Corrosion mitigation of carbon steel by spin coating with Ag–TiO2 gel films in acidic solution: Fabrication, characterization, electrochemical and quantum chemical approaches

Abstract

The overall objective of the present study is to develop new thin films based on Ag/TiO2 nanocomposites prepared by a sol-gel method with Chitosan as nano-assembling template and to test their ability to afford corrosion resistance properties. The fabricated Ag/TiO2 nanocomposites crystalline phase, characterization, composition and morphology of the coatings were examined by various spectroscopic techniques such as FTIR (Fourier Transform Infra-Red), XRD (X-Ray Diffraction), FESEM (Field Emission Scanning Electron microscopy), EDX (Energy Dispersive X-Ray), HRTEM (High Resolution Transmission Electron microscopy), BET (Brunauer–Emmett–Teller) and UV–Vis DRS (Diffuse Reflectance Spectroscopy). The corrosion resistance of the films was evaluated by using open circuit potential (OCP), potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. Quantum chemical computations at the DFT level were also performed on Ag/TiO2 nanocomposites with different Ag doping concentrations. The results evidenced that the thin film coating based on Ag/TiO2 nanocomposite at a concertation of Ag (5 wt%) exhibited the best performance as a coating system for carbon steel electrode compared with other thin films at different doping concentrations as well as the uncoated surface. Also, increasing the layer thickness of Ag/TiO2 nanocomposite thin films, co-dopant content in the coating systems and the nature of TiO2 crystalline phases affect the corrosion protection ability. AFM micrographs showed the formation of protective multilayer of different Ag/TiO2 thin films on the surface of carbon steel. The results from theoretical calculations revealed a significant decrease in the energy-band gap of Ag-doped TiO2 at an optimal doping concentration of 5% as a result of the overlap between the Ag & Ti states, which promotes the corrosion resistance of Ag-TiO2 thin films on the metal surface which agrees well with the experimental results.