Photocatalytic activity of zinc oxide/hemimorphite/silica aerogel materials: performance and mechanism

Low mass transfer and photon efficiency are the main problems compromising the practical application of photocatalysts. A novel hemimorphite/zinc oxide (ZnO)/silica (SiO₂) aerogel composite material for degradation of tetracycline (TC) was prepared by a mild direct precipitation-calcination method. By optimizing the preparation conditions, the loading of ZnO was determined to be 40% and the calcination temperature was 450 °C. Not only was the mass transfer efficiency of the system improved by the significant number of stacking holes, but also, the light absorption performance of hemimorphite/ZnO/SiO₂ was enhanced by the generation of a specific crystal phase, the hemimorphite phase. The results indicate that the equilibrium adsorption capacity and photocatalytic kinetic rate of the hemimorphite/ZnO/SiO₂ composite are 4.30 and 3.28 times higher than that of pure ZnO, respectively. The introduction of SiO₂ reduced the grain size of ZnO from 14.5 to 4.5 nm, inhibiting the agglomeration of ZnO. \(O_{2}^{ - }\) $O_2^{-}$ and \(h^{ + }\) $h^{+}$ were proved to be the primary and secondary active species for the degradation by EPR and radical scavenger tests.a The possible mechanism and intermediates of TC degradation process were speculated, including hydroxylation, ring opening and branch chain removal reactions. In a nutshell, this study provides a novel strategy for designing and preparing efficient photocatalytic materials.