By Abbas Nazil
Researchers have successfully synthesized nitrogen and sulfur co-doped carbon dots from lycium biomass that exhibit high corrosion inhibition efficiency for carbon steel in acidic environments.
The study, recently published in Scientific Reports, demonstrates that these biomass-derived carbon dots, produced using a hydrothermal method, can significantly reduce the rate of steel corrosion in 1 M hydrochloric acid solutions.
The carbon dots (CDs) obtained were found to be nearly quasi-spherical with an average size of approximately 20.3 nanometers and contained abundant oxygen-, nitrogen-, and sulfur-containing functional groups.
A detailed analysis of nitrogen species revealed that pyrrolic nitrogen accounted for over 65 percent of total nitrogen content, which played a key role in adsorption and corrosion inhibition.
Electrochemical measurements, including electrochemical impedance spectroscopy (EIS) and Tafel polarization, showed that the CDs acted as mixed-type inhibitors with predominant cathodic effects.
The inhibition efficiency increased with the concentration of carbon dots, reaching a maximum of 88.4 percent at 100 milligrams per liter, indicating a strong dose-dependent protective effect.
Surface characterizations using scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed that the CDs formed a uniform protective film on the steel surface.
The elemental analysis confirmed the presence of nitrogen and sulfur on the inhibited steel surface, suggesting that these heteroatoms facilitated chemical adsorption and contributed to the formation of a stable barrier against corrosive ions.
X-ray photoelectron spectroscopy further validated the adsorption mechanism, showing interactions between the nitrogen and sulfur atoms in the CDs and the vacant d orbitals of iron on the steel surface.
The adsorption of carbon dots onto the steel followed the Langmuir isotherm model, indicating a monolayer adsorption process and negligible interaction between adsorbed molecules.
The calculated standard free energy of adsorption suggested that the process was spontaneous and involved both physical and chemical interactions, providing a durable protective layer.
Additionally, the CDs’ small size and surface functionality allowed them to aggregate and form a compact film, reducing surface roughness and minimizing contact with aggressive HCl ions.
This green synthesis approach using biomass not only offers a cost-effective and sustainable method for producing high-performance corrosion inhibitors but also minimizes environmental pollution compared to traditional organic inhibitors.
The study provides strong evidence that biomass-derived, nitrogen- and sulfur-doped carbon dots can serve as efficient, eco-friendly corrosion inhibitors for industrial applications, particularly in processes involving acidic environments such as pickling, descaling, and chemical cleaning.
Researchers emphasize that the high content of pyrrolic nitrogen, combined with oxygen and sulfur functional groups, is essential for achieving maximum inhibition efficiency.