## 1 Introduction  
The industry's growth is inseparable from the increase in and complexity of mechanisms, leading to the usage of various lubricants. According to statistical data, the global demand for lubricants was 37 million metric tons in 2020 [1]. Unfortunately, almost one-third of this amount ends up in the environment and causes pollution [2, 3]. According to the entry methods into the environment, lubricants can be categorized as (i) lubricants used in closed systems and (ii) total loss lubricants. The lubricants from the first category can be collected. They enter the environment only due to leakage or during accidents. On the other hand, lubricants from the second category enter the environment after their first usage. Therefore, there is no possibility of collecting. Consequently, the former lubricants must be nontoxic, readily biodegradable, and, if possible, produced using renewable raw materials [4, 5]. Researchers have already suggested several environmentally friendly lubricants and their additives for a few decades that could replace the existing harmful ones [6, 7, 8, 9, 3, 10]. Vegetable oil-based lubricants were the first choice for many researchers and industrial applications. Owing to the inherent biodegradability, nontoxicity, and excellent lubricity of vegetable oils, they were suggested for various applications: metalworking fluids [11], engine oils [12], chain saw oils, hydraulic fluids [13], etc. However, despite the applied additives, poor oxidation stability limits their wider application. Another environmentally friendly lubricant alternative is water. Undoubtedly, it is an easily accessible, renewable,low-cost base fluid. In addition, additive-loaded water-based lubricating fluids possess excellent cooling capacity, good lubricity, and non-flammability [3; 14]. Due to the mentioned advantages, water-based lubricating fluids are widely applied in industry, particularly in metalworking and hydraulics [3]. Unfortunately, toxic additives with sulfur, phosphorus, and chlorine are used to enhance the tribological properties of water-based fluids. Therefore, various environmentally friendly alternatives are suggested [2; 14; 15; 16]. The third environmentally friendly lubricant alternative is synthetic esters. These substances can have desired properties and perform well when used with the proper additive package [13; 17; 18]. However, the main drawbacks limiting their application are the very high costs and complex synthesis procedures. Considering the above facts, environmentally friendly lubricants are not widely acknowledged due to performance drawbacks or considerably higher costs. Therefore, seeking new attractive lubrication materials at lower prices is essential to improve the usage of environmentally friendly lubricants. Consequently, it will lead to pollution reduction. Nanoparticles and ionic liquids have recently become the most exciting lubrication substances [19; 20; 21; 22; 23; 24]. Ionic liquids can be used as neat lubricants or lubricity-enhancing additives. Moving towards the development of environmentally friendly lubricants, protic ionic liquids (PILs) have been suggested [25; 26; 27]. Protic ionic liquids can be synthesized in a relatively simple acid-base neutralization reaction, investigated by [PERSON] in 1914 [28]. A few studies have confirmed the superior lubricity and the versatile applications of PILs. [PERSON] and coauthors revealed that triprotic ionic liquid bis (2-hydroxyethyl ammonium) succinate could be used as a neat lubricant or lubricity-improving additive in water-based fluids [26]. [PERSON] et al. suggested stearic and palmitic fatty acid anions containing PILs [29]. It was revealed that using PILs as additives in the water to lubricate the sapphire-stainless steel friction pair resulted in an 80% lower coefficient of friction. Usually, PILs only comprise C, O, and N elements and contain no heteroatoms. Therefore, the adsorption of polar molecules was noted to be responsible for their lubricity [30].