Fabrication of spong-like Ag₂O/ZnO composite photocatalysts and photocatalytic degradation for formaldehyde under visible light irradiation

In order to overcome the disadvantage of low activity of the ZnO nanocrystals under visible light irradiation, the six square wurtzite spong-like ZnO nanocrystals were prepared by liquid phase co-precipitation thermal decomposition method with zinc nitrate hexahydrate, hexamethylene tetramine and oxalic acid dihydrate as the raw materials. The as-prepared spong-like ZnO were composited with Ag₂O nanocrystals under alkaline condition. The obtained Ag₂O/ZnO composite photocatalysts were characterized by XRD, FTIR, UV-Vis diffuse reflection spectroscopy (UV-Vis DRS), FESEM, TEM and BET analysis. The dark adsorption and photocatalytic acivity of the Ag₂O/ZnO composite photocatalysts with different mole ratios were investigated with formaldehyde (HCHO) as a degradation model using visible light source. The results indicate that with the increase of Ag₂O, the dark adsorption of HCHO increases first and then decreases with the maximum removal of 43.34% in which the mole ratio of Ag₂O to ZnO is 1:5. On the other hand, the best degradation effect is achieved when the mole ratio of Ag₂O to ZnO is 1:10, and the photodegradation of HCHO also increases first and then decreases under visible light with 78% photodegradation of HCHO and 85% of HCHO total removal after 90 min of visible light irradiation.