Immobilizing Water into Crystal Lattice of Calcium Sulfate for its Separation from Water-in-Oil Emulsion

This work report a facile approach to efficiently separate surfactant-stabilized water (droplet diameter of around 2.0 μm) from water-in-oil emulsion via converting liquid water into solid crystal water followed by removal with centrifugation. The liquid–solid conversion is achieved through the solid-to-solid phase transition of calcium sulfate hemihydrate (CaSO₄. 0.5H₂O, HH) to dihydrate (CaSO₄·2H₂O, DH), which could immobilize the water into crystal lattice of DH. For emulsion of 10 mg mL^–1 water, the immobilization-separation process using polycrystalline HH nanoellipsoids could remove 95.87 wt % water at room temperature. The separation efficiency can be further improved to 99.85 wt % by optimizing the HH dosage, temperature, HH size and crystalline structure. Property examination of the recycled oil confirms that our method has neglectable side-effect on oil quality. The byproduct DH was recycled to alpha-HH (a valuable cemetitious material widely used in construction and binding field), which minimizes the risk of secondary pollution and promotes the practicality of our method. With the high separation efficiency, the “green” feature and the recyclability of DH byproduct, the HH-based immobilization-separation approach is highly promising in purifying oil with undesired water contamination

Identification of Active Hydrogen Species on Palladium Nanoparticles for an Enhanced Electrocatalytic Hydrodechlorination of 2,4-Dichlorophenol in Water

Clarifying hydrogen evolution and identifying the active hydrogen species are crucial to the understanding of the electrocatalytic hydrodechlorination (EHDC) mechanism. Here, monodisperse palladium nanoparticles (Pd NPs) are used as a model catalyst to demonstrate the potential-dependent evolutions of three hydrogen species, including adsorbed atomic hydrogen (H*_ads), absorbed atomic hydrogen (H*_abs), and molecular hydrogen (H₂) on Pd NPs, and then their effect on EHDC of 2,4-dichlorophenol (2,4-DCP). Our results show that H*_ads, H*_abs, and H₂ all emerge at −0.65 V (vs Ag/AgCl) and have increased amounts at more negative potentials, except for H*_ads that exhibits a reversed trend with the potential varying from −0.85 to −0.95 V. Overall, the concentrations of these three species evolve in an order of H*_abs < H*_ads < H₂ in the potential range of −0.65 to −0.85 V, H*_ads < H*_abs < H₂ in −0.85 to −1.00 V, and H*_ads < H₂ < H*_abs in −1.00 to −1.10 V. By correlating the evolution of each hydrogen species with 2,4-DCP EHDC kinetics and efficiency, we find that H*_ads is the active species, H*_abs is inert, while H₂ bubbles are detrimental to the EHDC reaction. Accordingly, for an efficient EHDC reaction, a moderate potential is desired to yield sufficient H*_ads and limit H₂ negative effect. Our work presents a systematic investigation on the reaction mechanism of EHDC on Pd catalysts, which should advance the application of EHDC technology in practical environmental remediation

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

Here we report a facile and cost-effective wet-chemical approach to the synthesis of calcium sulfate hemihydrate nanowires (HH NWs, CaSO₄·0.5H₂O), and their robust performance in immobilizing water molecules to the crystal lattice of CaSO₄ 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^–1) 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, CaSO₄·2H₂O, 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^–1) 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 Fe₃O₄ 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