Interfacial Chemistry of Phosphate-Functionalized Self-Doped TiO₂ Nanotube for Electrochemical Detection of Methylene...

Titanium dioxide nanotube (TNT) arrays were synthesized by electrochemical anodization of Ti sheets and subsequently modified by cathodic polarization at -1.5 V in phosphate buffer (pH 7.4), yielding self-doped TiO₂ nanotubes (SD-TNT). This treatment generated Ti-(III) states, enhancing conductivity and surface hydrophilicity while also promoting phosphate ion adsorption. Structural and morphological analyses confirmed the ordered nanotubular architecture, while electrochemical studies revealed improved charge-transfer properties. In acidic medium (pH 2.0), SD-TNT electrodes exhibited pronounced interaction with protonated methylene blue (MB²⁺), favoring its accumulation on the electrode surface. Cyclic voltammetry revealed distinct kinetic regimes depending on the scan rate, with Tafel analysis at low scan rates identifiying the second electron transfer as the rate-determining step, while resistive and capacitive effects became dominant at higher scan rates. The synergistic effect of self-doping and phosphate functionalization modulated the interfacial behavior of SD-TNT, enabling sensitive and reproducible electrochemical detection of MB²⁺. These findings highlight the role of surface chemistry in tuning charge-transfer processes and demonstrate the potential of SD-TNT as a model platform for interfacial electrochemistry studies and environmental sensing applications.