New eco-friendly anti-corrosion inhibitor of purple rice bran extract for boiler quality steel: Experimental and theoretical investigations

Abstract

In this present study, the extract of purple rice bran, an agricultural by-product enriched with antioxidants, was implemented as an eco-friendly natural corrosion inhibitor, often known as a green corrosion inhibitor. The inhibitor was extracted from purple rice bran using conventional extraction methods and characterized by HPLC, which revealed the presence of two prime compounds named cyaniding-3-glucoside (C3G) and peonidin-3-glucoside (P3G). This purple rice bran extract (PRBE) was used to inhibit as a green corrosion inhibitor on boiler quality (BQ) steel to assess its inhibition performance in 1 (M) HCl and 0.5 (M) H2SO4. The inhibition performance was investigated by some electrochemical techniques such as open circuit potential (OCP), potentiodynamic polarization test (PDP), electrochemical impedance spectroscopy (EIS). The investigation revealed that the maximum efficiency was 91.13% and 87.43% in the presence of 200 mgL−1 of PRBE in HCl and H2SO4 media, respectively. After applying various adsorption isotherm models, Langmuir isotherm was found as the best-fitted model that indicated both physical and chemical spontaneous adsorption of PRBE on the BQ surface. Both electrochemical and adsorption studies and indicated the PRBE as a mixed-type inhibitor. Various quantum chemical parameters were calculated to find out the active sites and the donor-acceptor interaction capability of the inhibitor molecules. The quantum chemical calculation was achieved with the help of density functional theory (DFT). The theoretical studies disclosed that P3G has a lower energy gap than C3G but higher dipole moment than C3G.