Characterization of nanofiltration membrane using microscopic methods

ABSTRACTSurface properties of two nanofiltration membranes NF11 and NF12 were investigated using Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM) in conjunction with two image processing softwares (WSxM 5.0 Develop 6.4 and Image J) in order to predict the one which will give better performance in the treatment of waste water. Atomic Force Microscope Atomic Force Microscope of the unused membranes was used in conjunction with conjunction with WSxM 5.0 Develop 6.4 to study different surface roughness measures (Bearing ratio, Power Spectrum Density and Histogram). The membranes were scanned on two scan sizes (1.0 m1.0 m and 5.0 m5.0 m). Scanning Electron Microscope (SEM) in conjunction with Image J will be used to estimate the pore size of both the fresh and used membrane sample as we progress with the work. These analyses will help to better understand fouling of nanofiltration membranes which is a major problem in waste water treatment. The result showed that NF11 membrane had highest RMS roughness than NF12. The RMS roughness for 5.0 m5.0 m ranged between 846.263 (NF11) and 691.314 (NF12), whereas for the 1.0 m1.0 m scan size, they ranged between 275.804 (NF11) and 242.406 (NF12). It was concluded that NF11 membrane will give better performance than NF12 in terms of flux ,there for the analysis that follow will be done using SEM on unused material and material used to treat waste water. TABLE OF CONTENTS

11.Introduction

2.Experimental analysis32.1.Experimental Set-up32.2.Experimental Procedure42.2.1.Atomic Force Microscope (AMF)43.Results and Discussion63.1.Bearing Analysis of unused membranes for 1.0 m 1.0 m scan size83.2.Bearing Analysis of unused membranes for 5.0 m 5.0 m scan size93.2Power Spectrum Density Analysis (PSD) for scan size 1.0 m 1.0 m and 5.0 m 5.0 104Conclusion145References14

LIST OF FIGURES

3Figure 1: Experimental set up.

Figure 2: Bearing ratio plot curve for NF11 and NF12 at 1.0 m 1.0 m.9Figure 3: Bearing ratio plot curve for NF11 and NF12 at 5.0m 5.0m.10Figure 4: Power spectral density curve for NF11 and NF12 at 1.0m 1.0m.11Figure 5: Power spectral density curve for NF11 and NF12 at 5.0m 5.0m.12Figure 6: Evolution of the roughness obtained by AFM for 1.0m1.0m and 5.0m5.0m windows.13

LIST OF TABLES7Table 1: 2D and 3D images of the membrane surface obtaining by Image processing software (WSxM 5.0 Develop 6.4).

Table 2: Summary of the statistical parameters that were used to quantitatively describe the surface roughness of the neat membranes with the aid of WXSM 5.0 software13

1. IntroductionAtomic force microscopy is a probe scanning technique commonly used to image surfaces for producing three-dimensional images; however, an important advantage of atomic force microscopy in the study of surface properties of materials, including membrane, is the ability to quantify both surface morphology and surface interactions with a single instrument [1]. Atomic force microscopy was first used in 1988 to study the structure of polymeric membranes [2]. Atomic force microscopy can be used under three modes: contact, non-contact and tapping [3]. In contact mode, the tip is "dragged" across the surface of the sample and the contours of the surface are measured either using the deflection of the cantilever directly or, more commonly, using the feedback signal required to keep the cantilever at a constant position. Thus, contact mode AFM is almost always done at a depth where the overall force is repulsive, that is, in firm "contact" with the solid surface below any adsorbed layers [4].In non-contact mode the tip of the cantilever does not contact the sample surface. The cantilever is instead oscillated at either its resonant frequency (frequency modulation) or just above (amplitude modulation) where the amplitude of oscillation is typically a few nanometers (