Because
of the water swelling of graphene oxide (GO) membranes,
the rejection of metal ions is generally low, especially for monovalent
metal cations. We prepared a thermally reduced graphene (TrGO) membrane
with excellent separation performance of water and NaCl by heat treating
GO membranes. Its blocking ability for Na+ is 1529 times
larger than that of the GO membrane with the same amount of GO, and
it is also much better than the reduced GO membranes prepared by NH3 or HI reduction. Using 3 M sucrose as the draw solution,
the 795 nm thick TrGO membrane has an ultrahigh rejection of more
than 99.56% for Na+ and maintains a water flux of 0.42
L m–2 h–1. TrGO membranes maintain
high stability during the penetration of a high-concentration salt
solution, and they have good mechanical properties to maintain operational
stability and can be used for a longer time. We characterized and
analyzed the separation mechanism of the TrGO membranes and believe
that the inner channels form three zones with different hydrophobicity
and uniform distribution. The ratio of the three zones can be changed
by adjusting the heat-treatment temperature, the duration to swelling
force, and the π–π attraction force.
For the development of sustainable and efficient separation technology for rare earth elements (REEs), the ionic liquid-type saponification strategy is first put forward in this paper. The extraction mechanism of [trihexyl(tetradecyl)phosphonium][sec-octylphenoxy acetate] ( [P 6,6,6,14 ][SOPAA]) prepared by ionic liquid-type saponification for Y(III) was indicated to be ion association. The mechanism contributes to avoiding the numerous saponification procedures and resulting saponification wastewater in the REE separation industry. Load capacity and stripping properties of [P 6,6,6,14 ][SOPAA] reveal advantages over its precursory sec-octylphenoxy acetic acid (HSOPAA). Extractability and selectivity of [P 6,6,6,14 ][SOPAA] for Y(III) are pronouncedly better than those of HSOPAA. Multistage extraction using functional ionic liquid as extractant for different REE separations is developed. After five stages of extraction sections and four stages of scrubbing sections, Lu(III) was successfully separated from Y(III) using the fractional extraction process. Moreover, stripping by distilled water was achieved in ionic liquid-based extraction for REE, which contributes to decrease the consumption of acid to a considerable extent.
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