Synthesis, characterization, and photocatalytic activity of stannum-doped MgIn2S4 microspheres

A series of Sn2+ doped MgIn2S4 photocatalysts were prepared via a facial hydrothermal method. The Sn dopants substitute the sites of Mg atom in MgIn2S4 unit cell, but not alter the crystal structure, demonstrated by the results of XRD and XPS. Compared to pristine MgIn2S4, Sn-doped MgIn2S4 samples exhibit significantly enhanced photocatalytic CO2 reduction activity. With increasing the Sn dopant content, the CO2 conversion rate first ascends, achieving the maximum rate at Sn-MgIn2S4-2 sample, and then decreases. After illumination for 4 h, the highest yield of CO and CH4 for Sn-MgIn2S4-2 sample reaches about 3.35 and 3.33 times higher than that of pristine MgIn2S4. The theoretical results based on density functional theory calculations reveal that Sn doping in MgIn2S4 tunes the band structure from the direct-transition of MgIn2S4 to indirect-transition, diminishes band gap and extends the light absorption range, reduces the effective masses of holes and promotes the migration of photoinduced carriers. The experimental results also demonstrate the positive role of Sn dopant in accelerating the separation and transportation of charges, and improving CO2 adsorption ability. This work systematically investigates and discusses the Sn2+ doping effect in MgIn2S4 on crystal structure, lattice variations, electronic band structures, CO2 adsorption ability, and photocatalytic CO2 reduction activity, which can provide a new hint for the fabrication of efficient photocatalyst by metal ion doping.