressure-driven filtration remains unexplored. Herein, we demonstrate that by incorporating GO to Ti3C2Tx membranes, we can greatly enhance the dye rejection properties of Ti3C2Tx-based membranes. In order to suppress the penetration of target molecules or ions through nonselective channels such as inter-edge defects or pinholes in the Ti3C2Tx membranes,14,15 GO (10 ~ 30 wt%) was mixed with Ti3C2Tx. Ti3C2TxGO composite membranes were prepared by filtering the aqueous dispersions of both materials through porous polymer supports, such as polycarbonate (PC) and nylon. As a result, high rejection was achieved for dye molecules at 5 bar. Additionally, the rejection of composite membranes was compared with GO and Ti3C2Tx membrane to clarify the enhanced molecular separation performance of composite membranes.


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RESULTS AND DISCUSSION

Figure 1 a) Photograph of the Ti3C2Tx/GO composite membrane for the water filtration (left) and the membrane structure (right) and the corresponding schematic illustration. b) Surface and cross-sectional SEM images of the composite membrane with 30 wt% of GO. c) EDS maps for Ti, C, and O in the composite membrane surface are shown in b). d) Raman G-band map of the composite membrane. e) Raman spectra obtained from indicated points on the G-band map.


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Figure 1a displays a photograph and a schematic of the Ti3C2Tx/GO composite membrane. In our experimental, the lateral size of GO was usually ranged around sub-micrometer and micrometer size GO was also observed. And the size of exfoliated Ti3C2Tx was in the range of several hundred nanometer scale (Figure S1). Because the size of GO was much larger than that of Ti3C2Tx and weight ratio of GO was lower than Ti3C2Tx, it seems that the main transport channels of Ti3C2Tx particles are covered with GO layers. Whereas the color of the GO membrane was dark brown, the color of the prepared composite membrane was dark gray and its texture was very close to that of a pristine Ti3C2Tx membrane (Figure S2). Small amounts of GO were mixed to cover defects in stacking and pinholes, which both have a higher probability to occur when only Ti3C2Tx sheets are used. The composite membranes displayed reproducible high rejection rates for dye molecules in our experiments, but we occasionally observed lower rejection rates for pristine Ti3C2Tx membranes without GO layers, which could be caused by the above mentioned defects Figure 1b shows top and cross-sectional SEM images of the Ti3C2Tx/GO composite membrane on a PC support (0.2 µm pore size) with ~30 wt% of GO. Large amounts of multilayer Ti3C2Tx particles were observed on the surface of pristine Ti3C2Tx membranes with individual particle sizes below 5 µm, while the surface of Ti3C2Tx/GO composite appeared to be smoother and covered mainly with thin GO layers (Figure S3a). This coverage was also observed in AFM measurements: the surface of a Ti3C2Tx/GO composite was smoother than that of the pristine Ti3C2Tx membrane (Figure S3c). Because the membrane thickness dominantly governs the permeance, we measured the cross-sectional thickness of the Ti3C2Tx/GO composite membrane by focused ion beam (FIB) and AFM (Figure S4). Pt layer was deposited on the membrane to prevent damage caused by the beam prior to the FIB measurements and to ensure


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structural integrity. The cross-sectional SEM images and AFM height profiles clearly indicate that the composite membrane was very thin (~90 nm thick), and that the composite layers on the PC support were well stacked and free of macroscopic defects and large pinhole structures. The presence and distribution of Ti3C2Tx and GO in the membrane were analyzed by elemental mapping of titanium, carbon, and oxygen atoms, as shown in Figure 1c and Figure S5. The energy-dispersive X-ray spectroscopy (EDS) spectrum clearly shows the distributions of titanium, carbon, and oxygen in the composite membranes, which are marked with blue, yellow, and green dots, respectively. The mapping results showed that titanium was present within the entire investigated area, indicating full coverage by the Ti3C2Tx layers. Intensities varied because of slight variances in height and surface morphology. Carbon and oxygen atoms were also well distributed throughout the investigated area, which were markedly clearer compared with that of titanium because the added GO also contained carbon and oxygen. To examine the distribution of the GO layers, Raman mapping (514 nm laser) at a wavenumber of 1590 cm−1, which corresponds to the G peak of graphitic carbon, was conducted on a 25 µm × 25 µm area of a Ti3C2Tx/GO membrane surface (Figure 1d). The entire mapping region has a G peak with significant intensity, indicating uniform coverage of the investigated are by GO. Raman spectra obtained from each marked site in Figure 1d have clear D-band and G-band peaks at 1356 and 1590 cm−1 (Figure 1e), which are representative of GO.16,17 We want to notice that the G band intensity of Raman spectrum from Ti3C2Tx was much lower than that of GO, thus the D bands of Raman mapping indicates the distribution of GO in the composite membrane (Figure S6). These results indicate that composite membranes with thicknesses of several tens of nanometers were formed by filtration of the diluted Ti3C2Tx/GO solution on the porous support. The membranes were utilized in the subsequent filtration tests discussed later.


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Figure 2 a) Water contact angles on GO, Ti3C2Tx, and composite membranes with 30 wt% of GO. b) XRD patterns of the Ti3C2Tx/GO membranes, showing dependence on the weight of GO contents. c) XRD patterns of GO, Ti3C2Tx, and the composite membranes after immersion in water for 24 h. Because the filtration performance of the 2D-material-based membrane is mainly governed by the surface properties and the interlayer distance, which are responsible for electrostatic


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repulsion and molecular sieving18, the water contact angles and XRD patterns of the composite membranes were investigated as shown in Figure 2. The measured contact angles of a water droplet on GO, Ti3C2Tx, and the Ti3C2Tx/GO composite membrane with 30 wt% of GO were around 37°, 62°, and 61°, respectively (Figure 2a), indicating the hydrophilic nature of the membranes due to abundant oxygen functional groups such as hydroxyl, carboxyl, and epoxy.19 A similar contact angle on both Ti3C2Tx and Ti3C2Tx/GO membranes (60°) indicates that the surface properties of the composite membranes were closer that of Ti3C2Tx rather than GO, which can be attributed to the wetting transparency of single-layer graphene oxide. Figure 2b displays XRD patterns of the composite membranes at different weight ratios of GO utilized during vacuum filtration. Here, the weight percent of GO to Ti3C2Tx is indicated in each graph. GO membranes produced a 2θ diffraction peak at 9.68°, which corresponds to the typical interlayer spacing of GO of around 9 Å.

16,20

For the composite membranes with a 70

wt% of GO, two diffraction peaks appeared at 6.07° (14.2 Å) and 9.07° (9.56 Å), which are attributed to the interlayer spacing of Ti3C2Tx and GO, respectively. This suggests excess of GO and formation of GO/GO stacks. Upon decreasing the weight ratio of GO to 40 wt%, the peak for the GO layers disappeared and the Ti3C2Tx diffraction peak shifted to 6.35°, which corresponds to 13.6 Å. Interestingly, the interlayer spacing of the composite membrane and pure Ti3C2Tx membrane were similar (13.5 Å) at approximately 30 wt% of GO in the composite membrane. The difference in interlayer spacing of the composite membranes by the ratio of GO to Ti3C2Tx may be explained by the irregular stacking of Ti3C2Tx near GO, arising from the differences in flake dimensions and stiffness, electrostatic repulsion between GO and Ti3C2Tx sheet, or filtration rate change (Figure S1 and Figure S7).21,22 We thus successfully prepared composite membranes mainly consisting of Ti3C2Tx nanochannels by using GO amount below


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30 wt% (10 wt% ~ 30 wt%). Since the focus of this study was to observe the separation properties of Ti3C2Tx, we only performed permeance and rejection tests with composite membranes prepared at this weigh ratio in our experiments. We compared the interlayer spacing of the composite membranes with that of pure Ti3C2Tx membranes before and after water swelling (Figure 2c) to examine the expanded interlayer spacing in aqueous environments in nanofiltration and desalination systems.

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To induce

swelling of the prepared membrane in water, each membrane was immersed in water for 1 day, and XRD investigations were conducted immediately after scooping the membrane from water. As previously reported, the interlayer spacing of the GO membranes increased from 9 Å to 13.13 Å,20,24 which corresponds to a diffraction peak shift from 9.16° to 6.76°. Both Ti3C2Tx and Ti3C2Tx/GO composite membranes (30 wt% of GO) displayed a similar expansion of the interlayer spacing to 14.28 Å and a diffraction peak at 6.2°, indicating that the membranes had a similar interlayer nature despite the insertion of GO. With the thickness of an OH-terminated Ti3C2Tx single sheet around 9.2 Å, the effective interlayer spacing of Ti3C2Tx or composite membranes was around 5 Å upon swelling due to water molecules.

Figure 3 a) Permeances of the Ti3C2Tx membrane (90 nm thickness) for various solutions at 5 bar. b) Permeances of the Ti3C2Tx/GO composite membrane (90 nm thickness) for various ionic and dye solutions. Insets are photographs of the dye solutions before and after filtration. c) Rejection of the various ionic and dye solutions indicated in b). The rejections of GO and


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Ti3C2Tx membranes were also included for the comparison. Concentrations of the salt solutions and dye solutions were 0.1 M and 10 mg L−1, respectively. All solutions were filtered at 5 bar. Before rejection tests on the prepared membrane, we investigated how the polarities of liquids influence the flow of various liquids through Ti3C2Tx. The fluxes of water, isopropyl alcohol (IPA), toluene, hexane, and c-hexane (polarities of 10.2, 4.3, 2.4, 0.06, and 0.1, respectively) through the Ti3C2Tx membrane with ~90 nm thickness are compared in Figure 3a. Unfortunately, because Ti3C2Tx/GO composite s to the alcohol and nonpolar solvents, resulting in the coagulation of 2D sheets in contact with the solvents.25 Each solvent was pressurized to 5 bar. The permeance for water was about 25 L m−2 h−1 bar−1, and those for hexane, toluene, and chexane were 6.62, 3.17, and 2.14 L m−2 h−1 bar−1, respectively. In particular, the permeance for IPA was 0.79 L m−2 h−1 bar−1, which is ~31 times lower than that of pure water. A similar decline in flux through GO was attributed to the hydrophobic interaction between sp2 carbon regions and nonpolar solvents.26 In contrast, the behavior of Ti3C2Tx may be influenced by the degree of intercalation of solvent molecules into nano-capillaries and the degree of hydrogen bonding between IPA and the charged Ti3C2Tx surface. According to the XRD results for the Ti3C2Tx membranes that swelled in various solvents, the interlayer spacing of Ti3C2Tx varied with the solvent type (Figure S8). Hexane and toluene were more favorable for intercalation than chexane and ethanol, even though they have weak interactions with Ti3C2Tx .27 The former two led to an increase in interlayer spacing to14.9 Å. In contrast, the XRD patterns of Ti3C2Tx membranes in ethanol and c-hexane showed much less intense peaks with interlayer spacing around 14.2 Å. The larger size of ethanol molecules (~5 Å) as compared with that of water (2.8 Å), and the strong hydrogen bonding between hydroxyl and oxygen groups on the Ti3C2Tx surface, may explain this hindered behavior28 : It seems that while the size of ethanol (Diameter: 4.2 Å) is smaller than that of hexane (5.11 Å), toluene (5.5 Å) and c-hexane (6 Å), strong


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hydrogen bonding between ethanol and oxygen function groups of Ti3C2Tx hinders the transport of ethanol molecules through interlayer. We tested the separation performance of the Ti3C2Tx/GO membrane for several dyes and ions in water solution (Figure 3b and 3c). NaCl, and MgSO4 solutions (0.1 M) were used for salt rejection tests, and the methyl red (MR, neutral charge, hydrated radius: 4.87 Å), methylene blue (MnB, positive charge, 5.04 Å), rose Bengal (RosB, negative charge, 5.88 Å), and brilliant blue (BB, negative charge, 7.98 Å) dye molecules at concentrations of 10 mg L−1 were used for tests on the rejection of organic solutes.16 All filtration tests were conducted at 5 bar using the deadend filtration apparatus pressurized with nitrogen gas. The permeances of the composite membrane for the NaCl, MgSO4, MR, MnB, RosB, and BB solutions were 2.25, 2.35, 2.1, 0.3, 0.67, and 0.23 L m−2 h−1 bar−1, respectively (Figure 3b). The permeances for Na2SO4 and MgCl2 were ~2 L m−2 h−1 bar−1, similar to those for the ionic salt solutions. The stoichiometric ratio of cations and anions in both feed and permeate salt solutions were same to maintain the neutral electrical balance of salt solutions.29 We observed distinctly low permeance values for the dyes with high rejection rate as compared with those for smaller ions with low rejection rates, because the filtered dye molecules clogged the pores for diffusion.30 And it seems that water permeation of composite membrane was lower than Ti3C2Tx membrane because added GO layer may increase the diffusion length of water. A photograph of the dye solutions and the permeates from the Ti3C2Tx/GO composite membrane (inset in Figure 3b) clearly shows the color change with respect to the rejection rate. The colors of the BB, RosB, MnB and MR solutions before filtration were purple, pink, blue and red-violet respectively, but the permeates of BB, RosB and MnB solutions became colorless after filtration. On the other hand, the permeate of MR solution retained its original color even though


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the absorbance intensity decreased (Figure S9). The overall rejection rates of ions and dye molecules, shown in Figure 3c as a function of the hydrated radii, are clearly related to the size. Rejection rates for MnB and BB were 99.5% and 100%, respectively, as confirmed by the marked reduction of UV–vis absorbance bands (Figure S9). Rejection rates for RosB and MR, however, were relatively low (93.5% and 61%, respectively). The lower rejection for MR may be ascribed to the relatively small size of its hydrated molecule and neutral charge. In the RosB case, the lower rejection in spite of a larger molecule size than MnB could be due to its negative charge, with less electrostatic attraction to MXene surfaces. The solutions of ionic salts had the minimal rejection rates (below 11%). It seems that while negatively charged surface of Ti3C2Tx partially rejected salt ions by Donnan exclusion, the interlayer spacing of swelled Ti3C2Tx was too large to completely sieve the salt ions. Especially, the performances of GO and Ti3C2Tx membrane were also compared in order to clarify the enhanced molecular separation performances of composite membranes in terms of rejection rate. The Ti3C2Tx membrane with 80 nm thickness without GO displayed a lower rejection than the composite membrane: 40% (MR), 94.6% (MnB), 66% (RosB) and 95.4% (BB) (Figure S10). And nonselective filtrations were often observed with the Ti3C2Tx membranes in our experiments. The filtration performance of GO membrane (20 nm thickness) also showed lower rejection compared with the composite membrane, with rejection rates of 63% ,92.6%, 66.8%, and 99% for MR, MnB, RosB and BB, respectively (Figure S11). Because GO membrane thicker than 40 nm thickness was highly impermeable in our experiments, we used thin GO membrane around 20 nm thickness.29,33 Especially, the salt rejections were negligible by both GO and Ti3C2Tx membrane in our experiments. 0% NaCl rejection and 5% MgSO4 rejection were observed with Ti3C2Tx membrane. The enhanced rejections of the Ti3C2Tx/GO membrane for dye molecules in


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comparison with the Ti3C2Tx membrane and the GO membrane indicate that added GO played critical role to achieve selective filtration of MXene membranes. And we proved that the nanochannel of MXene is effective in rejecting molecules larger than 5 Å of radii and charged molecules. Based on the above performance, Ti3C2Tx/GO composite membrane displayed the high rejection for dye molecules with sub-nanometer size, but low rejection for salt ions, similar to commercial polymer-based nanofiltration membranes,31 and reduced graphene oxide membrane. 32 However, the water permeation of Ti3C2Tx was decreased to the permeation range of RO membrane (~ 2 L m-2h-1bar-1) because of the barrier property of GO layer. Thus, we are expecting that the water permeation of the Ti3C2Tx/GO composite membrane can be improved by introducing nanopores in the basal plane of GO to provide additional channel entries.29


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Figure 4 a) Schematic diagrams for the sieving mechanism for hydrated ions and dye molecules on the Ti3C2Tx/GO membrane. XPS spectra for b) Ti 2p and c) O 1s. Although a previous report found that pure MXene membranes could reject molecules with sizes larger than 2.5 nm,13 the high rejection rate of sub-nanometer molecules on the Ti3C2Tx/GO membrane during pressure-driven filtration indicates the importance of GO layers in preventing the penetration of molecules into nonselective channels such as pinholes or poorly stacked regions in Ti3C2Tx (Figure 4a).21,22 The formation of non-selective channel can be attributed to the small lateral size of exfoliated Ti3C2Tx sheet around several hundred nanometer scale, or remaining multilayer sheets after exfoliation, which hindering the regular stacking of two dimensional materials.34 Because large GO sheet can block the defective pinholes and


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nonselective channels,35 the separation performance of the Ti3C2Tx/GO membrane is influenced by the interlayer structure of Ti3C2Tx. The high rejection of dye molecules such as BB may be attributed to molecular sieving through the stacked Ti3C2Tx structure with sub-nanometer interlayer spacing due to swelling involving several layers of water molecules (Figure 2c). Because surface of Ti3C2Tx is highly decorated with oxygen groups such as Ti-OH and Ti-O, electrostatic interaction (repulsion and adsorption) also plays a role to reject charged dye molecules such as MnB and RosB. There are several reports from experimental and simulation studies on ion diffusion through Ti3C2Tx: the selectivity of which depends on the size and charge of ions.6,36,37 However, the rejection rates observed in our pressure-driven filtration are lower than expected. There is more room for the Ti3C2Tx membranes to be adjusted to improve the rejection rates. First, XPS analysis of the surface termination of Ti3C2Tx revealed that the Ti 2p spectrum for Ti3C2Tx was composed of four doublets (Ti 2p3/2 and Ti 2p1/2) with a separation of 5.7 eV.38 Peaks at 454.9, 455.7, 457.1, and 459 eV indicate Ti–C and Ti–Cx (from substoichiometric TiCx) bonding as well as TixOy and TiO2, respectively (Figure 4b and Figure S12). This conclusion is also confirmed by the O 1s XPS spectrum in Figure 4c, which shows several peaks for adsorbed O2 (529.4 eV), Tix–Oy (530.9 eV), Ti–OH (532.5 eV), and Ti–H2O (533.1 eV).39 Previous membrane simulations assumed that the Ti3C2Tx surface was terminated with OH functional groups36; however, our results reveal that the prepared Ti3C2Tx membrane contains various terminal groups such as C– Ti–Ox, C–Ti–(OH)x, TiO2, as well as adsorbed water molecules, in agreement with earlier NMR and neutron scattering studies.40,41 The effective interlayer spacing of Ti3C2Tx can be modulated from 5 Å to 9.6 Å by the functional groups of neighboring sheets (Figure 4a). Obviously, narrow spacing is more effective for salt ion rejection by molecular sieving. The interlayer


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spacing of Ti3C2Tx materials is highly dependent on the functional groups and intercalated molecules.20 Second, by introducing spacers to chemically link the individual sheets together, the rejections rates are expected to be increased.29 At last, previously we observed the intercalation of monovalent ions such as Na+ and K+ between the Ti3C2Tx layers and ions with greater charge such as Mg2+ and Al3+ could diffuse into the interlayer after extended immersion or upon application of an electrical potential.42 Thus, applying pressure during filtration may facilitate intercalation of ions between Ti3C2Tx layers,43 eventually lowering the rejection rate of ions. However, Ti3C2Tx membranes have shown bactericidal properties against Gram (−) E. coli and Gram (+) B. subtilis bacteria,44 indicating their antifouling advantage as separation membranes. CONCLUSIONS We demonstrated the potential of the Ti3C2Tx/GO composite membrane in water treatment and molecular separations driven by hydraulic pressure. GO was mixed with Ti3C2Tx to prevent the formation of nonselective channels, such as regions with poor stacking and pinholes. We confirmed the composite membrane’s high rejection of organic dyes with hydrated radii larger than 5 Å, which is due to a combination of physical sieving and electrostatic interaction with Ti3C2Tx layers. Because the theoretical effective interlayer distance of OH-terminated Ti3C2Tx sheets is ~5 Å, controlling the terminal groups of Ti3C2Tx and cross-linking of laminated layers may be useful approaches in future research for developing membranes that strongly reject ions. The narrow interlayer spacing of MXene may offer new opportunities for rejecting small molecules during pressure driven filtration, and we believe our method incorporating graphene oxide with MXene can be widely adopted for other 2D materials to enhance the separation performance.


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METHODS Synthesis of Ti3C2Tx powder: We synthesized Ti3C2Tx powder by etching Ti3AlC2 powder, and the synthesis of Ti3AlC2 powder is described in our earlier paper.2 Lithium fluoride (LiF, 2.0 g, Alfa Aesar,98+%) was dissolved in 20 mL of 9 M hydrochloric acid (diluted from concentrated HCl, 48−51%, Sigma Aldrich) solution under stirring. Ti3AlC2 powder (2.0 g) was gradually added to the resulting solution over ~10 min to prevent overheating. The solution was stirred continuously at 600 rpm at 35 °C for 24 h. To remove the acid, around 100 mL of deionized water was added to the solution. The solution was then centrifuged at 3500 rpm for 5 min, and then the supernatant was decanted. The washing step was repeated until the pH of supernatant reached around 6. The solid residue was then vacuum-filtered and vacuum-dried to obtain multilayered Ti3C2Tx powder. Synthesis of GO powder: We prepared GO using the modified Hummers method.45 Graphite flakes (1 g; 99.95% pure, Graphit Kropfmuhl AG) were dispersed in 98% sulfuric acid (100 mL) solution at room temperature using a mechanical stirrer. After 10 min of stirring, 3 g of KMnO4 was added to the solution. The resulting solution was stirred for 5 h at 35 °C, and then distilled water and hydrogen peroxide solution were sequentially added in an ice bath to remove unreacted KMnO4. The reacted solution was filtered to collect the synthesized GO flakes, which were then rinsed several times with dilute hydrochloric acid and distilled water, and finally freeze-dried. Preparation of Ti3C2Tx/GO composite membranes: GO dispersions were prepared by sonicating GO powder dispersion in DI water at a concentration of 0.1 mg mL−1. Similarly, Ti3C2Tx was exfoliated by sonicating Ti3C2Tx powder dispersion at a concentration of 4 mg mL−1 for 1.5 hr


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under flowing Ar. We centrifuged the dispersions at 3500 rpm for 1 h to remove the remaining unexfoliated Ti3C2Tx particles or thick layers. The supernatant was collected to obtain wellexfoliated Ti3C2Tx in water, which concentration was measured by filtering certain volume of the colloidal solution in to filter and measure the weight of dried powders. In a typical procedure, we mixed 6 mL (concentration: 0.04 mg/mL) of the Ti3C2Tx solution and 1 mL (concentration: 0.03 mg/mL) of GO solution, diluted the mixture with 100 mL of DI water, and then vacuum filtered it through various porous substrates. Track-etched PC filters (0.2 µm pore size, Whatman) were used for ion- and dye-rejection tests, scanning electron microscopy (SEM), and electrondispersive X-ray spectroscopy (EDX) analysis. We utilized anodized aluminum oxide (0.2-µm pore size, Whatman) for X-ray diffraction (XRD) characterization, as well as nylon (0.2 µm pore size, Whatman) and cellulose acetate (0.2 µm pore size, Whatman) for the organic-solvent tests. Filtration performance and permeance: We determined the solvent flux and rejection rate of the membrane using a custom-made dead-end filtration apparatus29 (effective area: 4.52 cm2), which was pressurized with nitrogen gas at 5 bar. NaCl, Na2SO4, MgCl2, and MgSO4 aqueous solutions (0.1 M), as well as aqueous solutions of the dyes MR, MnB, RosB, and BB (hydrated radii: 4.87, 5.04, 5.88, and 7.98 Å, respectively) at concentrations of 10 mg L−1 were used for the ion filtration experiments. The rejection rates were calculated through the following equation: Rejection % = 1 −

× 100

: ! "#$, : &' "#$ We measured the concentration of salt ions using an ion conductivity meter (RS485, Mettler Toledo), and that of the dyes by UV–vis spectroscopy. Furthermore, we determined the liquid


19


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flux by measuring the mass of purified water and subsequently employing the following equation: Permeance =

,#$' &$ ! - " ! . ''/ '0 × &""$ ! / × $ ' ℎ

Typically, we obtained 5 g of permeate solutions to avoid concentration polarization or molecular adsorption during extended periods of dead-end filtration. Characterization: SEM and EDX mapping of the GO, Ti3C2Tx, and Ti3C2Tx/GO composite membranes were performed by using a Nova230 FE-SEM. Raman spectra were obtained with using a dispersive Raman spectrometer excitation, 514 nm laser (Aramis, Horiba Jobin Yvon). A conventional powder X-ray diffractometer (D/MAX-2500, Rigaku) using Cu Kα radiation (λ = 1.5406, 40 kV, 300 mA) was utilized to obtain XRD patterns. Atomic force microscopy (AFM) images were obtained on an XE-100 (Park Systems) in tapping mode. X-ray photoelectron spectroscopy (XPS) was performed with a Thermo VG Scientific Sigma probe. ASSOCIATED CONTENT Supporting Information Supporting information is available free of charge on the ACS publication website. It includes AFM, DLS, SEM, DLS, EDS, UV-vis absorbance, Raman spectra and XPS analysis. AUTHOR INFORMATION Corresponding Author Y. Gogotsi ([email protected]) and H.-T. Jung ([email protected]) K.M. Kang, D. W. Kim and C. E. Ren contributed equally to this work.


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ACKNOWLEDGMENTS This research was supported by the Ministry of Science, ICT, and Future Planning (MSIP; 2015R1A2A1A05001844), the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education (2015R1A6A3A04057367), the Climate Change Research Hub of KAIST (grant no. N1117056), the Leading Foreign Research Institute Recruitment Program funded by the MSIP (2016K1A4A3945038), and the Korean National Research Foundation via the NNFC-KAIST-Drexel Nano2 Co-op Center (NRF2015K1A4A3047100). REFERENCES (1) Anasori, B.; Lukatskaya, M. R.; Gogotsi, Y. 2D Metal Carbides and Nitrides (MXenes) for Energy Storage. Nat. Rev. Mater., 2017, 2, 16098. (2) Naguib, M.; Kurtoglu, M.; Presser, V.; Lu, J.; Niu, J.; Heon, M.; Hultman, L.; Gogotsi, Y.; Barsoum, M. W., Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2. Adv. Mater., 2011, 23, 4248-4253. (3) Zhao, M.-Q.; Torelli, M.; Ren, C. E.; Ghidiu, M.; Ling, Z.; Anasori, B.; Barsoum, M. W.; Gogotsi, Y. 2D Titanium Carbide and Transition Metal Oxides Hybrid Electrodes for Liion Storage. Nano Energy, 2016, 30, 603-613. (4) Zhang, C.; Kim, S. J.; Ghidiu, M.; Zhao, M.-Q.; Barsourm, M. W.; Nicolosi, V.; Gogotsi, Y.

Layered

Orthorhombic

Nb2O5@Nb4C3Tx

and

TiO2@Ti3C2Tx

Hierarchical

Composites for High Performance Li-ion Batteries. Adv. Funct. Mater., 2016, 26, 41434151. (5) Kim, S. J.; Naguib, M.; Zhao, M. Q.; Zhang, C. F.; Jung, H. T.; Barsoum, M. W.;


21


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Page 22 of 27

Gogotsi, Y. High Mass Loading, Binder-Free MXene Anodes for High Areal Capacity Li-Ion Batteries. Electrochim. Acta, 2015, 163, 246-251. (6) Ren, C. E.; Hatzell, K. B.; Alhabeb, M.; Ling, Z.; Mahmoud, K. A.; Gogotsi, Y. Chargeand Size-Selective Ion Sieving Through Ti3C2Tx MXene Membranes. J. Phys. Chem. Lett., 2015, 6, 4026-4031. (7) Shahzad, F.; Alhabeb, M.; Hatter, C. B.; Anasori, B.; Hong, S. M.; Koo, C. M.; Gogotsi, Y. Electromagnetic Interference Shielding with 2D Transition Metal Carbides (MXenes). Science, 2016, 353, 1137-1140. (8) Ling, Z.; Ren, C. E.; Zhao, M.-Q.; Yang, J.; Giammarco, J. M.; Qiu, J.; Barsoum, M. W.; Gogotsi, Y. Flexible and Conductive MXene films and Nanocomposites with high Capacitance. Proc. Natl. Acad. Sci. USA, 2014, 111, 16676-16681. (9) Dillon, A. D.; Ghidiu, M. J.; Krick, A. L.; Griggs, J.; May, S. J.; Gogotsi, Y.; Barsoum, M. W.; Fafarman, A. T. Highly Conductive Optical Quality Solution-Processed Films of 2D Titanium Carbide. Adv. Funct. Mater., 2016, 26, 4162-4168. (10)Hung, W. S.; Tsou, C. H.; De Guzman, M.; An, Q. F.; Liu, Y. L.; Zhang, Y. M.; Hu, C. C.; Lee, K. R.; Lai, J. Y. Cross-Linking with Diamine Monomers to Prepare Composite Graphene Oxide-Framework Membranes with Varying d-spacing. Chem. Mater., 2014, 26, 2983-2990. (11)Sun, L.; Huang, H.; Peng, X. Laminar MoS2 Membranes for Molecule Separation. Chem. Commun., 2013, 49, 10718. (12)Lei, W.; Portehault, D.; Liu, D.; Qin, S.; Chen, Y. Porous Boron Nitride Nanosheets for Effective Water Cleaning. Nat. Commun., 2013, 4, 1777. (13)Ding, L.; Wei, Y.; Wang, Y.; Chen, H.; Caro. J.; Wang, H. A Two-Dimensional Lamellar


22

Page 23 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Membrane: MXene Nanosheet Stacks. Angew. Chem. Int. Ed., 2017, 129, 1-6. (14)Sang, X.; Xie, Y.; Lin, M.-W. ; Alhabeb, M.;Van Aken, K. L.; Gogotsi, Y.; Kent, P. R. C.; Xiao. K.; Unocic. R. R. Atomic Defects in Monolayer Titanium Carbide (Ti3C2TX) MXene. ACS. Nano, 2016, 10, 9193-9200. (15)Ren, C. E; Zhao, M.-Q.; Makaryan, T.; Halim, J.; Kota, S.; Anasori, B.; Barsoum, M. W.; Gogotsi, Y. Porous Two-Dimensional Transition Metal Carbide (MXene) Flakes for High-Performance Li-Ion Strorage. ChemElectroChem, 2016, 3, 689-693. (16)Akbari, A.; Sheath, P.; Martin, S. T.; Shinde, D. B.; Shaibani, M.; Banerjee, P. C.; Tkacz, R.; Bhattacharyya, D.; Majumder, M. Large area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide. Nat. Commun., 2016, 7, 10891. (17)Kim, K. H.; Yang, M.; Cho, K. M.; Jun, Y.-S.; Lee, S. B.; Jung, H.-T. High Quality Reduced Graphene Oxide Through Repairing with Multi-Layered Graphene Ball Nanostructures. Sci. Rep., 2013, 3, 3251. (18)Cheng, C.; Jiang, G.; Garvey, C.J; Wang, Y.; Simon. P.; Liu, J. Z.; Dan, L. Ion Transport in Complex Layered Graphene-Based Membranes with Tunable Interlayer Spacing. Sci. Adv., 2016, 2, e1501272. (19)Wang, S.; Zhang, Y.; Abidi, N.; Cabrales, L. Wettability and Surface Free Energy of Graphene Films. Langmuir, 2009, 25, 11078-11081. (20)Kim, D. W.; Kim, D.; Min, B. H.; Lee, H.; Jung, H.-T. Sonication-Free Dispersion of Large-Area Graphene Oxide Sheets using Internal Pressure from Release of Intercalated Carbon Dioxide. Carbon, 2015, 88, 126-132. (21)Shen, J.; Liu, G. P.; Huang, K.; Chu, Z. Y.; Jin, W. Q.; Xu, N. P. Subnanometer Two-


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 27

Dimensional Graphene Oxide Channels for Ultrafast Gas Sieving. ACS Nano, 2016, 10, 3398-3409. (22)Xu, W.L.; Fang, C.; Zhou, F.; Song, Z.; Liu, Q.; Qiao, R.; Yu, M/ Self-Assembly: A Facile Way of Forming Ultrathin, High-Performance Graphene Oxide Membranes for Water Purification. Nano Lett., 2017, 17, 2928-2933. (23)Kim, D.; Kim, D.W.; Lim, H.-K.; Jeon, J.; Kim, H.; Jung, H.-T.; Lee, H. Intercalation of Gas Molecules in Graphene Oxide Interlayer: The Role of Water. J. Phys. Chem. C, 2014, 118, 11142-11148. (24)Cheng, C.; Jiang, G.; Garvey, C. J.; Wang, Y.; Simon, G. P.; Liu, J. Z.; Li, D. Ion Transport in Complex Layered Graphene-Based Membranes with Tunable Interlayer Spacing. Sci. Adv., 2016, 2, e1501272. (25)Gudarzi, M. M. Colloidal Stability of Graphene Oxide: Aggregation in Two Dimensions. Langmuir, 2016, 32, 5058−5068. (26)Liu, R.; Arabale, G.; Kim, J.; Sun, K.; Lee, Y.; Ryu, C.; Lee, C. Graphene Oxide Membrane for Liquid Phase Organic Molecular Separation. Carbon, 2014, 77, 933-938. (27)Maleski, K.; V.N. Mochalin; Y. Gogotsi, Dispersions of Two-Dimensional Titanium Carbide MXene in Organic Solvents. Chem. Mater., 2017, 29, 1632-1640. (28)Paredes, J. I.; Villar-Rodil, S.; Martínez-Alonso, A.; Tascón, J. M. D. Graphene Oxide Dispersions in Organic Solvents. Langmuir, 2008, 24, 10560-10564. (29)Kim, D, W.; Choi, J.; Kim, D.; Jung, H, T. Enhanced Water Permeation Based on Nanoporous Multilayer Graphene Membranes: the Role of Pore Size and Density. J. Mater. Chem. A, 2016, 4, 17773-17781. (30)Bruggen, B. V. D.; Vandecasteele, C. Flux Decline during Nanofiltration of Organic


24

Page 25 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Components in Aqueous Solution. Environ. Sci. Technol., 2001, 35, 3535-3540. (31)Fan, L.; Zhang, Q.; Yang, Z.; Zhang, R.; Liu, Y.; He, M.; Jiang, Z.; Su, Y. Improving Permeation and Antifouling Performance of Polyamide Nanofiltration Membranes through the Incorporation of Arginine. ACS Appl. Mater. Interfaces, 2017, 9, 1357713586. (32)Zhao, Y. J.; Li, C.; Fan, X. Y.; Wang, J. H.; Yuan. G.; Song, X. X.; Chen, J.; Li, Z. Study on the separation performance of the multi-channel reduced graphene oxide membranes. Appl. Surf. Sci., 2016, 384, 279-286. (33)Nam, Y. T.; Choi, J.; Kang, K. M.; Kim, D. W.; Jung, H.-T. Enhanced Stability of Laminated Graphene Oxide Membranes for Nanofiltration via Interstitial Amide Bonding. ACS Appl. Mater. Interfaces, 2016, 8, 27376-27382. (34)Chi, C.; Wang, X.; Peng, Y.; Qian, Y.; Hu, Z.; Dong, J.; Zhao, D. Facile Preparation of Graphene Oxide Membranes for Gas Separation. Chem. Mater., 2016, 28, 2921-2927. (35)Huang, A. S.; Liu, Q.; Wang, N. Y.; Zhu, Y. Q.; Caro, J. Bicontinuous Zeolitic Imidazolate Framework ZIF-8@GO Membrane with Enhanced Hydrogen Selectivity. J. Am. Chem. Soc., 2014, 136, 14686-14689. (36)Guo, X.; Zhang, X.; Zhao, S. High Adsorption Capacity of Heavy Metals on TwoDimensional MXenes: an ab initio Study with Molecular Dynamics Simulation. Phys. Chem. Chem. Phys., 2016, 18, 228-233. (37)Ghidiu, M.; Halim, J.; Kota, S.; Bish, D.; Gogotsi, Y.; Barsoum, M. W. Ion-Exchange and Cation Solvation Reactions in Ti3C2 MXene. Chem. Mater., 2016, 28, 3507-3514. (38)Rakhi, R. B.; Ahmed, B.; Hedhili, M. N.; Anjum, D. H.; Alshareef, H. N. Effect of Postetch Annealing Gas Composition on the Structural and Electrochemical Properties


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 27

of Ti2CTx MXene Electrodes for Supercapacitor Applications. Chem. Mater., 2015, 27, 5314-5323. (39)Halim, J.; Lukatskaya, M. R.; Cook, K. M.; Lu, J.; Smith, C. R.; Naslund, L. A.; May, S. J.; Hultman, L.; Gogotsi, Y.; Eklund, P.; Barsoum, M. W. Transparent Conductive TwoDimensional Titanium Carbide Epitaxial Thin Films. Chem. Mater. 2014, 26, 23742381. (40)Hope, M. A.; Forse, A. C.; Griffith, K. J.; Lukatskaya, M. R.; Ghidiu, M.; Gogotsi, Y.; Grey, C. P. NMR Reveals the Surface Functionalisation of Ti3C2 MXene. Phys. Chem. Chem. Phys., 2016, 18, 5099-5102. (41)Wang, H. W.; Naguib, M.; Page, K.; Wesolowski, D. J.; Gogotsi, Y. Resolving the Structure of Ti3C2Tx MXenes through Multilevel Structural Modeling of the Atomic Pair Distribution Function. Chem. Mater., 2016, 28, 349-359. (42)Mashtalir, O.; Naguib, M.; Mochalin, V. N.; Dall’Agnese, Y.; Heon, M.; Barsoum, M. W.; Gogotsi, Y. Intercalation and Delamination of Layered Carbides and Carbonitrides. Nat. Commun., 2013, 4, 1716. (43)Bano, S.; Mahmood, A.; Kim, S. J.; Lee, K. H. Graphene Oxide Modified Polyamide Nanofiltration Membrane with Improved Flux and Antifouling Properties. J. Mater. Chem. A, 2015, 3, 2065-2071. (44)Rasool, K.; Helal, M.; Ali, A.; Ren, C. E.; Gogotsi, Y.; Mahmoud, K. A. Antibacterial Activity of Ti3C2TX MXene. ACS Nano, 2016, 10, 3674-3684. (45)Hummers, W. S.; Offeman, R. E. Preparation of Graphitic Oxide. J. Am. Chem. Soc., 1958, 80, 1339.


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Selective Molecular Separation on Ti3C2TxâGraphene Oxide

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