A method of fabricating ultrathin (≈22–53 nm thick) graphene nanofiltration membranes (uGNMs) on microporous substrates is presented for efficient water purification using chemically converted graphene (CCG). The prepared uGNMs show well packed layer structure formed by CCG sheets, as characterized by scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The performance of the uGNMs for water treatment was evaluated on a dead end filtration device and the pure water flux of uGNMs was high (21.8 L m−2 h−1 bar−1). The uGNMs show high retention (>99%) for organic dyes and moderate retention (≈20–60%) for ion salts. The rejection mechanism of this kind of negatively charged membranes is intensively studied, and the results reveal that physical sieving and electrostatic interaction dominate the rejection process. Because of the ultrathin nature of uGNMs, 34 mg of CCG is sufficient for making a square meter of nanofiltration membrane, indicating that this new generation graphene-based nanofiltration technology would be resource saving and cost-effective. The integration of high performance, low cost, and simple solution-based fabrication process promises uGNMs great potential application in practical water purification.

Ultrathin Graphene Nanofiltration Membrane for Water Purification

Over the past decade, solvent resistant nanofiltration (SRNF) has gained a lot of attention, as it is a promising energy- and waste-efficient unit process to separate mixtures down to a molecular level This critical review focuses on all aspects related to this new burgeoning technology, occasionally also including literature obtained on aqueous applications or related membrane processes, if of relevance to understand SRNF better An overview of the different membrane materials and the methods to turn them into suitable SRNF-membranes will be given first The membrane transport mechanism and its modelling will receive attention in order to understand the process and the reported membrane performances better Finally, all SRNF-applications reported so far – in food chemistry, petrochemistry, catalysis, pharmaceutical manufacturing – will be reviewed exhaustively (324 references)

Solvent resistant nanofiltration: separating on a molecular level

Oil/water separation, especially emulsified oil/water mixture separation, has become a widespread concern because of the severe fouling problem caused by the easy adsorption of oil droplets onto the surfaces of filtration membranes. Many strategies have been employed to eliminate the fouling problem, but it remains a challenge and impedes the development of membrane technology. In this short review, we discuss the recent development of membrane technology for emulsified oil/water separation. As shown in the image, in addition to polymer- and ceramic-dominated traditional membranes, nanomaterial-based membranes have recently demonstrated their superiority and have achieved high performance.

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Recent progress in developing advanced membranes for emulsified oil/water separation

Inorganic fouling of pressure-driven membrane processes — A critical review

Advanced membranes that enable ultrafast permeance are very important for processes such as water purification and desalination. Ideally, an efficient ultrafast membrane should be as thin as possible to maximize the permeance, be robust enough to withstand the applied pressure and have a narrow distribution of pore size for excellent selectivity. Graphene oxide nanosheets offer an encouraging opportunity to assemble a brand new class of ultrathin, high-flux and energy-efficient sieving membranes because of their unique two-dimensional and mono-atom thick structure, outstanding mechanical strength and good flexibility as well as their facile and large-scale production in solution. The current state-of-the-art in graphene oxide membranes will be reviewed based on their exceptional separation performance (gas, ions and small molecules). We will focus on the structure of nanochannels within the graphene oxide membranes, the permeance and rejection rate, and the interactions between graphene oxide sheets. The separation performance of graphene oxide membranes can be easily influenced by the state of oxygen-containing groups on the graphene oxide sheets, which provides much more straightforward strategies to tune the pore size of graphene oxide nanochannels when compared to other filtration membranes. We will illustrate in the review theoretical calculations to elucidate the potential of precisely controlling the ionic and small molecular sieving and water transport behaviour through graphene oxide nanochannels. This review will serve as a valuable platform to fully understand how the ions, small molecules and water are transported through the laminar graphene oxide membrane as well as the latest progress in graphene oxide separation membranes.

Graphene oxide nanosheet: an emerging star material for novel separation membranes

Development and characterization of ceramic nanofiltration membranes

This article gives an overview about the preparation and characterization of asymmetric ceramic membranes that have been developed at our institute within the last years. Depending on the required pore size of the filter active layer for filtration applications ranging from microfiltration (MF) up to nanofiltration (NF) different preparation routes have to be applied.

Ceramic Membranes for Filtration Applications — Preparation and Characterization

Influence of the surface charge on the permeate flux in the dead-end filtration with ceramic membranes

Investigation of ceramic membrane materials by streaming potential measurements

One of the key urban air quality issues is pollution by nitrogen oxides (NOx). To reduce NOx, facade cladding could be provided with photocatalytic properties by incorporating titanium dioxide nanoparticles. For this purpose, a modified phosphoric acid anodizing process (MPAA) was developed for the facade alloy EN AW-5005, in which highly ordered anodized structures with a low degree of arborization and tortuosity were produced. Pore widths between 70 nm and 150 nm and layer thicknesses of about 2–3 μm were obtained. The subsequent impregnation was carried out by dip coating from water-based systems. Depending on the dip-coating parameters and the suspension used, the pores can be filled up to 60% with the TiO2 nanoparticles. Photocatalytic tests according to ISO 22197-1 certify a high photocatalytic activity was obtained with rPCE values > 8 and with rPCE > 2, achieving “photocatalytically active for air purification”. Tests on the corrosion resistance of the anodized coatings with a commercially available aluminum and facade cleaner confirm a protective effect of the anodized coatings when compared with nonanodized aluminum material, as well as with compacted anodized layers.

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S. Benfer

Papers

Development and characterization of ceramic nanofiltration membranes

Ceramic Membranes for Filtration Applications — Preparation and Characterization

Influence of the surface charge on the permeate flux in the dead-end filtration with ceramic membranes

Investigation of ceramic membrane materials by streaming potential measurements

Development of Photocatalytically Active Anodized Layers by a Modified Phosphoric Acid Anodizing Process for Air Purification