Defects in metal oxides can significantly improve their physical and chemical properties. However, the conventional methods to generate defects often require complex procedures and harsh conditions. In this study, we design a simple and room-temperature preparation route to prepare defective metal oxide nanoparticles with high yield. The formation of defects is attributed to the generation of oxygen vacancies (VO) and hydrogenation caused by charge transfer at a Mg-metal oxide junction structure. Defective TiO2 exhibits excellent performance toward wastewater cleaning and water splitting. The proposed route is promising in terms of convenience, low cost, and large-scale production.