Estudo de novos inibidores de corrosão com base em pontos quânticos de carbono co-dopados com N e Nb

Abstract

Corrosion is a recurring problem in metallic materials in various sectors of a country, such as industry, construction, health, transportation, and the like, generating annual costs that can reach 1 to 5% of GDP. In addition, this process tends to become even more aggressive with acidity and increased temperature of the environment where the material is inserted. In this context, the industry has been seeking alternatives to avoid the degradation and uselessness of carbon steel, an affordable, versatile alloy with excellent properties, which makes it the main alternative in the industrial sector. Therefore, this work aimed to synthesize and develop carbon quantum dots co-doped with nitrogen (N) and niobium (Nb) as new corrosion inhibitors for carbon steel parts in an acidic environment. The doped carbon quantum dots were obtained by the bottom- up route via thermal decomposition at 200 C, varying the amounts of the precursors citric acid, urea, and niobium ammonium oxalate. The inhibitory effect on the corrosion of carbon steel in a solution containing HCl 1 mol L -1 was compared. The gravimetric tests revealed that the inhibition efficiency of 100 mg L -1 of N-CD obtained with 1 g of urea and 5 g of citric acid and 100 mg L-1 Nb,N-CD obtained with the same citric acid and urea proportion with the addition of 2 g of niobium ammoniacal oxalate, for 6 hours of immersion at 25 oC, reached more than 80% with Nb,N-CD maintaining approximately this value at higher temperatures, while the N-CD had the inhibition efficiency decreased abruptly with temperature. TGA (Thermogravimetric Analysis) and DTA (Differential Thermal Analysis) were used to describe the thermal stability of the CDs and showed that the Nb addition to CDs improves their termal stability. The functional groups and suggested composition were verified using FTIR (Fourier Transform Infrared Spectroscopy), XPS (X-ray photoelectron spectroscopy), and XRF (X-ray Fluorescence) proving the presence of N and Nb in the CDs. Isotherm studies demonstrated that N-CD and Nb,N-CD obeyed the Langmuir adsorption isotherm and the eletrochemical measurements of impedance and potentiodynamic polarization showed that the CDs inbihited both anodic and cathodic reactions with IE of 84-85% for 200 ppm inhibitor. A series of experimental results demonstrated that niobium doping influenced the particle size, termal stability, and fluorescence, among other properties of the synthesized quantum dots, maintaining a high inhibition efficiency at high temperatures. These results reveal that using nitrogen and niobium doped CDs is a new and effective alternative to mitigate corrosion in carbon steel exposed to 1 mol L-1 HCl, especially at temperatures above room temperature.