Green biosynthesis of silver nanoparticles from Citrus aurantium leaves plant as corrosion inhibitor for carbon steel in sulfuric acid

Citrus aurantium leaves (CAL) and silver nanoparticles (AgNPs) were used in the biosynthesis of a corrosion inhibitor for low-carbon steel in 0.5 M H₂SO₄. The weight loss method was used to investigate the corrosion inhibition performance of the composite (CAL-AgNPs). It was found that the corrosion rate of low-carbon steel increased with temperature increase and decreased with CAL-AgNPs concentration increase. Maximum corrosion inhibition efficiency was 91.3 % at 10 ml/l and 30°C. Adsorption studies indicated that CAL-AgNPs can be adsorbed spontaneously on the metal surface. The adsorption mechanism was primarily physical and followed the Langmuir adsorption isotherm. The kinetics studies confirmed these outcomes, showing a higher activation energy in the presence of CAL-AgNPs compared to the blank solution. This indicated the formation of a protective layer on the metal surface that increased the energy barrier. The FTIR technique was used as a direct method of CAL functional group diagnosis and an indirect one for AgNPs presence. The FTIR spectra showed the stretching for functional groups like alcohols, phenols, N–H of amines, C–H stretching, esters, aldehydes, and carboxylic acids, which are common in capping biomolecules. In addition, spectra in the range of metal-O bonds, such as Ag–O or Ag–N, were observed.