Advantages of TiO2/carbon nanotube modified photocatalytic membranes in the purification of oil-in-water emulsions

Abstract

For the effective purification of emulsified oil contaminated waters advanced treatment methods have to be applied, such as membrane filtration, which is able to eliminate macro-, and even nanoscale oil droplets, however, membrane fouling is still a major problem, which prevents economic utilization. Therefore, fouling mitigation is one of the most important aspects in the field of membrane separation developments. In the present study, solely TiO2 and TiO2/carbon nanotubes (CNT) composite modified PVDF membranes were prepared and used to purify oil-in-water emulsions. Achievable fluxes, reversible and irreversible filtration resistances, fouling models, filtration efficiencies and photocatalytic activities were compared in case of different nanomaterial covered and unmodified PVDF membranes. Applying either solely TiO2 or solely CNT coating resulted in the significant reduction of total filtration resistance in both cases, but the combination of the two components (TiO2 with 1 wt% CNT) resulted in by far the highest flux and lowest resistance, meanwhile, the enhanced photocatalytic efficiency of the composite was also achieved. To the best of our knowledge, this study demonstrates the beneficial effects of the combination of TiO2 and CNT nanomaterials for the first time in the field of membrane separation of oil-in-water emulsions.

Intensification of the ultrafiltration of real oil-contaminated (produced) water with pre-ozonation and/or with TiO2, TiO2/CNT nanomaterial-coated membrane surfaces

“…Among the various nanomaterials, the ones with photocatalytic properties can provideapart from the increased hydrophilicitythe possibility to degrade organic fouling contaminants by simple UVor solar irradiation, which proved to be efficient to decompose oily contaminants from membrane surfaces (Chang et al 2014;Gondal et al 2014;Moslehyani et al 2015;Pan et al 2012;Shi et al 2016;Tan et al 2015). In our recent studies (Kovács et al 2018;Veréb et al 2018a), TiO 2 and TiO 2 /CNT coatings resulted in excellent antifouling effect during the ultrafiltration of synthetic oilin-water emulsions and, in addition, TiO 2 /CNT-compositemodified membrane showed increased photocatalytic activity.…”

“…In the present study, two recently published and very promising methods, namely, the nanomaterial-based modification of membranes (Veréb et al 2018a) and/or pre-ozonation (Veréb et al 2018b;Veréb et al 2019) were used separately and simultaneously for the mitigation of fouling during the ultrafiltration of an industrial oil-contaminated (produced) water. Investigated membrane materials widely used were polyethersulfone (PES), outstandingly durable polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF), which is widely used to prepare nanomaterial-modified membranes.…”

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

“…(a) Contact angle between water droplet and membrane surface (b) Contact angle between water and various modified membranes 106 …”

“…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).…”

TiO2 Nanoparticles Immobilized on Carbon Nanotubes: An Efficient Heterogeneous Catalyst in Cyclocondensation Reaction of Isatins with Malononitrile and 4‐Hydroxycoumarin or 3,4‐Methylenedioxyphenol under Mild Reaction Conditions

“…In addition, carbon nanotubes (CNTs) with their exceptional characteristic such as high quality active sites, excellent electron conductivity, chemical inertness, and retardation of electron–hole recombination are used as promising support materials for a variety of heterogeneous nanoparticle catalysts . The catalytic activity of TiO 2 NPs supported on carbon nanotubes (TiO 2 ‐CNTs) has been greatly enhanced due to their modified structural, chemical, electrical, and optical properties …”