Yeongbong Mok

Circulatory osmotic desalination driven by a mild temperature gradient based on lower critical solution temperature (LCST) phase transition materials.

Abrupt changes in effective concentration and osmotic pressure of lower critical solution temperature (LCST) mixtures facilitate the design of a continuous desalination method driven by a mild temperature gradient. We propose a prototype desalination system by circulating LCST mixtures between low and high temperature (low T and high T) units. Water molecules could be drawn from a high-salt solution to the LCST mixture through a semipermeable membrane at a temperature lower than the phase transition temperature, at which the effective osmotic pressure of the LCST mixture is higher than the high-salt solution. After transfer of water to the high T unit where the LCST mixture is phase-separated, the water-rich phase could release the drawn water into a well-diluted solution through the second membrane due to the significant decrease in effective concentration. The solute-rich phase could be recovered in the low T unit via a circulation process. The molar mass, phase transition temperature, and aqueous solubility of the LCST solute could be tuneable for the circulatory osmotic desalination system in which drawing, transfer, release of water, and the separation and recovery of the solutes could proceed simultaneously. Development of a practical desalination system that draws water molecules directly from seawater and produces low-salt water with high purity by mild temperature gradients, possibly induced by sunlight or waste heat, could be attainable by a careful design of the molecular structure and combination of the circulatory desalination systems based on low- and high-molar-mass LCST draw solutes.

Control of osmotic pressure through CO2-capture and release facilitated by the lower critical solution temperature (LCST) phase transition of acylated branched polyethylenimine

A solution of acylated polyethylenimine can absorb CO2 at low temperatures to elevate the osmotic pressure and draw water from a high-salt saline solution. Such a solution can be phase-separated to liberate CO2 by mild heating at 40 °C, and the osmotic pressure can be effectively reduced for water release into a low-salt saline solution. The osmotic pressure-controlling system has the potential to be used as a draw solution for forward osmosis.

Membrane of Functionalized Reduced Graphene Oxide Nanoplates with Angstrom-Level Channels

Membranes with atomic level pores or constrictions are valuable for separation and catalysis. We report a graphene-based membrane with an interlayer spacing of 3.7 angstrom (Å). When graphene oxide nanoplates are functionalized and then reduced, the laminated reduced graphene oxide (rGO) nanoplates or functionalized rGO membrane is little affected by an intercalated fluid, and the interlayer spacing of 3.7 Å increases only to 4.4 Å in wetted state, in contrast to the graphene oxide (GO) membrane whose interlayer spacing increases from 9 Å to 13 Å in wetted state. When applied to ion separation, this membrane reduced the permeation rate of small ions such as K+ and Na+ by three orders of magnitude compared to the GO membrane.

Unlocking the pH-responsive degradability of fumaramic acid derivatives using photoisomerization.

Fumaramic acid derivatives can be converted into their cis isomer maleamic acid derivatives under UV illumination, and these maleamic acid derivatives show pH-responsive degradability at acidic pH only after the preceding photoisomerization. The rate of the tandem photoisomerization-degradation of fumaramic acid derivatives can be finely controlled by changing the substituents on the double bond. Photoisomerization-based unlocking of the pH-responsive degradability of fumaramic acid derivatives has strong potential for the development of multisignal-responsive smart materials in biomedical applications.