Design of multifunctional p-type TiO₂/nitrogen-functionalized carbon dot hybrids for enhanced photo- and...

Achieving stable p-type TiO₂ with multifunctional catalytic activity remains a long-standing challenge due to intrinsic defect compensation and poor charge transport. Here, we report a hydrothermal strategy to synthesize stable p-type TiO₂ nanoparticles via surface modification with nitrogen-functionalized carbon dots (TiO₂/N-CD). Density functional theory (DFT)-based studies reveal strong electron transfer from N-CD to Ti- and O-vacancy sites on the Ti₁₄₃O₂₈₆ surface, stabilizing defects through electrostatic interaction and modulating Ti and O states near the Fermi level, resulting in titanium-vacancy-driven p-type conductivity. The structure, morphology, composition, texture, and optical and electrochemical properties of TiO₂/N-CD are thoroughly characterized. TiO₂/N-CD exhibits 96% photocatalytic degradation of tetracycline in water within 90 min (0.030 min^-1) attributed to in situ hydroxyl radical generation, which is corroborated by enhanced charge carrier mobility and confirmed by electrochemical impedance spectroscopy and enhanced photocurrent measurements. Additionally, TiO₂/N-CD₅ exhibited efficient and stable oxygen evolution in alkaline media for 24 h (η₁₀ = 322 mV, corresponding to a Tafel slope of 56 mV dec^-1). Computational results further indicate strong H₂O adsorption (E_ads = -1.37 eV), as corroborated by the wettability of the TiO₂/N-CD surface and a favorable pH-dependent lattice oxygen mechanism. This work establishes N-CD-modified p-type TiO₂ as a versatile platform for energy and environmental applications.