Flexible Hierarchical TiO₂/Fe₂O₃ Composite Membrane with High Separation Efficiency for Surfactant‐Stabilized Oil‐Water Emulsions

Abstract

Globally, efficient oil-water separation for surfactant-stabilized oil-water emulsions has been in urgent demand. The current options available for separation are neither sustainable nor resistant to fouling. Herein, we introduce a hierarchically nanostructured TiO2/Fe2O3 composite membrane, which is capable of separating surfactant-stabilized oil-water emulsions with high separation efficiency. The high oil rejection rate is contributed by the acquisition of an interconnected delicate network and underwater superoleophobic interface. Meanwhile, its self-cleaning function promote the facile recovery of the contaminated membrane. Furthermore, the mechanical flexible characteristic of the TiO2/Fe2O3 composite membrane widens its applicability in industrial employment. Thanks to these properties, this novel membrane can be considered as a practical option for treating surfactant-stabilized oil-water emulsions.

Photocatalytic membrane filtration and its advantages over conventional approaches in the treatment of oily wastewater: A review

“…The presence of nanocomposites can be beneficial for the flux and anti‐fouling properties until an optimal amount from which it can start to jeopardize membrane performance, for example, by reducing hydrophilicity, enlarging pore size, reducing rejection rate, increasing fouling layer, reducing flux, etc 106,197,198,200 Membrane regeneration can be almost complete as it was observed in most of the cited studies, because flux recovery was often ~100%, even after several cycles 155,191,199,200,202–204 Photocatalytic properties are often characterized by dye (e.g., methylene blue) decomposition, due to its relatively fast degradation and the relative ease of the analytic method, as it can be measured by a spectrophotometer.…”

“…Both membrane hydrophilicity and membrane oleophobicity have to be studied in depth in order to (a) prevent the permeation of oil droplets, (b) selectively separate water from the oil‐water mixtures, and (c) minimize the adhesion of the oil droplets 133,208 Most of the studies investigated photocatalysis followed by membrane filtration 173,197 or membrane filtration followed by photocatalytic cleaning 106,155,191,198–200,206,207 . There is a lack of research that combines decomposition and self‐cleaning simultaneously. The membrane stability—both UV, oxidation, and adherence—has to be studied in situ without making generalizations about the used material 115,138,154 …”

“…Durability of the nanocomposite membranes is the most poorly investigated part of this research field, even though it is a key parameter to successfully scale up this technique. Some studies compare the mechanical stability of the modified and the neat membrane, and/or before and after the filtration/cleaning experiments 78,106,120,155 . Some studies also evaluate the membrane stability after their utilization under the UV‐light‐initiated oxidative conditions, 156–158 but researchers use a wide range of methodologies, for example, measure fluxes and rejection rates, analyze morphology (SEM, XRD or FTIR analysis), follow the changes of photocatalytic activity in time, or use simple physical analysis methods (e.g., turbidity and weight).…”

Predicting kinetics of water-rich permeate flux through photocatalytic mesh under visible light illumination

“…Membranes with selective wettability have been incorporated with photocatalytic materials (e.g., TiO 2 6 , 33 , N-TiO 2 34 , α-Fe 2 O 3 16 , 35 , Fe 3 O 4 36 , WO 3 37 , ZnO 38 , BiVO 4 7 , α-FeOOH 39 , MoO 3 40 , Co 3 O 4 41 , Gd 2 ZnMnO 6 /ZnO 42 ) that can degrade the organic substances deposited on the surface upon light illumination. These membranes have demonstrated that they can oxidize (or reduce) the organic substances either dissolved in a liquid (e.g., water) or adsorbed on the membrane surface when irradiated by light with an energy higher than their bandgap energy 43 , 44 .…”

Selective Wettability Membrane for Continuous Oil−Water Separation and In Situ Visible Light‐Driven Photocatalytic Purification of Water

“…Recently, such membranes with selective wettability (i.e., hydrophilic and in air or underwater oleophobic) have been incorporated with a photocatalytic semiconductor (e.g., TiO 2 , [ 26 ] α‐Fe 2 O 3 , [ 27 ] WO 3 , [ 28 ] BiVO 4 , [ 29 ] β‐FeOOH, [ 30 ] g‐C 3 N 4 , [ 31 ] and CuWO 4 @Cu 2 O [ 32 ] ), which allows for catalytic degradation of the organic contaminants dissolved in the water‐rich permeate upon irradiation of light. Photocatalytic materials generate electron hole (e − ‐h + ) pairs upon irradiation of light with an energy greater than their bandgap energy ( E g ).…”