Polyindole/Chitosan/N-doped Carbon Dots Ternary Nanocomposite as Efficient Corrosion Inhibitor and Potent Antibacterial Agent

Abstract

This study focuses on the synthesis, characterization, and performance evaluation of novel polyindole based nanocomposites, PIn-NCQD and PIn-NCQD-CS, shedding light on their potential applications in corrosion protection and antibacterial activity. Nitrogen doped carbon quantum dots (NCQDs) were formed through one-step hydrothermal synthesis and polyindole (PIn) was synthesized by chemical oxidative polymerization. Nanocomposites were synthesized via in-situ chemical oxidative polymerization process. The incorporation of NCQDs and chitosan (CS) into the polymer matrix was confirmed using XRD, FTIR, SEM and UV-visible spectroscopy. XRD analysis indicated the amorphous nature of the nanocomposites. However, the addition of chitosan introduced some order of crytallinity in PIn-NCQD-CS. FTIR spectra of nanocomposites exhibited characteristic absorptions similar to pure polyindole, with an overlap between N-H stretching vibrations of PIn and O-H stretching vibrations of NCQDs. The distinct shifts in UV -visible peaks and appearance of new peaks in the UV region and at 344nm corresponding to NCQDs and chitosan, confirmed their successful integration in the polymer matrix. SEM analysis revealed the spherical particle nature of ternary nanocomposite, with an average particle size of 207 nm. The corrosion inhibition performance of PIn, PIn-NCQD and PIn-NCQD-CS modified nanocomposites was assessed through gravimetric and electrochemical analysis. Theoretical studies were employed to correlate the inhibitors' structure with their corrosion inhibition behavior. Remarkably, PIn-NCQD-CS demonstrated superior corrosion inhibition properties via gravimetric analysis, exhibiting 92% inhibition efficiency at a concentration of 100 ppm against the corrosion of aluminum-copper alloy in a 0.1 M hydrochloric acid solution. Electrochemical impedance spectroscopy (ElS) affirmed the formation of a protective film on the surface of aluminum alloy, with PIn-NCQD-CS (inhibition efficiency 92%) outperforming PIn-NCQD (inhibition efficiency 79.6%) and pure polyindole (inhibition efficiency 70%) as inhibitors. Polarization studies revealed that the tested inhibitors effectively suppressed both anodic and cathodic processes and the obtained corrosion potential values remained within 85m V, suggesting their role as mixed inhibitors. The results of quantum chemical calculations supported the experimental results and provided evidence for metal-inhibitor interaction. Surface morphological analysis of aluminum alloy substrate indicated the presence of corrosion products in uninhibited system, while substrates immersed in inhibited system showed smooth surface with few polishing marks. Furthermore, the nanocomposites displayed substantial antibacterial activity against four bacterial strains. Pln-NCQD-CS, in particular, exhibited notable antimicrobial efficacy, with significant inhibition against B. subtilis (inhibition zone = 11 .5 mm). In conclusion, the successful synthesis and characterization of PIn-NCQD and PIn-NCQD-CS nanocomposites showcase their promising applications as corrosion inhibitors and antimicrobial agents. The synergistic effects observed in their corrosion inhibition performance, along with their significant antibacterial activity, underline their potential for multifaceted industrial applications.