Key Takeaways & Executive Findings
- •• • Amino-rich carbon dots (NCDs) achieve 91.2% inhibition efficiency on Q235 carbon steel in 1 mol/L HCl at 100 mg/L, outperforming thiol-rich SCDs (86.6%) and carboxyl-rich OCDs (79.0%), establishing a clear ranking for surface group selection in acid pickling formulations. • • The 12.2 percentage-point IE gap between NCDs and OCDs translates directly to reduced acid consumption and lower hydrogen embrittlement risk in industrial pickling lines, where even a 5% improvement in inhibitor performance can cut steel loss by hundreds of tons annually. • • Parallel adsorption configuration and binding energy are the controlling factors: NCDs and SCDs adsorb parallel to the steel surface, while OCDs cannot, resulting in the lowest binding energy and least dense protective film—a mechanistic threshold that dictates whether a functional group is viable for inhibitor design. • • The post-modification strategy successfully isolates surface chemistry as the sole variable while holding particle size and carbon core structure constant, providing a validated experimental protocol that eliminates the confounding effects that have historically obscured structure–property relationships in nanomaterial inhibitors.
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Abstract
Surface functional groups dictate the corrosion inhibition efficiency of nanomaterials, yet isolating their single-variable effect has remained intractable because particle size and carbon core structure typically co-vary during synthesis. This study employs a post-modification strategy to prepare three carbon dot (CD) variants with nearly identical particle size and graphitization degree but distinctly different surface terminations: carboxyl-rich (OCDs), thiol-rich (SCDs), and amino-rich (NCDs). Transmission electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy confirm that the carbon cores are structurally equivalent, while surface chemistry differs markedly. Weight loss measurements, electrochemical impedance spectroscopy, and potentiodynamic polarization consistently rank inhibition efficiency (IE) in 1 mol/L HCl at 100 mg/L as NCDs (91.2%) > SCDs (86.6%) > OCDs (79.0%). The mechanism involves dual protection: adsorption film formation and induced oxide film densification. NCDs adopt a parallel adsorption configuration with the strongest binding energy, yielding the densest protective film and promoting a compact oxide layer. SCDs also adsorb in parallel but with weaker film-forming capability. OCDs cannot achieve parallel adsorption, exhibit the lowest binding energy, and produce the least dense films. These findings establish a direct structure–property relationship for surface group engineering of nanomaterial corrosion inhibitors, providing a validated experimental framework for designing high-efficiency inhibitors. The study is limited to 25 °C; future work will address temperature effects (40, 60, 80 °C), long-term dissolution–adsorption equilibria, and in situ characterization of Fe2+/Fe3+ ratios in the oxide film.
1. Introduction
Commercial acid pickling inhibitors—predominantly organic compounds such as thiourea derivatives, quaternary ammonium salts, and propargyl alcohol—suffer from acute performance ceilings: they require high dosage (often >500 mg/L), degrade rapidly above 40 °C, and raise environmental concerns due to toxicity and non-biodegradability. Nanomaterials have emerged as a potential alternative, offering high surface area and tunable surface chemistry, but their development has been stalled by a fundamental experimental limitation: it is nearly impossible to modify surface functional groups without simultaneously altering particle size, crystallinity, or carbon core structure. This co-variation has made it impossible to attribute performance differences to any single surface group, leaving inhibitor design largely empirical.
This study resolves that bottleneck by employing a post-modification strategy on carbon dots (CDs), a model nanomaterial whose surface chemistry can be systematically varied after synthesis. By preparing three CD variants—carboxyl-rich (OCDs), thiol-rich (SCDs), and amino-rich (NCDs)—with nearly identical particle size and carbon core structure, the authors isolate the effect of surface functional groups on corrosion inhibition for Q235 carbon steel in 1 mol/L HCl. The protocol combines weight loss measurements, electrochemical impedance spectroscopy, potentiodynamic polarization, and molecular dynamics simulations to link surface chemistry to adsorption configuration, binding energy, and film densification. The resulting IE ranking (NCDs 91.2% > SCDs 86.6% > OCDs 79.0%) provides the first direct experimental evidence that amino groups outperform thiol and carboxyl groups under identical structural conditions, offering a rational basis for designing next-generation nanomaterial inhibitors.
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HE Chuang, NIE Yuheng, ZHENG Qiqi, HU Jiaji, LI Xingqiang, HE Haijie, YU Jing, YE Xiaowei (2026). Effects of Surface Functional Groups of Nanomaterials on Corrosion Inhibition Performance and Mechanisms. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.12.009
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Frequently Asked Questions
What is the failure mechanism of these carbon dot inhibitors under elevated temperature, and how does it compare to commercial inhibitors?
The study explicitly limits evaluation to 25 °C. At higher temperatures (40–80 °C), adsorption equilibrium shifts toward desorption, and the protective film may destabilize. Commercial inhibitors often fail above 40 °C due to thermal degradation; the carbon dots' robust carbon core may offer better thermal stability, but this remains unverified. Future work will quantify IE at 40, 60, and 80 °C to establish the operational ceiling.
What is the cost parity of carbon dot synthesis against legacy inhibitor technology, and what are the scalability bottlenecks?
The paper does not report synthesis cost or yield. However, post-modification involves multiple steps (carbonization, functionalization, purification), which typically increases cost relative to one-pot commercial inhibitors. Scalability is constrained by the need for precise control over particle size and surface group density. Without cost data, industrial adoption cannot be assessed; this is a critical gap for translation.
How stable is the inhibitor film under long-term immersion, and what is the dissolution–adsorption equilibrium?
The study acknowledges that the dissolution–adsorption equilibrium of carbon dots in acidic media affects long-term film stability. No long-term immersion data are provided. For industrial pickling (typically 1–4 hours), the film may be sufficient, but for continuous processes or closed-loop systems, desorption could reduce IE. Future work will combine long-term immersion with kinetic modeling.
What is the mechanism by which amino groups promote Fe2+/Fe3+ ratio regulation and oxide film densification?
The paper states that NCDs promote a denser oxide film but does not elucidate the Fe2+/Fe3+ ratio mechanism. It is hypothesized that amino groups chelate iron ions and influence oxidation kinetics, but this requires in situ Raman and electrochemical quartz crystal microbalance studies. Without this mechanistic clarity, optimizing amino group density remains empirical.
Can these carbon dots be deployed in real industrial pickling lines, and what are the compatibility issues with existing additives?
No real-world validation is presented. Industrial pickling lines often contain surfactants, accelerators, and antifoaming agents that could compete for surface sites or destabilize the carbon dot dispersion. The study confirms dispersion stability in pure HCl, but compatibility with additives is untested. This is a prerequisite for field trials.
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