Research Note pubs.acs.org/IECR
A Facile Surface Modification for Antifouling Reverse Osmosis Membranes Using Polydopamine under UV Irradiation Youngbin Baek,†,§ Benny D. Freeman,‡ Andrew L. Zydney,§ and Jeyong Yoon*,† †
School of Chemical and Biological Engineering, Institute of Chemical Process (ICP), Seoul National University, Daehak-dong, Gwanak-gu, Seoul 08826, Republic of Korea ‡ Department of Chemical Engineering, Center for Energy and Environmental Resources, University of Texas at Austin, 10100 Burnet Road, Building 133, Austin, Texas 78758, United States § Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States S Supporting Information *
ABSTRACT: Polydopamine (PDA) is widely used to modify the membrane surface to increase the hydrophilicity with the goal of producing a low fouling membrane. However, current methods of PDA modification require alkali conditions and relatively long reaction times. Herein, we introduced the use of UV irradiation during the PDA modification of the membrane surface. The effects of UV irradiation on the characteristics of the synthesized PDA and the performance of the resulting membrane were evaluated. The PDA was rapidly synthesized in DI water, providing a significant increase in hydrophilicity and a reduction in surface roughness of the polyamide reverse osmosis (RO) membranes. The PDA-modified RO membranes exhibited excellent antifouling behavior upon exposure to alginate while maintaining good water permeability and salt rejection. The use of UV allowed the PDA modification to be conducted in DI water in less than 30 min, a significant improvement compared to current methods.
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the interaction between hydrophobic foulants and the membrane surface.17,18 Kasemset et al.15 showed that a PDAmodified membrane, produced by treatment with dopamine for more than 1 h under alkali conditions, had less fouling when used to filter oil/water emulsions. Membranes modified under acidic conditions or for short modification times showed similar fouling characteristics to the unmodified membrane, indicating that the PDA layer only forms in the presence of base. Xu et al.19,20 showed that dopamine can be used to fabricate nanofiltration (NF) membrane by co-deposition with branched polyethylenimine or octaammonium polyhedral oligomeric silsesquioxane. The resulting membranes were found to be very attractive for removal of cationic dyes. Dopamine has also been applied to forward osmosis (or pressure retarded osmosis) membranes to improve performance, including antifouling behavior.21−23 Additionally, PDA grafted with silver nanoparticles, poly(ethylene glycol) (PEG), and poly([2(methacryoyloxy)ethyl]trimethylammonium-chloride) have been shown to have anti-biofouling characteristics.24−26 However, the current methods used for PDA modification typically reduce the water flux, often by much more than 10%,
opamine, commonly known as a hormone and neurotransmitter of the catecholamine and phenethylamine families,1,2 has recently been used for surface modification of biomaterials, medical devices, and membranes.3,4 Surface modification is typically accomplished by reacting commercially available dopamine hydrochloride with a base (mostly tris(hydroxymethyl)aminomethane (Tris); pKa = 8.1) for at least 1 h, resulting in the formation of a polydopamine (PDA) layer.3 The advantages of PDA modification are strong adhesion, ultrathin and controllable thickness, and high hydrophilicity. The PDA strongly adheres to the substrate surface via both noncovalent interactions (i.e., hydrogen bonding, charge transfer, ionic interactions, and π stacking)5,6 and covalent linkages between monomers and quinhydrones. This strong adhesion also results in high stability of the PDA. Second, the PDA layer is very thin (tens of nanometers thick),7 with the final thickness determined by the choice of deposition time and initial dopamine concentration.8 Finally, the PDA modification provides a highly hydrophilic surface regardless of the substrate properties.9,10 PDA modification is now used in a broad range of applications including biotechnology,11,12 nanotechnology,13,14 and membrane technology.15,16 In the case of membranes, PDA modification has been primarily used to produce very low-fouling membranes for water treatment applications. A number of studies have shown that highly hydrophilic surfaces can prevent fouling by reducing © XXXX American Chemical Society
Received: Revised: Accepted: Published: A
December 20, 2016 March 14, 2017 May 2, 2017 May 2, 2017 DOI: 10.1021/acs.iecr.6b04926 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Research Note
Industrial & Engineering Chemistry Research
Figure 1. Synthesis of polydopamine (PDA) under different experimental conditions: (a) photographs showing extent of reaction in solution associated with color change, (b) UV absorbance for reaction in solution, (c) thickness of PDA layer on silicon wafers, and (d) XPS spectra of PDA layer on silicon wafers.
synthesis. Previous studies have shown that PDA is not synthesized at neutral or low pH under ambient conditions (in the absence of UV).10 Figure 1b presents the absorbance spectra of PDA solutions after 1 h of reaction time. The peak at 410 nm indicates the presence of PDA; this peak is greatest in the UV-irradiated sample at pH 8.5, with a much smaller peak observed for the sample in DI water under UV irradiation. The thickness of the PDA layer deposited on silicon wafers was measured directly using an ellipsometer, with results shown in Figure 1c. The thickness of the UV-irradiated sample at pH 8.5 was 11.3 nm after 3 h, while that of the nonirradiated sample was only 6.8 nm. The layer formed on the silicon wafer in DI water with UV irradiation was less than 1 nm thick after 3 h. Figure 1d shows the XPS spectra of PDA layer deposited on silicon wafers for 1 h, with the calculated elemental composition by atomic percent summarized in Table 1. The
due to the increase in membrane resistance. In addition, the use of alkaline pH and the relatively long time required for the PDA modification can create challenges for commercial application of this technology. Here we introduce the use of UV irradiation to facilitate the modification of membrane surfaces by PDA. Polyamide reverse osmosis (RO) membranes were modified with PDA under UV irradiation, leading to rapid formation of the PDA layer in DI water. The performance of the PDA-modified RO membrane was evaluated by measuring water permeability and salt passage, with the fouling characteristics determined using alginate solutions as a model foulant. These results demonstrate the effectiveness of using UV irradiation to facilitate membrane modification by PDA.
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RESULTS AND DISCUSSION Characteristics of Synthesized Polydopamine under UV Irradiation. The experimental procedures used for membrane modification are described in detail in the Supporting Information. Very briefly, commercial thin film composite polyamide membranes were treated with 2 g/L solutions of dopamine in DI water and at pH 8.5 both in the presence and in the absence of UV irradiation (approximately 1000 μW/cm2). The extent of PDA synthesis was indicated by a change in color as shown in Figure 1a. The UV-irradiated PDA solution at pH 8.5 was darker than the nonirradiated PDA solution, indicating that UV irradiation accelerated PDA synthesis, consistent with previous results showing activation of dopamine polymerization by sunlight.27 Interestingly, significant color appeared in the dopamine solution in DI water (pH 5.8) under UV irradiation, while the nonirradiated solution in DI water was transparent, indicating negligible PDA
Table 1. Elemental Composition by atom % of PDA Layer on Silicon Wafers for 1 h samples
C
N
O
Si
C/N
control DI water + hv pH 8.5 pH 8.5 + hv
11.5 12.2 40.1 59.1
0.2 0.6 4.9 8.3
41.6 40.7 32.9 27.6
46.7 46.5 22.1 5.0
50.4 21.7 8.1 7.1
percentage of carbon (at 285 eV) and nitrogen (at 398 eV) increased for the treated samples, consistent with the formation of PDA on the silicon surface. The levels of C and N (both increasing due to PDA) and O and Si (both decreasing due to coverage of the silicon surface) for the different samples are in a good agreement with the measured thickness of the PDA layer (Figure 1c). The surface modified RO membranes were also B
DOI: 10.1021/acs.iecr.6b04926 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Research Note
Industrial & Engineering Chemistry Research
Figure 2. Performance characteristics of the PDA-modified RO membranes: (a) water permeability and (b) NaCl transmission for modification at pH 8.5 (left panel) and in DI water (right panel) both with and without UV irradiation. Data were obtained with 2000 mg/L NaCl solution as a feed solution, 10.3 bar of applied pressure, 1.7 L/min cross-flow rate (Re = 1400) and 23 ± 2 °C temperature.
Figure 3. (a) Normalized flux of the different PDA-modified RO membranes during alginate fouling for 24 h compared with that of a commercial RO membrane, (b) contact angles of unmodified and PDA modified RO membranes (modification time, 10 min), and (c) AFM images with values of RMS roughness.
similar composition of PDA to the base polyamide in combination with the low signal from the very thin PDA layer. Membrane Performance with PDA Modification. Commercially available polyamide RO membranes were surface
examined by both XPS and ATR-FTIR. However, there were no observable changes in either the elemental composition analyzed (data not shown) or chemical functional groups after surface modification (Figure S1, ESI†), which likely reflects the C
DOI: 10.1021/acs.iecr.6b04926 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Research Note
Industrial & Engineering Chemistry Research
33.3 to 46.3 nm. The membranes with thicker PDA layers (results in Figure 1 c) tended to have a smoother surface (lower roughness).
modified with PDA (Figure S2, ESI). Limited data obtained with UF membranes showed significant flux decline after the PDA modification (Figure S3, ESI) due to formation of a PDA layer on and possibly within the membrane pores. Figure 2 shows the water permeability and salt passage for the RO membranes, evaluated in a lab-scale cross-flow RO membrane device,28 as a function of the modification time for membranes treated with dopamine alone, with dopamine in the presence of UV irradiation, and with UV irradiation alone at pH 8.5 and in DI water. The water permeability of the PDA-modified RO membrane significantly decreased from 9.9 to 6.9 LMH/bar when treated with UV irradiation at pH 8.5 with a slight reduction in the salt passage. The drop in permeability is due to the additional resistance provided by the PDA layer formed on the membrane surface; UV irradiation at pH 8.5 showed the thickest layer on the silicon wafer (Figure 1c). In contrast, the membrane modified in DI water showed only a slight decrease in permeability (from 9.3 to 8.3 LMH/bar after 30 min) with essentially no change in salt transmission. The water permeability of the RO membranes treated with just dopamine or UV irradiation remained relatively constant. However, the salt passage of the membrane treated with UV irradiation alone increased slightly, suggesting that the UV irradiation might have caused a very low level of degradation of the polyamide membrane, consistent with previous observations.29 Fouling Behavior. The fouling behavior of the PDAmodified RO membranes were examined using alginate, an important microbial polysaccharide that is commonly used as a model foulant in RO process.30 Four types of RO membranes were prepared: PDA-modified RO membranes with UV irradiation either at pH 8.5 or in DI water, a PDA-modified membrane at pH 8.5 but without UV irradiation, and a commercial RO membrane. In each case, the PDA modification was performed for 10 min. Figure 3a shows the permeate flux as a function of time during filtration of 100 mg/L alginate solution. The flux decline for both PDA-modified RO membranes formed with UV irradiation was approximately 11−12%, which is significantly less severe than the fouling seen for either the PDA-modified RO membrane without UV irradiation (25%) or the unmodified RO membrane (26%). Similar behavior was seen after multiple filtration cycles, indicating that the PDA modification provides long-term resistance to fouling by alginate. The fouling results are in good agreement with contact angle measurements for the surface-modified RO membranes (see ESI for more details) after 10 min exposure to the dopamine solution (Figure 3b). The contact angles for the nonirradiated PDA-modified RO membranes were 54° ± 1° (pH 8.5) and 56° ± 2° (DI water), which are similar to the value obtained with the unmodified RO membrane (referred to as the fabricated RO membrane without PDA modification; 56° ± 1°). In contrast, the contact angles of the UV-irradiated RO membranes decreased to 35° ± 1° (pH 8.5) and 43° ± 1° (DI water), which are much smaller (i.e., more hydrophilic) than that for the base polyamide membrane. These data clearly indicate that UV irradiation not only accelerates polymerization of the dopamine but also forms a PDA layer that is significantly more hydrophilic. Additionally, the surface roughness of the membranes was analyzed using atomic force microscopy (AFM), with typical images shown in Figure 3c. The commercial RO membrane has the largest value of RMS roughness (71.2 nm), while the RMS roughness of the PDA modified RO membranes ranged from
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CONCLUSIONS PDA modification in the presence of UV irradiation is a facile approach to prepare low-fouling membranes while maintaining good separation performance. Another attractive feature of this approach is that the UV irradiation significantly reduces the modification time (to as short as 10 min), which would greatly facilitate the adoption of this process in commercial membrane fabrication processes (i.e., incorporation of the PDA modification with UV irradiation directly in the roll-to-roll manufacturing process). Although additional work will be required to fully characterize PDA synthesis in the presence of UV irradiation and the associated cost of this type of surface modification, the results presented in this work demonstrate that this technique can be effectively used to fabricate lowfouling RO membranes with good water permeability and salt rejection.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.6b04926. Materials and methods, ATR FT-IR spectra of PDAmodified vs commercial RO membrane, schematic of preparation of PDA modified RO membrane, normalized flux as function of PDA modification time, and schematic of cross-flow RO membrane system (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Benny D. Freeman: 0000-0003-2779-7788 Jeyong Yoon: 0000-0002-8191-1396 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This research was supported by the Korea Ministry of Environment as “Converging technology project” (2014001640002).
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REFERENCES
(1) Zhang, A.; Neumeyer, J. L.; Baldessarini, R. J. Recent progress in development of dopamine receptor subtype-selective agents: potential therapeutics for neurological and psychiatric disorders. Chem. Rev. 2007, 107, 274−302. (2) Wightman, R. M.; May, L. J.; Michael, A. C. Detection of dopamine dynamics in the brain. Anal. Chem. 1988, 60, 769A−793A. (3) Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B. Mussel-inspired surface chemistry for multifunctional coatings. Science 2007, 318, 426−430. (4) Ye, Q.; Zhou, F.; Liu, W. Bioinspired catecholic chemistry for surface modification. Chem. Soc. Rev. 2011, 40, 4244−4258. (5) Dreyer, D. R.; Miller, D. J.; Freeman, B. D.; Paul, D. R.; Bielawski, C. W. Perspectives on poly (dopamine). Chem. Sci. 2013, 4, 3796− 3802. (6) Dreyer, D. R.; Miller, D. J.; Freeman, B. D.; Paul, D. R.; Bielawski, C. W. Elucidating the structure of poly (dopamine). Langmuir 2012, 28, 6428−6435.
D
DOI: 10.1021/acs.iecr.6b04926 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Research Note
Industrial & Engineering Chemistry Research
membranes with anti-biofouling properties. J. Membr. Sci. 2014, 468, 216−223. (26) Zhang, R.; Su, Y.; Zhou, L.; Zhou, T.; Zhao, X.; Li, Y.; Liu, Y.; Jiang, Z. Manipulating the multifunctionalities of polydopamine to prepare high-flux anti-biofouling composite nanofiltration membranes. RSC Adv. 2016, 6, 32863−32873. (27) Sheng, W.; Li, B.; Wang, X.; Dai, B.; Yu, B.; Jia, X.; Zhou, F. Brushing up from “anywhere” under sunlight: a universal surfaceinitiated polymerization from polydopamine-coated surfaces. Chem. Sci. 2015, 6, 2068−2073. (28) Van Wagner, E. M.; Sagle, A. C.; Sharma, M. M.; Freeman, B. D. Effect of crossflow testing conditions, including feed pH and continuous feed filtration, on commercial reverse osmosis membrane performance. J. Membr. Sci. 2009, 345, 97−109. (29) Lipp-Symonowicz, B.; Sztajnowski, S.; Kardas, I. Influence of UV radiation on the mechanical properties of polyamide and polypropylene fibres in aspect of their restructuring. AUTEX Res. J. 2006, 6, 196−203. (30) van den Brink, P.; Zwijnenburg, A.; Smith, G.; Temmink, H.; van Loosdrecht, M. Effect of free calcium concentration and ionic strength on alginate fouling in cross-flow membrane filtration. J. Membr. Sci. 2009, 345, 207−216.
(7) Jiang, J.; Zhu, L.; Zhu, L.; Zhu, B.; Xu, Y. Surface characteristics of a self-polymerized dopamine coating deposited on hydrophobic polymer films. Langmuir 2011, 27, 14180−14187. (8) Ball, V.; Del Frari, D.; Toniazzo, V.; Ruch, D. Kinetics of polydopamine film deposition as a function of pH and dopamine concentration: Insights in the polydopamine deposition mechanism. J. Colloid Interface Sci. 2012, 386, 366−372. (9) Zhang, W.; Yang, F. K.; Han, Y.; Gaikwad, R.; Leonenko, Z.; Zhao, B. Surface and tribological behaviors of the bioinspired polydopamine thin films under dry and wet conditions. Biomacromolecules 2013, 14, 394−405. (10) Wei, Q.; Zhang, F.; Li, J.; Li, B.; Zhao, C. Oxidant-induced dopamine polymerization for multifunctional coatings. Polym. Chem. 2010, 1, 1430−1433. (11) Ku, S. H.; Lee, J. S.; Park, C. B. Spatial control of cell adhesion and patterning through mussel-inspired surface modification by polydopamine. Langmuir 2010, 26, 15104−15108. (12) Ryu, J.; Ku, S. H.; Lee, H.; Park, C. B. Mussel-Inspired Polydopamine Coating as a Universal Route to Hydroxyapatite Crystallization. Adv. Funct. Mater. 2010, 20, 2132−2139. (13) Fei, B.; Qian, B.; Yang, Z.; Wang, R.; Liu, W. C.; Mak, C. L.; Xin, J. H. Coating carbon nanotubes by spontaneous oxidative polymerization of dopamine. Carbon 2008, 46, 1795−1797. (14) Hu, H.; Yu, B.; Ye, Q.; Gu, Y.; Zhou, F. Modification of carbon nanotubes with a nanothin polydopamine layer and polydimethylamino-ethyl methacrylate brushes. Carbon 2010, 48, 2347−2353. (15) Kasemset, S.; Lee, A.; Miller, D. J.; Freeman, B. D.; Sharma, M. M. Effect of polydopamine deposition conditions on fouling resistance, physical properties, and permeation properties of reverse osmosis membranes in oil/water separation. J. Membr. Sci. 2013, 425, 208−216. (16) McCloskey, B. D.; Park, H. B.; Ju, H.; Rowe, B. W.; Miller, D. J.; Chun, B. J.; Kin, K.; Freeman, B. D. Influence of polydopamine deposition conditions on pure water flux and foulant adhesion resistance of reverse osmosis, ultrafiltration, and microfiltration membranes. Polymer 2010, 51, 3472−3485. (17) Rana, D.; Matsuura, T. Surface modifications for antifouling membranes. Chem. Rev. 2010, 110, 2448−2471. (18) Azari, S.; Zou, L. Using zwitterionic amino acid l-DOPA to modify the surface of thin film composite polyamide reverse osmosis membranes to increase their fouling resistance. J. Membr. Sci. 2012, 401, 68−75. (19) Xu, Y. C.; Wang, Z. X.; Cheng, X. Q.; Xiao, Y. C.; Shao, L. Positively charged nanofiltration membranes via economically musselsubstance-simulated co-deposition for textile wastewater treatment. Chem. Eng. J. 2016, 303, 555−564. (20) Xu, Y. C.; Tang, Y. P.; Liu, L. F.; Guo, Z. H.; Shao, L. Nanocomposite organic solvent nanofiltration membranes by a highlyefficient mussel-inspired co-deposition strategy. J. Membr. Sci. 2017, 526, 32−42. (21) Han, G.; Zhang, S.; Li, X.; Widjojo, N.; Chung, T.-S. Thin film composite forward osmosis membranes based on polydopamine modified polysulfone substrates with enhancements in both water flux and salt rejection. Chem. Eng. Sci. 2012, 80, 219−231. (22) Han, G.; de Wit, J. S.; Chung, T.-S. Water reclamation from emulsified oily wastewater via effective forward osmosis hollow fiber membranes under the PRO mode. Water Res. 2015, 81, 54−63. (23) Zhao, D.; Qiu, G.; Li, X.; Wan, C.; Lu, K.; Chung, T.-S. Zwitterions coated hollow fiber membranes with enhanced antifouling properties for osmotic power generation from municipal wastewater. Water Res. 2016, 104, 389−396. (24) Araújo, P. A.; Miller, D. J.; Correia, P. B.; Van Loosdrecht, M. C. M.; Kruithof, J. C.; Freeman, B. D.; Paul, D. R.; Vrouwenvelder, J. S. Impact of feed spacer and membrane modification by hydrophilic, bactericidal and biocidal coating on biofouling control. Desalination 2012, 295, 1−10. (25) Blok, A. J.; Chhasatia, R.; Dilag, J.; Ellis, A. V. Surface initiated polydopamine grafted poly ([2-(methacryoyloxy) ethyl] trimethylammonium chloride) coatings to produce reverse osmosis desalination E
DOI: 10.1021/acs.iecr.6b04926 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
