Sensor quimiorresistor baseado em nanotubos de carbono para detecção de éter-amina

Abstract

The development of nanostructured sensors has become highly relevant for the detection of chemical and biological substances, as they require small concentrations and offer easy handling. In the context of detecting and reusing flocculants in iron ore flotation, Buckypapers (BPs) based on functionalized Multi-Walled Carbon Nanotubes (MWCNTs) were employed to serve as sensing elements in the investigation of samples containing deionized water (DW), ether-amine (EA), and salts (AlCl₃, FeO₄·7H₂O, CaCl₂·2H₂O, MgCl₂·6H₂O) at different pH levels. Morphological characterization of the BPs using Scanning Electron Microscopy revealed an aggregated organization of carbon nanotubes (CNTs), which appeared randomly distributed on the phenolic surface. Through chemoresistive testing, electrical resistance measurements over time (R × t) were obtained. The results, based on the sensor response (as a percentage increase) over time (seconds) for three cycles—each with 0.1 μL of the solutions prepared from DW, EA, sodium hydroxide (NaOH), and salts—showed that the sensor was able to distinguish between the solutions and their pH differences. It exhibited specific response (%), response time (s), and recovery time (s) for each solution tested. A notable increase in sensor response was observed with rising pH, with the solution containing 30 ppm EA + salts (pH 9.63) reaching an average response of 20.14%, an average response time of 188.60 s, and an average recovery time of 154.91 s, indicating that the sensor is more sensitive in alkaline environments. Vibrational analysis by Raman spectroscopy revealed sub-bands around the D band resulting from the chemical functionalization and solubilization processes of the MWCNTs, as well as sub-bands near the G band associated with vibrations of the inner and outer nanotube walls. For samples containing EA and salts, the results indicated charge transfer between the ether-amine and the outer layers of the CNTs in the BP. The presence of metallic salts influenced the G band profile, altering electron density and causing local distortions. Principal Component Analysis (PCA) showed that the distribution of scores could distinguish the 30 ppm EA samples with higher pH (9.76 and 10.70) and 30 ppm EA + salts (pH 9.63) from the NaOH samples (pH 9.80 and 10.74) and salt-only samples (pH 4.73 and 9.77), indicating the system's detection and differentiation capability toward ether-amine, NaOH, and salts. Thus, the nanostructured sensor demonstrated relevant results for EA detection and potential application in the industry to recover unutilized EA.