Tuning defects in Cu₂O nanostructures via room temperature mechanical pressing: impacts on defect-dependent optical and photoelectrochemical sensing performances

The optical and photoelectrochemical (PEC) sensing performances of transition metal oxides are greatly dependent on structural defects. However, defect engineering under ambient conditions remains challenging using conventional chemical methods. Here we propose that room temperature mechanical pressing is a simple defect tuning method that is compatible with a Cu2O nanostructure containing a high density of oxygen vacancy (V-O) defects. The room temperature oxygenation of oxygen-deficient Cu2O by atmospheric oxygen can be dramatically accelerated due to the introduced interface strain. As a result, the V-O-derived red emission intensity of the defective Cu2O nanostructure gradually reduces with the increasing mechanical static pressure applied within a short period of time. We reveal that the abundant surface V-O defects also endow the V-O-rich Cu2O nanostructure with superior SERS sensing performance attributable to the increased possibility of electron transition between Cu2O and the probe molecules. In contrast, the Cu2O with a modest V-O level remediated by optimal mechanical pressing exhibits a significantly enhanced PEC sensing performance to the electron acceptor molecules because of the restricted recombination of the photogenerated electron-hole pairs under visible light. This case study provides a convenient, energy-saving and low-cost strategy for V-O remediation in defective oxide nanostructures.