Hollow hemispherical Si-doped anatase for efficient carbamazepine degradation via photocatalytic activation of peroxymonosulfate

Abstract

Photocatalytic persulfate activation on semiconductor (such as TiO2) supported transition metal catalysts exhibits great potential in removing refractory organic pollutants, but it often encounters the issues of unsatisfactory activity and undesirable metal leaching. Herein, novel three-dimensional (3D) Si-doped TiO2 materials without transition metal doping are proposed for efficient photocatalytic activation of peroxymonosulfate (PMS). Unlike creating an inverse opal structure using polymer sphere templates in prior research, the SiO2 opal template enables the creation of hollow hemispherical structured Si-doped TiO2 (denoted as HHS-Si/TiO2) with hierarchical macro-mesopores. The SiO2 template also endows the HHS-Si/TiO2 materials excellent sintering-resistant properties and completely inhibits the crystalline phase transition from anatase to rutile at high temperatures, benefiting from the confinement effect and formation of Si-O-Ti bonds. The HHS-Si/TiO2 materials calcined at 400–900 °C show similar and excellent activities and stability in PMS activation under solar light irradiation to fast degrade carbamazepine (CBZ) and various other pollutants. The influences of PMS dosage, pH value and water matrix on CBZ degradation are illustrated. The HHS-Si/TiO2 materials are advantageous (especially at high calcination temperatures) over the commercial, the template-free synthesized and the inverse opal structured TiO2 materials for photocatalytic activation of PMS, because of their 3D hollow hemispherical structure, interconnected small anatase nanocrystals and Si-doping. PMS is mainly activated by the photo-generated electrons. HO• (dominant), SO4•− and holes are the reactive species responsible for CBZ degradation. This work provides enhanced understanding on the synthesis of 3D Si-doped TiO2 materials and it would provide useful information on developing efficient catalysts for photocatalytic PMS activation.