Chapter16 - Plant extracts as environmentally sustainable corrosion inhibitors I

Abstract

Recently, the active compounds extracted from roots, stems, leaves, flowers, fruits of plants as environmentally sustainable corrosion inhibitors have become one of the research hotspots. In general, these plant extracts contain several organic compounds, which are rich in heteroatoms (N, O, P, S, etc.), conjugated double bonds, electronegative groups, and so on. These active compounds can be effectively adsorbed on the metal surface. Plant extracts are an ideal alternative to replace expensive and toxic traditional corrosion inhibitors. Many kinds of plant corrosion inhibitors have been used for copper, mild steel, carbon steel, aluminum, and other metals in acidic (HCl, H2SO4, HNO3, H3PO4), alkaline (NaOH), and neutral (NaCl) environment. The inhibition efficiency of these extracts is generally evaluated through electrochemical methods which include electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurement, and weight loss test. The bonding information is analyzed through Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The surface morphology observations are performed through scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition, quantum chemical calculation and molecular dynamic simulation are adopted for theoretical analysis. In this chapter, extraction methods, factors, experimental methods, mechanism of plant extracts, recent advances of plant extracts, and modification of plant extracts are reviewed. Finally, the challenges facing the use of plant extracts as metal corrosion inhibitors and future directions have been proposed.