Chirality, hydrogen bond interaction and surface charge repulsion among sulfate CNCs have vital impact on the formation of a cholesteric mesogen in a suspension or solidified film. Therefore, changing surface charge density through mechanical disintegration is an effect way to tune the chiroptical properties of iridescent CNC films.

SFE-CO 2 is a novel, promising, environmentally benign and inexpensive extracting method developed over the past few years to overcome environmental problems encountered due to the use of conventional solvents. One component (the extractant) is separated from another (the matrix) using SCF-CO 2 as the extracting solvents. This method is widely used for extracting heavy metals from environmental contaminant, bioactive compounds like antioxidants, plant medicine and natural products or remediating heavy metal contaminated soil by using good binding activity of SCF-CO 2 to heavy metal ions. The major advantages of the use of SCF-CO 2 as a solvent are its superior mass transfer properties, easy recycling and lack of secondary waste formation. We try to focus on the recent advances in SCF-CO 2 extraction technology for heavy metal extraction. In this review, the mechanism, procedure, and application of heavy metal extraction by SCF-CO 2 are summarized in a comprehensive manner and the factors affecting the extraction efficiency are analyzed. We try to provide some meaningful information about heavy metal extraction by SCF-CO 2 and make it a preferable option in heavy metal treatments.

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