Visible light-induced catalytic syntheses of thioamides as biomass-based corrosion inhibitors for mild steel

It is a pioneering field for biomass valorization to construct high-efficient corrosion inhibitors for metal due to a big challenge and serious issue of metal corrosion during its industrial applications. Herein, we describe a visible light-induced three-component coupling of furfural, furylamine and (NH₄)₂S for biomass-based thioamide synthesis under mild conditions. The photo-catalyst for the coupling is well designed as Ni immobilized on a carbon-TiO₂ nanocomposite (Ni/C-TiO₂) with in-situ photo-generated hole (h⁺) and hydroxyl radical (·OH) as key oxidative species for thioamide formation. The photo-catalytic system is applicable to a variety of furfural-derived thioamides (20 examples). The anti-corrosive activities of typical thioamides are systematically investigated and compared with mild steel in 1.0 M HCl solution. Electron-rich furan ring (π-electrons system) with functional − NH − C(=S) − group (high electronic density of heteroatoms) endows these biomass-based thioamides high inhibition efficiencies towards the mild steel as mixed-type corrosion inhibitors for both cathode and anode.