Influence of Surface Properties of Filtration-Layer Metal Oxide on Ceramic Membrane Fouling during Ultrafiltration of Oil/Water Emulsion

Abstract

In this work, ceramic ultrafiltration membranes deposited with different metal oxides (i.e., TiO 2 , Fe 2 O 3 , MnO 2 , CuO, and CeO 2 ) of around 10 nm in thickness and similar roughness were tested for O/W emulsion treatment. A distinct membrane fouling tendency was observed, which closely correlated to the properties of the filtration-layer metal oxides (i.e., surface hydroxyl groups, hydrophilicity, surface charge, and adhesion energy for oil droplets). Consistent with the distinct bond strength of the surface hydroxyl groups, hydrophilicity of these common metal oxides is quite different. The differences in hydrophilicity consequently lead to different adhesion of these metal oxides toward oil droplets, consistent with the irreversible membrane fouling tendency. In addition, the surface charge of the metal oxide opposite to that of emulsion can help to alleviate irreversible membrane fouling in ultrafiltration. Highly hydrophilic Fe 2 O 3 with the lowest fouling tendency could be a potential filtration-layer material for the fabrication/modification of ceramic membranes for O/W emulsion treatment. To the best of our knowledge, this is the first study clearly showing the correlations between surface properties of filtration-layer metal oxides and ceramic membrane fouling tendency by O/W emulsion.

Antifouling membranes for oily wastewater treatment: Interplay between wetting and membrane fouling

“…When membranes with sufficient optical transparency in the wet state are used, the fouling dynamics can be directly observed under optical microscope (in-situ method). [3] Ex-situ methods, such as scanning electron microscopy (SEM) [13,17,22,24,49,50,93] and atomic force microscopy (AFM) [2] provide nanoscopic routes to observe the fouled membranes. The macroscopic fouling phenomenon, i.e., oil stain on the membrane, can also be utilized to test the fouling property of the membrane qualitatively.…”

“…[68,69] As membranes with higher underwater oleophobicity are more resistive to oil fouling, a general method of preparing antifouling membrane is to improve the hydrophilicity of the membrane. [17,22,24,28,40,53,60,77,79,94,[97][98][99][100] In addition, a hydration layer may form on the surface of some hydrophilic materials (such as zwitterionic polymers, polyelectrolytes and polyethylene glycol) under water. [24,30,[101][102][103][104][105] This hydration layer prevents oil from directly contacting the membrane and thus decreases the fouling tendency.…”

“…[16,30,74,84,85] Their influence on membrane fouling during wastewater treatment is multiple. [11,13,18,22,86,87] First, surfactants can be adsorbed on/in the membrane and increase its resistance to water permeation (especially for UF and NF membranes since they have small pores), and the surfactant micelles may also block the pores leading to flux decline. [11] In this respect, surfactants act as foulants during membrane filtration.…”

A Review on Current Development of Membranes for Oil Removal from Wastewaters

“…ZrO 2 UF membranes have been coated with the metal oxides TiO 2 , Fe 2 O 3 , MnO 2 , CuO, and CeO 2 , which had a size of around 10 nm, using a pulsed laser deposition procedure. The resulting membranes were tested for oil recovery from aqueous emulsions [61]. It was found that the higher the hydrophilicity of the deposited oxide, the lower the irreversible fouling tendency of ceramic membrane, in the order Fe 2 O 3 < TiO 2 < CuO < CeO 2 < MnO 2 .…”

Turning Tissue Waste into High-Performance Microfiber Filters for Oily Wastewater Treatment

“…It would thus significantly reduce the membrane flux and greatly increase the costs associated with increased energy consumption and membrane replacement [19]. To retard membrane fouling, many strategies including surface hydrophilization [20][21][22], zwitterionic coating [23,24], photocatalytic cleaning [25] and electrically enhanced antifouling [18,26], have been explored. However, these processes would increase the membrane fabrication cost and consume additional energy.…”