Persistent-Photoconductivity-Assisted Energy-Efficient Degradation of Pharmaceutical Pollutant Using p–n Heterojunction Er-TiO₂/Mn₃O₄

Sunlight, an inexhaustible source of energy, suffers from the drawback of intermittency. To ensure a consistent supply of renewable energy, the exploration of materials displaying robust postillumination activity or persistent photoconductivity (PPC) becomes imperative. This study delves into the realm of persistent photoconductivity within heterojunction nanocomposites of TiO2. In this work, a p–n heterojunction was established between Er-TiO2 and Mn3O4, facilitating efficient charge separation and enabling the broad solar spectrum to be harvested. The synergistic combination of TiO2 with other photoactive materials leads to a remarkable enhancement in catalytic efficiency. Intriguingly, transient photocurrent and photoluminescence investigations illuminate the pivotal role played by trapped electrons in defective Mn3O4, driving the persistent photoconductivity mechanism. Consequently, harnessed solar energy undertakes water treatment, even after the cessation of light. In contrast to the nonilluminated catalyst, the illuminated catalyst showcases a striking 3-fold surge in activity, achieved with merely 10 min of light exposure. Impressively, the catalyst demonstrates exceptional degradation efficacy across various real-world water systems, encompassing static water, river water, and sewage treatment plant wastewater. This discovery demonstrates a new way to utilize materials with persistent photoconductivity for solar-assisted water treatment plants.