Synthesis of core/shell cobalt-doped rutile TiO₂ nanorods for MB degradation under visible light

Although TiO₂ has been widely applied in many fields, the design and preparation of one-dimensional rutile TiO₂ nanomaterials for high-efficiency photocatalysis under visible light remain challenging. Herein, uniform Co-doped rutile TiO₂ nanorods with selective adsorption and photocatalytic activity for methylene blue (MB) have been developed <i>via</i> a one-pot molten salt flux method. Compared to pure rutile TiO₂ nanorods, the Co-doped rutile TiO₂ nanorods exhibited an obvious core/shell structure with smaller inner crystal face spacing (<i>d</i> ₀₀₁ = 0.20 nm) and a larger rough surface (the BET specific surface area is 25 m² g^-1). Furthermore, different dyes were employed to investigate the adsorption ability of Co-doped rutile TiO₂ nanorods. The density functional theory (DFT) calculations determined that both the electrostatic potential and molecular structure could influence the adsorption behavior on the photocatalyst surface. The results indicated that the Co-doped TiO₂ nanorods possessed a high selective adsorption capacity for MB (134.54 mg g^-1 in neutral solution). The degradation of MB using Co-doped rutile TiO₂ nanorods was conducted under visible light irradiation, yielding with an apparent rate constant of 0.301 min^-1 at pH = 7. The degradation mechanism was further explored through electron spin resonance (ESR) experiments, which identified the formation of superoxide anions (·O₂ ^-) and hydroxyl radicals (·OH) in the system. This study provides a new strategy for preparing novel rutile TiO₂ photocatalysts for the degradation of organic dyes under visible light.