Investigation of Mild Steel Corrosion Inhibition with Tamarindus indica Fiber Extract in 0.5 M Trichloroacetic Acid: Adsorption, Antifouling, Electrochemical and DFT Studies

The as-extracted Tamarindus indica fiber (TIF) extract and its structural insights were analyzed successfully by spectral, electrochemical, analytical and theoretical techniques. The maximum corrosion inhibition efficiency (90.16%) was found by weight loss technique at 308 K. Monolayer adsorption was found and it obeyed the Langmuir adoption model. The –∆H* values support an exothermic process and –∆S* values confirm TIF adsorbed on mild steel surface. The –∆G° values reveal that the TIF adsorption on mild steel is a spontaneous process. Mixed type inhibition behavior was confirmed by Tafel plots. Increased trend of charge transfer resistance (R_ct) and decreased trend of double layer capacitance (C_dl) with increasing TIF (0–25 mg/L) concentration by Nyquist plots. FTIR and UV-Visible result confirms the mild steel-TIF extract complex formation. FE-SEM, EDAX, mapping analysis and XPS study supports the adsorption of TIF extract on mild steel surface. DFT study suggests that the biomolecules present in TIF extract is responsible for the formation mono adsorption layer on mild steel surface. An appropriate mechanism for mild steel corrosion inhibition with TIF extract in 0.5 M TCA was proposed.