Facile template-free synthesis of new α-MnO2 nanorod/silver iodide p–n junction nanocomposites with high photocatalytic performance

Abstract

In the present study, a novel α-MnO₂/AgI photocatalyst was successfully fabricated by using hydrothermal/precipitation methods, and its photocatalytic performance was evaluated from the degradation of Acid blue 92 (AB92) dye under visible light irradiation. The surface and crystalline structure, morphology, and electro-chemical properties of the as-made photocatalyst were investigated by BET, XRD, XPS, SEM-EDS, TEM, DRS, PL, PC, and Raman analysis. The optimized nanocomposite (α-MnO₂/AgI) with a weight ratio of 1 : 15 showed the best photocatalytic activity in the decomposition of AB92 with a removal efficiency of 100% in 40 min which was better than that of pure α-MnO₂ (48%) and AgI (61%), confirming the synergistic effect in the as-prepared photocatalyst. The high photocatalytic activity of the nanocomposite is attributed to the high activity of AgI nanoparticles and the heterojunction between α-MnO₂ and AgI which can enhance light adsorption and the photo-generation of electron–hole (e⁻/h⁺) pairs. The effect of experimental parameters including initial solution pH, catalyst dosage, and concentration of dye was studied in the degradation reaction, and the results obtained indicated that in acidic media (pH = 4) when the catalyst dosage and dye concentration were 300 mg L⁻¹ and 10 mg L⁻¹, respectively, high activity was observed. Also, the reactive species trapping experiments were applied for investigation of the decomposition mechanism. Based on the results, the holes (h⁺) and superoxide radicals (O₂˙⁻) that are generated play a vital role in the photo-degradation process, while hydroxyl radicals (HO˙) showed a lower effect. The α-MnO₂/AgI nanocomposite exhibited high recyclability in four consecutive photocatalytic runs without losing the activity.