Inﬂuence of zinc oxide nanoparticles in the nanoﬁltration of hazardous Congo red dyes Nur Hanis Hayati Hairom a,c , Abdul Wahab Mohammad b,⇑ , Abdul Amir Hassan Kadhum b a Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia b Centre for Sustainable Process Technology (CESPRO), Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia c Department of Chemical Engineering Technology, Faculty of Engineering Technology, Universiti Tun Hussein Onn Malaysia, 86400 Parit Raja, Batu Pahat, Johor, Malaysia highlights  ZnO nanoparticles synthesised via precipitation method under various conditions.  Inﬂuence of ZnO nanoparticles in the nanoﬁltration of CR was investigated.  Membrane performances improved with ZnO-PVP-St addition in the solution.  ZnO interaction was inﬂuenced by the preparation methods and agglomerations. article info Article history: Received 14 May 2014 Received in revised form 16 August 2014 Accepted 19 August 2014 Available online 16 September 2014 Keywords: Zinc oxide Nanoparticles Precipitation Congo red dye Nanoﬁltration Fouling abstract Zinc oxide (ZnO) nanoparticles were produced via a simple and green precipitation method under stirring conditions (ZnO-St) and under ultrasonic radiation (ZnO-Us). The nanoparticles properties were charac- terised with X-ray ﬂuorescence (XRF), X-ray diffractometry (XRD) and transmission electron microscopy (TEM); and compared with commercial ZnO and no ZnO. Their inﬂuence in the nanoﬁltration (NF) of haz- ardous Congo red dyes was studied in order to provide the fundamental understanding in the interacting effect of ZnO and NF membranes. The membrane performances were signiﬁcantly improved after the addition of ZnO in the dye solution in descending order as follows: ZnO-Us > ZnO-St > commercial ZnO > no ZnO. It is believed that the preparation method, agglomerations and the morphology of nano- particles inﬂuence their interaction with dye molecules and membrane surfaces. Membrane characteri- sations using contact angle, X-ray ﬂuorescence (XRF), Field Emission Scanning electron microscopy (FESEM) and Energy Dispersive X-ray Analysis (EDX) conﬁrmed that ZnO nanoparticles have great poten- tial for fouling mitigation in industrial NF application. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Recent developments in the area of integrated membrane-pho- tocatalytic nanoparticles [1,2] have led to a renewed interest in the use of nanoparticles during membrane ﬁltration. Data from several reports have shown that the addition of nanoparticles in NF sys- tems has led to a reduction in the membrane fouling ﬂux with an increased total removal of colour and unwanted elements of wastewater dyes [3]. ZnO nanoparticles, in particular, would be of interest due to their higher reactivity, surface area, photosensi- tivity, chemical stability, non-toxic nature, and low cost [4]. Along with its stable wurtzite structure and wide bandgap (3.4 eV) compound semiconductor, ZnO has been mainly used as a catalyst for dye treatment [5,6]. Similarly within a photocatalytic mem- brane reactor, nanoparticles can be used as the photocatalyst to degrade the dyes while they are being separated and recycled at the same time through the use of membranes [7,8]. Therefore, the inﬂuence of such nanoparticles on membrane performance is an important issue in this research area. However, there are very limited detailed studies concerning the inﬂuence of ZnO nanopar- ticles on the performance of NF membranes in the dye wastewater treatment ﬁeld. Thus, this study aims to analyse the inﬂuence of the presence of ZnO nanoparticles on the rejection and ﬂux perfor- mance of the NF membrane. It should be noted that the characteristics of ZnO are dependent on its size and preparation methods [9]. Recent reports [10,11] have conﬁrmed that the photocatalytic activity of ZnO nanoparticles is http://dx.doi.org/10.1016/j.cej.2014.08.068 1385-8947/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: Wahabm@eng.ukm.my (A.W. Mohammad). Chemical Engineering Journal 260 (2015) 907–915 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej