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Application Prospects

CMs are applicable for the separation and purification of liquid mixtures [76], including decolorization of coke furnace wastewater [77], pervapora- tion of azeotropic benzene-cyclohexane mixtures [78] and ultrafiltration of water solutions [62].

In comparison to polymeric membranes, CMs show major advantages in stability in concentrated acid/base solution and wide application fields [78], as will be introduced in later sections.

Membrane Filtration

The most traditional application of CM is as a filtration medium for waste- water treatment.

For industrial textile wastewater, it shows good performances in terms of permeate flux and efficiency (retention of chemical oxygen demand (COD) and salinity of 50% and 30%, respectively) and almost total retention of turbidity and color [79].

Du et al. prepared a poly-3-methylthiophene/CM with switchable surface wettability between superhydrophobicity and superhydrophilicity from coating poly-3-methylthiophene (P(3-MTH)) on the highly porous and electrically conductive carbon nanofiber membranes. The separation efficiency reaches 99.5% for surfactant-stabled emulsions with various oil-water ratios [48].

Ayadi et al. also gained a very high removal efficiency and retention (more than 99%) of oil from an oil-in-water emulsion stabilized by a surfactant through the adoption of CMs [80].

Derbel et al. identified that the hydrophobic characteristic of CMs allows the application of air gap membrane distillation for oily waste water treatment with high salt, giving oil retention of about 99% [51].

Peydayesh et al. removed heavy metals from aqueous solutions by bench- scale dead-end vacuum filtration setup of a CM. Platinum and silver were recovered from saturated membranes by high temperature thermal reduction. After filtration, saturated hybrid membranes were collected and burned for 1 h at temperatures above 2000 and 1000 °C for platinum and silver, respectively. The recovered metal nuggets were mechanically pressed to obtain thin films [40].

Yang et al. almost removed 99.23% tetracycline hydrochloride and 83.88% cationic dye methylene blue from water with a high water permeation of 16.12 L nr2 fr1 bar'1, using all-carbon three-dimensional nanofiltration membranes [41].

Kishore et al. separated hexavalent chromium ions from an aqueous chromic acid solution, with apparent and intrinsic rejection of Cr6+ ions of the order of 70 and 90%, respectively [47].

Our group investigated the feasibility of CMs for removal of phosphorous acid, phenol and emulsified oil from wastewater: excellent separation properties and chemical stability were found during filtration [43, 44, 81].

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