Zn-free MOFs like MIL-53(Al) and MIL-125(Ti) for the preparation of defect-rich, ultrafine ZnO nanosheets with high photocatalytic performance

Metal organic frameworks (MOFs) are exploited in many applications of materials science and very recently were investigated as precursors or reagents for material synthesis. In a new way different from previous approaches, here we introduce for the first time the synthesis of metal oxide MxOy in the presence of M-free MOF acting partially as a sacrificial template and as a provider of doping metal atom. We demonstrate this approach in the case of ZnO prepared by a simple hydrothermal method in the presence of a Zn-free MOF like MIL-53(Al) or MIL-125(Ti). The resulting ZnO show low content of Al or Ti < 2% and properties are significantly different depending on whether MIL-53(Al) or MIL-125(Ti) are used or if no MOF is present. The nature and presence of MOF has different major effects on the morphology, the specific surface area of as prepared ZnO and also on the oxygen defects in its crystal structure. Corroborating the XPS, UV-vis DRS, PL, EPR and DFT studies evidence the role of such O-defects on band gap narrowing for samples calcined at 400 degrees C. These exhibit high efficiency in photodegradation of methyl orange (MO) compared to ZnO prepared in MOF-free conditions or previous literatures. The kinetics of MO degradation is different depending on the morphology, the specific surface and oxygen defects. The present data open the door to a new approach of the synthesis of metal oxides and a control of their properties.