Dispersion of ZnO or TiO2 nanoparticles onto P. australis stem-derived biochar for highly efficient photocatalytic removal of doxycycline antibiotic under visible light irradiation

Biochar (BC) derived from reed stems was prepared by high-temperature pyrolysis, and two types of ZnO/biochar (ZBC) and TiO2/biochar (TBC) composite materials were synthesized via a simple hydrolysis method. These composites, compared to pure ZnO and TiO2, exhibit not only improved but significantly enhanced crystalline structures and larger specific surface areas. This enhancement in the physical and chemical properties of ZBC and TBC composites is a crucial aspect of our research, as it leads to a distinct red-shifted absorption edge and excellent visible-light absorption characteristics. The photocatalytic degradation efficiency of ZBC and TBC composite materials, a key finding of our study, was evaluated using doxycycline antibiotic as a simulated pollutant under visible-light irradiation. The results demonstrate a 6.0-fold and 7.3-fold increase in photocatalytic degradation efficiency of ZBC and TBC composites compared to pure ZnO and TiO2, respectively, further underscoring the significance of these enhanced properties. Furthermore, active species trapping experiments reveal that ·OH radicals are the dominant reactive species in the photocatalytic degradation process of doxycycline. A Langmuir–Hinshelwood kinetic model accurately represents this degradation process. Kinetic data indicate that the degradation rate constants (k) of ZBC and TBC catalysts are 4.314 × 10−2 min−1 and 3.416 × 10−2 min−1, respectively. The photocatalysts exhibit no significant decrease in degradation efficiency for ZBC and TBC even after the fourth cycle, indicating their relatively high reusability. These results suggest that ZBC and TBC materials can be used as stable, efficient, cost-effective, and sustainable photocatalytic composite materials for antibiotic-contaminated wastewater treatment.