Preparation and Visible-light Photocatalytic Degradation on Metronidazole of Zn2SiO4-ZnO-biochar Composites

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.