This work reports the obtention of Si,N,S-CQDs from sugar cane bagasse and their inhibitory action on the mild steel corrosion in 1 mol L^-1 HCl solution. The CQDs were successfully obtained and characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, Dynamic light scattering, Raman, and UV-vis techniques, also showing endogenous self-doping. The anti-corrosive activity of CQDs was investigated by gravimetric tests, potentiodynamic polarization curves, electrochemical impedance measurements, atomic force microscopy, and scanning electron microscopy. The electrochemical results show that the CQDs present a predominant inhibitory action on the cathodic process, presenting inhibition efficiency of 82, 89, 91, and 94% for 15, 25, 50, and 100 ppm, respectively. Gravimetric tests varying temperature demonstrate that the inhibitor functions through physical adsorption and remains effective for up to 72 h, exhibiting corrosion efficiency of 80.2, 93.2, 96.3, and 97.8% at 15, 25, 50, and 100 ppm concentrations, respectively, after 72 h of immersion. Dynamic light scattering and zeta potential measurements indicate that agglomerations of CQDs play a crucial role in inhibiting corrosion. These results show an excellent alternative for using sugar cane bagasse to produce CQDs and its application as a corrosion inhibitor, valuing agricultural waste and simultaneously solving industry problems.

In this study, carbon quantum dots (CQDs) were successfully synthesized from garlic peel, with size dimensions confirmed by TEM and DLS analyses and photochemical properties validated by UV–vis and fluorescence spectroscopy. FTIR revealed chemical similarities with the precursor, while XPS revealed the presence of nitrogen and sulfur, indicating endogenous doping. The anticorrosive performance of the CQDs was demonstrated through gravimetric, electrochemical impedance, potentiodynamic polarization, and surface analyses including scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The CQDs exhibited high inhibition efficiencies with sustained performance over time, achieving maximum inhibition efficiencies of 79% for 2 h and 96% for 24 h, as determined by gravimetric studies. This inhibition was primarily mediated through physical interactions, as indicated by temperature-dependent studies. Electrochemical measurements further confirm that the CQDs act as mixed-type inhibitors, exhibiting a predominant anodic effect. Surface analyses confirmed the formation of a protective and hydrophobic film on the steel surface. XPS, DLS, and zeta potential studies, along with Arrhenius equation analysis, demonstrated that the film forms through physical and chemical interactions between mild steel and quantum dot aggregates. These findings highlight the potential of using agro-industrial waste, such as garlic peel, as a sustainable precursor for the synthesis of effective corrosion inhibitors.