Supporting Information
High-Performance, Free-Standing Symmetric
Hybrid Membrane for Osmotic Separations
Zhi Geng,1 Shiqiang Liang,1 Meng Sun,2 Chuhan Liu,1 Nan He,1 Xia Yang,1
Xiaochun Cui,1 Wei Fan,1 Xianze Wang*,1 and Yang Huo*,1
1 College of Environment, Research Centre for Municipal Wastewater Treatment and
Water Quality Protection, Northeast Normal University, Changchun 130117, China
SUPPORTING DISCUSSION
Supporting Information: There are three parts content of the material supplied as Supporting Information, (1) Synthesis of NH2-MIL-125 Nanoparticles/ POD Polymer/ POD-COOH Polymer/; (2) Membrane Performance Testing; (3) Characterization of the NH2-MIL-125 Nanoparticles/ Chemical Structures of POD,
POD-COOH and NH2-MIL-125/POD-COOH Hybrid Materials.
Synthesis of NH2-MIL-125 Nanoparticles
NH2-MIL-125 nanoparticles were prepared via solvothermal reaction.The preparation
process is as follows: 0.75 mmol TBT and 3 mmol H2ATA were dispersed in 10 ml
DMF and MeOH (1:1, v/v) mixture solution of for 3 h. After that, the solution was transferred to a 40 ml reactor with a magnetic stir bar and heated to 148 oC for 24 h,
and then cooled down to room temperature. The precipitates were washed with DMF and methanol three times. Lastly, the product was dried in a vacuum oven at 80 oC for
about 12 h, and then heated to 150 oC for 4 h. After cooling down to room
temperature, the product was grinded to obtain NH2-MIL-125 clusters.
Synthesis of POD Polymer
Poly(1,3,4-oxadiazoles) (POD) was synthesized by medium temperature polymerization, and the synthesis route was shown in Scheme 1. HS (1.0 g, 7.685 mmol), PPA (25.6 g, 76.852 mmol) and OBBA (1.654 g, 6.404 mmol) were mixed in a 100 ml three-necked flask fortified with a dry nitrogen inlet tube with a thermometer, a mechanical stirring paddle and a Dean-Stark trap with a condenser. The reaction atmosphere was kept free of water and oxygen before heating, then the temperature of reaction system was increased to 160 oC and maintained for 3 h with continuously
stirring throughout the polymerization procedure. Afterward, the viscous solution was poured into tepid 5% NaOH solution to acquire a threadlike polymer. Later the raw product was crushed into to powder by a high speed blender, and was neutralized with 5% NaOH solution for 12 h. Ultimately, the product was neutralized by washing it with hot DI water and dried by vacuum oven at 90 oC for about 24 h to obtain POD
by gel permeation chromatograms (GPC).
Scheme S1. Synthetic route of Poly(1,3,4-oxadiazoles) (POD). Synthesis of POD-COOH Polymer
The carboxylated poly(1,3,4-oxadiazole) (POD-COOH) was further synthesized from the above-mentioned POD, and the synthesis procedure was shown in Scheme 2. POD (1.011 g, 4.282 mmol) was dissolved in 20 ml NMP solvent in a 100 ml completely dried three-neck flask, after stirring at room temperature for about 2 h, p-ABA (0.588 g, 4.282 mmol) and PPA (0.1 g) were added, then the mixture was heated to 195 °C and maintained for 10 h under the protection of nitrogen. After that, the brownish solution in the flask was gushed into warm water to get a raw product. The as obtained raw product was then crushed into powder with the help of high-speed blender and the polymer powder was washed thoroughly with hot DI water to remove the unreacted precursors. Lastly, the powder was dried under vacuum at 90 oC for
about 24 h to obtain POD-COOH polymer. Mw: 2.48×105, Mn: 1.17×105,
polydispersity index (PDI): 2.12, determined by gel permeation chromatograms (GPC).
Characterization
The X-ray diffractometer (XRD) of the NH2-MIL-125 nanoparticles was measured by
a Japan Rigaku Co., Ltd. instrument (D/Max/III model) using Cu Kα excitation radiation (λ= 0.154 nm). 1H NMR spectra of polymers were recorded on a Bruker 510
NMR spectrometer (500 MHz) using DMSO-d6 as the reference solvent. Waters 410
gel permeation chromatograms (GPC) was used to test the molecular weight of POD and POD-COOH, using N,N-dimethylformamide (DMF) as the eluent and polystyrene as a standard, the testing flow rate was 1 ml min-1. FT-IR spectra were
performed using a Fourier transform infrared spectrometer (Nicolet Impact 410). FEI XL30 field emission scanning electron microscopy (FE-SEM) equipped with an energy dispersive spectrometer (EDS) detector was used to observe the microstructures of thin films and the dispersion of NH2-MIL-125 nanoparticles in the
films. The surface zeta potential (ζ) measurements of membranes were performed by an Anton Paar SurPASS 3 electrokinetic analyzer with AgCl electrodes. 0.01 M KCl was used as an electrolyte solution during the measurement of streaming potential. Automated pH titration was performed using hydrochloric acid (0.01 M) or sodium hydroxide (0.01 M). The water contact angles (CA) of the fabricated membranes were tested by a KRÜSS DSA 25 goniometer. A flat membrane was first fixed on the test bench, then a 3 μl liquid droplet of DI water was dropped onto the membrane surface with contact time of 3 s, and the water droplet was photographed by a standard CCD camera. To ensure the smallest error in the results, each membrane sample was tested at least three times at different locations for the final test result. The mechanical characteristics of fabricated membranes were measured by a Shimadzu AG-I universal testing machine at room temperature. The tensile rate during the test was 3 mm s-1 and the size of the film strip was 8 cm × 0.5 cm. Each sample was tested five
times for the final test results. Membrane Performance Testing
where ΔVfeed is the the increase in DS volume, Am is the effective membrane testing
area in the cell and Δt is the measuring time interval.
The conductivity change of FS was measured by a DDS-307 conductivity meter (Yidian Scientific Instrument Co. LTD, Shanghai, China), and the reverse salt flux (Js)
was calculated by using the following equation:
(S2) 0 0 t t s m C V C V J A t
where Ct and Co are the final and initial salt concentrations of the FS, respectively,
and Vt and Vo are the final and initial volumes of the FS, respectively.
The water permeability coefficient (A) was calculated by:
(S3) w RO J A P
where ΔP is the applied transmembrane pressure difference and 𝐽𝑅𝑂𝑤 is the pure water flux.
The salt rejection rate (R) was calculated using the following equation:
(S4) 100% f p f C C R C
where Cf and Cp are the salt concentrations in the feed and the permeate, respectively.
The salt permeability coefficient (B) was determined based on classical solution-diffusion theory according to the following equation:
(S5) 1 exp( ) RO wRO w J R B J R k
where k is the mass transfer coefficient, and k was calculated from:
(S6) h ShD k d
where D is the diffusion coefficient of Na2SO4, dh is the hydrodynamic diameter of
the flow channel, and Sh is the Sherwood number, which is calculated as:
(S7) 0.33 d 1.86(Re ) h Sh Sc L
Schmidt number, and Re and Sc were calculated using the formulas given below: (S8) udh Re (S9) Sc D
where ρ is the water density, μ is the dynamic viscosity of the solution, and u is the crossflow velocity.
K reflects the membrane resistance to solute diffusion, and K was determined from the
following equation: (S10) 1 d FO FO w w f B A K ln J B J A
where πd and πf are the osmotic pressures of the DS and FS, respectively.
Finally, the membrane structural parameter (S) was determined by:
(S11)
S KD
Characterization of the NH2-MIL-125 Nanoparticles
Figure S1. (a) XRD pattern; (b) FT-IR spectra and (c) SEM image of NH2-MIL-125
nanoparticles
The crystal form of the NH2-MIL-125 nanoparticles was determined by their X-ray
diffraction (XRD) patterns. As shown in Figure 1 (a), the featured peaks at 6.8°, 9.8°, 11.6°, 16.6° and 17.9° of the as-prepared NH2-MIL-125 particles are attributed to the
(101), (200), (211), (222) and (312) crystal planes, respectively, which are consistent with published literature results. [36] The chemical structures of the as-synthesized
NH2-MIL-125 nanoparticles were confirmed using Fourier transform infrared (FT-IR)
spectroscopy. As shown in Figure 1 (b), the bimodal peaks at 3372 cm-1 and 3444
cm-1 were ascribed to asymmetric and symmetric stretching vibration characteristic
absorption peaks of amino groups, respectively; the peaks at 1570 cm-1 and 1338 cm-1
were attributed to C-N stretching vibration and N-H bending vibration characteristic absorption peaks of aromatic amine groups, respectively; and the other peaks were consistent with previous literature results. [36] The XRD and FT-IR results suggested
that the NH2-MIL-125 nanoparticles were successfully synthesized. The scanning
electron microscopy (SEM) images of the NH2-MIL-125 nanoparticles are displayed
in Figure 1 (c). It could be observed that the NH2-MIL-125 nanoparticles had a
uniform circular plate structure with a particle size of approximately 200-400 nm. The morphology of the NH2-MIL-125 nanoparticles was also consistent with previously
Chemical Structures of POD, POD-COOH and NH2-MIL-125/POD-COOH
Hybrid Materials
(a) (b)
Figure S2. (a) 1H NMR spectra of POD; (b) 1H NMR spectra of POD-COOH
The chemical structures of the as-prepared POD and POD-COOH were determined by proton nuclear magnetic resonance (1H NMR) and FT-IR analyses. Figure 2 (a) shows
the 1H NMR spectra of POD. The double peaks from 7.1 to 7.5 ppm were designated
as phenyl protons adjacent to ether groups. The twin peaks from 8.1 to 8.4 ppm were ascribed to the phenyl protons adjacent to oxadiazole groups. [39] It has been reported
that the oxadiazole rings of POD are chemically unstable in acidic media. During the synthesis of POD, the dehydration cyclization reaction of hydrazide groups and hydrolytic ring-opening reaction of oxadiazole groups were carried out simultaneously. [40,41] Therefore, a sharp peak at 8.6 ppm representing H from
hydrazide groups was observed.
The 1H NMR spectra of POD-COOH are shown in Figure 2 (b). The double peaks
from 7.1 to 7.4 ppm were attributed to the H from phenyl groups adjacent to ether groups in the main chain. The twin peaks from 8.1 to 8.3 ppm were attributed to the H from phenyl groups adjacent to oxadiazole groups in the main chain. Because of the existence of hydrazide structures in POD-COOH, a sharp peak at 8.6 ppm representing H from hydrazide groups was also observed. The peaks from 7.4 to 7.6
groups of p-aminobenzoic acid (p-ABA) in the side chain, respectively. In addition, the peaks at approximately 10 to 11 ppm were attributed to the H from carboxyl groups of p-ABA in the side chain. The proportion of repeat units containing carboxyl groups in the POD-COOH chemical structure determined and calculated from the integral area ratio of the 1H NMR spectrum was ~15%, which was different from the
feeding molar ratio of p-ABA in the reaction system; this result indicated that the side chain grafting reaction was not complete and that only part of the p-ABA was grafted onto the side chain of POD.
Figure S3. FT-IR spectra of (a) POD, (b) POD-COOH, (c)
5%NH2-MIL-125/POD-COOH, (d) 10%NH2-MIL-125/POD-COOH
The FT-IR spectra of POD, POD-COOH and NH2-MIL-125/POD-COOH hybrid
materials are displayed in Figure 3, revealing the following: 1664 cm-1 (C=O bond of
hydrazide groups), 1600 cm-1 (C=C bond of the benzene ring), 1241 cm-1 (Ar-O-Ar
bond of OBBA), 1091 cm-1 and 1027 cm-1 (C-O-C bond of the oxadiazole ring). In
comparison to the FT-IR spectrum of POD presented in Figure 3 (a), a new characteristic absorption peak appeared at 1530 cm-1 in Figure 3 (b), equivalent to the
C=N stretching vibration from the triazole ring, [42] validating the effective formation
of the triazole ring in the POD-COOH chemical structure. The results from 1H NMR
Moreover, in contrast to the FT-IR spectrum of POD-COOH shown in Figure 3(b), a new characteristic absorbance peak at 1560 cm-1 associated with the N-H bond of acid
amide was detected, as shown in Figure 3 (c-d). Additionally, a new peak at 3365-3440 cm-1 ascribed to the -NH
2 band of NH2-MIL-125 nanoparticles was
observed, as shown in Figure 3 (c-d). The results confirmed that the NH2-MIL-125
nanoparticles were effectively grafted onto the side chains of the POD-COOH polymer matrix through covalent bonding and that NH2-MIL-125/POD-COOH hybrid
