Detecção SERS de inibidores de corrosão utilizando nanopartículas de Au e Ag imobilizadas sobre substratos de celulose

Abstract

Corrosion, especially the one that occurs in steel, can cause numerous inconveniences, damages, and economic losses in a wide variety of activities, due to the deterioration caused by different materials. Corrosion-related processes in the oil and petrochemical industries cause major losses throughout the production chain. The use of corrosion inhibitors is one of the most commonly used methods to control and reduce corrosive processes in these industries. Both corrosion inhibitors and scale inhibitors may be present in the water produced during oil extraction, which is a by-product in oil exploration, having a very complex matrix, containing various organic and inorganic substances, being potentially harmful to the environment, if the disposed properly. In Brazil, the disposal of produced water is regulated by CONAMA norm 393/2007, which limits the content of oils and greases (TOG) to a maximum monthly average concentration of 29 mg L-1 , with a daily maximum value of 42 mg L-1 . In this scenario, SERS spectroscopy has great potential for the analysis of corrosion inhibitors, especially those present in the production water, since this technique has a high sensitivity to organic analytes, in addition to providing important vibrational information of the molecules studied. In the present work, paper (cellulose) was used as a support for AuNP and AgNP immobilized at different concentrations for the construction of high-performance SERS substrates, which were investigated for the detection of the commercial corrosion inhibitors benzotriazole, benzimidazole, and L-methionine. Among the constructed substrates, the immobilization of AgNP on cellulose showed the best response for the application of the SERS technique to corrosion inhibitors at low concentrations. Experimentally, it was verified that the power density of the laser used (λ0= 632.8 nm) must be low, to avoid the degradation of the analytes. Using a nominal power of 5 mW from a He-Ne laser line at 632.8 nm, spectra of the corrosion inhibitor with a high S/N ratio were obtained at very low concentrations such as 1.0×10-7 mol L - 1 for benzotriazole. These results indicate that it is possible to obtain SERS spectra at very low concentrations of inhibitors on AgNP/paper substrates. For the corrosion inhibitors benzimidazole and L-methionine, the obtained spectra had Raman signal enhancement using AgNP; however, the process of photodegradation and formation of amorphous carbon did not allow obtaining high signal-to-noise ratio spectra.