Calcium Sulfate Hemihydrate Nanowires: One Robust Material in Separation of Water from Water-in-Oil Emulsion

Abstract

Here we report a facile and cost-effective wet-chemical approach to the synthesis of calcium sulfate hemihydrate nanowires (HH NWs, CaSO·0.5HO), and their robust performance in immobilizing water molecules to the crystal lattice of CaSO and then separating them from a surfactant-stabilized water-in-oil emulsion (mean droplet size of around 1.2 μm). Every gram of HH NWs are capable of treating 20 mL emulsion (water content: 10.00 mg mL) with a separation efficiency of 99.23% at room temperature, and this efficiency can be further improved by tuning the surface charge density of HH. Along with the water immobilization, HH NWs are converted to large cubic-like calcium sulfate dihydrate microparticles (DH, CaSO·2HO, mean size: 50 μm), and the accompanied size increment enables efficient collection of the solid phase from oil. DH microparticles can be regenerated into HH NWs, which retain the high performance of the original NWs. Such a unique renewable feature improves the economics of our method and simultaneously prevents the secondary pollution. Further economic evaluation finds that purification of every cubic meters of emulsion (water content: 10.00 mg mL) will cost about $34.18 for HH NWs, much lower than the $490.78 for the previously reported HH NPs, and $11 052.05-$23 420.32 FeO NP-based adsorbents, respectively. With the high efficiency, easy collection, low cost, and renewable feature, HH NWs show highly promising applications in the field of oil purification and recycle.

Preparation of PSF/FEP mixed matrix membrane with super hydrophobic surface for efficient water-in-oil emulsion separation

“…The separation efficiency of M-4 for water-in-oil emulsions was higher than the other reported membranes which were in different structures and materials. [42][43][44][45] To study the separation performance further, the membrane was exposed to the water-in-oil emulsion for a long time, which would cause unavoidable membrane fouling, leading to the reduction of membrane's service life and the separation efficiency. During a separation cycle, the membrane was immersed 20 mL ethanol for 2 h and dried in air.…”

Aspect ratio-controlled preparation of α-CaSO4·0.5H2O from phosphogypsum in potassium tartrate aqueous solution

“…The TG curve of the as-prepared rod-shaped crystals showed a 6.27% weight loss between 100 C and 500 C, which is consistent with the H 2 O mass fraction in CaSO 4 $0.5H 2 O crystals. 5 Moreover, the endothermic peak appearing at 128.5 C on the DSC curve also conrmed that the as-prepared crystals may be composed of CaSO 4 $0.5H 2 O crystals. 20 The XRD and TG-DSC results indicate that the as-prepared rod-shaped crystals are CaSO 4 $0.5H 2 O crystals.…”

“…3 In recent years, high-value utilization of I-PG has drawn signicant attention and so far, the most effective way to achieve high-value utilization of I-PG is to produce a-calcium sulphate hemihydrate (a-CaSO 4 $0.5H 2 O). [4][5][6] To date, methods for preparing a-CaSO 4 $0.5H 2 O crystals from CaSO 4 $2H 2 O mainly include autoclave hydrothermal, [7][8][9][10] atmospheric salt solution, [11][12][13][14] reverse microemulsion 15 and alcohol-water solution. [16][17][18] The autoclave hydrothermal method involves high temperature (usually above 120 C) and certain pressure, 19,20 which are not conducive to industrialization.…”

Nanostructured Three-Dimensional Percolative Channels for Separation of Oil-in-Water Emulsions

“…However, those conventional methods often fail to work when it comes down to the micro scale, which is most often the case in practical applications ( Zeng et al., 2017 ). To mitigate this, treatments such as chemical agents are often applied in demulsification technology ( Jiang et al., 2017 ). To achieve high-efficiency separation of micron-sized oil droplets in water (i.e., oil-water emulsion), major challenges remain in the high porosity and superhydrophilic surface as concomitants of the material itself.…”