Ascorbic Acid-Assisted ZIF-67-Derived TiO2/Co/C for Efficient Adsorption and Photocatalytic Degradation of Methylene Blue

In this work, a ZIF-67-derived TiO2/Co/C composite was prepared for the synergistic adsorption-photocatalytic degradation of methylene blue (MB). The innovative introduction of ascorbic acid (AA) as an auxiliary agent in the system effectively improved the degradation efficiency of MB. Structural characterization showed that the TiO2/Co/C composite retained a dodecahedral morphology with a relatively high specific surface area and was composed of TiO2, Co, and carbon. Through electrostatic interaction, π–π interaction, and hydrogen bonding, TiO2/Co/C composite exhibited strong MB adsorption capacity. Adsorption kinetics followed the pseudo-second-order model, while the equilibrium data fitted the Langmuir isotherm model, indicating monolayer adsorption with a maximum adsorption capacity of 21.03 mg g–1. Under visible-light irradiation, TiO2/Co/C composite achieved about 94.9% MB degradation within 120 min, and its apparent rate constant (0.0241 min–1) was markedly higher than those of Co/C and pure TiO2. The enhanced photocatalytic performance was attributed to improved charge separation, narrowed band gap, and increased oxygen vacancy concentration. Radical trapping experiments showed that •O2– and h+ were the main active species during photocatalysis. After AA addition, the degradation efficiency further increased to 97.7% within 60 min. AA acted as an electron donor to suppress Co oxidation and promote •O2– generation, thereby significantly improving the cycling stability of the photocatalytic system. This work highlights the potential of an AA-assisted adsorption-photocatalytic system and provides a feasible strategy for designing efficient dye degradation approaches.