Role of hydrochloric acid treated HZSM-5 zeolite in Sm 2Ti 2O 7/nHZSM-5 composite for photocatalytic degradation of ofloxacin

摘要

NaZSM-5 was treated in hydrochloric acid solution to prepare HZSM-5. The Sm2Ti2O7/nHZSM-5 composites were synthesized via a sol-gel route. The concentration of the hydrochloric acid solution could greatly influence the properties of the Sm2Ti2O7/nHZSM-5 composites, and the composites were characterized to clarify the role of the HZSM-5 zeolite. The pyrochlore phase Sm2Ti2O7was produced in the composites. The hydrochloric acid treatment resulted in the dealumination and enhanced crystallinity of the nHZSM-5 zeolites. The specific surface area of the zeolites was increased from 175.0?m2/g of NaZSM5 to 300.4?m2/g of 0.1HZSM-5, and the total pore volume in the ZSM-5 zeolites was notably enlarged too. The BET surface areas of the Sm2Ti2O7/nHZSM-5 composites (67.2–87.9?m2/g) were much larger than the surface area of the Sm2Ti2O7(5.6?m2/g). Large mesopores and macropores were formed in the Sm2Ti2O7layer of the composites. The band gap energies of the Sm2Ti2O7and the composites were between 3.52?eV and 3.69?eV. 93.5% of the ofloxacin molecules were degraded on the Sm2Ti2O7/0.3HZSM-5 composite after 150 min of reaction. At the same time, the degradation efficiencies on the Sm2Ti2O7/NaZSM-5 and Sm2Ti2O7were 70.0% and 45.1%. The reaction rate constants for the photocatalytic degradation of ofloxacin were 0.0163, 0.00769 and 0.00402?min?1for the Sm2Ti2O7/0.3HZSM-5, Sm2Ti2O7/NaZSM-5 and Sm2Ti2O7, respectively. The increased production of hydroxyl radicals was related to the enhanced photocatalytic activity of the Sm2Ti2O7/nHZSM-5 composites.