Modiﬁcation of polyamide thin-ﬁlm composite membranes with amino-cyclodextrins and diethylamino-cyclodextrins for water desalination Bhekani S. Mbuli a , Edward N. Nxumalo a , Rui W. Krause a , Visvanathan L. Pillay b , Yoram Oren c , Charles Linder c , Bhekie B. Mamba a,⇑ a University of Johannesburg, Department of Applied Chemistry, P.O. Box 17011, Doornfontein 2028, South Africa b Department of Process Engineering, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa c Department of Desalination and Water Treatment, Zuckerberg Institute for Water Research, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84109, Israel article info Article history: Received 9 July 2013 Received in revised form 17 September 2013 Accepted 22 September 2013 Available online 30 September 2013 Keywords: Thin-ﬁlm composite membrane Amino-cyclodextrins Diethylamino-cyclodextrins Hydrophilicity Polyamide Desalination abstract This paper discusses the modiﬁcation of polyamide thin-ﬁlm composite (TFC) membranes with amino- and diethylamino-cyclodextrins (CDs). An in situ modiﬁcation procedure was carried out using different concentrations of amino and diethylamino functionalised CDs (both a- and b-CDs) dispersed in m-phen- ylenediamine in water. These aqueous solutions were then reacted with trimesoyl chloride on polyether- sulphone (PES) ultraﬁltration support membranes through the interfacial polymerisation process. Contact-angle measurements demonstrate that the TFC membranes have improved hydrophilic proper- ties due to additional AOH functional groups of the CDs. The incorporation of the amino- and diethyl- amino-CDs within the membrane selective layer improved water permeability which was rationalised by the increased hydrophilicity and additional water channels in the modiﬁed membranes. Modiﬁed membranes exhibited signiﬁcantly improved water permeability (33.92 ± 2.00 l m 2 h 1 ) and maintained a high NaCl rejection (99.21% ± 0.65%). The unmodiﬁed membranes, however, had a ﬂux of 1.12 ± 0.5 l m 2 h 1 and a NaCl rejection of 95.69% ± 0.87%, at 6.89 bar. Membranes modiﬁed with diethylamino-CDs had a smoother surface while the unmodiﬁed membranes and membranes modiﬁed with amino-CDs had rough surfaces. The membranes modiﬁed with diethylamino-CDs had a compact and dense cross-linked polyamide thin-ﬁlm structure while membranes modiﬁed with amino-CDs had a less compact cross-linked structure. This is due to the ACACA chain of the diethylamino functionality that allowed for a maximum exposure of the pendent group to the trimesoyl chloride during the inter- facial polymerisation; as a result, the diethylamino-CDs were less subjected to steric hindrance than the amino-CDs. The pendent group of the amino-CDs was close to the molecule, making it difﬁcult to reach during the interfacial polymerisation due to steric hindrance. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Thin-ﬁlm composite (TFC) membranes such as reverse osmosis (RO) and nanoﬁltration (NF) membranes are widely used in water treatment to produce drinking water from seawater, brackish water and wastewater. The main challenges of using TFC membranes in desalination stems from their relatively low water permeability and fouling, rendering them expensive technologies [1–3]. The top-most ultra-thin polyamide layer on an ultraﬁltration (UF) support membrane determines the performance of TFC membranes since it controls the membrane solute-rejection and water-permeability properties. Therefore, research has been dedicated to modifying the polyamide thin ﬁlm with different additives in order to improve performance [4]. These modiﬁcation methods include soaking TFC-RO membranes in freshly prepared solutions containing glycerol, sodium lauryl sulphate and triethyl- amine salts with camphor-sulphonic acid [4,5]. This modiﬁcation increased the ﬂux up to 30–70% [4,5]. A post-treatment step during the preparation of TFC membranes employs aqueous buffer solu- tions with poly(vinyl alcohol) (PVA) to improve TFC physical prop- erties and enhance ﬂux stability [6,7]. Previously, researchers have focused on modifying the thin-layer interfaces of TFC membranes in order to make their surfaces less charged and more hydrophilic [8–10]. This helps achieve preferential sorption of water molecules on the pore walls and to reduce fouling [8–10]. Modiﬁcation methods such as graft polymerisation, free radical polymerisation and coating by 1383-5866/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.seppur.2013.09.022 ⇑ Corresponding author. Tel.: (+27) 011 559 6516; fax: +27 011 559 6425. E-mail address: bmamba@uj.ac.z (B.B. Mamba). Separation and Puriﬁcation Technology 120 (2013) 328–340 Contents lists available at ScienceDirect Separation and Puriﬁcation Technology journal homepage: www.elsevier.com/locate/seppur