TY - JOUR
T1 - Waterborne nanocellulose coatings for improving the antifouling and antibacterial properties of polyethersulfone membranes
AU - Aguilar Sanchez, Andrea
AU - Jalvo, Blanca
AU - Mautner, Andreas
AU - Nameer, Samer
AU - Pöhler, Tiina
AU - Tammelin, Tekla
AU - Mathew, Aji P.
N1 - Funding Information:
The CNC and T-CNF coatings also had a clear impact on wettability. Original uncoated membranes had a contact angle of 48.8 ± 5.8°, whereas for coated membranes the values were much lower reaching 25.4 ± 5.2° for CNC and 29.0 ± 5.2° for T-CNF coated samples, respectively (Table 1 and Supporting information Figure S5). Thus, both types of cellulose coatings increased the hydrophilicity of the membranes by up to 52%, due to the abundant hydroxyl groups in their structure [4]. The hydrophilic coating, facilitates the formation of a hydration layer on the membrane and that acts as a physical and energetic barrier and prevents the adsorption of protein and other foulants on the surface [5]. Also, an increase in hydrophilicity imparts better permeance compared to the uncoated membrane due to the affinity towards water, and is therefore expected to counteract the effect of the additional nanocellulose layer on the PES membrane.To study the antibiofouling properties of the coatings; bacterial colonization, biofilm formation and antibacterial properties were compared between the uncoated and coated membranes. The major difference between organic fouling, for instance with proteins, and biofouling is the cell proliferation and formation of a biofilm. Biofilms are microbial communities embedded in a matrix of extracellular polymeric substances, facilitating their survival in adverse environments. Fig. 5a, b and 5c show SEM micrographs of membranes kept in contact with E. coli cultures for 18 h. Uncoated PES membranes displayed moderate resistance to be colonized by E. coli (Fig. 5a). SEM images revealed that bacterial cells were present and attached to the surface of the uncoated membrane with a low amount of extracellular matrix surrounding the cells, indicating low biofilm formation. The membranes coated with CNC presented an important development of the extracellular matrix and biofilm formation upon contact with E.coli cultures, as shown in Fig. 5b compared to the uncoated membranes. Furthermore, bacteria were not only utilizing the CNC coating to enhance their adhesion to the surface but also degraded it. It is well established that E.coli exhibits a certain cellulolytic effect and can degrade cellulose, metabolizing it in ethanol and hydrogen and, presumably, using it as carbon source promoting their growth [ 36–38]. On the contrary, membranes coated with T-CNF exhibited high resistance to bacterial colonization and biofilm formation (Fig. 5c). Image J analysis of the SEM images showed 10.2, 5.6 and 0.2% bacteria coverage on the membrane surface in the case of uncoated, CNC coated and T-CNF coated membranes, respectively, indicating the significant reduction in bacterial adhesion for T-CNF coated membranes (see supporting information S6 for details of Image J analysis). The antifouling characteristics of T-CNF could be attributed to the presence of carboxylate groups located on the surface of the oxidized cellulose nanofibrils and, thus to the acidic environment that carboxyl groups promote [39], since the pH of the bacterial culture shifted from 7.2 to approximately 4.8 after 18 h of incubation of the E. coli inoculum with the T-CNF coated membranes. This pronounced variation in pH was not observed after the incubation of the cell culture with the uncoated membranes or with the CNC coated membranes. It is well known that microorganisms have certain general physiological requirements for survival and growth. These include an appropriate temperature range, nutrients, oxygen (or lack thereof, for anaerobic bacteria), moisture, and pH. High acidity or alkalinity can effectively limit the growth and survival of microorganisms, and the variation observed in our experiments is in agreement with the limiting growth range for many organisms, including coliforms such as E. coli [40,41]. Antifouling properties against microorganisms and bacterial adhesion were also influenced, among other factors, by the surface properties of the materials such as surface wettability and surface charge. The results obtained in this work related to these two properties could explain the adhesion of E. coli to PES uncoated membranes, which displayed intermediate hydrophobicity and, hence, are more prone to bacterial adhesion and fouling irrespective of the surface charge [15,42,43]. However, the results did not show significant differences between CNC coating and T-CNF coating in terms of water contact angle (25.4° and 29°, respectively, Table 1) and streaming ζ-potential measurements (Fig. 3d) suggesting that these parameters were not responsible of the antifouling properties of T-CNF but the variation in the pH after incubating the T-CNF coated membranes.This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 760601. The authors acknowledge Dr. Gilberto Siqueira (EMPA Swiss Federal Laboratories for Materials Science and Technology) and Dr. Björn Hansmann (Sartorius Stedim Biotech) for providing the materials used in this study and fruitful discussions. Special thanks to Professor Roberto Rosal (University of Alcalá) for the support during the bacterial studies, M.Sc. Vesa Kunnari (VTT Technical Research centre of Finland) for the help during the scalability assessment, Dr. Luis Valencia (Stockholm University) for the help during the data analysis and Lukas Brandfellner (Universität Wien) for support with MWCO studies.
Funding Information:
This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 760601. The authors acknowledge Dr. Gilberto Siqueira (EMPA Swiss Federal Laboratories for Materials Science and Technology) and Dr. Björn Hansmann (Sartorius Stedim Biotech) for providing the materials used in this study and fruitful discussions. Special thanks to Professor Roberto Rosal (University of Alcalá) for the support during the bacterial studies, M.Sc. Vesa Kunnari (VTT Technical Research centre of Finland) for the help during the scalability assessment, Dr. Luis Valencia ( Stockholm University ) for the help during the data analysis and Lukas Brandfellner (Universität Wien) for support with MWCO studies.
Publisher Copyright:
© 2020
PY - 2021/2/15
Y1 - 2021/2/15
N2 - This article presents a waterborne nanocellulose coating process to change the surface characteristics and mitigate fouling of commercially available polyethersulfone (PES) microfiltration membranes. An extensive comparative study between nanoporous and nano-textured layers composed of cellulose nanocrystals (CNC) or TEMPO-oxidized cellulose nanofibrils (T-CNF), which were coated on the PES membrane by taking advantage of the electrostatic interactions between the PES substrate, a polyallylamine hydrochloride (PAHCl) anchoring layer, and the nanocellulose functional layer. Coated PES membranes exhibited decreased surface roughness and pore sizes as well as rejection of compounds with a M w above 150 kDa, while the water permeability and mechanical properties of remained largely unaffected. The coatings improved the wettability as confirmed by a reduction of the contact angle by up to 52% and exhibited a higher negative surface charge compared to the uncoated membranes over a pH range of 4–8. A significant reduction in organic fouling was observed for the coated membranes demonstrated by bovine serum albumin (BSA) adsorption studies on T-CNF and CNC surfaces using Quartz Crystal Microbalance with Dissipation monitoring (QCM-D), UV–vis spectroscopy and FTIR mapping after exposing the membranes to dynamic adsorption of BSA. The T-CNF coating exhibited effective antibacterial action against Escherichia coli (E. coli) attributed to the pH reduction effect induced by the carboxyl groups; while CNC coatings did not show this property. This work demonstrates a simple, green, and easy-to-scale layer-by-layer coating process to tune the membrane rejection and to improve antifouling and antibacterial properties of commercially available membranes.
AB - This article presents a waterborne nanocellulose coating process to change the surface characteristics and mitigate fouling of commercially available polyethersulfone (PES) microfiltration membranes. An extensive comparative study between nanoporous and nano-textured layers composed of cellulose nanocrystals (CNC) or TEMPO-oxidized cellulose nanofibrils (T-CNF), which were coated on the PES membrane by taking advantage of the electrostatic interactions between the PES substrate, a polyallylamine hydrochloride (PAHCl) anchoring layer, and the nanocellulose functional layer. Coated PES membranes exhibited decreased surface roughness and pore sizes as well as rejection of compounds with a M w above 150 kDa, while the water permeability and mechanical properties of remained largely unaffected. The coatings improved the wettability as confirmed by a reduction of the contact angle by up to 52% and exhibited a higher negative surface charge compared to the uncoated membranes over a pH range of 4–8. A significant reduction in organic fouling was observed for the coated membranes demonstrated by bovine serum albumin (BSA) adsorption studies on T-CNF and CNC surfaces using Quartz Crystal Microbalance with Dissipation monitoring (QCM-D), UV–vis spectroscopy and FTIR mapping after exposing the membranes to dynamic adsorption of BSA. The T-CNF coating exhibited effective antibacterial action against Escherichia coli (E. coli) attributed to the pH reduction effect induced by the carboxyl groups; while CNC coatings did not show this property. This work demonstrates a simple, green, and easy-to-scale layer-by-layer coating process to tune the membrane rejection and to improve antifouling and antibacterial properties of commercially available membranes.
UR - http://www.scopus.com/inward/record.url?scp=85094628395&partnerID=8YFLogxK
U2 - 10.1016/j.memsci.2020.118842
DO - 10.1016/j.memsci.2020.118842
M3 - Article
SN - 0376-7388
VL - 620
JO - Journal of Membrane Science
JF - Journal of Membrane Science
M1 - 118842
ER -