Role of hydrochloric acid treated HZSM-5 zeolite in Sm2Ti2O7/nHZSM-5 composite for photocatalytic degradation of ofloxacin

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 Sm2Ti2O7 was 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 m(2)/g of NaZSM5 to 300.4 m(2)/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 m(2)/g) were much larger than the surface area of the Sm2Ti2O7 (5.6 m(2)/g). Large mesopores and macropores were formed in the Sm2Ti2O7 layer of the composites. The band gap energies of the Sm2Ti2O7 and 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 Sm2Ti2O7 were 70.0% and 45.1%. The reaction rate constants for the photocatalytic degradation of ofloxacin were 0.0163, 0.00769 and 0.00402 min(-1) for 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. (C) 2020 The Authors. Published by Elsevier B.V.