Recent developments in sustainable corrosion inhibition using ionic liquids: a review

Assessment of greenness corrosion inhibitors: TEACH and OSPAR commissions

In view of increasing ecological awareness, recent advancement in the field of corrosion science and engineering is directed towards the design- ing, development and implementation of environmental friendly alterna- tives for the traditional toxic corrosion inhibitors [31,32]. In this direction, several resources derived from nature such as plant extracts [33–35], chemical medicines [32,36–38] and bio-polymers including carbohy- drates, amino acids (AAs) latex, natural/Arabic gums [33,39] etc. are widely employed as metallic corrosion inhibitors. Along with natural re- sources, synthetic corrosion inhibitors synthesized using eco-friendly ap- proaches such one step multicomponent reactions (MCRs) [40,41], energy efficient microwave (MW) and ultrasound (US) heatings [42], using biological sustainable catalysts and green solvents such as water, ionic liquids and super critical CO₂ are considered to be environmental friendly alternatives [43–45]. There are numerous authorities to measure the environmental impact of the chemicals to be used for different pur- poses including as corrosion inhibitors. These authorities OSPAR (Oslo Paris Commission) and TEACH (Registration, Evaluation, Authorization and Restriction of the chemical). According to OSPAR and TEACH, a corro- sion inhibitor which is associated with high biodegradability, non- bioaccumulation behavior and negligible environmental toxicity would be considered as environmental friendly [46,47]. There are two indices namely, ethical concentration (EC₅₀) and lethal concentration (LC₅₀) that can be used as gauss for the measurement of toxicity. LC₅₀ and EC₅₀ represent the concentration of compound which causes death of 50% liv- ing population and concentration which adversely affect the growth of living population, respectively [48,49]. For a chemical to be treated as en- vironmental friendly its EC₅₀/LC₅₀ magnitude should be more than 10 mg/L [50]. According to OSPAR, biodegradation rate of an environmen- tal friendly chemical would 60% or more in 28 days [51]. Partition

Fig. 1. Examples of (a) acidic, (b) basic, (c) functionalized and (d) supported ionic liquids.

Fig. 2. Applications of ionic liquids in different field of science and technology.

coefficient (log K_OW or D^OW) is used as gauge for the measurement of bio- accumulation. A K_OW or D^OW with magnitude of lesser than 3 establishes the non-bioaccumulative behavior of the chemical [52,53]. Present review article provides an array of different environmental friendly alternatives being used as corrosion inhibitors. To the best of our knowledge this is the first article that collectively describes the all kinds of environmental friendly corrosion inhibitors. Different environmental friendly alternatives being used for traditional toxic corrosion inhibitors with their salient fea- tures are described herein.

3.