Design of Multifunctional p-Type TiO2/Nitrogen-Functionalized Carbon Dot Hybrids for Enhanced Photo- and Electrocatalysis

Abstract

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 study reveals 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, optical and electrochemical properties of TiO2/N-CD are thoroughly characterized. The 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, corroborated by enhanced charge carrier mobility, confirmed from electrochemical impedance spectroscopy and from enhanced photocurrent measurement. Additionally, TiO2/N-CD₅ exhibited efficient and stable oxygen evolution in alkaline media for 24 h (η₁₀ = 322 mV), corresponding to Tafel slope = 56 mV dec⁻¹). Computational results further indicate strong H₂O adsorption (Eads = −1.37 eV), corroborated by wettability on 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.