Single-atomic-layered graphene quantum dots with lateral sizes of ∼5 and 20 nm are not photosensitizers for photodynamic therapy.

The solid–liquid-phase equilibria of quaternary system K+, Mg2+, Na+//Cl––H2O and its three ternary subsystems K+, Mg2+//Cl––H2O; Mg2+, Na+//Cl––H2O; and K+, Na+//Cl––H2O at 278.15 and 288.15 K were studied by an isothermal solution equilibrium method. The quaternary system K+, Mg2+, Na+//Cl––H2O includes two invariant points, five univariant curves, and four crystallization regions. The double salt KCl·MgCl2·6H2O is found in the quaternary system but no solid solution. Based on the experimental results and the multitemperature comparison, the order of the solubilities of the single salts is KCl < NaCl < MgCl2 within a certain temperature range. As the temperature decreases from 288.15 to 278.15 K, all of the solubilities of KCl, MgCl2·6H2O, and NaCl decrease. The dissolution of MgCl2 and NaCl can affect the crystallization of KCl. From a thermodynamic point of view, low temperatures are beneficial to the crystallization of potassium chloride from the system. Therefore, it is important to control the low operating temperature, low concentration of NaCl, and high concentration of MgCl2 in the production process. The data obtained in this work have important implications for the design and optimization of the production process of potassium chloride from K-carnallite in low-temperature conditions.