Minwoo Noh

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.

Development of anti-biofouling interface on hydroxyapatite surface by coating zwitterionic MPC polymer containing calcium-binding moieties to prevent oral bacterial adhesion.

UNLABELLED The purpose of the present study is to synthesize a 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer capable of being immobilized on the tooth surface to prevent oral bacterial adhesion. The strategy is to develop an MPC-based polymer with Ca(2+)-binding moieties, i.e., phosphomonoester groups, for stronger binding with hydroxyapatite (HA) of the tooth surface. To this end, a 2-methacryloyloxyethyl phosphate (MOEP) monomer was synthesized and copolymerized with MPC by free radical polymerization. The coating efficiency of the synthesized polymer, MPC-ran-MOEP (abbreviated as PMP) with varied composition, onto a HA surface was estimated by means of contact angle measurement and X-ray photoelectron spectroscopy. The anti-biofouling nature of PMP-coated HA surfaces was estimated by analyzing protein adsorption, cell adhesion, and Streptococcus mutans adhesion. As a result, HA surface coated with a copolymer containing around 50% MPC (PMP50) showed the best performance in preventing protein adsorption and the downstream cell and bacterial adhesion. STATEMENT OF SIGNIFICANCE Preparation of anti-biofouling surface on the tooth enamel is the key technique to prevent dental and periodontal diseases, which are closely related with the biofilm formation that induced by the adsorption of salivary proteins and the adhesion of oral bacteria on the tooth surface. In this research, a PMP copolymer with an optimized ratio of zwitterionic and Ca(2+)-binding moieties could form a highly effective and robust anti-biofouling surface on HA surfaces by a simple coating method. The PMP-coated surface with high stability can provide a new strategy for an anti-adsorptive and anti-bacterial platform in dentistry and related fields.

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.

Systematic structure control of ammonium iodide salts as feasible UCST-type forward osmosis draw solutes for the treatment of wastewater

A variety of UCST-type thermoresponsive ammonium iodide salts is systematically designed and synthesised with desired aqueous solubility, phase-transition temperature, osmolality change, phase-transition concentration range, stability, and toxicity by controlling the ionic interactions, hydrophobicity, and symmetry of the salt structure. Suitable draw solutes can be selected based on the characteristics of the ammonium iodide salts as well as the feed solutions for feasible forward osmosis (FO)-based water purification. In this research, highly concentrated wastewater from a flue gas desulfuriser (FGD), with osmotic pressure three times higher than seawater, is targeted for purification by FO using the draw solutes. Two ammonium iodide salts (HM8I and HM10I) show a remarkable water flux from the wastewater samples and significantly lower salt leakage compared to conventional draw solutes. The osmolality of the phase-separated draw solution drops to less than one tenth of that of the initial feed solution, and reverse osmosis or nanofiltration can be applied to the solution with much lower external pressure for the final purification to produce fresh water. This systematic approach to the design and selection of suitable draw solutes can be an effective strategy for future practical FO-based wastewater treatment and seawater desalination.