Ionic liquids (ILs) and deep eutectic solvents (DESs) have been suggested as eco-friendly alternatives to organic solvents. A trace amount of water is often unavoidable as impurity, and water is also added on purpose to reduce their problematically high viscosity and lower their high price. Understanding the distinct effects of water on the properties of ILs/DESs is highly important. In this review, we collect published experimental and theoretical results for IL/DES–H₂O systems at varied water concentrations and analyze them. Results from mechanistic studies, thermodynamic modelling and advanced experiments are collected and critically discussed. Six commonly studied IL/DES–H₂O systems were selected to map experimental observations onto microscopic results obtained in mechanistic studies. A great variety of distinct contours of the excess properties can be observed over the entire compositional range, indicating that the properties of IL/DES–H₂O systems are highly unpredictable. Mechanistic studies clearly demonstrate that the added H₂O rapidly changes the heterogeneous 3D structures of pure ILs/DESs, leading to very different properties and behaviour. There are similarities between aqueous electrolytes and IL/DES solutions but the bulky and asymmetric organic cations in ILs/DESs do not conform to the standard salt dissolution and hydration concepts. Thermodynamic modelling previously assumes ILs/DESs to be either a neutral ion-pair or completely dissociated ions, neglecting specific ion hydration effects. A new conceptual framework is suggested for thermodynamic modelling of IL/DES–H₂O binary systems to enable new technologies for their practical applications.

As a new type of fluorescent carbon nanomaterials, carbon quantum dots have been widely concerned in recent years because of their good biocompatibility, low cytotoxicity and easy surface functionalization. In this paper, nitrogen-doped carbon quantum dots (N-CQDs) were prepared by one-step hydrothermal method with citric acid as the carbon source and urea as a nitrogen source. The fluorescence spectrophotometer, Fourier infrared spectrometer, X-ray diffractometer, and transmission electron microscope were utilized to discover the luminescence properties, structural characteristics, morphology and size of the synthesized N-CQDs. The results showed that the best reaction conditions for preparing N-CQDs were as follows: the hydrothermal process parameters were 240 °C for 10 h, and the concentration of nitrogen doping was 0.6 wt%. Under these conditions, the prepared N-CQDs with bright blue fluorescence solution was uniform and stable. And the results showed the structural characteristics were weak crystalline graphite carbon, and the shape characteristics were nearly spherical quantum dot with about 5–10 nm diameters.