CMs for Microfiltration, Ultrafiltration and Nanofiltration

Compression Technology

This technology is usually adopted owing to its merit of easy operation and setup. Different from gas separation, it is only applicable for CMs with a rough structure, and for liquid separation.

Peydayesh et al. prepared amyloid fibril hybrid membranes on the surface of cellulose filters with a diameter of 25 mm by vacuum filtration of a homogenous aqueous mixture of 2% (3-lactoglobulin fibril solution and 10 wt% activated carbon solution. The as-prepared macrofiltration CM has a surface area of 1.77 cm2 [40].

Yang et al. formed a three-dimensional all-carbon nanofiltration membrane with a thickness of 4.26 pm, which consists of multi-walled carbon nanotubes interposed between graphene oxide nanosheets. The membrane is also abundant in two-dimensional nanochannels that can physically sieve antibiotic molecules through electrostatic interaction [41].

Boffa et al. fabricated composite graphene oxide-humic acid-like biopolymer membranes with a high degree of disorder, leading to the benefit of an increased water permeation rate [42].

Our group made microfiltration CMs by compressing a powder blend of phenolic resin as precursor, sodium carboxymethyl cellulose as binder and hexamethylenetetramine as curing agent. During preparation, fillers such as diatomite, polyacrylonitrile microspheres and so forth could be utilized to tailor the microstructure and its oil-water emulsion separation properties [43, 44].

Chemical Vapor Deposition

As elaborated earlier, CVD is also feasible in the preparation of CMs for liquid mixture separation. Lebedev et al. produced an ion-selective CM by CVD on nanofibers via filtration of a Nafen nanofiber suspension through a porous support followed by drying and sintering. The deposition had obviously decreased the pore size and porosity compared with the pristine ceramic support and provided outstanding ion selectivity.

Prihandana et al. deposited a diamond-like carbon layer on nanoporous polyfether sulfones) membrane by ion-enhanced CVD. They investigated the effects of the composition of raw material (hexafluoroethane and acetylene) and deposition time. The adoption of fluoride in starting materials is favorable for lowering the hydrophilicity of resultant membranes [45].

Li et al. fabricated an 80-cm-long tubular-carbon-coated membrane by CVD of methane on a multilayered porous ceramic substrate at a temperature of 1000 °C. In comparison to the pristine carbon support, it has diminished pore size, as well as altered hydrophilicity, electric conductivity and heat conductivity. The membranes are expected to be applicable for microfiltration, ultrafiltration and nanofiltration [32].

Bae et al. dipped ceramic pipes in 0.5 M ferric sulfate solution, dried them at room temperature for 8 h, then heated under methane/nitrogen 20/80% (v/v) gas at 1100 °C to grow carbon whiskers by CVD of methane [46].

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