Abstract:

Using pine alkali hydrolysate to replace NaOH solution as zinc salt precipitator, the Zn₂SiO₄-ZnO-biochar (SOB-x-y, x is the dosage of pine powder, while y is the concentration of NaOH) ternary composites were prepared by hydrothermal method. The photocatalysts were characterized by different methods. The degradation of metronidazole over the H₂O₂ photocatalysis was studied. Results showed that the as-prepared photocatalysts were composed of jujube-type willemite Zn₂SiO₄ mesocrystals, hexagonal ZnO and pine biochar. Compared with pure hexagonal ZnO, the SOB-x-y photocatalysts has better H₂O₂ photocatalytic activity due to the higher surface area and pore volume, lower band gap energy, lower PL emission peak intensity. Metronidazole degradation using the H₂O₂ photocatalysis was well-fitted to a pseudo-first-order kinetic model by SOB-x-y. Its catalytic activity increased with the increase of NaOH concentration, and increased at first and then decreased with the increase of pine flour content. The SOB-3-4 has best photocatalytic acitivity. Meanwhile, rate constant (k) and degradation rate (η) of SOB-3-4 increase with the decrease of pH, increase with the increase of H₂O₂ concentration, increase firstly and then decrease with the increase of catalyst dosage. Degradation rate of metronidazole gradually decreases with the increase of its initial concentration. Under the optimal condition (pH=3, catalyst dosage of 0.4 g/L, H₂O₂ dosage of 80 mmol/L, initial metronidazole concentration of 300 mg/L), k value was 2.68×10 ^-2 min ^-1 and η reached 99.70% after reaction for 3 h. This study provides an important experimental basis for the treatment of pharmaceutical wastewater.

Key words: Zn₂SiO₄-ZnO-biochar composites, pine alkali hydrolysate, hydrothermal syntheticsis, photocatalysis, metronidazole