Natural deep eutectic solvents as a green inhibitor of carbon steel corrosion in sulphuric acid

Abstract

This study reports two distinct natural deep eutectic solvents (NADESs) as novel corrosion inhibitors of carbon steel in diluted sulphuric acid (H₂SO₄). The investigated NADES was synthesised from lactic acid as hydrogen bond donor and glucose or D-fructose as hydrogen bond acceptors. The effects of temperature, time, inhibitor concentration, and H₂SO₄ concentration were optimised. Then, the corrosion rate was assessed in the presence and absence of the inhibitors. The inhibition efficiency of the NADES was investigated at different temperatures. The inhibition mechanism was investigated using adsorption isotherms and kinetic models. The results indicated that 120 min, 298 K, and 0.5 mol/L of H₂SO₄ achieved the lowest corrosion rate. NADES prepared from lactic acid and D-fructose was the most efficient solvent as a corrosion inhibitor, demonstrating an inhibition efficiency of 82% at 120 min in 0.5 mol/L H₂SO₄ and 298 K. Furthermore, the Langmuir isotherm model closely fit the inhibition process, which suggests monolayer adsorption of green NADES on the carbon steel surface. The kinetic analysis reveals a mixed-type mechanism involving the physisorption of the green NADES inhibitors. The results provided insights into the development of benign and environmentally friendly inhibitors such as NADES in acidic media.